Let me clear much confusion here. Note that 5-wire panels are NOT necessarily Spectra panels. I’ve never broken down Acoustat’s panel evolution as “generations”, but here goes:
Gen #1 3 -wire panels with old coating. These are identified by 3 wires coming from each panel, with a red bias wire. This is Acoustat’s earliest production. There may have been some 2+2 built with these, but not many, if at all.
Gen #2 5-wire panels with old coating. These are identified by 5 wires coming from each panel, with a red bias wire. Many 2+2 were built with these panels. These were developed while Acoustat was an independent company.
Gen #3 5 wire panels with improved coating. These are identified by 5 wires coming from each panel, with a bias wire that is yellow with a red spiral stripe. The improved coating was developed while Acoustat was a division of the David Hafler Company. The final production of 2+2 used these panels.
Gen #4 5-wire panels with improved coating AND segmented stators. These are identified by 5 wires coming from each panel, a bias wire that is yellow with a red spiral stripe, AND segmented stators. These were used exclusively on Spectra models. These were also developed under the David Hafler Co, and continued under Rockford ownership. No changes to the panel occurred during Rockford's ownership - Rockford merely expanded the Spectra model line.
Now, it is true that a Spectra panel may be used as a replacement for any of the above, provided that the split stators are tied together (and therefore acting as an unsegmented panel). For that matter, any generation panel may be used as a replacement for an earlier generation, with the understanding that performance may not match exactly. But if you need to replace a panel, and all you can find is a later generation panel, it's a viable solution.
Hope this helps!
Gen #1 3 -wire panels with old coating. These are identified by 3 wires coming from each panel, with a red bias wire. This is Acoustat’s earliest production. There may have been some 2+2 built with these, but not many, if at all.
Gen #2 5-wire panels with old coating. These are identified by 5 wires coming from each panel, with a red bias wire. Many 2+2 were built with these panels. These were developed while Acoustat was an independent company.
Gen #3 5 wire panels with improved coating. These are identified by 5 wires coming from each panel, with a bias wire that is yellow with a red spiral stripe. The improved coating was developed while Acoustat was a division of the David Hafler Company. The final production of 2+2 used these panels.
Gen #4 5-wire panels with improved coating AND segmented stators. These are identified by 5 wires coming from each panel, a bias wire that is yellow with a red spiral stripe, AND segmented stators. These were used exclusively on Spectra models. These were also developed under the David Hafler Co, and continued under Rockford ownership. No changes to the panel occurred during Rockford's ownership - Rockford merely expanded the Spectra model line.
Now, it is true that a Spectra panel may be used as a replacement for any of the above, provided that the split stators are tied together (and therefore acting as an unsegmented panel). For that matter, any generation panel may be used as a replacement for an earlier generation, with the understanding that performance may not match exactly. But if you need to replace a panel, and all you can find is a later generation panel, it's a viable solution.
Hope this helps!
Acoustat did not typically publish efficiency ratings. One reason is that conventional efficiency measurements don't relate well to large-area radiators like an ESL, and a second reason is that the numbers would have been rather low (i.e., nothing to brag about!).
Can you try to define "low efficiency"? What sort of amplifier are you using? How large a room? What type of music? If you are accustomed to more efficient speakers, you may be just expecting too much of your system.
On the other hand, your bias power supplies may need refurbishing. This is a common malady as the speakers age...and any Model 4 is pretty old by now. The component change is fairly easy and cheap to do. You should replace all five diodes and five capacitors in each bias multiplier. Suggested modern equivalent components have been posted previously. I don't have the list handy here.
On the other hand, your bias power supplies may need refurbishing. This is a common malady as the speakers age...and any Model 4 is pretty old by now. The component change is fairly easy and cheap to do. You should replace all five diodes and five capacitors in each bias multiplier. Suggested modern equivalent components have been posted previously. I don't have the list handy here.
1) It is definitely worth doing. If you define distortions as "less than perfect passing of the signal" then AcoustatAnswerMan's post makes sense. What you will hear is better sounding music, some or all of the following: more clear, better soundstage, more depth. More real.
I used Panasonic EZP series caps, silicone-caulked to the chassis with a few dabs, 45mF + 10mF, and 10000 pF (0.01 mF) from Cornell Dubilier #940C30S1K-F.
2) I also removed the heavy gauge hookup wire and used 4x22 gauge solid core wire as hookup wire. (Four wires now soldered together at each end. 4x22 is equivalent to 1x16 gauge wire.) Why this works is due to minimizing "skin effect", which tends to roll off higher frequencies.
I did extensive listening tests of the changed wire. From my notes: The sound is clearer, a bit more engaging. Depth a little more. Highs improved. Bass not affected. (Note: bass does like low resistance, but as this is about two feet of wire, the added resistance compared to the heavy gauge wire is very, very small.)
If you do the C-Mod or change the wire, and like it, let us know.
Brandon
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For newbies, he is referring to the conductive coating on the diaphragm.
In my opinion, the 2+2 is superior to the Model 4, provided you have the required ceiling height. There's something magical about the full-height ESL that can't be had from a shorter model. You will find more precise stereo imaging from the 2+2 as well, due to the narrower dispersion profile. Downside? The Model 4 may have slightly greater bass response due to reduced front-to-back cancellation, thanks to the greater width. I think this is a very minor trade-off and is more than compensated by the above-mentioned advantages. The 2+2 has very good bass response.
This is the classic dilemma of the pre-Spectra models. They each have their strengths and weaknesses. Narrower models tend to have superior imaging, whereas the larger area/wider width models have better bass response and dynamic capacity (i.e. ability to play loud). These compromises largely disappeared with the Spectra models, as all models share very similar imaging characteristics, with increasing bass response/dynamic capacity as the size increase. In other words, the Spectra models have a more consistent "family" sound, the only difference between models being the amount of that good sound.
This is the classic dilemma of the pre-Spectra models. They each have their strengths and weaknesses. Narrower models tend to have superior imaging, whereas the larger area/wider width models have better bass response and dynamic capacity (i.e. ability to play loud). These compromises largely disappeared with the Spectra models, as all models share very similar imaging characteristics, with increasing bass response/dynamic capacity as the size increase. In other words, the Spectra models have a more consistent "family" sound, the only difference between models being the amount of that good sound.
The Spectra equivalent of the 2+2 would be the Spectra 44 or 4400. These models share the same four-panel, vertical arrangement as the 2+2. The only difference between the 44 and 4400 is purely cosmetic - sonically they are identical. Unfortunately, one doesn't see many Spectra models for sale, compared to the earlier models. Owners of the Spectra models just aren't giving them up yet! I have Spectra 4400s and will never part with them as long as I have any say about it. And I even have a spare interface "just in case".
BTW, there were never any factory modifications on the Spectra models, so you don't need to worry if a particular pair has been updated or not.
BTW, there were never any factory modifications on the Spectra models, so you don't need to worry if a particular pair has been updated or not.