BillFitzmaurice.info

TimpBizkit wrote: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!

Michael Ewald Hansen wrote: Wow, talk about missing the point of voltage limits.

TimpBizkit wrote:

Michael Ewald Hansen wrote: 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.

Bill Fitzmaurice wrote: 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.

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

Harley wrote:

TimpBizkit wrote: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.

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

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

Rich4349 wrote:Would smaller tubas, arranged around the room have made better bass IN the room, while lessening how far the bass traveled?