I noticed some comments in this thread about distortion, which is one of the areas where the 12Pi hornsub really shines. So I'd like to point out that the 12Pi Hornsub link has a lot of referenced documents, one of which contains a series of charts showing distortion of various subwoofer designs on the market. It's called "Push-pull benefits quantified".
Another interesting topic is the one called "Heat exchanger effectiveness", which talks about the cooling system, including power/thermal tests. It has a destructive test of a LAB12 woofer, where power was applied to the driver for an extended period, temperature measurements taken, and then power was slowly increased to the point of failure, taking measurements at each incremental increase. The same series of tests were run with a modified LAB12, one that has the cooling plug and plate installed. The amount of sustained power increased over 225%, and the driver never failed. This was also proven in the field, time and time again, in the controlled tests performed at the Prosound Shootouts in 2005, 2006 and 2007. The 12Pi Hornsub performs very well, as was demonstrated in these events.
I think that any discussion of SPL, distortion and/or thermal power handling where comparisons are made should be accompanied by measurements that rise to this level. We did measurements at various power levels, from 100 watts to over 2000 watts, and we measured both SPL and distortion. Not everyone has the equipment or location to perform such a test, but comparison between subs like this can't really be made without at least a few high-power sweeps made outdoors, far away from buildings or other large reflective surfaces.
Another interesting topic is the one called "Heat exchanger effectiveness", which talks about the cooling system, including power/thermal tests. It has a destructive test of a LAB12 woofer, where power was applied to the driver for an extended period, temperature measurements taken, and then power was slowly increased to the point of failure, taking measurements at each incremental increase. The same series of tests were run with a modified LAB12, one that has the cooling plug and plate installed. The amount of sustained power increased over 225%, and the driver never failed. This was also proven in the field, time and time again, in the controlled tests performed at the Prosound Shootouts in 2005, 2006 and 2007. The 12Pi Hornsub performs very well, as was demonstrated in these events.
I think that any discussion of SPL, distortion and/or thermal power handling where comparisons are made should be accompanied by measurements that rise to this level. We did measurements at various power levels, from 100 watts to over 2000 watts, and we measured both SPL and distortion. Not everyone has the equipment or location to perform such a test, but comparison between subs like this can't really be made without at least a few high-power sweeps made outdoors, far away from buildings or other large reflective surfaces.
I recommend you consider using a cooling plug fitted to the pole piece. The center pole and front plate get hottest, and are usually between 50° and 75° Fahrenheit hotter than the back plate when a powerful woofer is running at full tilt. That's why a good interface to the center pole works best. You won't get nearly as good results if you just try to wick the heat from the rear plate. Best results when the center pole to cooling plug thermal interface is good, i.e. maximize surface area and make a snug fit. Use thermal grease for that last bit of performance.
Thank you for the information, Wayne
Shame I don't have easy access to x-ray equipment anymore, I would of shot an image of the woofer and plug and adjusted as necessary. ( I worked on medical equipment for 25 years)
The LAB12 is in the running for my 18Hz tuned push-pull subwoofer so it is nice to "cheat" and get the cooling plug from you.
Is there an issue with the thermal paste moving or should I use a touch of thermal epoxy--not near the tip! Mix the thermal epoxy with thermal goop about 50/50 and it allows fairly easy removal for experiments.
Shame I don't have easy access to x-ray equipment anymore, I would of shot an image of the woofer and plug and adjusted as necessary. ( I worked on medical equipment for 25 years)
The LAB12 is in the running for my 18Hz tuned push-pull subwoofer so it is nice to "cheat" and get the cooling plug from you.
Is there an issue with the thermal paste moving or should I use a touch of thermal epoxy--not near the tip! Mix the thermal epoxy with thermal goop about 50/50 and it allows fairly easy removal for experiments.
If you have the speakers mounted in such a way that the cooling plug can be press fit - a slight interference fit - then you'll gain the best of both worlds: Good thermal interface and semi-permanent mounting. An interference fit will give you some pressure as well as surface area, which provides a better thermal interface. Of course, you'll need a gear puller to remove it.
In my situation, the cooling plug is attached to a plate which doubles as the heatsink and access for the woofer. So the plug has to be removable. In that case, the best way is to machine the pole piece bore smooth, to accept the plug as a perfect fit, like a brake cyliner and piston. This gives good contact with lots of surface area. The thermal interface isn't as good as would be if there were pressure applied (by an interference fit) but it is good enough to provide about 225% improvement in thermal power handling.
We have an OEM woofer manufactured specifically for this purpose, and it is essentially the same thing as a LAB12 but with the pole piece machined smooth to accept our cooling plug. The plate is attached to that, and as I said, that serves as access panel and heat sink, so it is held in place with mounting screws.
Another arrangement that would work well is to mount the woofer, insert the plug, and then mount a heatsink on the plug that can be attached to the cabinet wall in some way. It doesn't necessarily have to be external, although that would probably be better. It could also be placed in the vicinity of a port, to gain convection past the heatsink, perhaps blowing over fins. Even without that though, the main thing is wicking the heat out of the motor core. If used inside a sealed cabinet, with heatsink internal too, the internal air temperature would heat up a couple dozen degrees over ambient, but that would be a small price to pay for reducing motor core temperatures 100°. Better to put the heatsink outside, sure, but even if it's inside, you'll gain considerable benefit from a cooling plug and dissipation plate.
In my situation, the cooling plug is attached to a plate which doubles as the heatsink and access for the woofer. So the plug has to be removable. In that case, the best way is to machine the pole piece bore smooth, to accept the plug as a perfect fit, like a brake cyliner and piston. This gives good contact with lots of surface area. The thermal interface isn't as good as would be if there were pressure applied (by an interference fit) but it is good enough to provide about 225% improvement in thermal power handling.
We have an OEM woofer manufactured specifically for this purpose, and it is essentially the same thing as a LAB12 but with the pole piece machined smooth to accept our cooling plug. The plate is attached to that, and as I said, that serves as access panel and heat sink, so it is held in place with mounting screws.
Another arrangement that would work well is to mount the woofer, insert the plug, and then mount a heatsink on the plug that can be attached to the cabinet wall in some way. It doesn't necessarily have to be external, although that would probably be better. It could also be placed in the vicinity of a port, to gain convection past the heatsink, perhaps blowing over fins. Even without that though, the main thing is wicking the heat out of the motor core. If used inside a sealed cabinet, with heatsink internal too, the internal air temperature would heat up a couple dozen degrees over ambient, but that would be a small price to pay for reducing motor core temperatures 100°. Better to put the heatsink outside, sure, but even if it's inside, you'll gain considerable benefit from a cooling plug and dissipation plate.
If you are breaking down the driver and have the motor structure opened up, it should be fairly simple to ream the vent to accept a lathed slug. A hydraulic press is not too expensive and would do just fine.
Of course, if the vent is not a "standard" size, you'd have to drill/mill it out first seeing as reamers don't typically come in drill increments.
Absolutely. This was one of my original compaints of the LABhorn. It was being promoted on a hifi site as a good subwoofer for home theater. That would be OK, I suppose, except they proposed no high-pass was needed because power levels were low. They were saying it would operate in "direct radiator mode" down low, safely, as long as power levels were kept within reason. I suggested that made it a distortion generator, and that any of the real deep bass would be converted into amplified harmonics. Nothing but distortion from signals below cutoff. There's little risk of damage, at moderately low power levels, but as for quality - well, I'd probably go a different way.
I proposed several smaller direct radiating subs would be more viable for home hifi, and in fact, better in terms of performance. At the lower power levels, distortion wouldn't be a problem and by using multiple subs, you could smooth room modes too.
I mean, if you have a huge room, then basshorns might be cool. They're spectacle, hugely powerful, and in the passband, distortion is really low. So maybe I was too hard on the guys that were pushing the LABhorn as a home theater sub. But then again, if you're going to be zealous enough to put basshorns in your home, I think some more analysys is in order.
At least with the 12Pi hornsub, you have push-pull drive. That keeps it from being a distortion generator, even if run below cutoff. I wouldn't suggest it from a power-handling perspective if used at high power like its intended use. But if signals are presented below the passband, the 12Pi basshorn is just dead quiet.
It's kind of weird, really, when you compare the 12Pi basshorn with other basshorns. Start a sweep down low, say at 20Hz. The 12Pi hornsub is dead quiet until the sweep signal enters the passband. Then it becomes loud rapidly.
Most basshorns are fairly loud even below their passbands, because the harmonics are amplified. Of course, it isn't as loud as when the sweep enters the passband, but it's definitely making sound when below-cutoff signals are presented, and it's pretty loud. A traditional basshorn gradually increases SPL as you rise up through cutoff and enter the passband.
But then connect the 12Pi basshorn and run a sweep. It's dead quiet down low, below cutoff. Then as the sweep rises into the passband, the sound rapidly becomes louder. The operation of the push-pull drive is obvious, and the SPL output is striking. It's one thing to see it in the charts, quite another to hear it at 1600 watts.
There is much more information in the referenced documents at the link below, including testing methodologies, results, etc. Be sure to look at the cooling plug tests, the LAB12 destructive testing, and so on.
Also of possible interest is the measurement test results from the Prosound Shootouts in 2005, 2006 and 2007. The test plan shows the method of finding impedance (used to set voltage for specific power levels), distortion, etc. There is also a handy distortion conversion chart that shows decibels and corresponding percentage.
At 800 watts the 12Pi distortion goes up to 28% at 30 Hz, more than three times that of my standard front loaded Lab 12s in a 7.76 cubic feet gross, Fb 36 Hz ported cabinet.
Surprises me you did not hear that amount of distortion, perhaps the low portion of the sweep you use is too short to be apparent to your ear.
I did not see any Labhorn tests in your links, did you measure a Labhorn's distortion?
Art Welter
I'd say you're not very good at interpreting measurement results, or perhaps you just want to spin it hoping to make some kind of case that the data won't support.
Compare the distortion measurements of a vented cabinet (or horn, for that matter) below cutoff with my 12Pi below cutoff. The vented cabinet distortion is well above 100%, and most horns are too. The fact that my hornsub is only 28% below cutoff is excellent evidence that the push-pull drive reduces distortion a significant amount.
Tell you what. Where do you live? Let's get together sometime this summer and measure your vented LAB12 box and your tapped horn on the LMS system, side by side with my 12Pi hornsubs. You can run the tests, if you want.
But let me warn you, you'll be seriously embarassed.
Compare the distortion measurements of a vented cabinet (or horn, for that matter) below cutoff with my 12Pi below cutoff. The vented cabinet distortion is well above 100%, and most horns are too. The fact that my hornsub is only 28% below cutoff is excellent evidence that the push-pull drive reduces distortion a significant amount.
Tell you what. Where do you live? Let's get together sometime this summer and measure your vented LAB12 box and your tapped horn on the LMS system, side by side with my 12Pi hornsubs. You can run the tests, if you want.
But let me warn you, you'll be seriously embarassed.
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Love the smack talking on here 
Wayne are the prices correct on your site?
http://www.pispeakers.com/catalog/product_info.php/cPath/4/products_id/72
that seems kind of steep no? and +$900 for a different type of wood? woofaaa!~
Wayne are the prices correct on your site?
http://www.pispeakers.com/catalog/product_info.php/cPath/4/products_id/72
that seems kind of steep no? and +$900 for a different type of wood? woofaaa!~
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I love those little tweeter horns, but the machine time is sooo expensive. When I first started making them, I had a target price of $400 for the lyptus version. But after making a few, the shop hit me with the bill and told be they had to be nearly double that. Truly sucks.Love the smack talking on here
Wayne are the prices correct on your site?
http://www.pispeakers.com/catalog/product_info.php/cPath/4/products_id/72
that seems kind of steep no? and +$900 for a different type of wood? woofaaa!~
As for the other wood species available, it's kind of the same deal. The costs are just huge. They have to start out with a big chunk of wood, and when you're buying birds eye or mottled woods, large pieces are extremely expensive. Heck, even veneers of those kinds of woods are kind of pricey, but the large blocks of wood are like serious bucks. So that's just the way it is.
As for the "smack down", I'm dead serious. I'd love to do another Prosound Shootout this October. They're a lot of work, but they're also a lot of fun. Everyone has a camaraderie that isn't anything like the bravado sometimes displayed on audio messageboards. It's more like a race track, where if a guy blows an engine, the next guy over will loan him a spare. We all pull together, help load out and load back in, and deal with any issues that come up. I really feel a kinship with all the guys that have come each year.
But weltersys is still gonna be seriously embarassed!
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I live in Madrid, New Mexico.
I have compared the 30 cycle response of my dual Lab 12 ported (Fb 36) cabinets and Keystone (Fb 37) cabinets, they have far less distortion than the 12Pi at that frequency.
The 12Pi does have less distortion through the pass band at 800 watts than the ported Lab 12s.
Lets try four of my dual Lab 12 subs to one 12Pi, as they take up 1/4 the truck space. I can ratchet strap them together and wheel them around like a 12Pi :^).
Or two of my Keystone subs, which outperform the dual Lab 12s, and are half the size of the 12Pi.
Or one Keystone sub with the extender, which still is much smaller when broken down than the 12Pi.
Having looked at the output of the 12Pi compared to the JBL SRX 728, and having compared the output of my cabinets to the 728, I am confident that my cabinets will not cause me any embarrassment.
Art Welter
Very good, I'll contact the track and see about setting up another event.
I suggest you refrain from comparing your results with others until we've sorted this out. Your measurements clearly don't pass the sniff test.
I mean, come on - a vented box against a hornsub with the same drivers? You don't compete on any level, SPL, distortion or power handling. Well, there is one place the vented box is better, it is smaller. And that's not trivial. But to suggest that the performance is anywhere close to equal, well, that's just not even close to reality.
I think maybe you forget that I build vented LAB12 boxes too. Love them for what they are. But it's like a small block against a blown big block.
You're going to have it handed to you.
I suggest you refrain from comparing your results with others until we've sorted this out. Your measurements clearly don't pass the sniff test.
I mean, come on - a vented box against a hornsub with the same drivers? You don't compete on any level, SPL, distortion or power handling. Well, there is one place the vented box is better, it is smaller. And that's not trivial. But to suggest that the performance is anywhere close to equal, well, that's just not even close to reality.
I think maybe you forget that I build vented LAB12 boxes too. Love them for what they are. But it's like a small block against a blown big block.
You're going to have it handed to you.
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I read a great analogy in "The Physics of Music" (lightweight early chapters, which is as far as I've gotten having just bought it, but good reading nonetheless). They were describing the ear which is close to a reversed horn in some respects. They described a fist punching and how much air that moves, vs a fist punching a sheet of plywood and how much that does. The horn, obviously, is the plywood.
Hi Wayne,
By Wayne Parnham: "...a vented box against a hornsub with the same drivers?"
I think Art is suggesting to compare four of his dual LAB12 subs to one 12Pi.
Weltersys: "...try four of my dual Lab 12 subs to one 12Pi, as they take up 1/4 the truck space."
Or in other words eight LAB12 drivers v. two.
Anyway, do you have a Hornresp Input for your 12Pi Sub that you could share?
Regards,
By Wayne Parnham: "...a vented box against a hornsub with the same drivers?"
I think Art is suggesting to compare four of his dual LAB12 subs to one 12Pi.
Weltersys: "...try four of my dual Lab 12 subs to one 12Pi, as they take up 1/4 the truck space."
Or in other words eight LAB12 drivers v. two.
Anyway, do you have a Hornresp Input for your 12Pi Sub that you could share?
Regards,
You don't read for beans.
I said:
Lets try four of my dual Lab 12 subs to one 12Pi, as they take up 1/4 the truck space. I can ratchet strap them together and wheel them around like a 12Pi :^).
Or two of my Keystone subs, which outperform the dual Lab 12s, and are half the size of the 12Pi.
Or one Keystone sub with the extender, which still is much smaller when broken down than the 12Pi.
I never had any delusions that a dual Lab12 in a cabinet 1/4 the size of your monster would out perform it.
BTW, I have not forgot that you "build vented LAB12 boxes too" where is the distortion and output data for them ?
Art Welter
Yeah, you said that after you realized we might have an honest side-by-side comparison with a measurement system designed to measure this sort of thing.
But for quite some time, in my absense, you've been running around here telling everyone how superior your speaker designs are in terms of distortion, irregardless of the numbers used. Even now, you insist that your vented boxes don't distort much at full power, even below cutoff. That's rubbish. Below the Helmholtz frequency, your cabinets do like any other cabinet - distortion skyrockets. That's what we'll see in the traces. We'll see THD from 20Hz to 200Hz when we measure distorton, and we'll see SPL of the fundamental when we measure response.
I have no problem agreeing to measure a group of your boxes. But we should measure single and duals too. And if we stick to the plan we've always used, the voltage applied is determined by measuring Zmin and using Ohms law to determine the level required to generate 100 watts, 200 watts, etc. We'll keep going until you cry uncle.
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