Acoustic properties of reticulated foam speaker grills?

[cvanc]

Do we know of any discussions on sonic properties of this? I haven't found much. Surely it does a little something, right?

And what about your PPIs? Seems 30ppi is readily available, is that considered good stuff for the high end crowd?

Examples:
Speaker Grill Foam Filter | Foam Factory, Inc.

The Foam Factory, Open Cell Foam, Speaker Foam, Filter Foam

 

[RogerGustavsson]

30 PPI will soak uo some high frequencies. I have had thin 10 PPI on some speakers and that made a difference over 20 PPI.

 

[Galu]

The following information is taken from: Sound-Damping and Acoustic Materials in DIY Speakers

Grille foams are, by nature, acoustically transparent. Also known as reticulated foam, the cell-like structure is of an open weave arrangement and easily permits the passage of air. Each cell is around 0.7mm in diameter and the number of cells per linear inch specifies the structure. For this application 35ppi, (particles per inch). Usually black in colour the open cell structure has little intrinsic strength and the material has to be supported on some type of frame. The material will not take to stretching as the restoring force is minimal and once stretched the original dimensions cannot be recovered. The minimum usable thickness is around 10mm. At 20 / 25mm the material becomes self supporting, (depending on area and hence avoids the effects of grille frames). Susceptible to UV light, sunlight, the material slowly crumbles and has a usable lifetime of 10 / 15 years before requiring replacement. Often used on designs of the 70's and 80's.

 

[cvanc]

30 PPI will soak uo some high frequencies. I have had thin 10 PPI on some speakers and that made a difference over 20 PPI.

Exactly what I needed to know, sir. Thank you!

Do we know of a good source for 10PPI? I've only found one so far, with a steep minimum order.

 

[bentoronto]

Can't imagine any question that is easier to test. You stick your laptop in front of the speaker and do and before-and-after test. No special mic needed. You can do it in an audio store.

I have a thin synthetic paisley cloth over my ESL panels. I can double and quadruple the thickness for testing.

Here's a plot of with- and with-out. Maybe the 1 dB loss north of 13kHz is real if entirely inaudible. But any odd deviation might be due to a truck driving past at that moment. Or maybe dust since I've used those cloths on those panels for 45 years.

B.

 

[Galu]

Do we know of a good source for 10PPI?

The industry standard for speaker grille foam appears to be R35 HIFI (35 ppi) and, consequently, many suppliers of the material don't indicate the ppi rating.

P.S. You don't say what thickness (mm) and area (mm x mm) you require.

 

[AVWERK]

Does it have to be foam?
Stretched Spandex has always worked well and easily sourced

 

[AllenB]

Aquarium filter foam.

 

[geraldfryjr]

Hi There, I gotta bunch of the stuff from Foam Factory this summer !!!

I haven't had the chance to use it on the project yet but he is a link to their data sheet of charts.

https://www.foambymail.com/pdf/graph.pdf

Their curve is the green line and it pretty much has the same shape of most all of the types they list have, only with the more thicker foams being more effective of course.

I was actually looking for some 10PPI stuff to bury my midranges in but i am sure for the thickness of the build when I am done will suffice, I am glad to hear that this 30 PPI material I have should do fine for the high end.

My system will have 4 mid's and 8 tweeters in a line array fashion, I will have the tweeters and midranges time aligned together but unfortunately I won't be able to time align them with the woofers.

Here are a few pics of the build and mock up with the foam on my bench, stuff looks very nice and got to me within a week or so.

I'll be finishing this build sometime before the summer comes.

Cheers !!

jer

 

[geraldfryjr]

Sorry had to go fetch my pic's, what's left of them. :/

My local working data drive got wiped out by a poorly written Debian installers............
Aren't they all?, Debian is the worst !!!

I tell it to load the whole new drive, it chooses my working data ubuntu install and I didn't catch it.

Whatever 5 years of data Gone!!

Anyhow here are those pics of my build only one of the stacks of the cabinets are shown and some closeups of the foam, but it is gonna look really nice.

cheers!!



jer

 

[Galu]

Thanks for the update - looking good!