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-   -   Use Delay to cancel room mode @ 25hz??? (http://www.diyaudio.com/forums/subwoofers/228978-use-delay-cancel-room-mode-25hz.html)

JapanDave 30th January 2013 06:24 AM

Use Delay to cancel room mode @ 25hz???
 
I have multiple Subwoofers and I was wondering if I could use a delay to cancel a room mode @ 25hz? I am still trying to understand about phase, polarity etc, but I am still coming to grips with all the technical terms.

So Could someone help me understand this and how much delay would I need to achieve this?

And forgive my ignorance, I am doing my best to learn what I can.

Cheers Dave

DAMIC 30th January 2013 08:58 AM

Hi,

I don't beleive you will cancel the room mode with delay. Btw, I also have multi subs (4) and use a couple parametric eq functions from electronic dsp x-o, for reducing the room modes.

It seems, you have a realy big room.

rgds,

JapanDave 30th January 2013 09:32 AM

The room is not that big. Approx 3500cf, but it is solid concrete. This is the waterfall and you can see the decay @ 25 hz is really bad. I was led to believe that changing the phase would cancel out a certain frequency? Or is delay and phase different altogether?

http://www.avsforum.com/content/type/61/id/134089/

Cheers Dave

weltersys 30th January 2013 03:09 PM

Quote:

Originally Posted by JapanDave (Post 3348352)
The room is not that big. Approx 3500cf, but it is solid concrete. This is the waterfall and you can see the decay @ 25 hz is really bad. I was led to believe that changing the phase would cancel out a certain frequency? Or is delay and phase different altogether?

Dave,

Delay and phase are two different things.

A 25 Hz cycle is twice as long as 50 Hz, it's decay will show up as twice as long on a waterfall even without figuring room reverb.

Using two LF sources, one delayed, you could cancel certain frequencies in certain places, while increasing their amplitude in others. Not a good idea.

JapanDave 31st January 2013 01:38 AM

Thanks for the info. So how do you change the phase of a speaker to help cancel out a problem frequency?

weltersys 31st January 2013 02:36 PM

Quote:

Originally Posted by JapanDave (Post 3349450)
Thanks for the info. So how do you change the phase of a speaker to help cancel out a problem frequency?

If the "problem frequency" is at the crossover point, delaying the upper or lower band (usually upper) may be required to get a smooth phase response through the crossover region.

Generally parametric or graphic EQ are used to reduce or boost amplitude at problem frequencies within the pass band of the speaker.
The correct application of EQ also smooths the phase response as the frequency response is flattened.

EQ won't correct room problems, but will make them more tolerable.

tvrgeek 31st January 2013 11:27 PM

You use delay to reduce the differences in position between sub and main to help the crossover range integration. Bass traps, as in real ones, not a block of foam in the corner, can do wonders. Moving them around can help. If your peak is that low, I would try and reduce the sub output by playing with the alignment a bit. Make sure you don't have it in the corner. Center between the mains is easiest to integrate. Then try some eq. My personal taste has them roll off in that range. Just no music down there. killing a peak is pretty easy to do with eq. Trying to boost dips is where subs get into trouble.

Speedskater 1st February 2013 09:26 PM

A recent SMWTMS club meeting video:

Earl Geddes on Multiple Subwoofers in Rooms

Earl Geddes on Multiple Subwoofers in Rooms, smwtms Captured on Ustream:Earl Geddes on Multiple Subwoofers in Small Rooms, plus a CES Report, and New Faces...

tsiros 1st February 2013 09:37 PM

This is odd.

First, response is flat down to 10 Hz. Second, i don't see any other resonances. Is your room completely cubic, 3 m * 3 m * 3m ?

audiomagnate 1st February 2013 11:51 PM

Quote:

Originally Posted by Speedskater (Post 3352149)

Is that link supposed to be a joke? You can't hear what they guy is saying because of the organ music.


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