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Re: 12π and 15π horn loudspeakers [message #45761 is a reply to message #45759] |
Mon, 08 November 2004 09:59 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Larry Acklin
Messages: 54 Registered: May 2009
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Baron |
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Hi Wayne et all: Been following this one with great interest, since i've been using folded horn subs for PA for a while. Wayne, look at www.stage-accompany.com and look how they have employed forced air cooling into the performer series. ("Air system"). Basic form is a fan, and a speed controller that reacts to averages of progam levels- then adjusts speed of the fan to the conditions. Also remember that most PA subs are not being used at below 40-45 hz. Nothing down there, too much potential for sstage rumble, or runaway subsonic feedback, etc. Some systems don't operate below 60 hz. Larry Acklin
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Re: 12π and 15π horn loudspeakers [message #45763 is a reply to message #45760] |
Mon, 08 November 2004 13:50 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18748 Registered: January 2001
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Illuminati (33rd Degree) |
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You are right that the rear chamber in the LABhorn is very small, and the air behind it plays a significant role. Another way of looking at it is the small sealed chamber shifts the resonant frequency so that motor chamber resonance is in the passband of the horn. It is set to create a peak at lower cutoff which augments output. This is sometimes called reactance annulling.However, what is significant about this new horn is the push-pull plenum, which counteracts motor asymmetry. There is nothing in the LABhorn design that deals with this. It is well-known that the cause for harmonic distortion is primarily due to asymmetries in the motor assembly, not the mechanical suspension or pneumatic loading. That is why shorting rings are used in low-distortion drivers - They counteract the major cause of asymmetry, which is flux modulation. Another way to counteract it is the push-pull plenum arrangent. There are many things a horn does that reduce distortion, but it cannot address flux modulation. There is no mechanism to restore symmetry. Horns reduce excursion and reduce bandwidth, both of which reduce distortion components. But asymmetry is not reduced by horn loading, so the push-pull plenum has been added to address this. If a woofer with a sufficiently large shorting ring were used, that would do it too.
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Re: 12π and 15π horn loudspeakers [message #45769 is a reply to message #45732] |
Mon, 08 November 2004 21:57 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Adrian Mack
Messages: 568 Registered: May 2009
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Illuminati (1st Degree) |
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Nice horn Wayne! I wonder if that plenum is a little large to gain complete effects of push/pull loading. How long is the pathway and mouth area? Got any Hornresp response predictions of this horn? The pathway is interesting, I've not seen a horn before that has the pathway split off into two directions. Is it the same as having one pathway with double the area/volume?
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Re: 12π and 15π horn loudspeakers [message #45772 is a reply to message #45771] |
Mon, 08 November 2004 22:48 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Adrian Mack
Messages: 568 Registered: May 2009
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Illuminati (1st Degree) |
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Hey Wayne Im sure the push/pull config will reduce distortion - John Sheerin did something similar in a dual 10" CSX basshorn, and noted very good improvements in 2nd HD. Ducting to get cool air from the outside - reminds me of the cold air intake/induction system I put on my car made from 90mm piping :P If you were to do the ducting on the vented pole piece, I think make the piping larger than the vent itself so that the airflow doesnt cause a restriction and start creating noise and air pressure buildup of its own, which would mean more distortion. Adrian
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Re: 12π and 15π horn loudspeakers [message #45777 is a reply to message #45764] |
Tue, 09 November 2004 13:51 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Larry Acklin
Messages: 54 Registered: May 2009
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Baron |
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Hi Wayne- When you go to the site, click on the SA logo. Go to the performer series, scroll down and click on the air system logo. Basic info there, and lots of good info in the PDF stuff. I saw a design (beta) where the woofer and mids also had air plenums and cooling.
Dimension that box you are looking at for Delta 15's and you got a winner. Larry
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Re: 12π and 15π horn loudspeakers [message #45829 is a reply to message #45763] |
Fri, 19 November 2004 04:22 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to previous message](/forum/theme/AudioRoundTable/images/down.png) |
jake
Messages: 8 Registered: May 2009
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Esquire |
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Please let me first say that I am all for trying to improve on the Lab Sub and am simply playing devils advocate. As far as I am aware the main cause of second harmonic distortion created by magnet structures is due to asymmetries in the magnetic field either side of the gap and therefore is not going to be addressed by a shorting ring which is usually used for reducing third harmonic distortion. Also the ear tends to be very insensitive to harmonic distortion at low frequencies and as the main second harmonic artefacts are going to be produced when the driver is working at the lowest frequencies of its passband then the main area of second harmonics are going to be in the 60-80Hz region and thirds higher again. By limiting the high frequency output to the horn acoustically by designing the throat chamber/throat area to have a cutoff frequency equal to your electrical cutoff frequency then you will minimize the second and third harmonics in the next driver’s passband. Two of the main areas of weakness in the Labsub seem to be dust caps detaching and heat problems, the former likely caused by the pressure on the rear of the dome due to the small rear chamber and hence high pressures and the latter through trying to dissipate upwards 200watts of heat in a very small insulated space. I therefore think that if you could get both drivers magnet structures in the throat chamber this would greatly decrease the forces acting on the dome and also reduce thermal stresses leading to reduced power compression giving a useful long-term gain in acoustic output. Putting one drivers magnet assembly in a small chamber and not the other may have it's own set of linearity problems that are not encountered in the classic closed and reflex box arrangments. Regards JakePS A quick off topic plug---The new Firefox browser is A1+++ and so is Thunderbird email client http://www.mozilla.org/products/firefox/ greater resistance to viruses and addware etc blah blah blah, don't forget to donate towards the cause.
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