Transmission Line damping

I was wondering if we have any transmission line experts here.
I discovered on the Meadowlark site that they use natural wool - "...transmission line that is well damped with long hair sheep’s wool - a material long regarded as the ‘gold standard’ in line damping"
1) I am using poly fill from Michaels - would the sheeps hair sound better?
2) Should the total length of the transmission line be damped?
3) Will a ceramic magnet speaker rebuilt with (not original) ferro fluid voice coils change the required length of the transmission line?

I have 7' transmission lines yet only damped the first 2.5' when I put the speakers together. Reference ESS AMT1A tower

Thanks,

Clay

 

Not positive about the first two--I recall from an old article that the entire line may have been damped, and they also used dacron fiber-fill for it. I've thought about attempting to make some TL speakers myself.

As for #3, I recall the formula for a TL speaker is a "quarter wavelength" design, based on Fs (resonant frequency) of the driver in free air. If the new voice coil changes the resonant frequency, then the TL would not be the optimum length. I believe Fs is based more on the suspension (spider, surround) and weight of the woofer cone, not the motor driving it (magnet and voice coil). If the surround and/or spider were replaced when the voice coils were changed, then you very well could have a different resonant frequency to the driver.

 

Thank Rudy,

Is there any easy way to measure the resonant frequency of a woofer?
Anyone in the Bay area have the equipment to measure this?
I could bring the speaker and a 12 pack.

Also if anyone is interested in building the AMT 1A 1/4 wavelength transmission line speaker box (10" woofer), I have reverse engineered it so I could make my second one. The original 1/2 of my set became someones subwoofer.

 

You can actually buy a device at Parts Express that hooks to a PC and will help measure a drive's parameters (Vas, Qes, Qms, Fs, etc.). I think it was in the neighborhood of $100. I don't know if I would ever need to get anything like that, but they claim that the published driver specs are sometimes not close to what the actual measured parameters are.

 

In response to:
1) It seems to me that natural wool would absorb moisture meaning that its damping characteristics could change with humidity. I'd think artificial fibers would be superior, at least in that respect. But maybe that's just me...

2) It is my understanding that the entire length should be damped.

3) See http://sound.westhost.com/tsp.htm You can substitute a CD player and a static tone disc if you can get by with lower resolution (this may also allow you to do without the frequency counter). It is best to start with higher frequencies and work your way down toward resonance. Also once you see you're past the impedance peak ; stop, speakers can really tear themselves up when driven below resonance.

 

Wow! Gerry that is a really cool link. Lot of articles to learn about electronics.
I may need to get one of my engineer buddies over to help me with the testing.

 

One thought regarding wool vs. synthetics: how is wool going to hold up in 5, 10 or even 20 years? I would think synthetic would retain its original properties longer.