Multiple Sub/Dipole/horns for small room? - diyAudio
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Old 25th February 2009, 11:30 AM   #1
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Default Multiple Sub/Dipole/horns for small room?

Pls help me solve my bass problem. My music listening room is smallish (3mx4mx5m) with hard concrete floor/Ceiling/Walls Yikes! I have a window in the front and thats the only V low frequency absorber I got. I did a lot of research and decided to go for pourous foam solution. I use am using big thick ones (2.5mx1mx35cm) 40 cm away from walls on all room corners. This is helping the FR at my seating position tremendously 80Hz and up.
For sub 80z, room modes are domination the FR with swings +=13DB! Hence I decided Filter the lows from my main using Deq2496 and build new subs.

From what I read, Good Bass requires:

1) Flat FR response with window gate time of 50ms (Ear integration duration at V low freq)
2) Low Distortion and dynamic compression.
3) EVEN LF decay across frequencies with steady state signal.
4) Good transient response.

So far this is what I have:

1)huge bumps and humps around 60Hz/70Hz even with a short 50ms window.
2)good non linear distortion since my listening volume is not high
3)Floor/Ceiling mode is domination my waterfall plot from 0->300ms)
4) Not so good transient response: Producing a 30Hz sine wave outdoor always give me a weak first cycle (6DB less then the 2nd one). and after the signal stop, the driver decay to -12DB after a full cycle. Results for 20Hz/40Hz/50/60/70 almost similar. Not sure how how muich this decay contribute to the final sound quality since the room add a much longer and stronger decay. Maybe horns can produce better results....

After many reading, I noticed that horns/Dipole deal with room modes better then sealed monopole box. Horn is more directional and dipole have figure of 8, both lead to less room interaction. so they should help me with #1 and #4. I also read a GREAT article on JBL by Mr. Todd Welti on room acoustics and using multiple subs. He says 4 subs placed at specific location in a rectangular room will diminish Room modes effect considerably PLUS I will get more even bass across the room. And since <80Hz can't be lcoalized am considering this solution as well for my setup.

Any inputs? Should I go 4 sealed subs? or 2 Horns? or 2 dipoles?

My total budget is 1.5-2K.

Tkx, Sam.
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Old 25th February 2009, 12:12 PM   #2
MaVo is offline MaVo  Germany
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I have basically the same room problems. Multiple subs as recommended in the harman white papers is a possible solution, yet requires a stupid amount of sub output. The flatter the response gets this way, the more the woofers just seem to push air for nothing, or rather, for the flat response. I have 4 12inch woofers, which struggle to make 20hz listenable with harman style configuration. As an option, try to put your woofers in the same room corner and measure the response near the corners and walls, which gets quite a flat response in my room. Another option is nearfield listening, with an ear to woofer distance as small as possible, for example less than 50cm.

Dipole wont help. I went this way and got back to closed box woofers as the box type has little influence on the room interaction. Horns are a great option, since you can trade their efficiency for a flat response with the harman multsub placements.

Geddes also has his own recipe, but seems to be rather good for well damped rooms. I couldnt find a random placement that worked, in my room.
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Old 25th February 2009, 01:14 PM   #3
GM is offline GM  United States
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Did you try one or more subs wall mounted up high as he recommends? It takes a 3D solution to average out a 3D problem, especially one where the vertical modes are 'stacking' up.

GM
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Old 25th February 2009, 03:25 PM   #4
MaVo is offline MaVo  Germany
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I did. Tried with one and two subs above room midpoint. My rooms problem is, that it is nearly undamped with little loss (raw stone walls in basement) and has only two leaks, one smallish window and the door. Even with lots of excited modes, the response is peaky and has deep notches. I suppose, alot of damping would help here, but as long as other means exist, i would rather try those. After lots of trying around, i vote for nearfiled listening. The response is nearly textbook like if you get close enough and the maxspl is pretty good.
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Old 25th February 2009, 04:16 PM   #5
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Quote:
Originally posted by MaVo
I have basically the same room problems. Multiple subs as recommended in the harman white papers is a possible solution, yet requires a stupid amount of sub output. The flatter the response gets this way, the more the woofers just seem to push air for nothing, or rather, for the flat response. I have 4 12inch woofers, which struggle to make 20hz listenable with harman style configuration.
Glad to see others have similar settings and sorry about this Feel you...
I was expecting lower output with multi sub at different location . But not to this extent. I am thinking about 4x horn setup. But since horns are BIG and my room is smalll, I might consider a TH setup. Not sure if 4 of them can be built in my budget... Then again, since the smallest mode in my room is around 34Hz, I might can go monopole for 20-34Hz (Not sure if its really needed for music). my room will nicely boost this range without bouncing them. Then get 4 small horns for 34Hz-80Hz region. Let me know what you think pls. And thanks for letting me about your multi sub/dipole results, This will save me a lot of research!



As an option, try to put your woofers in the same room corner and measure the response near the corners and walls, which gets quite a flat response in my room. Another option is nearfield listening, with an ear to woofer distance as small as possible, for example less than 50cm.

Dipole wont help. I went this way and got back to closed box woofers as the box type has little influence on the room interaction. Horns are a great option, since you can trade their efficiency for a flat response with the harman multsub placements.

Geddes also has his own recipe, but seems to be rather good for well damped rooms. I couldnt find a random placement that worked, in my room.
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Old 25th February 2009, 04:16 PM   #6
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Quote:
Originally posted by MaVo
Another option is nearfield listening, with an ear to woofer distance as small as possible, for example less than 50cm.
[/B]
Tried that and apparenlty my room is so small and modal so strong that 50cm is not enough to be nearfield. Even at this distance, Direct/reflected is low....
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Old 25th February 2009, 04:16 PM   #7
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Quote:
Originally posted by GM
Did you try one or more subs wall mounted up high as he recommends? It takes a 3D solution to average out a 3D problem, especially one where the vertical modes are 'stacking' up.

GM
I can place the sub at middle height and cancel first floor/Ceiling standing wave. Tried that several days ago and discovered and other weaker modes showed up. Tried many many placement and was never able to avoid them all or at least get descent +-5DB response across 20-80Hz. And if I did, it was enoug to move my head few cms and get out of range.....
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Old 25th February 2009, 05:08 PM   #8
GM is offline GM  United States
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Quote:
Originally posted by MaVo

After lots of trying around, i vote for nearfiled listening.
Yeah, in a room like that, this is the only easy/cheap option I'm aware of as it takes either a lot of subs or tapered wall diaphragmatic absorbers to average out all those high Q modes.

GM
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Old 25th February 2009, 07:53 PM   #9
MaVo is offline MaVo  Germany
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If nearfield is out of the question, i would try to sit close to a wall and put the sub in a corner - until you decide to make a more complex solution. This way, i got into the +-5db area and even small subs work great in a corner. Of course, sitting next to a wall will lead to comb filtering, but this wasnt half as bad as having a boomy bass. You can allways add a little fibrous damping to the wall, if its unbearable.

And thanks for the advice, GM. Its allways appreciated
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Old 26th February 2009, 01:48 PM   #10
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Tkx for all the help.

I will build 1 Sub and place it for near field listening. In case I didn't like the result ior this was 2 unconvenient space wise, I ll build 3 more and place them at corners with some eq.

Now what DIY sub would you recomend. I would a solution where drivers and amp are easily available on line (<500$ both). a Sub for 25/30-80Hz range. High listening levels is not crucial. My carpenting skills are very basics and hence I will most porpably outsource the wood work to a Pro friend of mine.

Tkx, Sam.
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