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In Reply to: RE: Anybody know Altec 604 -8H LF Woofer equivalent ? posted by usaaus on June 24, 2007 at 16:28:39
Thanks very much for that!
Having recently switched to external HF horns, I was thinking about switching out the 604's for the LF only equivalent (515C's !!!) to do away with the now idle coax horn (which resonates a bit). I could go to a different driver altogether but I spent a lot of time on the present boxes and don't feel like getting rid of them just yet.
Bill put forward the possibility that the 604 HF driver's magnet could be giving some support to the LF motor. If so then I may not be able to get the same performance from the stand alone unit.
I'm trying to avoid becoming too deeply enraptured by the speaker world as doing amps pretty well has me stretched to my limit. However(!) Bill also suggested using the horn as a mounting base for a phase plug. That might have me tinkering around with this 604 for a while yet. `,;^D
Thanks again very much for your help!
Follow Ups:
"Bill put forward the possibility that the 604 HF driver's magnet could be giving some support to the LF motor". - Impossible!: They are two separate structures, not a combined unit like Tannoy, Stephens, Stromberg-Carlson utilize in their coaxes. If you want to use a 604 as a bass driver only, remove the HF back cover, diaphagm and horn with its surrounding felt (it will leave a scar that does not affect performance) and install an unvented four inch dust cover. The vent in the dust dome used by Altec on their LF units constitutes a front to back air-leak. By implementing this suggestion (which I have done with a pile of 604E drivers for 4 x 15 cabinets) the venting is through the magnet assembly instead of through the dome. I removed the HF plate, pole piece with phasing plug and magnet also). Forget about the 3" bullet and don't even think of calling it a phase plug at such low frequencies which it can never be. It would serve as a cavity filler and would mount via the two tapped holes in the LF pole piece to mount the HF horn. Good luck!
I was already grateful for your first reply. This is more than I expected. Bonus ! Thanks!!
I understand taking off the back HF cover and diaphragm and can probably figure out how to take out the HF magnet assembly if it's meant to be removeable.
What I'm not sure about is the four inch unvented dust cover. If that goes on the back the driver won't vent from the rear so I'm guessing you mean a dome on the front. The 8H doesn't have a felt disc but a spider that looks pretty well locked on to the outside of the horn at the base of the flare.
Bill's recommendation came when I mentioned to him that it looked on first inspection like the spider would be flapping in the breeze if I pulled the horn out. The idea for the 'phase plug' was to build the structure over the whole horn, thus not making a bullet but a 7 inch dia. very short cone capped with a 7" diameter cap. (Like a shallow conical bowl with an upsidedown plate on top - I've once saw something similar on some other speakers [forget the name but I was told they were a '"classic" product] and they did sound very good)
Thanks again !
"I understand taking off the back HF cover and diaphragm and can probably figure out how to take out the HF magnet assembly if it's meant to be removeable."
No it was not meant to be removed but it can be once the three cover screws are out. The top plate is held to the tube by magnetic force.
But no read need to remove the magnet and pole and plate in the hf section.
"What I'm not sure about is the four inch unvented dust cover. If that goes on the back the driver won't vent from the rear so I'm guessing you mean a dome on the front. The 8H doesn't have a felt disc but a spider that looks pretty well locked on to the outside of the horn at the base of the flare."
So is the flare a mantaray or multicell? I advise that after removing the horn, you cut the spider near the cone so it is absent; there will be a ring of fabric left on the cone if that doesn't bother you. Now glue the four inch dome where a speaker dust-dome belongs. Remove the cover and HF diaphragm. If there is a tangerine plug, whack it sideways with a rubber mallet and it will fall out. You can sell each part on ebay or send them to me for free!
"Bill's recommendation came when I mentioned to him that it looked on first inspection like the spider would be flapping in the breeze if I pulled the horn out. The idea for the 'phase plug' was to build the structure over the whole horn, thus not making a bullet but a 7 inch dia. very short cone capped with a 7" diameter cap. (Like a shallow conical bowl with an upsidedown plate on top - I've once saw something similar on some other speakers [forget the name but I was told they were a '"classic" product] and they did sound very good)"
... but not because of this acoustical plug (modifies top octave directivity). Aren't you comparing an 8" full range Lowther to an Altec 15" woofer?
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