[jparkhur]

Danny,

Was there any discussion on a line source ish using the 3 inch driver...  Something ......

[Danny Richie]

In short, they don't work.

To minimize comb filtering of upper frequency ranges the acoustic centers need to be less then 3/4" apart. Or in the case of a continues diaphragm like a ribbon or planar magnetic driver then the surface edges have to be less then 3/4" apart.

And then you still have to adjust for comb filtering up and down the line.

When you run a line of 3" woofers like that (or 3" full range drivers) then the comb filtering effects cancel out upper frequency range output down into the 2kHz range and up. And the top two octaves are pretty much gone.

I heard a similar design at RMAF one year. And I thought to myself, what are they thinking? That will have no upper end at all. So I listened to them. And they had no upper range at all. No highs, no detail, no real resolution at all. It was pretty much just a mush.

If you allow only one driver to play full range and limit the rest of them to 200Hz or less then it can work really well. But to match sensitivities you typically can't use much more than four of the same drivers to cover the bottom end while allowing the one to play full range.   

[bdp24]

Geez I love hearing people who know what they're talking about explain technical truths! There are a lot of charlatans in the high end, faking their way through design. Danny gives us the truth about speaker design, Roger Modjeski (Music Reference) and Frank Van Alstine (and a few others) do the same about electronics.

[Danny Richie]

Let's put a little meat on what I said about comb filtering.

I have some 3" TB full range drivers in small cube sized ported boxes. I have a pair of them. The cubes are 5" wide by 5.5" tall, and 6.5" deep.

This is the woofer model: http://www.tb-speaker.com/products/w3-871sc

So I set one on top of the other and send them both a full range signal. The green and red lines are each one playing individually and the blue line is the two of them playing together. Note the 6db gain that you get when they are in phase.



Also note that the blue line showing them completely in phase across the whole range is very hard to achieve. If just a quarter of an inch off then the top end starts to drop away. And this is from 1 meter away with a 1 watt input.

This one was taken exactly the same way. They were each shot individually (red and green lines) and then the blue line was the two of them playing together. But the microphone was moved up 4".



So they are out of phase now in the top octave and they create a huge suck out that is much less output than either of the two drivers playing by themselves.

Now here are the same drivers measured the same way but with the microphone moved up 8".



And now at 12" up from center with the mic.



Now there is cancellation down to 2kHz with dips in three areas. And guys this is just with two drivers.

When you add more drivers then you get a lot of cancellation areas up top and a lot of reduced output while you get more and more coupling and increases in output down low where the wavelengths are long. So you get a lot of bottom end but no highs at all.

[Captainhemo]

Exellent   explantions Danny .. 

I'm assuming that runing a  higher effiiciency tweet with two or three  3" dirvers above and below playing mids (# depneding on  c/o point wavelength and  acousitc centers) and multiple  3" drives above and belwow playing lower octaves (c/o  wavelength / acousitc centers shouldn't be a corncern here as  the  wae length will be  large) would work  rather  well

Trick seems to be about  keeping distance between acoustic cneters shorter than the  wave length of the  heghest frewqencey being played by the drivers making up those  centers...... I think 

jay

[Danny Richie]

Exellent   explantions Danny .. 

I'm assuming that runing a  higher effiiciency tweet with two or three  3" dirvers above and below playing mids (# depneding on  c/o point wavelength and  acousitc centers) and multiple  3" drives above and belwow playing lower octaves (c/o  wavelength / acousitc centers shouldn't be a corncern here as  the  wae length will be  large) would work  rather  well

Trick seems to be about  keeping distance between acoustic cneters shorter than the  wave length of the  heghest frewqencey being played by the drivers making up those  centers...... I think 

jay

I think you have it.