Tom: Well, we've arrived at a basic design, which did not involve the use of any of the "normal" rules of thumb that seem to govern horn design, and instead fine-tuned the design based on its performance modeled in the computer. The result should be a subwoofer that should outperform most similar sized boxes. Of course, this won't be known as a fact until people have built them. Harry: So no one has built this sub yet? Tom: No, two of the people involved in the project are working on CAD drawings. The drawings I posted are enough for me to build a prototype and then get the final dimensions - but since the CAD capability is there, and with two people who know how to do it, they will be able to come up with the final dimensions without sawdust. Harry: Did you pretty much design the LAB sub as far as sonics, or was it collaboration with others? Tom: Basically, I took what the computer said would be perfect so far as the driver - and then modeled the actual horn and then fine tuned the driver parameters based on the real life horn. Too Tall: It (performance) may not be known then because it seems to be very hard to get measurement data on other subs. Tom: Well, hard data is sometimes hard to find in the audio industry. However, side-by-side comparisons should also show the results. Steve Gray: Is cooling really going to be an issue with the LAB sub? Tom: I should have thought more carefully about mentioning that - the heat issue would certainly be no greater with this box than another. The aluminum panel that I put in the design is there more for clearance of the driver magnet than anything else. I threw in the mention of the heat issue because it sounded like a good marketing gimmick. Steve Gray: I've been thinking about this "bilge pump idea" for cooling; diaphragm and some quiet check valves. Tom: "Bilge pump" - as in boat??? Steve Gray: Now come on....Diaphragm is the back of the cone providing mechanical energy to move air through a pair of check valves. Tom: In a highly efficient horn, one does not want any non-sound radiating load on the cone as the power comes right off of the efficiency side of the equation. On the other hand, cooling a voice coil, for example, even a small amount of air flow causes a significant increase in heat capacity. On the other, other hand the cooling system in our Servodrive's also takes power off the efficiency side so maybe some kind of check valve system would be useable. Steve Gray: My concern also. The venting would also make the rear enclosure somewhat a periodic. Tom: One would not want to lower the Q of that resonance very much - again because that would reduce the efficiency. The horn actually depends on the stiffness of the driver suspension and rear volume for that resonance. Weogo: Maybe Steve has something here. As cone moves forward, a couple check valves open on one side of the box, close on the other. Cone moves back and reverse happens. Tom: Yes, it's possible that would work - we could try it on the LAB woofer. Steve Gray: So where do find some quiet "valves"? Tom: Well, they don't have to be too quiet because they will be right next to something making a lot of sound. Seriously, I have a large antique engine, which uses a leather flap valve, and it doesn't make any noise. Al Limberg: Some years ago I believe it was SAE that used a passive liquid cooling system on some of their amplifiers - probably a refrigerator coil/coolant sort of thing. That might be a solution, with the 'coils' thru the speaker chamber walls. Tom: Yes, there is thing called a heat pipe - which uses capillary action and for their size can conduct a surprising amount of heat from one place to another. Al Limberg: Air moving in the horn throat might aid the process as well. Tom: Yeah - that could be a good spot. jack arnott: How about combine the two, make the motion of the woofer power the capillary pump? Tom: This is getting a little past the goal of the initial LAB sub - maybe later once there is bunch out there, we could do a phase two custom hot-rodding session. Weogo: Tom, I know we all wish you well in your endeavors. What do YOU want of the LAB sound community? Other than a bunch of box orders?! Tom: I want my kids to be able to enjoy concerts without going deaf. Moderator: Final question...and everyone feel free to transfer the chat over to a PSW chat room and also on the Subwoofer Forum... Here goes: Ron S: Hey Tom I read your recent posts on line arrays and I'm working on a project right now. Would I be better off instead of using two 12-in drivers and a horn, using a single 12-in, a 10-in and a horn ( 3-way )? And will a regular horn flare with a 40-degree vertical work? Tom: There are so many variables that I can't really give much of an opinion. This may be more than we can tackle right now. Moderator: Ron - might try posting on the LAB - sure to get plenty of input. Moderator: OK Tom, just one more: What's the most impressive sound you've ever heard? Tom: One of the first payloads I worked on at Intersonics was for a sounding rocket flight. I attended the launch in White Sands, NM - we watched from a concrete bunker about 500 ft. from the launch pad. When the count got to about 15 about half of the people in the bunker walked outside (out of the safety of the bunker) to watch the launch. I went out too and stood there in awe as the rocket ignited and a half a second later the sound arrived! The only thing I can describe it as - a close lightning strike that keeps going - a big KABOOOOOM!!!! that was so loud it made my pant legs flap in the wind. The sad part was the rocket payload we had worked a year on was smashed to tiny bits when the parachute opened at 250,000 feet, melted into the ball - and then failed to slow the rocket into re-entry. It made a 3-ft deep crater in the desert! Weogo: I think I'll stick to the shuttle launch recording thru td-1s and Contrabasses! Tom: Oh, that was fun, too. Moderator: This concludes our chat session with Tom Danley - Tom, thanks so much for your time, contributions to audio and also to the LAB and Subwoofer Forums! And thanks Toni! Charlie Hughes: Tom, thanks for your candor & sharing your knowledge & experiences with us. Tom: Thanks all - I really like coming to the LAB - let's do this
again!
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