In past few posts, I've been describing the "more defined bass" effect that seems to result from using a supertweeter. I did not invent this idea, you can find it in many other blogs.
And there is another claimed effect from supertweeters. It is claimed they do not make the sound more harsh. That is the weak form of the claim. The strong form is that they actually reduce harshness.
If you look into the claims made for supertweeters, these and many more are common.
Others scratch their head with incredulity, and say that they can't hear as high as their current tweeter can play, so why do they need something that plays higher? Others say they may get too many highs, or at least too much stridency and harshness, as it is, so why would they ever want more (and apparently they don't believe the claim that supertweeters do not increase and may decrease apparent harshness).
Many of these skeptics have not even heard any supertweeter. And since most supertweeter setups are consumer addons (though I'm just guessing, it could be the other way around), or even otherwise, it can always be claimed that the supertweeter setups they have heard were not "properly integrated". Supertweeter integration is a large topic that you could read about endlessly.
On the other hand, I'm not aware of any blind tests, and it may not even be possible in many cases to do a blind test. It is likely beyond the means of most hobbyists.
Well I never say my tests are ultimate and definitive, but I continue to sense the supertweeter as decreasing harshness, though sometimes adding a distinct unwanted sonic signature or localization.
Last night I did another test of the +10dB and +15dB crossover levels for the supertweeter (at the current 15.5khz crossover setting). Listening to "Lucky Man" from Emerson Lake & Palmer, I was thinking Greg Lake sounded a bit strident. (A lot of that, no doubt, is the recording, intended to give Greg an otherworldly sound.) So I then changed to the +10dB level. No particular change in Greg Lake's vocals, but now the highs seemed more chaotic from all over the soundfield, there were lots of distractions in the high frequency range. Restoring the +15dB level restored sanity, though perhaps you could claim a kind of totalitarian simplicity, with Lake's voice commanding a swirling mix of instruments.
I have now read some claim the Elac 4pi tweeters can sound metallic if played too loud, and I am struggling with that. To get the most good effects from the supertweeter, it has to be played loud enough. Perhaps to get any good effects... But then, at times the supertweeter can give itself away. The supertweeter can be "hidden" completely by making it's level low enough. But then it doesn't seem to have the good effects. So there is a fine line between not-loud-enough and too-loud, and sometimes one can wonder if there's a line at all.
I think there is, unfortunately, a tendency toward metallic sound from the Elac. If the Elacs were perfect, like the pulsating plasma in Hill Plasmatronics, they might not have that sound. The sound can possibly be tweaked with DSP, class A amplifier, cables, etc., etc. But it complicates the integration problem.
Speaking of Plasmatronics, I had a friend who was combining the plasma driver with Acoustats back in the late 1970's. It sounded great then. But I don't consider the Plasmatronic driver to be particularly practical and I'm not even sure I'd want two in my living room.
Friday, January 28, 2011
Thursday, January 27, 2011
Bedroom System loves DVD-Audio and HDCD's
Last night spent some time listening to Bedroom System, notably the DVD-Audio of Queen's Night at the Races. Wow! The dynamic range on this DVD-Audio presentation (I used 96kHz PCM stereo mode) is fantastic!
Last year Bedroom System got a new preowned universal disc player, a Denon 5900. This is one of the all time great universal disc (except Blu Ray) players, featuring one of the best Burr Brown DAC's, 120dB signal to noise ratio, and separate power supplies for audio and digital. Weighs almost 30 pounds, originally cost $2000.
Unfortunately, I was not as lucky with this second purchase of a 5900 as I was with the first which went into my living room. The second was not as clean looking, and has a noticeable whine on high speed discs like DVD-Audio and SACD. It may need internal cleaning and/or a new bearing or drive mechanism. Mind you, the unit works OK, it plays every disc I throw at it, it's just more mechanically noisy than a top shelf unit should be.
I figured I might be able to get the noise fixed at the Denon service center about 100 miles away at probable cost $100-$250.
But I had a cheaper solution. I simply avoided retiring my previous bedroom player, a Denon 2900. Very similar to the 5900 except lacking the dual power supplies and also lacking HDCD. It uses the early-production version of the same DAC as the 5900. This 2900 I bought a few years ago is minty clean.
So what I do is this: I play low speed discs, CD's and HDCD's, on the 5900, and I play high speed discs, DVD-Audio and SACD, on the 2900. Only the 2900 needs a video connection, and it connects to video monitor using S-Video through a isolation transformer to prevent contaminating the audio.
This is only for actual discs. Mostly I listed to computer files through my Sonos system. But Sonos doesn't handle high resolution formats, and I don't necessarily have all my discs copied to Sonos (copying discs to an online library is an unbelievable amount of work if you are somewhat perfectionistic about it).
In the long run, I have two nearly identical machines, so one could serve as spare parts for the other. I've even thought about transferring the quiet mechanism from the 2900 to the 5900, but for the time being, why bother?
Both players feed analog into my digitally processed system. For many years, I have used a TacT RCS 2.0 preamp in the bedroom, which feeds Behringer DEQ 2496 and DCX 2496. Unfortuantely, the analog input on the Tact features a somewhat outdated analog-to-digital converter which effectively only has about 16 bit performance.
But late last year I bought a new analog-to-digital converter (ADC). It's actually another Behringer DEQ 2496, which I plan to use for other purposes also, but inside the DEQ is a fairly decent AKM ADC.
I've had this hooked up, but not very well until last night. Previously I ran the Denon players through my Acurus L10 preamp to set the level, then into the DEQ. But last night I decided to bypass the gain stage and volume control of the Acurus, and use the tape output instead. That seemed to really open it up, just like the living room system when I play advanced resolution discs.
And of all the kooky things I was not connecting the Behringer "ADC" to my Tact very well. I was using the optical output of the Behringer. But then it had to share the optical input on the Tact (which has only one optical input) with my carousel DVD player. Last night I got tired of switching the optical cables, and decided to connect the Behringer using AES/EBU instead.
Last year Bedroom System got a new preowned universal disc player, a Denon 5900. This is one of the all time great universal disc (except Blu Ray) players, featuring one of the best Burr Brown DAC's, 120dB signal to noise ratio, and separate power supplies for audio and digital. Weighs almost 30 pounds, originally cost $2000.
Unfortunately, I was not as lucky with this second purchase of a 5900 as I was with the first which went into my living room. The second was not as clean looking, and has a noticeable whine on high speed discs like DVD-Audio and SACD. It may need internal cleaning and/or a new bearing or drive mechanism. Mind you, the unit works OK, it plays every disc I throw at it, it's just more mechanically noisy than a top shelf unit should be.
I figured I might be able to get the noise fixed at the Denon service center about 100 miles away at probable cost $100-$250.
But I had a cheaper solution. I simply avoided retiring my previous bedroom player, a Denon 2900. Very similar to the 5900 except lacking the dual power supplies and also lacking HDCD. It uses the early-production version of the same DAC as the 5900. This 2900 I bought a few years ago is minty clean.
So what I do is this: I play low speed discs, CD's and HDCD's, on the 5900, and I play high speed discs, DVD-Audio and SACD, on the 2900. Only the 2900 needs a video connection, and it connects to video monitor using S-Video through a isolation transformer to prevent contaminating the audio.
This is only for actual discs. Mostly I listed to computer files through my Sonos system. But Sonos doesn't handle high resolution formats, and I don't necessarily have all my discs copied to Sonos (copying discs to an online library is an unbelievable amount of work if you are somewhat perfectionistic about it).
In the long run, I have two nearly identical machines, so one could serve as spare parts for the other. I've even thought about transferring the quiet mechanism from the 2900 to the 5900, but for the time being, why bother?
Both players feed analog into my digitally processed system. For many years, I have used a TacT RCS 2.0 preamp in the bedroom, which feeds Behringer DEQ 2496 and DCX 2496. Unfortuantely, the analog input on the Tact features a somewhat outdated analog-to-digital converter which effectively only has about 16 bit performance.
But late last year I bought a new analog-to-digital converter (ADC). It's actually another Behringer DEQ 2496, which I plan to use for other purposes also, but inside the DEQ is a fairly decent AKM ADC.
I've had this hooked up, but not very well until last night. Previously I ran the Denon players through my Acurus L10 preamp to set the level, then into the DEQ. But last night I decided to bypass the gain stage and volume control of the Acurus, and use the tape output instead. That seemed to really open it up, just like the living room system when I play advanced resolution discs.
And of all the kooky things I was not connecting the Behringer "ADC" to my Tact very well. I was using the optical output of the Behringer. But then it had to share the optical input on the Tact (which has only one optical input) with my carousel DVD player. Last night I got tired of switching the optical cables, and decided to connect the Behringer using AES/EBU instead.
Wednesday, January 26, 2011
Better Highs with Better Bias
One of the ideas in last post was to re-bias Acurus A250 amplifier which currently drives supertweeters. Here's a discussion on exactly this sort of thing with a virtually identical Acurus A200, where it is claimed by several posters that increased bias removes the steely highs of this amplifier:
http://www.diyaudio.com/forums/solid-state/157213-acurus-a200-schematic-here.html
Increasing bias to 6-7mA (measured across 0.5 ohm emitter resistors) is said to improve highs immensely.
It's not entirely clear to me if the R11 potentiometer is the bias adjustment; that's the only potentiometer I see on the schematic. Is there no offset adjustment then?
http://www.diyaudio.com/forums/solid-state/157213-acurus-a200-schematic-here.html
Increasing bias to 6-7mA (measured across 0.5 ohm emitter resistors) is said to improve highs immensely.
It's not entirely clear to me if the R11 potentiometer is the bias adjustment; that's the only potentiometer I see on the schematic. Is there no offset adjustment then?
Supertweeter integration and buyer's remorse
Listening to a very hot (in many ways) brass band recording called "Hot House" by Arturo Sandeval, it seemed like my Elac 4pi supertweeters were sounding metallic. Of course, the recording itself is very brassy, and very bright, so perhaps it's not surprising that the supertweeters are adding the brassy sound that the Acoustats are unable to reproduce. Listening to the supertweeter(s) (or just one) by itself, it was like pure brassiness. Way over the top.
This has begun to bug me a bit. My current supertweeter integration, with much higher supertweeter level and lower crossover point than I used last year, still leaves something to be desired.
One sacrifice I have already decided to make. I might have liked to sit closer to the speakers for a wider stereo image, but can't because the supertweeters begin to become prominently noticeable as a sound source.* So then I found a new compromise position 10 inches back, about 6 feet from the speakers, which is much better on that score (and six feet back from the speakers is probably a good idea anyway). But still not perfect. I still do feel I can hear the supertweeters as a separate source on some music. Sometimes what I seem to hear is that the acoustats have a bump on the side where the supertweeter is, and it is this whole oddly shaped conglomeration that is the speaker. I suppose ideally I wouldn't hear any speaker at all, and some recordings can pull off that trick.
(*The correct solution for wider stereo image would not be to try to sit closer than 6 feet from speakers. That is not good for most speakers anyway. The correct solution would be to move the speakers more than 5.5 feet apart. Unfortunately, room geometry and multi-purposing does not permit that. The speakers are already as wide apart as I can practically get them, except possibly my moving closer to the wall, but then that wouldn't increase the stereo angle either.)
I also heard some brassiness on Computer World by Kraaftwork, though it varied from track to track. I believe this recording is 100% synthesized, shouldn't sound very brassy.
For what it's worth, I've come up with a new compromise cutoff point for the supertweeter, 15.5kHz. The old "magic" 14.2 is just way over the top on a brassy recording. The refined (and accurate by some measurements) 16.5kHz just doesn't have enough supertweeter magic. I previously argued that 14.8kHz was the top of the magic range, but have decided that 15.5kHz has just enough trickery to still be fun.
Interesting that lots of supertweeter users never even bother to set the supertweeter level. For many supertweeters, you simply set the cutoff frequency to make the supertweeter unobtrusive. Supertweeters are generally designed to be more efficient than most loudspeakers, so following the cutoff-only adjustment will lead to excess output, but the heightened response above hearing range is described as a "feature" making up for hearing loss.
In my case, I'm following the apparent guidance of two ancient uncalibrated Class A SPL meters, and setting the supertweeter level so that the range 18-24kHz is, as best I can measure, essentially the same as the level at 1kHz. It's possible my meters are so old they are not showing as much high frequency output as they should, so actually I am adjusting the level far higher than it should be (which is what my iPhone RTA app says).
But, for now I'm sticking with the +15dB level setting on the Behringer crossover, attenuated with a 6dB attenuator at the input of the Acurus amplifier. That seems to be the correct level, and the one that can provide the magic supertweeter effect (including, for example, tighter bass).
I'm thinking perhaps the sound could be improved with a better amplifier on the Elacs, like a Class A transistor or tube amp. Or perhaps just re-biasing the current Acurus A250 amplifier. Old Acurus amplifiers are notorious for developing a low bias condition. The bias was already set pretty low (the amp runs cold at idle) compared with sister upline Aragon amplifiers. The Aragon amps differed partly by having about 2-3x the amount of bias. So if the already low bias of the Acurus gets lowered even more through part ageing, you start to get noticeable crossover notch distortion. Such distortion is especially noticeable around the smallest voltage swings, close to 0 volts output, exactly what is required to drive a supertweeter. So I mean to put this on my to-do list for real-soon-now: rebias the Acurus amp, possibly to slightly higher than factory bias. I could also try one of my other spare amplifiers; the Marantz 15 and Parasound HCA-1000A are good possibilities. Unfortunately, my McIntosh MC225, a 25 watt per channel tube amp with high bias Class AB operation and unity coupled output, needs to be refurbished, but it might be a great amp for this amplification.
One thing I barely think of at all, and that is putting lowpass crossover on the Acoustats above 14kHz or even lower, to help suppress their natural resonance around 13.8kHz. I just don't want to do it, but it might actually help. Despite protestation to the contrary, I am still relying on TacT RCS system to do the final frequency balancing, which can't really be done entirely with crossover hacking anyway.
I believe it was Harry Pearson (famous Founder of The Absolute Sound) who said the Acoustats pull off a trick. They make up for lack of extreme highs (above 14kHz) by having somewhat elevated response below that in the 10-13khz range. I am trying to undo this compromise with a supertweeter (something Harry, IIRC, suggested that the Acoustat designer James Strickland should look into) giving me fully extended response. It follows that, at some point I need to remove the 10-14kHz elevation.
A curious thing about the Elacs is that it does not seem to radiate most sound from the center of any face. It seems to radiate from the edges. This may result from the unique kind of sawtooth aluminum ribbon that Elac uses. It almost seems that it might operate like a Heil tweeter, but all the information I have suggests that it is a pure aluminum ribbon operating in a circular magnetic field. The sawtooth construction allows the ribbon to expand in a linear fashion, which is a great idea. But it may also cause curious radiation patterns, even potential resonances. Put right next to another speaker, it extends the radiating pattern farther to the side than you might predict.
I might get some benefit putting a damping foam wedge between the Elac tweeters and the Acoustat sides which are only a few inches apart. Strangely, I do not seem to hear anything like diffraction around that edge. I can hear the supertweeter perfectly well on the edge across the front of the Acoustat grille...incredible! But when I put my hand, curved, in between the speakers I though it took away some of the metallic sound.
Finally, one thing which has really begun to spark my curiosity comes from measurements I made a few days ago. Achieving what looked like a 14kHz acoustic crossover on the Elac supertweeters required
a 16.5kHz crossover setting on the Behringer 2496 DCX crossover. This was using 48dB Linkwitz-Riley crossover setting (LR48). Given that the response of the Elacs is quite flat from 8kHz to 35kHz (though I'm having trouble finding a graph right now online), setting the crossover that high should not have been necessary.
That makes me wonder a lot if the built-in crossover of the supertweters, which is something like 12dB/octave at 8kHz, is actually detuning the LR48 crossover somehow, and resulting in less than optimal highpass performance at 14kHz.
I keep thinking about this, and on the one hand it seems impossible and other the other hand quite plausible. And if, indeed, the steep electronic crossover is being made less steep because of a passive network attached to the speaker, what should be done about it? (Removing the passive network inside the Elacs would probably not be a good idea for safety reasons...it protects the driver from damage which is quite possible inside my madhouse).
This has begun to bug me a bit. My current supertweeter integration, with much higher supertweeter level and lower crossover point than I used last year, still leaves something to be desired.
One sacrifice I have already decided to make. I might have liked to sit closer to the speakers for a wider stereo image, but can't because the supertweeters begin to become prominently noticeable as a sound source.* So then I found a new compromise position 10 inches back, about 6 feet from the speakers, which is much better on that score (and six feet back from the speakers is probably a good idea anyway). But still not perfect. I still do feel I can hear the supertweeters as a separate source on some music. Sometimes what I seem to hear is that the acoustats have a bump on the side where the supertweeter is, and it is this whole oddly shaped conglomeration that is the speaker. I suppose ideally I wouldn't hear any speaker at all, and some recordings can pull off that trick.
(*The correct solution for wider stereo image would not be to try to sit closer than 6 feet from speakers. That is not good for most speakers anyway. The correct solution would be to move the speakers more than 5.5 feet apart. Unfortunately, room geometry and multi-purposing does not permit that. The speakers are already as wide apart as I can practically get them, except possibly my moving closer to the wall, but then that wouldn't increase the stereo angle either.)
I also heard some brassiness on Computer World by Kraaftwork, though it varied from track to track. I believe this recording is 100% synthesized, shouldn't sound very brassy.
For what it's worth, I've come up with a new compromise cutoff point for the supertweeter, 15.5kHz. The old "magic" 14.2 is just way over the top on a brassy recording. The refined (and accurate by some measurements) 16.5kHz just doesn't have enough supertweeter magic. I previously argued that 14.8kHz was the top of the magic range, but have decided that 15.5kHz has just enough trickery to still be fun.
Interesting that lots of supertweeter users never even bother to set the supertweeter level. For many supertweeters, you simply set the cutoff frequency to make the supertweeter unobtrusive. Supertweeters are generally designed to be more efficient than most loudspeakers, so following the cutoff-only adjustment will lead to excess output, but the heightened response above hearing range is described as a "feature" making up for hearing loss.
In my case, I'm following the apparent guidance of two ancient uncalibrated Class A SPL meters, and setting the supertweeter level so that the range 18-24kHz is, as best I can measure, essentially the same as the level at 1kHz. It's possible my meters are so old they are not showing as much high frequency output as they should, so actually I am adjusting the level far higher than it should be (which is what my iPhone RTA app says).
But, for now I'm sticking with the +15dB level setting on the Behringer crossover, attenuated with a 6dB attenuator at the input of the Acurus amplifier. That seems to be the correct level, and the one that can provide the magic supertweeter effect (including, for example, tighter bass).
I'm thinking perhaps the sound could be improved with a better amplifier on the Elacs, like a Class A transistor or tube amp. Or perhaps just re-biasing the current Acurus A250 amplifier. Old Acurus amplifiers are notorious for developing a low bias condition. The bias was already set pretty low (the amp runs cold at idle) compared with sister upline Aragon amplifiers. The Aragon amps differed partly by having about 2-3x the amount of bias. So if the already low bias of the Acurus gets lowered even more through part ageing, you start to get noticeable crossover notch distortion. Such distortion is especially noticeable around the smallest voltage swings, close to 0 volts output, exactly what is required to drive a supertweeter. So I mean to put this on my to-do list for real-soon-now: rebias the Acurus amp, possibly to slightly higher than factory bias. I could also try one of my other spare amplifiers; the Marantz 15 and Parasound HCA-1000A are good possibilities. Unfortunately, my McIntosh MC225, a 25 watt per channel tube amp with high bias Class AB operation and unity coupled output, needs to be refurbished, but it might be a great amp for this amplification.
One thing I barely think of at all, and that is putting lowpass crossover on the Acoustats above 14kHz or even lower, to help suppress their natural resonance around 13.8kHz. I just don't want to do it, but it might actually help. Despite protestation to the contrary, I am still relying on TacT RCS system to do the final frequency balancing, which can't really be done entirely with crossover hacking anyway.
I believe it was Harry Pearson (famous Founder of The Absolute Sound) who said the Acoustats pull off a trick. They make up for lack of extreme highs (above 14kHz) by having somewhat elevated response below that in the 10-13khz range. I am trying to undo this compromise with a supertweeter (something Harry, IIRC, suggested that the Acoustat designer James Strickland should look into) giving me fully extended response. It follows that, at some point I need to remove the 10-14kHz elevation.
A curious thing about the Elacs is that it does not seem to radiate most sound from the center of any face. It seems to radiate from the edges. This may result from the unique kind of sawtooth aluminum ribbon that Elac uses. It almost seems that it might operate like a Heil tweeter, but all the information I have suggests that it is a pure aluminum ribbon operating in a circular magnetic field. The sawtooth construction allows the ribbon to expand in a linear fashion, which is a great idea. But it may also cause curious radiation patterns, even potential resonances. Put right next to another speaker, it extends the radiating pattern farther to the side than you might predict.
I might get some benefit putting a damping foam wedge between the Elac tweeters and the Acoustat sides which are only a few inches apart. Strangely, I do not seem to hear anything like diffraction around that edge. I can hear the supertweeter perfectly well on the edge across the front of the Acoustat grille...incredible! But when I put my hand, curved, in between the speakers I though it took away some of the metallic sound.
Finally, one thing which has really begun to spark my curiosity comes from measurements I made a few days ago. Achieving what looked like a 14kHz acoustic crossover on the Elac supertweeters required
a 16.5kHz crossover setting on the Behringer 2496 DCX crossover. This was using 48dB Linkwitz-Riley crossover setting (LR48). Given that the response of the Elacs is quite flat from 8kHz to 35kHz (though I'm having trouble finding a graph right now online), setting the crossover that high should not have been necessary.
That makes me wonder a lot if the built-in crossover of the supertweters, which is something like 12dB/octave at 8kHz, is actually detuning the LR48 crossover somehow, and resulting in less than optimal highpass performance at 14kHz.
I keep thinking about this, and on the one hand it seems impossible and other the other hand quite plausible. And if, indeed, the steep electronic crossover is being made less steep because of a passive network attached to the speaker, what should be done about it? (Removing the passive network inside the Elacs would probably not be a good idea for safety reasons...it protects the driver from damage which is quite possible inside my madhouse).
Monday, January 24, 2011
Chair position adjustment and The Near Field
While it was a big improvement in audio realism to move my new listening chair from the far wall to the center of the room last year, I had some difficulty determining how far back into the room (from the speakers) to place the chair. I ended up with a kind of compromise position. Compared to other systems I have heard, it does not give me the widest possible separation. I think it's just shy of 60 degrees angle between the speakers, perhaps 55 degrees. But it is way more separation than I had been accustomed to, having previously listened only from the back of the room.
But it seemed to me that when I placed the speakers even closer to the speakers, the center image fell apart, and that was the main reason for not positioning the listening chair even closer to the speakers.
I've also had a longstanding problem with the center image (usually the lead vocal) not being exactly in the center. When I notice the lead being off to the side in some way not intended, it bothers me a lot. During the past year, I've found that speaker positioning to the nearest 5mm, or delay adjustments as small as 0.03 milliseconds can make a difference in center image stability. But the best thing to insure center image stability is (1) exact chair and speaker positioning, and (2) subwoofer levels. For some reason, the subwoofer levels have an uncanny effect on the center image.
So now that's I've got those problems "solved", and since I am still procrastinating on doing a new Room Correction with Tact, I thought I'd look at the chair position issue again.
I tried a position about 10 inches closer to the front of the room (I define "front" as where the speakers are) than my current position. It did have a noticeably (though not compellingly) wider stereo image. And center image position and stability (assessed by playing Supertramp Crime of the Century) seemed OK. But now what seems irksome is that it appears possible to "hear" the supertweeters as a distinct source. My new much higher supertweeter levels contribute to that.
I tried fiddling with the supertweeter crossover adjustments to make it work better. Of course, I had to increase time delay because of the angles involved. But that wasn't enough. I raised the crossover point. It helped if I raised crossover up to 14.8kKz, but that still didn't make the supertweeter disappear. 16.5kHz did make the supertweeter invisible, but then I loose all the new WOW factor of my fully extended highs which I am really beginning to appreciate.
What is happening is that when I get too close to the speaker (this position was 5 feet from the panels) I start listening from something like "the near field" which tends to exaggerate highs and bass. The room acoustics interact little and are relatively unimportant. In some ways this is good, but most recordings and speakers aren't designed to sound good this way.
So I went back to my "old" position, or really a new "old" position that is still about 5 inches closer to the speakers than last year. It is indicated by my ears lining up with the back edge of the largest side bookcase. This is about 6 feet back from the speakers. Last year I had my ears line up with the forward edge of the next bookcase.
Now I have completed the preliminaries to Room Correction. I have set up low and high frequency crossovers and chosen a listening position. System is sounding very good even without correction, though slightly weak in the 100-500Hz region, lumpy in the deep bass around 45Hz, and just a little too prominent in the upper highs starting at 10K. Those are exactly the kinds of issues that can be solved with room correction. What my RCS 2.0 system cannot do is set up the crossover optimally, but that work is now done, at least good enough for this time around.
But it seemed to me that when I placed the speakers even closer to the speakers, the center image fell apart, and that was the main reason for not positioning the listening chair even closer to the speakers.
I've also had a longstanding problem with the center image (usually the lead vocal) not being exactly in the center. When I notice the lead being off to the side in some way not intended, it bothers me a lot. During the past year, I've found that speaker positioning to the nearest 5mm, or delay adjustments as small as 0.03 milliseconds can make a difference in center image stability. But the best thing to insure center image stability is (1) exact chair and speaker positioning, and (2) subwoofer levels. For some reason, the subwoofer levels have an uncanny effect on the center image.
So now that's I've got those problems "solved", and since I am still procrastinating on doing a new Room Correction with Tact, I thought I'd look at the chair position issue again.
I tried a position about 10 inches closer to the front of the room (I define "front" as where the speakers are) than my current position. It did have a noticeably (though not compellingly) wider stereo image. And center image position and stability (assessed by playing Supertramp Crime of the Century) seemed OK. But now what seems irksome is that it appears possible to "hear" the supertweeters as a distinct source. My new much higher supertweeter levels contribute to that.
I tried fiddling with the supertweeter crossover adjustments to make it work better. Of course, I had to increase time delay because of the angles involved. But that wasn't enough. I raised the crossover point. It helped if I raised crossover up to 14.8kKz, but that still didn't make the supertweeter disappear. 16.5kHz did make the supertweeter invisible, but then I loose all the new WOW factor of my fully extended highs which I am really beginning to appreciate.
What is happening is that when I get too close to the speaker (this position was 5 feet from the panels) I start listening from something like "the near field" which tends to exaggerate highs and bass. The room acoustics interact little and are relatively unimportant. In some ways this is good, but most recordings and speakers aren't designed to sound good this way.
So I went back to my "old" position, or really a new "old" position that is still about 5 inches closer to the speakers than last year. It is indicated by my ears lining up with the back edge of the largest side bookcase. This is about 6 feet back from the speakers. Last year I had my ears line up with the forward edge of the next bookcase.
Now I have completed the preliminaries to Room Correction. I have set up low and high frequency crossovers and chosen a listening position. System is sounding very good even without correction, though slightly weak in the 100-500Hz region, lumpy in the deep bass around 45Hz, and just a little too prominent in the upper highs starting at 10K. Those are exactly the kinds of issues that can be solved with room correction. What my RCS 2.0 system cannot do is set up the crossover optimally, but that work is now done, at least good enough for this time around.
Saturday, January 22, 2011
14.2kHz highpass brings back the magic ultraviolet
Well, all the measurements that led to setting the crossover up to 16.5kHz were based on this assumption: we want to cross the drivers over, not blend them. One driver should be the main contributor, or the other one, thus maximum frequency specificity.
It's a good idea, anyway. But in listening to Bass Erotica and We Want To Be Loved, it seemed to me the magic I heard the other night, the magic was gone, even replaced by a barely noticable harshness (making you think the answer would be to turn the high pass up even more, get them tweeters outa there).
So I went back to 14.2, and the magic was back. It was pretty good at 14.8, quite good at 14.5, and virtually unlistenable at 13.9. At 12kHz, it was intolerable. So 14.8-14.2 seems to be the sweet spot, with 14.2 having the most magic.
Doing a sweep, it does not appear that the Elac supertweeters are contributing much to the peaks of the Acoustat below 14kHz. At 13.9 kHz specifically, turning off the Elacs only reduced the level of a peak by 1dB.
But played by themselves, the Elacs would now be acceptable with another driver crossed over as low as 12khz, according to previous tests. So the current crossover seems to be more of a "blending", with the Elac and Acoustats complementing each other in the range 12-14kHz.
Strangely, however, if I could make the Elacs acoustically cross exactly where I want, I would choose 14.2, and that is also what I have dialed in, but based on listening tests rather than measurements.
An overall sweep shows barely any difference, perhaps the 14.2 provides somewhat greater stability and non-directionality thanks to greater coverage by the omndirectional tweeter rather than the narrowing beam of an electrostatic driver at its upper limits.
It's a good idea, anyway. But in listening to Bass Erotica and We Want To Be Loved, it seemed to me the magic I heard the other night, the magic was gone, even replaced by a barely noticable harshness (making you think the answer would be to turn the high pass up even more, get them tweeters outa there).
So I went back to 14.2, and the magic was back. It was pretty good at 14.8, quite good at 14.5, and virtually unlistenable at 13.9. At 12kHz, it was intolerable. So 14.8-14.2 seems to be the sweet spot, with 14.2 having the most magic.
Doing a sweep, it does not appear that the Elac supertweeters are contributing much to the peaks of the Acoustat below 14kHz. At 13.9 kHz specifically, turning off the Elacs only reduced the level of a peak by 1dB.
But played by themselves, the Elacs would now be acceptable with another driver crossed over as low as 12khz, according to previous tests. So the current crossover seems to be more of a "blending", with the Elac and Acoustats complementing each other in the range 12-14kHz.
Strangely, however, if I could make the Elacs acoustically cross exactly where I want, I would choose 14.2, and that is also what I have dialed in, but based on listening tests rather than measurements.
An overall sweep shows barely any difference, perhaps the 14.2 provides somewhat greater stability and non-directionality thanks to greater coverage by the omndirectional tweeter rather than the narrowing beam of an electrostatic driver at its upper limits.
14-35kHz
And perhaps I shouldn't brag about this, but the extremes in this 14Hz-35kHz are not rolled off, or at least the 14Hz isn't. Output is just as strong at 14Hz as it is at 1Khz, and the subwoofer doesn't even seem to be moving at all. Why I should be bragging is that if I have problems, it is not so much at the extremes, it is in the middle. And all audiophiles know you have to get the middle right first. Well my middle is pretty much all the Acoustat 1+1 speaker, one of the most well regarded speakers in audio history. But by the standards of frequency flatness in my room, it does not at all have flat frequency response. It has too little lower midrange and too much upper midrange. But I am planning, ultimately, to fix that with my Tact RCS 2.0. But even as it is now, with considerable variation in the middle range frequency response, it sounds very very good.
And I am running those supertweeters from 14kHz to 35kHz. (So now you can see the title of this blog entry is also a pun.)
Last night's liveblogging gave you a feel for what would have been 10 minutes of fiddling if I hadn't been trying to blog also, which turned it into an incredibly tedious 45 minutes. It also gave you a feel for how inconsistencies are constantly popping up and you have to decide which ones to investigate. That's just the way it is being an Audio Investigator.
But what I've done since last night is to fully sweep out the left channel (which looks just as good or better than the right...goes down 1Hz lower!). And get around to re-adjusting the supertweeter crossover, which hadn't been done after I raised the supertweeter level from +10 to +15 on the Behringer crossover.
The intent, all along, has been smooth transition between drivers, with no bulge or notch at the crossover. On the supertweeter, I am not lowpassing the Acoustat panels, I am letting them naturally roll off. I thought they naturally rolled off around 18kHz, but my measurements are making it look more like 14kHz. They certainly begin to take a dive at 14kHz, and I found some other measurements on the web to confirm that. In the lower 14kHz range, a serious drop out begins unless you start filling it in with the supertweeter, which is what (at great effort) I have accomplished.
So my intent is to begin the supertweeter at 14kHz. Previously, at the +10dB level, I had decided the correct crossover point was 14.8kHz. Now, in the right (other) channel, and +15dB level, it seems the output doesn't drop -6dB (as would be required by Linkwitz-Riley crossover type) until 12kHz. After many minutes of fiddling and measuring (with the meter needle swinging wildly because of the pure sine waves I am using because I don't have a warble generator) I found that 16.5kHz was required to make the supertweeters have a 14kHz acoustic cutoff (so the nice "filling" described in the above paragraph actually happens, without contributing to peaks caused by the Acoustat below 14kHz...or at least contributing more than a tiny amount).
Now why it is necessary to adjust the crossover to 16.5 kHz (as high or higher than I set it last year...before the supertweeter religion really set in) when what I want is a 14kHz crossover? I often (but incorrectly) assume that the combination of the supertweeter's own built-in crossover (at 8kHz or so) and my electronic line-level crossover (which is in cascade with no interaction) would raise the crossover point, so if I wanted 14kHz I'd need to set 12kHz (?)
Now I think it works the other way, perhaps the supertweeter's built-in crossover, if it is having any significant effect at all, would be to LOWER the high pass cutoff from whatever I set. So it could actually be (though I doubt this is the entire explanation) that I would need to set a 16.5kHz cutoff to actually get 14kHz, just as I have done.
Or maybe it's something else that I haven't thought of yet.
But that's the way these things often are. Anyway, my measurements suggest that at the +15dB level, I need a 16.5kHz cutoff to get nice separation between the Acoustat panels and the Elac supertweeters at 14kHz.
I'm hoping this won't kill the magic time travel I've been experiencing through audio since I boosted the supertweeters to +15dB a few days ago.
(BTW, clarification of earlier post, supertweeter amplifier now has a 6dB attenuator.)
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