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build quality of porn horns

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Timber_MG View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 15 November 2005 at 3:35am
Calibrate the mic to any random value and try a range of values off axis and you'll see the difference whne you add them to a response family.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dom Quote  Post ReplyReply Direct Link To This Post Posted: 15 November 2005 at 1:19pm

Is there any chance you could explain that in a bit more detail???

"It sounded like a million fire engines chasing ten million ambulances through a war zone and it was played at a volume that made the empty chair beside me bleed."
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 15 November 2005 at 2:23pm
A picture is worth a thousand words some say. So here goes...



I just had a very quick look earlier, the two responses are very similar indeed...is that the small Selenium 2" (rumoured to be a Tractrix)? The horn is too small for the porn mid really and I have thought for a long time that there was supposed to be a small cone-horn between the two. Iirc PAP were working on such a unit (for the Ciare 6" mind methinks) a while back.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davey t Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2005 at 6:15pm

sorry, whats that plot showing? what are the different colored lines

I used the selenium horn with a 1.5" to 2" adaptor. Have only tested out the porns in my garage and they sound as good as any speaker can without bass! the top seems to go up high and be nice and smooth and easy on the ears.

here's a pic

Got 4 in total, trying 2 out with the labs tomorrow, i'l let you know how it sounds.

What do you mean by "the horn is too small for the porn mid"?

Has anyone measured the total overall response of a porn horn?

ta



Edited by davey t - 17 November 2005 at 6:18pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2005 at 7:13am
The plot is of a 5" dia horn with roughly CD characteristic. Bandwidth starts at 2kHz (i.e. 2kHz per division after 2kHz) and the lines show a roughly CD dispersion (guesstimated 10 degrees ange between plots).

A small horn cannot provide much directivity (directivity at LF is mostly linked to size) and thus you can EQ a porn horn flat on axis but off axis you will get much more energy in the mids (in the case of the porn the cross at 2kHz means that the mid is beaming and the tweeter isn't. It also makes for problems in a stack in the critical vocal band (2kHz being the most imprtant contributor to intelligibility)

My ECM8000 seems to have a bit of a peak around 13kHz but the relative levels should be roughly alright.


Edited by Timber_MG - 18 November 2005 at 7:15am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote loophole Quote  Post ReplyReply Direct Link To This Post Posted: 13 December 2005 at 6:12pm
martin, could you clarify?

are you saying that the lack of directivity is in the mid horns or the tops? i think mid, and this would match what ive heard in mine

either way, putting in a 6 in between would obviously elimate the problem at 2khz which is going to improve the clarity considerably, but would also just shift the problem to either the 12/6 xover or the 6/1.5, or in the worst case, both

if the two devices at the high and low end of the vocal range are mismatched in dispersion, then no matter how many intermediate horns you put in between, theres always going to be eq issues at a x-over point somewhere

i think the porns need a 6" high mid, but also a change of compression driver and horn to match. a 1" would be the obvious option, with a slightly wider dispersion horn to match that on the 12"

edit: just came across dom's plots. they clearly show that a lower 12 fh and a wider top are whats needed.
at the same time, is it also possible that the plot is not entirely representative of what happens in a array situation. there certainly is a mismatch of dispersion, but the plots make the 12 out to be a little less directional than i think it is - presumably they have been taken in free space on a single unit? this will mean that you're going to see more diffraction at low freqs around the edges of the cabinet, than if it was arrayed with one either side, hence the particularly wild dispersion even at 500hz and 1khz

Edited by loophole - 13 December 2005 at 6:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2005 at 5:38pm
Erm, arraying is not quite that simple as the diffraction at the horns' mouths add to the dilemma (i.e. there is not only the wave front curvature to considder, but the diffraction at the mouth is responsible for overlaying "secondary sources" onto the response. Having the side-walls of two adjacent cabs run parallell (or CD horns with -6dB polars at those points) is in no way a guarantee that the polar response will be clean when you plot it over a given arc in front of the stack. Most arrays are a  bit of a botch but some do end up sounding quite respectable.

A horn only becomes significantly directive at frequencies where it is large enough in terms of the wavelength being reproduced. This means that while the 12" porn horn might already be at 40 degrees or whatever the case may be at 2kHz, the HF horn is too small to add significant directivity at 2kHz and only becomes more directive at higher frequencies. The crossover not being instant smooths this transition over to some extent but cannot correct for the power response anomaly which becomes especially apparent off axis and in the reverberation excited by the speaker.

A larger horn has the advantage off adding more directivity (= sensitivity within the coverage angle) at lower frequencies and loading the driver better at lower frequecies. At higher frequencies the role of the wavefront (influenced by the horn boundaries up to the point where the driver exit itself beams too much...though theoretically this needsn't be the case if the driver has a matching wavefront at higher frequencies) determines the progression of directivity. Some horns add directivity to compensate for the power response roll-off at about 3kHz evident in all compression drivers (mass corner related, TAD get up to 4kHz). CD horns (constant directivity) don't add this directivity and thus have a 6dB/oct roll-off above this point.

I suggest you look into the 18Sound 1.4" elyptical waveguide. It is said to work well with the 1.5" exit 3" diaphragm P.Audio drivers (a German fellow uses them with the MT122 and claimed good results). Seeing that you run a  mono-stack most of the time this waveguide would be quite suitable.

I have been gone for a while and will likely not be active on this board much due to work, life and other factors. I am reachable via skype and e-mail most of the time (if my PC doesn't screw up, darn spyware)

Martin
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