diy modification on drivers to lower mechanical losses - diyAudio
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Old 16th September 2002, 03:32 AM   #1
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Default diy modification on drivers to lower mechanical losses

While it is still not clear whether Rms as a whole is important for precise bass sound (http://www.diyaudio.com/forums/showt...=&postid=60555), I have found a couple of references on the subject of unfavorable air flow conditions. A modern woofer will have any or all of the following features to improve venting and hence lower turbulence and air compression:
a) phase plug
b) magnet venting holes
c) venting holes in the semi-sealed volume between the centring diaphraghm (is this the correct word?) and the cage

I wonder if it is possible to implement this on vintage drivers that are still very good except for venting.

b) will probably destroy the speaker

a) should be doable. One would have to cut a big circular hole in the dustcap and then stick some sort of metal column through the hole and glue it to the magnet

c) should also be possible if the cage is dye cast aluminum. Maybe one must use low rpms or even a hand drill. Or would a router be preferable?

Anybody tried this?

Eric
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Old 17th September 2002, 08:24 AM   #2
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Thought this was a prime DIY subject, but it hasn't elicited any posts yet.

I should receive some used Eton speakes shortly and, unless somebody posts a report of failure, will try option c, i.e. drill holes in the basket to vent the space between diapragm/spider and magnet. I will measure TSP before and after modification.

Any ideas of how to keep little pieces of aluminum from getting into the gap? I had thought of a vacuum cleaner and very low drill rmps.

Eric
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Old 17th September 2002, 08:40 AM   #3
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Default Re: diy modification on drivers to lower mechanical losses

Quote:
Originally posted by capslock
a) should be doable. One would have to cut a big circular hole in the dustcap and then stick some sort of metal column through the hole and glue it to the magnet
Dustcapectomy. usually beneficial. Phase plugs can also be made of wood, woolfelt, lipstick tops

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Old 17th September 2002, 08:57 AM   #4
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Model rockets such as Estes use balsa and plastic nose cones in lots o sizes which could be used as phase plugs. You can order just the cones from Estes and others
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Old 17th September 2002, 09:29 AM   #5
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Quote:
Originally posted by Variac
You can order just the cones from Estes and others
Got some URLS?

dave
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Old 17th September 2002, 09:40 AM   #6
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Default Dustcapectomy

Got experience there?

Do you remove the whole cap or cut a circle and leave a dustcap rim behind?

What should the gap between the plug and the hole be? Too large and you have an acoustical short, too small, and you don't improve mechanical loss.

Wood would have no cooling effect but then I doubt that that is much needed.
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Old 17th September 2002, 05:44 PM   #7
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Default Re: Dustcapectomy

Quote:
Originally posted by capslock
Got experience there?

Do you remove the whole cap or cut a circle and leave a dustcap rim behind?

What should the gap between the plug and the hole be? Too large and you have an acoustical short, too small, and you don't improve mechanical loss.

Wood would have no cooling effect but then I doubt that that is much needed.
not as much as i'd like.

seems to work best if the entire dust cap goes (my experience ranges from 2" to 8")

A gain in cooling comes from just letting the VC breathe.

dave
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Old 17th September 2002, 11:40 PM   #8
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Default optimum gap between phase plug and cone

The question about the optimum gap still remains to be answered. What is the gap in typical Seas drivers?

Had a look at the hard paper Vifa drivers in my T+A. The minimum cone diameter is definitely smaller than the dust cap diameter. It wouln't hurt (and might improve stability) to let some of the dust cap remain.
Wonder if it could be done with a hot aluminum or stell cylinder. Would work on plastics, but I doubt it would work on the coated fabric dust cap in the Vifas.

Eric
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Old 17th September 2002, 11:44 PM   #9
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Default boring the magnet

Had a look at two different Vifa drivers. The magnet seems to consist of one or two ferrite rings, chromium-coated steel pole plates and an aluminum or steel seal in the center of the pole plates. Should be possible to drill through the seal without hurting the ferrite.

How does one keep metal particles from entering the gap, though? Is there any way to deglue the surround from the basket or the basket from the magnet?

Eric
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Old 18th September 2002, 02:26 AM   #10
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Default Re: optimum gap between phase plug and cone

Quote:
Originally posted by capslock
[B]The question about the optimum gap still remains to be answered.
I meant to answer, but was doing too much multi-tasking. I try to get the PPlug the same diameter as the pole piece.

As to how you drill without metal filings getting into the works, i have no real idea. I have seen some drivers after-the-fact that have had serious surgery like this. I could ask how it was done (although knowing him he probably demagnetized the ferrite, did surgery and then remagnatized the magnet).

dave
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