# Tapered Quarter Wave Tube - TQWT. Anyone built one here?



## HionHiFi (Feb 18, 2007)

I built a pair of these speakers in the past and was wondering why I don't see more of them around. 

They were easy to build, the sound was decent with the driver I used which was a low end Radio Shack RS 40-1354. Using something like a Lowther, or Fostex, the sound can be very nice. 


Any thoughts? 

Here's a bit of info on the TQWT, or a ML TQWT, ML= Mass Loaded. 

First described by Paul Voigt in 1930, TQWTs allow a good quality-to-price ratio. They are also easy to build.

Similar to transmission lines, the TQWT is different by its shape, a kind of horn is used as back load but the driver is not placed at the beginning of the cone as usual but on its side.

The port is used to adjust the rear flow according to the driver type, internal damping and desired response.

The resonance frequency depends only on the length L of the cone and the driver position is calculated by the formula indicated on the schematic.

During the tune-up, it's a good idea not to close definitely a side of the box to allow an easy modification of the internal damping.

The height of the port should also be adjusted through both measurements and listening sessions.

It's not advisable to select a very low frequency cutoff as a not very refined bass could be obtained.

The TQWT adapts very well to full-band drivers or bass-medium drivers of small dimensions.

The folded horn gives a very practical loudspeaker with a driver positioned at the right height without any support.
(info courtesy of http://www.bonavolta.ch/hobby/en/audio/tqwt.htm)


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## JCD (Apr 20, 2006)

I think you'll find a few single driver system out there. I think the current favorite is a Fostex 108E.

In fact, not that I want you to go elsewhere, but there is a whole website devoted to these types of projects.

JCD


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## drf (Oct 22, 2006)

Personally I am not convinced they are exceptionally better than any other properly designed 2/3 way system. The physics of sound is a very measurable/verifiable science, and thus, if single driver systems offered a significant advantage over multiple driver systems, they then would be the industry standard for studio's, auditioning/screening rooms and other places where exceptional quality is required. Having said that, I also know just how objective sound is and strongly recommend everyone try everthing at least once and keep what you enjoy.


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## dlneubec (Oct 9, 2006)

Here is a 2way ML-TQWT I recently completed (other than the finish). I call them the Duo's since they are convertable between two speaker designs using the same box, but a different set of drivers, baffles, crossovers and ports that can be swapped out. They are a hybrid omnidirectional design with a time aligned tweeter that is in a 1/2" waveguide (per Zaph Audio). You can read more about them at this link.http://htguide.com/forum/showthread.php4?t=29620
The low cost version is called the Duo-T and uses about $150 worth of drivers and crossover parts. The second version is called the Duo-S, uses Scanspeak drivers and has just under $600 in driver costs and crossover parts. Below are some measured frequency responces (gated) of the Duo-S and Duo-T and some photos of the construction.

Duo-S









Duo-T


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## Bill Fitzmaurice (Jun 14, 2008)

intelonetwo said:


>


Technically this design is a bass reflex. Conceptually that's easy to see if you imagine the cabinet 'unfolded', as a pyramidal tower. The long internal pathway can result in a useful quarter-wave resonance, but it still operates primarily as a reflex box, which an impedance chart would make clear.


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## dlneubec (Oct 9, 2006)

If it would be helpful, here is the measured impedance plot from the Duo-S project mentioned above. this is the left speaker plotted over the right speaker.


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## HionHiFi (Feb 18, 2007)

dlneubec, 
Nice design. Very nice.

I've been to the fullrange driver website. Actually when I built my my set, this an other website are the sites I used for research. Very good info on the topic.


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## Bill Fitzmaurice (Jun 14, 2008)

dlneubec said:


> If it would be helpful, here is the measured impedance plot from the Duo-S project mentioned above. this is the left speaker plotted over the right speaker.


A classic bass reflex chart, with the fb at 32Hz.


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