cabinet frequency response

[AstroSonic]

As long as we're porting cabinets and pumping significant amounts of air, has any thought been given to ducting the port air past the voice coils for a 'semi-active cooling' effect? (I understand the issue with damping batting...) Or even in the case of sealed cabinets, employing internal finned heat exchangers thermally bonded to the coils and/or frame and running a (possibly fan-assisted) convection air path through the cabinet?

If 95% of 1000W/cabinet turns into heat, it seems as if even a small improvement in heat dissipation could be A Good Thing...

Yes, that's a lot of heat to dissipate. Efforts at this have tended to focus on transfering the heat from the voice coil to the magnetic structure and magnet, and on increased air flow through the gap and pole piece. Start with a large area voice coil (as mentioned by Alex). 'Serious' 12 and 15 inch drivers use 3 - 4 inch voice coils, with sealed dust caps and vented pole pieces (with particulate filters). Neo magnets de-magnatize at relatively low temperatures, so they usually are heat-sinked with both fins and a massive cast frame (especially next to the magnet structure).

Drivers with a lower power capacity need less drastic measures. They can still be good drivers but have more limited power handling and are more subject to thermal compression.

It is worth considering that only 3db of thermal compression means that fully half of your amplifier power is wasted. Also, less power is being developed by the amplifier because it is operating into a higher impedance. The cab may be rated as 4 ohms, but when really pushed into thermal compression the voice coil impedance rises, often well past 8 ohms. So you are getting whatever the amp can deliver into 8 ohms (or higher), not the 4 ohms the cab is rated at. Even though amplifier power has never been cheaper, at some point the best way to get increased spl is by using more speakers.

 

[Mike Arnopol]

I'm with Alex---I think that electric bass poses the biggest challenge to designers. I can get a speaker to do nasty stuff (given enough power) with EB way before the same perceived volume with even lower frequency information in a PA or DJ setup. As I said before I think it's because with a speaker pushed at higher volume where it hasn't yet reached the area of sounding funky---if you attack the note just a bit harder--or if you throw in a hard attack---if you have the watts available you can be calling on double the power.

And I also agree that Xmax is becoming less of a hurtle and now we have to look at heat-induced power compression. And I think that the amps are actually being driven harder with electric bass because of the constant demand of high transients. I think that---heat-wise---EB is just as brutal on amps as it is on speakers.

My '76 Music Man bass would put my power amp (years ago) into thermal overload way before source material that appeared to be twice as loud.

 

[B-string]

For the 'power' I was figuring convection falls into the 'cheap and better than nothing' category, especially if the duct is vertical. We're talking about hundreds of watts of heat although there's an efficiency loss across the thermal interface. If you can cool a 1000W amp with a 'quiet enough' fan surely you can do the same with a cabinet... They only make enough heat for it to matter when they're loud...

I donno how exactly you'd get the heat conducted but so far I've only spent 20 minutes on the problem ;-)

I believe high-performance tweeters are using ferrofluid to get heat from the transducer to the frame for improved cooling. Maybe super-duper copper braid a la grounding strap (or solder-wick on steroids...) would conduct enough heat to the relatively fixed 'radiator' in the heat-exchanger duct without affecting the sound (by conducting it to the structure).

The amp is 65-95% efficient (depending on output typology), the speaker is around 5%.

95% of several hundred watts is just heat generation?! I hadn't considered that before, no wonder the specs change during hard playing.....

Yes that is why . Speakers are the weak link, they "convert" electrical power to mechanical movement, audible sound is more of a byproduct than a direct conversion.

 

[AlexanderB]

More on cooling: Bruce Howze from Community designed a fan cooled massive PA speaker ("Airforce"). I remember reading about it in the 90s. Tom Danley also had cooling fans in the Servodrives, I think.

And speaking of Community speakers, I think they are one of few companies that use Ferrofluid for improved power handling also in the cone mid range spekaers. Anyone who has used their Solution series can testify about the massive output from moderate sized enclosures. (I have the SLS 920s myself.)

 

[dhsierra1]

audible sound is more of a byproduct than a direct conversion.

great way of looking at this issue.

So now all this has me wondering about what I can do NOW with what I have since I use old JBLs.

My porting is symmetrical (4, one in each corner) on the front baffle but since they're not doing much above 100 Hz or so........

 

[bryanspkr]

Some transducer manufacturers (Volt comes to mind for new-ish gear) have inverted the motor and frame structure and has by that created a big heat sink area OUTSIDE the cabinet. Must work wonders for thermal compression.

Invalid Link Removed

Others, like JBL and Cerwin Vega have had the shorting rings in their woofers for decades. This is also beneficial for "heavy duty" use.

I definitely think things are getting better and better in the loudspeaker world. The vintage gear is available to those that want that and we also get to use state of the art speakers that are amazing engineering and still affordable: woofers with 5" or 6" voice coils, kW in power handling, massive excursion and low weight.

the volt radial chassis design is very old by the way.

 

[radbass]

I want to thank everyone involved in this thread. It is like attending a seminar on bass speakers with some of the most brilliant people from all over the world, but it has shown me that most of what I thought I knew about what causes my equipment to not work the way I want it to needs rethinking. I have developed a fear of very low frequencies over the years because, in certain situations, they made it hard to hear what I was playing or hard to hear the band or the vocals. I play mostly in small clubs or bars and too much low, low end or now I think low mids screwed up by distorted low end made it difficult to hear myself or the rest of the band. Outside or in a big room this was never as much as a problem. It seems like reflecting low mids off the walls or vibrating wooden stages are causing phasing problems that make it difficult to hear myself or the rest of the band, so the sound that usually works for me is not much below about 50hz, and a slight peak at 2.5k. Recently, though, everything I thought I knew about bass sound went out the window. The older I get the less I know. Mike A. generously invited me to try out the Big E cabs. Every cab sounded slightly different, but what they all had in common was that they all went crazy low. I've heard and played cabs from the low end kings, like Acme, but at stupid volume levels there was no boominess and you could hear conversations in the the room. They are also the most transparent cabs I have ever heard. Playing music through them is the closest I have heard to a live setting. The dispersion is nuts, it almost sounds the same standing over the cab as out in front of it. This deal with the vortex makes very little sense to me, but it seems to work. Perhaps someone could explain it. There was talk of nothing being new in speaker design, but I have been building speakers for over 40 years, and I've never seen or heard anything like these. If anyone can point to any old technology that the Big E's rely on, please let me know.

 

[alexclaber]

As long as we're porting cabinets and pumping significant amounts of air, has any thought been given to ducting the port air past the voice coils for a 'semi-active cooling' effect? (I understand the issue with damping batting...) Or even in the case of sealed cabinets, employing internal finned heat exchangers thermally bonded to the coils and/or frame and running a (possibly fan-assisted) convection air path through the cabinet?

If 95% of 1000W/cabinet turns into heat, it seems as if even a small improvement in heat dissipation could be A Good Thing...

I'd had quite a few ideas about this and then, having done some power compression and maximum power testing, decided we need to do as much as possible to get the heat out of the enclosure in future designs. A key part of that is designing the drivers and enclosure to generate as little heat as possible in the first place!

 

[RockNRollAl]

Another thing to remember is that there is lots of 'breathing space' between the notes when amplifying a bass guitar. With compressed programmed music, it is a bit different thing (i.e., a DJ cranking tunes for hours at a time with massive sub-bass, etc.). For the typical bass guitar backline application, I would think that most power amps will never reach even close to their rated output, and if they do, it is at very, very brief transients.

That depends on the style of music you're playing. For example, if you're in a classic rock trio using compression, there's not much rest time in a lot of songs.

 

[seamonkey]

If anyone can point to any old technology that the Big E's rely on, please let me know.

They are a bass reflex with the drivers alignment crossfire in the form of a line array when you stack more in a cab.

Would like to see actually measurements but that will never happen. The youtube and other recordings are quite crappy so I doubt they represent these well. There doesn't seem to be much interest by Big-E to have a better sound recording.

Patent pending, but patents don't actually need to work. If it does work then the patents there to protect the IP. Anybody can build off a patent to test and/or improve a design.

I'm afraid it is just going to be endless story's of how these sound "so great", but not real measurements to every go by. Unless/Until BGM takes a whack on a review and Big-E may not like what the benchtests say.

There is some bull hockey about how these can't be measured, but from what I read that was up around 1kz, far above what I care about.

 

[1n3]

This has been an unusually good technical discussion so far. My thanks to the posters for their contributions. I'm still chewing on what has been presented, and hope there will be more to come.

There are a several active threads about Big E. Rather than derail this thread, could you please take those discussions to one of those threads?

 

[winegamd]

we need to do as much as possible to get the heat out of the enclosure in future designs

If I remember correctly, JBL use to have ferrofluid cooled large format drivers back in the eighties/early nineties. I understand the expense in that, though.

Another option would be to make the baffle a heat sink. Aluminum is light and stiff, as well as an excellent heat exchanger, however, would be more costly than wood.

A copper heat tube heat exchanger could be designed for the motor assembly, similar to those made for gaming PC's.

There were some autosound competitors in the nineties who had liquid cooling systems for their subs. They lived it hot climates and wanted more efficiency and durability.

The Velodyne method of servo control could work with heat sensors to throttle available power in relation to the temp of the motor.

Without getting crazy, though, there is not much to be done, while still maintaining the air leak integrity of the enclosure. I think the modern neo JBL drivers have the best remedy, which is extremely exaggerated heat sinks on the motor/magnet assembly. Plus, most of these methods would just be extreme for a bass instrument system, and more suitable to highend PA applicstions.

 

[dhsierra1]

Another option would be to make the baffle a heat sink. Aluminum is light and stiff, as well as an excellent heat exchanger, however, would be more costly than wood.

This is an interesting idea. A rather thin sheet of Al (say 1-2 mm to keep costs down) ultimately linked mechanically to cooling fins on the baffle or sides maybe?

Use thermal conducting grease to aid in heat transference like for power transistors, voltage regulator etc attachment to heat sinks? Could maybe work as an air tight sealing gasket for the driver to Al sheet, too.

 

[Mike Arnopol]

I have not once mentioned the Big E cabs nor referred to them in this discussion. And after this post I'd prefer to put the subject to rest. I'm really enjoying the discussion in this thread. But as this comment appears to be a mean spirited diss I feel that it's in my rights to respond.

Actually There have been many measurements. And we're finding that these measurements support what we say.

Obviously you have your mind made up but we measured the 85 against the Thunderchild 15 as a reference.If you took the time to look at the threads rather than repeating rhetoric that has been present for months it might provide some insights. The 85 was within 2 db's of the Thunderchild--which is likely the flattest bass speaker out there.I posted the graph.

And I don't know one bass speaker manufacturer that provides any measurement below 200 hz. It's all modeled.Fortunately there are apparently many under our evil spell that have purchased the cabs and are extremely happy with them. Like one owner of a 48 that compared it to his high end two 3015lf based cab. He said that the 48 went just as loud with a stronger low end. Another customer is buying a 48 to replace his high end 215 with 3015lf's . The VD of the four 8's is 720 cc's. The VD of the two 3015lf's is nearly 1700 cc's. And we're not talking thin low end like many of the new speakers that I'm seeing .

So I really don't give a rat's touchas (sp) about the clammering for measurements. I've posted some as stated---with a direct comparison to a known quantity.I see many respected speaker manufacturers that claim "a usable frequency response to---" which I know is a -10db figure. I don't hear any complaints or test results requests for these.



Fortunately for me the guys buying these are actually gigging with them. The comments on the function of these cabinets in the real world holds the most weight for me.

Oh---and on the new 10" based speaker we have measured the response and are getting a true -3db response at around 39hz.

And the only thing that drawing has in common is that the drivers are cross-fired. Ours is not a reflex design. The frequency response (measured) of what's coming out of the ports is the entire spectrum to 4khz. They do not pass on much after 4k. If you knew a modicum about speaker design you would know that a reflex port only supports the lowest octave. (well maybe a touch higher). And it's obviously not horn loaded. A horn would have to be huge to go that low.

As far as recordings--I'm with you--I never would have released that. They did it with the best intentions but it doesn't vaguely represent what the speakers can do.And to be honest---we probably will ---but I'd be very happy with no stupid Youtube stuff. If someone would base an opinion on any posted clip---and the same person said that they needed to see measurements----maybe they're better at interpolating the sound from published specs and a recording with no low end information than I am.

I have not (until now) said anything about our cabs in this discussion.Other manufacturers have referenced their speaker in this discussion. All the parties involved are good guys that are not using this thread to push their speakers.

The person who did mention our speakers heard a 45 (vd of 160cc's) against his 3012lf (vd of 496cc's) and 6" mid cab. He said that it went as loud and with better lows.He also listened to all of the other cabinets. He doesn't own one.




I]in a real[/I]

They are a bass reflex with the drivers alignment crossfire in the form of a line array when you stack more in a cab.

Would like to see actually measurements but that will never happen. The youtube and other recordings are quite crappy so I doubt they represent these well. There doesn't seem to be much interest by Big-E to have a better sound recording.

Patent pending, but patents don't actually need to work. If it does work then the patents there to protect the IP. Anybody can build off a patent to test and/or improve a design.

I'm afraid it is just going to be endless story's of how these sound "so great", but not real measurements to every go by. Unless/Until BGM takes a whack on a review and Big-E may not like what the benchtests say.

There is some bull hockey about how these can't be measured, but from what I read that was up around 1kz, far above what I care about.

 

[B-string]

Don't worry too much Mike. I personally find 90% of what he says to be useless other than to present an opposite, often poorly founded view.

YMMV

 

[Sonicfrog]

Cabs don't kill grooves, people kill grooves.

I've butchered a few grooves, but never murdered one... OK. I have! But nobody recorded it... You can't prove a thing!!!!

 

[DukeLeJeune]

They are a bass reflex with the drivers alignment crossfire in the form of a line array when you stack more in a cab.

They might look like reflex cabs, but they're not.

...we measured the 85 against the Thunderchild 15 as a reference. The 85 was within 2 db's of the Thunderchild...

I'm the guy who builds the cab Mike compared his 85 to, and I've seen the curves. When I first saw them I missed the labelling, but was easily able to pick out which was my cab because his measurements revealed their characteristic zigs and zags that I'm familiar with, so I'm confident his measurements are perfectly valid. Overall the two curves are more alike than different, have almost exactly the same low end extension, and if anything 85's curve looks better to me. And now my marketing department wants to have a word with me...

 

[B-string]

Oh you bad boy...........BEND OVER.

 

[curbowkid]

Oh you bad boy...........BEND OVER.

Well


That escallated quickly

 

[B-string]

Well


That escallated quickly

I see a switch in his future and not the electrical kind.