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Old 26th December 2009, 07:35 PM   #1
Borat is offline Borat  United States
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Default Calling Mister Geddes

So i just had a brilliant idea and i want some input on whether it makes any sense or not.

There are 2 ways to achieve a certain subwoofer Q - we can do it through TS parameters of with EQualization.

however it HAZ OCCURED to me that a subwoofer doesn't act to damp its own oscillation but also to damp the very standing wave that it sets up in the room.

since we can always achieve target Q for the sub through equalization alone why not tune the TS parameters for maximum damping of room standing waves instead of for subwoofer's own Q ?

anybody who thinks they understand what i am trying to say is welcome to chime in - it's not strictly a Geddes question.
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Old 26th December 2009, 07:42 PM   #2
Borat is offline Borat  United States
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also if we continue with this logic then high efficiency subs should be preferred as they will be better bass traps.

just like surfaces that more readily transmit radiation are also ones that more readily absorb it so it should be with subs.
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Old 26th December 2009, 07:44 PM   #3
tvrgeek is offline tvrgeek  United States
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We don't actually change the Q of the driver system, but equalize it to follow a response curve as if we had. The Q remains the same.

Now, what you are really talking about is active noise cancellation. I have not heard of it applied to room standing waves, but worth some contemplation although I don't see how it could work. You could cancel a given wave at a given point, but then again, all that does is move the dead spot around. Outside the seating range maybe.
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Old 26th December 2009, 08:01 PM   #4
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I don't see how it could work. You could cancel a given wave at a given point, but then again, all that does is move the dead spot around. Outside the seating range maybe.
i didn't think of it this way.

so are you trying to say that the position of the sub defines the standing wave pattern and regardless of how the output of the sub is processed whether it is actively or by passive reaction to room mode the result will be the same - namely none whatsoever - on the room modes ?

i guess i am an idiot and didn't think it through. didn't really sleep since 2 days ago.

so you guys think about it and report back.
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Old 27th December 2009, 08:40 AM   #5
Borat is offline Borat  United States
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with multiple subs though i think it would still have a purpose.

the effect would be similar to equalizing different subs individually to minimize standing wave modes - only it would happen automatically through room coupling.

to what extent it would be effective i don't know. however it makes perfect sense. if you need multiple subs and/or mutliple bass traps for good bass then why not think of subs as bass traps ( since they are ) and optimize their positioning around the room accordingly.

GEDDES !

where are you ?
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Old 27th December 2009, 02:40 PM   #6
gedlee is offline gedlee  United States
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if you need multiple subs and/or mutliple bass traps for good bass then why not think of subs as bass traps ( since they are ) and optimize their positioning around the room accordingly.

GEDDES !

where are you ?
When using multiple subs each sub does work as a source and a sink at different frequencies and positioning them arround the room for optimization is what I have been saying. However, one is seldom free to put the subs where they should go, so you put them where they CAN go and EQ for best results. The more subs you use the less critical the locations are.
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Old 27th December 2009, 04:22 PM   #7
Borat is offline Borat  United States
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When using multiple subs each sub does work as a source and a sink at different frequencies and positioning them arround the room for optimization is what I have been saying. However, one is seldom free to put the subs where they should go, so you put them where they CAN go and EQ for best results. The more subs you use the less critical the locations are.
thanks for replying.

right.

but the computer model JBL used to optimize response with multiple subs didn't account for their behavior as a sink as far as i can tell.

so for example they said a sub at the middle of each wall works better than a sub at each corner although a sub at each corner gives greater overall SPL.

but a sub in the corner should be much more effective as a bass trap so if the model took that into account maybe the sub in each corner scheme would not only be louder but flatter as well ?

what i am saying is if we think of subs also as sinks maybe we will need to design the sub itself as well as its position in the room differently.

are you suggesting that its not worth bothering with ?
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Old 27th December 2009, 05:53 PM   #8
godfrey is offline godfrey  South Africa
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also if we continue with this logic then high efficiency subs should be preferred as they will be better bass traps.

just like surfaces that more readily transmit radiation are also ones that more readily absorb it so it should be with subs.
I believe this is a big part of the reason why properly loaded bass horns work well in corners.

With "normal" box speakers, room corners are the worst position for stimulating room resonances in the bass. With big horns, though, you get much better acoustical impedance matching and thus also more uniform output vs frequency. As you suggested, they sink as well as they source and act as "traps", damping the room resonances.
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Old 28th December 2009, 03:06 AM   #9
gedlee is offline gedlee  United States
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thanks for replying.

are you suggesting that its not worth bothering with ?
The order of the effect is the same magnitude as the efficiency of the source. That's about 2-3%. Not much of a carret to be working on.
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Old 28th December 2009, 06:59 AM   #10
Borat is offline Borat  United States
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Ok. i think you both make valid points.

Fine.
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