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Old 18th October 2011, 03:54 PM   #1
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Default blocking the vents of B&W 802

hi.

I have 802 B&W driven by krell FPB 600. 600w rms each into 8 ohm. Now i have crossed over the mains with 2 paradigm 15 inch woofers below 40 hZ drivern by 600 W rms pro amplifier and Benringer FBD with room equalization

I have no electronic cross over in the cd-dac-pream-amp chain. The pre is KRC_HR krell and DAC is ACCUSTIC ARTS MK4 DAC2.

Problem: the 802 bottoms out at high volumes. Althought the mains go deep but they do bottom out particulary with HT. So what can i do to prevent bottoming oput i.e restricting output below port resonance without using any passive or electronic cross over.

Any ideas about sealing the port with cloth or something like that.
regards.
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Old 18th October 2011, 04:25 PM   #2
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I think the problems is that the room EQ is sending exceesive boost to your main speakers. Blocking the port may or may not help, try it and see. But the real answer is an electronic filter for your 802's.
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Old 18th October 2011, 04:45 PM   #3
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no sir, nothing is in the signal path to the main speakers. the room equalization is for subwoofer below 40 Hz only to equalizle low rol off of dual sealed subs.
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Old 18th October 2011, 04:48 PM   #4
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Here is the measurement i took from interner. Red is the woofer response .blue is port. it seems to be tuned to 26 Hz.1.jpg
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Old 18th October 2011, 04:50 PM   #5
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and we can see roll off below 40 Hz. i want to block all frequencies below 40 hz to limit the woofer excrusion, thermal heating and greater and cleaner power handling. below 40. the 15 inch dual paradigm can take over. regards
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Old 18th October 2011, 05:21 PM   #6
EUVL is offline EUVL  Europe
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Suggest you contact B&W for advice.
My experience with them has been positive and helpful.


Patrick
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Old 18th October 2011, 05:53 PM   #7
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Quote:
Originally Posted by muddasirwaheedmalik View Post
Problem: the 802 bottoms out at high volumes. Althought the mains go deep but they do bottom out particulary with HT. So what can i do to prevent bottoming oput i.e restricting output below port resonance without using any passive or electronic cross over.

Any ideas about sealing the port with cloth or something like that.
regards.
Jamming rolled up socks in ports can effectively seal the cabinet, synthetic socks work best as they "breath " less.
Hard foam works well too, but requires careful shaping, a bread knife works well.

If your subs are sealed, covering the 802 ports probably will make the two different cabinets "play together" better, you may actually need less power to sound louder and cleaner.
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Old 18th October 2011, 11:02 PM   #8
CR500 is offline CR500  United States
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I would not recommend covering the ports. Above the port tuning frequency, the displacement of the driver will be less with an open port rather than sealing it up.

What is the recommended power amp size for the 802's?

You probably need to either turn it down or decrease the bass going to the B&Ws.
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Old 19th October 2011, 07:01 AM   #9
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Exactly, thats what i want to do. but i as i mentioned earlies i cannot/donot want to alter the signal path to reduce bass to maintin signal purity. a high end DAC-audiophile grade pre-amp-power amp. no bass/tone control so turning down or decreasing bass is not possible. the only way is to physically limit the bass respone of the B&W drivers to 40 Hz. any suggestions?
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Old 19th October 2011, 07:16 AM   #10
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It may sound condescending but why not just turn down the volume until they stop bottoming out??

otherwise a passive high pass in the signal path to the 802s is possible but the values are very high and if you use electrolytics you may ( Possible ) here a little degradation in SQ.
Something around 400uF will limit excursion at the nominal 6dB per octave, setting the XO a little higher would probably work better in practice
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