Refreshing my RTA 15TLs

bcwsrt

Let me check ... yeah, I have just enough left to do six more!

xschop

Good work. With anodizing as shoddy as that, I'd paint 'em too.

bcwsrt

Thanks. Without the right angle and/or lighting you'd never notice it, especially installed in the speakers, but yeah, it wasn't the greatest work I'd ever seen.

I'm anxious to get them installed along with the BH5. Just need to find the right block of time and mood where I'd rather be working on the speakers vs. listening to them. Maybe if they didn't sound so (expletive) good just the way they are ...

xschop

Just don't forget to insulate your coil leads.

Midrange-wise, I'm curious what your impressions are of the BH5 and "shouty-roar" you were experiencing also.

bcwsrt

Just to check my understanding on the BH5 ... I currently have four 4"x18" strips. On the 15s, the MWs are ~13 3/4" from the top of the basket on the top one to the bottom of the basket on the bottom one. So, I should put two 4"x14" strips (cut the bottom 4” off at the top of the blue painter's tape) directly behind the MWs in each speaker, correct?



I should be able to get @shaneybob my scraps a little quicker if that’s the case.

And then the factory Dacron goes back over the top of the BH5? That seems a little counterintuitive, but it is wrapped around the sides and back of the cabinet at the moment.

xschop

I would cut the foam rectangles to match the top two MW fasteners and down to the lower two MW fasteners. And place them directly behind those 4 locations.

F1nut

Put a 3 inch (preferred) or 4 inch wide strip behind the top two drivers and the bottom two drivers. No BH5 required behind the tweeter. Put the factory poly fill back where you found it.

bcwsrt

I know I’m probably being too anal about this, but I was sure the 4” width had been settled on. 3” is preferred these days? Or, maybe 3” is more suitable for the narrower 15TL cabinet?

Gardenstater

The magnet itself is a little under 3-1/2" in dia.. There are probably 2 things at play here: Attenuation of standing waves and backwave absorption. We know with sound waves that angle of incidence equals angle of reflection. I think further experimentation is warranted.

pitdogg2

bcwsrt wrote: »

I know I’m probably being too anal about this, but I was sure the 4” width had been settled on. 3” is preferred these days? Or, maybe 3” is more suitable for the narrower 15TL cabinet?

I did 4" behind my drivers in the 2.3tl's.

stevep

Gardenstater wrote: »

There are probably 2 things at play here: Attenuation of standing waves and backwave absorption. We know with sound waves that angle of incidence equals angle of reflection. I think further experimentation is warranted.

I think these are really one thing. Think about how long the waves are. 1kHz is about 1 foot and 30Hz is about 38 feet. The pressure "waves" are going to be scattered all over the place in the box and the materials are going to be attenuating the local pressure and time of reflection.

I suspect there are computer models that could be run or you could probe the pressure along various points at different frequencies. If you wanted to change the tuning you could fill the box with CO2 and make it seem bigger by slowing the sound "waves" down.

bcwsrt

Thanks for all the discussion. I'm going to try two 4"x12" pieces behind each of the driver pairs and hope I land on a happy medium. I'm not looking to experiment with these, just enjoy them. If it doesn't work, I'm totally happy to go back to the way they are now.

F1nut

It works, so don't worry about that.

Gardenstater

stevep wrote: »

Gardenstater wrote: »

There are probably 2 things at play here: Attenuation of standing waves and backwave absorption. We know with sound waves that angle of incidence equals angle of reflection. I think further experimentation is warranted.

I think these are really one thing. Think about how long the waves are. 1kHz is about 1 foot and 30Hz is about 38 feet. The pressure "waves" are going to be scattered all over the place in the box and the materials are going to be attenuating the local pressure and time of reflection.

I suspect there are computer models that could be run or you could probe the pressure along various points at different frequencies. If you wanted to change the tuning you could fill the box with CO2 and make it seem bigger by slowing the sound "waves" down.

Standing waves are only formed between parallel walls and they are fixed in place and the only thing changing is the amplitude with time but not the frequency or location of the nodes. I put the internal dimensions of the 7B into a standing wave calculator and got these results, with the ones in red presumably the worst. I would think 870 and 900 would be the ones of most concern. BH5 would be pretty good at attenuating that frequency being thick dense open cell foam and placement in the center of the cabinet seems a logical choice for this purpose. I think backwaves can be more on the order of what you said about "bouncing all over the place".

bcwsrt

F1nut wrote: »

It works, so don't worry about that.

Yep, poor choice of words on my part. Should have said, "if it doesn't produce the desired results ..." or, "if it sucks the life out of 'em ..." I'm sure it'll be all good, though.

Gonna see if I can knock everything out during the day on Tuesday. 🤞

bcwsrt

Slowly but surely making some progress. Didn’t have as much of the day to myself as I’d hoped, but got the BH5 and tweeter plate done on one of them.

Did the 4”x12” strip of BH5 behind the top two drivers, but the POS er, uh … lovely rear-firing passive is directly behind the lowest driver (DUH!), so I just did a 4”x4” piece behind the one below the tweeter.

Billet tweeter plate is one solid, nicely done piece! Fits like a glove. Ivan provided me with some of the Larry’s rings which worked great, except I had to clearance the cabinet brace that runs front to back immediately behind the upper right-hand screw. Being right-handed didn’t help, but I was able to carve just enough away to get the ring to seat on that side. I think I like the stainless hardware with the black plate. Let’s you know something is “different.”

Other one should go faster tomorrow.

F1nut

but the POS er, uh … lovey rear-firing passive is directly behind the lowest driver (DUH!), so I just did a 4”x4” piece behind the one below the tweeter.

Good catch. I completely forgot about that one.

bcwsrt

F1nut wrote: »

but the POS er, uh … lovey rear-firing passive is directly behind the lowest driver (DUH!), so I just did a 4”x4” piece behind the one below the tweeter.

Good catch. I completely forgot about that one.

Yeah, me too, until I opened them back up!

I know I probably shouldn't have listened to it this way, but I can definitely hear a difference between the two. Think I'll turn it back off because I'm not real sure I like it. Lol More tomorrow or the next day ...

Jazzhead

You're getting there. The good thing about BH5/Sonic Barrier is that you can subtract the amount you use until you optimize. Sometimes you have to live with it for a while before you can decide. A little can go a long way. There's a sweet spot where you stop the "shouty" when you push your speakers, but not "suck the life out" otherwise. The only pain is having to repeatedly open and close up your speakers (the price of experimentation).

xschop

Looking good. Maybe you can place that last piece on the factory cross-brace behind the lower woofer?

I agree with Jazz, you'll be opening them up a few times for adjustments.
Have you read into the @decato modded 15TL's?

bcwsrt

Right now, I’m thinking they definitely don’t need more BH5, but I need to wait and see what they sound like together with the same amount and not listen at the end of the day when I’m dog tired. Lol But, how does one go about “subtracting” that stuff until you optimize? Not sure I can cut through that 4x12 piece with it installed.

I read the decato thread numerous times back when I was researching what to do with these, but it’s been a while. I don’t think he used BH5.

decato

I do not like BH5 or any of these resonance-reducing foam sheets on vintage Polk speakers. Every time I tried them, I found it made upper bass sound "tubby" or "chesty". The same sound emerged when I overdamped the cabinet with too much dacron. Your RTA 15TL has the two braces that go from side to side. I've seen some where no such braces exist. Adding them (and making sure they're tight) makes a big difference. I also used SoundCoat from Percy Audio some 20 years ago, but I don't see it on the market anymore. Nonetheless, I feel the best solution is solid bracing.

xschop

bcwsrt wrote: »

Right now, I’m thinking they definitely don’t need more BH5, but I need to wait and see what they sound like together with the same amount and not listen at the end of the day when I’m dog tired. Lol But, how does one go about “subtracting” that stuff until you optimize? Not sure I can cut through that 4x12 piece with it installed.

I read the decato thread numerous times back when I was researching what to do with these, but it’s been a while. I don’t think he used BH5.

I was referring to the "boomy" mitigation he addressed.

xschop

decato wrote: »

I do not like BH5 or any of these resonance-reducing foam sheets on vintage Polk speakers. Every time I tried them, I found it made upper bass sound "tubby" or "chesty". The same sound emerged when I overdamped the cabinet with too much dacron. Your RTA 15TL has the two braces that go from side to side. I've seen some where no such braces exist. Adding them (and making sure they're tight) makes a big difference. I also used SoundCoat from Percy Audio some 20 years ago, but I don't see it on the market anymore. Nonetheless, I feel the best solution is solid bracing.

I can't agree more, it is the cabinet structure or lack thereof, that affects mid-bass boom the most. I believe it is more prudent to brace all the flex out without taking up much airspace. It is a challenge, but can be accomplished.

Jazzhead

@Sitka, when I had to reduce some Sonic Barrier I used an extremely sharp filet knife and a small straight edge to score, and then peel off a bit. The glue is pretty tenacious. And yes, one hates to waste that material as it is expensive. There are other ways perhaps? Trust your ears in the process, and it helps if you can be around some live/real music (calibrates the brain). If given the choice I would rather have a speaker that is a bit reserved as opposed to any sort of sonic glare (I can't stand it). It's nice to be able to really open up your system (I do this sometimes when in an adjacent kitchen) and not get that shouty thing going.

Jazzhead

Sorry, above post for @bcwsrt, not @Sitka - not enough coffee yet today (pathetic, lol)...

F1nut

Every time I tried them, I found it made upper bass sound "tubby" or "chesty"

My experience is the opposite, the BH5 cleans that issue right up.

bcwsrt

I was actually gonna say that if anything I thought the one I added the BH5 to was clearly less boomy (and possibly too much so), but I’m dumb for even listening to it the way I did last night, so that is why I didn’t say it … until now.

bcwsrt

Thanks, @Jazzhead !

F1nut

3 inch blocks or strips. Too much BH5 will result in the upper bass sounding tubby or chesty just like too much Dacron.