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?
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.
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.
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.
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.
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.
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.
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
angled corner(s) volume
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
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
But the frequencies of interest don’t see the bend. The ones that do, you want to lose.
dave
In the full range case, yup... And one of the reasons I hesitated in replying, as this is in the FR forum.
I started wondering about possible benefits to woofers then.
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).
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.
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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