Foam surrounds and ports will never give accurate response. It only
allows for a slower base response to go lower in a smaller box. To
understand that after each note, the speaker must get back to "0" as
fast as possible. Foam surrounds need a sealed box to do this. Good
bass reflex speakers count on a rigid surround and tuned port to
accomplish the same task.

John
Bruce Tyler wrote:

On Tue, 16 Dec 2003 01:48:27 GMT, "Jebus"
wrote:


Hello. I currently have 2 old (about 30 years old), but very nice (made out
of 2 in. thick wood). However, as many woofers are made today, they have
the cone in the back for air to come out. Well these tanks have something
like that, but in the front. However, isteand of anything plastic, there's
a piece of fabric covering the hole (almost like a small grill). Over time

from all the use of the speakers, this cloth has become stretched and causes

unwanted vibrations/sound in the bass parts especially. Is it safe to
remove this or should i replace the cloth? or should i just replace it with
another part? would adding more of these holes produce better sound?
Thanks.



I would say, by all means cut it away, especially if it is causing a
vibration with bass rumble as this is very annoying. It may be
possible to fit/add a modern fitting to enhance your bass reflex as 30
years ago, not many speakers really had inverted port fittings like
many bass boxes nowadays do.. They simply had holes as ports which
still helped but because of better speaker travel in modern bass
cones, it is better to have inverted ports to suck out the best of the
bass echo... I suppose there is an art to getting the best post size
per the box size but the fact that your boxes already have a port,
this would be a guide to the needed size...

I had a similar experience just a month ago to a few days ago. Here's
how...

About 12 or 13 years ago I built a pair of speaker boxes. They
measured 550mm(H) x 410mm(W) x 300mm(D),, thats about 22"x 16.5"x
12".. They were built from a very dense 1" custom board (not the best
wood but nice and solid and I mean "solid" and very heavy for their
size) and I put into each of them a 10" bass and a midrange/tweeter
approx 3" dia and lined the insides with an a polyester fibre cloth
about 2" thich,, similar to what they use in sleeping bags and quilts.
They worked really well as all-rounder speakers..

4 Months ago, right..!!! I hear a funny "furry" gushing sound out of
one of these speakers. I looked closely to see that the foam surrounds
on the bass cones has literally rotted to the point where I touched
them only to see them crumble away before my eyes. The
midrange/tweeters suffered the same fate as well - rotten.. I decided
to retire these speakers althogether, putting them out in the garage
for the time being. I bought a pair of P/A type speakers with 12" bass
units in them and replaced the 12" drivers with a better pair. Wow,,
what a difference. I was thrilled to bits with the outcome...

Well about a month ago I decided to re-use the boxes out in the
garrage. I made a template up and cut out bigger holes, so as to fit
12" bass units from the 10" units that were in them before they got
the rot.. I bought two more 12" units like in the above modified P/A
speakers above. These 12" bass units were so good on their own, that I
decided to use them as sub type woofers in the old boxes. They worked
exceptionally well,, but,, they had a gaping great big 3" hole in each
cabinet where the tweeters sat. Although they acted as a reflex port,
they looked an eye-sore so I visited the local electronics store and
found some plastic ports of "identical" size. What a stroke of luck.
They fitted straight in - no gluing or screwing required,, simply
pushed them in nice and tight... These ports are about 4" deep,
slightly tapered and somewhat enhanced the bass echo even further.
Before, you could feel a definite pout of air from the naked hole as
the bass cones moved back and forth. The reflected bass was good but a
little "boomie". Now, with the plastic ports, there is little air gust
but a lot of deep, rich sound coming from the port... I guess I struck
it reasonably correct, by luck...

As for your boxes,, I suggest that "if" you can,, try to do something
similar. If your boxes are good (and it sounds as if they are),, try
not to destroy the essential design and character of them but old
and/or tatty bits of fabric will do little to help so it may be a
pre-requisite to get rid of the cloth and forge ahead...