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Old 4th February 2009, 01:06 AM   #591
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...

This is by far the best response I have seen over a wide area. I think a DBA with a little eq based on multi-position measurement would be a killer setup.

As I said a few posts ago. I think the DBA make room response a done deal. 4 woofers on front and 4 on back walls, wired in series/parallel, a delay/Eq (My Beringer DEQ2496 should do nicely) and a stereo amp.

If done correctly eight subs would yield a smooth response in any simulation. Its the real world that counts.

What do you think Todd, what could you do with eight subs?
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Old 4th February 2009, 03:11 AM   #592
youngho is offline youngho  United States
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Hi Dr Geddes, do you feel that bass trapping is beneficial if one uses multiple subwoofers, or do you feel that your approach completely obviates the need for bass absorption? My impression is the former, but at least one fan of your approach remembers the latter. If bass trapping would indeed be helpful but one is working with an already constructed room where the boundaries cannot be re-mounted in such a way as to flex as much as possible, do you tend to look kindly upon diaphragmatic absorbers or Helmholtz absorbers because they tend to avoid absorption at mid- and high frequencies? Thanks for clarifying.
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Old 4th February 2009, 12:22 PM   #593
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Quote:
Originally posted by gedlee



If done correctly eight subs would yield a smooth response in any simulation. Its the real world that counts.

What do you think Todd, what could you do with eight subs?
Yes, if done correctly. But you need to figure out what correctly is.


Yes, other configurations can be found with 8 woofers. For example you can take Todd's 4 woofer floor array, 1/4 wave length from walls and lift it 1/4 wave length off the floor. Then add a second 4 woofer array 1/4 wave length off the ceiling. This will give pretty smooth response as long as you are near the center of the 1/4 wave boundaries. Thew first excited modes are (4,0,0), (0,4,0), (0,0,4), (4,4,0), (0,4,4) and (4,0,4). And the response follows the MP response at low frequency too! But don't sit too far off center. However, the DBA seems to give pretty good response just about independently of listening position and all the woofer are mounted in places which are out of the way.

Yes the real world counts, but I have my doubts that is something simulated bad it will be good in the real world. The question is more that if it simulates good, how well will it really work in the real world.
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Old 4th February 2009, 12:43 PM   #594
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Quote:
Originally posted by markus76
John, fixing everything below 100Hz is good but how will you fix the higher frequencies up to the Schroeder frequency? Applying porous absorbers will affect performance of the DBA. I can't quantify that effect so I guess we will have to wait until you show some measurements

Best, Markus

I do hope to set up a DBA but it won't be tomorrow. But in terms of consistency of response with changes in listening position I have yet to simulate anything that comes close. See the thing is I have no vested interest in what works or doesn't work. Heck, the DBA isn't my idea. If I could get a 2, 3 or 4 woofer result that appeared to work as well I'll try it.
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Old 4th February 2009, 01:35 PM   #595
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...
If I could get a 2, 3 or 4 woofer result that appeared to work as well I'll try it.

Its a question of working "well enough". Eight woofers mounted in the wall of a perfect rectangle is not very practical. Three or four subs placed arround the room at convenient locations is. And if the former yields little or no audible advantage then whats the point?
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Old 4th February 2009, 01:40 PM   #596
gedlee is offline gedlee  United States
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Quote:
Originally posted by youngho
Hi Dr Geddes, do you feel that bass trapping is beneficial if one uses multiple subwoofers, or do you feel that your approach completely obviates the need for bass absorption? My impression is the former, but at least one fan of your approach remembers the latter. If bass trapping would indeed be helpful but one is working with an already constructed room where the boundaries cannot be re-mounted in such a way as to flex as much as possible, do you tend to look kindly upon diaphragmatic absorbers or Helmholtz absorbers because they tend to avoid absorption at mid- and high frequencies? Thanks for clarifying.

I really believe that some LF absorption is essential to good bass. The combination of good LF absorption and multiple subs creates, IMO, and ideal bass situation. If you can do one and not the other then do multiple subs, but absorption adds a lot to the modal interactions and smoothness of the response.

Some "bass traps" are more absorptive at mid to HFs than they are at LFs, these must be avoided. What I have found works well is very heavy drapes behind the speaks, since in that location even HF absorption is positive. But HF absorption anywhere forward of the speakers should be avoided.
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Old 4th February 2009, 02:03 PM   #597
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Quote:
Originally posted by gedlee



If done correctly eight subs would yield a smooth response in any simulation. Its the real world that counts.

What do you think Todd, what could you do with eight subs?
I am up to 5
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Old 4th February 2009, 03:15 PM   #598
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Quote:
Originally posted by gedlee



Its a question of working "well enough". Eight woofers mounted in the wall of a perfect rectangle is not very practical. Three or four subs placed arround the room at convenient locations is. And if the former yields little or no audible advantage then whats the point?
Eight woofers mounted in the wall of a perfect rectangle is not very practical only to those who don't have rectangular rooms. As lot of people do have such rooms. It may be more convenient to mount the woofer out of the way in a wall. And by who's definition are the optimum positions of a 3 woofer system convenient? If I give you the dimension of my rectangular room can you tell me where to put those 3 woofers?

But the question is, "Is there an audible advantage?" You don't know unless you try it. To dismiss it out of hand is unreasonable. Unless the woofer low frequency output is MP then looking only at the amplitude response is only 1/2 the story. It says nothing about the decay. If the response is MP then we know about the decay. If I know I have the same MP response at a listening position in two different rooms then I know I will have the same decay and if I apply MP eq to one system I know that the same eq applied to the second system will yield the same result. You can't say that with a non-MP system.

Now if you will excuse me I'm going to listen to a little music in a nonrectangular room with 2 cardioid woofers and dipole panels.
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Old 4th February 2009, 03:32 PM   #599
gedlee is offline gedlee  United States
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John

You are the one who is "dimissing out of hand" the proposed woofer setup being discussed here by saying that XYZ is better. You have done neither.
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Old 4th February 2009, 03:53 PM   #600
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A) Why should I, or anyone except your declaration of good enough? A Kia may be good enough for you. I might feel a BMW or Lexus is required to be good enough for me. Is it wrong to strive for something better than good enough? How about better yet? I think "better yet" might be superior to "good enough".

B) On one hand you talk about science. What is the science behind good enough?

C) You don't have any idea what I have or have not done, or will or will not do in my listening environment, so please don't assume.

D) I don't have to do it to show that scientifically something is potentially better than something else.

E) I haven't dismissed anything. I have presented the results of my simulations. When I get around to testing for sure I'll look and listen to a 3 woofer system in the same room.

F) If I want to set up a 3 woofer system in a 14' L x 12'W x 7' 8" H room, where should I place them? Ok, one is a corner, then what? I know exactly where to start with a 4 woofer Welti set up and for an 8 woofer DBA from the science. What does the science say about the placement of a 3 woofer system?

Back to the music. Brahms ND is so soothing.
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