Sound damping material

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Wolfgang
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Sound damping material

Post by Wolfgang » Sat Mar 14, 2020 3:25 pm

I have finished my first OB sub with servo controlled woofers (second one in the making) and was wondering if cheaper damping sheets than "No Rez" or "Black Hole 5" would have the same effect?
http://gr-research.com/norez24x27sheet. ... s/amps.htm
http://www.speakercity.com/Merchant2/me ... de=damping

Parts-Express offers damping sheets like this one:

https://www.parts-express.com/sonic-bar ... 4--260-525

I am not sure about the "mass loading" effect"(gr-research) : "Some material sold for use in loudspeakers incorporate this sound barrier layer with no damper at all. So it has little to no effectiveness in resonance control, and it adds the adverse effect caused from mass loading of the woofer. " Could this be a problem with OB subs?

The vibrations in the 1,5" MDF material are nothing less than brutal.

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pre65
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Re: Sound damping material

Post by pre65 » Sat Mar 14, 2020 3:34 pm

Wolfgang wrote:
Sat Mar 14, 2020 3:25 pm

The vibrations in the 1,5" MDF material are nothing less than brutal.
Some would consider MDF only fit for building prototypes, because it's cheaper than "proper" materials.
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Re: Sound damping material

Post by steve s » Sat Mar 14, 2020 3:45 pm

Car sound deadening carpet works a treat. You can use double or triple layers
I have some sheets of Rolls Royce damping, ( factory off cuts so the seller said) its about 25 mm thick.
It works well in my speakers
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Wolfgang
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Re: Sound damping material

Post by Wolfgang » Sat Mar 14, 2020 6:26 pm

Some would consider MDF only fit for building prototypes, because it's cheaper than "proper" materials.
The only material which sounds more "dead" if you knock on it is some kind of resin which is used for those very expensive speakers (like WilsonAudio etc). Normally MDF is considered to be acoustically pretty dead.
If you take a look at the picture there is only very little surface which hasn't been braced or connected by a dado joint.
OB sub.jpg
It's not that the MDF would create some "sound" but the woofers rattle the whole cabinet. So added mass from some acoustic damping material would be beneficial, I guess, as long as it doesn't do this "mass loading of the woofer" (whatever this means). The question is: Does it have to be $45 or $70 per sheet or would damping material for cars for example do the same job?

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Re: Sound damping material

Post by JohnG » Sat Mar 14, 2020 6:44 pm

Hi Wolfgang,
as you are in Europe, you could look into 'Eki' there is a range of Products produced, they do sheets of Acoustic Control Foams.

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rowuk
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Re: Sound damping material

Post by rowuk » Sat Mar 14, 2020 7:06 pm

I think that we can forget about „damping“ vibration with elastic materials. As the woofer is attached directly to the frame, it will move unless something with greater strength (mass or coupling to another more rigid structure) helps it. Maybe adding a granite base would help?
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Ray P
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Re: Sound damping material

Post by Ray P » Sat Mar 14, 2020 7:07 pm

JohnG wrote:
Sat Mar 14, 2020 6:44 pm
...as you are in Europe...
:lol: Wolfgang is well on the way to being as far from Europe as you can be at our latitude - Oregon, USA.

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Re: Sound damping material

Post by steve s » Sat Mar 14, 2020 10:54 pm

Wolfgang wrote:
Sat Mar 14, 2020 6:26 pm



It's not that the MDF would create some "sound" but the woofers rattle the whole cabinet.
That does not seem right.
Damping is to stop resonances not rattles..
To me a rattle sounds like the speaker is exceeding its Xmax .
If that's the case damping won't help.
The drivers look a little small for open baffle use but It may be the pics giving the wrong impression.

open baffle speakers need reasonable amount of self damping in my experience.
Hope I'm wrong !
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number

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Re: Sound damping material

Post by Wolfgang » Sun Mar 15, 2020 2:09 am

To me a rattle sounds like the speaker is exceeding its Xmax .
You are right, Steve! I've found the problem.

These amps have a lot of extra settings and the servo settings in combination with the typical x-over/PEQ settings was not correct. The servo control (extension filter) can be set to low/mid/hi damping and combined with corner frequencies 14Hz/20Hz/28Hz plus all the typical controls like subsonic filter etc.There is no real manual or what I would call a manual. It's rather based on intuition/testing to find out how it all works together.

The H-frame itself is exactly built according to plans that come with these drivers. Overall - and if everything is set up correctly - it's a wonderful piece of technology. Sound is amazing. These are 12" drivers and with OB in a large room it needs 2 subs. But even with only one sub the cones actually don't move so much in order to produce really great satisfying deep fast bass. This is the first sub that can keep up with the Klipsch bass horns.

I will decide later if it needs additional damping. At the moment I cannot hear any disturbing resonances. But the final measurements will show what's going on and needs to be done or not.

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Re: Sound damping material

Post by JohnG » Sun Mar 15, 2020 9:59 am

Wolfgang
I am taking it, that by a previous comment offered, I got your location quite wrong.
My apologies for my assumptions.

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Re: Sound damping material

Post by simon » Sun Mar 15, 2020 10:36 am

So what are these 12" OB subs Wolfgang? They sound interesting.

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Re: Sound damping material

Post by steve s » Sun Mar 15, 2020 11:37 am

Good news that it was easy sorted
I will decide later if it needs additional damping. At the moment I cannot hear any disturbing resonances. But the final measurements will show what's going on and needs to be done or not.
The resonances are not easily heard until you remove them.. Then you can tell the differences when they are gone.
All black car deadening carpet, lining the internals will make a difference, and you will be able place them closer to rear walls... if that's a advantage of course
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number

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Re: Sound damping material

Post by Scottmoose » Sun Mar 15, 2020 4:51 pm

There are two types of damping material. Panel damping, which adds mass to the panels & damps out their vibrations (i.e. lowers the resonant Q), and acoustic damping, intended to absorb standing waves etc. in the cabinet. The former is usually bitumen or variations along those lines. The latter can be open cell (has to be open-cell) foam, acoustical fibreglass, various felts, jute, hollow-fibre fill etc.

Danny Richie at GR Research has evidently combined a layer of bitumen (or similar) with a layer of open cell foam in an attempt to kill two birds with one stone. Whether you actually need both though is another matter entirely. The mass-loading effect Danny is referring to is in reference to damping products were where a layer of bitumen is sandwiched between a layer of open-cell foam on each side. Useful for some industrial applications, worthless for loudspeakers since if you want panel damping, the bitumen needs to be firmly affixed to the panels rather than being suspended between two layers of foam, and if it's covering a complete internal wall, all it's doing is taking up enclosure volume, thus the air mass-loads the driver.
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Re: Sound damping material

Post by Wolfgang » Sun Mar 15, 2020 11:38 pm

I am taking it, that by a previous comment offered, I got your location quite wrong.
No problem, John.
The resonances are not easily heard until you remove them..
The bass sounds so clean, fast, and real compared to my previous sub (active/closed box) that it probably will take a while before I start looking for possible resonances.
So what are these 12" OB subs Wolfgang? They sound interesting.
They add a new level of reality to the music. Like adding some missing room information (like a room response of the recording session or from the added digital delay to the bass note?) and of course the last bit of bass resolution. If I mute the main speakers I can hear exactly what the sub adds. It doesn’t sound much at 70Hz x-over point with most Jazz and Classical music but without it (speakers full range, sub muted) the music sounds suddenly a little anemic. It cannot be compared to other subs I had because all “smearing” is gone which appears in the music as lacking speed and trying to catch up with the rest of the bass notes. This is very obvious with piano, sax, and acoustic bass. Actually it’s shocking how empty the music sounds without this last bit of low frequency resolution. Old recordings like for example J. Coltrane/Lush Life benefit even more. Never before I have heard the sax and the acoustic bass like this, almost life. But I don’t want to give the wrong impression: as long as you don’t hear the difference A/B, a good audio system can just sound fine even without the last bit of bass information. But as soon as you have heard the difference there is no way back. I am happy as a clam with my new set up.
The mass-loading effect Danny is referring to is in reference to damping products were where a layer of bitumen is sandwiched between a layer of open-cell foam on each side. Useful for some industrial applications, worthless for loudspeakers since if you want panel damping, the bitumen needs to be firmly affixed to the panels rather than being suspended between two layers of foam, and if it's covering a complete internal wall, all it's doing is taking up enclosure volume, thus the air mass-loads the driver.
Thanks for the explanation. Makes sense.

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Re: Sound damping material

Post by simon » Mon Mar 16, 2020 9:52 pm

I know exactly what you're talking about Wolfgang, it's surprising how the low bass affects the overall balance of the music.

But what are the speakers? Which drivers/baffle design?

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