Enclosure for vintage 18inch alnicos - diyAudio
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Old 21st November 2012, 12:10 PM   #1
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Default Enclosure for vintage 15inch alnicos

Hi All:

Some time ago I bought a pair of 15'' Alnico speakers on ebay. Apart from knowing that they work and that they have a 4 Ohm impedance I haven't any tech spec from them. I've tried finding some info Googling but its really hard since they don't come branded... just a "6522" in the backside of the membrane and "205" in the metal frame.

I bought them in order to build two subwoofers for my home stereo, based on a KT88 push pull amplifier and -by now- a B&W CM2 speakers. My aim is, obviously, improving lows without transforming my home in a disco. I mean I like listening music at low volumes and what I want is sound quality much before than watts.

My first idea is building a pair of sealed subwoofers but, as I said, I don't have tech info about speakers and I'm not able to determine the enclosure volume... I have to admit I an absolute lammer when talking about subwoofers. My questions are:
  • How the enclosure volume affect to the subwoofer response (higher volume -> lower freq. cutoff?)
  • Might I use a passive low pass filter or might I rely on enclosure response for cutting of freq?
  • And maybe summarizing previous questions, what might be the recommended volume for a system like what I want to get?

Any help would be really appreciated. Thanks in advance.

Last edited by GaryKrant; 22nd November 2012 at 08:26 AM.
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Old 21st November 2012, 01:00 PM   #2
epa is offline epa  Netherlands
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buenos dias gary
you got a few options.
you could measure the ts parameters or
you could bild a test box to see how it preforms.anywhere between 50 to 150 lts
you need filters ,because a closed box gives the full spectrum of the woofers output
maybe if you have a sepperate amp you could go active for the best sq.
i use a hypex AS100 wich has a fully configurable dsp
use the 18"only in the sub range and let the B&W CM2 do the rest of the sound.
x-over 60~80hz
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Last edited by epa; 21st November 2012 at 01:03 PM.
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Old 21st November 2012, 01:55 PM   #3
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goedemiddag epa

Very useful thoughts for various reasons:
  • I plan to "rack" the subwoofers in a library and luckily I have two kinds of placements: Two modules have a volume of 170 l. (each) and the other two have a volume of 80 l. (each), so it's really easy to check what enclosure volume fits better to my sound tastes.
  • Fully agree with you about letting CM2 drive mids and hights, a task that they perform very very well.
  • Luckily CM2 frequency response starts from 60Hz, so a xo as you say would be perfect.

Thank you very much.
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Old 21st November 2012, 04:36 PM   #4
Juhazi is offline Juhazi  Finland
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Hi, Your plans are quite similar to mine (2 15" elements)

I think that your alnicos might are best suited for sealed boxes or dipole (open baffle) with very modest spl. Perhaps they are from some musical instrument (guitar amp/speaker) which are often in leaking (aperiodic) or semiopen cabinets
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Last edited by Juhazi; 21st November 2012 at 04:40 PM.
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Old 21st November 2012, 05:03 PM   #5
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HI Juhazi:

Since I plan to put them in a library, and since a open baffle can be considered an unfinished sealed box I'll start testing with open baffles, though I'm not very confident about its sound quality since I understand that mostly depends on what is behind the baffle.

I've been reviewing the ebay sale and I can say that the seller claimed they where a pair of Gefco speakers. They are marked with what I believe is a EIA code 205, though this code is not associated to any manufacturer. They are marked too as X1320 in the frame and as 6522 in the back of the cone. In any case it's hard to find info about Gefco speakers as impossible about these pair, so any info about them would be appreciated.
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