Armacell Foam Inside SDA Speaker Baskets - My Experience
DarqueKnight
Posts: 6,765
Introduction
There is a discussion of this topic where some have reported improved performance by applying Armacell foam tape on the inside of SDA driver baskets:
https://forum.polkaudio.com/discussion/195562/must-try-mod-foam-inside-the-stamped-steel-baskets-yes/p1
I did not progress far enough to do an audio evaluation of this modification. I was discouraged by the difficulty encountered in removing the Armacell from the basket. It was a harrowing experience akin to close quarters combat. Due to the very small working space, there is considerable risk of damaging the cone, rubber surround, and spider during installation and removal of the Amacell foam tape. The Armacell tape can be scraped off, but it leaves a sticky residue that requires the use of a chemical solvent to fully remove. The tight working space makes removal particularly difficult.
After the Amacell was removed from one of the drivers, the frequency response and electromechanical (Thiele/Small or T/S) parameters were closer to the modified driver than to the stock driver.
The original plan was to evaluate this modification on the MW6503 and MW6511 drivers in my SDA SRS 1.2TL loudspeakers. For preliminary tests, two MW6503 and two MW6511 drivers were selected from spare parts stock. The frequency response and Thiele/Small parameters were measured using the Dayton Audio DATS V2 speaker measuring system. Room response measurements (frequency response, total harmonic distortion, and bass decay) before and after modification would have been taken using the Dayton Audio OmniMic system.
On the one MW6511 driver that before and after measurements were done, there was confirmation of differences in frequency response and electromechanical parameters. I do not doubt that these differences could result in an improvement in stereophonic performance. However, since I did not progress to audio evaluations, I am not sure that the perceived improvement(s) in one or more areas did not come at the cost of deficits in one or more other areas.
Armacell Configuration
Figure 1. One thing this exercise taught me: I did not have to worry about the Armacell falling off the basket over time.
Figure 2. The Armacell was cut into approximate 1" squares, put in place with long-nose pliers, and pressed in place with a finger. I said "approximate 1" squares" because Armacell is nominally 2" wide, but my roll actually measured 1-15/16" wide.
MW65xx Test Drivers
Figure 3. My spare SDA drivers are individually boxed and stored in a safe place.
Figure 4. MW6503 and MW6511 test drivers.
Issues With Armacell Removal
Figure 5. After the Armacell proved impossible to cleanly peel off, I used a serrated letter opener to slice the bulk of it off.
Figure 6. The remainder of the sticky foam residue and adhesive was removed by carefully painting on paint thinner with a small artist's brush, letting it sit for 10 minutes, scraping off the largest parts of foam residue with a flat blade screwdriver, then slowly wiping off the remaining softened residue with small pieces of paper towel. This process took one hour and six minutes for one driver. It was tedious work because I had to be mindful of the spider, cone, rubber surround, wires, and magnet.
Due to the difficulty in removing the Armacell, I did not proceed with before and after tests with the other three drivers, nor with before and after tests with the sixteen drivers in my SDA SRS 1.2TLs. I was also concerned that the MW6511#1 did not appear to fully return to its premodified electrical and mechanical measurements.
Measurements
Prior to doing measurements on the drivers in my loudspeakers, I wanted to get an idea of how close repeated measurements were to each other. The Thiele/Small parameters of each driver was measured five times and averaged. MW6511 #1 was measured before Armacell installation, with Armacell installation, and after the Armacell was removed. The other three drivers were only measured in their stock forms. Definitions for the Thiele/Small parameters are easily found online.
Modified MW6511 #1 Measurements
Figure 7. MW6511 #1 stock - Thiele/Small measurements.
Figure 8. MW6511 #1 modified with Armacell foam inside basket - Thiele/Small measurements.
Figure 9. MW6511 #1 - Armacell foam completely removed - Thiele/Small measurements.
Figure 10. MW6511 #1 stock frequency response.
Figure 11. MW6511 #1 Armacell inside basket frequency response.
Figure 12. MW6511 #1 Armacell removed frequency response.
Unmodified MW6511 #2, MW6503 #1 and MW6503 #2 Measurements
Figure 13. Stock MW6511 #2 first Thiele/Small measurements.
Figure 14. Stock MW6511 #2 second Thiele/Small measurements.
Figure 15. Stock MW6503 #1 Thiele/Small measurements.
Figure 16. Stock MW6503 #2 Thiele/Small measurements.
Conclusion
In the future, when I am more dedicated to audio than I am now, I may revisit this modification with one of my SDA CRS pairs. In that case, there would only be four drivers to modify compared to the sixteen in my SDA SRS 1.2TLs. There would also only be four drivers to scrape Armacell off if things did not work out. By the way, all of the tweeter and driver gaskets in all five pairs of my SDA loudspeakers are Armacell foam tape.
Another thing that comes to mind is the advice of the Polk engineer who guided me through my first SDA loudspeaker modification in 1990. Among other things, he (Chris) advised applying foam tape to the outside of the baskets to diminish ringing. He did not mention applying vibration absorbing material to the inside of the basket. Unfortunately, we can no longer just ring up Polk Audio's engineering department for modification advice.
This is not an attempt to discourage anyone from trying this modification. If it appeals to you, by all means jump in. I am merely relating my experience. Have fun, and be careful.
There is a discussion of this topic where some have reported improved performance by applying Armacell foam tape on the inside of SDA driver baskets:
https://forum.polkaudio.com/discussion/195562/must-try-mod-foam-inside-the-stamped-steel-baskets-yes/p1
I did not progress far enough to do an audio evaluation of this modification. I was discouraged by the difficulty encountered in removing the Armacell from the basket. It was a harrowing experience akin to close quarters combat. Due to the very small working space, there is considerable risk of damaging the cone, rubber surround, and spider during installation and removal of the Amacell foam tape. The Armacell tape can be scraped off, but it leaves a sticky residue that requires the use of a chemical solvent to fully remove. The tight working space makes removal particularly difficult.
After the Amacell was removed from one of the drivers, the frequency response and electromechanical (Thiele/Small or T/S) parameters were closer to the modified driver than to the stock driver.
The original plan was to evaluate this modification on the MW6503 and MW6511 drivers in my SDA SRS 1.2TL loudspeakers. For preliminary tests, two MW6503 and two MW6511 drivers were selected from spare parts stock. The frequency response and Thiele/Small parameters were measured using the Dayton Audio DATS V2 speaker measuring system. Room response measurements (frequency response, total harmonic distortion, and bass decay) before and after modification would have been taken using the Dayton Audio OmniMic system.
On the one MW6511 driver that before and after measurements were done, there was confirmation of differences in frequency response and electromechanical parameters. I do not doubt that these differences could result in an improvement in stereophonic performance. However, since I did not progress to audio evaluations, I am not sure that the perceived improvement(s) in one or more areas did not come at the cost of deficits in one or more other areas.
Armacell Configuration
Figure 1. One thing this exercise taught me: I did not have to worry about the Armacell falling off the basket over time.
Figure 2. The Armacell was cut into approximate 1" squares, put in place with long-nose pliers, and pressed in place with a finger. I said "approximate 1" squares" because Armacell is nominally 2" wide, but my roll actually measured 1-15/16" wide.
MW65xx Test Drivers
Figure 3. My spare SDA drivers are individually boxed and stored in a safe place.
Figure 4. MW6503 and MW6511 test drivers.
Issues With Armacell Removal
Figure 5. After the Armacell proved impossible to cleanly peel off, I used a serrated letter opener to slice the bulk of it off.
Figure 6. The remainder of the sticky foam residue and adhesive was removed by carefully painting on paint thinner with a small artist's brush, letting it sit for 10 minutes, scraping off the largest parts of foam residue with a flat blade screwdriver, then slowly wiping off the remaining softened residue with small pieces of paper towel. This process took one hour and six minutes for one driver. It was tedious work because I had to be mindful of the spider, cone, rubber surround, wires, and magnet.
Due to the difficulty in removing the Armacell, I did not proceed with before and after tests with the other three drivers, nor with before and after tests with the sixteen drivers in my SDA SRS 1.2TLs. I was also concerned that the MW6511#1 did not appear to fully return to its premodified electrical and mechanical measurements.
Measurements
Prior to doing measurements on the drivers in my loudspeakers, I wanted to get an idea of how close repeated measurements were to each other. The Thiele/Small parameters of each driver was measured five times and averaged. MW6511 #1 was measured before Armacell installation, with Armacell installation, and after the Armacell was removed. The other three drivers were only measured in their stock forms. Definitions for the Thiele/Small parameters are easily found online.
Modified MW6511 #1 Measurements
Figure 7. MW6511 #1 stock - Thiele/Small measurements.
Figure 8. MW6511 #1 modified with Armacell foam inside basket - Thiele/Small measurements.
Figure 9. MW6511 #1 - Armacell foam completely removed - Thiele/Small measurements.
Figure 10. MW6511 #1 stock frequency response.
Figure 11. MW6511 #1 Armacell inside basket frequency response.
Figure 12. MW6511 #1 Armacell removed frequency response.
Unmodified MW6511 #2, MW6503 #1 and MW6503 #2 Measurements
Figure 13. Stock MW6511 #2 first Thiele/Small measurements.
Figure 14. Stock MW6511 #2 second Thiele/Small measurements.
Figure 15. Stock MW6503 #1 Thiele/Small measurements.
Figure 16. Stock MW6503 #2 Thiele/Small measurements.
Conclusion
In the future, when I am more dedicated to audio than I am now, I may revisit this modification with one of my SDA CRS pairs. In that case, there would only be four drivers to modify compared to the sixteen in my SDA SRS 1.2TLs. There would also only be four drivers to scrape Armacell off if things did not work out. By the way, all of the tweeter and driver gaskets in all five pairs of my SDA loudspeakers are Armacell foam tape.
Another thing that comes to mind is the advice of the Polk engineer who guided me through my first SDA loudspeaker modification in 1990. Among other things, he (Chris) advised applying foam tape to the outside of the baskets to diminish ringing. He did not mention applying vibration absorbing material to the inside of the basket. Unfortunately, we can no longer just ring up Polk Audio's engineering department for modification advice.
This is not an attempt to discourage anyone from trying this modification. If it appeals to you, by all means jump in. I am merely relating my experience. Have fun, and be careful.
Proud and loyal citizen of the Digital Domain and Solid State Country!
Comments
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Thanks Raife,
Drivers are getting harder and harder to get, so I'm in no hurry to do my 12 drivers.
I'm good with the dynamat/second skin outer mod to dampen to basket.
My last mod will be the new tweeter billet bezels. -
Who is doing the tweeter billet bezels and when will they be available?
Proud and loyal citizen of the Digital Domain and Solid State Country! -
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Crazy, I was just talking to Rob last night about you Ray, and had you purchased any of these Tweeter Bezels from him, and how great it would be to see a write up from you about them..
Ironic or fate?? -
Crazy, I was just talking to Rob last night about you Ray, and had you purchased any of these Tweeter Bezels from him, and how great it would be to see a write up from you about them..
Ironic or fate??
Both and Timely."Sometimes you have to look to the past to understand where you are going in the future"Anger is just anger. It isn’t good. It isn’t bad. It just is. What you do with it is what matters.
You can use it to build or to destroy. You just have to make the choice. Jim Butcher
Harry / Marietta GA -
@xschopDarqueKnight wrote: »Who is doing the tweeter billet bezels and when will they be available?
https://forum.polkaudio.com/discussion/191870/rd0-billet-faceplate-upgrade/p1
Edit...Ooops, just saw pitdogg2 said same, above. What he said...lol. Do it, Ray! Also agree w/Larry.......how great it would be to see a write up from you about them.
Although I documented my progress/results, I'm just chatter to most. When EF@DarqueKnight speaks, everybody listens. For those of you old enough to remember...
https://www.youtube.com/watch?v=2_ygqPepLjM
➀Speakers: Polk1.2tl's (Uber Mods) ➁Pre/Amp/DAC: PS Audio BHK Signature & 250, DirectStream ➂Cables/IC's: MIT S1Bi-Wire/S1 Balanced +Avel Lindberg 1000VA "Dreadnought" ➃Power Conditioner: PS Audio P15 Power Plant ➄Power Cords: Core Power Technologies Gold, DH Labs Power Plus DIY w/Neotech NC-P301 & P311ends ➅Streaming: Roon ROCK on wifi'd NUC, TP-Link WAP, & Uptone EtherREGEN, AfterDark, Emperor Double Crown Clock, Black Modernize LPS, PS Audio AirLens⟿Ω☯☥☮⟿🔊♩♪♫♬♩♪♫♬♩♪♫♬ -
Aluminum tweeter plates are ordered. Review is forthcoming.Although I documented my progress/results, ....
Link please. I looked through your comments and discussions and didn't see it.Proud and loyal citizen of the Digital Domain and Solid State Country! -
NICE !! Looking forward to it.... Try not to get more dedicated to audio thou
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@DarqueKnight Meticulous as always!! Some were afraid that the foam would fall off and end up on the floors of their speakers and some were afraid they couldn't remove if they didn't like it. Your input will help those people.
Really looking forward to SPL vs Freq. and Harmonic Distortion vs Freq., especially the latter because wouldn't that be where out of phase reflections of the back wave impacting and transmitting through the cone would most likely have a noticeable effect?
How does some foam on the basket affect the free air resonance of Impedance vs. Freq. (Fs)? I'm still learning. I think that there is an error in the Qts calculation for the unmodded driver though, which if corrected, makes the avg. for unmodded vs modded pretty insignificantly different. Qts = (Qes x Qms)/(Qes + Qms). I think the Fs of 36.34 in Meas. 1 of unmodded driver is a bit of an outlier and maybe could be thrown out, also, bringing the avgs. closer for unmodded vs modded?
Thanks for attempting to shed more light on this for us, in a scientific manner, which is what we have all come to admire in you.
George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
➀Speakers: Polk1.2tl's (Uber Mods) ➁Pre/Amp/DAC: PS Audio BHK Signature & 250, DirectStream ➂Cables/IC's: MIT S1Bi-Wire/S1 Balanced +Avel Lindberg 1000VA "Dreadnought" ➃Power Conditioner: PS Audio P15 Power Plant ➄Power Cords: Core Power Technologies Gold, DH Labs Power Plus DIY w/Neotech NC-P301 & P311ends ➅Streaming: Roon ROCK on wifi'd NUC, TP-Link WAP, & Uptone EtherREGEN, AfterDark, Emperor Double Crown Clock, Black Modernize LPS, PS Audio AirLens⟿Ω☯☥☮⟿🔊♩♪♫♬♩♪♫♬♩♪♫♬
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Gardenstater wrote: »Really looking forward to SPL vs Freq. and Harmonic Distortion vs Freq., especially the latter because wouldn't that be where out of phase reflections of the back wave impacting and transmitting through the cone would most likely have a noticeable effect?
In recalling the efforts of DIY speaker builders I have studied, they tended to concentrate on stiffening the basket and reducing its vibrations, rather than reducing reflections from the inside of it.
I agree that frequency response and harmonic distortion tests would have revealed more useful information that the T/S parameters. However, I was scared off by the vice grip of the Armacell. I might be braver in the future, with a smaller size SDA loudspeaker.Gardenstater wrote: »How does some foam on the basket affect the free air resonance of Impedance vs. Freq. (Fs)? I'm still learning.
The foam, like any damping material, has more effect on vibration abatement, which reduces overall coloration due to basket vibration. Ideally, the only thing that should be moving is the cone/voice coil/surround assembly. Taking out the vibration from the cabinet, basket, and baffle allows the driver to operate more cleanly and efficiently because it isn't "fighting" with the basket.Gardenstater wrote: »I think that there is an error in the Qts calculation for the unmodded driver though, which if corrected, makes the avg. for unmodded vs modded pretty insignificantly different. Qts = (Qes x Qms)/(Qes + Qms).
Thank you for catching that. The number in my handwritten notes is "0.3138" and I wrote it incorrectly when transferring to the Excel spreadsheet.
I don't know the design details of SDA drivers well enough to know what numerical amount of difference in the T/S parameters is considered significant/insignificant. I do know that when it comes to loudspeakers, small changes, like a few degrees of change of toe in, or a change in tweeter dome material, can have significant audible effect. SDAs are a non-conventional speaker design. Something that might be numerically insignificant in a conventional speaker might be a big deal with SDAs. I would love to be able to discuss my measurements with a Polk engineer...but those days are long gone.
Most intriguing were the measurements of the mod-reversed driver being closer to the modded driver than the stock driver. However, this was a small sample size of one. It's possible this driver is an outlier.Gardenstater wrote: »I think the Fs of 36.34 in Meas. 1 of unmodded driver is a bit of an outlier and maybe could be thrown out, also, bringing the avgs. closer for unmodded vs modded?
I don't know that that measurement is an outlier. A driver is always going to react a little bit differently to successive electrical test signals. Also, I did not use lab grade test equipment with close to identical test signals for repeated trials. That is why I did five frequency sweeps and averaged them.Proud and loyal citizen of the Digital Domain and Solid State Country! -
DarqueKnight wrote: »"In recalling the efforts of DIY speaker builders I have studied, they tended to concentrate on stiffening the basket and reducing its vibrations, rather than reducing reflections from the inside of it."
"The foam, like any damping material, has more effect on vibration abatement, which reduces overall coloration due to basket vibration. Ideally, the only thing that should be moving is the cone/voice coil/surround assembly. Taking out the vibration from the cabinet, basket, and baffle allows the driver to operate more cleanly and efficiently because it isn't "fighting" with the basket."
I got this idea largely from reading the Vandersteen Midrange Driver Patent, where he addresses the undesireable effect of internal basket and magnet motor reflections that are time delayed and out of phase with the desired signal, coming back and impinging upon the rear of the cone where some fraction of them are again reflected back and another fraction are absorbed, and the remaining fraction is actually transmitted through the cone to the listener in the form of undesirable distortion.
He doesn't go into mechanical vibrations attenuation of the basket at all in his patented midrange driver design. As far as my foam mod goes, I am sure that is at play, but to a much lesser extent. When I did only my left speaker I had to raise that speaker's signal by 0.4dB to bring it back to being balanced with the right speaker with whitenoise. Both were balanced as closely as possible with the equipment I had, to within 0.1dB prior, with whitenoise. I believe that was due to the attenuation of those backwave reflections Vandersteen talks about in his patent. This is the same thing KEF is doing with their new META speaker.George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
Gardenstater wrote: »I got this idea largely from reading the Vandersteen Midrange Driver Patent, where he addresses the undesireable effect of internal basket and magnet motor reflections that are time delayed and out of phase with the desired signal, coming back and impinging upon the rear of the cone where some fraction of them are again reflected back and another fraction are absorbed, and the remaining fraction is actually transmitted through the cone to the listener in the form of undesirable distortion.
He doesn't go into mechanical vibrations attenuation of the basket at all in his patented midrange driver design. As far as my foam mod goes, I am sure that is at play, but to a much lesser extent. When I did only my left speaker I had to raise that speaker's signal by 0.4dB to bring it back to being balanced with the right speaker with whitenoise. Both were balanced as closely as possible with the equipment I had, to within 0.1dB prior, with whitenoise. I believe that was due to the attenuation of those backwave reflections Vandersteen talks about in his patent. This is the same thing KEF is doing with their new META speaker.
I obtained a copy of Vandersteen's 1991 Midrange Driver Patent #5,073,948. A PDF is attached for the interested reader. I also reviewed the information, including a short video, on KEF's website regarding their META technology. Both address backwave reflection inside the driver with a holistic approach which required a complete redesign of the driver.
Some SDA owners have addressed the absorption of backwave reflections with the installation of sound absorbing material directly behind the drivers. In my SDA SRS 1.2TLs, I use 3" wide x 27" long strips of Black Hole 5 damping material behind each column of drivers. This is in addition to the polyfill material and the installation of additional strips of Black Hole 5 on the interior sides of the cabinets in the driver area.
https://forum.polkaudio.com/discussion/comment/1985692
The thread linked above shows that I am fully in favor of cancelling back wave reflections. I'm not so sure that putting sound absorbing material inside the driver is the best way to address this issue, particularly with our scarce, decades-old SDA drivers. Vandersteen appears to agree. The quote below is from pages 5-6 of the Vandersteen patent, beginning at line 65 of column 2 on page 5:
"In accordance with the present invention, several features of the speaker driver design have been modified in order to eliminate internal reflections from the speaker involving three structures. These include, first, the basket structure itself; second, the magnet structure; and third, the zone of space between the diaphragm and the basket and magnet structures. An alternative, but less desirable structure employs sound absorbers and dispersers mounted within the speaker driver itself.
It has been found that a redesign of the basket structure and the magnet structure can reduce the projected area as seen by the rear wave from values of 50%: or more, as found in conventional designs, to values well below 50%. This serves to eliminate the internal reflecting wave to a substantial degree. Further, by designing the basket arms so that reflections are directed away from the diaphragm also reduces the unwanted rear wave reflection. Redesign of the magnet structure has been undertaken, in accordance with this invention, in a way which elongates the magnet structure while reducing its overall diameter so that its projected area is also substantially reduced."
Further down, beginning at line 46 of column 3, Vandersteen discusses the use of sound absorbers inside the driver.
Now that I see how Vandersteen and KEF addressed the issue of backwave reflection, I am curious to see what Sonus faber says about it...since I am a shameless Sf fanboy.
I am very enthusiastic about experimenting and I like to see others engage in experimenting. I am pleased that some have enhanced their listening pleasure with this modification.Proud and loyal citizen of the Digital Domain and Solid State Country! -
I've also BH5 mine behind the drivers as well as factory dacron roll. I actually played with just a bit more dacron but went back to the factory amount. That extra turn on the roll was too much.
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DarqueKnight, it is very rewarding to see your tenaciousness again in all that you do."Sometimes you have to look to the past to understand where you are going in the future"Anger is just anger. It isn’t good. It isn’t bad. It just is. What you do with it is what matters.
You can use it to build or to destroy. You just have to make the choice. Jim Butcher
Harry / Marietta GA -
I've followed Matt Polk's advice and experimented whole-heartedly on many of his designs. Of all the mods, this was the least investment for the return and I like how it clears up the last bit of smear in vocals at higher volume. The semi-curved frame uprights do take up alot of real estate compared to the open windows. At what point of frame area/window area ratio does the backwave start causing issues is the real question IMO. Newer drivers are all thin-frame upright castings that ameliorate this issue that Gstater set out to address with this modification.
Don't take experimental gene therapies from known eugenicists. -
The semi-curved frame uprights do take up alot of real estate compared to the open windows.
Yes. When I was trying to get the Armacell out of the uprights, for a brief moment, I thought about cutting away 50% of the uprights with a Dremel.At what point of frame area/window area ratio does the backwave start causing issues is the real question IMO.
I wonder how much thought Polk gave to this issue in the SDA era. The LSiM and Legend drivers have spider leg baskets.Newer drivers are all thin-frame upright castings that ameliorate this issue that Gstater set out to address with this modification.
I just came from the Sonus faber website. They use thin-frame baskets and extensive vibration abatement techniques throughout the cabinets.Proud and loyal citizen of the Digital Domain and Solid State Country! -
The legend series are stamped baskets with wide spikes similar to sda- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit. -
I remembered the Legend narrow spikes and not the wide ones.
Proud and loyal citizen of the Digital Domain and Solid State Country! -
Looks to be similar. Compared to the lsim and most modern drivers the spokes are pretty wide- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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It looks like the Legend driver has 2 spiders sandwiched together. Possibly their attempt to correct reflections and/or improve voice coil concentricity/travel that plague SDA/Monitor drivers?Don't take experimental gene therapies from known eugenicists.
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The cat has been out of the bag for a long long time with the higher end driver manufacturers! I posted this in my Foam Mod thread but I'll put it here too for some comments hopefully, where it got none before:
SEAS Prestige Titan H1869-08 / L16RNX3 6" Aluminum Cone Woofer
L16RNX3 is a High Fidelity woofer with an injection moulded metal chassis, intended for bass reflex and closed box designs.
Optimized cone design combined with the stiff and light weight aluminium gives a high break-up point to allow for easier crossover design and wider bandwith than common aluminium cones.
Titanium voice coil former with a very long copper coil winding and a bumped back-plate for excellent force transfer, transient sound reproduction and large linear excursion.
A heavy copper ring below the T-shaped pole piece reduces non linear and modulation distortion.
Extremely stiff and stable injection moulded metal basket keeps the critical components in perfect alignment. Large windows in the basket both above and below the spider reduce sound reflection, air flow noise and cavity resonance to a minimum.
https://www.madisoundspeakerstore.com/approx-6-7-woofers-seas/seas-prestige-l16rnx3-6-aluminum-cone-woofer-h1869-8-ohm/
@xschop you can clearly see how they deliberately removed the electrical connection tabs from the reflection zone so, as you know, you were on the right track with that......
George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
I emailed the following two questions to Polk's customer service department, and asked that they be forwarded to Polk's engineering department, (specifically to Stu Lumsden if he is still available to answer questions).
Question 1: This question concerns the MW6XXX series midwoofers in the vintage SDA series.
Would there be any performance issues with applying a small 1-1/4" x 1-1/14" square of sound absorbing foam to the inside of the basket uprights? The purpose would be to absorb backwave reflections from the uprights and provide additional clarity of sound. See pictures below.
People who have tried this modification report an increase in overall clarity.
The foam used here is Armacell tape, which is an insulating tape for homes.
Question 2: The picture below is a new MW6511 driver on the left and an original MW6511 driver on the right. The new 6511 has basket uprights with a "channel" in the middle, whereas the basket uprights on the original 6511 are smooth.
Was the upright channel added in the new 6511 for added strength, to scatter backwave reflection, or for ease of manufacturing?
Comparing the original MW6503, MW6510, and MW6511 drivers to their newer replacement counterparts, there appears to be some consideration given to mitigating backwave reflections.
Figure 1. New MW6511 top, original MW6511 bottom. The new MW6511 has basket windows that are a little taller, 1.056" compared to 0.9695" in the original. The original MW6511 basket windows are a little wider, 2.476" compared to 2.3925" in the new MW6511. The windows in the new MW6511 are overall a little larger.
Referring to figure 1, the terminal tabs of the new MW6511 are positioned up out of the way of the basket window. The new MW6510 and new MW6511 drivers only have two terminal tabs. The new MW6503 driver has four terminal tabs. The terminal tabs of the new MW65XX drivers are not pressed down into the basket windows. Each of the basket uprights of the new MW65XX drivers has a channel in the middle. This could be for backwave scattering, added strength, ease of manufacturing, or a combination of these. I asked Polk engineering to clarify.
I measured the circumference of the old and new MW6511 window openings by applying a bead of Mortite rope caulk around the window edges and measuring the length of the cords.
Figure 2. One of the terminal tabs of the original MW6511 was cut off with a Dremel cutoff wheel for comparison with the tabbed window opening.
Figure 3. Window of original MW6511 with Mortite bead.
Figure 4. Terminal tab of original MW6511 with Mortite bead.
Figure 5. New MW6511 window with Mortite bead.
Figure 6. The terminal tab in the original MW6511 takes up 1" of window circumference, reducing it to an effective 5.25". The window circumference of the original MW6511 with the terminal tab removed is 6.25". The window circumference of the new MW6511 is 6.5".
Figure 7. New MW6511 on left, original MW6511 on right.
Proud and loyal citizen of the Digital Domain and Solid State Country! -
@DarqueKinght good stuff there......was the newer MW6511 stamped out of the same gage of steel or was it thinner?
Here's some photos from a Sept. 2009 article that people may now find more interesting:
https://www.ultraaudio.com/features/20090901.htmGeorge / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
The new MW6511 steel is much thinner, measured at the rim. This can easily be seen when they are side by side.
New MW6511 left, rim thickness 0.80 mm. Original MW6511 right, rim thickness 1.28 mm. The rim thickness of one of my new MW6510s is also 0.80 mm.
The thickness of the window rims of the new MW6511 varied from 0.71 mm to 0.83mm. The thickness of the original MW6511 window rims varied from 1.14 mm to 1.32 mm.
Measurements taken with Mitutoyo model # 500-196-20 digital calipers.Proud and loyal citizen of the Digital Domain and Solid State Country! -
I've been clipping those worthless tabs off for ages now. The corrugated upright on new 6511 driver is technically stronger assuming same gauge stamped steel used. Nice to see that they extended leads further to get the terminals out of the window(s).
This is the last mod I'll be doing to the 8TL's MWs. Gold plated copper and smallest I had enough of to do all 4 mids. The wire leads actually reach easily, moreso than trying to bend tab upwards and re-solder...
They came with the little insulators that are perfect for the gauge steel and a layer of butyl mat. But looks like I have to cut away about 5/8 diameter circle of the mat around the terminals because it is aluminum-backed...
Post edited by xschop onDon't take experimental gene therapies from known eugenicists. -
@DarqueKnight Another way to measure the basket window areas would be to trace the windows out on a piece of paper or shirt cardboard which is on the inside of the basket and cut them out and weigh them.
Can you weigh the new 65xx drivers vs the old ones?
@xschop Are those threaded posts hollow on the inside for the wire to be soldered into and then there is a nut to secure to basket with the electrical insulators in place? Just trying to picture.....George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
Yep, hollow with stainless nuts and mini lockwashers. Once all snugged down. I'll hit the nut and thread with solder.
And the new MWs have even cheaper stamped steel baskets, I see.Don't take experimental gene therapies from known eugenicists. -
The original MW6511 weighs 2.4 lbs. The new MW6511 weights 2.2 lbs. The scale was a Befour FS0900.
Toys and tools have now been put away for the evening. Enjoy your weekend.
Proud and loyal citizen of the Digital Domain and Solid State Country!
