Blackhole5 in RTA 8TLs

On3s&Z3r0s

Has anyone ever put BH5 in any of the MTM speaker cabinets? I've got a pair of RTA 8TLs I'm going to be upgrading and some BH5 I could use. I was thinking of starting with just a 2 inch strip behind the tweeter and upper MW.

I definitely don't want to overdo it on these. The bass is reasonably decent just as they are. They actually have a little more internal bracing than I'm used to seeing in Polks of this vintage and are so far the best stock speakers I've heard from the Monitor / SDA era. They're also the first speakers I've heard with stock SL-2500 tweeters so that might have a lot to do with it too.

Anyway, is 2" from the tweeter up to the top of the cab likely to be too much or too little?

westmassguy

I did a pair of 11TLs with BH5. Behind each woofer, strips on the sides, and top. Sound was incredible.



6.

On3s&Z3r0s

That's more than I would have thought to try at least at first. Thanks for the pics! I'll definitely give them the all-sides treatment and see how that works out. I assume the polyfill goes back in after the BH5 as usual?

westmassguy

I had plenty of BH5 leftover from another project, that's why I did the sides and top as well as the back wall. If it degraded the sound, I could always remove some. In this case, it worked out perfectly, and the upped bass and midrange were smooth, detailed and crystal clear.
The acoustic batting is re-installed in the same position. I usually tack it to the sides with 1/4" staples, to prevent it from ever sliding down. Make sure the batting extends no lower than the top of the PR opening. You want the entire lower section empty.

EndersShadow

Awww yeah... Highlighted this thread for reference if I ever do my 11TLs lol

skrol

I did my RTA11TL's with Sonic Barrier except behind the PR's and it made a nice improvement in mid-bass clarity. I would think the BH5 would do nicely in the 8TL's.

westmassguy

The whole point is to absorb the upper bass and midrange back-wave frequencies produced by the woofers. You don't need, nor should you cover every square inch of the upper portion. Doing so may suck the life out of the mids, and decrease the internal volume enough to alter the tuning of the port or PR. I use 4" wide strips, others use 3". There are no set rules, other than absolutely nothing in the lower section. Experiment, and find what sounds best to your ears.

EndersShadow

westmassguy wrote: »

The whole point is to absorb the upper bass and midrange back-wave frequencies produced by the woofers. You don't need, nor should you cover every square inch of the upper portion. Doing so may suck the life out of the mids, and decrease the internal volume enough to alter the tuning of the port or PR. I use 4" wide strips, others use 3". There are no set rules, other than absolutely nothing in the lower section. Experiment, and find what sounds best to your ears.

4" by what length? And do you think there is any need to re-seal the cabinets while your in there?

westmassguy

EndersShadow wrote: »

westmassguy wrote: »

The whole point is to absorb the upper bass and midrange back-wave frequencies produced by the woofers. You don't need, nor should you cover every square inch of the upper portion. Doing so may suck the life out of the mids, and decrease the internal volume enough to alter the tuning of the port or PR. I use 4" wide strips, others use 3". There are no set rules, other than absolutely nothing in the lower section. Experiment, and find what sounds best to your ears.

4" by what length? And do you think there is any need to re-seal the cabinets while your in there?

The 11 and 15s are broken up by internal bracing (not sure about the 8s). I ended up putting blocks, some square, some rectangular. Unlike most SDAs I've worked on, where there's a single center brace, and you can run a strip up the back wall.
Running a bead of Loctite Power Grab along the back and side seams, is a good Idea. Won't hurt. The front seam is usually not a problem. I've deduced that the cabinets were assembled face down, with the top, bottom and sides done first. There's normally a lot of hot glue slathered all over the front joints. The back panel was done last, and if there were any gaps, that's most likely where they would be.

On3s&Z3r0s

Just to close the loop on my experimentation with the 8TLs, less turned out to be more. The 8TLs are a ported design rather than being sealed with PRs. I'm not sure if that was making a difference or if it's just the much smaller overall cabinet interior volume.

The bracing on the 8TLs is a cross going front-to-back and side-to-side of about 4" wide strips of MDF (should have measured or photographed, but didn't think of it at the time). The brace is just below the lower MW.

I started off with a 18" x 3" wide strip of BH5 running from the lower MW to the top of the cabinet on the back and two 3" x 6" strips on the sides of each cabinet in the middle of that upper area around the tweeter. Could be that my placement was off in addition to there being too much BH5 in there, but the effect was just as westmassguy described. It sounded like someone was sitting on the mids and stuffed the port with tube socks. I did the BH5 the same time I did crossover upgrades and the effect was so huge I though maybe I missed soldering something.

I took the pieces off the sides (and did a visual inspection of the XOs) and most of the mids came back, but the bass was still weak as compared with what they sounded like stock. When I finally got down to 3" by 8" on the back toward the top they sounded more like their old selves with a little less boom in the low mid bass. That is what I was going for so I stopped messing with them since and have been letting the XOs burn in.

It sounds like it might be better to divide the BH5 so that there is some behind each MW? Right now it's all behind the upper one and the tweeter. Maybe after I feel like they're done settling I'll go back to the 3" x 6" pieces divided behind the two MWs. That stuff is pretty crazy. This is the first time I heard what too much does.