Originally Posted by LTD02
interesting cj, is there a post or link to a page where mark or somebody explains the "gain-matching" approach?
It was in the threads sivadselim linked to. Basically to "gain-match" you set the gains to equal levels. If you're not sure that setting both subs to, say, 50% gain on their amps, will result in "equal" gains, the way to test it is as follows:
Set sub #1 in the middle of the room, as far from the influence boundary walls as possible. Set the mic about 6" in front of the driver. Play a a noise signal in the bandwidth of interest and record the level. Now set sub #2 in the exact same position and measure the same noise signal. Set sub #2 for the exact same level as sub #1. You have now essentially "gain-matched" the two subs. You can now set them in dissimilar locations and know that, no matter how they interact with the room, they will reach maximum output at the same point. (In Mark Seaton's setups, maximum output is a very high priority.)
This may, (or may *not*), result in the smoothest possible FR. However, it ensures that one sub is not "crippled" by the gain setting of the other. If one sub is bottoming, compressing or distorting while the other sub still has gas left in the tank, that is an ineffective utilization of the subwoofer resources. Still, if one's priorities are smoothest FR, it may be preferable to sacrifice that last iota of output for smoother response.
As I stated in one of my first posts in this thread, (Post #86):
Originally Posted by craig john
I think it is very important to note that Dr. Geddes's (and DS-21's) highest priority is smoothness of response. I assume his primary usage is musical reproduction. If this is also *your* priority, then Dr. Geddes's approach of 3 lesser subs and his setup techniques may be the "best". However, if high output and deep ULF response, (down to and below 20 Hz), is *your* priority, especially for Home Theater applications, then other setup techniques will optimize those capabilities better.
For example, due to the fact that the gains are set differently, Dr. Geddes's approach will limit the max output capabilities of the higher-set sub and/or under-utilize the capability of the lower-set sub(s). In a music-oriented system, 105 dB from 25 Hz up may well be sufficient, and should be easily do-able with 3 lesser subs, even with their gains set differently. However, in an HT system where Reference Level of 115 dB from below 20 Hz is desired, the full dynamic output capability of all the subs in the system will be required, and better subwoofers will always be beneficial.
...this is all about differing priorities: those being; maximum output, maximum extension or smoothest response. Some of us are willing to sacrifice one for the other. Dr. Geddes's highest priority is obviously smoothest FR. He may well be sacrificing some max-output, or some VLF extension to get his smoothest output in his BW of interest. That's fine for him. For me, I am willing to sacrifice a few +/-dB for some more output, especially at <20 Hz. My gain-matched (Master/Slave) setting allows this.
(PS. I also first asked the question about Audyssey in post #86):
Originally Posted by craig john
Dr. Geddes, have you ever used an Audyssey-enabled receiver or pre-pro? I would be interested in your thoughts on the frequency and time-based EQ capabilities of Audyssey MultEQ XT.
Yes... that's Audyssey.. which you have now declared as "flawed"! In fact, I think you referred to it as a "disaster".
IME, Audyssey has been a godsend. I have used "equalizers" for years. My first exposure to a graphic EQ goes back to the late 70's with the Soundcraftsmen PE2217 preamp/EQ. I have had many EQ's in the interim, the most recent being the digital, parametric, OSD Velodyne SMS-1.
IME, Audyssey trumps them all... and by no small margin.
Your complaint that Audyssy EQ's above the modal region is moot. Audyssey's primary effect above the modal region/Schroeder frequency/transition zone/"whatever-you-want-to-call-it" is to implement their "target curve", which is a shallow rolloff of the high frequencies, (-3 dB at 20 kHz). In my system, you can implement Audyssey EQ, and then turn it off. The only significant difference you'll hear is a difference in the articulation of the bass. The mids and highs are virtually unchanged. However, the improvement in articulation of the bass is quite impressive. Bass lines are much easier to follow. Distinction of the bass instrument, (guitar or standup, electric or acoustic), from the bass drum is much easier to delineate. OTOH, bass drums are still percussive and tactile, just as they are in real life, (of course this depends on the recording).
Bottom line, there are *many* ways to attempt to optimize the bass performance of subwoofer systems. There are also differing priorities about the importance of various performance criteria. One needs to decide their own priorities and then select the setup routine that optimizes those priorities.