Multiple Small Subs - Geddes Approach - Page 11 - diyAudio
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Old 12th December 2008, 01:02 AM   #101
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Thanks Bill. I left out the final settings intentionally because the average websurfer simply doesn't read and in the end there will be people that use my settings and wonder why they don't get a flat low frequency response...

Who could follow the recommendations then? Using LR2 or LR4, 80Hz or 160Hz would make a huge difference in setting the subs up. It is good to see some samples.

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Bill
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Old 12th December 2008, 01:09 AM   #102
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You have to compare different settings by doing measurements. You should reread my page.
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Old 12th December 2008, 01:36 AM   #103
gedlee is online now gedlee  United States
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Originally posted by otto88
Hi Earl

> I do favor "sealed", but sealed bandpass, not direct radiating.

Do sealed BP avoid the poorer transient decay of that vented BPs can have?

Cheers

Suns don't have a "transient response" per see. They have one, of course, but being LF limited its always very slow to rise and rings out a long time. All subs will do this. And again, you have to consider ALL of this in context of room modes. The modes ring out far longer than any sub. So in the end if the total room response is smooth the net result will be a smooth "impulse response". Its a big mistake to consider any LF source out of the context of the room that its in, which has to also include all the other sources. At LFs, the room and all of the sources become one system with the sources being dominated by the room.
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Old 12th December 2008, 09:39 AM   #104
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Dr Geddes,

Very interesting thread, as always!
Perdone me my english is poor so I am not confortable to read tons of
AES papers so maybe I am sure missed something.
If I have well understood, Welti's approch "solve"95% of problem below 80Hz.
But what about the (even) more important 100/300Hz range?
What is your "medicine" for it ?

Cheers,
Paolo
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Old 12th December 2008, 10:43 AM   #105
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by gedlee



Suns don't have a "transient response" per see. They have one, of course, but being LF limited its always very slow to rise and rings out a long time. All subs will do this. And again, you have to consider ALL of this in context of room modes. The modes ring out far longer than any sub. So in the end if the total room response is smooth the net result will be a smooth "impulse response". Its a big mistake to consider any LF source out of the context of the room that its in, which has to also include all the other sources. At LFs, the room and all of the sources become one system with the sources being dominated by the room.
It's also necessary to consider the type of music being produced. I do agree the there is very little percussion type instruments that have very low frequency content. Nor do many people have listened to these type of instruments live. However, if one wants to reproduce these kinds of instruments in a more accurate manner, the initial impact and the following timbre should be alligned as closly as possible. If not, then the sound image will shift. Normally when room modes or other form of resonance take effects, you will feel the sound source changing from the front to no aparent image source.
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Old 12th December 2008, 01:21 PM   #106
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What percussion instruments would that be? At what frequencies does the transient part of those instruments occur?

Best, Markus
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Old 12th December 2008, 02:04 PM   #107
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by markus76
What percussion instruments would that be? At what frequencies does the transient part of those instruments occur?

Best, Markus
See below:
Note that the transient part of percussion instruments is when struck by the performer.
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Old 12th December 2008, 02:30 PM   #108
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Send me a soundfile and I'll show you that your idea of low frequency perception is completely wrong.
The drum in your example shows a transient part when the stick hits the drumhead. The frequency of that sound is nowhere near the low frequency range. That makes the drum localizable. The low frequency part of the drum sound takes some time to build up after the first hit.

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Old 12th December 2008, 02:46 PM   #109
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Quote:
Originally posted by inertial
If I have well understood, Welti's approch "solve "95% of problem below 80Hz.
But what about the (even) more important 100/300Hz range?
I have found the room modes get bunched up pretty well towards the higher end of that 100-300Hz band. Rooms usually shift from being modal to reverberent in this range.

There is one exception: Floor bounce. Tower speakers or speakers on stands often have a notch in the lower midrange causesd by self-interference from floor bounce. It's usually around 100Hz to 200Hz, depending on speaker height. And it isn't usually mitigated by carpeting, as some might think. Sound absorbtion isn't good at that frequency because the carpet and pad aren't nearly thick enough, not even close.

This can be solved with the same sort of approach that the multisub approach uses. In fact, you'll never see floor bounce from a line array for that very reason. You can also smooth the notch when blending a woofer with a midrange, if the midrange is crossed over low enough. They're stacked vertically on the baffle, so their vertical offset smoothes the notch by "filling it in". Likewise, a "sub" that's placed fairly close and crossed over high enough will do it, provided they are positioned with vertical offset.

If you're running two-way speakers and have them on stands, try placing two subs on the floor, near the mains. Low-pass them a little higher than you might normally, so they blend in the range where floor bounce is. Then you might put one or two other subs further away to smooth modes at lower frequency.
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Old 12th December 2008, 03:21 PM   #110
badman is offline badman  United States
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Quote:
Originally posted by Wayne Parham



There is one exception: Floor bounce. Tower speakers or speakers on stands often have a notch in the lower midrange causesd by self-interference from floor bounce. It's usually around 100Hz to 200Hz, depending on speaker height. And it isn't usually mitigated by carpeting, as some might think. Sound absorbtion isn't good at that frequency because the carpet and pad aren't nearly thick enough, not even close.

This can be solved with the same sort of approach that the multisub approach uses. In fact, you'll never see floor bounce from a line array for that very reason. You can also smooth the notch when blending a woofer with a midrange, if the midrange is crossed over low enough. They're stacked vertically on the baffle, so their vertical offset smoothes the notch by "filling it in". Likewise, a "sub" that's placed fairly close and crossed over high enough will do it, provided they are positioned with vertical offset.

If you're running two-way speakers and have them on stands, try placing two subs on the floor, near the mains. Low-pass them a little higher than you might normally, so they blend in the range where floor bounce is. Then you might put one or two other subs further away to smooth modes at lower frequency.
An interesting thought is whether larger woofers exhibit reduced floor bounce (or at least smooth/spread it over a wider range of frequencies) due to the larger excitation surface. Yet another reason to use 15"s whenever possible
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