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Old 1st May 2013, 03:44 PM   #1
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Default OB speakers and room acoustics

Wasn't sure where to post this so if this needs to be moved i apologize in advance:

My speakers are a hybrid OB (sealed bass) OB mid tweeter. My room is rectangular 12x17ft I made the room reflective (or live) from the plane of the baffle back. In the seating area i made it a combination of diffuse and absorbtive. Does this sound correct? I think making the area behind the speaker absorbtive goes against the idea of an OB speaker. Suggestions appreciated.
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Old 1st May 2013, 04:17 PM   #2
Rudolf is offline Rudolf  Germany
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From my experience the live end should be behind you. The front end behind the OB should be at least diffusive, and probably absorptive at the first reflection points. Why do you think that "making the area behind the speaker absorbtive goes against the idea of an OB speaker"?

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Old 1st May 2013, 04:29 PM   #3
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I totally agree with Rudolf on this. I think early-arriving front end reflections are very damaging to sound quality in general.
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Old 1st May 2013, 04:34 PM   #4
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OK not sure if I was clear. From the baffle forward (into the listening area) It is a mix of absorbtive and diffuse. Details i did not provide are absorbtive panels at first reflection point (using mirror method) and diffuse on cieling and floor has carpet. Wall behind listener could be considered diffuse (book case

The reason I was not thinking absorbing sound behind speakers is because it would deaden the rear wave which is what we are after, no?
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Old 1st May 2013, 04:34 PM   #5
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I also agree, more or less. Diffusive behind a dipole if you've got lots of space back there (and I mean a lot, not like a foot and a half), or if you must have them close to wall behind, absorptive.
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Old 1st May 2013, 04:37 PM   #6
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I'd for for absorptive anyway, regardless of the distance between speakers and front wall.

Yes - that means killing off the rear radiation.
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Old 1st May 2013, 04:46 PM   #7
ra7 is offline ra7  United States
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So Stig, if you are going to kill off all the rear radiation, what is advantage of an OB compared to a sealed woofer? Directivity in the lower octaves?
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Old 1st May 2013, 05:16 PM   #8
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If the rear wave of an OB is considered detrimental then why use OBs in the first place?
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Old 1st May 2013, 05:41 PM   #9
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Quote:
Originally Posted by dumptruck View Post
I also agree, more or less. Diffusive behind a dipole if you've got lots of space back there (and I mean a lot, not like a foot and a half), or if you must have them close to wall behind, absorptive.
I should post a room layout
The speakers are at least 3 ft from front wall and about just under 2 ft from side walls. I have GIK wall diffusors I can use. I also make 1 1/2 inch thich absorbtive panels.
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Old 1st May 2013, 06:39 PM   #10
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Quote:
Originally Posted by ra7 View Post
So Stig, if you are going to kill off all the rear radiation, what is advantage of an OB compared to a sealed woofer? Directivity in the lower octaves?
Directivity is one thing. An other is that the dipole is a velocity source instead of a pressure source; properly placed it will excite the room modes less. And lastly, you avoid the speaker box (cavity) with all it's inherent problems.

The price you pay for this is very low efficiency, that's maybe why dipole bass is not common in commercial speakers I guess.
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