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In Reply to: Best bass posted by rick57 on September 25, 2002 at 22:56:43:
Very interesting and ambitious project you have there, Richard! I was an amateur speaker builder for almost 20 years, and still dabble in it from time to time. But I never undertook anything as ambitious as your project.Most of my projects were transmission lines, but I do not recommend a transmission line for your application. A TL is not a sure bet, and in my opinion the main advantage of a TL over a transient-optimized reflex tuning is better midrange because the stuffing absorbs the backwave in the midrange. But your dipole PHL midrange will be better than a transmission line would have been.
The lower down you can maintain that high 95 dB efficiency, the better. So I'd say take your main speakers down to 40 Hz or so if you can. The very bottom octave can then be reproduced by a less efficient sub. This scheme will preserve the outstanding dynamics of your PHL mid and ribbon tweet over the widest range possible.
My personal suggestion would be to use a high quality 15" woofer from 300 Hz on down to the 40 Hz ballpark. This will almost certainly be a vented box, because woofers whose parameters give the kind of efficiency you want are best suited for vented boxes. If you are leaning towards the Lambdas, shoot me an e-mail. I know someone looking to sell a pair of TD15X's.
There are relatively few woofers that will take you all the way down to 18 Hz. I looked around and found an interesting 18" driver made by a company called "BluePrint". You would need equalization to get flat response down to 18 Hz, but this driver has enormous displacement capability (two inches peak-to-peak excursion) so it can take more equalization than most other drivers can. I've never heard this driver, so I'm not endorsing it - just mentioning it as a possible candidate for your subwoofer.
Duke
Follow Ups:
Maybe I didn't make my intention clear. The possible TL would just be for the subs, probably in the corners. The bass main drivers would be in separate boxes in a 'normal' position a few feet from the walls (with the diploe mids, and tweeters time aligned above). So the TL is only relevant/ an option for bass below about 80 Hz.
You're right I'm a little ambitious, if I'm going to do it I went a pretty damn good result.
Your suggestion of high quality 15" woofer from 300 Hz to 40 Hz seems good.
Thanks I'll have a look at the BluePrint I'll have to seek some opinions on this too.
Re Lambdas, it's a little too early to pick the driverThanks
Richard
Thanks for the clarification on your intended use of transmission lines, Richard.I still wouldn't suggest TL's for the subs. In my experience, the odds are that a TL won't deliver the bottom end performance expected. This is because, to the best of my knowledge, TL's don't follow the classic design theories. There have been a few new theories put forth recently (including a particularly interesting one by Jon Risch), but I have no experience building with the new theories. I have no doubt that there are manufacturers who know how to mathmatically model a TL, but I don't think that information has been made available to the general public.
I once built a pair of 16-foot transmission lines, following the conventional wisdom of the day regarding line cross-sectional area. Despite quite a bit of playing around with stuffing density, I never got any serious deep bass out of the line.
Over the years I did quite a bit of experimenting, and finally got good results with an intuitive rather than mathematical design that in retrospect probably worked by sheer chance. I used multiple drivers in an "offset" configuration (borrowing that term from the 6th edition of the Loudspeaker Design Cookcook), with a line geometry somewhat reminiscent of the "chambered" line.
If you use a large vented cabinet and tune it very low, you will get a very gradual rolloff with correspondingly very good transient behavior. A large driver x-max is called for to keep the woofer from bottoming out. You might try modelling the BluePrint 18" woofer in a 10 or 12 cubic foot box, tuned to 18 Hz or so, with a 4th order low pass filter at 40 Hz (it would have to be an active filter). System efficiency will be in the mid-80's, but you might not even need any equalization.
Best of luck!
build one using IM Frieds designs. Mine play 10 hz at 80+ dbs.
Some questions: What are IM Frieds designs (is there a web reference)?
Are they complex, how long are the lines and how large the boxes, and what sort of spec and $ drivers do they need to do this?Rick
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