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Old 2nd March 2006, 01:48 PM   #1
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Default sealed sub 15" 20hz or lower

eh guys,looking for a sealed sub that will do 20hz or lower.i'm very flexible on box size.any suggestions on subwoofers...thanks
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Old 2nd March 2006, 02:31 PM   #2
forr is offline forr  France
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Hi Chainenoble

Louis D. Fielder & Eric M. Benjamin, in their JAES article "Subwoofer performance for accurate reproduction of music", suggest there is a room gain of +12 dB/o starting (towards down) at 25 Hz in typical listening locations. So a closed box with a resonance around 25 Hz should suffice to get 12 Hz at 0 dB.

I have written a spreadsheet which calculates the rendition of a closed box in a typical location having a first room gain starting at 140 Hz (+1 dB) at a rate of +2 or +3 dB/o in the down direction and a second room gain starting at 25 Hz with +12 dB/o in the down direction. The resonance frequency and the Qtb of the enclosure are the input data, and the ouput is the THEORICAL response : it shows that with resonance frequencies less than 40 Hz, you can go with less than +/- 3 dB variations down to 12 Hz. Drop an email if you would like to receive this spredsheet I made using OpenOffice.

The problem is how to get a very low resonance frequency between 25 and 40 Hz. Many people on this forum suggest the most simple would be to use a Linkwitz transform. More elaborate solutions are either using Stahl's techniques or a servo-sub which lowers the resonant frequency by increasing the apparent moving mass (a fact almost unknown).

~~~~~ Forr

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Old 2nd March 2006, 03:15 PM   #3
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Default Re: sealed sub 15" 20hz or lower

Quote:
Originally posted by chainenoble
eh guys,looking for a sealed sub that will do 20hz or lower.i'm very flexible on box size.any suggestions on subwoofers...thanks

Quote:
Originally posted by forr
Hi Chainenoble

using Stahl's techniques or a servo-sub which lowers the resonant frequency by increasing the apparent moving mass (a fact almost unknown).

~~~~~ Forr

In a sealed box getting 20Hz at decent volumes is very difficult, the displacement needs increase a lot, a sealed box with the trapped air reduces the cone x max as air pressure increases inside the box.

I know about the servo subwoofers but there powerhandling is lower right? you need some kind of electronic circuit to compensate for the roll off and a very powerful amplifier.
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Old 2nd March 2006, 03:40 PM   #4
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how about a passive radar set-up then
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Old 2nd March 2006, 08:56 PM   #5
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Thats a great idea, an ABR can extend LF really well and stay musical as well.
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Old 2nd March 2006, 09:26 PM   #6
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any suggestions?i just bought the adires ada 1200 and now need something to match it with
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Old 2nd March 2006, 09:31 PM   #7
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Default Re: Re: sealed sub 15" 20hz or lower

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Originally posted by Iron-Wizard
In a sealed box getting 20Hz at decent volumes is very difficult, the displacement needs increase a lot, a sealed box with the trapped air reduces the cone x max as air pressure increases inside the box.
Not true.

A linkwitz transform alignment in a sealed enclosure can get down to as low as the sub and amp will handle, so providing you've got a robust driver with a good strong motor, plenty of displacement and around 500-1000w your laughing. These things aren't particularly expensive nowadays either and you could build yourself some thing for around 600 quite easily.

I had a XXX 15" with 72mm of xmax peak to peak going flat to 15hz and with an SPL of ~105dB at 20hz, both in-room. That's both deep and loud, infact it was quite easy to scare yourself with it.
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Old 2nd March 2006, 09:35 PM   #8
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Default Re: Re: Re: sealed sub 15" 20hz or lower

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Originally posted by ShinOBIWAN


Not true.

A linkwitz transform alignment
What is a linkwitz alingment? i have never heard of that or this, what is it again?
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Old 2nd March 2006, 09:42 PM   #9
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Default Re: Re: Re: Re: sealed sub 15" 20hz or lower

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Originally posted by Iron-Wizard


What is a linkwitz alingment? i have never heard of that or this, what is it again?
Its a circuit that changes the Q and Fs of the driver/box with the use of inverse equalisation to offset the rolloff to a point determined by the builder of the circuit.

Do a google on linkwitz transform and you'll get a load of hits. The best site to checkout is the Linkwitz lab.
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Old 2nd March 2006, 09:50 PM   #10
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This is going to take some reading, i be back tomorrow, thanks.
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