Woofer Cooling Device Bass Horns

[Michael Ewald Hansen]

For a while I thought heat build up inside the rear chambers of horns would be a bit of a problem with horns driven at high power levels, especially in the bass section. Ported boxes wouldn't have this problem, but due to them usually being less efficient, would generate more heat in the first place.

THE NATURE OF MUSIC
Music like jazz often has peaks of bass, spaced with quite a large amount of silence, such that the average power levels are quite low even if the peaks are high. The woofer had a comparatively easy time keeping cool, especially at the more sedate listening levels compared to today.

DEMAND FOR BASS
More and more of today's music, particularly the aggressive drum and bass, extended sine wave rap music, heavy metal and dubstep places continuous power demands on subwoofers.
The question of how loud is too loud raises questions. Whilst high frequencies become fatiguing above a certain level (you can comfortably say that cranking a DR280 or XF412 to its highest level in your living room far exceeds a comfortable level for anyone), I'd argue it takes far more to do that with bass frequencies, and while Bill Fitzmaurice might think it a poor idea to put a T60 in a car, Steve Meade would probably think it not loud enough! Just think about how popular it is to cram a car with subwoofers and trying to reproduce this level at a large outdoor gig (millions of watts and thousands of Tubas or Titans no doubt).
The take home message is no matter how efficient or high power you make your subs, expect them to be pushed at some point. (I don't care if Tom Danley comes out with his new TH100/15!)

POWER COMPRESSION AND THERMAL FAILURE
The importance of thermal power handling is often understated on here, with things like - most drivers go from over excursion. With the high pass and voltage limits this is less likely, but things can still get warm, power compression comes in and encourages the cranking of volume controls further!
Face it: most loudspeakers aren't particularly good at keeping cool. 100 Watts continuous is a filament lightbulb or a very high power soldering iron. Think how hot even the lightbulb gets, and think about the voice coil in the back of a speaker. Then consider 100 watts is quite a tame power rating for an amplifier. I read an article on the 12Pi Bass horn and the designer Wayne said that even with the vented pole piece, there was significant heat build up in the magnets and coil, such that a Lab 12 overheated 40V sine wave 15 seconds on/off cycles after only 90 minutes and was significantly hot the first 5 - 20!
I will link you to his article http://audioroundtable.com/PiSpeakers/m ... 17646.html
Things look quite promising - over a 200% power handling increase! The second Lab 12 survived 60 Volts on/off for 2 hours unscathed and didn't get as hot as the first!

Wow, talk about missing the point of voltage limits.

Tim, thermal power handling is not understated on this board, its just not such an issue with subwoofer as the driver will mechanically break way before they fail thermally - period.

It doesnt matter that you put CoolerMaster Extreme 3000 on your driver when the coil is hammering the back plate, spider being shredded to pieces or the surround punctures..

So while you may cool the driver substantially you wont gain a whole lot for a huge amount of work to get it..

Just my 2 cents..

[Bill Fitzmaurice]

Wow, talk about missing the point of voltage limits.

+1.
As for the 12pi, Wayne Parham has a long standing feud with Tom Danley. Danley's LAB Sub was the first major DIY folded horn subwoofer design, and Parham created the 12pi for the specific reason of beating it, and therefore Danley.
The LAB Sub suffered from driver overheating, because the rear chamber was too small. That wasn't Danley's fault, as the design was altered by someone between what he originally specified and what was eventually released. But the damage being done Parham capitalized on that fact and came up with the additional cooling device to further increase the supposed superiority of the 12pi over the LAB Sub.

BTW, the T60 beats both the LAB and 12pi, and as the rear chamber is adequately sized additional cooling devices are not required.

[Michael M]

The more I read on here, the more I know I came to the right place.

[byacey]

Even reflex enclosures suffer from heat build-up. The air within the cabinet isn't exchanged with the outside air through the port as much as you would imagine. What it pushes out, it pulls back in just as quickly.

[Radian]

Tim, thermal power handling is not understated on this board, its just not such an issue with subwoofer as the driver will mechanically break way before they fail thermally - period.

This is true for extreme transients - putting 3000 watts at 35Hz (well above the voltage limit) for half a second may cause the driver to bottom out horribly and self destruct before the voice coil has had time to heat up. Running below the recommended pass band with even a comparatively small amp could do this too. The voltage limit is there to make sure the subwoofer won't overextend anywhere within the pass band.
Thermal limits can be reached on continuous duty, and with higher frequencies where excursion is less. Voltage limits are good against over excursion, and obvious excessive input.

BTW, the T60 beats both the LAB and 12pi, and as the rear chamber is adequately sized additional cooling devices are not required.

This driver was tested free air with 40 Volts (15 second on/off assume high freq to stop mechanical damage) and failed after 1h 30. Wayne found it more important to conduct the heat away from the magnet and central core than anything. The T60 will trade some 'loud' for 'low' as they are about the same size. If there was a 60" Titan that would be a good comparison imo. I'd rather move a T60 around or group smaller cabs if I didn't need to go as low.

Again this is mostly for people who beat the snot out of their subs with a lot of bass content (the sort of stuff WiSound plays in his club setups). Some modern songs are relentless with a continuous sine wave or loud distortion kicks in the 50-100Hz range that may be safe in the excursion zone but are working it hard enough all the time to fry a coil.

Timp, you're absurdly late this time around. Bill, Tom, Wayne, Bruce, and many others were all over it.....EIGHT years ago. There's nothing left to discuss.

You missed that party by a long shot bro.

[Harley]

Again this is mostly for people who beat the snot out of their subs with a lot of bass content .

Timpbizkit! Those people are rare on this forum and if they do crop up, they soon get the message or depart. For some odd reason your feathers are impervious to advice and subtle hints.

[escapemcp]

Again this is mostly for people who beat the snot out of their subs with a lot of bass content .

Timpbizkit! Those people are rare on this forum and if they do crop up, they soon get the message or depart. For some odd reason your feathers are impervious to advice and subtle hints.

ouch boyo!

[bassmonster]

Again this is mostly for people who beat the snot out of their subs with a lot of bass content

If you need to redline your subs to get the volume you want, you need more cabinets.

[bassmonster]

If you rent my gear, you rent me along with it.

[Rich4349]

If you need to redline your subs to get the volume you want, you need more cabinets.

+1

Between properly setting the voltage limiter (well within the manufacture's rating), proper highpass crossover setting, and using the right number of cabs for the space, I don't know how one would cook a driver, anyway. I set up my pair of v-plated 30" T-39s (3012LF loaded), as stated above, in a medium sized banquet room (30?x60?) and pounded the bass all night, no problemos. (Although the complaints from the other side of the hotel might indicate some overkill.) Would smaller tubas, arranged around the room have made better bass IN the room, while lessening how far the bass traveled?

[Bill Fitzmaurice]

Would smaller tubas, arranged around the room have made better bass IN the room, while lessening how far the bass traveled?

Slightly. In the directional frequencies distributed systems work quite well maximizing SPL within the listening area while minimizing SPL outside of the listening area. But in the subwoofer range where radiation is omni-directional it doesn't work that well.