Cabasse Mid/Bass for TL?

[Mike C]

I've been researching a possible small TL design, to use 6.5 or 7 inch driver in a
medium size box (say 40ins high, 8.5ins wide max), for use with a 300B SET amp.
Efficiency of 90dB is desired. High quality is essential (to try to improve on my
current SEAS based IPL S3TL).

The Cabasse 17M18LB looks possible, from the small amount of data that I have on it:
90dB; Fo 53Hz; and Qts 0.45
It appears to be a high quality unit.

I've searched in several places but found nothing more, hence these questions.

. are these drivers available, if so where?
. does anyone have FR plots?
. would they work well in a TL?

Otherwise, the Focal 6W4311 remains top of the list so far ....

[GM]

Greets!

Well, the obvious place to find tech info is at a manufacturer's website, which Google quickly provided, so check with them to find out from whom/where to purchase them: http://www.cabasse.com/english/haut_...rs/17M18LB.php

Yes, any open back driver will 'work' in a TL, but the app determines which driver's specs are 'best' for it. Since 300B amps usually have a high output impedance, this driver appears at a glance to be well suited for a TL as long as it's not jammed into a corner. A potential deal breaker is the low effective half space efficiency that can be as low as ~88.8dB/W/m (assumes 3 ohms).

Even though I didn't see a FR plot, its very low Le implies a wide, smooth FR up its break-up modes, but there's nothing in the specs to indicate how bad they may be or whether or not it has a rising response above its effective mass corner (~163 Hz assuming 3 ohms) so depending on the XO point/slope, a contour network may be required to tame it.

WRT size, for an end loaded straight pipe to be 40" long means a ~65.5Hz Fp with a rather 'fat' 169.5"^2 CSA assuming fiberglass insulation stuffing is used, so to keep it narrow will require it to be deep. FYI, 53 Hz Fp = 50.4" long/CSA = 130.06"^2. If you shrink the CSA then LF gain will suffer ~proportionately. If you shorten it but want to tune it to Fs, then it will need to be reverse tapered.

Comparing sims, there's precious little difference beyond the longer one requiring a lower stuffing density (1.25 Vs 1.5 lbs/ft^3), so any audible differences would be subtle at best.

To take advantage of the gains available with this combo requires a longer pipe (ML-TL) with the driver offset: Fp = 33.5 Hz, 65.42" long/107.515"^2 CSA, 5" diameter x 0.75" long vent near/at the bottom with the driver down ~22.875" from top, which puts it about right for adding the mid/HF below it without them being too low once a base is added.

Below ~75 Hz, this pipe has some serious gain over the other two, ~ +3 dB/60 Hz, ~ +5 dB/50 Hz, ~ +6 dB/40 Hz, etc., though it ultimately rolls off at ~ 24 dB/octave, but fine tuning with stuffing will smooth it out enough that I doubt there would be any audible difference WRT impulse response.

Anyway, not being familiar with your current TL I don't have a clue if any of these are an SQ improvement or not, but if the published specs are ~accurate then none of these will be slouches in the BW controlled by the cab, especially the ML-TL.

(Note that all dims are inside.)

GM

[Mike C]

Many thanks; I've studied the manufacturers web site but I'll ask them myself about
this unit and suppliers.

Re the TL design; it's only the box that can't easily be more than 40inches; I intend
to use a folded pipe and had already come up with an initial starting point of about
60ins (for simulation and analysis) for the Focal 6W4311. This will fit OK into the
package; in fact, the present speaker line is about 65ins.

The present speaker has the bass unit at the top of the baffle, with a line going
across the top, down the back, up the front and venting to the sides level with
the tweeter which is close below the bass driver. 6.5in SEAS driver. The initial
area behind the driver is 2.3x cone area; the top of the line is 1.3x cone; end of
line is 0.7x cone; and total vent area is 0.6x cone. I'll put all this into Martin's
simulation to see where I've gone wrong
Actually, the sound is pretty good; I like the bass a lot. A better design of line may
gain some bass quality but mainly I hope to get improvements from better
quality drive units and a touch more efficiency.

Ta for the info. It's all a great learning process! So far, this is showing me how
little I know.
But with my engineering background, analytical skills and willingness to have a
go (simulate, build, measure, revise) I'll learn. With help from you folks.

Regards
Mike