1/4 wave enclosure question.

[EEatKSU]

I've got a basic idea of how a quarter wave enclosure works and I've got a simple question on one aspect of it.

*Non tapered, simple 1/4 wave length 'tube' enclosure*

How does the cross sectional area -assuming a square or circle cross section- affect the amplitude of the wave being produced by the speaker? Is it best to have a height/diameter equal to that of the speaker cone diameter? Does it matter if it is larger or smaller, how exactly does this work?

I've been reading some on Martin King's site and if I missed something and you could link me to it I'd be happy to go back and re-read it.

Thanks

-Ryan

[Bjohannesen]

Hi Ryan, have you looked at my notes ".. for DUMMIES" on
http://www.t-linespeakers.org/

About volume (cross section). As a general rule, this should be bigger than 2 times Sd, maybe up to 4 times Sd. I normally use 3 times Sd as a starting point.

Use Martin J. Kings excellent software to learn more about TL/Quarter wave design.

Hi from Bjorn

[bjorno]

*Non tapered, simple 1/4 wavelength 'tube' enclosure*…..

This implies a straight tube, with circular or square cross-section, and obvious no stuffing at all.

As a general rule, this should be bigger than 2 times Sd…..

No general thumb rule applies here especially not for the obviously given non-stuffed straight QWT where the driver acoustically only is intentional controlled at and around the tube quarter wavelength.

Look at the ` MJK ` simulations using an arbitrarily chosen driver like the 3“ driver Aura NS3-184-8E with the following T/S parameters:

fd = 125 Hz: Vad = 1.22 liter: Re = 6.7 Ohm: Lvc= 3mH: Qmd = 5.8482: Qed= 0.772: Qtd = 0.682: Bl= 4.48 newton/amp: Sd= 27.86 cm2: in a pipe with length L= 27.0866 in = 0.688m.

The quarter wavelength (no stuffing) will be about 344/ 4 x 125 = 0.688 m.

Test with 3 tubes varying the cross section area only (0.5:about1: 2), one with (3” x 3”) / 2 square area, one with 3” x 3” area and last with an (3” x 3”) x 2 where the area 3”x 3” is very close to the driver Sd area. See the pictures.

For this particular driver the conclusions are: Best smoothest LF performance is achieved with the tube: (3” x 3”) / 2 labelled with an * in the pictures.

Who wants peaky performance from a QWT in the upper bass area, lower midrange area as to start with?

…Does it matter if it is larger or smaller, how exactly does this work?…

Only two cents worth of explanation:

Best control of the driver can be seen in (a) at the QW frequency = 125 Hz and in (h) giving the smoothest system FR in (d) and (m).

The driver fd gives the tube QWT length, the Vad value together with the CSA times tube length = V, gives indirect the driver slope in (f) depending on the Qt = Qts x sqrt (1 + Vad/V) where also the driver at fd can be seen excursion suppressed (damped SPL at fd).

The peaky FR response for this driver above the middle midrange (300+(Hz)) can only be lowered by inserting damping materials into the volume but this converts the QWT to a different animal (and not asked for?) best covered and explained by MJK.

b

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