Originally Posted by loopguru
Dr. Geddes, just in a general way, I'm curious about your road map for GedLee Speakers. In another thread, I've seen mention of car audio; what I've not seen, though it may be out there, is talk about a floor stander. Would there be any point in doing a TL, or some other bass accentuating cab design, if you're not digging all that low (in frequencies) to begin with?
Thats a good question and brings up what is one of the most unique aspects of my approach. SInce the use of multiple subs can be shown to be the only viable way to deal with the small room LF modal situation, I assume that people will be doing this. If they arn't, well they should be and when they hear it they will be.
Now if one assumes that the room will have multiple subs and that these subs will handle the LFs, then there is no need to worry about LFs in the mains. This allows a design approch that optimizes the mains for response and distortion above 100 Hz only. This is a huge adavantage over trying to take a design down to say 40-50 Hz, let alone 20-30 Hz. The driver have very low cone excursion and they can be close box which results in a very nice monopole.
Of course the obviuos question then becomes - then why use such BIG LF drivers if you are not trying to go low with them. Its not at all obviuos why I do this. I use big drivers for one reason and one reason only - directivity. Only a big driver will get as directional as my waveguides at the crossover. And it is CRITICAL to have the LF driver and the HF driver have the exact same directivity at the crossover.
Unlike many loudspeaker systems, mine are designed from the HF down. I designed these systems arround the critical 1000 - 8000 Hz band where, if this band isn't right then the sound won't be right. This required NO crossovers in this band since crossovers - at best - don't work very well. Thus a crossover at 1 kHz is dictated. Its also important that the HF region be fairly narrow directivity to avoid the very early room reflections. Quickly you can see that the response at 1000 Hz is going to be narrow and that for the LF driver to match the waveguide at 1000 Hz it too has to have a narrow response. A little calculation will show that for a 90 degree pattern at 1 kHz one needs a LF driver no smaller than 12" and 15" is better.
So, you can see that the choice of LF driver had nothing to do with its LF response. The fact that it is so large and has such high efficiency and output is truely an asset, but that was not the primary reason for its choice.
So, yes, I could do a floor stander, but I still wouldn't want to try and extend the LF response since this would add little to the design but subtract a lot. The best option is to just use a stand.
There is a lot to a good loudspeaker system design, much of which is not obvious. A good reference is my white paper as Matt suggests.
Thanks for the great question.