Cancelling a fundamental resonance...

...of a typical listening room like mine.

My room always had one "nice" hump in the bass (10dB too strong!). See the red curve on the plot below which was measured at my listening position showing the fundamental resonance frequency of my room (most strong behind the speakers, in the middle of the room and at the rear end of the room).

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This hump was bothering for a long time already as I am listening in the middle of the room... I have been trying a lot of things to get rid of it but was never 100% successful. I've tried resonators (big ones!) which only partly cured the problem but introduced others in return and I have tried to EQ it within the Ultimate Subwoofer system signal with some success but still not 100% to my satisfaction as this only worked on one position in the room but is disturbing all other listening positions and who wants to have that...

The best option to work around this problem is to cure it at the source but I do not want to have any digital devices in my main signal path as these only will add jitter and other problems.

The only solution left to try that I came up with is an extra set of bass speakers placed in the corners behind the main speakers trying to absorb the extra energy before the room resonance can build up enough strength to annoy.

So I bought myself a pair of little REL Quake subwoofers to experiment. :grin:

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It took a while to blend these in though but the main trick used is to copy the measured hump (see the green curve) and shift the phase (close to 180 degrees) of this added signal which then cancels out the hump (see yellow curve). The REL signal only has to be 6dB down compared to the main acoustical signal strength and it solved the problem, no matter where you are in the room!

Again, the Behringer helped out here. I now use this device to tame one big resonance (see the REL cancelling curve) and to EQ the Ultimate Subwoofer separately without disturbing my main signal path... :cool:

Bert

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BD-Design - Only the Best!

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Room EQ

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Hallo Bert!

Very well done! I´ve worked the same way, using a Velodyne SMS and a subwoofer to cancel a nearly similar room mode!
Best regards
Stephan

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Wow!

I was familiar with several subs spread over a room, but I don't think any of the approaches were as elegant and exact as yours. In true style. :wink:

Ivo

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Hello Bert,

Were do you place the subwoofers: exactly on the corners? and what kind of measurement and adjustment yo do to tune the phase and volume of the subwoofers?

Regards

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Hello Charles,

Were do you place the subwoofers: exactly on the corners? and what kind of measurement and adjustment yo do to tune the phase and volume of the subwoofers?

I have them placed as far in the corners as possible as this makes the little subs most efficient in the lower frequencies but it is also the best place as room boudaries usually start in the corners and then this is the most effective place to cancel them too (or better said to prevent them to build up too much energy).

Measuring and checking the adjustments were done with Clio and a Behringer Ultracurve was used to create the needed signal (amplitude and phase).

Cheers,

bert

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BD-Design - Only the Best!

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Cancelling a fundamental resonance... (Tweaks)