Lab 12 occupied volume and other Vb subtractions. - diyAudio
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Old 23rd June 2012, 08:02 PM   #1
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Default Lab 12 occupied volume and other Vb subtractions.

Greeting fellow Bass lovers,
Ok, I know some one is going to say...
"a quick search of this site will give you the answer..."
but I searched and had no luck. The word volume isn't exactly specific.

If anyone knows the volume (liters or cc or whatever) occupied by the rear of the Lab 12 mkII (with 0V DC) I would be very grateful if you would post it.

Also, in the case of a flared port, would the space in the internally flared section not counted toward the port length count as box volume? Perhaps I'm splitting hairs here but I'd like to be specific so that real life measurements can allow me to make more precise adjustments. I realize that the answer is complex and dependent on the case but I have found no data on the subject in general.

Lastly, some forms of stuffing will reportedly increase the apparent Vb of the system. In a vented application is there a way of approximating this effect? Is there any research one could point me to regarding balancing the benefits of stuffing vs the decreased port SPL output from the losses generated by it. (I really need AES membership for the article database but then all I would do is read)

Many thanks in advance.

-Matt Long
San Francisco, CA

PS I don't have the driver in hand or I would measure it myself.
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Old 24th June 2012, 02:59 AM   #2
OscarS is offline OscarS  United States
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The flare section counts as part of the port, but doesn't really add to the port length since it is not linear. Only a small fraction of the flare length actually counts.

As for driver displacement, the Eminence website should have it.

Stuffing to increase box volume mostly only works in sealed systems. In ported systems it acts more to dampen out standing waves and smooth out the response.
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Old 24th June 2012, 03:08 AM   #3
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Some box design software can show you the ( approximate ? ) affect of damping used inside the box. Bass Box Pro for example can do this and I'm sure many others could also do that. Check it at HT Audio home page

Eminence themselves have a version of this software. Maybe they have an evaluation version ? Check it out at Eminence Speaker | The most trusted name in audio since 1966. Great upgrades for JBL, Celestion, Jensen, and Fane.
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Old 25th June 2012, 10:54 AM   #4
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Thanks for chiming in guys.
I found the driver displacement but strangely it wasn't on the spec pdf but a resellers website.

The Lab 12 Driver Volume Displaced: 188.6 cu.in. / 3.09 liters.

As for the stuffing I've decided to not use any. Instead I plan to just use a material, or perhaps a combination, to coat the interior with to damp panel resonance. I was thinking of Acoust-x by acry-tec as I am already using Dura-tex for paint.
Speaker Cabinet Coating - Acoust-X Sound Damping Coating

-Matt Long
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Old 25th June 2012, 07:24 PM   #5
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Quote:
Originally Posted by mattlong8 View Post

As for the stuffing I've decided to not use any. Instead I plan to just use a material, or perhaps a combination, to coat the interior with to damp panel resonance. I was thinking of Acoust-x by acry-tec as I am already using Dura-tex for paint.
-Matt Long
Matt,

Just finished painting several cabinets with DuraTex, great stuff.

If the cabinet you are designing is so small that an accurate volume displacement of the driver makes a difference, the panels will most likely be too small to resonate in the sub passband.

Damping panels using a product like Acoust-x is not an efficient use of materials, though it would help in something like a car trunk used as a sub enclosure, or sheet metal HF horns.

Using bracing, rather than damping to eliminate panel resonance makes the panel stiff, increasing efficiency.

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