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From: rdp@atexrd.UUCP (Dick Pierce)
Newsgroups: sci.electronics,rec.audio
Subject: Re: reconing speakers
Keywords: loudspeaker
Message-ID: <120@grace.atexrd.UUCP>
Date: 3 Aug 88 17:28:29 GMT
References: <904@wucs2.UUCP>
Reply-To: rdp@grace.UUCP (Dick Pierce)
Organization: Atex Inc., Bedford, MA
Lines: 70

In article <904@wucs2.UUCP> jps@wucs2.UUCP (James Sterbenz) writes:
>I'm not sure about posting this to sci.electronics, but there isn't
>a sci.electroacoustics :-), and I thought I might reach some of those
>who don't read "wreck.audio"
>
>I've got a pair of Electro-Voice EV14-A speakers, purchased in 1974.
>The woofers are 10" acoustic suspension type, and the ring of foam
>which supports the paper cone has deteriorated very badly (i.e. holes).
>The cone itself seems fine.
>
>I called E-V, and they sent me a replacement pair of woofers, pure
>junk.  These sound far worse, than with the old ones (with holes).  They are
>poorly constructed, have a magnet that must be measured in grams :-),
>and are made in Taiwan.
>
>So two questions: Has anyone had experience with rebuilding speaker
>cones.  I'm more interested in finding out if I should try to find
>someone who can do it, rather than trying it myself (although it 
>may be fairly simple since its only the foam that is in bad shape.
>
>Any suggestions for a good 10" woofer that would be compatible with 
>the EV14-A.  It's a 2-way, but I don't remember the crossover frequency
>offhand.  How critical is the enclosure geometry in acoustic suspension
>systems?
>

As the engineer in charge at Precision, I have had quite a bit of 
with reconing drivers. It is not a job that is easily done without the
precision fictures necessary. Usually, the job is done in several
steps: 
	1.	After the old cone is removed and all the glue areas thoroughly
		cleaned, the voice coil is inserted into the gap with a jig
		that simultaneously centers it radially and axially in the gap
		Glue is applied to the vc and the basket where the spider is
		attached, and the spider is then put in place.
    2.	Glue is now applied to the voice coil where the cone attaches
		and to the periphery of the basket where the spider attaches.
		An assembly consisting of the cone, surround and tinsel leads
		is then lowered over the voice coil and clamped in place.
    3.	The voice coil leads are soldered to the tinsel leads, and
		the dust cap is glued in place.

All of this requires the right adhesives and fixtures, and is not a
simple home job.

The alternative solution is to replace the woofer. In this case, indeed
a good knowledge of the cabinet parameters is necessary to find the
right replacements. Also a 10 inch 2-way system is really stretching
the capabilities of both the woofer and the tweeter a bit much,
especially given that EV undoubtedly used a paper cone in the woofer.
Newer drivers have far better capabilities in this respect, so the
system may need significant changes to work right. The end results,
if done properly, may well be significantly better than what you
originally started with, but it's not clear that its worth the effort.

Incidentally, the deterioration you discovered is quite common 
amongst polyurthane foam surrounds from a variety of manufacturers.
This is due to the fact that the kind of foam they use is conducive
to mold and mildew growth, which simply eats the foam. Newer
surrounds use an ether-based foam which is hostile to such growth,
and is somewhat more UV resistant (making it somewhat longer living
in cars). There is no visible or performance difference between the
two (at least while both are intact :-)).



-- 
Dick Pierce
EPPS, Bedford, MA
----