Hi
Is the pi an upgrade to a lab?
Better it is to ask what is a labsub first?
Some time ago, in a live audio forum far away, a bunch of people were talking about building some traditional bass horns, “W” bins.
I like DIY, was disgusted with several “big name” horn subwoofers on the market and had some casual rules at my job at the time (Servodrive) so I offered to take a whack at a “modern” horn alignment and a rough layout, based on the cumulative inputs from the participants here on LAB.
The group decided on the standard truck pack dimension of 45 by 45 by 22 ½ inches this was as large and heavy as anyone wanted to move around. A group of 6 should be good to about 30 Hz, it should be as powerful as possible.
Using the modern horn math was where Wayne first popped into the lab sub picture, over on the Audio Asylum forum. He was first criticizing the use a horn for this project (low frequency) and then of the Marshal Leach’s math (which I used as a starting point) vs the older hifi lore approach (of a low mass driver etc).
A search of the archives there would be humorous if your bored.
Anyway, I derived a set of driver parameters for what would be a “modern” driver alignment and laid out the horn similar to another one I had designed, the Servodrive BT-7 which worked well.
The driver was not a stock part or close to any stock driver at the time, this was a problem. I posted the needed parameters so any speaker company could make a driver for the project.
As this was not a company asking for a new driver but rather an internet forum, only one company ended up actually being both willing and able to make a driver.
I have to hand it to Jerry at Eminence for stepping up to the plate on a speculative driver for the project.
Wayne, somewhere along the line “converted” to the view that maybe the heavy lab sub alignment /driver might work, he has made a somewhat larger version, the pi 12.
However, his measured curve for one pi 12 and 1 measured lab sub are only about 1 dB different at most, the measured lab sub is nicer than his model of it fwiw.
The push pull driver arrangement has the same advantage that a push pull transformer does, it reduces the (drivers electromechanical portion) of the 2 nd harmonic (which is also the least audible of all of them) but does not improve the others or any of the odd (most objectionable) ones, hence it is rarely considered worth the bother.
Part of the reason for the odd front volume shape /size on the lab sub is that by lowering the upper passband limit with the un obvious acoustic low pass filter, one can reduce all the higher distortion components (at a given output level) at the same time.
Under some duty cycle conditions the cooling plugs probably increase the long term power capacity.
Under other more musical, dynamic conditions (pink noise has a Peak to Average ratio of only 6 dB, even compressed FM rock is more like 10dB P/A) with larger dynamic ranges it would be unlikely to have a significant effect. It only takes seconds to smoke a voice coil and bass signals are more like large amplitude, low frequency tone bursts.
This is a DIY project, one can layout a different horn of course if you have a different space, one fellow (Brad I think his name was) did that with 4 or 6 at a Church or something I think. If you search the archives here, one finds the acoustic dimensions and such are given if you want to roll your own horn and this is / was a DIY project.
As long as you keep the throat area and front / rear volumes in the neighborhood, the lab sub driver / horn alignment works.
Heck, Wayne went from being a vocal critic of the premise, the basic design philosophy and driver on the A.A., to now occasionally promoting a close copy of it and his website here so I guess that says something.
Lastly, keep in mind the idea behind this was using a modern design approach, to make a VERY powerful subwoofer for “live sound” that keeps up with / beats 95% of the other subs available at any price, that you can build yourself.
Many have found the lab to be more than they expected so far as acoustic power.
Wayne’s box would be very powerful too.
Hope that helps,
Tom Danley
Danley Sound Labs
Author
Topic: Is the 12pi Subwoofer an upgrade to the LAB? (Read 24606 times)