# 20-39 PC+ Duals reaching limit...?



## Vader (Jul 8, 2006)

Hi all,

I just finished watching "How to Train Your Dragon," and I think I found my new bass demo... At the end, when the big guy impacts the ground, if I didn't put a crack in the foundation, I don't have something set up right (read: the entire house shook). Therein lies my query: I heard what I thought might be the subs bottoming during the explosion, but it wasn't the loud metallic "clack" I had come to associate with the event. So, I watched the same sequence three times, each time isolating a different channel to find where the sound I was concerned about was coming from: L/R mains, center, and subs. I established that the sound was coming from the mains (and a little from the center), and was indeed part of the soundtrack. There was not a trace in the subs. What I did hear, however, was some minor "cracking" distortion at the peak of the bass output (with the other channels active, I would never have heard it). Otherwise, the bass output was smooth and loud (no puffing, no worbeling - yes, I made that word up).

Here are the details of my setup and volume levels:

1) The room is approx 3200 ft^3
2) the dual 20-39 PC+ cylinders are about 10 feet apart flanking the front channel. After a ton of experimentation, I found this to give the best response. Look at the link in my signature to give you a better idea.
3) They are calibrated flat at 82dB at MV00 (vs 72dB for the mains and satellites) using SD-DVE: they are not run hot. They are also EQ'ed via a BFD.
4) I was watching at approximately 12dB _below_ reference
5) I did not think to get my meter out, but I would guess that the bass peaked between 105 and 110dB
6) The only time these subs have been bottomed in this configuration was when they were calibrated using the HD-DVD DVE. After a lot of troubleshooting with Roger Dressler, we determined that the sub tones are wrong on the HD-DVD version (they are 5dB cold, relative to SD-DVE, which is correct, as determined by comparisons with AVIA). As a result, I was running them 5dB too hot. That, combined with pushing the subs too hard by about 3dB, means that I should have about 8dB headroom...?

I know that all speakers have some distortion at high volume levels, so is that what I am hearing here?


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## goyop (May 4, 2010)

It is not quite clear to me what is the final observation of the event. You said when you repeated the scene that the subs in fact did not overdrive but you still heard some evidence of overdriven mains? Can you clarify this? If you had to guess, what is the approximate frequency of the distortion? Any ballpark description.

A thunderous bass event usually has accompanying higher frequency tones. For example, on a kick drum there are two components - the whack of the pedal which is around 400 Hz I believe, then the thump of the drum which is much lower. A bass guitar has the same thing. So if your subs are not being overdriven then it could be higher frequencies attached to the bass sound or the particular setup of your system and crossover ranges and filters, etc., and this unique passage just hit your system with a perfect storm. So you may have overdriven the mains or satellites or whatever for this one particular sound event.


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## Vader (Jul 8, 2006)

Hi, Goyop!

I don't think I overdrove (is that a word?) the mains at all. I heard the clap of the explosion (part of the sound effect on the track) only in the mains, and not in the subs (meaning that they did not bottom). I was just curious as to if the minor cracking I _did_ hear from the subs were indicative of pushing them too hard. As I said, they showed no other signs of distress (like huffing,compression, etc) and I should have about 8dB headroom, based on a previous bottoming event. Just being paranoid, I guess...


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## goyop (May 4, 2010)

I think if you are not seeing this as any kind of regular experience I wouldn't worry about it. Clearly you don't want to slam any speaker into its maximum excursion but even if that is what happened (I doubt it) a one shot deal shouldn't cause damage. And if they were damaged you would know it!

As I said before, I believe it was a perfect storm of the passage and your system giving you some weird transient that didn't sound good. It seems you have taken great care in selecting and setting up your system.


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## Vader (Jul 8, 2006)

Goyop,

Thanks! Admittedly, I am somewhat OCD (or so my wife tell me...), so you are probably right. But then, OCD is pretty common among HT geeks and collectors...


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