Hey everyone, happy weekend!
So I picked up a pair of working Acoustat Spectra 1100s at an estate sale for $425. They look pretty good and sound decent. I've always wanted to experiment with electrostats so here is my chance. These things are big! Anyway....underwhelmed so far. I don't really have an amp that can drive them well yet - running on a Pass DIY Zen v4 right now. Totally not the best match lol. The previous owner was running them with an Adcom GFA-555 Mk II. I think the panels have potential with some fresh modern caps, a strong amp and more placement tweaking. Was wondering how much that step-up transformer colors the sound. The bass though needs a lot work.
Two questions/observations:
1. The treble on one side is quieter than the other and the problem follows the crossover box. Nothing looks bad on the crossover boards, and while I did not measure anything yet, I am starting with the assumption it could just be related to 30 year old caps beginning to wear out.
2. Most importantly right now. The bass is overblown! Noticeably way too loud and boomy. The drivers match pictures online, so I am assuming they are the correct units. Still though, the bass does not integrate well with the sound from the panels. Whether the speakers are 3 ft from the back wall or 11 ft from any wall in the middle of my basement, the bass is just too loud and thick. I noticed the woofer boxes are stuffed with polyfill....was thinking I could removed some and see if the sound at least tightens up.
What are you thoughts on this, especially the bass response.
Side note: They claim these are 8" woofers, but they measure nearly identical to the 7" in my Energy Pro 22 Reference Connoisseurs. They look like 7" too. They sound like subwoofers more than woofers.
So I picked up a pair of working Acoustat Spectra 1100s at an estate sale for $425. They look pretty good and sound decent. I've always wanted to experiment with electrostats so here is my chance. These things are big! Anyway....underwhelmed so far. I don't really have an amp that can drive them well yet - running on a Pass DIY Zen v4 right now. Totally not the best match lol. The previous owner was running them with an Adcom GFA-555 Mk II. I think the panels have potential with some fresh modern caps, a strong amp and more placement tweaking. Was wondering how much that step-up transformer colors the sound. The bass though needs a lot work.
Two questions/observations:
1. The treble on one side is quieter than the other and the problem follows the crossover box. Nothing looks bad on the crossover boards, and while I did not measure anything yet, I am starting with the assumption it could just be related to 30 year old caps beginning to wear out.
2. Most importantly right now. The bass is overblown! Noticeably way too loud and boomy. The drivers match pictures online, so I am assuming they are the correct units. Still though, the bass does not integrate well with the sound from the panels. Whether the speakers are 3 ft from the back wall or 11 ft from any wall in the middle of my basement, the bass is just too loud and thick. I noticed the woofer boxes are stuffed with polyfill....was thinking I could removed some and see if the sound at least tightens up.
What are you thoughts on this, especially the bass response.
Side note: They claim these are 8" woofers, but they measure nearly identical to the 7" in my Energy Pro 22 Reference Connoisseurs. They look like 7" too. They sound like subwoofers more than woofers.
The relative performance of the woofer section cannot be properly evaluated without first ensuring that the ESL portion is working properly. If the ESL is working at less than normal volume, the woofer will seem too loud. Since you already observed a channel imbalance in the ESL portions, the first order of business is to make sure the high voltage bias is working and set properly.
Review the attached documents. If, after examining the components in your interfaces, you determine that your speakers have not been updated, then by all means perform that modification first. "Spectra 1100 schematic & board layout" will be useful in locating parts. The easy thing to check is the red wire exiting the bias transformer - if it lacks the second wire wrapped around it, it needs to be modified. See item 9 on the "BiasFix Diagram". Follow all cautionary statements, and if at any time you're not sure what you're doing, then STOP!
The next step is to adjust the bias voltage per instructions "biasadj". The step is vital to ensure both channel balance and level-matching with the woofer.
If the above fails to fix the issues, then I suggest replacing the high voltage diodes and capacitors, see "Bias Multiplier Parts". Repeat bias voltage adjustment after replacing parts.
I don't believe there is an industry standard for measuring woofer diameter. So one man's 7" is another man's 8". The crossover is set for the ESL portion to cover as broad a range as practical for a single panel, with the woofer kicking in around 150 Hz.
These speakers hunger for both voltage and current. I know nothing about your amp, so cannot comment on its suitability. 100 watts per channel is generally considered a minimum, with a max of 250 wpc, used with common sense and caution.
Review the attached documents. If, after examining the components in your interfaces, you determine that your speakers have not been updated, then by all means perform that modification first. "Spectra 1100 schematic & board layout" will be useful in locating parts. The easy thing to check is the red wire exiting the bias transformer - if it lacks the second wire wrapped around it, it needs to be modified. See item 9 on the "BiasFix Diagram". Follow all cautionary statements, and if at any time you're not sure what you're doing, then STOP!
The next step is to adjust the bias voltage per instructions "biasadj". The step is vital to ensure both channel balance and level-matching with the woofer.
If the above fails to fix the issues, then I suggest replacing the high voltage diodes and capacitors, see "Bias Multiplier Parts". Repeat bias voltage adjustment after replacing parts.
I don't believe there is an industry standard for measuring woofer diameter. So one man's 7" is another man's 8". The crossover is set for the ESL portion to cover as broad a range as practical for a single panel, with the woofer kicking in around 150 Hz.
These speakers hunger for both voltage and current. I know nothing about your amp, so cannot comment on its suitability. 100 watts per channel is generally considered a minimum, with a max of 250 wpc, used with common sense and caution.
Thank you for the great information. I discovered your thread on DiyAudio about a day after I started this new one. I will work on this over the next few days and report back.
The bass seems to be about 3-5db too loud, which is what Stereophile reported when they reviewed the 11 and the 1100 in the early 90s. Besides the level mismatch though, they really liked the quality of the bass the woofer provided at the time. We'll see, one step at a time.
The Zen amp I am using currently is a 25-50 watt design running from a single transistor per side. I have a class A 100 watt design I need to finish that will be a better match to this speaker.
The bass seems to be about 3-5db too loud, which is what Stereophile reported when they reviewed the 11 and the 1100 in the early 90s. Besides the level mismatch though, they really liked the quality of the bass the woofer provided at the time. We'll see, one step at a time.
The Zen amp I am using currently is a 25-50 watt design running from a single transistor per side. I have a class A 100 watt design I need to finish that will be a better match to this speaker.
Thanks again for the information. I didn’t realize how much of an effect the bias has on the panel performance. I rebuilt and adjusted the crossovers/bias sections today and it made a big difference in the balance and quality. They sound completely normal, if not even a bit polite now. The two boards even had different components between them. Blended with my sub they are nice and filling. Now I need a better amp lol. Position not finalized.
Oh yes, the level of bias is very important, and especially for a hybrid, its exact level is vital for proper integration between woofer and ESL. Make sure you have the left and right speakers oriented correctly. For the single-panel Spectras (Models 11 and 1100) the high frequencies should be radiating from the outer edge of each speaker.