Acoustat Answer Man is here

Hi All,

I'm not an Acoustat owner (but my brother has a Model 1 or 11, so do I qualify as part of the discussion ??).

Just wanted to add that for repairs or DIY builds you can get mylar of various thicknesses and conductive coating very cheaply from here: Electrostatic Loudspeakers By ER Audio . I have the ER Audio ESL-3, a thin membrane (3.4 micron) superfast stat, fabulous sounding speaker btw.

Regards,

Steve M.


An externally hosted image should be here but it was not working when we last tested it.
 
Andy, no problem... you certainly have information that I just don't know anything about at all...

hella, I did not end up with an angle! :D

The whole idea was to have the "wings" be adjustable. Which they are. In practice I think I ended up using them at an angle that was similar to the factory frames. Although I did at times angle the inside cells a bit more than usual to get better imaging (you "see" mostly the center cell) without losing the bass and mids... but that was somewhat specific to my particular room set up (more than 2x longer than the width at 14' - but the listening position varied between ~ 10ft back to double that or more...).

There's not much to look at with them as I never really got the thing to a finished state, although it is/was functional. When you look at it is is 3 cells more or less floating in air, held from behind at some distance by a frame... with the spectra cells in place there are a lot of wires dripping out the bottom! :D I did put one set into nice silvery woven sleeves... better.

_-_-bear

That is a most interesting sounding setup, bear. Do you have any photos? My somewhat slapped-together 3+1 setup is sort of hideous looking to most (especially the girlfriend) but they do sound rather good. :) If I could live with only 3 panels per side I'd definitely try your design. Unfortunately, I've heard what 4, 6, & 8 (and the more, the better) panels per side sounds like in my room, and I know I can't settle for less than 6 per side in the long run; the bass is just too good, particularly with rock, which I listen to a lot, and on large orchestral music. The greater weight and impact are worth it to me. The increased number of panels just seemed to energize the room in an invigorating and immersive fashion.
 
Hella, as I said what I did was not really a finished design... more a cobb'd together prototype... I don't have any pix of it on hand, but I might share them with you privately... it's not suitable for public distribution. Heh.

The 3s bass is not as strong as the 4s, that is for sure. But I use my own design subwoofers, so that was not a big issue for me. You can see them with CLS on top if you go to my website and look at the speakers page and then to the Quadripole subs... no lack of weight with them, they'll hit you in the gut if they need to. But in my room the 3s had better imaging and still good midbass.

I had tried a floor to ceiling 1+1 stack (low ceiling) and did not like the upper bass nor did I like the imaging due to the gap at the top of the cell going to the next cell... fwiw. I figured if I
was going to have put wings on it I would then rather go with a 2+2 or 3+3 (aka 6) anyhow, and the point of the 1+1 experiment was imaging...

_-_-bear
 
Just out of interest, what do you guys reckon a pair of Acoustat Spectra 66 in good condition are worth these days? I know they have become unobtainium and are highly respected.

Regards,

Steve M.

There weren't many of the 66 or 6600's produced, and most people who have them don't want to part with them (and I can hardly blame them!). But if you were to find a pair in good condition, and they were actually for sale, I wouldn't expect the price to be any less than $2000/pr, possibly much more. Being such a large speaker, it's often a matter of finding the right seller & buyer in the right place, since shipping is usually out of the question.

I was lucky in finding my Spectra 4400's, which I bought several years after I left Rockford. I bought them from another ex-Rockford employee, who unfortunately had them stored unprotected, so there was some cosmetic re-hab work to do before they were ready for the living room. That meant that I was able to get them for a very nice price (don't ask), but with my familiarity with the product, I was able to get them looking almost new. And NO, they are NOT for sale!
 
Thanks Andy, can you tell me does the Spectra 66/6600 sound different from the other Acoustat models, especially in the treble response? I thought I read somewhere they might use a smaller (less wide) treble strip for a stronger more extended treble response?

This is exactly what the ER Audio ESL-3 that I posted above has, it is a two way design with a dedicated 2" wide central treble strip that is capable of doing 25 kHz. When you hear it, it makes other stats like Martin Logan and my brother's Acoustat Model 1 sound a little lacking in treble attack.

Regards,

Steve.
 
Difference in treble response...

Steve: I cannot remember the diaphragm thickness of the ESL lll but it is either 6 or 3 microns probably 6 microns thick polyester. The Acoustat has a 65 gage HS Mylar diaphragm. That's .65 mil thick so the ER is a far lighter thinner diaphragm film. That is likely the difference which accounts for what you are hearing as far as treble response goes. The Quad ESL 63 uses a 3 micron diaphragm. Remember most dynamic speakers use a one inch dome for their high frequency reproduction so it is easy to see that even a narrow vertical line source ESL has no trouble making more than enough treble output. Regards Moray James.
 
Hi Moray: you are spot on about the membrane thicknesses and the resultant treble response, my ESL-3 is 3.4 microns thick so is light and is superfast. However, there's also the aspect that a highly charged 2" wide mylar ESL strip produces much higher frequencies and intensity than a 6" wide one, or one that is generally wide and operating full range like an ML or Acoustat.

Here's a pic of the guts of my ESL (ESL-3 at Left) ...it is designed as a 'true two way' with a treble strip in the middle and two full range ESL drivers on the sides. There are inherent advantages with this approach, better upper frequency response for one (up to 25kHz), and extreme d'appolito type focus to the soundfield. I'm surprised more ESL speaker designers don't do it this way as it takes the ESL concept to another level, IMHO.

An externally hosted image should be here but it was not working when we last tested it.


Regards,

Steve.
 
Last edited:
Steve: the size of the ESL panel has no impact on its upper frequency response. Six inches square or one inch square will extend to the same frequency if they have the same diaphragm material. The narrow line source strip will provide wide dispersion of high frequencies. As SY mentioned there will be interaction between the panel sections in the horizontal plane. I don't imagine this will be any worse than with the 5 or 6 degree angle between vertical panels in a 2+2 Acoustat for example. But I think that when you compare a 2+2 Acoustat to a 0ne plus 0ne Acoustat the difference in stage and image is likely as a result of the interaction of the two vertical panels in the 2+2. The 0ne plus 0ne provides better stage and image at the cost of overall output and bass level. Best regards Moray James.
 
Thanks Andy, can you tell me does the Spectra 66/6600 sound different from the other Acoustat models, especially in the treble response? I thought I read somewhere they might use a smaller (less wide) treble strip for a stronger more extended treble response?

This is exactly what the ER Audio ESL-3 that I posted above has, it is a two way design with a dedicated 2" wide central treble strip that is capable of doing 25 kHz. When you hear it, it makes other stats like Martin Logan and my brother's Acoustat Model 1 sound a little lacking in treble attack.

Regards,

Steve.

All Spectra models, regardless of size, use the same 1/2-panel width for the full range sector (i.e. the only area playing high frequencies). Therefore, I think the sound of all the Spectra models is very similar, with only bass extension and dynamics increasing in the larger models. In this way, the Spectra series solved the compromises inherent in the older models - that is, narrower models tended to have the best imaging but limited bass capabilities, whereas the wider models had better bass response but inferior imaging. With the Spectra series, the same character of sound is available across the model line, with merely more of it as the size and price goes up. Perhaps you can tell I'm pretty proud of what we accomplished in the Spectra series - I am!

When I left Rockford, I was using Spectra 1100's, and a few years later when I switched to 4400's, I felt that I lost NONE of the imaging qualities of the smaller speaker. The only changes were positive - more impact and bass extension. So, if you like what you hear in one of the smaller models, I feel confident that you will also like any of the larger models.
 
All Spectra models, regardless of size, use the same 1/2-panel width for the full range sector (i.e. the only area playing high frequencies). Therefore, I think the sound of all the Spectra models is very similar, with only bass extension and dynamics increasing in the larger models. In this way, the Spectra series solved the compromises inherent in the older models - that is, narrower models tended to have the best imaging but limited bass capabilities, whereas the wider models had better bass response but inferior imaging. With the Spectra series, the same character of sound is available across the model line, with merely more of it as the size and price goes up. Perhaps you can tell I'm pretty proud of what we accomplished in the Spectra series - I am!
What he said, only in graphical form ;)
 

Attachments

  • spectra_sectors.jpg
    spectra_sectors.jpg
    69.9 KB · Views: 960
When developing the larger Spectra models(3 panels wide) did you experiment with the horizontal placement of the 1/2 panel portion playing full range? (inside placement .vs. centered .vs. outside)

No, we did not. The resistors feeding the mids/lows and lows-only sectors create a time delay (as do all R-C filters), which effectively creates the curved dispersion: electrically curved instead of mechanically curved. Therefore, it makes sense that the full range sector is close to the the inner edge of each speaker, so that adjacent sectors are time-delayed (or curved away from the listener) for a smooth dispersion pattern.

If you didn't know, Spectra is an acronym for Symmetric Pair Electrically Curved TRansducer.

This is not to say that other arrangements of the sectors would not yield acceptable results, to some ears, but I think the factory arrangements do make for the best imaging/sound stage in the widest variety of rooms.
 
No, we did not. The resistors feeding the mids/lows and lows-only sectors create a time delay (as do all R-C filters), which effectively creates the curved dispersion: electrically curved instead of mechanically curved. Therefore, it makes sense that the full range sector is close to the the inner edge of each speaker, so that adjacent sectors are time-delayed (or curved away from the listener) for a smooth dispersion pattern.

If you didn't know, Spectra is an acronym for Symmetric Pair Electrically Curved TRansducer.

This is not to say that other arrangements of the sectors would not yield acceptable results, to some ears, but I think the factory arrangements do make for the best imaging/sound stage in the widest variety of rooms.

Thanks for the info and the nicely drawn Spectra hookup diaphragm. :up:

The reason I had asked about the placement of the full range section in the larger Spectra models is that I have been experimenting with my own wire ESLs. In general I found the sweet spot to be larger and imaging more stable when the full range section was placed in the center and the ladder resistor networks worked outwards toward the inner and outer edges of the panel. However, my panels are not nearly as wide as the Spectra 6600 so perhaps keeping the full range section away from the side walls with the large Spectra panels is more advantageous.