felt on baffle

The use of felt was mentioned in a previous post called "Material Covered Baffles." I don't think that using the felt would produce any negative effects. It can help diffuse and break up energy thats traveling across the front baffle. Somebody mentioned that this design was used in certain Vandersteen speakers, and probably others.
 
The Duntech speaker used felt on the baffles of aall their models, and John Dunlavy had a paptent on baffles with acoustically absorbent materials on them.

<center>United States Patent <a href="http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='4167985'.WKU.&OS=PN/4167985&RS=PN/4167985">4,167,985</a>
Dunlavy September 18, 1979

Speaker system</center>
Abstract
A speaker system in which at least one driver is mounted on an enclosure and is adapted to radiate sound waves outwardly from said enclosure in response to an input signal. A sound absorbing material is disposed on at least a portion of the outer surface area of said enclosure to reduce the effect of diffractions and reflections of said sound waves relative to said enclosure.


<center>Regards
James</center>
 
The Rogers LS-3/5A was doing the same thing years before that patent was issued. Also, I think the Dahlquist DQ-10 had some felt around some of its drivers. I'm sure there were probably others, as well. I'm curious as to how they managed to get around 'prior art' considerations to get that patent.
If I can squeak some time, I'll try to take a look at the patent and see if they've got something else going on.
Anyway, felt/foam/whatever works well for that purpose.

Grey
 
DQM's for sure did

have some sort of "felt" - actually standy upy fabric which was supposed to cause less diffraction. This was early 80's, and covered all of the front of the speakers.

So hard to see this patent either still out there, or valid at any point. But given the current state of patents, who knows? People are patenting stupid stuff just to show how stupid the system has become - pen lasers as cat toys for example.
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
The LS3/5a has a square of 1/2" square section felt around its tweeter.

I've been rounding the edges of my baffles (1" radius) and covering them with felt since 1981. I also cover the front plate of the tweeter. The effect is to clean up the off-axis response and reduce lobing. Oh, and it looks pretty. There are other colours than black, you know.
 

Attachments

  • speakers.jpg
    speakers.jpg
    38.3 KB · Views: 711
Grey: USPTO doesn't do a very good job of finding prior art. Normally, all they search is patents, not commercial disclosures or usage nor textbooks. In theory, it's the duty of the applicant to disclose such art, but that often doesn't happen. Patents get granted, lawyers get rich. A goof-up like that from USPTO nearly put my company out of business a few years back.

From what I understand, Dunlavey wisely did not try to initiate any litigation on the basis of that patent- it would have resulted, IMO, in the patent's invalidation.

I don't often say, "The Europeans do it better," but clearly their system of making applications available to the public for comment is a much better way of filtering out stuff like this- competitors have much more of a motivation to find prior art than civil servants.
 
EC8010 said:
I've been rounding the edges of my baffles (1" radius) and covering them with felt since 1981. I also cover the front plate of the tweeter. The effect is to clean up the off-axis response and reduce lobing. Oh, and it looks pretty. There are other colours than black, you know.

Nice job... should be some inspiration to others to make all sorts of interesting looking boxes.

Did you use real wool-felt or is that the "plastic" craft felt?

I scooped the felt on my pipes out of a 30+ year old Marsland speaker box.

[IMGHTTPDEAD]http://members.shaw.ca/t-linespeakers/FALL/images/BD-pipes-foster-orangeNose.jpg[/IMGHTTPDEAD]

More pics

The intention is that once i get a tweeter choosen and mounted & the felt cut to accomodate, i'll stiffen the back of the felt and use it as a grill frame.

dave
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
I've no idea what sort of felt it was. I thought felt was felt, was felt. How do you tell whether it's felt made from hand-washed organic sheep or synthetic?

I assume the twiddly cuts on your felt are to break up the boundary to the felt and reduce reflections from the otherwise abrupt change of impedance?
 
EC8010 said:
I've no idea what sort of felt it was. I thought felt was felt, was felt. How do you tell whether it's felt made from hand-washed organic sheep or synthetic?

Most thin craft-felt is made from a ployester type material and has little effect. If you put a match to it they will have distinctly different reactions (and smells).

I assume the twiddly cuts on your felt are to break up the boundary to the felt and reduce reflections from the otherwise abrupt change of impedance?

Exactly -- you will also note that is has an odd number of points and the number is prime (the latter probably only easthetic). The cut outs are also on a bevel.

dave
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
planet10 said:
you will also note that is has an odd number of points and the number is prime

I hadn't previously noticed that there were eleven of them, but that sounds like a good idea, and prime numbers are no more expensive than any other number. Should I also assume that the pipe's cross-sectional dimensions are related by the Golden Mean or some other suitably irrational number?:devily:
 
EC8010 said:
Should I also assume that the pipe's cross-sectional dimensions are related by the Golden Mean or some other suitably irrational number?

These pipes are actually Bert Doppenburg's design and i've never bothered to run the numbers backwards -- being mass-loaded voigt pipes they only have the sides parallel.

All my designs employ irrational ratios.

dave