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| Re: 12 π basshorn - just about ready for prime time [message #63824 is a reply to message #62468 ] |
Fri, 15 July 2005 12:43   |
 Gareth James
Messages: 231
Registered: December 2004
Location: UK |
Has No Life |
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Hi Wayne,
Just had another look at your simulation results, u seem to be putting 2.83v into the load, aren't u using dual Lab12's?
If so isn't that a 3ohm nominal (or 4 as some other posts ive read suggest) load?
You need to be putting 1W in which would be 2.00v for a 4ohm load, just double click and use the auto es tool to work out what voltage 1w is at whatever impedance the cab is.
Also your measurements at 45v input show that the drivers are at their limit by 30hz, thats only 750w input (depending on how you rate the impedance of the cab).
I think in making a longer horn you've reached the limits of the LAB12 drivers in terms of low end excursion capabilities.
Maybe you could try rejigging it with 15's? They might allow that little extra at the bottom end.
Good luck
Gareth James
[Updated on: Fri, 15 July 2005 12:53]
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| Re: 12 π basshorn - just about ready for prime time [message #64005 is a reply to message #63824 ] |
Sun, 17 July 2005 03:11 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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The 2.83v input was used to show a baseline for response, and I didn't really care to get a 1W/M level. It was the response curve I was looking for. On the other end of the scale, 45 volts is about all you should expect to go with a LAB12 driver. We haven't done destructive tests yet, so I can't tell you how much the cooling system raises that amount yet. But it lowers temperature of the pole piece surrounding the voice coil significantly.
[Updated on: Wed, 24 August 2005 12:00]
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: 12 π basshorn - just about ready for prime time [message #64182 is a reply to message #64041 ] |
Mon, 18 July 2005 05:45 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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Certainly, you can send a high-voltage, low-frequency signal and over-extend the driver. But I don't think that's what most failures are the result of. From 35Hz up, heat buildup must be the primary cause of failure. I imagine it probably melts or fatigues the glue that holds the voice coil in place.
Tako Tamas has done excursion measurements of the LAB12 driver in the LABhorn and in Brad Litz's basshorn. You can see the results here. His tests indicate that at 40VRMS, the driver stays well under excursion limits in the passband of the horn, above 35Hz.
I am currently running heat tests. At full power, the pole piece temperature is hot enough to boil water. The air surrounding it becomes superheated and venting becomes less effective. By conducting heat away and removing it from the box, the temperatures around the coil can be significantly reduced.
It will be interesting to see destructive tests at various frequencies, 20, 25, 30, 35, 40Hz for example. It would also be helpful to run tests using the LAB12 in various cabinets to see where the limits were, and if failure was caused by mechanical interference or voice coil heat. I don't think anyone has ever done this, so comments about limits and failure modes are largely speculative.
From what I've done so far, I believe that the thermal limit is the primary cause of failure in the LABhorn. Without the cooling system, that would probably be the primary mode of failure in the 12Pi basshorn as well, and it may still be, but hopefully at a much higher power level. We will see.
[Updated on: Wed, 24 August 2005 12:01]
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: Wayne-will this also be for the DIY crowd [message #64211 is a reply to message #63819 ] |
Mon, 18 July 2005 09:05 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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As with all of my designs, the plans will be available free, along with test results and what not. We do a sort of "open source" policy. It helps give exposure and good will, if nothing else.
Pi Speakers is an Eminence dealer, and we sell kits and parts at real good prices, so that's where I make a buck on them. Pi Speakers also sells finished cabinets. But no one needs to buy anything from me, they can build using the plans, no obligation or whatever.
Kits will include the cooling system and the drivers. We'll also sell just the cooling tube by itself, so LABhorn owners can bolt it right onto their existing access panel. This assumes the access panel is aluminum, of course. And a hole will need to be drilled to mount the tube. But it comes with everything, the tube, mounting hardware and heat sink compound.
That's my shameless plug.
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: 12Pi basshorn - just about ready for prime time [message #80385 is a reply to message #80336 ] |
Tue, 11 October 2005 03:01 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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We considered using Sonotube to reduce front chamber volume, and that's probably a pretty good way to do it. Sections could be cut to fit the chamber and throat, and then the area behind could be filled with closed cell foam to seal it to the throat and fill any gaps.
But the fill pieces we chose instead are very easy to cut and fit. We were able to set the volume precisely in each front chamber with them. Compared with all the braces and other panels, the front chamber fill pieces are probably the easiest part. They're small and easy to work with.
[Updated on: Tue, 11 October 2005 04:59]
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: 12Pi basshorn - just about ready for prime time [message #80915 is a reply to message #80411 ] |
Thu, 13 October 2005 02:04 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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The 12Pi is a no-compromise design. The features that make it superior are the things that make it a little more difficult to build than other designs. The cooling plug must fit precisely, which means that the driver mounts in the motor chamber, motor chamber fits onto the side panels, and access hole mounts for the heat exchanger / access panels all have to be in precise alignment.
We built the prototype with a table saw and hand tools. I didn't think cutting the fill pieces was all that difficult, but precise cuts for cooling plug alignment are challenging. The heat exchanger provides such a huge benefit in driver performance and longevity, it is definitely worth it.
[Updated on: Thu, 13 October 2005 13:32]
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: 12Pi basshorn - just about ready for prime time [message #80972 is a reply to message #80915 ] |
Thu, 13 October 2005 10:41 |
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Wayne ,
This is wishing you " Best of luck " for the 12pi in the shootout ,
Rajeev
RL
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| Re: 12Pi basshorn - just about ready for prime time [message #81165 is a reply to message #80972 ] |
Fri, 14 October 2005 03:40 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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Thanks, we'll post results as soon as we compile them.
Wayne Parham
π Speakers
PiSpeakers.com
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