Swap foam in the back cap of 4" drivers to felt?

[Flodstroem]

I found this on eBay:
http://www.ebay.com/itm/JBL-375-2440...kAAOSwIgNXwY-G
He also sells other formats too.

My self purchased felt (self adhesive) from the McMASTER-CARR (1/4" x 12" x 12") a brownish type of felt that works excellent Only drawback, I had to cut the pattern my self , but its OK with a sharp scissor......

[toddalin]

When I redid my three 2420s, I used the carpet cushion padding to replace the deteriorated foams. It's the stuff that looks like blue head cheese.

[sebackman]

Dear all,

Attached is a measure of a 2450SL with a brand new 475Nd diaphragm and both foam and felt back cap. They show very little (if any) change when swapping from foam to felt as per above.

Soundwise I do think the felt version sounds tighter in the mid but I'm sure it is just placebo saying that I should hear some payback for the work I put in.



Kind regards
//RoB

[pos]

Very interesting, thank you!
Main changes appear to be just under 3kHz.
That is were I always measure accidents, and also where the 2452 and 2450SL cores differ the most in my measurements.
Could you use a longer window to get more precision in that range, with a close measurement?

[sebackman]

Hi POS,

Please tell me what you want me to do. The M2 will give odd results numbers close up but the VTX could be fine. -Or do you mean without horn? Please advise.

Indoor and longer than 6ms gives to much artifacts on 60cm. I can probably do out door measurement in about 2 weeks, won't be home until then.

Kind regards
//RoB

[pos]

Yes a VTX/PT waveguide will probably be more consistent up close.
A very close measurement, something like 10cm, would let you use a long window without issue in door.
Of course it would not be representative of the driver/waveguide behavior, but perfect for comparison purpose.
A very long window (ie no added window and something like 1/24 frequency-domain smoothing would probably give accurate results.

[sebackman]

I will give it a try and post here. I have a few different horns/wg so I can try them.

Kind regards
//RoB

[macsic]

I did it today.
I did not take measures before or after, just listen it and all sound good.


See what I did:

First as you see the foam is in poor shape, dry and fall in little parts when I touch it:






I have felt about 10mm:



Clean it all with Brake cleaner:



I take the cover to trace the pattern and it fit good



Glue the felt with silicone glue, it is Goop in automotive parts.



It's time to reassembly








And after go listen to music

[sebackman]

Good job.

Now your driver are good for annother 100 years! Excellent with pictures.

Kind regards
//Rob