Need advice on a TL build

[IG81]

Hi there,

I have two 8 inch woofers from ADS L500 speakers that have no tweeters. Part number 206-0316.

Here are the parameters I measured, average of two drivers:

Znom: 4 ohm
Re: 3.0 ohm
Fs: 22.5Hz
Qms: 1.95
Qes: 0.33
Qts: 0.282
Sd: 211 sq.cm - approx
Vas: 50.5 liters
BL: 9 N/A
SPL: 84.4dB/W/m

I've been wanting to build a TL for a long time now and have not gotten around to it. These drivers would have the following TL alignement, according to the MJK fashion:

L = 147 inches
SL/SO = 1 (what I chose for simplicity and better ripple response despite low-Qts that might call for expanding line)
Xsectional area: 32.5 sq.inches
Driver offset would be about 43 inches

Although the line lenght is insane, the tiny Xsection makes it manageable in a double-fold enclosure of 48 inches high. Xsection would be 8 inches wide and 4 inches deep. I would end-up with external dimensions of 48 inches high by 15 inches deep by 9.5 inches wide, not bad. Fits in two 4'x8' sheets of 3/4 ply.

And although it does not pertain to my question, that would be a 2-way design, with a soft-dome tweeter.

How does that sound?

IG

[speakerdoctor]

Why don't you ask MJK?
Visit Quarter Wavelength Loudspeaker Design to gain access to the QW forum. He visits the forum frequently to help folks just like you.

[IG81]

Originally Posted by speakerdoctor

Why don't you ask MJK?
Visit Quarter Wavelength Loudspeaker Design to gain access to the QW forum. He visits the forum frequently to help folks just like you.

I'm not currently a member over there and I know there's many knowledgeable folks around these parts too, so I thought I'd post here for now.

My main concern is about the driver's parameters, which are quite unusual, with very low Fs and low Qts. I have never attempted a DIY project with something like that and have never read about projects that employed similar drivers. This is a perfect driver for a sealed enclosure, which is what the ADS L500 is, but the resulting TL geometry is a very long and very thin line. I wonder what are the inherent issues here, cause I'm certain there's gotta be some.

And about the driver; in it's sealed enclosure it starts rolling-off way above it's Fs, probably around 50-60 Hz, but the calculated TL would attempt to use it down to it's Fs, unless I tune it a bit higher, which I probably should, say around 35Hz. The low Qts also suggests that this may be a wise thing to do.

Well, I'll see if I get the advice I need here first!

IG

[speakerdoctor]

Good luck with getting good advice here.
Keep in mind that TL"s aren't known for for their low freq. extension. Folks like them because of their sound. The biggest challenge with TL's is taming the response ripples.

[bjorno]

Hi IG81,

Try learn HR (Horn-response) but I advise you to take a step-by step approach when using the program for a TL design (no stuffing is used) = OD or Nd in HR.

See the plots in my submitted pictures that for the very last pictures and plots
show an identical airways un-stuffed/stuffed MJK FR plots to compare with.

IMO: Its clear that your TL = straight QWP design lack a low f-3dB point when just by calculating your driver in box seen equivalent Qt value ( depending of the closed pipe volume).

b

[GM]

The driver's specs are suited for B%$3 WC, TH or similar loading, but I assume don't have enough Xmax for acceptable performance anywhere near its Fs.

The long, tiny pipe will compression load the driver, reducing its effective Qts, further over-damping them. It won't make for an accurate reproducer, but it will be very 'tight'/'fast'. A max flat impedance TL OTOH will work well, though will have a much higher tuning same as a T/S max flat vented alignment (22.5/0.282 = ~79.8 Hz), but a much slower roll off, so much more accurate with ~transient perfect response.

Driving these with a high output impedance will raise its effective Qts which will in turn increase the net pipe volume required, lowering its compression loading, max flat impedance tuning.

WRT choosing a TL alignment with a Qts < ~0.4, calculating a T/S max flat alignment to get an acceptable cross sectional area (CSA), tuning has worked well enough for me, but I did these long before MJK's work, so tend to be larger in the few I've compared, though should still be fine for choosing a tuning (~32 Hz for this driver). For > ~0.4 Qts, I use a max flat impedance alignment.

GM

[head_unit]

Google for George Augspurger's article, I think in the old Voice Coil magazine. He also had a software he wrote, probably the best TL calculator to date.

Study the question of stuffing a lot. Rock wool is good but settles over time; I think the chunk-y fiberglass may be better. And of course, bends can reduce some end-to-end reflections, but sharp bends are hard on proper operation.

I do think your unusual parameters seem like good candidates for a TL. Good luck!

[planet10]

Originally Posted by head_unit

...George Augspurger's article, I think in the old Voice Coil magazine. He also had a software he wrote, probably the best TL calculator to date.

It has never been updated & is very limited in what it will calculate. MJK is better.

dave

[IG81]

Thanks for the info you guys!

Before I got to read your answers, I already calculated for a ~35Hz tuning. It would yield pretty much the same external box dimension, with a single fold this time, CSA increasing a bit this time.

I checked with the physical build with ¾ ply and would have the following geometry:

L = 89.5", yielding a theoritical 37.7Hz tuning
CSA = 8" by 6.5", 52sq.in
driver offset (0.349) = 31.35"

I think that would be a saner aproach. I'll try to look it up in HR, see what I can do. For now I seem to be unable to download HR, websites seem to be down or something.

Here's what it'd look like:

ADS_TL.gif

48" high, 15.25" deep, 10.5" wide. The side panels would sandwich all the other 8" wide front, back and interior baffles. Not show are corner 45deg braces and perhaps a few braces along the way to subdivide baffles into smaller sub-panels. I would initially stuff the first 2/3 of the line and experiment to suit my taste.

IG

[pkitt]

Other than actual bracing, those 45-degree corner braces don't perform any function, certainly not any acoustical ones. They don't "direct" the sound waves around the bends as was believed eons ago; the wavelengths of the lower frequencies, which is what a TL is mostly about, are too long to even "see" the deflectors, and the higher frequencies will be absorbed by any stuffing installed in the line.
Paul

Originally Posted by IG81

Thanks for the info you guys!

Before I got to read your answers, I already calculated for a ~35Hz tuning. It would yield pretty much the same external box dimension, with a single fold this time, CSA increasing a bit this time.

I checked with the physical build with ¾ ply and would have the following geometry:

L = 89.5", yielding a theoritical 37.7Hz tuning
CSA = 8" by 6.5", 52sq.in
driver offset (0.349) = 31.35"

I think that would be a saner aproach. I'll try to look it up in HR, see what I can do. For now I seem to be unable to download HR, websites seem to be down or something.

Here's what it'd look like:

Attachment 189817

48" high, 15.25" deep, 10.5" wide. The side panels would sandwich all the other 8" wide front, back and interior baffles. Not show are corner 45deg braces and perhaps a few braces along the way to subdivide baffles into smaller sub-panels. I would initially stuff the first 2/3 of the line and experiment to suit my taste.

IG