As some of you know, I recently came upon a pair of ESS AMT 1Cs. Great speakers, lovely Heils, terrible shape. I performed necessary repairs to the surround (rubber) and replaced the passives with a 'bay special. I also recapped the crossovers to polypropylenes. So far so good.
I also have a pair of ESS PS4As, which also sound great with Heils, but are monopole. They were easy as pie to get going and sounding great (recap was all I had to do). These dipoles, while sounding much more open and less 'boxy' with a much wider soundstage and sweet spot are much more difficult to get to sound good.
I currently have two amplifiers. It's a somewhat unorthodox setup, but it sounds good. My main power amp is an old Pioneer Elite VSX-49TX, which has a blown pre-amp, so I am using it as an amp. It's 65lbs of power goodness, with extremely low noise/THD/etc., is one of the few receivers that actually puts out more power than rated (even all channels driven), and handles low impedances with ease. But since the preamp is blown, I can use it as a 7 channel integrated amp, since the volume and channel trims still work using the 7 channel ext-in in the back. I have it powering my mains (LCR), and zone 2 and 3 (stereo). There is no crosstalk/channel bleed at all.
My main preamp/receiver is a Denon 3808ci, which is a wonderful receiver full of the (nearly) latest features including HDMI etc. with Audyssey MultiEQ XT. This room correction blows away what the Pioneer had. The Audyssey Flat EQ curve really does amazing things to my speakers, and when it's done it shows you a nice little graphical chart of all that it had to do to correct the speaker's response characteristics to achieve the target EQ curve. It's pretty fancy and I've always been pleased with how it corrects any flaws in my speakers.
So all of that background to get to the point. Those ESS have two knobs on them, one for midrange presence and one for brilliance. Using Audyssey's measurement results as a guide, I would run a calibration, adjust the knobs, look at the crossover points and graph results, tweak, and run it again. It was rather time consuming, but all in the spirit of audio perfection.
Anyway, time and time again the calibration system would pick 150Hz as the ideal crossover point to my subwoofers. I thought this was nuts as these ESS have 12" woofers. So I kept turning down the knobs and kept measuring. I found that they crossed over at 40Hz (80 after doing a full room recal) at a knob position that is almost all the way down. Nuts!
So I listened for a while this way. It did sound quite good. However, I felt that the dynamics that these Heils are so good at were missing. It occurred to me that attenuating the Heils that much must be killing the dynamics. So I played with the knobs (in direct mode now) and confirmed my suspicions - those LPads do affect sensitivity which affects dynamics. So I really wanted to be able to listen to these Heils unattenuated - I wanted the best of both worlds - relatively flat response, and great dynamics. I just wanted it all; what's wrong with that?
Then it occurred to me that those Denon amps are sitting there doing nothing for my front channels. They already get the same signal, so it was just a matter of putting them to work. So after a little googling (I wanted to make sure passive biamping was safe to do) I got to work.
I opened up my speakers again, and I drew out the crossover on my nearest pad of paper. I found that the woofer connects to the main inputs in three places - the 95uF cap, the 20W resistor for the - line, and the iron core inductor on the + line. So I grabbed the soldering iron, ran another set of wires to the outside through the existing plug's holes, and connected the woofer leads to the new wires. After verifying that the woofer and tweeter were seperate and being properly crossed over still, I hooked the Denon up to the Heil, and the woofer up to the Pioneer.
I then tried to run the calibration again. This time it picked 200Hz crossover (ack!) so running the two flat didn't help. But when I seperately turned up the woofers 3db, magic happened. The recal results were at 60Hz, and the graphs looked much better. The Heil was almost flat in its frequency range, and the woofers still needed correction, (I can see what people mean in that the low mids do have problems on these..) but it was much closer to a reasonable value now.
When I fired it up.. aww yeah. Audyssey corrected out any odd anomolies with the midrange on these woofers, and the power, presence, and dynamics are all there now. The Heils scream unencumbered with the knobs maxed out, and the woofer has much more power to itself. It's a beautiful thing.
While I have read that passive biamping (leaving each crossover in place) doesn't really do much, in my case, since I needed to compensate for a massively more efficient tweeter vs. the woofer, it works wonders.
I could possibly do more tweaks like remove the lpads altogether, but I'm not really comfortable with that step at this point.
Short of adding a midrange, this is probably the best I can do at this point. Any other thoughts? I hope you enjoyed my story.
IBJamon
I also have a pair of ESS PS4As, which also sound great with Heils, but are monopole. They were easy as pie to get going and sounding great (recap was all I had to do). These dipoles, while sounding much more open and less 'boxy' with a much wider soundstage and sweet spot are much more difficult to get to sound good.
I currently have two amplifiers. It's a somewhat unorthodox setup, but it sounds good. My main power amp is an old Pioneer Elite VSX-49TX, which has a blown pre-amp, so I am using it as an amp. It's 65lbs of power goodness, with extremely low noise/THD/etc., is one of the few receivers that actually puts out more power than rated (even all channels driven), and handles low impedances with ease. But since the preamp is blown, I can use it as a 7 channel integrated amp, since the volume and channel trims still work using the 7 channel ext-in in the back. I have it powering my mains (LCR), and zone 2 and 3 (stereo). There is no crosstalk/channel bleed at all.
My main preamp/receiver is a Denon 3808ci, which is a wonderful receiver full of the (nearly) latest features including HDMI etc. with Audyssey MultiEQ XT. This room correction blows away what the Pioneer had. The Audyssey Flat EQ curve really does amazing things to my speakers, and when it's done it shows you a nice little graphical chart of all that it had to do to correct the speaker's response characteristics to achieve the target EQ curve. It's pretty fancy and I've always been pleased with how it corrects any flaws in my speakers.
So all of that background to get to the point. Those ESS have two knobs on them, one for midrange presence and one for brilliance. Using Audyssey's measurement results as a guide, I would run a calibration, adjust the knobs, look at the crossover points and graph results, tweak, and run it again. It was rather time consuming, but all in the spirit of audio perfection.
Anyway, time and time again the calibration system would pick 150Hz as the ideal crossover point to my subwoofers. I thought this was nuts as these ESS have 12" woofers. So I kept turning down the knobs and kept measuring. I found that they crossed over at 40Hz (80 after doing a full room recal) at a knob position that is almost all the way down. Nuts!
So I listened for a while this way. It did sound quite good. However, I felt that the dynamics that these Heils are so good at were missing. It occurred to me that attenuating the Heils that much must be killing the dynamics. So I played with the knobs (in direct mode now) and confirmed my suspicions - those LPads do affect sensitivity which affects dynamics. So I really wanted to be able to listen to these Heils unattenuated - I wanted the best of both worlds - relatively flat response, and great dynamics. I just wanted it all; what's wrong with that?
Then it occurred to me that those Denon amps are sitting there doing nothing for my front channels. They already get the same signal, so it was just a matter of putting them to work. So after a little googling (I wanted to make sure passive biamping was safe to do) I got to work.
I opened up my speakers again, and I drew out the crossover on my nearest pad of paper. I found that the woofer connects to the main inputs in three places - the 95uF cap, the 20W resistor for the - line, and the iron core inductor on the + line. So I grabbed the soldering iron, ran another set of wires to the outside through the existing plug's holes, and connected the woofer leads to the new wires. After verifying that the woofer and tweeter were seperate and being properly crossed over still, I hooked the Denon up to the Heil, and the woofer up to the Pioneer.
I then tried to run the calibration again. This time it picked 200Hz crossover (ack!) so running the two flat didn't help. But when I seperately turned up the woofers 3db, magic happened. The recal results were at 60Hz, and the graphs looked much better. The Heil was almost flat in its frequency range, and the woofers still needed correction, (I can see what people mean in that the low mids do have problems on these..) but it was much closer to a reasonable value now.
When I fired it up.. aww yeah. Audyssey corrected out any odd anomolies with the midrange on these woofers, and the power, presence, and dynamics are all there now. The Heils scream unencumbered with the knobs maxed out, and the woofer has much more power to itself. It's a beautiful thing.
While I have read that passive biamping (leaving each crossover in place) doesn't really do much, in my case, since I needed to compensate for a massively more efficient tweeter vs. the woofer, it works wonders.
I could possibly do more tweaks like remove the lpads altogether, but I'm not really comfortable with that step at this point.
Short of adding a midrange, this is probably the best I can do at this point. Any other thoughts? I hope you enjoyed my story.
IBJamon