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[Wayne Parham]

Hi all,

Some of you might be interested in the new 12 Pi horn I'm working on.  I've made a lot of initial tests and models, and we're making a prototype of the full device this month.

See http://www.AudioRoundTable.com/PiSpeakers/messages/17387.htm l

Craig, this is kind of what you're talking about in your announcement about posting new designs.  So if you want to delete the post, I understand.  (Don't you love it when guys give you permission what to do in your own house?   )

I felt it was appropriate to post here because I think it is fundamentally on-topic in the LABsub forum.  Also, Tom and I have discussed several issues over the years that I've tried to address in this design.  So I thought it would be good to bring attention to it here.

Wayne

[Craig Leerman]

Quote:

Craig, this is kind of what you're talking about in your announcement about posting new designs.

Exactly!  

Nice looking design BTW. Please post test results after you fire up the prototype.

Craig

[Wayne Parham]

Will do.

[Steve Shafer]

Wayne:

Glad to see this is coming together for you.  Do you plan to make this a DIY project and to post drawings and plans here on the LAB?

BTW-what drivers did you settle on?  

Steve S

[Gareth James]

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

[Wayne Parham]

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.

[Gareth James]

Hi wayne,

Yes in theory you're not supposed to put more than the 400w per driver that the LAB12's are rated at in, but my point was about the excursion limited maximum input.

What i mean is aren't u going to reach the excursion limited maximum before the thermal anyway?

Does anyone else have any views ideas on this? Don't want to sound like im putting the guys idea down if im wrong!

Gareth James

[Wayne Parham]

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.

[Wayne Parham]

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]

The 12Pi basshorn subwoofer is 45" x 45" x 28", which fits nicely in semi trucks. Trucks are 90" wide, so truck packs are usually 45x45x22.5 or 45x45x30. The 12Pi basshorn uses a pair of LAB12's in push-pull which reduces harmonic distortion. It also has a heat exchanger which increases power handling over 225%.

• 12Pi basshorn design and history
• 12Pi basshorn construction photos
• LAB12 destructive test
• Woofer cooling device - Test Cycle with Heat Exchanger Installed

As some of you may have seen, the 12Pi basshorn subwoofer will be at the Prosound Shootout this Friday.

[[x]]

Apparently simple construction doesn't mean much to you, after seeing the construction photos. Instead of those filler panels to reduce the volume behind the woofers, you should have used lengths of Sonotube, the round concrete forming stuff. A lot easier to cut and install. Since it's cylindrical, the fact that it is thin (only about 1/4" at the most) doesn't matter because deforming forces are distributed evenly along the circumference. You ought to make that change to the plans

[Wayne Parham]

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.

[[x]]

yeah. I just suggest that you look into using one-piece solutions like sonotube instead of things with angles that will need to be calculated and measured, etc. for your design to reach maximum acceptance. I'm pretty sure that's why Walt's Punisher horn has taken off as well as it has (though primarily with overseas users.)

[Wayne Parham]

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.

[raj]

Wayne ,
This is wishing you " Best of luck " for the 12pi in the shootout ,
Rajeev

[Wayne Parham]

Thanks, we'll post results as soon as we compile them.