8" Subwoofer - AVS Forum
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post #1 of 9 Old 02-05-2013, 08:02 AM - Thread Starter
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hi

I want to build a subwoofer but I only have 8" speakers which has freq response from 40 Hz to up... So my question is : Is it possible to get lower frequenxies if I put two 8" speakers in the same box in parallel? I checked them on www.audiocheck.net so I can hear 20hz on them or 30hz but its to quiet so from 40 and up I can hear it much louder. So if bass mean more air moving I guess 2 speakers can do the job to hear louder those 30 Hz at least. Thats my oppinion I need expert's. Thanks
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post #2 of 9 Old 02-05-2013, 08:05 AM
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Quote:
Originally Posted by Zoran Monevski View Post

hi

I want to build a subwoofer but I only have 8" speakers which has freq response from 40 Hz to up... So my question is : Is it possible to get lower frequenxies if I put two 8" speakers in the same box in parallel?
No. Two drivers will go louder than one, but no lower.

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post #3 of 9 Old 02-05-2013, 08:14 AM
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Right, but since there's 'some' output from 20 on up, with two drivers there will be 'some more' from 20 on up, which might make for acceptable response in a fully configured and equalized system down to some value a bit below 40, no?

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post #4 of 9 Old 02-05-2013, 08:33 AM
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^^^ The relative levels stay the same. Yes, there will be a little more output at 20 Hz, and also more at 40 Hz. If he uses an equalizer (filter) to reduce the signal above 40 Hz and/or boost it below, he could obtain more output at 20 Hz relative to 40 Hz, but again the ratio is fixed by the driver's response. Adding drivers will increase the total SPL but will not increase the very LF signal's level relative to the higher-frequency signals, everything moves together...

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post #5 of 9 Old 02-05-2013, 08:40 AM
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OK, thanks. I figured as much.

Yes, it's clearly "sub"-optimal to use drivers down that much in FR for deep bass, but I know that for instance in my setup, I have a fair amount more sub than I need to make room filling bass, so I can basically just dial back all the frequencies that don't dip badly (ignoring modes for the moment) and still have sufficient volume over a wide frequency range.

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post #6 of 9 Old 02-05-2013, 08:51 AM - Thread Starter
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Thanks a lot for the answer. I wanted to make an extra subwoofer but it won't worth it. I previously made a speaker (like soundbar) using 8" as woofer 6" middle and 2.5" as a tweeter.
I use also a 3 way crossover and when I play those sound tests on audiocheck.net I started to hear from 40 and as it goes up some freqs I hear quiet than next freqs for example, the 80Hz I hear it quiet than 70Hz and 90Hz and around 120 get quieter results also.. What cause that problem

this is my speaker : http://img167.imagevenue.com/img.php?image=79224__DSC9651_122_964lo.JPG
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post #7 of 9 Old 02-05-2013, 09:09 AM
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Look up room modes and comb filtering... Essentially at low frequencies and certain positions in the room the volume will be much higher or lower due to the sound bouncing off walls/floor/ceiling, combining with the direct sound, and either adding up or cancelling out.

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post #8 of 9 Old 02-05-2013, 09:10 AM
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You're hearing the room suck outs. Google bass room modes or something like that. Those frequencies reflect around the room and sometimes you get constructive summing and sometime destructive summing.
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post #9 of 9 Old 02-05-2013, 12:16 PM
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Wish I'd said that... smile.gif

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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