All Acoustat panels can give

[tyu]

Lot been said here on this site about Acoustat ESLs....
But I have had Acoustat panels an interfaces ....around/playing.....over 25years
Lot magic ...Voodoo..mods-tweeks.....on panels... make them a solid grid......SO the mixers don't have to drive a open wire....upgreaded parts...adjustable outboard bias 4-7k...panels just lad in frames,...no screws

But one thing I have Never done... is run the panels open ....fronts an backs
No stock felt....no tape....open!
...Martinlogan gets a good 3 more db out of there panels all open
An I know people that drive there stock Acoutats with Dynaco 35 watt tube amps.....or other small tube amps.....
So if we can get 3 more db ....open backet....we can get better /more output .....less drive is need....looks like a win-win...

So I have M3s setup...3 9"panels .....so I have opened the panel on the inside
in each speaker...
Big tone....lot more of the magic......biger stage...image....more bal/even sound.....this can be done on any ESL panels.....Acoustat,quad 57s/63 not sure
Sound lab.....no back.....see pic...

So now with the help of others.....

why is this a bad thing??.......
is it bad for the interfaces?.......
Bad for the panels?
dose it make the amp work harder?
what the down side?
An then there this...........has anyone lived with open front an back Acoustat panel?.........................why not?......
an for the diyers anyone put backing on the back of there ESL panels?

After all this time for me..... with ESLs ... Acoustat still have more of there magic too give...........
thanks for any an all info on ESLs

 

[tyu]

For this setup ....I have started...... with a 200mf cap ..... on the input of the M3s 121 interfaces....this sets a 6db type crossover.....with the all open panels ...theres still a lot of lower bass coming from the panels.....an sound for the frist time ....like 100% output... of the panels ..... with the baking off all 3 panels. now.....
No ESL I have ever heard.... have give this type of
Big ....massive sound!.....fullbody...open, texture sound.... its like the missing link!
Having any type of Backing on the panels......in one way.... if the room is right...gives.. Big full bass!......nothing bad about that......right?
but at what cost..........lot of lost magic...

Looks like most of the noise these panels make comes from the stock felt on the back....buzzs....Mylar slaping....over load....
big part comes from the way we mount the panels in a frame...........the stock MDF...that can smears the sound.....
unlike real wood.... that would turn most unwonted resonant ....in to heat an it wood... pull away from the panels......like feeds back on the panels ...any resonant from the room....interfaces box.... or the Amp driving the interfaces.....

Like seting up a outboard Adjustable Bias .....if anyone hears how much just a little more are less bias can make on the sound....all would have one!

One BAD thing about this panel mod........you may never go to go back to the stock setup!
but for myself this give so much better sound....Big tone....anyone would say ..hear what I have been missing.......
If we were at 80% ....of the best sound from stock setup Acoustats..........
this is a ezey 40 more %.......
Vary ezey mod for anyone to try....you can always go back.....
Acoustat just keep getting better......where the competition......way up there $$$$$
Long Live Acoustat Panels......

 

[tyu]

Runing the Acoustat 121 interfaces.... more are less as Jim Strickland setup the Spectra interfaces.... not to give full output...in the bass response......... if you look at the Spectra mixer schematics posted here you well see that the first res that feeds all the panels output res is 100k....with the .01 6k cap.....this is the Spectra fulrang output tap...
I have the Spectra 3....an even when the 100mf cap at the input is bypast..there still no where near the low bass output of the older 121 setups......even if all the Spectra panels input are all ran from the fullrang output point............this is how I run my Spectra 3.....it just sounds better to me......but I have lived with the sound of older Acoustat for over 25 years
An yes I know the 2123 interfaces use diff transfourmers than the 121.
but this is what I hear......when there setup side by side........

The Acoustat 121 interfaces uses a 50k res an the same 01. 6k cap in that same spot in the mixer as the 100k 0.1 6k cap in the Spectra
this 50k res lowers the frc ...vary low....if the 121 50k is replaced with 100k.. you lose lower bass output.....then if you add the 100mf cap on the input...it will move the crossover point up to above 100hz just like the Spectra...
All the Spectra interfaces mixers setup were made to have a 8"-10" driver in the setup to fill in the missing low .....

Now runing the 121...2123 this way with less lower output....an pulling the felt are any backing of the panels well give .....I say about 30-40% more output ...an way better sound.. more even frc response in the room.....that well shock anyone that hears this setup...Apogee,Magnepan,MartinLogan were always my fall back speakers.... vary closes sound to the Acoustats with mods......
this mod...tweek...an yes Voodoo magic..the sound with all open panels.....now the other speakers.... there not even close!

Getting good bass today is so ezey.....
jim new there were BIG gains in Spectra 2123 mixer setups sound .....with a littel less bass on the panels .........better lower mid....upper mids....an much better topend
is worth a littel less bass output......from these panels ....this IS the sound I have been looking for........................
All just one ESL lovers finding......

 

[harryz]

Very interesting

I recently bought some modded Acoustats that were probably model 4s, originally. Interfaces are modded Medallion reds with fuses and chokes (?) removed from the circuit, but still there. One 8" and one 9" panel side by side and stacked like 2+2s, and no back felt. I love the sound but they can boom on some material, even though they are 4' from the back wall in my room.

I want to have the interfaces restored to stock, so will try your mods. Seems to make more sense than tube traps or adding felt back to the rear of the panels...

Harry

 

[tyu]

"can boom on some material, even though they are 4' from the back wall in my room".

Only the model X,3,4,6,8s.....use the 8" panels....with the Xs-1+1-2+2s type setups
...when panels set on the floor... this adds to much bass reinforcement ........it well be hard to get them sound right....without backing..
Use paper tape.....
you well not lose topend..an it ezey to add an remove as needed to tune the panels sound..
the stock felt eats topend...... if you back off the panels screws...you well get more an better sound.... stock felt backing an to tight screws ....well add uneeded panel mass....

Running your panels full range.......adding paper tape on the panels back.. the panels won't over lode..an well sound better.............good luck

 

[harryz]

Thanks. I will buy some paper tape to try today.

Harry Z

 

[tyu]

Yes paper tape.... small price to pay ...if you don't like..take it off....
let us know what you think...find...thanks
I was playing with adding more tape.....an the topend output increases... the more you add...but then you got back off...get to be to much..tune it to you room.....
I think the tape sounds vary close to the sound of the plastic...mylar in the panels...an adds low mass ...but dappens just a nuf....
My setup is M3...flat....3ea 9" panels...no 8"...12"off the floor....open on the bottem...one more place to pic up better sound an output.....most stock setups have closed in bottems under the panels....this cuts about 30% of the output.....sounds nuts but....
just like most mods.........people say ....NO WAY...then thay hear.... the Voodoo magic..an say I never go back..........have fun...

 

[harryz]

So far,so good. Will try more on the bottom panels shortly. Thanks

 

[Mendel24]

I have been experimenting with the felt on my Spectra 22 for a few months now. I have found that the bass only outer panels really need some felt backing on them or the bass does not sound quite right. Can't really explain better than that, the bass is still there with tape only but doesn't sound.....quite right. Since these panels in my set up do not produce any high frequencies, I have glued all three felt pieces back.
The other panels, which do produce high frequencies in the Spectra setup, sound better with some of the felt replaced with masking tape. More extended and open sounding. Currently using only the larger felt on these panels, with the smaller pieces above and bellow replaced by masking tape. I have not tried removing the tape entirely and may do so now that I read tyu's report.
I think a lot of this depends on the size of the room (mine is small only 12 X 16 feet so I listen in a near field set up) and the amount of panels per side you are running. Also depends on whether your panels are running full range or in Spectra configuration. Needless to say, the felt pads have a big influence on the sound and experimentation is free and easy and very worthwhile.
I don't know if its the changes in the felt, the loosening of the bolts, the break in of caps and parts on my renovated interfaces, the new 6kv bias supply, etc. but the sound I am getting from these 25+ year old speakers is really amazing. These things are like a microscope on my system, every change I make, from tube rolling to contact cleaning to VTA changes on the turntable is easy to hear and judge. Details in the music I had not heard before on my Totem Hawks are found on just about every album, many that I have played 100s of times. The bass in very good, just wish it had a little more punch (I know I'm being greedy). I would add subs at the bottom, but the cost for the subs and a crossover of high enough quality to satisfy me would probably be 3 or 4 times what I have spent on the speakers.
Long live Acoustat!

 

[WrineX]

damping the resonance is useful, i dont know how much acoustat rely on extending the low frequency with the resonance frequency. over damping will make it then sound thin, but can harm higher frequency as well. tobad noone ever tries nylon mesh on the inside to get rid of the resonance at least a bit and not use the felt and potential harm higher frequencies. ofc this all is almost impossible to determin without any measurements

 

[tyu]

There are diff types of tape also......the paper tape is for the best topend...but duck well add more mass.... or clear packing tape has it sound also....ML has used some like the clear for backing....you can see though it........you may like the sound..
Also..add more paper tape to the lower part of the panels less on top..
2 panel Acoustats have always been tuff....I have never been abel to get the sound right ....add one more panel....seems to work best with the interfaces.....one thing over looket by minny.....interface panels match...
then you add the Spectra setup...that is not full rang...like the frist 121 interfaces........

"These things are like a microscope on my system, every change I make, from tube rolling to contact cleaning to VTA changes on the turntable is easy to hear and judge"
Boy you got that right....an thanks for posting the work your doing....
All the Acoustats are that way..... most never even pull the socks off...down...must less do any work on getting the best we can out of the panels....an that's fine....but theres a lot of magic still to be had out of the panels.....

My Spectra 3s.....I run all the panels off the full rang tap...an you can hear a big diff in the low output of the them....next to the older 121 interfaces driving my M3s....

 

[charlesp210]

Very interesting idea. Now it occurs to me the Acoustat must use some kind of resonance to augment the bass, though this may be less true on your model than my 1+1's. Because it's an open dipole, bass is acoustically short circuited below 100-200Hz (not sure about exact frequency). The panels make up for this, I would expect, by having a resonance there, somewhere in the 100-200Hz range. I would presume the felt is there to keep this getting out of hand. But if you cross over to something else you might not need this resonance. If you remove the felt, keep an ear out for membrane hitting the stators.

The Acoustats may also have a few upper resonances. (BTW, if you want to see serious treble resonances, look no further than the esteemed Quad ESL-63's, which have big resonance at 11.5kHz and others, somewhat hidden by HF roll off.) I'm seeing one resonance around 6Khz and other in the lower teens. As you go off axis the upper resonances disappear quickly but the highs remain plenty strong at least to 30 degrees off axis, which is the new angle I'm experimenting with.

 

[bolserst]

… if you want to see serious treble resonances, look no further than the esteemed Quad ESL-63's, which have big resonance at 11.5kHz and others, somewhat hidden by HF roll off.) I'm seeing one resonance around 6Khz and other in the lower teens...

From your description it sounds like your Quads are in their stock configuration with front and rear dust covers in place? The majority of the peak-valley behavior in the top two octaves of the ESL-63 and successors is due to the passive dust cover diaphragms on the outside of the stators. Even though they are only 2μm - 3μm thick they are not completely acoustically transparent in the top octaves, and reflections between the driven diaphragm and the dust covers are readily apparent in measurements. Just to be perfectly clear, the dust covers are Mylar film, not grill cloth. These dust covers are Quad’s way engineering for a long product life by guaranteeing that no dust makes its way into the air-gap.

I know I have read that some owners removed the dust covers to improve top-end clarity.
But, I am not aware of any before-and-after measurement sets showing explicitly the effect of the dust covers on the response.

 

[WrineX]

From your description it sounds like your Quads are in their stock configuration with front and rear dust covers in place? The majority of the peak-valley behavior in the top two octaves of the ESL-63 and successors is due to the passive dust cover diaphragms on the outside of the stators. Even though they are only 2μm - 3μm thick they are not completely acoustically transparent in the top octaves, and reflections between the driven diaphragm and the dust covers are readily apparent in measurements. Just to be perfectly clear, the dust covers are Mylar film, not grill cloth. These dust covers are Quad’s way engineering for a long product life by guaranteeing that no dust makes its way into the air-gap.

I know I have read that some owners removed the dust covers to improve top-end clarity.
But, I am not aware of any before-and-after measurement sets showing explicitly the effect of the dust covers on the response.

i could make that measurement in the near future. never seen a real difference. i can imagine the steel grill and thick cloth has more effect then the 3um foil

 

[tyu]

To my ears.....the only thing that has set the sound apart ...an gave the Quad 57-63......it true magic tone....even if limed .....was the so called dust cover....that is a unupstruded all open....to the ear... flat mylar ESL drivers....an yes..
some owners removed the dust covers to improve top-end clarity....but to me thay lose magic.....the dust cover make the sound...
For years I have ask....why know one has made there Esl panels this way....Well???

An as for ...the steel grill and thick cloth......that's the first thing that has to go for the best sound of any speaker.....right?

This post was started to....talk of geting a more open to the ear sound out of Acoustat ESL panels...
by getting the baking off these great panels....lot fun..biger tone-image-sound stage...I said before... with ..are with out the backing....hard to make these panels sound bad.....

But over the years I have toyed with putting dust cover over my 3ea 9" Acoustat panels...
less see...that would be
27"X 46"flat peace of mylar ..all open to the ear.........could we make this work...?....
Acoustat dreams....seems to be the story of my life....
thanks to any an all for there.... input on get better sound.....

 

[bolserst]

…ofc this all is almost impossible to determine without any measurements

+1

i could make that measurement in the near future. never seen a real difference. i can imagine the steel grill and thick cloth has more effect then the 3um foil

I have never measured an ESL-63, but I did experiment with 3µm dust covers on my ESL and in the end opted for grill cloth because of the effect the dust covers had on the sound. The dimensions of my ESL (ie distance from diaphragm to dust covers) are no doubt different than ESL-63 but you should see similar results to this.

Attachment #1: Measurements of ESL with dust covers on both sides, just front, or just rear.
The bottom plot is normalized to the reference response (ie no dust covers) so is easier to see the effect.
Attachment #2: Measurements(normalized) of dust covers compared to a simple lumped model.(surprisingly good match)
Attachment #3: Measurements(normalized) of dust covers vs. grill cloth.
This was the thickest grill cloth I tested, and even it had minimal effect compared to the dust covers.

Perforated steel grills will produce effects somewhere between that of the grill cloth and the dust covers.
The thinner and more open area they are, the more like the grill cloth they will be.

***
I meant to mention that the closer you can get the dust covers to the diaphragm the higher in frequency the peaks and dips are moved.
Because of my stator construction technique, I couldn't get them closer than about 20mm.

 

[bolserst]

This post was started to....talk of geting a more open to the ear sound out of Acoustat ESL panels...

I hope you don’t feel this talk of dust covers is drifting too far off your topic. The reason I brought it up is that the tape you are adding to the rear stator to replace the felt is likely causing similar peaks and dips in the top octaves. Since the tape is thicker than dust covers, the reflections will be stronger, but they are limited to the area covered by the tape. Somebody will need to measure it to see what exactly the end result is.

Any high frequency boost that can be added to Acoustats is usually welcome. The effect you are hearing is likely similar to the “phase plates” often used on the front of dynamic tweeters to boost the top end and improve off-axis performance.

I posted some measurements in another thread here:
Note also that the perforated sheet metal had minimal effect compared to the thin mylar tape "donut"
Perforated plate Experimental Results

 

[tyu]

..bolserst.. there no such thing as drift.... in my post..well maybe drift wood...hehe
thanks for all your work ....your helping us with....seeing what these mods too ESLs look like on paper....while it ezey for me to say what I hear....others can see what changes are real....an not my Voodoo magic....
Please fell free....to add any thing any time....I would be lost with out all the help here..

 

[tyu]

I had to take these 2+2 off a guys hands......no one need a 8' full rang ESL that as good anything $25k speaker made to day by hand in the USA.........
I have been running 6ea 9" panels off one interface.......anyone have any input on the down side?? thanks

 

[bear]

Suggest that super live walls *without* any diffusion may not be the best thing.

Your match is not what Strickland called for. But what happens on the bottom is the same as when you run IIs on the "IV" tap! Pretty much. The match for the LF changes.

The match for the HF changes too, but since they never used a "tap" for that, it will fly.

You can actually test this *if* you have a means to do a freq resp test. You'd want to test on center of a cell, nearfield, like 6-12" away. Run with only the "bass" xfmr, then run only with the "HF" xfmr. You'll see where the overlap is. Btw, they overlap a few octaves, it's not a standard "crossover" as many would expect. You may see some minor "droop" on the top of the HF, which may or may not sound better or worse depending on all sorts of factors in the room and signal chain.