[ctviggen]

So, what is the reason for the foam on the tweeter?  I assume the reason is dispersion characteristics, but is there anything else?  What's the detriment of not using the foam?

[Brian Cheney]

1. The foam reduces the diffraction path to just about zero

2. the slot forms an acoustic lens which improves dispersion.

Imaging is considerably more precise with the foam on.

[zybar]

I found that putting foam along each side of the ribbons further enhanced imaging and focus.

George

[John Casler]

I found that putting foam along each side of the ribbons further enhanced imaging and focus.

George

I second that suggestion, and now offer that it should be 3-4" minimum of the "wedge" type foam.

[zybar]

You mean like this:



George

[CornellAlum]

What did you guys use to attach the foam that wasn't going to cause permanent damage?

Daryan

[JoshK]

What did you guys use to attach the foam that wasn't going to cause permanent damage?

Daryan

double sided clear sticky tape should work.  I used it to tape down the guides when I was routing out the mid panels on my RM40s.  It came right off (thanks to the laquer) when peeled without any residue.

[mikef]

I'd like to try that modification. It's so easy even I could do it. Where did you guys get that wedge of foam to use? It looks like one single wedge.

Thanks

Mike Fox

[ted_b]

I have a question:  I own RM/X's and have never taken the grills off.  The grills are on so tight that I was initially worried I might break a tab/post or two (as others have), and now 10 months later I am pleased with the overall sound and never gave it another thought.  However, this talk of foam along side the ribbons is intriguing.  So I guess I have two questions, especially for BC and RM/X owners like Eric:
1) what differences, positive and negative, will I find with grills off (I know, "find out for yourself"...except I'm worried that the tight fit will make it a permanent change)?
2) are the RM/X's a good candidate for the ribbon foam wedge treatment?

Thx,
Ted

[CornellAlum]

I have a bunch of extra 3 inch wedge foam I can let sopme folks have.  Just pm me with how much you need.  WARNING:  it is purple, my favorite color.  Just fyi

Daryan

[John Casler]

2) are the RM/X's a good candidate for the ribbon foam wedge treatment?

...

Hi Ted,

I actually created the "Sonic Lapels" tweak to make the RM40's approach the same imaging ability of the RM/x.

The idea is to reduce baffle defraction and lateral dispersion, by placing the foam on either side of the panels.

Since the RM/x has this area "scooped" out by design, it would not derive the same benefit from adding foam.

I would however (carefully) remove the grills for a listen.

[ted_b]

John,
Thanks.  Duh!  I guess I would have realized that obvious design advantage after looking at the problem.....

It's the vicoding talking....spent 5 hrs yesterday in the ER with a morphine drip, then got sent home with vicodin......first kidney stone of my life...at age 51!   Hoping it leaves soon!!!  

Ted

[ctviggen]

The reason I asked was because sometimes I sit off center, such as during movies.   Instead of moving the speakers, I was thinking that I could remove the foam to provide wider dispersion.  I can move the speakers, too, but this is a bit of a pain, as I use wedges under the speakers because the tile floor is not level.  I forgot about the lapel trick.  I'll have to use that one after I order some foam for the ceiling.

[John Casler]

You mean like this:



George

Yep, that is it.  Although you and I (in the pic below) used 3" foam, I think the 4" will work better and can be mounted right up to the neopanel frame.

[zybar]

Actually mine was 4" foam.

Unfortunately it is the foam by mail stuff...

George

[eico1]

Here is a tip from John Dunlavy from usenet:

concern about reflections, diffraction and cavity resonance
that might result from recessing the tweeter relative to the mids (and
mids when separate woofers are employed) is worth considering.
Without proper acoustical damping and absorbing materials to mitigate
the situation, the impulse, step and frequency responses can be
substantially degraded by recessing drivers to obtain time/path
alignment.  Likewise, diffraction of sound from the edges of an
enclosure can drastically alter response properties. (I was issued a
U.S. patent in 1979, covering the use of efficient absorbing materials
to mitigate the problem.)  Although various densities and grades of
open-cell foam work well for damping the internal cavities of speaker
enclosures, they generally do not perform very well on the outer
surfaces near drivers.  We have found that different types of felt
material, especially those with a high percentage of natural wool, in
various densities and thicknesses, exhibit excellent properties. A
proper choice of felt can provide much better results than any foam
materials I have tried.

steve

[John Casler]

Actually mine was 4" foam.

Unfortunately it is the foam by mail stuff...

George

I take it you read Ethan's comments on how badly the Foam by Mail tested?

Mine was also from FBM, and I have to say it certainly helped, but I think another more reputable brand, might work better.

[tkp]

Actually mine was 4" foam.

Unfortunately it is the foam by mail stuff...

George

I take it you read Ethan's comments on how badly the Foam by Mail tested?

Mine was also from FBM, and I have to say it certainly helped, but I think another more reputable brand, might work better.

Althought I did not get the 8" foam tile from FBM, the stuff I ordered from www.foamandupholstery.com is much lighter and did not feel as dense as the 8" wedge foam that Xitrum got from a recording studio.  The stuff does work because there is a definite improvement from having no foam pannel between speakers at all.   They block the infared signal completely so maybe it is not all that bad.

Maybe we should setup a list of place that selling foam with faulty data to prevent others from making the same mistake.

It was a good thing that I bought 3lb and 6lb rigit fiber glass pannel to treat my second room.

[John Casler]

Here is a tip from John Dunlavy from usenet:

concern about reflections, diffraction and cavity resonance
that might result from recessing the tweeter relative to the mids (and
mids when separate woofers are employed) is worth considering.
Without proper acoustical damping and absorbing materials to mitigate
the situation, the impulse, step and frequency responses can be
substantially degraded by recessing drivers to obtain time/path
alignment.  Likewise, diffraction of sound from the edges of an
enclosure can drastically alter response properties. (I was issued a
U.S. patent in 1979, covering the use of efficient absorbing materials
to mitigate the problem.) Although various densities and grades of
open-cell foam work well for damping the internal cavities of speaker
enclosures, they generally do not perform very well on the outer
surfaces near drivers. We have found that different types of felt
material, especially those with a high percentage of natural wool, in
various densities and thicknesses, exhibit excellent properties. A
proper choice of felt can provide much better results than any foam
materials I have tried.

steve...

Hi Steve,

Yes "felt" can be very effective for "Baffle diffraction", and some of my "tweaks" with the foam wedge lapels had felt at their base (against the speaker)

The wedge foam however was also to reduce "lateral dispersion", which baffle mounted felt would not do.