Originally Posted by Mark Seaton
This would imply one of three possibilities. First, always double check the wiring. Ideally drive each with the same longer cable with a scene or signal which demonstrates the limit to confirm. If the subs were purchased at different times it is certainly a possibility that the gain of the amps in the two batches is different. The two drivers could also be reaching their limits at different output levels due to any number of reasons.
I would find a test signal which can easily highlight the overload, probably a VLF sine wave or one at the excursion maximum above tuning (20-30Hz). Using the exact same drive signal to both subs, match the gains so the drive signal is as close to the overload level as possible for each subwoofer. Now you will know one won't overload prior to the other.
As I posted already in this thread, this is not the only method to calibrate by, but each choice has a different set of compromises. SVS's own EQ calibrates separately, and can yield good results. I have calibrated subwoofers with different EQ curves (but usually keeping similar drive level as possible) to good effect as well. A major qualification for any approaches being discussed lies in the tools available and the patience or persistence of the person optimizing the system.
I was hoping you would chime in Mark since I was following your preferred method of calibrating dual, non-colocated subs.
I received the Ultras a month apart so they may be from different batches.
A little backgroud...
When I purchased my first Ultra, I quickly realized that one sub was not going to be enough for me in my ~6400 cu ft basement.
The first thing that Ed from SVS suggested to me when I ordered the second sub was that I set the new Ultra 3dB higher than the first. He thought I may have already put the first through too much stress (too many occurances of the popping). I assured him that the popping had only occurred around 6 times. I couldn't believe that I could have possibly hurt my Ultra in such a small amount of time.
In my defense, the popping sneaks up on you, especially with movies that you haven't ever watched before.
In the beginning I noticed that the two subs were playing nice together at the same gain levels. Now (a couple of months later), I have noticed that the original sub plays 1 dB less at the same gain on the amp. Perhaps that is the reason why it is hitting it's limits first.
Although I don't play my movies all that loud, -10 at the most (usually -15), I found that movies like Flight of the Phoenix and The Incredible Hulk caused my subs to hit their limits at those volume levels (actually around -20). I later realized, after a long battle in the Audyssey thread, that Audyssey MultEQ XT wasn't correctly detecting the natural rolloff of the subs. I tried everything. I ran Audyssey and REW so many times in a month's period that I was beginning to lose my mind.
Finally, Ed at SVS told me that he was able to re-create my problem over and over again in his lab when using MultEQ XT. He told me that Audyssey Pro would correct my problem because it was working for him. He was right. I have run Audyssey Pro 3 times, and every time my subs' natural rolloff was detected perfectly. As a matter of fact, Audyssey Pro came up with the same trim levels for each channel every time I ran it (within .5 db). Audyssey Pro is very consistent, as opposed to regular MultEQ XT. All in all, I fear that Audyssey initially put my subs through some unneccessary stress.
This is why, when you mentioned you were going to be running Audyssey Pro on one of your submersives a little while back, that I asked you please post some REW graphs so I could compare them to my Ultras.
I will try your suggestions and report back. It will take some time for me to get in the "tweaking" mood again though.