A new Center Channel Design study...

[JonMarsh]

OK, folks, this is HT Guide, and someone reminded me that my moderator contract requires me to design a new center channel speaker once every ten years! And I'm in violation of that, as the NeoD CC was launched in 2007! My, how time flies! Well, I'd better get busy...

The funny thing is, I collect driver information and do some testing on an ongoing basis, much of it isn't interesting enough to report here, and some, like lately, I just haven't had time to... but occasionally an idea coalesces out of all that raw data which suggests an "interesting" (as ET would say) new approach. Or, at least different approach. Not necessarily the "right" approach by normal standards, but "interesting".

This looks to be a tale with that sort of narrative.

Maybe like a wedding- something old, something new, something borrowed, something... black.


One thing I personally want to see out of a center channel is crystal clear mid and highs, low distortion and plenty of dynamic range.

This got me thinking about solutions that are straddling the pro sound area...

On the bottom end, reasonable dynamics, easy to work with frequency response, and, Geeze folks, AVAILABILITY!

BTW, the latest update today on E180HE-44 is July 29 expected in stock. That's not really reasonable, to me, after two months of "Back in stock any day now". (I have some on backorder)


I'm calling this a design study for now, too, because one of the things I'm going to explore doing is implementing a Harsch asymmetric crossover for the treble to midrange solution- This crossover type has some very specific requirements, and this may not work out, but an early back of the napkin solution for an Eminence STTI CD horn and cone mid showed feasibility. Of course, this being the "New Abnormal" the SSTI has been discontinued. Too bad, it's a nice part.


So, next I'm just going to post my proposed parts, to give an overview. Have too much other work today to do more explanation... that will come soon, but later.

[JonMarsh]

Proposed HF solution

Let's make this a top down disclosure- starting with a proposed HF solution. Just the basics...

After doing a metric ton of driver research, I may have found the 1" CD equivalent of the Peerless DA25TX, as regards value proposition. Now, I really, really like the NSD1095 performance, but the price would be off putting to many- I'm not necessarily proposing a budget project here, but I'm trying to be reasonable.

So, for your consideration, I suggest this driver from SB Audience


BIANCO-44CD-PK




This is remarkable extension and smoothness for a 1" driver. I expect to use something like a 1700Hz to 2000Hz crossover frequency nominally, but with the special characteristics required for a Harsch crossover. Note, the Harsch delivers near transient perfect impulse response and low phase shift and low group delay. There is no phase rotation.





This impedance curve smoothness is rarely matched in compression drivers, and makes it much easier to work with and lower cost for the crossover, assuming one does not want interaction between the impedance of the driver and crossover network, which would introduce irregularities in the response.






There is a Neo version of this part, to lighten the moving load for live sound, but of course it costs more. This version is about $62.


Eighteen Sound XT1086

For the constant directivity horn, I do have a favorite, after some testing, and reviewing tests by others (including Kimmo) and so we're going to go with the Eighteen Sound XT1086. A lot of BEM analysis went into this part to achieve the directivity consistency, as well as to make a very stiff and resonance free structure.

[JonMarsh]

Midrange proposal: SB Audience NERO 6RMN150D

OK, now, about the midrange...

I first looked at the Nero-6RMND150D as a midrange solution for a mini Isiris. It's another fairly new driver in the SB Audience pro line up. For me, it's a reminder of the Audax Pro 6.5" midranges I worked with in the 70's... due to the surround and cone design. But the motor seems to be far more sophisticated, of course.

Yes, there are certain elements of "nostalgia" I am indulging in this design... at least, my nostalgia. Maybe not yours. This isn't the only one...


NERO-6RMND150D















Plenty of sensitivity to pad down for response shaping as needed. Overall behavior in the range I want is quite smooth...

[JonMarsh]

Esoteric ES180TiA

OK, let's finish up with the "FUNdamentals"... pun intended.

This is another bit of "nostalgia" for me- 8 years ago when I first started looking at these Esoteric versions from Dayton, and their follow up with an improved cone. The main aspect of the nostalgia though is the fundamental design, based on a large diameter voice coil in a smallish diameter woofer, like the D6.8 HiVi used in the NeoD CC, and of course, both copying their British predecessors and Israeli imitator.

The ES180TiA is an improved version of the ES180Ti, with a smoother better controlled top end, though in this case that's not really a concern. Sensitivity is moderate, as is Xmax. In a sealed box, the output limit for a pair is about 104dB at 50Hz, but this is much lower than normal HT CC range. The pair can squeak out 110 dB at 90Hz, which should be adequate for reasonable hearing damage. The chassis rear is quite open, as is the large pole piece vent.

Le's hear it for nostalgia! I have the original version on hand, but need to order the improved "A" version. Unlike the E180HE-44, they are in stock.


ES180TiA

[Scottg]

If I remember correctly, the Kms on these drivers is really low - so not much mechanical resistance at low spl's (which should improve low-level detail as with hall-sound). Would of course require an enclosure (or no enclosure) that add's little resistance to the stroke to get the most out of it.

[augerpro]

I have 4 ES180TiA for sale if anyone wants them. Just pulled from the box for measurements in a project that is sidelined, so like-new condition.

[theSven]

Very exciting project to start off summer. Also like that you got your signature updated with all the other projects you have done Jon!

[JonMarsh]

Yeah, this is basically the center channel that Evil Twin would build if he had a home theater system- but you know, those Imperial shuttles just don't have that much room! Hard times and hard realities!

Now, the new (to me) SB Audience compression drivers came in today, and I certainly understand why they have a Neo version of this part for touring rigs. Geez, if they gave out awards for pounds per dollar for compression drivers, I'm sure this baby would take it! Now the spec sheets say just 5 lb, and the Neo version is 3 lB, but I've been handling some other 1" throat drivers, too, and most of those are around 2-1/2 lb. Just 'sayin.


I may go an order a couple more of these- I was going to be testing some Peerless CD's on the Eminence SST1 (seems appropriate; discontinued CD horn and discontinued compression driver) but I"m pondering changing my mind on that. I won't be able to do any testing for at least a couple of weeks, but lets just say, my spidey sense is tingling. Of course, I don't have a spidey sense, so maybe its just spring allergies!

I left the cutting knife in the picture for scale... this is big puppy for a 1" throat driver.

[augerpro]

Jon, why not try the Peerless with the 45mm voice coil? Basically the same design as the one you have but also includes a shorting ring IIRC. Comparing against the SB would be interesting.

[JonMarsh]

To explain briefly, I'm considering as part of this "Design Study" investigation a small parallel project using dual Esoteric 5.5" woofers (conveniently on hand) and the SST1, for which I'd already worked out some back of the napkin dimensional stuff for a Harsch crossover. This is literally just an initial "proof of concept" study for a first pass with the Harsch crossover approach.

For grins, we could call this a "Calliope CC Mini Supreme", just as a code name. However, I'm not convinced about how the lateral dispersion would work out with the two mid woofers flanking the CD, I'm more interested in testing the Harsch concept. But this is as close to a "sound bar" solution as we're likely to come with this approach!

[JonMarsh]

Jon, why not try the Peerless with the 45mm voice coil? Basically the same design as the one you have but also includes a shorting ring IIRC. Comparing against the SB would be interesting.

I've gotta check my project bin and see if I have one or two. I know at one point I was trying to order them and they were out of stock. (Gee, out of stock? How could that be? )

I have the NSD1095's. They're pretty easy to get hold of through multiple sources. But, they are about 4x the cost. Not that that would stop me for a stereo setup, but here I'm thinking to optimize this speaker for CC activities and keep the price under control.


Just checked and the 2544 is STILL backordered; not till the end of time, but the end of June at least.

I'll keep an eye on the availability status.

[vineethkumar01]

Another very interesting project..
Here is the link that contains some recent measurements done on popular 1inch CDs including the Bianco 1inch driver here:

https://drive.google.com/file/d/184Kg5kq9Qj5TO3ueZjqSrhOxaoctpxS1/view?usp=sharing

(I am sharing my personal google drive link since I am unable to upload the PDF here)
These measurements were done by Scott Hinson, who is one of the moderators of DIYRM and DIY Loudspeaker project Pad groups on facebook.

Another question I have is what is the difference between the BIANCO-44CD-PK considered here and the BIANCO-44CD-K versions for which measurements are available here: https://audioxpress.com/article/test...m-sb-acoustics

Both of their frequency responses look similar. However, the diaphragm material is PEEK in the 'PK' version and Kapton in the 'K' version. Does it make a big difference audibly even though pricewise very close? (Can one be substituted with the other in a use case like the project here, except for the sensitivity difference)

Thanks
Vineeth

[JonMarsh]

First, thanks for sharing the measurement data with us. Much appreciated, I'm looking forward to having some time (in a week or so! a lot going on now) and going through it in detail.

As to the two versions of the Bianco 44 compression driver, my perspective is that this reminds me of HiFi tweeter with dome materials of different compositions. Practically speaking, as compression drivers normally have replacement diaphragms offered, it would not be hard to convert a "K" model to a "PK model.

Looking at the manufacturer's data measured on their horn, there seem to be both difference in the mass of the diaphragm (impacting low frequency resonances) as well as possible subtle differences in the upper range behavior.

BIANCO 44CD-K







BIANCO 44CD-PK




If one is doing a perfectionist crossover, and using resistive attenuation, then the LCR shunt networks down low will need to be different.


The top end behavior is pretty similar. I chose the PK because of the overall flatness between 2K and 10K. You have to start somewhere... and of course, how it will measure and need to be compensated on a different CD horn is another matter, too. Sometimes folks overlook that fact that drivers have different throat angles internally, but in general they work best with a CD horn that is designed around that throat angle or throat angle range. These BIANCO 44 CD's have a throat exit angle of 10.86 degrees, and 3rd party info seems to indicate that will be OK with the XT1086. Unfortunately, Eighteen Sound doesn't specify this in the data sheet

[Evil Twin]

I now have clear orders now from the "Chancellor"....





"Let loose the dogs of war..."


This "design study" will be moving soon to a full project... once additional measurements and evaluations are completed for component selection. These will be given high priority, pending completion of some issues of facility construction, and fabrication of test enclosures.

Naturally, at this point, becoming a project, it should have a name, befitting it's recipient, which as alluded in internal communications and operating code names will be adopted officially:


CC Supreme.


Moving forward, the PuriFi PTT8.0X04-NAB-02 has been selected as the low frequency driver, due to the potential performance characteristics determined from system analysis, and the results of initial linearity and distortion evaluations.


CSD and distortion analysis will determine the final choice of midrange driver; between the originally nominated NERO-6MRN150D, and the Faital 6RS140. As a result of initial impedance curve examination, it is expected that the Faital part is the more likely candidate, and with the chosen woofer configuration, can meet the necessary efficiency target.

Both the SST1 and the XT-1086 will be examined closely for the treble range, and several drivers are on hand for testing. There could be a wide discrepancy in price versus performance for these solutions- naturally, the Chancellor will only receive the best solution, but others may be interested in "adequate" solutions that are not so financially demanding. The proof of concept system will of necessity feature an adjustable offset treble section, like the cabinet of the larger Wilson Audio CC, but for rather different reasons and a different optimization target, using the Harsch Asymmetric Linear Phase crossover design.

[Chancellor]

Your apparent attitude towards assuming control and responsibility for this project are commendable...

Just be sure that the results do not disappoint, in comparison to the expectations you are setting...

[theSven]

I agree with the Chancellor comment above. These are some really good components for this build. I'm interested to see how the testing goes to see which driver will make the cut for the treble.

[Evil Twin]

Picking up the development path with new tools is usually an interesting challenge- but a basic model drawing for a Proof of Concept evaluation/development cabinet has been prepared which appears suited to the requirements of the low frequency and midrange driver in this center channel application. The midrange portion extends the full depth of the test cabinet so that layered densities of damping material may be employed. interchangeable and adjustable assemblies will be employed on top for testing the high frequency configurations...

Cabinet fabrication materials have been received early, along with new driver components. Everything appears to be proceeding according to plan...

[Evil Twin]

Mr. Marsh has "advised" me of the benefits of his two stage drawing technique and the superior visualization results possible as well as the correct implementation of 2D piece part drawings - the working model of this technological center channel terror has been completely reworked from the ground up.

Unlike Captain Needa, he has proven once again his skills and insights...

[Evil Twin]

Later today it is expected that fabrication of test panels will commence. A preliminary drawing has been prepared through the expediency of importing the crude GIF from the manufacturer into EzDraw on a reference layer, and creating a scaled drawing with approximate dimensional details on another layer.

This should suffice for the POC testing for crossover filter concepts.

[Evil Twin]

So far, this design is developing just as I have foreseen...

[theSven]

Later today it is expected that fabrication of test panels will commence. A preliminary drawing has been prepared through the expediency of importing the crude GIF from the manufacturer into EzDraw on a reference layer, and creating a scaled drawing with approximate dimensional details on another layer.

This should suffice for the POC testing for crossover filter concepts.

Is it me, or does that drawing somewhat resemble a tie fighter? The only thing missing is the circle capsule in the middle, but I definitely see the force strong in this drawing. Will the tweeter mount in a separate box?

[Evil Twin]

It is most interesting in a psychological sense to observe how some images arouse an atavistic response based on the similarity to objects or situation having a profound past emotional impact.


This drawing is the overlay tracing produced in a specialized 2D drawing program which had the Eighteen Sounds mechanical drawing imported and scaled to the reference scaling system, in order to prepare a moderately accurate 3D model.

All of the work you see in this thread is for what we would describe as a POC build, or Proof Of Concept. This means it is conceived to arrive flexibly at determining a configuration that meets the overall system targets and establishes that those targets are feasible and reachable.

Because of the nature of the specialized midrange to high frequency crossover configuration and possible need to tune the Z-axis alignment, (as done with many Wilson Audio speakers on production systems) the XT1086 constant directivity horn will be mounted on a separate platform that can be relocated in the Z-axis to achieve the correct offset for the final crossover configuration. It may be possible that this is flush with the mounting plane of the woofer, but the offset required is directly related to the crossover frequency, as previously described.

This is an acoustical test process; once the final system parameters are determined, they will be handed over to SMJ Audio director Steve Manning for a "commercial implementation"

[theSven]

Very exciting and thank you for the clarification on the design.

[Evil Twin]

The fabrication facilities I have to work with are very much in a state of flux and update- so though one must deal with primitive working conditions, it is mandatory to prepare a test platform as soon as feasible.

Today's efforts were focused on the primary test cabinet front panel, for the midrange and woofers, and for the test stand for the XT1086 + driver for the high frequencies.

After cutting out a 1-1/4" maple ply blank to the outside dimensions, the next step was marking up the cutting outline per the print and locating drill holes for the interior cuts.




A quick check shows the CD horn fits as expected from the front, prior to doing the panel edge round overs.



To ensure a precision fit with the base support, a biscuit joiner was planned with inserts in three locations.

[Evil Twin]

And then there is the more complex task of the front panel... unfortunately, my Sith apprentice seemed to be occupied elsewhere, and I was left with this task to execute... and not a shop droid in sight!

Round overs were executed first, then the panels were marked and double checked for the outer rebate diameter and inner pass through.





Of course, the true test is the fit of the drivers...

[Absinthe]

[/QUOTE]

I've always been curious how others mount drivers that do not have a round mounting face. This is usually what I've come down to as I do not have a CNC. I did fit one driver by hand sing a chisel, but it was a long process. I'm still looking for a better way to do this but for now, if this is good enough for the Empire, its good enough for me!

[Evil Twin]

Consider that for diffraction control purposes, it is quite simple to cut 1/4” think felt strips into these shapes and fill the gaps between driver and the baffle. That is the plan for this POC build. For Steve, CNC is a given and he has supplementary information already from Faital on the shaping.

[Evil Twin]

On e additional task remains for the front panel, besides biscuit joiners, which is adding in the backside 45 degree relief bevels for the driver openings

[Steve Manning]

I've always been curious how others mount drivers that do not have a round mounting face. This is usually what I've come down to as I do not have a CNC. I did fit one driver by hand sing a chisel, but it was a long process. I'm still looking for a better way to do this but for now, if this is good enough for the Empire, its good enough for me![/QUOTE]

You can also make a template for use with a standard router and a flush trim bit. You would need to cut the inside hole as ET has done so the speaker flange sits flush to the substrate surface. Then trace the flange profile onto the substrate. Some careful cutting with a jigsaw to the out the profile. If you have an oscillating spindle sander it would come in handy to smooth out the profile. Then your ready to go.

[Evil Twin]

This is quite similar to what was done for the Accuton midranges on the Kurosawa project, or for the Ardent builds using the C79 driver. There are shallow door trim router bits that work well for this approach, with a cutting section only about 1/4" to 3/8" deep.

[Evil Twin]

A few members have been curious about the concept of asymmetric crossovers and this one in particular... of course, requiring a specific Z axis offset is an intrinsic "feature" of the crossovers developed for systems such as the Natalie P. I have created a simple "POC demonstrator" of this concept, relevant to the specific requirements for this system design. As shown, it does not include the low frequency crossover, or the necessary equalization for the CD driver and horn, but it does demonstrate the basic concept acceptably. The nominal driver impedance and equalized sensitivity were used as starting points; this is 100dB for the CD horn with NSD1095 driver and about 7 ohms impedance after zobel networks, and 90 dB for the midrange, with a nominal impedance of 6 ohms, reflecting the actual RDS of the 6RS140 which is described as an 8 ohm driver.


Reminder- low pass is basically a 4th order Butterworth, high pass is a 2nd order Bessel. This makes the choice of drivers and their capabilities fairly important.

As with my own "special" LR3, certain tweaks are useful and desirable.





Filter response:





SPL response:




Impedance plot:

[Evil Twin]

You may find it interesting in the case of aloe proposition optimization that the long out of stock Peeerless 2544 is now back in stock at Parts Express. At under $100, it is about 1/2 of the exquisitely designed NSD1095, but exhibits fairly adequate (by my standards) levels of performance.

[Evil Twin]

The critical factor would be evaluating it’s performance in a higher grade horn assembly than the Peerless products- this effort may commence after my return from a remote sector reconnaissance trip.

[Evil Twin]

The remote sector reconnaissance trip literally turned into something more like a baby sitting proposition for an ill equipped situation- the return through a warp tunnel deposited the crew in a very different sector than expected, and laborious methods have had to be employed in order to get to a location where this effort could be resumed.

However, more drivers have been sourced for testing, and the POC test cabinet assembly is approaching final stages, including basic finishing sanding...




Next I will commence the installation of panel damping sheets incorporating polymer, adhesive, and a mass loading metal panel.

[Evil Twin]

The Chancellor has become concerned of late over the lack of obvious progress for this effort, though work has continued behind the scenes. However, in conformance with some expectations by the selected manufacturer of retaining proprietary knowledge, information has been "closely held".

This information was found in transmission by Rebel spies, so there is little benefit to continue the blackout, as opposed to a brief summary of current status.


The POC (Proof Of Concept) cabinet build has been completed, and in accordance with directives very thorough damping of the back wave of drivers...







As one may note from visual inspection, with the Chancellor's agreement, the midrange has been upgraded to the PuriFi PTT6.5MF04 component from the Fatail 6RS140- due to its very low distortion.






Viewing the complete POC system ready for test, some astute observers may note that the HF element has been changed for this evaluation, and is now a professional grade AMT driver with CD horn. This is an investigation in progress; other solutions are still available and may be tested also.

[Evil Twin]

Some may note that this form factor is not remotely similar to popular commercial sound bars proposed by crass manufacturers as an adequate substitute for a Dolby Theater spec system, for mass market stores.

As a curious coincidence, it was found after choosing this format and driver sizes for the midrange and woofer and building the first test cabinet, that an Earth sector company located in Provo Utah produces a center channel product with the same driver sizes for the woofers and midrange. Whether those drivers from Scanspeak are of the same caliber of performance as those PuriFi drivers selected here is an interesting question- but irrelevant for the development of this system.

Preliminary measurements confirm the suitability of application and the enclosure format, and demonstrate the required range of performance to attempt the innovative crossover configuration described previously:


PTT8.0X04:










PTT6.5MF04:








TPL150H:





No further information will be shared without approval of the Chancellor.

[Chancellor]

Very interesting progress that you report.

It seems there has been some thoughtful evolution of the design concept and execution- we will await more detailed and definitive results with expectations that your efforts will not have been spent fruitlessly...

Failure is not an option.... keep this in mind at all times, for your future security and livelihood.

[Chancellor]

With further development, perhaps it would not be premature to arrange a promotion of this effort to an actual "Project" classification...

[theSven]

Sounds like a winning combination coming together for this "PROJECT"...

[Evil Twin]

Additional measurements have been collected, and five iterations of the filter network development have been completed- it is now at a stage where is seems feasible to prepare a component BOM and commence construction of POC crossovers to evaluate. Inductors are all normalized to commercially available values for components and DCR.

The planned goals for an asymmetric Harsch crossover for the midrange to HF seem to have been realized, and normalized to the Z axis time delay of the actual selected drivers. This will have to be proved out in testing, and may identify a need for small adjustments in the crossover frequency to optimize the summing with exact time delays for HF which are a function of the crossover frequency and the physical properties of the HF driver, a Beyma TPL150H.


Predicted SPL response:




Predicted Impedance:




Filter functions:

[Evil Twin]

In these times assembling the ideal components can be a surprisingly long effort, so in the name of expediency some parts available from past development efforts are being used for initial POC test builds.


The HF crossover test board is only awaiting the arrival of new wiring supplies at the Imperial logistics terminal, which my "assistants" have assured me should occur by this coming Wednesday... I reminded them of Captain Needa and that failure to deliver would have no excuses or reprieves...




Delivery of some components for the midrange test board are also pending, and it will be soon ready for wiring and testing...




The woofer crossover requires LCR zobel stabilization of the LF impedance due to the small enclosure concept and the T/S characteristics of the PuriFi PTT8.0X04 drivers. Components in storage from the Kurosawa project seem adequate to meet the immediate POC build requirements.


The individual testing and subsequent integration of the asymmetric crossover for the midrange and HF driver are the critical next steps... to verify that what is predicted in VituixCAD can be achieved with hardware.


Of note, there have been some inquiries as to whether this design might have a wider range of application.... in point of fact, there is no obvious reason why this could not be transferred to a configuration like the Ardent D, but with noting that the characteristics of the PTT8.0X04 mandate a large enclosure to achieve extended LF performance, whether ported or with passive radiators.

[Evil Twin]

The POC crossover for high frequency module based on the TPL150H AMT driver has been assembled and initial test results recorded. Conformance to the target acoustic response seems to be realized as planned, and the overall performance, including directivity, is in compliance with expectations...

A reminder, this driver combination is intended to deliver a HF characteristic with a +/- 30 degrees horizontal polar response for maximum impact, with output dropping further off axis to suppress spurious room responses.


Distortion characteristics with the POC crossover are highly satisfactory...



Given the professional level efficiency and output level capabilities of the TPL150 (102dB for 2.83VRMS), this is hardly surprising performance.

What may be surprising to those only familiar with conventional direct radiator loudspeakers is how much lower the level is off axis- secondary sound reflections should be well controlled.


This polar plot highlights why....

[Evil Twin]

A few have been curious to see the "wired" junk box HF crossover... in this instance, I will "happily" oblige...




As regards my "feelings" about the conformance to the planned acoustical target...

[Evil Twin]

The POC midrange test crossover has been constructed.... so the next necessary step is test with the tweeter crossover and verify if the asymmetric concept as simulated in VituixCAD is truly feasible and functional...




The midrange functionality with 300Hz and 2400 Hz targets was evaluated...





The expected sensitivity to Z-axis alignment was verified, as well as the range of optimum positioning...

The following is a measurement at 2 meters...





And this plot includes distortion measurement at the 2.83VRMS drive level:




It is hoped that the Chancellor will find this result satisfactory...

[Steve Manning]

Here ya go Sven ...... Getting some MDF sized for glue up for rib fabrication.