Saint-Saëns planar- AKA SMJ-40- time for a project now?

[JonMarsh]

This project concept has an unusual history and evolution. It started out in early mid 2021 based on the idea of a short narrow column bass system, originally targeting the recently introduced Dayton E180HD-44.






This dual magnet long excursion driver seemed to represent some very innovative thinking- and was certainly "interesting" looking, to say the least... and the early graphs showed it should be easy to work with up to 400 or 500Hz for a crossover point. The impedance curve gave some hints that this driver really was designed like a subwoofer, with a significant rise in the impedance between 125Hz and 1kHz. So, distortion might not be what we want in the upper midrange for a two way.

I acquired 4, and tested them, and discovered (as many have) that instead of having monotonically falling HD above 100 Hz, it's rising, due to inductivity modulation. So those parts got set aside, and I began looking at others, including several PuriFi models, and even pre-orders 8 of the PuriFi 8" parts. But while the 6.5" PuriF parts had physical parameters suited to small enclosures, the 8" parts are closer to monkey coffin drivers...

Hmmm, looks like we'll need to do a comprehensive data sheet review...


At the same time, I started looking at AMT style drivers for the tweeters, and was hearing things about B&G planers being taken over by GRS. But also I was impressed by the half dozen PuriFi cone midranges I'd bought as samples, initially just for the Isiris update project.

A lot going on with house buying and moving, and then in May of 2022 Steve sent me a video of the PS Audio FR30, which was quite a new implementation for them compared with speaker systems they'd shown previously with side mounted woofers near the floor, midwoofer/low mid link drivers, etc. Someone new was doing some new thinking there. And the LF section looked just like what I had in mind for the as yet unnamed project.

While PS Audio was cagey about showing the planar drivers in any of their videos, except for one slip up I noted, GRS was introducing their B&G based lineup, in the US through Parts Express, with much better detailed data sheets than B&G every offered. Hmmm... something to check out.

Being somewhat familiar with Magneplanars from the old days, I was wondering just how the diaphragms and overall motor systems were tuned and implemented. And of course, that woofer driver needed to be defined, also. I could see the "resemblance" to a certain family of Peerless woofers, but these days via their volume requirements for purchases Peerless has basically pulled out of the DIY market.

In the end, a Dayton woofer showed a remarkable balance of desirable woofer characteristic bordering on subwoofer turf, as it actually is part of a series of subwoofer drivers.

• Very linear cone behavior out to 4kHz, with breakup mode at 5kHz; much better behaved than the RS225 woofer, with its large dip before the breakup region.
• Useful Xmax of 9 mm one way.
• Three ring motor with good midrange distortion characteristics also.

This one plot was taken near field at a drive level target for one driver equal to the four driver series/parallel array at 91 dB (at 2.83VRMS drive for the net 4 ohm array):





Though this test included a PR, due to QNF microphone placement the PR contribution (on the back of the cabinet) is not a significant factor in the measurement.

A variety of enclosure sizes and PR alignments and drivers were evaluated, and the example chosen at this time uses 4 RSS210HF-4 with 4 Seas SL26R XM003 passive radiators, with mass added to bring the PR mass to 350g. The calculated results look very promising with the target SPL of 110dB being achieved with 40W per woofer...






Note, the maximum excursion is about 60% of the RSS210HF rating. So this is not on the ragged edge...

An alternative PR close in performance is the Dayton RSS265PR; I chose the Seas part because of their reputation for assiduous monitoring of production compliance linearity, which is necessary for low distortion at high output levels.


Now, about those planar drivers...

It should be noted that the PT2522 tweeter is offered in two formats; one open back dipole, and one with a closed back. The differences gives some clues about the challenges working with these planar parts, both the midrange and tweeter. The midrange is only offered in an open back parts. Well after development evaluations started, GRS introduced some mounting panels, which helps significantly with testing and implementation.


Factory DS SPL plots for PT2522 (dipole)









Factory DS SPL plots for PT2522C. ("c" for closed back)






My experience measuring these parts was "interesting". I concluded that neither was an optimal solution- the factory 2522c parts did not measure like the DS graph, though the dipole 2522 more resembled the factory curve, but with a more extreme dip. But what these charts do display with some fidelity is the variation in response level depending on where the diaphragm resonance occurs, which can be measured with some accuracy looking at the impedance curve. My conclusion was that the "optimum" rear volume would be heavily damped and somewhere between open back and the very shallow factory cup, which results in a series of four experiments in search of what might be the best alignment, as conventional modeling tools would not handle this.


The midrange planer in dipole mode as from the factory presents the same fundamental issues- and in fact I had some success in modeling it and determining lumped parameters, but not fully accurately modeling the overall response profile.





This measured impedance curve on one sample was quite similar, and correlates well with some observed behavior in the data sheet SPL plot.







That also resulted in several test configuration, once again taking four test articles to home in on what seems to be the best compromise for SPL, even though I could accurately predict the Fb for a given volume. The "raw" response in dipole mode shows a 10dB range over the desired operational range from 400-500Hz to 2-2.2kHz. How can one get to a more optimum response level in this range?


This version has been selected as the POC target for system integration, and already verified in a POC crossover design.






The impedance curve of the POC target configuration:








Next I'll talk about the planned Proof Of Concept enclosure build.

[JonMarsh]

The enclosure concept for this project has gone through several stages, both as driver selection and layout have updated, and also due to considerations about materials and dimensions related to both performance concerns and to cost concerns; that is, for example, how many panels could be produced from the planned starting materials, which in some cases are common to two past projects, including the Ardent D, but I'd say not exactly mainstream for DIY builders (anyone else on HT Guide fond of piano pin block maple ply for front panels and other pieces? Besides Evil Twin? Nah, didn't think so!


😆



This will be a two piece enclosure, which gives some flexibility if I decide, Mmmm, man, that Midrange-HF build didn't work out so well, let's try that part again!


Also, I believe it will be necessary to have some outrigger legs to the sides, but they aren't shown in these drawings.



ISO View, complete speaker (LF and MF/HF)






Comments/Explanations:

• Overall height is about 58-3/4", LF cabinet is 40-1/2" tall. Depth is about 26", width is 10-1/2", down from 12" originally.
• With changes in the enclosure materials, the sides were changed from 3/4" bamboo boards with inner layment of 1/2" BB ply to a 1" bamboo ply construction, with updates to the lateral bracing on panels; this allowed reducing the outer width without significant changes to the inner volume.
• The LF front panels are two layers of 1-1/4" maple ply. The HF module front panel is a single layer of 1-1/4. The enclosure tops and backs are 1-1/4" maple ply. Bottom are a combination of 3/4" bamboo board and 1/4" phenolic.
• Internal LF braces are 3/4" bamboo board. The LF cabinet center brace extends front to back; the other braces extend only to the PR cut outs.
• The PR's are located close to the back of the cabinet to be as far as possible into the rear pressure zone.

Rear View







LF crossover will be in the lower cabinet, with options to use feedthrough cable for HF or connect directly to MF/HF at top module.






All fabrication materials are here and ready as soon as I finish a couple of other pending projects, one for Steve.

[theSven]

A lot going on with house buying and moving, and then in May of 2022 Steve sent me a video of the PS Audio FR30, which was quite a new implementation for them compared with speaker systems they'd shown previously with side mounted woofers near the floor, midwoofer/low mid link drivers, etc.

Crazy how fast the time has gone by since May of last year! None the less my excitement for a new design after one of my favorite composers...

[technodanvan]

Interesting you ended up going with the Seas PR over the Dayton. Does it even have a mounting system for weights? I was under the impression it was pretuned for the L26ROY.

This looks to be a really nice system, but I'm unsure I'd have the space for this one! Maybe if I didn't have other plans for a home theater setup...

[JonMarsh]

The Seas IS pre-tuned for the LROY 10" driver, but it has provision for bolting on additional disk weights, though it doesn't come with them. As mentioned, I admire the SL26R because of the QA effort Seas has made in the past to assure the suspension linearity with travel. Note, this is the newer just released version with a redesigned frame. And yes, I have 8 on hand.

No, I wouldn't expect this to be a "hit" for HT setups. For me, it's an experiment that I'd been thinking about for a few years as regards the LF section (short column array with very effective radiation pattern regarding dealing with floor bounce, and +3dB sensitivity due to driver coupling). I believe I fully understand the reasons Chris Brunhaver switched to this from what PS Audio had been doing previously wiht their hybrid speaker experiments. This version is a tad larger, a somewhat less efficient, and will play lower flat than the FR30, by analysis. Hoffman's Iron Law, and HiFi News measurements of the FR30 confirm it.

As they say, many a slip twixt the cup and the lip, and a lot of up front work before making the first saw dust. Speaking of which....

[JonMarsh]

Using the newest planar driver configurations and measurements, another POC (Proof of Concept) crossover network has been developed, to keep evaluating the issues as I go along and to try to minimize changes later in the build process.

That has proven interesting, because with the rising response and phase behavior of the midrange panel, I found it is necessary to have the tweeter ahead of it on the Z axis to get the best crossover integration and reverse phase nulls.

Looking at the POC SPL response from 100Hz to 40kHz, with the current data including simulated woofer data on the baffle design, and including Z axis offsets and using an RMS average of the forward polar response for the tweeter for +/- 30 degrees, things are looking pretty fair...




Predicted reverse null behavior looks pretty good... hard to imagine much better.








But this necessitates an update to the upper module cabinet design...






Which will complicate fabrication, but I have a plan...


The complete cabinet system is now proposed like this:






And yes, I checked the optimized crossover without the Z axis offset between midrange and tweeter, and it degrades the response level in the crossover region between 2 and 3 kHz by about 1 dB...





And more notably, substantially worsens the revers null behavior:

[technodanvan]

I might have to rethink this project, the top end is so cost-effective that it would make a fun project that could end up being a gift for family or a friend, especially if one just used MDF instead of more exotic options (given even the cost of baltic birch these days). I think I'd probably check the tuning for the Dayton PR though and use that in place of the Seas - just for the sake of a unified appearance. One would need to wait for the Dayton RSS210-HF to go on sale again though.

Edit: Does the midrange/tweeter cabinet need to be the full depth of the bass cabinet?

[JonMarsh]

Hey Danny!

Here's the current plan and thinking.

Something not shown in this drawing is the midrange sub enclosure. At first, that was going to be a complete box open on just the side facing the front panel, but what with narrowing the cabinet from 12" to 10-1/2", it will just be like a "C" structure, three pieces, going side to side (to match the current dimensions of the preferred rear enclosure for the midrange panel). That needs to be 8" deep behind the front panel. I'll share details about that and the recommended sub-enclosure damping on a 1:1 basis.

Then, there is the matter of the crossovers- it's not known exactly how big those will be, though based on my current POC effort I will do some floor planning soon. I don't expect the midrange and HF panel crossovers to change much, as they're based on usable cabinet measurements of a sort already.

Now, if you look at the cabinet drawing and ponder things a bit, you might wonder how those crossovers will get in there! My current tentative plan is to have a removable base, and of course it's possible, possibly convenient, to mount the crossovers on that and just plug the driver cables into them when doing final assembly of the cabinet. IF you want to shrink the cabinet depth, then using wide velcro tape to mount them to the inside walls might be a workable alternative. Of course, the whole rear panel could be a screw on assembly instead of an integral fluid wall, and the crossovers mounted on the back of that; that would probably yield the shallowest overall cabinet. That could probably also be accomplished via the removable base.

This is about DIY, and individual choice plus sweat equity, so "you're the boss!" should be considered the "rule of the day".

Planned wiring on the mid and tweeter is the GR Research version of 12TC braided cable (on hand). I'll probably use that for a run from the top to the bottom of the "bass bin" so that only short external jumpers would be needed to connect from the dual inputs at the bottom. I will probably arrange the dual inputs so that they can be jumped at the input from one amplifier to speaker cadet using the Dayton Audio PJMP-G gold jumpers.

I haven't heard music through this setup; my plan right now is to build one of the bass cabinets and use my existing rough test cabinet to check this out and finish POC crossover development and see how it sounds... given the pretty low distortion on the midrange the way it's setup now, I have some reasonable hopes for a good bang for the buck ROI!

All drivers and construction materials are on hand, so it's just a question of clearing the decks of another project for Steve and Sven. And regardless of that, I do allow myself to work on this one on Sundays... no day of rest here!

[technodanvan]

Hey Jon, can you confirm the part number of the top end? Just adding things to my cart for later...

[Evil Twin]

For the special tweeter build (it is not used in stock condition) the component part number is PT-2522c. The back is removed, a sub enclosure wall of a specific depth is fabricated, and the original back is used with a selected enclosure damping materials. PM me for more details.

The PE part number is 272-124.

[technodanvan]

And the mid? Guessing from the CAD drawings it's the 10" GRS PT5010-8?

[Evil Twin]

Preparations are underway for an upper module crossover test. Parts for a "junk box" crossover build have been collected, and a few additional needed items ordered. This is an expensive "junk box" build as it includes Clarity MR caps, Clarity PUR, Clarity CSA, Audyn Cap Plus, and Jantzen Z-Superior, and Jantzen Alumen film caps.

Waste not, want not.

Detailed part drawings are in preparation from the 3D CAD model.

[Evil Twin]

Purely as a preliminary preview, I am sharing the upper module front panel drawing as an image and a PDF which can be downloaded. This will most likely be the more challenging part to fabricate for this design- in fact, component fabrication is underway at this time, as testing the MF-HF module with POC crossovers is considered a priority step for the overall execution.

[JonMarsh]

Some questions have come up about the low frequency design, including comparisons to measurements in a test review of a commercial system, plus questions about the need or desirability of adding a subwoofer to this system... all valid and interesting, so I thought maybe a brief summary here would be helpful. That, and sharing some other results of the initial design concept, and comparisons to alternatives.

A reminder of the current design target, as posted above, normalized to 2.83VRMS drive:



This does not include the effect of baffle step, compared with an IB measurement data from driver data sheet. To compare with an actual speaker measurement, the SPL must be reduced by around 5-6 dB.



Note, at the target output level of 110dB, the RSS210HF are operating at a peak excursion of 2/3 of Xmax with this alignment.

Now, just to remind everyone, crafting a solid LF design includes examining a host of issues and tradeoffs, especially when considering a passive radiator design. All woofers are not created equal, and neither are all passive radiators. Then, too, there is Hoffman's Iron law, and the intrinsic tradeoffs involved regarding enclosure size, efficiency, and extension. It's not like Amazon's slogan for Prime, pick two: Low price and free delivery. Instead, it's a balancing act, and if LF extension with clean performance is expected, then efficiency may go down, and enclosure size may have to go up. This project, originally conceived as a design study, is a classic example, I think...

For DIY systems it is possible to select the focus on a personal basis for which performance aspect you prefer to emphasize- so if LF extension and quality is a prime consideration, it's reasonable to select the necessary components to foster that goal, and if desired ignore commercial realities about cost, shipping size and weight, and system sensitivity with regards to power amplifier requirements. Commercially, having a recommended power rating of 50W and up may be much more "attractive" to the potential clientele and their belief systems than having a rating of 100W and up. Those are the sorts of differences that engineering decisions can hinge on for the commercial market.

Let's be realistic- the technology characteristics of drivers of a given size can be all over the map, as DaveFred's topic about 8" woofer testing shows. A similar though usually lesser spread of characteristics exists for passive radiators. Those characteristics are intrinsic to the LF performance- including basic T/S parameters to meet the given enclosure LF extension plus cone and motor design to optimize linearity. With passive radiators, key issues are the basic physical parameters establishing Qms as a function of Mms (usually adjustable) and Cms, and how these interact with the enclosure and woofers to achieve a response target- not just a given FB, but the effective range of response of the passive radiator contribution and it's contribution to the LF corner Q, which has a considerable impact on both SPL response and step response.


So, let's consider the measured response characteristics of a commercial system with a similar LF concept- 4 - 8" woofers, and 4 - 10" passive radiators:




Measuring a wide range loudspeaker system in room with accuracy can be a tricky affair, but it should be noted that this is a result from a sister publication to Stereophile using the same highly regarded and rarely disputed measurement techniques from JA at Stereophile Magazine.


The measured characteristics are a bit curious to me, but not difficult to summarize in the terms of classic design tools like Unibox-

• Nominal system sensitivity of ~88 dB
• LF F3 of 50 Hz.
• "Classic" Roll off of 12 dB/octave for 10 dB drop until the passive radiators "engage/contribute" significantly to LF output at about 30Hz
• A relatively narrow PR contribution peaking about 6.5 dB at about 26Hz, suggesting a somewhat "high Q" part which is likely to have an "interesting" effect on system step response.

A key reason I find this measured result as "curious" is because of the Saint-Saëns configuration alignment posted above, and noting that PR tuning for Fb is similar, at 25Hz, but the -6.5 dB point for PR output going upwards is 40Hz, not 30Hz, while the calculated woofer contribution (light black line) is at about the -10 dB level at about 28Hz. This PR output spread can be achieved with two PR's that I have actually tested, the RSS265PR with 350g Mms configuration, and the Seas SL26R XM003, also with 350g configuration. This has been confirmed with QNF measurements for a single woofer and single PR mounted on the back of the cabinet.

The results are very similar to the modeling in Unibox of the chosen configuration. QNF measurement of the RSS210HF confirms an F3 for the RSS210HF of 45 Hz, along with the calculated PR profile. The PR response profile was chosen to have a soft corner, more like a Bessel function, as this will usually optimize step response, and boundary lift will compensate the response drop with correct placement.


To illustrate the impact on step response, I'll compare a "classic" orthodox approach for a new high excursion/low distortion subwoofer series from Dayton Audio, the RSS390HE-22 combined with the RSS460PR in a similar sized enclosure, 100L.







Fairly complete setting of the step response is reached at about 90 msec. The first full cycle of ringing takes 40 msec.


Comparing this to the Saint-Saëns / SMJ-40 alignment is interesting, considering how similar the F3 and Fb frequencies are. Overall sensitivity is similar- the SMJ-40 alignment requires 200W power for 110dB; the RSS390HE-22 delivers 114dB with 500W power.




Fairly complete settling of the step response ring appears to be met at about 40-50 msec. The first full cycle transition occurs at about 20 msec.



I believe you can approach this step behavior for the RSS390HE-22 by using a much larger enclosure and a different PR configuration, but that would not follow "orthodoxy" in PR based subwoofers, where achieving a compact enclosure design is often an overriding design goal. In fact, the RSS390HE-22 is advertised as designed for very small enclosures, but I personally don't really find that to be the case- OTOH, it's 50% longer Xmax, very low distortion motor design, and 3dB higher sensitivity compared with the Dayton Ultimax subwoofer should be appreciated by anyone, regardless of other design targets and considerations.

For using the RSS390HE-22, I would be inclined to take advantage of its sensitivity and long throw low distortion motor and go sealed with EQ.

Sealed calculated step response in a 75L cabinet is shown here:

[JonMarsh]

What with the big CC project, this one hasn't gotten as much lovin' as I would like to have time for, but there is what you might call "behind the scenes" sort of progress.

• tools ordered specific to the planned construction process, including some new solid carbide router bits and a track guide for cutting large pieces of 1" bamboo play have all arrived
• A "junk bin" collection of all crossover parts as been set aside for POC builds in individual bins for the woofer, midrange, and tweeter crossover builds, and custom configured C-Core inductors ordered for the woofer crossovers from a Jantzen dealer in the UK. (They're expected to take about a month for delivery). Mind you, I have a pretty high class "junk bin", including Clarity MR and PUR caps, Jantzen Alumen film and foil caps, Jantzen Z-Superior, and some reasonably high grade inductors, including foil wrap and Litz wire as appropriate.
• The current working VituixCAD evaluation is derived from direct measurements of the midrange and tweeter elements in a test cabinet, but the woofer is derived from QNF measurements of the driver in a test cabinet and baffle modeling via VituixCAD capabilities.
• Junk bin board layouts have been prepared using my long fave for that task and many others, EazyDraw.
• Cabinet materials are on hand, but the weather has not been cooperative for opening the garage door and setting up for cutting large pieces- we have hard freezing temps overnight still, and snow forecast for this coming week. This is not normal- I should be doing grass seeding two weeks ago. Of course, 25" of rain in Fort Lauderdale in 24 hours is not "normal" either (considered a 1,000-2,000 year event), so I'm happy to have our situation and not something more intense.

Note: PR output was not captured for the woofer data used in this evaluation:







Note: Phase tracking with the proposed baffle Z-Axis alignment and crossover is pretty much spot on.







Boards are cut and prepped for crossover construction- hopefully that will start next weekend!

[technodanvan]

Boards are cut and prepped for crossover construction- hopefully that will start next weekend!

Xover boards going to be complete before the cabinets are? Craziness! What router bit did you get to help with that bevel on the mid? Something custom from Whiteside or Amana?

[JonMarsh]

Xover boards going to be complete before the cabinets are? Craziness! What router bit did you get to help with that bevel on the mid? Something custom from Whiteside or Amana?

Not custom, but off the shelf. Between Woodcraft and Amazon one can find a lot of stuff... But the bits received this time from Woodpecker, new models, are for a more basic part of the construction, getting the front panel edges flush with the side walls and top after construction- usually cut those just slightly over sized.

For the 45 deg bevels, parts like the Whiteside 2306 and 2302 get the job done nicely... it will take a special "process" to wind up with the right configuration for mounting the midrange, but I think I have it figure out OK.

I have two bins filled with router bits, in their storage boxes, one for 1/2" shaft, one for 1/4" shaft. Most routers are setup for one specific task and left that way, but a couple that are useful and fast to setup for a variety of trim tasks get swapped around, like my Bosch 1517EVS and one of the Hitachi's.

Keep in mind, I'm a wires and sparks kind of guy, not a wood worker, so the ways I approach the latter activities probably aren't very conventional... I have more routers than my son-in-law has guns, but just barely, and that's saying a lot, unfortunately.

[JonMarsh]

The 2" version of these is what came in this week...

[technodanvan]

I just saw those the other day, you'll have to report back on how well they work! Mine are getting a bit long in the tooth...

[JonMarsh]

So were mine…

[JonMarsh]

My experience with their solid carbide bits to date has been exceptional

[JonMarsh]

Don't forget! Sundays are Fundays!



Time to work on my "personal" projects... starting POC crossover assembly!

[JonMarsh]

Well, what with the other "urgent" projects related to Steve's SMJ efforts, this is "only" a Sunday-Funday affair at this time...


However, that does not mean it's not in my "thoughts and prayers" and getting some significant effort in the allocated time...

While these are nominally "junk box" crossovers, even though it might seem like my "junk box" "runneth over", I've also had to order some parts for this and the CC Supreme POC crossovers. a couple of shipments are expected this coming Monday, but one for this project probably won't arrive until about May 15 (build to order), though I may be able to do some testing with not quite right junk box parts in the mean time...


So, the HF POC board is nearly ready for wiring, waiting for some new wire supplies that should be arriving Tuesday.





And the midrange POC crossover board has components loaded- with luck and speed will start wiring it also on Sunday...





The weather here has not been remotely springlike, so my plan to open the garage doors and shuffle stuff around to get organized for the next phase of woodworking is still in abeyance...

Once every six years or so, this area gets one snowfall in April, of an inch or so. April is 2/3 finished, and we already have two "events" like that this month, and typical overnight lows are usually hard freezes. The locals are scratching their heads.... many trees are still not budding out.

Of course, I shouldn't complain, this isn't Minnesota, and we're actually slightly farther south here than Minneapolis... but if I'd wanted to live in Minneapolis (been there a lot on business) I would have moved there!

[JonMarsh]

I have finally gotten back to looking at the "alternative" HF solution I had been testing much earlier this year after acquiring two samples late last year, the Beyma TPL75.



As is known from my own measurements and published measurements of the PS Audio FR30, the GRS PT2522 in it's two formats or my own modified version is not as smooth the data sheet claims or as one might desire...





While the TPL75 is not ruler flat either, the response is fairly smooth and the issues are fairly straight forward to work with...






Another "pass" on a possible design is proposed, using this part, with slight modifications to crossover points and of course a dedicated crossover concept for this AMT tweeter, and should get a plan for a "junk bin" POC build soon... to accompany the other test builds in progress.

Calculated on axis response:





Reverse connection of midrange check for nulls depth and symmetry:

[JonMarsh]

Well, the pursuit of crossover development has proceeded far enough on paper that parts were ordered Monday and Tuesday, arriving today and tomorrow, and a POC test board has already been started, based on the "junk bin" parts on hand...




The "relative" simplicity of the crossover (even while including an input LCR zobel just to flatten the system impedance, like typical waveguide designs) has further piqued my interest, to the point of updating the top module design in advance of doing the first tests with this crossover concept.

Note, the PT2522 crossover board is also well along the assembly path.





I won't go further into fabrication until I have test data with the existing POC driver eval baffles and POC crossovers, but I think this is a solid parallel track worthy of evaluation due to it's intrinsic smoothness, lack of need to LCR notch filters (unlike the PT2522) and extended top end. Of course, there is that matter of the price, but what I'm paying through a European distributor is far more economical than, say, high end ScanSpeak tweeters.

The revised cabinet design is about an inch taller...

Fabrication for the midrange and tweeter driver mounting will even raise the bar over the Wavecor Ardent...

I have some ideas to pursue, but heavens, we all know I'm not the wood worker!

[technodanvan]

Yeah, I'm thinking I'll have Steve make me a baffle for the top portion of this speaker. I'm confident I could do the mid, less confident about getting the tweeter flush mounted.

[JonMarsh]

My plans for the front baffles are still evolving, and at this point may involve some maple overlays with specific grain patterns.

Materials ordered from Woodcraft, and writing up a "process" in my planning tool (Outline)

[theSven]

My plans for the front baffles are still evolving, and at this point may involve some maple overlays with specific grain patterns.

Materials ordered from Woodcraft, and writing up a "process" in my planning tool (Outline)

We all love any excuse that comes up to buy new tools 😂. Great to see progress on this design.

[JonMarsh]

Progress sometimes happens when the subconscious co-processor "speaks up" at a convenient time of the day like 2AM this morning!

After mulling things over a bit, I ordered the maple stock to "skin" the existing front panel stock, and went back to bed.


Of course, inspiration must always result in a certain amount of perspiration, and so this AM updated the LF and MF/HF module plans....




the LF update is based on adding a 1/4" skin of figured maple, adjusting the side bevels, and noting how the spacing was working out, incorporate a 1/4" round over on the woofer rebates. This makes the effective depth of the woofer mounting an additional 1/4" behind the surface of the front panel, and for those who might be thinking in terms of grille cloths, should make that easier and with more margin.


The HF/HF module was updated also; a driving issue with creating the front panel "skins" is a fabrication methods for doing the TPL75 rebates cleanly... ET gave me the idea in a dream (Force Hints?), but swore me to secrecy for now...




This update will also facilitate increasing the Z-axis offset of the midrange to the tweeter from 0.75" to 1.0", which in the crossover POC development proved to be "optimum".

Note, again, this is only applicable/necessary for a possible TPL75 variant. OTOH, you may note that the interest level in this option means that a POC crossover for testing is already fabricated.



A tooling process has already been outlined, where else, but in my Outline application.

https://www.outline.app

It's my go-to for tracking ideas and work accomplished; similar to Microsoft OneNote, and will read and write OneNote files, but has some additional features I use often, so OneNote has fallen by the wayside for me.

[technodanvan]

In the FR30, it quickly became apparent we could not source from even the most advanced driver manufacturers in the world the ultra low-distortion high-dynamic output drivers we would need to build the FR30.

As is known from my own measurements and published measurements of the PS Audio FR30, the GRS PT2522 in it's two formats or my own modified version is not as smooth the data sheet claims or as one might desire...

Wait, are you saying the $30,000 FR30 uses a commercially available $40 tweeter?

[JonMarsh]

Don't forget that the primary goal of developing and selling "high end" speakers is to make profits...

[JonMarsh]

Hey Danny!

I'm going to first put on my "Kaptain Obvious" suit and ask you a quick question- does this top end response curve above 2kHz look like what you'd really expect or prefer for a $30K speaker in this day and age? BTW, HiFi News is part of the same magazine family as Stereophile and uses the same basic measurement techniques and equipment.




Question number 2, are you aware of the long history/back story of PS Audio and Chris Brunhaver with Bohlendar-Graebener? Are you aware that the intellectual property and manufacturing tooling of Bohlendar-Graebener were bought out by the Chinese company GRS about a couple of years ago? That's where the much improved data sheet come from, compared to what B-G was doing on their own, for starters.

Have you compared the data sheet for the B-G NEO3W with deep back cup to the data sheet of the GRSPT2522c? (the GRS version that comes with a back cup).



Now, one of B-G's talking points was the update they did switching to the Kaladex instead of Mylar, which according to B-G has a higher thermal limit, lower mass, and better durability.

If you peruse PS Audio's material, particularly YouTube videos, you'll note they are touting Teonnex, a newer material. One presumes further improvements over Kaladex. My personal surmise is that this pushes the diaphragm response frequencies up a bit compared with the PT2522 series, and that's what we seem to see comparing the HiFi News measurements to my measurements of the PT2522c with a modified sub-enclosure.



One thing you may have observed, perhaps not consciously, is that PS Audio has generally been VERY careful to not have pictures of the FR30 with the front grille covers removed. However, a time or two they have gotten a little careless.... like when they had a short video showing an FR20 prototype lying down, and there's little question about the ID of the midrange, and while the tweeter isn't installed, the MDF cabinet shows my supposition of mounting the tweeter planar forward in the Z-axis based on the design of the front cover. The MDF cabinet confirms that.



But the high resolution version of the FR30 cutaway (not used in the HiFi News article) leaves little doubt (IMO), if you focus on just the mid-top module:




There's an extra frame bit around the 5010 midrange, but otherwise, it seems pretty clear, as does the cabinet front panel, which reveals a Z-Axis offset that I suspected based on the front cover and my measurements of the 5010 and it's SPL and phase characteristic.




I've been meaning to do a rough calculation of the size of the rear enclosure they use; I think it's a bit larger than the "optimum" I think I determined by experimentation (but then, the diaphragm materials are different, so this may be optimum for the version of the 5010 they use. (suggest 7.5L for the GRSPT5010)


Now, I have not "abandoned" the PT02522 MOD4 configuration and have nearly finished a crossover for it which includes two series notch filters that can be bypassed individually with the setting of a toggle switch. That will be tested, along with the TPL75 version, but it requires a couple of component changes of the midrange crossover depending on which tweeter you want to use.

On general principles, I tend to favor the more extended response of the TPL75 and its lack of resonances in the response curve and the impedance curve. But with the right crossover approach, and sub-enclosure, the PT2522c may deliver a lot of "tweet" for the buck (good tweeters don't delver "bangs" !)

[technodanvan]

1. The top end certainly appears 'slightly' peaky, to put it mildly. Absolute Sound "Speaker of the Year" right here folks! To think I previously liked that magazine...

2. I was not aware of that relationship, but it only takes a glance at PS Audios other product lineup to know quite a lot about the company and what they think of their customers.

As an aside, I think it's interesting the FR20 prototype still features the inverted mid/tweeter cabinet. I'd think with the shorter bass cabinet a traditional TMWW would make more sense. That said, I understand the desire to 'keep it in the family'.

[Chancellor]

The tweeter location is also about seated listening height. Do recall that the FR20 video specifies a significant change in the T/S parameters of the woofer, to boost the sensitivity- this in turn requires more volume for the cabinet than might be expected.

It is not unlike the differences between the PuriFi PTT8.0X04 versus the RSS210HF.

It may not be obvious to most, but the 4 driver array picks up a 3dB increase in sensitivity like you would expect from the small line array it is, compared with a single driver of the same impedance.

[Evil Twin]

It is well worth noting that Chris Brunhaver brought considerable design skills and acumen to this project... PS Audio had been working on many variations of speakers using the B-G drivers for mid and tweeter, with recent rather ineffective approaches of using two side mounted woofers near the floor, then a 6" mid bass link driver and crossover between those with their side dispersion and the planar midrange.

With this four woofer array I am reminded of the benefits of minimizing floor bounce fluctuations in frequency response brought by the Kurosawa's three Accuton AS190 woofers. But, like the Tidal Audio inspiration for the Kurosawa, the Akira, there seem to be tuning compromises in the LF array- possibly due to a combination of an LF cabinet smaller than optimum for the woofers, and seeking to tune the passive radiators to a low FB to get output in the mid 20's, there appears a gap in LF performance between 60Hz and 30Hz if the HiFi News measurements are accurate.

[JonMarsh]

Let's put a few points in perspective... re Chris Brunhaver and The Absolute Sound and Anthony Cordesman.

• I would liken Chris to a hired gun, brought in because of his background and wide experience, to put together an effective system design with the mid and tweeter configuration, well, let's say, sort of dictated to him. Not with the freedom I have in my DIY projects.
• He created a very different base system configuration than PS Audo's earlier efforts, clearly with a goal to optimize the overall presentation in a sensible and (cost) effective manner, using high value proposition Peerless drivers.
• The results in the bottom 7 octaves pretty much speak for themselves, and due to the driver design and his 4+4 driver array should achieve very credible in room results, with more immunity than average to room positioning and acoustics in the first 4-5 octaves. Certainly a much better configuration than PS Audio previously was using, and likely more cost effective considering the Peerless driver series involved. The overall configuration of woofers, midrange, and tweeter in the middle are optimized for a seated listening position. Duh! Isn't that what is expected? (BTW, my internal name for this project is Saint-Saëns Planar, to distinguish it from the earlier concept design, "Saint-Saëns LA" (Line Array), a two way line array concept, which I happen to still have all the drivers for...)
• Call me on this if I'm off base, but if one wanted to make a glib pronouncement about the guys at The Absolute Sound, it's a collection of old guys with a strong love of music, a lot of listening experience but not a strong technical orientation, and a flair for journalistic endeavors to keep their audience on the hook. Let's just take the reviewer of the FR30, Anthony Cordesman, whom I recall reading reviews way, WAY back in Audio Magazine (how many of you remember Audio Magazine?) and in his bio admits to getting his first experience with high end selling it in the 1950's in order to get part of the money for his tuition at the University of Chicago, so yeah, he makes even ME feel young!
• Note, his day job was as a national security analyst, is the author of a wide range of studies in that area, and authored over 50 books on that topic (prolific; for my last employer, I "only" managed 55-60 publications)

🤣

• And Cordesman is very truthful and open in his review, citing his prior experience with the Infinity IRS as one of his defining audio experiences (My words) in the earlier days of the Absolute Sound. So, I'm going to go out on a limb here and project a bit, and suggest that for his encounter with the FR30's, it was like the Natasha Bedingfield song, "Pocketful of Sunshine", because within the limits of his current hearing and his memory of the earlier experience, it was probably like going home to a treasured place and time. I'm sure the IRS will play louder than the FR30s, but within the constraints of a typical home setup, and possibly Anthony's current setup and listening preferences, the FR30's would be quite wonderful and I totally get why he ponied up and bought the review samples after giving them a "Golden Ear" award. (hope he got a friendly price...)

And yeah, he's a geezer compared to me (in my opinion) but hey, he's still getting around and doing interesting things... let's hope we all are at that age.

[technodanvan]

"within the limits of his current hearing"

That's a very good point Jon, something easily forgotten is we lose the ability to hear much of that top octave or so as we age (and bottom octaves, for that matter). I certainly don't read as many reviews as others do on high end speakers, but I am curious if the trend is for such speakers that measure on the 'bright' side simply because the target audience is usually a bit more mature - that being the sort of folks that may have the disposable income necessary for such an investment. In any case, those changes would certainly play a role in how speakers are perceived - as evidenced by the reviews from AXPONA attendees showing a wide array of feelings toward not just the FR30, but plenty other high-end to ultra-high-end speakers.

This is not to say that lack of sensitivity to certain frequencies is the only reason that people comment favorably or unfavorably at such events, as we all certainly have preferences beyond that singular metric.

Great posts Jon!

[JonMarsh]

Slow work takes time, but eventually gets done! (in most cases...)


Like building the TPL75 POC test crossover board, and, hey, why not, actually testing it!

Another "junk bin build", but that's not to say the parts are junk...





BUT, no Alumen film and foil, no Clarity PUR or MR!



So, how's it look? Keep in mind, measurement is with the POC crossover connected, so the target is defined by the VituixCAD concept...


This is on axis with 2nd and 3rd harmonic distortion.




Very much what I hoped/expected to see, but may not appeal to some of the other older guys...

Considering my rock and roll live performance past, actually, even ignoring it, my hearing is rather good for my age, but then I've always been a big believer in ear protection. You're a fuul to stand in front of a double stack Marshall rig cranked up with out it... or in a workshop.


This is the 0-50 degree polar, at 10 degree increments, but you have to be on a big monitor pixel peeping to see the difference between 0 and 10 degrees- they are that close.





0-10-20 is excellent, and 30 degrees isn't too bad for an AMT driver, or even many domes, so I think it's worth trying a cabinet build with this. It's premature to fine tune the crossover until it's in an actual test cabinet.


For a reference comparison, here's the PT2522C MOD4 from 0-40 deg- I have a test crossover nearly finished for it too, with switchable filters to address the issues at 6-10kHz and 10-14kHz. In simulation, if you knock those down in level to be nearly flat on axis, then you lose quite a bit off axis between 9kHz and 20kHz.





Note, this is the smoothest of several PT2522 MOD builds I've measured. But not as extended.

Contrast with this:






Now, it's clear there is more energy off axis above 10kHz if you go with the second one... question becomes, which might sound better? Maybe just a subtle notch filter on the lower blip? with two switchable filters, I can evaluate. Might even investigate tweaking the crossover frequency a bit and going with the newest cabinet update.

Decisions, decisions.

[JonMarsh]

Slow work takes time, but can be very worth it...

---

The POC junk bin test build for the midrange was completed... not a pretty site, bordering on a case of six gallons of stuff in a five gallon can...





However, "pretty is" as "pretty does"... in this case, it "does" pretty well...






And just as important, polar response to target with high consistency...






Targets pretty much on the money- no further adjustment until target cabinets are ready.

Considering how well the response tracks off axis, I'm expecting a nice in room presentation.

I should also note that the convoluted impulse response of the driver plus crossover was very clean, quite ideal.

Additionally, the aspect ratio of this part means that floor and ceiling bounce are better controlled than for a conventional cone driver.

All are plusses.... how this will affect the presentation with music will be interesting to see....

[JonMarsh]

Some new crossover parts arriving yesterday, tested and LF crossover reviewed and updated... and more parts ordered. Plodding progress, you might say, but I'll take any form of genuine progress.

SPL for the LF update...




And a mid reverse null check...

[JonMarsh]

The "fine details" on the cabinet designs are pretty much in the bag now, after a bit of thought- and probably some luck, considering how things just fit together really well, for example, with integrating my midrange 7L sub enclosure into the planned MF-HF top module. Also, the plan for a 3/8" phenolic sheet panel on the back of the LF cabinet and the MF/HF cabinet has been implemented, and a rough fabrication plan worked out. A key point for this design element is facilitating loading crossover boards, as well as some flexibility for connectors and controls.


First, the front view of the MF-HF top module:




And also a back view, for a better "picture" of how the connection interface will work- and any possible level controls. (not yet decided- initial design is for placement at a distance from rear wall- may implement mid and HF boost for closer boundary placement). (However, an alternate approach with LF zobel networks (as implemented for the CC Supreme crossover) adjusts the LF output level- this may prove to be a "cleaner" solution.)







I adjusted the side wall render colors to be closer to the new bamboo pieces which are not carbonized as originally envisioned. Nothing really close in the tool, so I just went with a pine veneer surface.






The LF enclosure has had some similar updates for connector panels/interfaces, in particular to support using spade lug equipped cables:




And front and rear renders:







Note, all design updates are implemented in conjunction with available tooling concepts and acquisition of those tools! I have no intention of painting myself into a corner with facile CAD designs...

Of course, good intentions go before a fall, or so the old saying goes. One must keep system design and tooling design marching in step with each other.

[JonMarsh]

Not shown in these drawings are the footer extensions for lateral stability- have to keep a few secrets, right?

[JonMarsh]

Also, no drawing survives second thoughts the same day, and a few more things have been tweaked in the LF drawing.

[JonMarsh]

Note, the internal dimensions of the midrange sub enclosure (width, height, depth) follow the last test enclosure exactly. Obviously, at this point I want to just replicate the currently achieved performance.

[JonMarsh]

A very quick but encouraging update-

I decided to try measuring the PT5010 test cab and TPL75 test assembly together with the crossovers, even though I knew the CTC would be all messed up due to the cabinet designs, but maybe it would show some promise...

I offer this picture to illustrate the unlikelihood of getting a clear picture of the behavior with crossovers.... the drivers are practically in different zip codes!



Note, the PT2522 is NOT being tested, just the planar midrange and the AMT tweeter.


Well, I got everything hooked up, and well, I had a Gomer Pyle moment...
(how many of you remember him?)




I made sure the HF forward offset was set as per the VituixCAD simulations based on individual driver measurements...




No right to be able to expect something like this with decent mic placement...


Analyzing for distortion, nothing to complain about here!





Time to install the new table saw extension and finish organizing the garage workshop!

The last of the tooling stuff I think I need has been ordered and should be hear by no later than early next week...

[JonMarsh]

How's that saying go? "Progress is our most important product"

I'm in the progress of creating the 2D part drawings on the last iteration of cabinet design, as for now I think I'm "freezing" this for the build... after I make sure every thing is buildable with the tooling I plan, I'll release PDF's too. But for now, just a few image teasers of the documentation, to give you an idea of how this has been going.


On the top module and bottom module, the most complex parts are the front and rear panels. For the LF cabinet, that's actually an inner and outer front panel.

[technodanvan]

Very fancy figures you have there Jon! I'd love to make these with you at the same time, but I just don't think space will allow for it right now. I'll be using the GRS tweeter as the 'high value' PE option - plus it'll look somewhat more uniform that way. May have to experiment with various modifications given the low cost!

[JonMarsh]

I understand the space issues... I have rooms that have temporary functional assignments that will change as projects become completed and things get moved around, and as later this year a work shed gets constructed, like the one I used to have in Danville.

Slow work takes time...

I have an MTM concept based around the 2522 tweeter and Faital mid woofers- will be a while until I get back to that! Besides the Saint-Saëns, there is the CC Supreme and likely an Ardent configuration based on the same drivers, plus the Natalie P Ultra, and the budget PE Ardent with two RS210HF- which might wind up looking like an SMJ-20, but with the MOD4 PT2522- you'd probably approve of that! But find room for it? Well, it will be a bit smaller, mostly shallower.

[technodanvan]

Jon, have you seen the new 8" version of the L26ROY?

https://www.madisoundspeakerstore.com/subwoofers/seas-extreme-l22roy2-08-8-subwoofer-8-ohm/

Based on the response graph posted on Madisound I don't believe it would be suitable for a version of this project, but I was perusing the website and thought it looked interesting nonetheless. Unsure where it really fits in given the relatively high cost of the driver, and I'm curious if they'll be creating another speaker design (a la the King Coax) specifically for it.

[JonMarsh]

I hadn't seen this part yet, though I've heard rumors about it for a while- I've kind of had my head down pedaling as fast as I can with current projects!

Now, it is worth a few comments, I think... including the nature of Seas data sheet graphs, for those that may not be familiar with their somewhat unusual methodology. I've marked up this copy of the DS graph with a few arrows to make it easier to follow my explanation...

• As you mention, this is an interesting part, but not readily applicable to the Saint-Saëns project
• It incorporates an improved motor with an additional aluminum inductance linearizing ring (aka shorting ring), to reduce distortion with high excursion. This driver has a heavy copper ring and the aluminum ring. The impedance curve is impressively flat. The amplitude response isn't. More on that shortly.
• The RSS210HF has three shorting rings.
• The L22ROY2 has an Xmax of 11.5 mm; the RSS210HF "only" 9 mm. It would be very interesting to see a Kippel analysis of the L22ROY2- I'd expect it to be excellent, given the development time and all the trouble they've gone to.
• Comparing Mms and Cms is interesting- the Seas is only slightly higher for Mms, at 84 g versus 78 g for the RSS210HF. Both have identical VC diameters, at 51mm. Both have an Fs near 30Hz, the Seas is slightly higher in spite of the higher Mms due to lower compliance.
• Seas SPL plots are always done in a specified size enclosure (22L in this case) (red arrow I added above), and they provide a dotted line curve for the estimated IB LF curve, as might be measured in a more conventional test environment. Driver sensitivity of the Seas part is very good for an 8 ohm long throw woofer, one might expect bit lower from the greater Xmax. But this is where the massive magnet comes in...
• It's pretty clear that optimizing the midrange linearity and breakup mode behavior of the cone was not on their agenda- as Danny comments, it would not be a good choice in the Saint-Saëns, as the mode at 1kHz is at about 1/4 the breakup frequency of the RSS210HF, and overall is higher Q. Both will have a significant impact on midrange distortion. That's disappointing given the price of the driver. However, it's much more likely this part is intended for compact subwoofer applications with a PR or in a force cancelling configuration with EQ. And for my own system applications, I'm always looking for drivers that straddle the boundary between subwoofer and woofer. I'd say the L22ROY2-08 is firmly on the subwoofer side! Even through my wholesale European distributor, it's not a minor investment!

[JonMarsh]

I am at times amazed at the rate of update releases for Shapr3D, currently my preferred tool out of several I have licensed. The image below is not an update on the actual design, but rather an update on the part piece 2D drawing for the front panel of the MF-HF module. Shapr3D has added new software interfaces, mainly a new dedicated panel on the right, and a slew of options regarding the title block configuration. After experimenting a bit with the tool the last two weeks, I've also decided to "standardize" on an ANSI B size print drawing, and have been updating some that were C size; I'll be able to print these easily on one of my smaller Epson photo printers.

The next to most recent update a few weeks ago now supports importing images, and this drawing uses two instances of that, one for a mech drawing of the midrange mounting plate, which is shown adjacent to the front view of the piece part aligned for the size and vertical positioning that would fit in the front panel. The other is an image of the front panel piece captured from the 3D working screen, which I think is a nicer way to give something like an orthogonal 3D view as compared with the line drawing version in the view options of the software.

Now, the free version of this doesn't generate nice big PDFs, but if you're working on a larger screen, like the LG 43" 4K I prefer for CAD work, a simple screen capture using Preview (on the Mac) or other clipping tools on a PC does a pretty fair job saved as a PNG file. (No jpeg jaggies)



If there is interest later, when the design has been tested and locked down, I'll upload PDF files in a post for downloading.

[duvixan]

I'm always looking for drivers that straddle the boundary between subwoofer and woofer.

What is your opinion on SB23MFCL45-8 ? Does it qualify?

[JonMarsh]

Well, I could first respond diplomatically that "beauty is in the eye of the beholder". So, the SB23MFCL45-8 could be right for someone or for you...

I have had some specific notions for a long time (over 15 years) for what qualifies as a "good straddle" for a candidate driver... I have a friend whose self created nickname for himself is "Snobby Robby", and he concedes that at times I beat him out quite readily over being "particular".

• Smooth flat extended frequency response with an initial cone breakup mode over 1kHz, preferably over 2kHz. By smooth and flat, I mean no drop off until at least 500Hz.
• An Xmax for linear one way travel over 8 mm.
• A falling level of distortion with increasing frequency- this requires low inductivity modulation, which in term usually requires low inductance and the use of Faraday rings in the gap.
• Linear Cms over the stated Xmax-
• Reasonably linear inductance at least between resting position and 50% of Xmax.

I could come up with a few more, but then we're getting deep into Kippel territory, and getting those measurement results isn't easy unless you have the rig yourself. I don't.


Now, the factory data from SB Acoustics looks promising for this driver...







Now, it's not my intention to "beat up" on SB Acoustics, but like Faital, I see some common issues in measurements across different drivers of the same type, like this dip here in the 50Hz area. Also, because the Fs peak is high, and the ultimate impedance at 20kHz is high, the resolution down where we're more interested (under 20 ohms) is pretty poor. However, even given that, it's obvious there is an impedance discontinuity at about 900Hz, which to me looks a lot like a surround or surround + edge resonance, and we see a corresponding dip in that frequency range. So, we'r not really making it to above 1kHz clean, though the real cone upper range resonance is a pretty typical plateau effect for SB, between 2500Hz and 5kHz.

Now, in line with the motto of "trust but verify", since I can't verify this driver myself, I would have to go to someone I have enough information on to reasonably trust- in this case, we get lucky, as HiFi Compass has tested this part. I'm only going to share two graphs from his comprehensive test results:

SPL




Distortion




These plots both tell the tale, IMO, and put this driver in the class of subwoofer.

The SPL response drops about 4dB above the low to mid bass area, from 200Hz to 800Hz, where we can see the same edge/surround resonance dip due to out of phase radiation. This drop off is very similar to the E810HE-44 data sheet, the original candidate for this project.


The other concern/criteria is the distortion behavior- as frequency increases, distortion should drop, because the cone travel required to output a given SPL drops, barring some other nonlinear frequency dependent mechanism, like inductivity modulation.

well, gosh folks, this doesn't look so good, as we can see H3 (3rd harmonic) climbing by 15 dB between 100Hz and 1kHz. At the very least, I'd want to see that stay flat.

I know SB can do better, because the SB woofer (MWE19P-8) I used in the Calliope for SMJ Audio has 3rd harmonic DROPPING by 15 dB between 100Hz and 1kHz.


So, to recapitulate in the same post, here's how the RSS210HF looks in my test, which didn't record the PR data:







3rd harmonic is flat, 2nd harmonic is dropping quite a bit. Not ideal, but since the levels are also about 10-15 dB lower than typical, it's something I can live with. And the general response linearity as a function of the cone and surround are nothing less than superb in my opinion- far better than the Dayton 8" woofer, the RSS225.

I looked at every 8" woofer and "subwoofer" I could find before settling on the RSS210HF- I didn't see anything else with a similar balance of characteristics that I wanted. Now I'm developing an MTM with this part, and looking at a lower buck Ardent- the upper range gives options one wouldn't usually consider with a driver like this.

[duvixan]

I appreciate you taking the time to exhaustively answer the question

[JonMarsh]

Glad to hear that! The idea was to get you enough info so that you would know what characteristics might be useful to look at closely for your selection process in the future.

[duvixan]

Could I ask another thing?
I've noticed there's a certain reluctance in the diy world with using two 4 ohm woofers in series for bass.
2x8 ohm in parallel is much more common.
I'm not sure why? seems like the sensitivity is the same, but you also get an easier impendance load, which is always desirable.