APEX TQWT

Thanks Guys. I know that the thickness is 15( i posted it much time ago),
So, TQWT has thin end profile compared to thick beginning of Line. How about driver position, I've heard about 1/3 of total lenght, is that true? Volume of cabinet is worth attention or only lenght and profile compared to Sd?
 
adamkaktus said:
So, TQWT has thin end profile compared to thick beginning of Line.
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Traditionally speaking yes, but as I say, only a handful of people (like GM & myself) describe them that way. These days, most people use the term it to describe the opposite, i.e. a pipe expanding toward the terminus. It doesn't really matter though -it's just a name.

How about driver position, I've heard about 1/3 of total lenght, is that true?
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That's sometimes used, but location of the driver along the line ultimately depends on the design & your objectives, & ideally the CSA of the line as well as it's acoustical length, so there's no one-size-fits-all answer unfortunately. See Martin's alignment tables for some more: http://www.quarter-wave.com/TLs/Alignment_Tables.pdf (& an Excel file derived from these: http://www.quarter-wave.com/TLs/Alignment_Tables_Calculator_3_3_09.xls )

Volume of cabinet is worth attention...
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Very much so. QW lines are like any other vented alignment in needing to have sufficient volume for your target alignment.

...or only lenght and profile compared to Sd?
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TL cross section has zero functional relationship to Sd. That is part of QW / TL myth that significantly hampered many designs.
 
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thank you, your answers are very helpful. Can you say more about volume of cabinet? Is it nearly the same value like classic bass reflex designs or it is more complex to find it?
 
Scottmoose said:
Traditionally, it was used to describe the opposite, i.e. a pipe that narrows toward the terminus, although very few people use the term in that way these days (GM, myself & presumably the OP here also, but that seems to be about it).
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Although only you & GM use it that way, and have not been able to supply references. In his original patents, Voigt uses the term (or similar) to describe his expanding pipe. That is pretty traditional source.

Modern usage has a TQWT expanding towards the terminus, why confuse the issue?

Technically any taped pipe open at one end is a tapered quarter wave tube no matter what way it tapers.

dave
 
Oh, I'm the master of confusion. 😉 'can't supply what doesn't exist in writing alas. :sad: Or not as far as I know anyway. I gather that's how the old Altec engineers described them when Greg visited. Which is good enough for me, since it makes good sense. If a pipe expands it's a horn, since it has a degree of 1/2 wave behaviour which is not present in an untapered or narrowing pipe.

Re volume, this is a function of the alignment, i.e. you need to have enough to support the response to the desired frequency & avoid over-damping. One of the major problems often encountered with basing line CSA on driver Sd was that you ended up with nothing like sufficient Vb, so the LF output was severely over-damped.
 
While a tapered electrical transmission line [TL] can mean either inverse or expanding, an expanding pipe used for sound transmission has existed since at least biblical times as a horn [or its equivalent if this word hadn't been invented yet], so this only leaves the inverse tapered one to be called something else, making Voigt, MJK, et al that uses TQWT or similar to define a horn seems as misleading as claiming Voigt being the absolute authority on TL designs to my way of thinking, not to mention all the expanding pipe designers over the centuries that chose to use 'horn' to differentiate them from other sound reproduction [cab] alignments.

Even if we continue to use TQWT erroneously to define a horn, some other word needs to be used for clarification to define an inverse tapered one, otherwise we don't know what the person is referring to unless either a picture and/or a sufficient description is included.

GM
 
adamkaktus said:
Can you say more about volume of cabinet? Is it nearly the same value like classic bass reflex designs or it is more complex to find it?
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I used classic 'BR' alignments early on, but found them to be a bit small unless it was the early charts [pre-1960] that assumed a significant amount of added series resistance, though would actually be driven with a low output impedance; ditto with T/S except for when the driver's Qts = < ~0.4, but when I calculated the volume of a long vent that would be required to get an 'ideal' Av = Sd and added it to the cab's......Voila! Enough net Vb to allow a bit of fine tuning and/or allow for the often significant difference between published and measured specs.

I haven't compared it to MJK's Classic TL alignments, though I assume they will be 'pared down to the bone' same as T/S predicts for a simple reflex, i.e. somewhat smaller, so probably should be used for measured specs unless you do want some flexibility for fine tuning and/or trying other drivers.

GM
 
Okey, so let's say- i don't want to build typical horn ( SPL is not the main target), I would like to achieve extended bass response. So if i understand it right it should be TQWT with narrowing end. As you mentioned Volume of cabinet should be a bit higher than typical BR cabinet. This volume is calculated from axis of driver to closed end of cabinet, am i right?
 
It's just the total internal volume of the box, minus that taken up by the driver internal panels etc.

A narrowing pipe will allow a lower tuning for a given physical length. Use Martin's tables or the Excel file I linked to to determine the required length for a given taper ratio.

You will achieve an extended bass response if the driver is capable of it. If it isn't, you will not -QW / TL cabinets can't get blood out of a stone. If you tell us what driver it is you're looking at + the spec., we can help.
 
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Unless the driver Qts is very low/high, try a MLTL first. That's a straight pipe, no taper. Very low Q drivers tend to work better in an expanding TL (a horn), very high Q drivers tend to work better in a contracting TL -- narrow at the port. But you really must model your driver/cabinet to get optimum results.

Bob
 
Those are explained in the Alignment Table pdf. You don't need to worry about them; Dz is a resistance function, Dr a peak shape function.

Driver looks decent; not too sure about the bobble around 1.5KHz -an impedance plot would be revealing. Be that as it may, I'd concur with Bob about an MLTL likely being a better bet, which you can't calculate from that file or the tables. Will have a look when I have time later.
 
Thank you. I've never heard this type of cabinet, so i have to read more. By now i heard TQWT with oval philips and I was shocked... by now i'm looking for something on small driver which doesn't need subwoofer, only 2CH stereo. So i decided to order this speaker. (this company also manufactures HF driver with ceramic cone which can work on very low frequencies- ideally for this application)

I see , nearly the same but ending like bass reflex, i think more complicated 🙂 to calculate, then to build but if worth trying-ok.
 
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adamkaktus said:
what do you think about this:
http://www.diyaudio.com/forums/full-range/231951-accidental-mltl-technique.html

isn't it good idea to make good sounding Bass Reflex cabinet(and add about 0,5-1 Liters for further improvements), then adopt it to work as TQWT? in the worst case we achieve not bad BR.
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AMLTL works best with moderate Qts drivers (above 0.35). It won't let you make a TQWT though - for that you need a model to optimize. Although as you say, the worst you may have is a bass reflex - but you will have resonances due to the length and damping or stuffing will be needed in general.
 
Ok, so i have to wait for ordered drivers. Maybe it's good to wait for help from scottmoose, if he gonna have free time for me. I have another question to ML TL. What is better- to tune BR lower than Pipe or better to build TL for lower Frequency and install BR to work little higher than TL?
 
A max-flat MLTL would be 44.75in long, CSA of 59.5in^2. Driver centre down 16in from internal top. 3in diameter x 5.625in long vent, centre 4.25in up from internal base. Line all internal faces with 1in acoustic fiberglass, rockwool, BAF wadding or similar & adjust tuning via vent length to suit. Fb = 34Hz.

A tapered pipe (narrowing to the terminus) of similar tuning & a 10:1 taper ratio would be 50in long, throat CSA 74.375in^2, terminus CSA 7.4375in^2, driver centre 10in down from internal top. Line the first half, all internal faces, per the above.
 
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Thank you Scottmooser. Which of these two would you prefer? There's no need to build ml-TQWT but only ML-TL? I have to check few arrangement of line in cabinet and try to pack it in not too big box.Another question, Narrowing should by conical or can i fold it 3-4 times to achieve needed CSA?
 
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