Lol, show me a sim of multiple enclosures that is confirmed by a measurement.
Exactly, there has been no empirical confirmation I've seen suggesting whether or not there's a difference. Yet we're parroting the line that there will be no difference with THs. Based on what evidence?
What I'm sure of though is Hornresp is pretty good at simming what happens to the impedance curve when the cabinet is loaded differently, i.e. placed next to a wall (the mouth orthogonal to the wall), something I've also confirmed with measurements. - on a TH that I built. The shift was small, but it was there. As predicted. I'd published the results here some time ago. And if the impedance curve changes, the FR will change too.
So, my bet would lie with the Hornresp sim being correct. Until empirical measurements prove otherwise
.I hear you, but Danley claims this is so, (no extra LF extension) as does his main tech who posts on several forums.
I imagine that THEY have done careful measurements. Since TH is Danley's baby, it would be very odd marketing to claim this if it weren't true.
I can't wrap my head around the physics of it, though. It's kind of counter-intuitive. As you say, you'd think there would be less gain, but at least SOME.
x cableaddictid:
a folded sub, for example the hd15, of how many db improves down in groups of 2 or 4?
I found these simulations, but they are 1.0xpi, so hard to compare ..
15tbx100
I said the 1.0xpi simulation is hard to compare, or at least I do not know how to get the 1.0xpi chart from the 1.0xpi: I have combined a wbin and here are the results:
40hz spl 88.1db -1,0xpi 81.8db -2,0xpi
90hz spl 109.6db -1,0xpi 107,2db -2,0xpi
120hz spl 108 db -1,0xpi 104,5db -2,0xpi
so I do not think it's easy to find a transformation formula ..
x chris:
in pdf do not understand how to assemble, where does the woofer?
a folded sub, for example the hd15, of how many db improves down in groups of 2 or 4?
I found these simulations, but they are 1.0xpi, so hard to compare ..
15tbx100
I said the 1.0xpi simulation is hard to compare, or at least I do not know how to get the 1.0xpi chart from the 1.0xpi: I have combined a wbin and here are the results:
40hz spl 88.1db -1,0xpi 81.8db -2,0xpi
90hz spl 109.6db -1,0xpi 107,2db -2,0xpi
120hz spl 108 db -1,0xpi 104,5db -2,0xpi
so I do not think it's easy to find a transformation formula ..
x chris:
in pdf do not understand how to assemble, where does the woofer?
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Perhaps, but then again look what happened to their measurements of the TH118...
If we had a FLH with the same path length and throat and mouth sizes, I bet no-one would question that the resonance frequency would be lowered if we put two side by side. But then it's claimed that doesn't happen if those FLHs are replaced with THs. Why?
If a horn mouth is too small to efficiently couple to air, total emitted acoustical power increases fourfold (+6 dB) when you add an extra cabinet. 3 dB is because input power doubles. The other 3 dB is because acoustic pressure doubles at the horn mouth due to the other cabinet, which increases radiated sound power for a given air displacement: power output = pressure * volume velocity (ignoring phase between them). This happens at almost all loudspeakers, except for full sized horns.
If the mouth is sufficiently large, total emitted acoustical power only doubles (+3 dB) as the loudspeaker cannot gain efficiency. It's already as efficient as a loudspeaker can be.
Front loaded horn subwoofers usually are made with a too small mouth for low frequencies, while it is sufficiently large for low-midrange frequencies. Emitted power goes up by 6 dB at low and 3 dB at low-midrange frequencies when another cabinet is added. So it goes deeper.
Tapped horn subwoofers typically have too small mouths to efficiently couple to air, even at the upper end of their pass bands, so they gain 6 dB over their whole frequency range when a second cabinet is added.
If the mouth is sufficiently large, total emitted acoustical power only doubles (+3 dB) as the loudspeaker cannot gain efficiency. It's already as efficient as a loudspeaker can be.
Front loaded horn subwoofers usually are made with a too small mouth for low frequencies, while it is sufficiently large for low-midrange frequencies. Emitted power goes up by 6 dB at low and 3 dB at low-midrange frequencies when another cabinet is added. So it goes deeper.
Tapped horn subwoofers typically have too small mouths to efficiently couple to air, even at the upper end of their pass bands, so they gain 6 dB over their whole frequency range when a second cabinet is added.
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Not disagreement there. However, it's not going to be a step change, i.e. the delta increase in efficiency will not suddenly go from 3 to 6 dB, but transitions between the two as mouth size decreases. That means that even with smaller mouths, you should see a measurable difference, even if that difference is very small.
One thing I'm pretty certain of - if there's a change in the system's impedance curve, there will be an observable change in the system's frequency response as well, as the two are linked. With that said, I repeated the impedance curve test with my POC3 TH this morning, with the mouth facing up, mouth on the ground (2PI loading) and mouth adjacent and orthogonal to wall (to emulate 1PI loading). It's a five-minute exercise that anyone can do if they have a TH, DATS and REW (to compare the impedance curves). As I noticed the last time that I did this test, there were minor but noticeable changes to the impedance curve, which suggests that the FR would change as well. This TH has a pretty small mouth (925 cm^2). I suspect any changes will be even more noticeable with THs with larger mouths.
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Perhaps, but then again look what happened to their measurements of the TH118...
True dat.
P
If we had a FLH with the same path length and throat and mouth sizes, I bet no-one would question that the resonance frequency would be lowered if we put two side by side. But then it's claimed that doesn't happen if those FLHs are replaced with THs. Why?
There is also an issue with impedance, and IIRC, compression ratio. - The same factors, as far as I can tell, that make Art's Keystone mouth extension work.
But let's face it, I don't fully understand ANY of the physics here. I'm just throwing out other factors to look at.
We toyed with the idea of achieving good multiple units coupling when we developed the THAM18, it's a tapped horn with a 63 deg expansion roughly from the center of the driver to the end of the last segment, the coupling area is ~3733cm2, since it did not hurt the results so we went with it.
I'm sorry to say I do not know, one would have to compare it with a similar design with significantly less coupling area, but as I wrote it was juat a thought, and seeing that it only seemed to bring a slightly higher sensistivity in the upper passband range in the simulations we thought it did not hurt to keep it.
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