I have spent the last couple of nights calibrating my new dedicated theater room. The speaker system is composed of 8 Triad Gold speakers - 2 in-wall LCR's, 1 in-room Center, 2 on-wall surrounds, 2 in-wall surrounds, and 1 Powersub. The audio system is composed of, among other things, a Lexicon MC-1 surround processor, 7 channels of Adcom amps, and an Audio Control Bijou 5.1 channel EQ. I also have an Audio Control R-130 Real Time Analyzer.
EQ'ing the system without the RTA would be next to impossible, and even WITH the RTA, it's non-trivial. First off, pink noise is not continuous but has a randomness to it. Rather than seeing a nice stable set of 30 LED's, there is a lot of flickering, even at the "slow" setting. Missing from the R-130 is the ability to average over a longer period of time such as 20 seconds. This makes it necessary to "manually average" by watching the LED's and noting what percentage of the time each one is on.
Second, moving the microphone a small distance can result in different results. If you measure from just one position, you can potentially make all other positions worse, attempting to improve one. The "Home THX Equalization Manual" published by Lucasfilm recommends averaging the measurements from four locations. That sounds good except that the equalization curves from these four locations can all be different, which can result in some frequencies being made better but some being made WORSE at each position. In my case most of the changes cancelled each other out, leaving only the worst and most consistant problems to be equalized out. My room seems to have about a 6dB peak somewhere in the 160-200Hz region, although the center channel seems to peak at a somewhat lower frequency, which leaves me scratching my head. The low bass region has been "interesting" to EQ. The RTA is a 1/3 octave RTA, so there are only 6 LED's covering 80Hz and below whereas there are 11 sliders on the EQ each covering 1/6 octave. Either my peaks and nulls are falling in between these 1/3 octaves or I am blessed with a room which has few problems in the lower bass region. The only LED's that consistantly stray from a flat line are those at 32.5 and 25 Hz, and I am having a hard time bringing myself to cutting frequencies that are normally hard to come by!
The attached picture is a shot of the RTA display for my front left channel only - (no subwoofer and no EQ. Of the 30 LED's, the lower 6 are the region below 100Hz so the rolloff is normal, and the top 12 LED's are the region above 1KHz, which is "dominated by the direct field", so it can also be ignored. The 11 LED's in between, covering the third octaves between 80 Hz and 800 Hz inclusive, is what is being EQ'd. It shows about a 4 dB peak, really more a HUMP than a peak, at 200 Hz. I am wondering if this is the region addressed by the accoustic treatments, of which I do not have enough. If wonder if I could cover another 50 square feet with acoustic insulation if this hump might be lower? That's academic however since I don't have another 50 sq ft of wall available short of covering my fireplace and some raised panel oak doors!
I wasn't able to achieve a perfectly flat response from 20 Hz to 1 KHz, nor did I really try that hard to do so, but I did end up with the RTA showing the response being +/- 2dB over most of this range, with a couple of flickering lights outside that range.
I haven't done any serious AB comparisons yet since I haven't had a switcher monkey to push the bypass switch on the Bijou for me, but I did watch the "Corrs: Live in London" DVD tonight at reference level (i.e. LOUD) and found nothing to complain about. It sounded pretty fantastic. The Triad Gold's can handle the full output from the 150w/ch Adcom amp (the clipping LED's were flickering) without audible distress and the 15" Gold Powersub just totally cranks. Someday I will add a second sub, but for now the single sub equits itself QUITE well.
Given the ultimately minor EQ I ended up dialing in, I have to say Dennis' theater design is quite excellent. His construction techniques are also proving themselves as the room makes narry a buzz or rattle. As for the EQ, I could probably replace the Bijou with a Helmholtz resonator since almost all the EQ is focused around the 160-200Hz bump. Aside from that bump I don't think I needed any more than 2dB of adjustment anywhere else.
David
EQ'ing the system without the RTA would be next to impossible, and even WITH the RTA, it's non-trivial. First off, pink noise is not continuous but has a randomness to it. Rather than seeing a nice stable set of 30 LED's, there is a lot of flickering, even at the "slow" setting. Missing from the R-130 is the ability to average over a longer period of time such as 20 seconds. This makes it necessary to "manually average" by watching the LED's and noting what percentage of the time each one is on.
Second, moving the microphone a small distance can result in different results. If you measure from just one position, you can potentially make all other positions worse, attempting to improve one. The "Home THX Equalization Manual" published by Lucasfilm recommends averaging the measurements from four locations. That sounds good except that the equalization curves from these four locations can all be different, which can result in some frequencies being made better but some being made WORSE at each position. In my case most of the changes cancelled each other out, leaving only the worst and most consistant problems to be equalized out. My room seems to have about a 6dB peak somewhere in the 160-200Hz region, although the center channel seems to peak at a somewhat lower frequency, which leaves me scratching my head. The low bass region has been "interesting" to EQ. The RTA is a 1/3 octave RTA, so there are only 6 LED's covering 80Hz and below whereas there are 11 sliders on the EQ each covering 1/6 octave. Either my peaks and nulls are falling in between these 1/3 octaves or I am blessed with a room which has few problems in the lower bass region. The only LED's that consistantly stray from a flat line are those at 32.5 and 25 Hz, and I am having a hard time bringing myself to cutting frequencies that are normally hard to come by!
The attached picture is a shot of the RTA display for my front left channel only - (no subwoofer and no EQ. Of the 30 LED's, the lower 6 are the region below 100Hz so the rolloff is normal, and the top 12 LED's are the region above 1KHz, which is "dominated by the direct field", so it can also be ignored. The 11 LED's in between, covering the third octaves between 80 Hz and 800 Hz inclusive, is what is being EQ'd. It shows about a 4 dB peak, really more a HUMP than a peak, at 200 Hz. I am wondering if this is the region addressed by the accoustic treatments, of which I do not have enough. If wonder if I could cover another 50 square feet with acoustic insulation if this hump might be lower? That's academic however since I don't have another 50 sq ft of wall available short of covering my fireplace and some raised panel oak doors!
I wasn't able to achieve a perfectly flat response from 20 Hz to 1 KHz, nor did I really try that hard to do so, but I did end up with the RTA showing the response being +/- 2dB over most of this range, with a couple of flickering lights outside that range.
I haven't done any serious AB comparisons yet since I haven't had a switcher monkey to push the bypass switch on the Bijou for me, but I did watch the "Corrs: Live in London" DVD tonight at reference level (i.e. LOUD) and found nothing to complain about. It sounded pretty fantastic. The Triad Gold's can handle the full output from the 150w/ch Adcom amp (the clipping LED's were flickering) without audible distress and the 15" Gold Powersub just totally cranks. Someday I will add a second sub, but for now the single sub equits itself QUITE well.
Given the ultimately minor EQ I ended up dialing in, I have to say Dennis' theater design is quite excellent. His construction techniques are also proving themselves as the room makes narry a buzz or rattle. As for the EQ, I could probably replace the Bijou with a Helmholtz resonator since almost all the EQ is focused around the 160-200Hz bump. Aside from that bump I don't think I needed any more than 2dB of adjustment anywhere else.
David