Advice on 7B Dynamat on Speaker Baffle and Blackhole5?

Gardenstater

So I Dynamat Extreme'd the midbass drivers some time ago and yesterday finally got around to doing the passive radiators and wow was I surprised what a difference it made on the PR's. Got a lot of *thwack* (apologies if I made this word up?) that I didn't have, especially on instruments like congas! I also added the 4 missing screws on the passives while I was at it.

Question #1 is should I put a piece of Dynamat on the inside of each side of the baffle, to the sides of the midbass drivers and region between the midbass and PR's? I can most definitely detect vibration here with my fingertips, especially in the area right between midbass and PR.

Question #2 If I do the Blackhole5, what would be the recommended location and sizes of pieces to install?

Thanks, in advance.

pitdogg2

Black hole should only be behind the MW. You will only need like a 6x6 piece, use too much will suck the life right out of the music. I would not put any Dynamat on the speaker cabinet itself if that is your thought.

When I did my 2.3tl's I used a just enough to cover behind the midwoofers on both sides of the cabinet.

Gardenstater

@pitdogg2 OK cool, so just a 6" x 6" piece directly behind each MW, which would put it just a wee bit above the crossover cups. I have a lot of polyfill up there already, so is that a problem, or does the Blackhole5 piece just go behind it?

I wasn't thinking of putting the Dynamat on the cabinet externally, but inside the front panel (baffle?) where the drivers are mounted. You don't think it's an issue that I feel the baffle vibrating with my fingers? I think if it didn't work out I could *possibly* remove it but that might not be a task without a lot of cursing involved! I suppose Larry's Rings (or maybe even carbon fiber rings), especially if they were epoxied to the baffle would help with this, but I'd have to make my own I suppose.

PS: Congratulations on owning those 2.3 TL's. That's certainly an upgrade from what I have. Maybe someday for the master bedroom in this house I could set up another system with those, as that is a much bigger room at 14ft x 24ft vs. 11ft x 16ft for this room with the 7B's.

pitdogg2

You will still use the polyfil the BH5 will go behind it of course. It has an adhesive that sticks really well to the cabinet. I removed the polyfil and the reinserted once the BH5 was done. Do not use Dynamat on the cabinet anywhere. Just get that out of your head.

Gardenstater

You don't know how stubborn I am lol. Would the problem be that the vibration of the baffle somehow contributes a warmness or coloration to the sound that actually helps the frequency response curve somehow, and dampening it wouldn't sound good?

pitdogg2

If it sounds like poo when you're done to remove it, it will tear the particle board to pieces. You are creating a problem where there is none.

F1nut

^ THIS ^

Gardenstater

OK that's why I ask. Thanks!

I certainly have enough scraps of this Dynamat left over. I may do an experiment where I take a piece of scrap particle board and treat it with some clear penetrating epoxy and see if the dynamat can be removed with a sharp scraper without ruining the particle board, and check the resonant frequency before and after by rapping on it with my knuckles and recording with a microphone into a frequency analyzer.

PS: But what if it doesn't sound like poo. I could become the hero of Club Polk!

F1nut

Oh boy.....

Gardenstater

But seriously......we KNOW that manufacturers of high end, high SQ speaker enclosures do NOT want their speaker cabinets resonating or vibrating. They are not making violins or acoustic guitars, so nothing I am talking about here is off the deep end at all and it is a great hobby where you can make little tweaks and actually hear the difference and it's better! The facts of life were that this was a good value when I bought it, but it was only $350! There was only so much engineering that went into this and Matthew Polk's genius was in coming up with such a value and knowing what low hanging fruit in the design process to go after.

Here's a pretty interesting article for anyone who might be interested.

Part 1: Myths & Facts about Loudspeaker Cabinets: Identifying Legitimately High Fidelity Designs

https://www.audioholics.com/loudspeaker-design/loudspeaker-cabinets

Part 2: Identifying Legitimately High Fidelity Loudspeakers: The Cabinet Face & Stuffing

https://www.audioholics.com/loudspeaker-design/loudspeaker-cabinets/identifying-legitimately-high-fidelity-loudspeaker-the-cabinet-face-stuffing

F1nut

That's not true, there are quite a number of speaker manufacturers that use the cabinet resonance to their advantage. Harbeth, Sonus Faber and Viking Acoustics are but a few examples.

FYI, using audioholics for advice is not a good idea.

Gardenstater

Yeah I know about Harbeth and their design philosophy. Those speakers rely on coloration to produce a pleasing sound, like a violin is pleasing. It's sort of like the MQA vs unadulterated high res argument. I'm in the no colorations camp but that is virtually impossible to achieve in a real world environment. I should have said "with some exceptions". I even saw an exotica speaker at one of the New York Audio Shows that looked like a Violin LOL.

F1nut

George, if you're really into the no colorations camp the 7B's are seriously the wrong speaker for you. Get some studio monitors, maybe ATC. However, I'll bet you can't listen to them without fatigue setting in quickly.

Gardenstater

Well bottom line is I'm an experimenter. That's a lot of the fun in it for me, second always to the music. I think the Dynamat on the Passive Radiator gave me much more impact to instruments like Congas for a REASON. If something is vibrating that you don't want to be vibrating, like a speaker basket, or a speaker mounting baffle, that means that the short term energy transients are partially lost due to energizing something other than the passive radiator cone. That's why I perceived a great deal more *thwack* after the passives were dynamated. The energy being sucked up by the basket vibrating was allowed to go where needed, producing a much more dynamic transient.

treitz3

Their is another speaker company that designs their speakers using resonance to their advantage. Joshua with JMW Acoustics. It's the main premise behind his latest designs.

http://www.jwmacoustics.com/

https://parttimeaudiophile.com/2019/05/22/jwm-acoustics-lone-star-audio-fest-2019/

Tom

pitdogg2

Putting a reflective surface like dynamat inside. While yes it deadens sound because of the butyl backing would it not also reflect sound inside? Those standing waves inside must go somewhere so would the passive or driver now be that exit point?
Just thinking out loud here. While I do love to experiment, this seems to me you're creating a whole set of others gremlins to battle.

Gardenstater

I may not use the Dynamat. I may use Iso-Damp, along with density enhancing clear penetrating epoxy. But I don't think that Dynamat is any more reflective of sound than a piece of smooth dense MDF or particle board. Do you mean because it has a shiny foil layer that is reflective to visible light? By the way, my cabinet looks to be made of MDF, not particle board.

I think the piece of Blackhole5 directly behind the midbass driver is for the purpose of reducing sound reflections from the midbass coming back and corrupting the midbass cones vibrations itself, as undesireable feedback, and also to make sure that, time-wise, it is more of the initial pressure pulse that is received by the passive from the bottom quadrant of the midbass cone, rather than a time delayed additional pressure pulse due to the first reflection from the back of the speaker cabinet.

I think of the Dynamat as more of a vibration dampening substance that reduces the amplitude of vibration of the material it is bonded to, rather than an acoustical wave absorption device.

Ideally, the front baffle of the 7B should have probably been more like 1.5" thick MDF, or at least 1", with chamfers on the baffle where the windows of the basket are located, especially the bottom 3 quadrants.

pitdogg2

Blackhole 5 and the polyfil slow the wave to make the cabinet appear larger than it actually is. No I was not thinking of reflection like light. I've stood in large metal containers and large wooden containers and they have vastly different echo sound reflection properties. So my thought went to the aluminum skin and the sound bouncing off. The larger SDA SRS cabinets have dado's cut into them to break up standing waves within the enclosure. On my 2.3tl's I also ran a small strip of blackhole5 down the side along one of the dados on both sides of the cabinet the length of the midwoofers. I do agree with your assessment of how the dynamat, secondskin and the like work, it just like you have encapsulated the metal in syrup or tar to a certain extent. The metal foil is just to keep it in one place and not stick to anything you put next to it or on it.

gp4jesus

Black hole 5? Sort of a super stuffing for sealed closures?

My first hearing of it. I’m a little more than curious.

Tony

JayCee

gp4jesus wrote: »

Black hole 5? Sort of a super stuffing for sealed closures? My first hearing of it. I’m a little more than curious.
Tony

Tons of info on CP. This'll satisfy your curiosity....and more :

https://www.google.com/search?q=polk+audio+blackhole5+review+site:forum.polkaudio.com&sa=X&ved=2ahUKEwi9xoSs8JfnAhWPoJ4KHa83D5kQrQIoBDAAegQIBBAP&biw=1089&bih=735

Gardenstater

@pitdogg2 I think I'm inclined to only use the Dynamat Xtreme, and other similar thick foil backed dampening products, on metal objects like the stamped steel speaker baskets. I think if I were to try to experiment with dampening the speaker baffle, I would use a thin material with no foil like isodamp. It's because I do agree that it's true that the density and smoothness and flatness of a material will effect the way sound is reflected, diffused, or absorbed by it, as in your example of being inside enclosures constructed of different materials and physical properties such as thickness, rigidity, etc.., and putting thick aluminum foil on particle board would definitely have an effect upon those that would be no doubt different than particle board which is less dense and less smooth than the aluminum foil. The metal foil, it seems to me, is largely there to protect the dampening material to some extent, but also to allow it to conform to highly irregularly shaped surfaces due to it's ability to wrinkle and crunch up and stay that way.

Reflection, Diffusion, and Absorption of Sound:

https://build.com.au/reflection-diffusion-and-absorption-sound


We also need to consider that sound probably travels faster through the particleboard than it does through the air volume in the cabinet. I think the sound wave in air generated by the midbass driver can energize the passive radiator basket and make it resonate, just as the soundwave or vibration wave which is transmitted even faster through the particleboard can also do so. The Dynamat helps with both I think, by reducing the amplitude of the vibrations of the basket and preventing it from resonating, thus only allowing the direct energy of the airborne soundwave from the midbass driver to go towards driving the cone in the passive and doing so more cleanly too.

Just my thoughts on it at the moment FWIW.

gp4jesus

IME ANYTHING you can put on a speaker frame, cast, stamped, whatever to cover those reflective surfaces & damp the ringing WILL make a diff.

I “Armacelled” one RTi A1 MW frame. Even put a little piece on the back of the tweeter. Did some internal wiring upgrades while I was inside.

Removed the jumper straps to listen for bass response differences. Connected them to a high current warm sounding amp. Cranked up some Donald Fagen.

I panned between the two channel expecting better, tighter bass response - hardly noticeable, really. But what I couldn’t miss was all the metallic sounds coming out of the unmodified A1.

Been an advocate ever since. BTW: Pipe wrap from Lowe’s/HD is about the same as Armacell; stickier too

Months later I did the same inside my CC, towers, and surrounds. Link of my work in my A3 surrounds; pics in the beginning.

https://forum.polkaudio.com/discussion/173492/rti-a3s-wall-mounted-as-surrounds#latest

Tony

Gardenstater

@gp4jesus Poor man's Dynamat.....very cool. Thanks for sharing.

gp4jesus

Gardenstater wrote: »

@gp4jesus Poor man's Dynamat.....very cool. Thanks for sharing.

If your budget is TIGHT, way better than nuthin’! Applied in random and/or asymmetrical “patterns” can help.

I won’t deny other products (eg DM) work better than Armacell and the like. I believe DM or similar is best for subs, larger closure* walls especially the poorly braced. Perhaps F10, F11, or F12 felt on all magnet rears - very reflective & shiny. Armacell
* towers

gp4jesus

Gardenstater wrote: »

@pitdogg2 I think I'm inclined to only use the Dynamat Xtreme, and other similar thick foil backed dampening products...

what does the foil backing do?

Side note: look for an inexpensive source of 1/2” F10, F11, or F12 felt for around tweeters & mids

thanks, Tony

F1nut

The foil makes it easier to work with otherwise it sticks to itself and everything else.

gp4jesus

F1nut wrote: »

The foil makes it easier to work with otherwise it sticks to itself and everything else.

ooooohh yeah.

Duh... thnx

F1nut