3-way designs with transmission line midrange

[luvdunhill]

hi! I was wondering if there are any documented DIY projects that use a TL mid in conjunction with a sealed or vented woofer? I am new to the TL concept and read in the Loudspeaker Cookbook that using a TL for a mid is something that is beneficial and is not often found in commercial designs. I know the Vandersteen speakers use this approach, and I was just curious if anyone else has done it and perhaps if there were any details on how one might design such a beast.

Thanks!

[owdi]

I've heard of it being done before, and even saw a project somewhere. It's a neat idea, because you can eliminate the impedance peak that prevents you from using a 1st order highpass filter on the mid.

Dan

[Dave Bullet]

I am planning a 3 way and was also thinking of TLing the midrange. Dickason (from memory) recommended a TL if the low/mid xo point was at least 2 octaves from midrange Fs (and sealed otherwise) - or I might have that the wrong way around.

In any case I presume the advantage of TL loading is reducing backwave pressure from a conventional sealed enclosure resulting in a more neutral midrange sound (aka open baffle) - but have the asthetic advantage of a "box" speaker (if you consider that an asthetic advantage).

David.

[Jonasz]

http://www.htguide.com/forum/showthread.php4?t=25932

Maybe not a TL but a damped open back midrange. Supposed to be really good!

[Ap]

I guess it really depends on how low you want the mid to go, if its crossed at 300hz then there is not much difference to having a large sealed/stuffed box.
For my 3 ways I just used exaclty that, with a non-parallel top/bottom, so the mid chamber reduces in size towards the back of the enclosure (kind of like a TL).
If your mid was crossed first order at 100hz then it maybe beneficial.
Andrew.

[DAMIC]

http://digilander.libero.it/piani/ca...generale-2.jpg

TDL made speakers with T/L mid and woofer, so maybe you will get some idea.

[luvdunhill]

Originally posted by Ap
I guess it really depends on how low you want the mid to go, if its crossed at 300hz then there is not much difference to having a large sealed/stuffed box.
For my 3 ways I just used exaclty that, with a non-parallel top/bottom, so the mid chamber reduces in size towards the back of the enclosure (kind of like a TL).
If your mid was crossed first order at 100hz then it maybe beneficial.
Andrew.

Ap: cool! do you have any plans / pics I could take a peek at?

Also, I'm thinking first-order at around 150 Hz

So in the above case that Jonasz gave, a TL with taper of 1 is used. Are there some formulas or guidance on what different widths and lengths, or geometries will do in the case of a midrange? LDC has some good information for some of the more popular geometries... I wouldn't consider any folded options, maybe the straight, tapered, or the other one listed in LDC and then vary the stuffing of the line for tuning.

Also, are there any indications from the T/S parameters if a mid would work well in these TL shapes?

[luvdunhill]

also, another question in addition to the above. What do people use to model transmission lines? The formulas given in LDC are really too general, they don't even have tables for a straight line with taper = 1.

[Ap]

This is a plan view which gives you a bit of an idea.
Essentially the mid box is non-paralleled stuffed with wool/poly.
Crossover is 300hz 2nd order so the drivers dont do any bass.
As for formulas I built a TL (or tapered quarter wave) sub using the 1/4 length of Fs (tuning) & taper of 1.25 x Sd to 1 x Sd,
there is some good modelling software around which can model response for you.

Andrew.

[luvdunhill]

Originally posted by Ap
there is some good modelling software around which can model response for you.

links?



looks very nice. I'm thinking more of a straight TL with taper = 1, but once I get something to model things, I may find something I like better. I will need a configuration that will load the mid to low frequencies though ...