MLTL geometry.

[Scottmoose]

I understand the taper spreads/bunches the higher pipe modes. Isn't that a benefit/difference from a straight MLTL?

Possibly in some cases; most MLTLs though have shunted harmonics to sufficiently low a level that it's a non-issue though.

 

[Philosophil]

As in window / ladder braces? Providing you don't go mad, not to such an extent as to have a major impact; the wavelengths are too long to be overly worried by minor discontinuities.

If ladder-like braces were added (I have my own design that I'd like to try) would the external measurements need to be increased to maintain the internal volume and, if so, would the increase have to occur along the width or depth, or could you increase the length instead?

 

[planet10]

TQWT used to refer to a narrowing pipe. I suspect GM and I are the only people who use that definition any more though. Alas.

Yet to see a reference. In Voigt's 1920s, expanding pipe is implied to be TQWP.

dave

 

[planet10]

Would the addition of horizontal braces

Run them vertically. One of the rules of good bracing is that the aspect ratio of the subpanels should be higher than that of the panel they are bracing.

dave

 

[chrisb]

Dave- doesn't the longitudinal orientation "rule" apply mostly to intentionally quarter wave action designs (as discussed herein), and less so to sealed or "standard" BRs?

 

[j.michael droke]

volume change

If ladder-like braces were added (I have my own design that I'd like to try)

would the external measurements need to be increased to maintain the internal volume?

and, if so, would the increase have to occur along the width or depth, or could you increase the length instead?

Hi there P: You can try this out for your design using hornresp (HR), to see how volume change affects response. ...regards, Michael

 

[GM]

Run them vertically. One of the rules of good bracing is that the aspect ratio of the subpanels should be higher than that of the panel they are bracing.

dave

Not to mention that in an open, closed pipe the pressure wave is concentrated down the middle, so normally don't want any horizontal braces acting as flow restrictors unless planned as part of a damping scheme..........

GM

 

[planet10]

Dave- doesn't the longitudinal orientation "rule" apply mostly to intentionally quarter wave action designs (as discussed herein), and less so to sealed or "standard" BRs?

No. It is universally applicable. It just convieniently falls in the direction best for a qw design.

dave

 

[midrange]

Mötley geometry

So, just so that I can nail this:
if the Fs of a drive unit is, say 50 Hz, and the un mass loaded length of the line was "x" to match it, would mass loading the line lower the response of the combined speaker/box to say 45 Hz.
Or would the response stay at 50, and the line would need to be shortened to match 50 Hz.

To put it another way, if an unmass loaded line perfectly matched the driver; would they still be perfectly matched if the line was mass loaded?

 

[Bob Brines]

There is no "perfectly matched" line. There are an infinite number of possible alignments that will be useful for one purpose or another. You seem to be laboring around the old rules of thumb -- set line length to 1/4λ at Fs, them some magic about Sd. When applying modern physics, well, modern two centuries ago, you will see this is nonsense. Have you read Transmission Line Theory?

Bob

 

[Scottmoose]

It depends how you mean 'perfectly matched.' If you mean by that that 'the pipe is tuned to the driver's Fs' then no, since as you will have gathered from the above, mass loading said pipe will lower the box tuning frequency (amongst other things). However; as I mentioned, tuning a box to Fs is not automatically a good idea. In fact, with certain exceptions, it usually isn't.

 

[midrange]

Mltl geometry

Thank you Bob, I have read the Martin King site you mention(I cannot follow a lot of the Maths). In his Classic Transmission Line Enclosure Alignment Tables page 18 he says "Mass Loading of the TL 's open end is not included in these tables". Furthermore I cannot find anywhere where the effect of ML is mentioned.

To go back to my original question I again quote Martin King
"I can see a real advantage for tapered transmission line enclosure geometries if a classic transmission line is to be designed and constructed"
And
"A strong argument can be made for the advantage of tapered transmission line design"
Both of these quotes are from page 33 of Anatomy of a Transmission Line Loudspeaker. (Please note tapered means narrowing towards the open end.)
Are these views only applicable to designs not having ML?

 

[Scottmoose]

Yes.

For mass loading, see Lowther DX Series of Drivers in a ML TL Enclosure and the links at the bottom of the page.

Note that a tapered (i.e. narrowing to the terminus) line is inherently mass-loaded. That's why all other things being equal it's shorter than a straight or expanding line (aka 'a horn') for a given Fb.

 

[Bob Brines]

It'd unfortunate that you can't follow the logic. I can follow the logic, but its been 50 years since my last calculus class. IIRC Martin does not make this point: Mathematically, speakers are a continuum sealed>>bass reflex>>quarter wave>>horn. There is no clear cut line between one and another. Assuming quarter wave pipes, again it is a continuum classic TL>>straight pipe>>positive taper pipe (horn).

Note 1. Be very careful about the names applied to the various tapers. Some will call a classic TL positive taper (probably wrong) and some negative.

Note 2. Many (most) back loaded horns are really quarter wave pipes. I am not a horn expert and that is the last I will say on the subject.

On to mass loading: Mass loading amounts to substituting a slug of air for part of the pipe length. The electrical analog is an inductively loaded quarter wave radio antenna. You have no doubt seen whip antennas with a large coil at the bottom. Same difference. Now, you want to use a classic TL, i.e. larger at the driver than at the vent. You want to do it without mass loading. The problem here is that a classic TL is inherently mass loaded. A classic TL will always be shorter than a straight pipe when tuned to the same frequency. The stronger the taper, the shorter the line. The reason that I usually stay away from negatively tapered lines is that it is much harder to suppress unwanted harmonics in a tapered pipe vs a mass loaded straight pipe.

One final comment on classic TL's. You are required to stuff the pipe until the second impedance hump disappears. But, by doing that, the bass is reduced to just a little worse than an infinite baffle. So, what's the point?

Bob

 

[GM]

FWIW, historically, a BLH's actual horn loading [1/2 WL BW] is limited to the mid-bass, tapering off through the acoustic XO BW [a point few designs seem to correctly address, even some post MJK ones] to create a nominally flat 2pi space down to around 60-80 Hz depending on whether it's strictly for 2pi space or there's enough room gain to allow a higher roll off.

GM

 

[midrange]

Thanks everyone. Very useful link Scotmoose, and thank you Bob for your patience and generosity of time. I have also learnt the lesson that I must be more careful with my words. Believe or not my expressions:matching pipe length to driver, and perfect length of pipe were my efforts NOT to be referring to 1/4wavelength at Fs. I was trying to say you have the length to give the alignment you want. Not good.