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Author Topic: Preferred Subwoofer Damping Material?  (Read 1174 times)

Tim Gurske

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Re: Preferred Subwoofer Damping Material?
« Reply #10 on: April 27, 2017, 12:52:09 am »

The specifications are from Eminence and say "fill = minimal." Their phone support said that they snap their fingers in the box and when it stops ringing/echoing then you have enough fill.

So, it sounds like they are using fill like you would in a studio, rather than as a way to slow down the air and emulate a bigger box. I'm not sure what that accomplishes in a sub but maybe it cuts out noice or something.

I think I will try it without foam and then throw some foam in it to see if I can tell the difference.

Also, I am building it with 1" think baltic birch and biscuits so hopefully it'll be a "solid, dead, rock-hard cabinet" from the construction alone.

Thank you for the help!
« Last Edit: April 27, 2017, 12:56:48 am by Tim Gurske »
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Chris Grimshaw

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Re: Preferred Subwoofer Damping Material?
« Reply #11 on: April 27, 2017, 03:31:46 am »

The information about filling/lining cabinets is freely available online. Rod Elliott's website is a good source of info: http://sound.whsites.net/articles/boxstuff.htm

For subs, any stuffing or lining is going to absorb energy. With sealed boxes, the driver might feel like it's in a slightly (of the order of 5-10%) bigger cabinet, while ported boxes will find a loss in output around the port tuning frequency, since the port is activated by pressure inside the cabinet.

Ports often have secondary resonances somewhere in the kHz range, and filling or lining will help attenuate those at the expense of a little low-frequency output. As a result, you'll often find some lining in "full-range" speakers where the cone is producing a wide bandwidth, but for low-frequency-only situations, I'd leave it out.
If you really want to add some, go for lining, not stuffing, since the latter will really kill port output.

With any of these, make sure that whatever you use will not disintegrate or expel dust. Modern sub drivers pump a lot of air through the motor at high power levels - getting the vents clogged up will take it's toll on the driver's thermal power handling and you might find they burn out unexpectedly. A layer or two of cloth over the lining will keep everything in place.

Chris
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lindsay Dean

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Re: Preferred Subwoofer Damping Material?
« Reply #12 on: April 27, 2017, 03:27:32 pm »

     Building a home brew sub starts with proven designs,
quality materials
and construction.
   Any  movement in the box is wasting output energy.
  brace,brace, brace.
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Mark Wilkinson

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Re: Preferred Subwoofer Damping Material?
« Reply #13 on: April 27, 2017, 06:02:43 pm »

     Building a home brew sub starts with proven designs,
quality materials
and construction.
   Any  movement in the box is wasting output energy.
  brace,brace, brace.

Amen to all points. 

I just built some home brew single 18"s, designed using the great software floating around.
4 corner ports, well braced, and still vibrates like no tomorrow. 
Told my girlfriend to have a seat on one when I cranked up Crystallize by Lindsey Stirling.  She blushed deeply.... ;D

I don't know how much bracing it would take to completely tame today's drivers...other than I would want Tim's forklift handles...!
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Stephen Kirby

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Re: Preferred Subwoofer Damping Material?
« Reply #14 on: April 27, 2017, 09:32:45 pm »

I built some similar sized cabinets some years ago.  I turned the handles the other way though.  It was easier to hold them against my hips while moving them around and much easier to do a two person move.

I did make the mistake of tuning them too low thinking I could get some extension out of them only to get into over excursion issues and having to raise the HP.

My current cabs have the clover four side cut outs that allow for grabbing from multiple directions.
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Mark Wilkinson

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Re: Preferred Subwoofer Damping Material?
« Reply #15 on: April 28, 2017, 12:11:46 pm »

I built some similar sized cabinets some years ago.  I turned the handles the other way though.  It was easier to hold them against my hips while moving them around and much easier to do a two person move.

I did make the mistake of tuning them too low thinking I could get some extension out of them only to get into over excursion issues and having to raise the HP.

My current cabs have the clover four side cut outs that allow for grabbing from multiple directions.

Yeah, I can't say I really like my handle placement / orientation all that much.  I'm just not sure what would be substantially better, and their location didn't interfere with ports or efficient bracing.

The subs are kinda big for a single 18" at 23x23x30 because I wanted plenty of port area and length.  They are tuned to 31 Hz, initial measurements look great.


To the OP's question, I use acoustic foam for port or box resonances .https://b2b.parts-express.com/sonic-barrier-1-acoustic-sound-damping-foam-with-psa-18-x-24--260-525
HornResp is a fantastic modeling program, and shows both. http://www.diyaudio.com/forums/subwoofers/119854-hornresp.html
That said, I didn't use any foam in mine.....

As far as fill, like the guys said, the models show it effectively increases box volume.  But I really think it's much more for use with sealed subs, than ported. 
I also modeled and built some sealed boxes for use with the same drivers that are in my ported boxes (bms18n862).  Fill did make a difference, but not a lot.

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Jeff Robinson

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Re: Preferred Subwoofer Damping Material?
« Reply #16 on: April 28, 2017, 05:02:56 pm »

It seems like there are many options. Is there a preferred material that "the pros" use or does everybody have a different preference? As always I am looking for cheap and best, although I realize that those might be mutually exclusive in most situations.

And, before the "it depends" answer :-), I will give some details about the application: I am building a basic ported cabinet for a single 18" subwoofer that will be used for playing general music (top 40 mostly) sometimes indoors and sometime outdoors.

Thank you in advance!

Here is a single word to research: Adiabatic (as it relates to compression/rarefaction of air), Fiberglas fill enables this characteristic (in sealed boxes).
I also suggest reading "Bullock on Boxes".

HTH,
Jeff Robinson
« Last Edit: April 28, 2017, 05:07:07 pm by Jeff Robinson »
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Jeff Bankston

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Re: Preferred Subwoofer Damping Material?
« Reply #17 on: May 04, 2017, 05:10:02 pm »

I have 15" and 18" woofers in ported boxes. I dont use fill. Use 1" no void batic birch with a few side to side and top to bottom braces for additional cabinet stiffness.
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Chris Grimshaw

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Re: Preferred Subwoofer Damping Material?
« Reply #18 on: May 04, 2017, 05:33:03 pm »

Amen to all points. 

I just built some home brew single 18"s, designed using the great software floating around.
4 corner ports, well braced, and still vibrates like no tomorrow. 
Told my girlfriend to have a seat on one when I cranked up Crystallize by Lindsey Stirling.  She blushed deeply.... ;D

I don't know how much bracing it would take to completely tame today's drivers...other than I would want Tim's forklift handles...!

Depends which way it's vibrating. If the cabinet itself is moving due to the reaction force of the driver, then you simply need a heavier cabinet, or a better way of anchoring it to the ground. Bracing will stop the cabinet ballooning in response to the pressure, but it won't stop the whole cabinet moving the opposite way to the cone.

I had a Beyma 15P1200Nd in a fairly lightweight box for a while. Bridged a PV2600 into it for around 2KW, and found the cabinet (on wooden feet) was lifting itself up and rattling on the concrete floor. Fortunately, I had a sports bag with lots of SpeakOn to weigh it down. Wasn't pretty, but it was very early days for me so I probaly got away with it.

Modern sub drivers have very strong (heavy) cones, and a lot of motor force, so the cabinet needs to be solid and heavy to avoid walking around. Alternatively, opposed drivers (not isobaric) will get you some force cancellation, but now you're moving double-18" cabs.

Chris
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Len Zenith Jr

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Re: Preferred Subwoofer Damping Material?
« Reply #19 on: May 04, 2017, 07:26:01 pm »

Depends which way it's vibrating. If the cabinet itself is moving due to the reaction force of the driver, then you simply need a heavier cabinet, or a better way of anchoring it to the ground. Bracing will stop the cabinet ballooning in response to the pressure, but it won't stop the whole cabinet moving the opposite way to the cone.

I had a Beyma 15P1200Nd in a fairly lightweight box for a while. Bridged a PV2600 into it for around 2KW, and found the cabinet (on wooden feet) was lifting itself up and rattling on the concrete floor. Fortunately, I had a sports bag with lots of SpeakOn to weigh it down. Wasn't pretty, but it was very early days for me so I probaly got away with it.

Modern sub drivers have very strong (heavy) cones, and a lot of motor force, so the cabinet needs to be solid and heavy to avoid walking around. Alternatively, opposed drivers (not isobaric) will get you some force cancellation, but now you're moving double-18" cabs.

Chris

I just did some calculations the other day on this matter and I'm going to have to say that the inertial force of the cone was not at play. The cabinet walking was either the bottom feet vibrating due to panel flex or air pressure changes from the sound waves lifting the cabinet. Here are my calculations, feel free to correct me if I missed something:

Newtons 3rd law states that for every action there is an equal and opposite reaction;

force=mass x acceleration or f=ma

so using newtons 3rd law;

mass(cabinet) x acceleration (cabinet) = mass(cones) x acceleration (cones)

Assuming the mass of the cones of a double 18" cabinet is ~210 grams each so mass(cones) = 420 grams for the both of them or mass(cones) = 0.42 kg

and acceleration = 2 x distance / time squared

lets find acceleration of the cones at 60 hz:

time @ 60 hz = 1/60 = 0.0167 seconds
distance of cone travel (x-max) lets assume full bore is 18mm = 0.018 meters

acceleration (cones) = 2 x 0.018 m / (0.0167 s)squared
acceleration(cones) = 129 m/s2

assume the mass(cabinet) = 112 kg

back to newtons 3rd law:
mass(cabinet) x acceleration (cabinet) = mass(cones) x acceleration (cones)
112 kg x acceleration (cabinet) = 0.42 kg x 129 m/s2

gives us acceleration (cabinet) = 0.484 m/s2

now distance the cabinet moves d = 1/2at2
d= 1/2 x 0.484 m/s2 x 0.0167 s x 0.0167 s
d= 0.0000674 m
d = 0.067 mm

So there you have it, hanging in free space with a 60 hz tone playing at full balls to the wall 18mm x-max the cabinets are vibrating back and forth 0.067 mm or less than 3 thousands of an inch.

If you think about it, a driver sitting on the workbench playing at x-max doesn't even move the driver, nevermind the whole subwoofer cabinet.

Edit: Although if the cabinet had a natural resonance frequency within the drivers passband, the vibrations could add constructively like pushing someone on a swing.
« Last Edit: May 04, 2017, 08:08:04 pm by Len Zenith Jr »
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