Question for TL-wizzards

[Empee]

Hello all !

I got a pair of 12" drivers with these specs:

Fs 30 Hz
Re 7.7 ohm
Qms 4.27
Qes 0.96
Qts 0.78
Vas 181 ltr.
Sd 0.049 m2
Mms 52 gr

Any care to help me on the dimentions for a (mass-loaded) TL ?

Tuned (very) low, as I intent to make a four-way
(sort-of like the Rogers Monitor / Pro 9 / Cambridge Audio R50)


Cheers, and thanks in advance !

Empee

[bjorno]

Hi,
Go for an Aperiodic ML-TL, tuned at 12-13 Hz :Internal dimensions: L48"xW14"xD16.5"
Port=4"dia: L=12", port stuffed with 22 (g) and the entire enclosure with 2.2 kg wool.
Driver at 32” and port at 42" from top, internal dimensions.
Se picture: 1(1)

b

1(1)

[qwad]

l agree with bjorno, with those T/S parameters there is no way you can build a pro 9 tl or anything like a trad tl cheers T.C.

[Empee]

Hi !

Thank you both, for your calculation and comment.

But regarding the outcome.... waaah !!
a cab (essentially a reflex, as I see it) of 181 liter is BIG, man !!

I thought TL's could have a high Qts

What would happen if one was to use such a high Qts in a TL,
boominess or just the other way around, lean bass ?

Cheers !

Empee

[qwad]

Sorry qts around 0.27 to 033 is more suitable , l believe VIFA peerless and scanspek have sutable 12"drivers in their catalogue
cheers T.C.

[Empee]

Hi T.C. !


that's strange, on the t-linespeakers.org there is an article called "Martin J King for Dummies" in wich he states;

Original text by MJK
Qts -- I use a Qts value of 0.35 to distinguish between high and low Qts. You might have another definition. Drivers with a high Qts perform better than driver with low Qts in a quarter wave design. On the other hand, the lower Qts driver seems to require less volume, thereby resulting in a smaller enclosure. Low Qts drivers have a roll off that starts earlier than high Qts drivers, and drivers with a moderate or high Qts will often result in the best low end performance. But this is also a matter of taste and preferences. "Good sound" is defined by you only. The output from the opening is broader with high Qts drivers, compared to low Qts drivers that have a narrower output from the opening. Drivers with a Qts lower than 0.30 seem to be difficult to control in a TL.

also in this text it says;

choose a speaker/subwoofer with a Qts between 0.4 – 0.6, and an fs of reasonable depth.

Is there such a thing as a Qtc for transmissionlines as it is with sealed cabinets ?


Cheers,

Empee


Cheers,

Empee

[GM]

Originally posted by Empee

a cab (essentially a reflex, as I see it) of 181 liter is BIG, man !!

I thought TL's could have a high Qts

What would happen if one was to use such a high Qts in a TL,
boominess or just the other way around, lean bass ?

Cheers !

Empee

TLs work extremely well with high Q drivers, yielding a lower f3 for a given Fp, but when you have both a high Q and high Vas they require a lot of Vb. Indeed, my default alignment for this high a Q driver is a max flat impedance TL (38.46 Hz Fp) which weighs in at a plump 292 L, though it does have enough more gain to probably not need any BSC if otherwise required and is much better damped than a 181 L MLTL/whatever. Cutting the Vb in half to 146 L raises F3 from 40 to 50 Hz, so no joy there unless it's an acceptable trade-off.

Bottom line, for a given Qts, F3, the lower Vas is, the smaller the TL, etc., Vb is, ditto Vas Vs Qts, though F3 rises at a rapid rate as Vb shrinks.

GM

[GM]

Originally posted by Empee

Is there such a thing as a Qtc for transmissionlines as it is with sealed cabinets ?

Other than the max flat impedance I referenced, I don't recall anything specific, though you can match a TL's roll off slope to known Qtc values down to where it finally rolls off at a vented alignment's 4th order. IOW, If I tune your driver to Fs with an acoustically tiny CSA = Sd and stuff it heavily it will theoretically have a critically damped 0.5 Qtc down to Fs where it will start transitioning to 4th order somewhere below 10 Hz along with a nominally flat acoustic and impedance phase. This is 'ideal' compression horn performance, i.e. this is as good as it gets as far as it goes. The trade-off is an unacceptably high ~100 Hz F3 due to its tiny acoustic size plus stuffing being used to mass load (damp) the driver into a much lower effective Fs, Qts.

GM

[qwad]

OK , have it your way, l was thinking more the classic tl ie; imf, tdl and pro 9 tl etc, cant say l've paid any attention to MJK's work along these lines[ no pun intended] perhaps he might chip in as l know he frequents DIY AUDIO from time to time......... or else download his design program and start with a fresh sheet of paper rather than try and shoehorn your diver into an existg enclosure design'
cheers T.C,

[Empee]

Hey T.C. & G.M. !


Thank you very much for your input, and no, I'm not trying to shoehorn my driver into something that won't work. That's the whole reaseon for me asking your knowledge !

As G.M. stated, - and G.M.; thank you very much for that ! - it's the high Vas that does it (or doesn't do it, actually)

I see now a classic TL won't work, and thinking WAF, the max-flat variation won't either, so I still don't know what to do with this
driver.

However, I still do not understand how this thing could have worked so well in the original 80 ltr. closed cabinet Philips orginally put this driver in.

check this speakercabinet