OLA Fiberglass Insulation vs Foam Stuffing in Cabinet

[Brad1234]

I wanted to share with the group my experience with restoring 2 pairs of OLA's, one with fiberglass insulation (early pre-1975 version 1 xover) and one with foam in cabinet (post 1975 version 2 xover). I did a full restoration with new caps and resistors, new inductor to replace "red-dot inductor" that is prone to failure, woofers fully rebuilt with reglued and sealed masonite and new foams, and sealing of drivers to baffle with foam weatherstripping. 

After setting all 4 up for A/B comparison and trying out stacking, it was clear the fiberglass insulation earlier model had noticeably reduced bass and flat, tinny sound compared to the newer OLA with foam stuffing. All things were equal between the 4 speakers except cabinet stuffing (though woofers do look slightly different, see pics) and all were well sealed with slowly returning woofer when pushed in. I decided to try out swapping the fiberglass for foam stuffing in the cabinet and, wow, the difference in bass response is incredible!  The foam sounds so much better than fiberglass. Deeper bass and the mids sound warmer and more clear as well. I guess there was a reason Advent switched to foam stuffing over insulation sometime before 1975. See pics and let me know what u think?

[JKent]

Very interesting. I had some OLAs for a while. Did a complete restoration including all new caps, resistors and inductors but somewhere along the line I was advised to replace the foam with fg. I had AR-2ax's at the time and when I compared Advent vs AR my opinion of the Advents was "meh". Ended up selling them. In retrospect, too bad I didn't keep the foam.

I imagine others will have opinions on this.

Nice work.

Kent

 

[jessiAV]

    Sounds like an interesting experiment!   Since my OLA's are all early models, I haven't any foam as an example of what was used by Advent. Is it open or closed cell? And how much material was placed in the cabinet (photos please? Brad)?

[Brad1234]

6 hours ago, jessiAV said:

    Sounds like an interesting experiment!   Since my OLA's are all early models, I haven't any foam as an example of what was used by Advent. Is it open or closed cell? And how much material was placed in the cabinet (photos please? Brad)?

I used high density foam like they use for couch seat cushions (actually it was some old couch seat cushions I had kept for reusing when we got a new couch), the newer original Large Advents had 12"x12"x2"-3"? squares of high density foam, I think 3 behind tweeter and 2 behind woofer for the dampening, so I just tried to copy that.  If anyone remembers the foam size and number of blocks for Large Advents feel free to chime in.

 New foam sheets 2"-3" thick run about $40-50, so for my experiment I just cut the foam couch cushions to fit in the OLA, they exactly matched the OLA foam in density, color and weight.   I didn't get any good pics of the foam dampening, here are some from my OLA's with original foam in them that I could find. 

[jessiAV]

Thanks Brad, that does help a lot. Since I want to examine the foam personally, I may look for some when I'm in a larger city.

[Doug G.]

I have never heard any real difference between my Advents with fiberglass and my Advents with foam and I just don't think Advent would have made a change which resulted in such a drastic difference in their sound.

Doug

[Brad1234]

I know it seems odd, but I have tried it on 2 separate pairs and it made the bass depper and better with foam on both. First I swapped the original foam to insulation on a pair of utility cabinet OLAs and they had less bass response, so swapped back to the foam on them. Then I had 2 sets of OLA's and noticed the bass deeper on the set with foam over the set with insulation. All other variables were the same, newly refoamed woofers and well sealed cabinets. It had to have been the foam increasing the bass, these were just my findings so sharing with group.