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Old 11th April 2002, 09:08 PM   #1
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Question how much dampining should i put in my sub enclosure?

i have resently constructed a sub enclosure.....
my question is how thick of dampining should i line the inside walls with?

1/4 inch 1/2 inch 1inch 2inchs.....please help i am not relly sure.....

thanks,
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Old 11th April 2002, 10:31 PM   #2
Keld is offline Keld  Sweden
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1"
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Old 11th April 2002, 10:35 PM   #3
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Check out this link.

http://integra.cyberglobe.net/caraud...ces/fiberfill/

If it were me, I'd start with about 2 lb's in a box your size and go from there.
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Old 12th April 2002, 12:27 PM   #4
dex-rex is offline dex-rex  Australia
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It depends on:1)working principle of the sub(sealed,ported,band pass...)
2)specific driver and enclosure alignment(Q factor)
3)damping material(glass fibres,natural wool,polyester fibres,cotton...)
4)amplifier characteristic(damping factor and subjective "something" factor that seems still not found in amp spec`s)
5)Your taste.
As a general rule: do not overdamp ported designs.Sealed designes often reqiure more stuffening with more damp effective materials such as glass and natural wool.In sealed designs I`m always using glass since it have best absorption of low frequency compared to anything,but it represent certain health hazard and it`s no longer used for ported boxes. Band pass and transmission line damping is more critical.Let your ears be final judge.
Best regards,
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Old 12th April 2002, 02:04 PM   #5
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Dustin Haug:

An interesting link on fiber-fill. Only problem is, David Weems has written that the increase in low frequency extension comes at the expense of overall system sensitivity.

If that is true, than I imagine what is happening is this. Suppose we have a box that is 90 dB @ 1M/1W through the midrange and down through the midbass, then is 6 dB down at 42 Hz. We add fiber-fill. We now are only 3 dB down at 42 Hz-quite a pickup. However, our speaker is only 87 dB @ 1M/1W through the midrange and midbass.

If this is the case, we haven't picked up anything. We have simply knocked down the midrange and midbass sensitivity, so the bottom end sounds larger, without really increasing the bass output.

Weems did not say this is what happens specifically. But he did say that overall system sensitivity goes down when you add fiberfill as the bass extension goes up, and I just extrapolated from there.

Tom Nousaine's article did not mention overall sensitivity of the system. However, Weems did.

Now, if the system adds 3 dB extra at the low end while subtracting only 1 dB throughout the rest of the midbass and midrange, that would be a different story. Until we have an article that deals with specific tests, or someone conducts specific tests themselves, we won't know. Until then, I think it is sensible to assume that any 3 dB in extra bass is counterbalanced by a 3 dB decrease in midrange/midbass sensitivity, for a total of zero increase in bass output.

My question is, have you tried this, or do you have an article that deals with this issue specifically?
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Old 12th April 2002, 06:32 PM   #6
CHRIS8 is offline CHRIS8  United States
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Using fill or lining in a reflex subwoofer cabinet is not desirable IMO. Too bad it's required in midbass applications.

The article did not provide enough information on what actually happens when fill is added to a reflex.

In a reflex enclosure, the box volume itself must remain a resonator to excite the 2nd resonator(port/radiator), by adding fill you do infact lower H(Fs/Fsb), but in doing so you lower Qb(resonance efficiency of box), thus while lowering effective low frequency extension, you have also proportionately lowered low frequency efficiency. It is suprising that the artilce leaves this 'little' fact out.

I see no reason to use fill in a subwoofer, becuase of this fact. In midbass applications, an enclosure shape with minimal standing wave gain should be used so that minmal amounts of lining can be used, that is if you wish to retain maximum bass efficiency.

KelticWizard: Weems was referring to overall sensitivity of the bass alignment, as this is totally seperate and not related to the efficiency of the mms/bl behaviour of the speaker.



-Chris
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Old 13th April 2002, 10:50 PM   #7
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Tom`s article is interesting but his conclusions are somewhat constrained IMHO.He took for granted dacron-polyester fibre is best damp material outhere,and that`s true considering anti-moth,price and ecological qualities.Every sound absorbing fibre material has different absorbing coefficient on specific audio spectrum,and polyester don`t shine on any part of it,comparing to glass fibre,cotton,natural wool,polyurethane soft foam ,in same thickness of course.It`s good on mid`s and high`s,but have poor absorption on bass.For instance,cotton fibres are very good on upper bass,on mid`s,and excellent on upper mid`s and high`s.Best absorption on bass is with glass fibres,and it will give the greatest "pretending to be bigger box then actually"effect.For the same reason polyester is desirable in ported designs:doesn`t damage much Q alignment,and do the job on mid`s and upper.

If you ever put your ear on bass reflex port you will hear why you need lining.Do not think that terrible noise consisting of resonances and standing waves couldn`t find their way out of box together with original signal.
Further seems logical to me that when you add fill and loose some efficiency on mids,only thing that is lost is the same noise,not wanted in the first place.This can be checked comparing driver response in well-damped sealed box vs.infinite baffle fitted driver, but I didn`t try this.
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Old 14th April 2002, 12:22 AM   #8
CHRIS8 is offline CHRIS8  United States
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Dex-Rex:

While the stuffing has little to no effect on long wavelength frequencies as far as direct acoustic absorbtion, this is not relevant to the bass alignment. Aside from standing waves and other non-bass related noises in a normal enclosure, the stuffing/lining is abosorbing energy indirectly, this means that the pressurization oscillation(resonance) characteristics of the box is changed, to the friction caused by the stuffing. This is why fibergalss or acoustastuff, with a greater effective path of resistance is more effective than simple polyfill at increasing 'apparent' volume size of the enclosure. But, by this same reason, you DECREASE efficiency of the box as a resonator! This causes a poorer coupling to the vent or radiator, decreasing effective output levels. You should remember that the port/vent is primarily responsible for SPL at and around port tuning.

Use of stuffing and/or lining in a ported box should done conservatively, and NONE should be used in subwoofer applications. This means that midrange-bass enclosure shapes that reduce their inherent standing waves efficiently in the first place due to non paralel walls will be able to achieve higher amplitudes around tuning of the box than the same volume and port tuning with significanty higher amounts of stuffing.

-Chris
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Old 14th April 2002, 08:11 PM   #9
dex-rex is offline dex-rex  Australia
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CHRIS8,

Considering pure sub,ported/vented enclosures I agree 100%.But referring to closed mid/bas enclosures I think that good stuffing is unavoidable and very beneficial.You do loose some efficency on mids,but isn`t it the "bad thing" go away?
In sealed box design the mid/bass driver cone excursion is not affected by the dampening in the mids(and upper),so we get same amplitude on the cone but lower output.I wonder what`s the energy we lost?I suspect that is unwanted sound consisting of resonances,reflections and standing waves.Stuffed closed box on frequencies from low mids to high`s acts as much larger enclosure because of the fact that signal front wave sent into box is introduced with fill,where it`s attenuated AND time-delayed just like if the box sides were much,much further from driver,closing to infinite baffle response.That`s the way I see it.

Check this out: http://www.t-linespeakers.org/projec...dix/index.html

Greet`s
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Old 14th April 2002, 08:27 PM   #10
CHRIS8 is offline CHRIS8  United States
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I am in agreement. Perhaps since you seem to be new to English language, your phrasing was a bit confusing, and you did not quite understand me either.

My point is that if an internal shape for a midbass application is chosen that minimizes standing waves, then less stuffing/lining can be used, and then you only need to worry primarly about the midrange reflections that will leave the port opening.

Have a nice day.

-Chris
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