how much is enough

[kartsmart]

Im finishing up a load speaker project and was geting ready to add some sound deating material , is there a way to measure the damping by the electral Q ? All I found was from a ad that said /Most sealed and vented enclosures require 1/2 lb. of dampening material per cubic foot of enclosure.
what type seems to work the best? does damping material add resistance to the Q or not?

[spkrman57]

For sealed systems, I prefer a more damped(stuffed fuller) situation.

For ported systems: I prefer to line every other wall with either 1" or 2" insulation depending on the losses of the cabinets and other factors. If you do some searching(see posts by "Giskard") and you will find a wealth of info!

Just my opinions on this, not necessarily the correct solutions!

Regards, Ron

[Ian Mackenzie]

Im finishing up a load speaker project and was geting ready to add some sound deating material , is there a way to measure the damping by the electral Q ? All I found was from a ad that said /Most sealed and vented enclosures require 1/2 lb. of dampening material per cubic foot of enclosure.
what type seems to work the best? does damping material add resistance to the Q or not?

Okay there is a bit to it and not easy to explain...The Loudspeaker Cook Book on Amazon is a good read.

There are several ways to use damping.

Boundary layer where plastic coated foam rubber is used to control pressure induced standing waves.

A roll of dacron or other material just behind the woofer..often done in small acoustic suspension systems to stop mid band transmission back through the cone.

A layer of fibre glass termed fill in Bass Box used as absorbant to help control internal reflections.

To answer your question....it effects mechanical system Q, in sealed systems ths is refer to Qmc , the Q of a closed boxed woofer resonance and takes into consideration only electro mechanical non electro magnetic resistances (loss or damping).

You can measure the effects on Q but this involves a whole bunch of tests and some maths.

The electrial aspects of Q, know as Qes is another element of Q that makes up the total Q known as Qts.

Damping depending on how much is used and adds real volume to an enclosure. Generally Vented encl use minimal lining when properly tuned system.

This must be accounted for in the design (software will often do this for you)

Ian

[duaneage]

Fiberglass turns mechanical sound energy into heat, poly fill works much the same. I look at the impedance peaks and maximum impedance of the peaks to get an idea of how effective damping is. I have found the peaks have a lower imp. with increased damping up to a point where the stuffing begins to move the peaks too far.

The location of the stuffing can have a big effect. Generally you should leave the baffle free of stuffing. Try and do three walls only and see how that works.
By combining additional bracing material and fiberglass you can get a happy medium where the fill damps the backwaves and the solid bracing material keeps the box from being too compliant ( e.g large)

I spray fiberglass with a light coat of spray paint to keep the fibers from coming loose and causing problems.

[kartsmart]

so far this has been great help, thanks for your input, keep em coming

[kartsmart]

this is my project and could use some input http://www.e-speakers.com/products/diy.html its the 4003-1602 tad referance system with some changes, will be using JBL 2420 horn driver with 2345 horn / for now / and TAD 1602 bass drivers. how low will the uper range go and preform well. the speaker caninet is 7.3 cu ft 72"x23.5x9 ID with 4 3" ports near 22" / 2 on top 2 on bottom

[Mr. Widget]

this is my project and could use some input...

Did you get the cabinets from Andre?

Too bad you don't have the 4003s.... The 2345 and 2420 are really only supposed to be used to 800Hz.


Widget

[kartsmart]

no I built them my self

[Zilch]

There was an excellent post illustrating in BassBox Pro the effect of varying levels of damping materials.

I have put some effort into finding it to link here, without success.

Perhaps some other forum member remembers where it is and will do that, please?

I believe it was in the last year....

[kartsmart]

need some advice , looks like I need to make this a 3 way system, what would be the best midrange to fill the gap between the twin tad 1602's and the jbl 2420. thankx