Dual Woofer TL?

[Phear]

Hi all!
This is my first post here.

I´m thinking of building a pair of folded TL subs with dual Vifa XT18W009 (www.d-s-t.com/vifa/index.htm) units. If I want to use 2 woofers i a TL, do I simply take the woofer´s conearea x2 when determining the area of the TL?
The advantage of using 2 woofer TL is that it´s possible to use a bit lower tuningfreq. than the 1 woofer TL. Have I got it right?

Any other advantages in using dual woofers?
Any disadvantages?


regards/Per

[phase_accurate]

By clever placement you can dampen some higher resonant frequencies that are responsible for the irregular FR in the upper-bass/lower-midrange of some TLs.
I'm not sure anymore whether it was at one fith and one third of the linelength. If there is noone else on the forum (Dave ?) who can supply details i could dig the info out but this might take some time.

Regards

Charles

[Phear]

Hi Charles.

Interesting. It would be great if you could find the info. I'm in no hurry, though - Haven´t bought the drivers yet.

I found this at http://www.seas.no/thor.htm

The two W18E001 woofers excite the line at slightly different points,
smoothing the response and increasing the range of bass output. The
transmission line produces 4 dB of bass lift from 20Hz to 110HZ, with
less than 1 dB of ripple. The -3dB point is 45Hz, with roll off of 12dB per
octave below 45Hz. Usable in-room bass response extends well into the
low 30Hz range.

/Per

[peterr]

Look here:http://www.quarter-wave.com/General/..._Articles.html
the rest of this site is very interesting also. You should look on the website of planet10 as well. He is the TL guru here.http://www.t-linespeakers.org/index.html

[Andypairo]

take a look at this site : www.theloudspeakerkit.com
They have a project (actually a kit) named TL6 that uses 2 P17WJ from Vifa in a TL.

Since I have 4 of these woofers I wanted to build one, but I have no drawing sheets, so I should make a sort of reverse-engineering from the photos in the mounting instructions.

Since they sell a kit I don't think they will be willing to give anyone drawings for the enclosure (unless you purchase the kit without cabinet of course)... that's a pity.

Reverse-engineering can give approximated measures, but to be true I don't know how much TL systems are sensitive to slight changes in the cabinet.

Does anybody know?

Cheers

Andrea

[BAM]

I have seen some of the newer Bose acoustimass modules that use long-excursion 5.25" woofers (I actually looked at them while they were running and they were VERY high excursion woofers) and they look like they use transmission lines. How does Bose get away with using transmission lines that are much smaller than the woofer's surface area?

(The results aren't bad, either. They're still Acoustimass modules and they're still Bose, but they are a major step up from the older 8th-order Bandpass modules in the area of impact and deeper response that seems like it goes down to about 40 Hz. Much better than the old modules' measured 62 Hz.)

[phase_accurate]

I found the article again. It was in the German magazine Klang & Ton issue #2 2002.

The drivers are in fact placed at one third and at one fith of the linelength.

Because they can be quite far apart from each other, the principle is best suited for three-way systems.

I am not sure wheter it would work fine with a 2.5 way as well.

Even if you don't place them in the aforementioned positions, two woofers can offer the possibility to drive the line more evenly than one driver. I.e. the resonance will be weaker but wider.

One company selling multi-woofer TLs is the German manufacturer Newtronics: www.newtronics.de

Something special about this company is the fact that they offer kits as well. One is presented in the current issue of Klang & Ton. It uses two slightly different 18 cm Vifa woofers, one of which has a "wooden" cone.

Regards

Charles

[Andypairo]

How about posting the article?
of course, if it is in a readable language for everyone (English)

Cheers

Andrea

[navin]

I am trying to design a variation of the 2 woofer TL.

my idea is a 4 in line full range driver system using 4 3" 871S drviers available at CSS. CSS sells them in boxes of 20. 20 / 5 (the 5 came from 5.1) and you get 4 drivers per channel.

can any help?

the 4 drivers will be in line (sort of short line source) and will be wired as a 1.5 way (2 drivers full range and 2 drivers providing bass reinforcement / baffle step compensation only.

many moons ago I had read an article in Speaker Builder (1985/86/87) where someone has built a 4 in line TL using 2 coax drivers and 2 drivers that had their coax tweeters missing (WFFW). i dont know if anyof you have access to this article maybe it wil provide a few clues on how I can build my system.

[planet10]

Two bass drivers in a TL can be made to work fine -- of course i suggesy push-push loading them

I am currently working on a design using Vifa P17s OEM units for PSB. (i have a box of 20 and need to make some space). After considering many options i have decided on a push-push MTM in an exolinear alphaTL*. I haven't decided what tweeter to use -- i have an aluminum dome Vifa, a Stryke magnetostat ribbon, and some DynaAudio D21(?).

* i'll be able to say more on the alphaTL after Rick's article appears in audioXpress. What it is a simple algorithm for determining optimum TL size for a tightly defined TL configuration.

Keep in mind that the old rule-of-thumb about basing the TLs x-section on the driver cone area has proven to be complete myth. X-section is mostly based on the Vas of the driver (and an entire design can be run off this, Qt, and Fs, plus some design decisions).

I would highly recommend getting into Martin's TL articles at his quarterwave.com site and a visit to my site will give you some design ideas & some historical background.

As Rick Shultz (exolinear) churns out more of his cookie cutter design algorithms (he is already working on the next one), doing a TL will become as easy as making a sealed box.

dave