Damping TL cabinets?

[planet10]

Thanx Martin for the succinct summary

dave

 

[skrivis]

I'd say the latter... i've been following MJKs work since before it was published (i was the original publisher). This includes his papers, forum interaction and direct mail....

all the things i've said are from these interactions.

All your agrguments seem to go against the flow of what is published... if i get more time i'll address your specific issues.

For instance, just looking at the MJK tables, one can see how the line taper directly affects the line resonance.... Voigt pipes are longer than traditional tapered lines for the same fundemental.

dave

Back to the drawing board. It's difficult to absorb all the info I've been getting on t-lines in the last month or so. I went from having read one of the Bailey articles years ago, to suddenly having enough material to fill a book, and the math to back it up.

Thank you for correcting me.

-sgk

 

[skrivis]

The stuffing really has a minimal effect on the speed of sound inside a stuffed TL. I think the lowest value I use is about 320 m/sec for a 1.0 lb/ft^3 fiber density. Compared to the free air value of about 344 m/sec, this is less than a 10% reduction. I personally believe that this reduction in the speed of sound is due to heat transfer that occurs between the air and the fibers as a sound wave passes through the tangle, similar to the apparent increase in closed box volume that occurs when stuffing is added. I don't believe it is due to moving fibers which was commonly accepted TL theory for many years. In the past, people have claimed a 50% reduction in the speed of sound for a stuffed TL resulting in a much shorter required length. I believe the shorter length is due to geometry and has nothing to do with fiber stuffing.

This is what I was thinking of, and I remembered the figures. I was trying to point out that there _is_ an effect. Several people I've talked to have claimed that there is no effect at all. Perhaps it's minimal enough that it can be ignored, and that's what they were getting at.

The shape of the line is everything! Look at my alignment tables and see what length is required to achieve the same tuning frequency for different area ratios. I believe that the shape of a TL is one of the most important properties of the design.

Ok, I was thinking that the length was solely responsible for the fundamental resonance, and that shape and area worked on higher frequencies.

You re getting tangled up in labels. I do apply labels to my designs that try and express the physics behind each. But there are no sharp dividing lines and arguing over labels is a waste of time.

I did put a smiley in there...

many people (Dave, GM, and Bob Brines are probably the biggest contributors) have provided constructive feedback and we have all learned together. Dave's summary above is exactly what I am thinking and have tried to express. Maybe the different points are scattered in too many places on my site to allow a new reader to identify them up quickly. Sometimes you have to think about what has been written, I may not have explained things in the clearest manner. I am still learning!

Ok, I'll see if I can pick up on anything Dave, GM, and Bob Brines have written about this. Maybe a different explanation will help get the point across. (I'm not saying your explanations are bad!)

I haven't been able to get Matchcad Explorer to install, but I'll keep working on that so I can see what's happening as I change various parameters.

Thanks for all your help! I'm still learning too.

 

[bzdang]

Have searches and read about damping TL cabinets. After what i have read there seems to be various methods... I am now finishing building the Seas Thor speakers, and i am a little unsure about the damping/stuffing...

I suggest that you can download some test software, for instance www.audiotester.de and begin to measure impedance as you experiment with stuffing. You can post your results here and ask for advice. If you can buy or borrow a mic then you will be able to see even better the effect of stuffing on your speakers.

Dave