# What to do about this 80 Hz null?



## Rrolack (Jan 17, 2010)

After using REW, I'm finding that my main speakers produce a null that's 15 db deep, centered at 80 Hz, with the width spanning from 70 Hz to 90 Hz. However, when I test each main speaker alone, there is no dip at 80 Hz from either one.

This suggests that I'm getting some kind of cancellation between the mains. Any ideas about what I can do about this? Moving my speakers around a bit has done little to alleviate the issue. Regarding treatments, I have a pair of corner bass traps in my room, and I'm planning to install some acoustical paneling. 

One possible solution is to cross over to my sub at 100 Hz, rather than at 80 Hz, as I'm finding that the sub alone measures flat around 80 Hz. However, I'd prefer not to increase the crossover, in order to preserve stereo separation (I have no trouble localizing a 100 Hz sound in a blind test).


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## bpape (Sep 14, 2006)

When you get the null, is it JUST the mains or is the sub engaged too? If you're crossing at 80 to a sub and not running them full range PLUS the sub, it's likely that at least part of it is phase setting on the sub.

Bryan


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## Rrolack (Jan 17, 2010)

It's actually just the mains.


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## bpape (Sep 14, 2006)

OK. Well, pretty much the same story though. If you have a null at 80 with just the mains and you're crossing at 80, it's similar to just having a steeper xover slope realistically.

The cancellation between them can be a couple things. Do you have multiples or same dimensions between the speakers as you do from them to the side wall? 

Bryan


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## Rrolack (Jan 17, 2010)

I'd say that the two speakers aren't equidistant from their respective side walls.


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## bpape (Sep 14, 2006)

That can certainly be an issue. My question though was if the distance from one speaker center to the side wall was the same as the distance between the speakers.

Bryan


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## Rrolack (Jan 17, 2010)

Sorry, I misunderstood; this isn't the case either.


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