Transmission line corners, square, round or chamfered?

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smart51

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Joined 2017
#1
I'm considering building some transmission line speakers and have been reading up about them. One thing seems to be rarely discussed. Where the line is folded, some leave the corners square, others put an angled plate in the corners and some make the corners round. What difference does the treatment of the internal corners make?
 
#3
For the most part, it doesn't matter much. There are some slight differences, but they're generally higher in frequency than is pertinent to the line, and should be effectively non-issues if it's a stuffed line.

Unless the TLs are HUGE. If they're 10 ft^3 enclosures, you might have to put in "reflector" plates. Angled would be fine in those, round isn't worth the effort.
 
#4
My first were square. Later went to the reflector plates. Did not make any audible difference.
But if was building again I would cut and install the plates. Always draw out real size and calculate the plate in the center at the expanding radius. It should make a difference. At worst it stiffens the enclosure.
 
#5
Thanks for the replies guys. My thoughts were that if the back wall is parallel to the baffle then a reflected wave will come back through the cone. A 45° reflector will send the wave a bit further down the line. But then if it makes no audible difference, why do it?

Perhaps the best thing is to put one in at the first corner behind the driver. The waves will get more damped as they go through the stuffing so the orther corners make less difference anyway.
 
#7
Right, you ideally don't want any eigenmodes reflecting back through the cone, so either have a sufficiently large > 12 deg angle deflector for the intended passband or add damping to quell them, which of course will reduce passband efficiency.

GM
 
#8
I've finished the speakers and wow! I don't think I've ever heard bass as deep. I had the same drivers in a reflex cabinet and the transmission lines are much better. I keep sneeking up to my listening room just to have another go with them.
 
#9
If one inserts a plate into the corner then ensure the duct area as it passes the plate is NOT LESS than the area of the duct.
Either side of the plate, the duct area will be bigger than the straight duct leading upto that point.
Don't form a constriction.
 
#10
I've been mooting potential benefits of angle plates or corner treatments.
I may be getting it all wrong though. 🙂

It seems to me that an angle plate will act to diffuse any standing wave action between parallel walls. Or at least smear it over more frequencies.
 
#12
Jerms said:
It seems to me that an angle plate will act to diffuse any standing wave action between parallel walls. Or at least smear it over more frequencies.
Click to expand...

The way I look at it, the plate area defines its WL deflection BW, so as already noted, it takes really large ones to affect a typical TL's/horn's BW, ergo normally only a big deal with a folded FLH.

Factor in that the 'sharp' corners act as an acoustic low pass filter, better to just add damping in them if you're concerned about any high frequency parallel wall reflections.

For long WLs, the bends should be <1/4 WL of its passband, so a stepped spiral folding or functional equivalent is desirable.

GM
 
#13
angled corner(s) volume

Jerms said:
I've been mooting potential benefits of angle plates or corner treatments.I may be getting it all wrong though. ... It seems to me that an angle plate will act to diffuse any standing wave action between parallel walls. Or at least smear it over more frequencies.
Click to expand...

Hi there J: Most computer calculation programs do not account for angled corners. Therefore, adding this piece of wood to a corner(s) will reduce the volume (Vb) of the line. So hand calculate the volume reduction of all the angled corners you have added to the line and find a way to return the line Vb to the calculation programs predicted Vb. For multiple fold TLs this could be significant. ...regards, Michael
 
#16
Eh? It doesn't make any difference if it's a wideband driver or a woofer; if you're using it to prop up the LF a QW/TL variation is like any other back load, i.e. only usable over a very restricted BW above which you want the output attenuated. All the frequencies that would be affected by internal strike plates are unwanted so there's largely no point, other than if necessary near the driver to avoid early reflections to the cone (a separate issue).
 
#17
Scottmoose said:
Eh? It doesn't make any difference if it's a wideband driver or a woofer; if you're using it to prop up the LF a QW/TL variation is like any other back load, i.e. only usable over a very restricted BW above which you want the output attenuated. All the frequencies that would be affected by internal strike plates are unwanted so there's largely no point, other than if necessary near the driver to avoid early reflections to the cone (a separate issue).
Click to expand...

Assuming an LPF on a woofer/sub, I wondered if plates could help reduce peaks in standing waves within the cab.

Maybe it's a thought waiting for a problem that hasn't happened yet. 😀
 
#18
As noted, in the [narrow] LF operating passband, the wavelengths are too long to give a trajectory copulation. The only frequencies that are affected are the shorter higher frequency ones, which you don't want & are deliberately damping out because they're of no use to you anyway unless you happen to enjoy the results of GD. 😉
 
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