TL Subs sounding mediocre

[bigwill]

I built some stereo transmission line subwoofers a while ago, and I'm getting annoyed with their sound. They seem to be good at deep bass, they get down to about 20Hz but at the same time they feel gutless! Sometimes bass drums give a nice punch but a lot of the time you're left dissappointed when you think you're going to get hit in the stomache and nothing comes. They're used up to 100Hz, and seem really sensitive around there, then there's a massive dip between about 50-90Hz, then below that it gets loud until it tapers off around 20Hz. The result of this is quite a waffly muddled mess on some songs (but on others they sound great). Two things that may be causing this:

1. No stuffing in the line at all

2. I didn't use MJK's model, I kind of guessed the design since I didn't have a complete set of TS parameters for my drivers

I think I'm going to add some stuffing to the line tommorow to bring up this midbass range.

I know this is a vague sort of thread so does anyone have any vague sort of suggestions that would help me improve the sound of my TLs?

[bigwill]

One improvement seems to be lowering the crossover point to about 50-60Hz and turning them up... seems a lot better now. Maybe a big echoey resonating wooden enclosure isn't really suitable for midbass?

[chops]

Yeah, I'd say stick around the 50-60Hz crossover point and adjust the gain so that they blend nicely with your mains. Hopefully your mains have usable clean output at 50-60Hz.

BTW, do you have any details on your TLs?... drivers, size, PICS?! I always enjoy seeing pics of DIY projects. They give me the opportunity to get some ideas for my own projects.

[bigwill]

Sure thing

Here are the plans:



Here are some pictures (linked because they're quite big):

Pic 1
Pic 2
Pic 3
Pic 4

The driver used is an MCM 55-1480, only £18 (around $30 in the US I believe)

WinISD says they'll only go down to about 50Hz in a box, but in these TLs they go down to 20hz!

[rjb]

I don't have the full T&S parameters, but taking a guess at these, and feeding into MJK worksheets with your box shows a massive peak of 15+ db at about 35 or 40 Hz, and with no stuffing, major ripples above 100 Hz.

This is a low Q driver with a low resonance so not as well suited to your TL design as it could be, and one option would be to convert your box to a BR.

The best option is to use the worksheets to see
a) the effect of stuffing
b) the effect of adding a series resistor of 1 or 2 ohms to bring up the Qts.

You will probably need to do both.

Note that these options will not "bring up the midrange" but will lower the bass peak to a more reasonable figure. Presently the low bass will be overemphasised and very wooly, not a clean "punch"

[bigwill]

Originally posted by rjb
I don't have the full T&S parameters, but taking a guess at these, and feeding into MJK worksheets with your box shows a massive peak of 15+ db at about 35 or 40 Hz, and with no stuffing, major ripples above 100 Hz.

Yeah I noticed that, 35Hz is massively loud. I thought it was just a room resonance

Despite this I actually get quite a big punch at the moment with the crossovers set lower, it's currently sounding pretty good but obviously my TL isn't optimal.. Maybe the Qts parameter on the datasheet is underestimated, so the peak isn't so bad? MCM are known for bad TS parameters, or so I heard..



Any chance you could post the worksheet with all the info in it?

[Volenti]

It would still be worth while to expriment with some fill, you shouldn't need to use much, try lightly stuffing the first 1/3 of the line (easy to access behind the driver). Having two identical enclosures should make comparasons easy.

In my straight TL it only takes a small amount of fill to damp the low frequency output considerably.

[Nuuk]

My TL subs sound great (no stuffing) but I don't crossover them over above 70-80Hz.

Having said that, I am about to replace them with dipole woofers!

[bigwill]

Would rockwool make good stuffing for a TL? (I have a lot of the safe type on hand at the moment)

[bigwill]

Ok, I added some stuffing, it made a HUGE difference! It sound awesome now!