Build Thread: SMJ-40 PE MOD X

[technodanvan]

We'll need the marketing guys to come up with a suitable name for this one. I'm not sure "Saint-Saëns Technodanvan Edition" rolls off the tongue any better, so we're stuck with this for now. At least it's descriptive, if one were following JonMarsh in the original thread. In any case, I have begun the initial work on a set of SMJ-40s that feature only those parts available from Parts Express. So to be clear, here's what I'm using:

2x GRS PT2522C-4 3-1/2" Planar Tweeter with Back Cup plus face plate, MODified by Jon with an extended back cup (I state MOD X as I might try several before settling on one)
2x GRS PT5010-8 10" Planar Mid/Tweeter plus face plate
8x Dayton Audio RSS210HF-4 8" Reference Series Subwoofers
8x Dayton Audio RSS265-PR 10" Reference Series Aluminum Cone Passive Radiator

Jon has discussed the MOD variants of the PT2522C in his thread so I won't go into that. The main difference here is the use of Dayton Audio passive radiators in place of the Seas SL26R. I did this for a few reasons, but the two that stand out are price and appearance. The Seas likely has better linear performance that the Dayton, however I think the audible difference will be small (at least to my ears).

Cabinet construction will likewise be of more common materials in an aim to keep costs lower. The baffles will be 3x18mm Baltic Birch plywood, with all sides being a laminate of 18mm Baltic Birch and 1/2" MDF. I will probably mirror Jon's efforts with the phenolic plates and such as that seems integral to the design. The entire visible exterior will be Baltic Birch, so I'm thinking I might just go simple and clearcoat the whole thing...perhaps with a few hardwood inlays here and there if I have time. We shall see.

As I often do, I have enlisted one Steve Manning to assist me with the baffles. We're doing something a little different than Jon did, and it's going to require a CNC (and skills) I do not have.

Finally, in addition to the Crescendos I'm working on side by side with this, I'm hoping to take these with me to IowaDIY this year - that is, if Jon isn't going himself! In addition to praying I have enough time to finish everything, this also assumes I have enough room in my van to safely transport two sets of enormous speakers ~3,000 miles round trip.

[technodanvan]

First note regarding the Dayton passive radiators. Jon sent me his initial Unibox files demonstrating what they are capable of. After playing around with it I can say that the large volume we're talking about is very forgiving - different tuning weights and minor variations in volume result in very small changes to the output. Should be easy to recreate the model.

Edit: This is roughly what Jon's original plans show. 100w to the lower cab looks to be the maximum for sub 30 Hz bass.

[theSven]

Love seeing another built thread here on the forum! I plan on having Steve helping me with the SMJ-40 build too. However I have a center channel to complete first... Then after that I can get in the queue again. Exciting to see how this build goes.

[JonMarsh]

Well, ya know, with two cabs, knocking on the door of 110 dB, should make most folks happy and set off your Apple Watch dangerous sound pressure warning!

😮

[JonMarsh]

Finally, in addition to the Crescendos I'm working on side by side with this, I'm hoping to take these with me to IowaDIY this year - that is, if Jon isn't going himself! In addition to praying I have enough time to finish everything, this also assumes I have enough room in my van to safely transport two sets of enormous speakers ~3,000 miles round trip.

I'll give you first crack at that... I think I could get these into my FJ Cruiser, by myself, but it wouldn't be trivial!

[technodanvan]

If you like Jon, you can pick the music with which to demo these. Last year they played a four minute clip of 'house' tracks, then a four minute clip of 'builder/designer' tracks. I'll be using...nonstandard...music for the Crescendos.

[JonMarsh]

Ah, don't you love the smell of panels laminating in the springtime?

I'm still in the process of re-arranging my work space to enable working space for the big panels...

[technodanvan]

This is a problem for me too. The heat is coming (I mean, it's already in the 80s here) and I want to have enough room in the garage for the van. Competing priorities...need more garages.

[JonMarsh]

Need more garages? I can relate- theoretically a 4 car garage (one lane double deep) but too much stuff. Moving the bikes around, but expect to be bringing back one more pretty soon, assuming the new battery arrives on time, and it starts back up. (it will be trailered, but have to get it into the trailer by myself!

This is my "Goldie oldie"- a '98 VFR800 I bought new - you guessed it, back in '98! It's a great around town bike, especially since I got the Corbin seat for it and found a really cool magnetic strap securing matching tank bag!

Trying to close out this storage unit by the end of the month and take $650 off my monthly bills! CA is 3-4x more expensive than Idaho for storage. But then, I'm regularly paying close to $7 a gallon for gas in CA on my recent trips, and they have multiple refineries there! No refineries in Idaho, but at Costco I'm often under $4 a gallon! Go figure...

[Browncoat]

Love the gear-driven cam VFRs.

[JonMarsh]

Yup! Wish my VFR1200 had that, too!

[technodanvan]

Beautiful color! One we may see again quite soon...

[JonMarsh]

Hints! Always with the hints! ;^)

[technodanvan]

I placed an order just now for a fair chunk of the crossover parts from PE using their 14% off code today. Gotta take advantage while I can, even with PE-only sourced parts crossovers with this many components get pricey quick. I ended up just purchasing the woofer and mid sections for now, I'll have to wait for another sale to grab the tweeter section. There were a handful of parts I'll need to source from Madisound and/or HifiCollective as PE just doesn't see to carry a few critical values in the qualities I'm looking for.

I also purchased some inductors from Jule Fidelity - if you don't frequent the MAC/DIY forums you may not have heard of them. This is a venture by another hobbyist turned professional who (I think) helps sponsor IowaDIY. They have a lot of oddball values that I was looking for. Plus they just look really nice!

[technodanvan]

JonMarsh, I've been conversing with Steve Manning about the MOD variant of this project and we're stuck on the Z-offset value for the GRS tweeter. It looks like you initially tried 0.75" but ended up expanding to 1" for the TPL75. Would a similar offset be appropriate for the MOD3? You had some crossovers designed for it, presumably in VituixCAD, so I'm guessing you had some Z-offset entered in the box design portion of the software?

[JonMarsh]

I not only had crossovers designed for it, I'd built and tested them with the TPL75. As I explained to Steve this weekend, with the original front baffle, which is 1.5" thick, the tweeter is mounted on the front surface, and the midrange on a 1/2" BB Ply insert, for which the back is flush with the rear of the front panel.




The main issue with this configuration is diffraction reflections and cancellations from the beveled side walls.

The original flat surface test boxes were aligned for a 1" offset, and the measured results with TPL75 were "in the ballpark" as previously modeled based on individual driver testing and as desired.



The PT2522C MOD3 hasn't been tested this way in a build, only modeled based on individual measurements- same ones for the midrange, and this data as measured with the new sub enclosures (relatively new- "300 series". This is 0-50 degrees, the 0 and 10 are basically right on top of each other.




A crossover was developed for this part based on the old front panel. That will have to be changed. This is why we call it WIP- Work In Progress.

With the first version of front panel, and this PT2522 MOD300 tweeter, I could get fairly nice on axis behavior - based on VituixCAD analysis.



It took a lot of changes from the original crossovers, for both the midrange and tweeter- more parts, more LCR networks. I had some help from ET, who seems to enjoy beating recalcitrant acoustical issues into submission...

Now, If one goes to a smooth flat front panel, then the midrange response looks like the original test configuration - no diffraction stuff to deal with to speak of.




As my former colleague Bob Yee would quip, "Me likey!"

So, there is no reference for a crossover configuration for the tweeter to work in this front panel configuration. The last version modeled in VituixCAD for the other front panel might be close, as both mid and tweeter were not kluged to work together, but made to follow the concept target curve.

I hope this clarifies things for now.

Nice looking inductor, is that a laminated solid core?


Progress in construction here- the hiking trip my wife wanted to go on in Eastern Idaho this last weekend was a big time and energy sink- recommended by one of her Russian gal friends, but with little info to go on. No mention of the starting elevation of 7000 ft! Marina's husband was concerned when he found out about the recommendation, considering that I am bilaterally bionic. Also, we got bad info from Marina on the local temps- my check with Apple weather didn't agree with what my wife insisted Marina said, so we were overdressed. It was interesting, I got to prove to myself that I can sustain 130-135 bpm for 3 hours straight for the climb up in what turned out to be rough country trails at altitude... but I wouldn't call that a pleasure! Of course, going back down was easier- a piffling 110-115 BPM. Fortunately we brought 2x as much water as we thought we would need, at my insistence, and we drank it all!

[JonMarsh]

Got a few more questions from Steve, and comments regarding his discussions with other members- so, I'm going to post a little more about the PT5010, and remind folks about a few necessary points to keep in mind....

• The GRS PT-5010 is not necessarily the same driver as PS Audio uses. From the talk they give, it sounds like theirs has a different film material. Maybe there are other detail differences. Just think about all the variations in behavior that B&G produced with nearly identical looking drivers
• The GRS PT-5010 has a rising response above the primary usage range, however which way you measure it. See below. I expect the part that PSAudio uses does also. Why?
• Pictures of the FR30 showing the cabinet front in exploded view and a screenshot from a video preview of the FR20 clearly show the mounting plane of their tweeter similar/equivalent to the PT2522 mounted FOWARD in the Z axis from the midrange mounting plane. Clear as a hot day in Idaho. See below.
• The POC1 version crossover with RSS210HF, PT=5010 in 7 L, and TPL75 have the tweeter 26mm in front of the midrange in the Z axis. Please review at your leisure...

PT5010 7L QNF on axis




PT-5010 7L Polar 0-10-30-40 degrees






FR 30 Upper module cutaway from HiFi News, England. Note the Z-axis setback of the planar midrange.


VituixCAD SPL simulations, midrange set 26 mm back from the tweeter plane.




And with midrange wired in reverse phase, for phase null check.

[Steve Manning]

On to the next adventure. Danny has asked me to make the baffles for his rendition of Jon's SMJ-40 project.

Different materials are being used and a few surprises along the way. The bulk of baffles and cabinet will be Baltic Birch.

The smaller pieces on the right are for the HF module and the rest are for the bass cabinet.





And some other stuff .....

[technodanvan]

I'm really looking forward to this Steve. The hardwood you selected looks really very nice. We'll have to chat about appropriate finishes sometime...and probably long-term care.

[JonMarsh]

you mean like a long term care home? I think you're a bit young to be worrying about that yet!

🤣

[technodanvan]

Hey, gotta think ahead! These might be 'the' speakers for me for the next 20+ years!

(yeah right)

[JonMarsh]

Hey, gotta think ahead! These might be 'the' speakers for me for the next 20+ years!

(yeah right)

That's supposed to be my line! Assuming I live, say, as long as Linus Pauling!

[Steve Manning]

Doing the slow work waltz .....

While (hopefully) the last of the Baltic Birch gets glued into slabs I got to machining the first upper baffle.





Rather than doing chamfers with a router after the fact, I worked it into the CNC process this go around.



This is the bit I got to try out for the first time. That's a 1/2" diameter shaft for perspective. I still did it a a couple of passes, still a lot faster, once I figured out how to program it!

[JonMarsh]

Practice makes perfect, right?

[technodanvan]

Very cool stuff Steve, I'm always glad to see the behind the scenes of the baker baking!

[Steve Manning]

Well it was my time for fun with inserts today. Though Rampa has become the insert of choice they did not have the size I needed .... had to go for some EZ Locks. I'm no longer a fan now that I've used the Rampa brand!



I was also reminded why it's a good idea to have drivers on hand for test fitting. Sometimes the manufacturers drawings are not always correct. I suspected this was going to be the case for the radius of the inner cutouts ..... sure enough the driver would not fit.

I ended up making a flush trim template .... Jon's favorite ..... so I could adjust the corners.



Some of that double sided tape to hold it in place (it was also used to hold the wood in place on the CNC for machining





Here you can see how much needs to be removed.



After removal .... I didn't need to go very deep for the driver to fit.



Both upper baffles awaiting the tweeter modules.

[JonMarsh]

Very nice... what is it they say about practice making perfecta? I completely agree about the desirability of having drivers on hand and cross checking the manufacturer's drawings.

[technodanvan]

Beautiful work Steve!

[technodanvan]

Almost every single primary component of this design is on sale at PE right now, including the woofers, mid, mid faceplate, and tweeter faceplate. Oddly, the 10" passive radiator and tweeter are not, presumably because they both have limited quantities available right now. All other PRs are on sale though, I'm thinking of grabbing some of the 8" model, as are many of the Dayton reference line drivers.

[Scareurpasenger]

If you leave it in the cart you get another coupon!

[technodanvan]

Did you get 11%? This is so tempting but now is not really a good time....too many other purchases.

[Scareurpasenger]

Up to 12%

[Steve Manning]

Well a little more fun with inserts. These are for attaching what has been labeled "The Bulge"



Then there has been a bunch of work creating and testing CAM files to machine a test Bulge.

The first run went fairly well even though it produced some of the expected tear out along sharp edges on the part. Adjustments are required.







Just as an FYI, there are 20 different operations that go into machining each of these. Though some of them can be combined there's a whole bunch of tool changes required for the different bits. Oh for an automatic tool changer!

So now I'm setting up for a second sample with a modified approach.

[Evil Twin]

Most promising results for your efforts, Mr. Manning- you would have been a good example for Captain Needa...

[Steve Manning]

A small update .... machined the inner baffle pieces for the base cabinet today.

[JonMarsh]

Gee, you know, there's something here that looks familiar... but you have such nicer tools than I do!

[JonMarsh]

At least tomorrow under the negotiated agreement, I get to work on speaker stuff Saturday and Sunday, instead of Gazebo stuff. Stuff like this...

[technodanvan]

Ooh, are we ready for measurements?

[JonMarsh]

Maybe by the time you get here- right now, it needs the back panels and pass through wiring installed (Oval Analysis 12), the woofers, and the PR's. See, I have a "deal"- I work on the gazebo Monday through Friday, and whatever I want on Saturday and Sunday. Of course, the official footer bottom panel needs to be fabricated, along with deciding on the configuration, and the top side interface panel to the HF module (you know, a thin back layer)

Meanwhile, at Casa de Juan,




And Steve notes, that since buying one more ladder as a support tool from Costco yesterday, I now have almost as many ladders as routers...

They're my "mother's little helper(s)"... (this is an assembly job that is described by the vendor as requiring 3-4 persons to complete. I hear Steve is starting a wager pool to see how far I get...

And the first line is the punchline, for some of us!

Now, the "mother" in the song sounds an awful lot like someone with ADHD, but I don't think the pills they're talking about are the right kind...

[Steve Manning]

Things are moving along despite having grand parent duty and yard work.

The last of the glue ups for the second lower baffle





The first baffle waiting in the wings for inserts to be installed and some rear chamfers to be routered.

[JonMarsh]

Progress is your most important product, after stuff to ship to folks like Danny!

[technodanvan]

I'm not sure it was mentioned previously, but I'm having several tweeter assemblies manufactured by Steve. We decided to make 'the bulge' a feature to be seen, not something we tried to hide, and I wanted several variations such that it could be swapped out over time depending on other furniture and such in the listening room. We also discussed materials other than wood, and in that vein I had two pairs of these manufactured along with the bases for the Ensemble series. Finishing has yet to be sorted out, but I'm pretty sure I know what I'm doing for one pair. The second...well we'll see. I have some ideas but nothing firm yet.

[JonMarsh]

as someone I know is wont to say, "Shiny!"

[Steve Manning]

Looks like the guy did a nice good on the machining. Hopefully the wood parts turn out half as well. 😁

[technodanvan]

Couldn't have done it without your model Steve! I'm just glad he realized the inner holes were for screws and asked before drilling them out!

He did say he could sandblast them to remove some tooling marks, but I decided to keep them 'raw' like the Ensemble parts so the finisher can decide what is best.

[Steve Manning]

Couldn't have done it without your model Steve! I'm just glad he realized the inner holes were for screws and asked before drilling them out!

He did say he could sandblast them to remove some tooling marks, but I decided to keep them 'raw' like the Ensemble parts so the finisher can decide what is best.

Yeah that was a good catch on his part.

[Steve Manning]

A minor update .... I cut two more test samples of the bulges with Baltic Birch to tweak a few parameters. With that out of the way I'm prepping the rough lumber into machining blanks.

First up is the Tiger Maple





Then we have the Macassar Ebony ..... this stuff is absolutely stunning wood!





Last in the wings waiting for glue is the Tasmanian Blackwood.



So far processing though the jointer and planer has gone well ..... hopefully that continues when it comes time for the CNC.

[theSven]

That is some nice looking wood! Looking forward to how this comes out on the CNC.

[letiennam]

The wood panels look great. I will be making this version too. T bought full drivers, capacitors, inductors.
Because the bamboo wood distributors didn't have the 25mm thickness available, I had to order it for them to produce. They take 10 days to manufacture

[technodanvan]

Just an FYI, the crossover is not finalized so there will likely be some changes to the parts list upcoming.

It's interesting that you can order the bamboo in custom thicknesses in your area! I'm sure that comes at a cost, but the end product should be very nice.

[Steve Manning]

Productive day getting material finished for machining as well as getting the first set machined.

These are machined down to thickness and are big enough to make some nice baffles



Reduced to required size for machining.







This is the Tasmanian Blackwood and as one can see it's rather prone to tear out!

Things cleaned up with the finishing passes. First article in place for a test fit.