Approaching to TQWT

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Hornrsp
Leonard Audio TL simulator
AkAbAk
AJ Horn

All can handle various types of tapered pipes. Although I'm not sure why a TQWT is 'wonderful'. It's just a particular type of cabinet load (a parabolic horn, assuming you're referring to a pipe with parallel sides expanding toward the terminus), with its own balances of advantages and disadvantages.
 
TQWT in my opinion may be wonderful because nothing else until now has been able to make sound a 6.5 inches paper cone like I've listened, one of the finest, rock solid, dry but extended bass response ever heard. Certainly other TQWT I've listened was boomy or anything else but at least one TQWT was the best two way ever listened so I've decided to study about it.
Thanks for the suggestion about simulators, but any theorical well made treatment about TQWT?
 
TQWT in my opinion may be wonderful because nothing else until now has been able to make sound a 6.5 inches paper cone like I've listened, one of the finest, rock solid, dry but extended bass response ever heard. Certainly other TQWT I've listened was boomy or anything else but at least one TQWT was the best two way ever listened so I've decided to study about it.
Thanks for the suggestion about simulators, but any theorical well made treatment about TQWT?

Ottima scelta :) anche io sono appassionato di linee di trasmissione... C'era un simulatore ottimo stilato da bullock e white... Però hanno tolto dalla rete il link...
Trattati sulle linee non ne ho trovati molti... Adesso nemmeno ricordo, però sono vecchi studi con vecchie concezioni che hanno poco a che fare con l'aufiofilia...
Quello che puo essere riciclato da questi studi è che è necessario disaccoppiare il woofer con un volume di carico prima della linea (funziona da passabasso) anche se rende la linea meno efficiente, e usare lana a fibra lunga, per smorzare i picchi di risonanza che si generano a ogni raddoppio di ottava...
E di mantenere il condotto a sezione costante...

La cosa migliore è simulare progettare e misurare...
Che altoparlante hai in mente di adoperare?
 
English or a translation to accompany would be appreciated -note diyAudio's rule 10.

For the rest, since you don't say what 6.5in paper cone driver, nor the cabinet in which it was mounted, it's almost impossible to help. What you describe as a TQWT will almost certainly be a tapped parabolic horn, which may or may not be mass-loaded. Beyond that, since there are an infinite number of differing design methods / target objectives for such an enclosure, it's not possible to point you in the direction of the specific typology you wish to employ & the appropriate design approach. As an absolute minimum we need to know what the driver was, and what the cabinet was. As a start:

http://www.quarter-wave.com/TLs/TL_Anatomy.pdf
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf (note: Martin's goal with these alignment tables is a TL rather than necessarily an especially resonant line. It assumes a uniform stuffing density of 0.5lbs ft^3 of Dacron hollow-fill throughout the box, and that the pipe is tuned to Fs)
OrdinaThor_Loudspeakers_TQWT - Tapered Quarter Wave Tube alias Voight pipe - fullrange speakers, horn, high efficiency, tqwt, multiple arrays, general audio topics>
Resonances of open air columns

If the box you refer to was a type calculated purely off driver Fs and Sd, then it may not (probably will not) be possible for you to replicate the results with a different unit using the same calculations, since that approach ignores the fact that line resonant frequency is a function of both axial length & taper, and also all of the driver's requirements for internal volume, which like any other vented box are dominated by system Q and Vas. Hence the reason we need some details to point you in the right direction.
 

GM

Member
Joined 2003
Google translate:

Excellent choice I am also fond of transmission lines ... There was a great simulator drafted by bullock and white ... But they removed from the network link ...
Treaties on I have not found many lines ... Now even I remember, however, are old studies with old ideas that have little to do with the aufiofilia ...
what can be recycled from these studies is that it is necessary to decouple the woofer with a load volume before the line (works by low-pass) even if it makes the line less efficient, and use long fiber wool, to dampen the resonance peaks which are generated in every doubling of eighth ...
and to keep the duct with constant cross section ... the best thing is to design and simulate measure ... That speaker you plan to use?
 
Magic. :)

I remember that old simulator -I think I've got a copy on one of my old HDDs somewhere. IIRC it was limited but didn't work too badly for unstuffed lines -the damping assumptions went a bit pear-shaped if it's the one I'm thinking of as they were going off Bradbury's aerodynamic drag equations. Didn't somebody do a nominal 12Hz TL subwoofer based off that one a few years back?
 
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Dunno, but there are [use to be?] at least one on-line calculator of it. I learned of it from the Altec distributor's engineering group, which viewed such alignments as nothing more than marketing tools to wow the 'great unwashed' [audio wise] same as a certain company did/would do with all these old 'oddball' alignments once the various patents had been dead for awhile.

GM
 
Excuse me for the late, great, thanks! Let's go with order: woofer I've listened and liked/loved has these parameters (I prefer not to say brand and model to respect author's work and intellectual rights..), it was just a 6.5'' woofer that we can call "woofer A":

Qms 1.58 / Qes 0.39 / Qts 0.32
Re 5.9 Ohms / Le 0.67 mH / Bxl 7.2 N/A
Fs 37 Hz / Vas 32 Litres / Mms 14.0 g
Sd 136 cm2 / Xmax 12 mm / Voice Coil Diameter 39 mm / Sensitivity (2,83V, 1m) 88.5 dB

Apparently one of the thousands "normal" drivers available on the market at reasonable price. I was convinced that for a punchy sound driver must have high Qms and high Bxl, I'd never have chosen this driver: I didn't believe my ears listening it in that configuration.. Author didn't know me and told that driver was working in a sort of mix of trapezoidal labirint and bass reflex, didn't tell me anything else, but it was obvious for me that I was listening the best ML TQWT ever heard. Box was approx cm 90x25x40 (HxWxD), port was downfiring against a marble basement about 10 cm far. Impact was really really exciting, bass extended but not boomy, a sense of solidity and strenght never heard before.
My idea is to try to repeat that project or project a similar one using the Peerless 830869 HDS 8'' instead, which I court for long time; I can use a pair of SIPE tweeter (recycled from my old Chario Syntar 2 but still in good conditions) because I like them very much and to set up a simple and cheap but good sounding two way system.
Now I would use the woofer A parameters and try to project a system to see if I'll obtain a box similar to the listened one, and after try to project one ad hoc for the Peerless.
One of the most misunderstood things is the necessity of a high Qts driver as seen somewhere: woofer A doesn't have a high Qts at all and worked well in a about 60-70 litres cabinet..!
However, I'll try to make some simulation this weekend using calculators you suggested, yesterday I just took a look to LeonardAudio TL simulator and I've found it very versatile but I must learn a method to scratch the basic dimensions stating from driver parameters, as Qts more than Sd and Fs.
Another opinion: is a downfiring port really more useful than a normal backfrontfiring one?
Thanks.
 
@ Zedda: what do you intend for "decouple the woofer with a load volume before the line (works by low-pass)", id this similar to a 4th order bandpass with a closed chamber and a TL instead of the rear vented chamber? I don't want to build a subwoofer but a two way system with crosspoint at around 1.500 Hz.
 
Hi All,

FWIW: Comparing Seas ER 18 RNX versus Peerless HDS-P830869.

b:)
 

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Another opinion: is a downfiring port really more useful than a normal backfrontfiring one?

Well, it allows one to mass load the vent or TQWT terminus to a lower Fbox [Fb, Fp].

You've been talking about TQWTs and now a ML-TQWT, so which is it and which way does it taper?

FWIW, I did an inverse tapered TQWT since these drivers are low Qt and both look typical for the genre in ~80 L with a gradual roll-off below each driver's HF corner [~2*Fs/Qts], basically a mid-bass alignment tuned to ~32 Hz.

GM
 
The woofer dont stay directly in the line duct... But in a chamber that reduce the frequency resonance at fs multiple from the output duct... Because with this chamber the air mass in the duct is decoupled from the woofer at high frequency...
From the duct output isn't necessary produce high frequency... But only bass frequency...
For maximaze the low pass effect from the line duct output it's necessary to use a long fiber isolant...

For the woofer parameters:
Yes, the old studies talk about a high qts woofer for transmission line...
But i use only very low qts woofer for my PA project in transmission line
With low qts the bass frequency are perfect, controlled...
 
@ Bjorno: thanks for simulations, but I don't understand in what type of TQWT are made, can you post a scratch please?

@ GM: my question about downfiring vent was if its being in down rather than in backfront position is better.
However, of course, I'd want to understand TQWT but system I've listened I believe was a ML TQWT. Please help me to make clarity: if I don't go wrong a TQWT is a transmission line with narrow in the top and large in the bottom where there is mouth with woofer mounted at 2/3 of total height, in folded variation in which it assumes a normal rectangular lateral shape. After, there's the ML variation (Mass Loaded right?), in which the mouth is substituted by a vent, that brings to the system a lower Fc and better harmonics filtering, called ML TQWT, have I gone right?
If yes, the listened system was a ML TQWT because I felt through hand the circular shape of a vent in the bottom of the cabinet firing against marble as said. So I suppose that inner shape of cabinet was like this:
supposed ML-TQWT.png
Do you intend this for "inverse tapered TQWT since these drivers are low Qt" or other else? If so can you attach a scratch too of what you intend please?

@ Zedda: very very interesting the "prefiltering" camera, if I can call it so! So how that communicates with the line duct, through a vent (should it be similar to a bass reflex with a line duct after the vent)? Or is that simply a camera with an open side communicating with the line duct? (of course, my english is not fine..)

Thanks
 
What you are describing as a TQWT (mass-loaded or otherwise) is technically a Voigt style tapped parabolic horn; he partially described lines like this as tapered quarter-wave pipes in his patent of the 1930s. In GM's parlance (and mine, since I've adopted it, but I suspect we're the only people left in this camp) a TQWT is the opposite, i.e. a pipe that contracts toward the terminus.

Be that as it may, an expanding pipe (aka 'horn') operates over a wider BW than an untapered pipe or one that contracts toward the terminus. Ergo, it can be useful for a low Q driver with a moderately high mass-corner frequency, since they tend to need more output from the enclosure over a wider frequency range. Note system Q rather than necessarily the driver Q alone is significant here -depends on the output impedance of the amplifier and any series R in the circuit.
 
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