TL Reasonant Freq

[mashypie]

Hello,

At the risk of sounding a bit dumb...

What is the reasonant freq of a TL pipe?

Is it the first time the output is out of phase with the driver (assuming you are doing a freq sweep upwards)

Or is it when the output of the pipe is greater than the output of the cone?

And the cones Fs, is that when it is moving at its most, or at its least?

[planet10]

What is the reasonant freq of a TL pipe?

The lowest, primary resonance. Approx 4L is a straight pipe (ignoring end correction)

And the cones Fs, is that when it is moving at its most, or at its least?

At resonance cone motion should be reduced just as in a bass reflex.

dave

[mashypie]

But how do I know when this reasonance is?

Say I've a 83cm long tube (inc end correction) which is supposed to be a 100Hz tube, but I dont think it reasonates then at all, there are peaks at 80-90ish and a really bad one at 140, I'm guessing the peaks around 80-90 are going to be the true reasonance of the pipe?

[Arty]

Quarter Wavelength Loudspeaker Design
happy building.

[planet10]

Originally Posted by mashypie

there are peaks at 80-90ish and a really bad one at 140, I'm guessing the peaks around 80-90 are going to be the true reasonance of the pipe?

Are you getting those numbers from measuring a speaker in a room?

dave

[mashypie]

I am

[Dave Jones]

The garden variety quarter wave pipe naturally reinforces some frequencies, particularly one around 4x the length of the pipe, and it nulls-out other frequencies. That is not resonance, but rather addition of the front and back waves. Stuffing is used to suppress the higher frequency comb filtering. Some designs are quite resonant however. The "mass loaded" tuned quarter wave pipe combines the effects of bass reflex (resonance) with pipe effects.

N.b. a bass reflex speaker has two resonant peaks, neither of which is the maximum of the response curve.

[mashypie]

Originally Posted by Dave Jones

The garden variety quarter wave pipe naturally reinforces some frequencies, particularly one around 4x the length of the pipe, and it nulls-out other frequencies. That is not resonance, but rather addition of the front and back waves. Stuffing is used to suppress the higher frequency comb filtering. Some designs are quite resonant however. The "mass loaded" tuned quarter wave pipe combines the effects of bass reflex (resonance) with pipe effects.

It does resonate though, according to what I've read, it has a fundamental frequency, and reasonates at odd multiples thereafter

But what I'm getting at is that the fundamental freq of the pipe can be different to that of its length, say if it is tapered or uses a coupling chamber, or to quote Augsberger, 'this is nomially a 109Hz pipe but it actually resonates at 100Hz'

But I dont know why that would be, if its just due to end correction, or how you would go about finding out what its actual fundamental was

And I'm well aware that MJK has tapered line tables on there but I'm experimenting with a chambered TL at the moment and I think it resonates lower than what I've designed it for but I dont know how to find out.....

[Dave Jones]

Originally Posted by mashypie

But how do I know when this reasonance is?

Say I've a 83cm long tube (inc end correction) which is supposed to be a 100Hz tube, but I dont think it reasonates then at all, there are peaks at 80-90ish and a really bad one at 140, I'm guessing the peaks around 80-90 are going to be the true reasonance of the pipe?

Do not confuse SPL output peaks with resonance. Those are two entirely different things. A straight pipe has infinitely many resonant peaks, none of them at maximum SPL, and the impedance converges to a maximum as the frequency goes to zero. You can pretty much ignore resonance for regular pipes.

The peak at 140Hz could be due to floor bounce.

[Dave Jones]

Originally Posted by mashypie

It does resonate though, according to what I've read, it has a fundamental frequency, and reasonates at odd multiples thereafter

But what I'm getting at is that the fundamental freq of the pipe can be different to that of its length, say if it is tapered or uses a coupling chamber, or to quote Augsberger, 'this is nomially a 109Hz pipe but it actually resonates at 100Hz'

But I dont know why that would be, if its just due to end correction, or how you would go about finding out what its actual fundamental was

And I'm well aware that MJK has tapered line tables on there but I'm experimenting with a chambered TL at the moment and I think it resonates lower than what I've designed it for but I dont know how to find out.....

What you are describing is comb-filtering, not resonance. Resonance does not correspond to output peaks.