it's like the 7V System IV and Nonsuch 4

[BAM]

I have a question about this one thing that both these speakers do, and I've seen it described on either Bandor's or E.J. Jordan's website. These speakers both feature four drivers, closely spaced in a very short vertical array. What is the reason for this? I have eight 4" full-range drivers that I need to do something with, and I need to know if it would be dumb to do a similar thing with the four drivers tightly spaced in the short vertical array with these particular drivers.

[sreten]

Multiple drivers improve power handling and efficiency over a
single driver.

Four drivers in series/parallel give the same impedance.

Layout for four drivers is 4x1 (vertical), 2x2 or 1x4 (horizontal).

Interestingly Jordan used to use horizontal array's in their older
designs, claiming it gave a 'planar image' whatever that means.

A vertical array gives a consistent horizontal dispersion
characteristic with lobing in the vertical plane, a horizontal array
unsurpringly gives lobing in the horizontal plane with consistent
vertical dispersion.

Its now generally accepted that consistent horizontal dispersion
is more important than vertical dispersion for stereo imaging from
different seating positions.

The 2x2 layout was only ever used when four units were used
as a composite bass driver, as it lobes at higher frequencies in
both planes.

So the best layout for four small drivers is vertical, but in real life
theres a lot more to it than wiring them in series/ parrallel.
/sreten.

[7V]

BAM, I use the four 2" drivers in a vertical array but have to get them as close together as possible to avoid combing at high frequencies. This is where the high frequencies cancel each other out. Even getting the drivers as close as I do, I lose output over 10kHz if I stand up to listen (it's worth it for the great sounds that I can get when sitting).

With four 4" drivers (per side) you'd have real problems owing to the distances between the drivers. To get an idea, download the VPR (Vertical Polar Response) program from The FRD Consortium. This should give you an understanding of what goes on.

You could still produce a great system with your 4" drivers. Either add a filter network to cut out the high frequencies from all but one of the drivers or add a tweeter. I believe that Timn8ter has done something similar and I'm sure he would offer advise if you go this route.www.allegriaaudio.com.

[sreten]

Just add to 7V's excellent comments :

Unless your drivers are specifically designed to be full range treble
response will be very poor, as most drivers will be designed for a
smooth 2nd order roll off above 5 kHz.

4 inch drivers are too large for a vertical array (IMO), lobing / combing
effects in the vertical plane will be severe.

Overall frequency response is likely to be very poor.

You could do a lot worse than a design based on the mission 753.
(see picture)

The top two drivers are used in a sealed enclosure and crossed
over to a tweeter. The bottom two drivers are used in a larger
volume reflex loaded enclosure.

Note the two sections are run in parralell in the bass, the bottom
section 1st order rolloff to effect 'baffle step compensation'.

The crossover for the top section is obviously a more complicated
affair, there are advantages to only running the top unit in the
crossover region (lobing / combing again !)


/sreten.

[Timn8ter]

I believe that Timn8ter has done something similar

In a side by side comparison with the two driver ELF 1.5 and my four driver Isa, the Isa has a much wider sound stage, plays louder with the same power, and will go a tad bit lower producing a fuller sound. The vertical dispersion Steve describes for the Nonsuch occurs on my design too. It seems that the four driver arrangement comes close to acting like an array, a cylindrical sound field rather than the spherical one of a single point source. Backing away into the far sound field this effect is much less but who wants to stand clear back there anyway? I did use a BDSC network on the lower two drivers.

[kelticwizard]

Originally posted by Timn8ter

.... two driver ELF 1.5 and my four driver Isa....

....I did use a BDSC network on the lower two drivers.

A) ELF, (Extended Low Frequency): Is that the enclosure type where you make a ported box much smaller than optimum, tune the box much lower than usual, and then equalize the low frequencies upward?

B) BDSC network: I am unfamiliar with this. Can you please explain?

[sreten]

makes sense regarding the two lower drivers /sreten.

[sreten]

try again ?

[Timn8ter]

Originally posted by kelticwizard


A) ELF, (Extended Low Frequency): Is that the enclosure type where you make a ported box much smaller than optimum, tune the box much lower than usual, and then equalize the low frequencies upward?

B) BDSC network: I am unfamiliar with this. Can you please explain?

A) Not in my case.

B)
Baffle Diffraction Step Compensation- The lower two drivers roll off the high frequencies at the same rate the upper two drivers roll off lower frequencies as they move from 2 pi to 4 pi.


BDSC networks

[usekgb]

Another advantage to using at least four drivers in a line is, you only lose 3 dB when you double the distance instead of 6 dB. This is caused by acoustic coupling of a "line array" of at least four drivers.

Cheers,
Zach