"Transmission Line" Sub experiment?

[johngalt47]

Ok, so I want to start experimenting with "transmission line" subs. Which driver is a good candidate? I'm looking for 8 or 10 inch just to keep the size down while experimenting. I thought the TB W8-1363 would work based on the T/S, but I bought one and the measured Qts was too high.

The RS225-8 looks good but I would like something more in the line of a sub driver.

I'm looking for recommendations based on actual measurements, not catalog data.

[r-carpenter]

Re: "Transmission Line" Sub experiment?

Problem with TL subs is that they generate rather unpleasant standing waves that are fairly long, strong and hard to deal with.

[Sydney]

Re: "Transmission Line" Sub experiment?

* Disclaimer: have not made one so...
Peerless drivers are frequently used ( seen numerous builds w them ).
Traditionally, lines are tapered and damping ( such as wool ) carefully placed to help attenuate standing waves.

[johngalt47]

Re: "Transmission Line" Sub experiment?

Problem with TL subs is that they generate rather unpleasant standing waves that are fairly long, strong and hard to deal with.

What is it about TLs that generate standing waves while "normal" vented ones do not?

[r-carpenter]

Re: "Transmission Line" Sub experiment?

http://techtalk.parts-express.com/sh...ssion-line-sub
this one came out quite alright.

TL is generally a large pipe. Then you fold TL, each section of the pipe becomes a resonator. This: http://techtalk.parts-express.com/al...chmentid=26381 for example is a 9ft folded line that caught couple of resonances at 90hz. Such a resonance is very close to the pass-band of the sub and can't be dealt with easily.
All depends, how big is the driver and how low you want to go.

[Pete Basel]

Re: "Transmission Line" Sub experiment?

What is it about TLs that generate standing waves while "normal" vented ones do not?

A TL is a distributed mass/compliance system whereas a vented box is ideally what we
call a lumped system. Distributed systems have repeating resonances at harmonic
frequencies much like a vibrating string. Lumped systems ideally have one fundamental
resonance at Fb that is what makes such designs work.

Before someone jumps in here, all systems are distributed but for reasonably small
dimensions a vented box models very well as a lumped system. T&S theory is based
on lumped system models.

[Sydney]

Re: "Transmission Line" Sub experiment?

What is it about TLs that generate standing waves while "normal" vented ones do not?

Look at the cross-section of this classic design.
http://www.t-linespeakers.org/classics/TLS80/
http://www.t-linespeakers.org/

As an example of the effect of the shape of a enclosed volume of air: think of a flute.
http://hyperphysics.phy-astr.gsu.edu...es/opecol.html

http://www.quarter-wave.com/

[Beau]

Re: "Transmission Line" Sub experiment?

I am pretty sure someone on this forum designed an RS-225 T-line that another member built.

I'll search later if I have time - but I sure think its been done.

Edit - here is the one I was thinking of: http://techtalk.parts-express.com/sh...ed-the-trigger

[Pete Schumacher]

Re: "Transmission Line" Sub experiment?

Problem with TL subs is that they generate rather unpleasant standing waves that are fairly long, strong and hard to deal with.

Not a problem at all. That's what the stuffing is for, to control resonances outside the quarter wave resonance.

Any driver that works in a vented enclosure will also work in a TL of similar overall volume. Usually the TL is slightly larger than a comparable vented enclosure but the performance above tuning when properly damped is superior to a vented box due to the lack of port resonances that accompany a vented enclosure.

For subwoofer duty, TLs offer no advantages over vented enclosures since the bandwidth is limited to 100Hz and below. But for woofer duty where the woofer reaches to 300Hz or higher, TLs can offer improved sound due to their superior control of the back wave and enclosure/port resonances.

[Paul K.]

Re: "Transmission Line" Sub experiment?

What, specifically, are you hoping to achieve, like F3, SPL, box size, etc? For any specific driver there will be a specific system tuning frequency that will be optimum. After that, the volume in the line will determine F3 and the driver's excursion capabilities will determine how loud. I have actual T/S measurements for the RS225-8 and can do a TL model fairly quickly for you. Oh, it would most likely be tapered and appropriately stuffed to eliminate those "unpleasant standing waves", as well as folded to fit into a reasonably sized and shaped box. That said and in agreement with Pete, I don't think a TL offers any particular advantage for subwoofer duties, other than likely having a much lower air velocity in its terminus compared to a vented box.
Paul

Ok, so I want to start experimenting with "transmission line" subs. Which driver is a good candidate? I'm looking for 8 or 10 inch just to keep the size down while experimenting. I thought the TB W8-1363 would work based on the T/S, but I bought one and the measured Qts was too high.

The RS225-8 looks good but I would like something more in the line of a sub driver.

I'm looking for recommendations based on actual measurements, not catalog data.

[r-carpenter]

Re: "Transmission Line" Sub experiment?

Not a problem at all. That's what the stuffing is for, to control resonances outside the quarter wave resonance.

stuffing isn't going to do much at a low frequencies if you have a high Q standing wave. Of course you can keep adding the stuffing but it'll decrease the output of main resonance as well.

[johngalt47]

Re: "Transmission Line" Sub experiment?

I'm looking for sound quality and I want to experiment to see for myself if it "sounds" any differently. I have a RS225-8 that is shielded that I can play with. While I was playing arpund with rebuilding that Pioneer HPM 40, I discovered that the shielded version requires a bigger box than the non shielded variety.

Do you need my measured specs to produce a design?

What, specifically, are you hoping to achieve, like F3, SPL, box size, etc? For any specific driver there will be a specific system tuning frequency that will be optimum. After that, the volume in the line will determine F3 and the driver's excursion capabilities will determine how loud. I have actual T/S measurements for the RS225-8 and can do a TL model fairly quickly for you. Oh, it would most likely be tapered and appropriately stuffed to eliminate those "unpleasant standing waves", as well as folded to fit into a reasonably sized and shaped box. That said and in agreement with Pete, I don't think a TL offers any particular advantage for subwoofer duties, other than likely having a much lower air velocity in its terminus compared to a vented box.
Paul

[Pete Schumacher]

Re: "Transmission Line" Sub experiment?

stuffing isn't going to do much at a low frequencies if you have a high Q standing wave. Of course you can keep adding the stuffing but it'll decrease the output of main resonance as well.

If the enclosure is properly sized with the correct taper ratio, the standing wave will not be a problem, even without stuffing. If the signal is band limited like all subs receive, stuffing isn't really needed. And if the driver is properly positioned along the line, the standing waves above the primary quarter wave resonance are pretty well eliminated.

Below are a couple of plots of a woofer at 1/5th the distance of the line from the closed end. Taper is 10:1. One is with no damping material, the other with the first half of the line damped with 1 pound per cubic foot of fiber.

[richard t]

Re: "Transmission Line" Sub experiment?

I am pretty sure someone on this forum designed an RS-225 T-line that another member built.

I'll search later if I have time - but I sure think its been done.

Edit - here is the one I was thinking of: http://techtalk.parts-express.com/sh...ed-the-trigger

That was mine and it sounds great. Lots of detail. More than you would expect in a sub and very dynamic and it uses the RS225-8. I believe I posted some pics on that thread.

[richard t]

Re: "Transmission Line" Sub experiment?

What, specifically, are you hoping to achieve, like F3, SPL, box size, etc? For any specific driver there will be a specific system tuning frequency that will be optimum. After that, the volume in the line will determine F3 and the driver's excursion capabilities will determine how loud. I have actual T/S measurements for the RS225-8 and can do a TL model fairly quickly for you. Oh, it would most likely be tapered and appropriately stuffed to eliminate those "unpleasant standing waves", as well as folded to fit into a reasonably sized and shaped box. That said and in agreement with Pete, I don't think a TL offers any particular advantage for subwoofer duties, other than likely having a much lower air velocity in its terminus compared to a vented box.
Paul

I have to disagree a little with you Paul. Seems silly but I know you've never used a TL sub you've designed. It does make a difference. Prior to building yours, I was using a nice 10 inch Wharfdale that I was very happy with for years and there was a definite improvement over that with the TLs.