# open back mids or not?



## vince (Oct 19, 2007)

Hello, I have all peerless six inchers for bass, three inch woofers for mids and a scan speak 9500 for the tweeter. All speakers are electroniclly crossed, 24 db per octave. My main question is to put the peerless mid/woofers in thier own cabinet sealed or just leave the back of the mids enclouser open on the back and place insulation lightly in the space behind them?. I have read that the open back situation eliminates standing waves and resonances in the cone. Anyone have any input?? the mids will operate in the range of approx. 450-4000hz.
Thanks,
Vince


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## JCD (Apr 20, 2006)

Just to be sure I've got this right, your question is if you should have an independently sealed enclosure for your mids as opposed to an open backed enclosure with insulation lightly packed behind the speaker cone?

If I have your question correct, I would ask a follow up question:
Are the woofers also open backed?

If the answer to the above question is yes, then you shouldn't have any insulation and go with a full blown open baffle speaker design.

If the answer is no, then you need to seal up the enclosure. 

What you read is correct to a point, but is taken out of contect I think.

If I have your scenario messed up, please clarify and I'll try again. :bigsmile:

Oh, and is this a design you came up with? Or is it something that's already been designed?

JCD


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## Bill Fitzmaurice (Jun 14, 2008)

Seal them up, and fully line the cab with damping. Standing waves are a non-issue with mids as damping alone is sufficient to eliminate internal reflections. With the small dimensions of modern woofer and sub woofer cabs it's pretty much a non-issue with those as well.


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## vince (Oct 19, 2007)

Hey guys, yes my two peerless six inch woofers where going to be in a ported enclouser. and the two three inch mids I was going to have in the center with the tweeter, but just leave the back of the box open in back of the mids only, and the tweeter of course. I guess people refer to it as a WMTMW design. I currently have diffinitive WTW forward firing, front ported mid size monitors, that i took the passives out of and made a electronic crossover settup for all speakers in my home theater, quite an improvement, but the Diffinitive drivers are middle of the road and seem a bit stressed at times. So I thought I would make a three way design which should be easy being electronicly crossed as opposed to passive design. I just think each speaker will have less of a demand placed on it in the three way condiguration. Anyway these are my thoughts...

Vince


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## looneybomber (Sep 20, 2006)

Are you thinking of something like this?
http://www.htguide.com/forum/showpost.php4?p=348258&postcount=228


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## vince (Oct 19, 2007)

Yes, thats pretty much what I had in mind. My only concern is will this design effect the power handliing of the mids (unloaded situation) vs. a sealed enclouser. They will only be operating in the range of about 450-4000hz at a roll off of 24db per actave, so I don't even know if this should be a concern or not. What do you guy's think?
Vince


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## looneybomber (Sep 20, 2006)

No, the effect should be negligable. Cone movement increases 4x for each octave dropped while maintaining the same input power. That's why OB/IB (sub)woofers must be used with care. For mids, the frequencies are high enough that cone movement is not really effected/controlled by the enclosure like a subwoofer is.

You can always try open backed mids to help open up the soundstage, but if it introduces too many room uglies, you can always close them back up and modify the XO a bit if you need to.


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## mayhem13 (Feb 2, 2008)

I was under the impression that OB dipole radiating systems were less likely to excite room issues?


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## vince (Oct 19, 2007)

Yes, that sounds like the way to go, make the proper size enclouser, leave it open and test with my program and mike, then seal it up and measure again and see which has a flatter response, and perform listening test. Maybe even play around with damping and different cross points. 
Thanks guy's
Vince


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