OB efficiency with 2 or 4 woofers

[tinitus]

Hi

Been thinking about this one

Will there be any advantage of having 4 woofers, ending with 8ohm, where as the 2 woofer design will be 4ohm

Also the 4 woofer design will have the woofers closer to the edge

The 2 woofer design will have relative more baffle at the sides

Any thoughts about this issue ?

[Rudolf]

Originally posted by tinitus
Also the 4 woofer design will have the woofers closer to the edge
The 2 woofer design will have relative more baffle at the sides
Any thoughts about this issue ?

I just did a simulation comparing two 10" woofers on a 100x50 cm baffle. First one woofer on top of the other, second both woofers side by side at the bottom. My results gave a 1-2 dB loss from the missing baffle sides. Since your OB is quadratic the loss should be more pronounced. While you would expect a 6 dB gain from doubling the cone area, you probably will only gain ~ 4 dB.

[tinitus]

Thanks Rudolf, thats in line with my thoughts ... more baffle is almost free

[LineArray]

Hi tinitus,

the advantage of the 4 woofers is a more benign baffle
step.

See attached pic for floorstanding baffle.

GREEN = 4 Woofers
PINK = 2 Woofers

At low frequencies power efficiency doubles using the
four woofers and max acoustic power output is x 4, when
using the 4 woofers instead of 2, if all woofers are equal.

"Voltage efficiency" of both configurations you propose
is about the same at low frequencies, since your 4 Woofers
have double impedance.

There seems 1 dB loss at low frequencies, due to the
driver placement when using 4 Woofers.

So we can say, the baffle configuration with the 2 Woofers
in itself is bit more efficient at low frequencies, with the price of
a far more accentuated baffle step.

This is how i see it.

Cheers

[LineArray]

Originally posted by Rudolf


My results gave a 1-2 dB loss from the missing baffle sides.

Sorry Rudolf, you were faster ...


Regards

[tinitus]

Thanks guys,

Below 100hz there seems very little to gain from multiple drivers, surprisingly little, or could it be a matter of which driver is used in the simulation

If possible, could I please ask you to simulate with this driver

http://www.aespeakers.com/drivers.php?driver_id=8

[LineArray]

If you would wire the 4 drivers in parallel, there would be
5dB gain instead of 6dB.

It is still 5dB gain in SPL.

The 1db you loose, is due to the placement of drivers.

If you compare a 2 woofer and a 4 woofer configuration
with SAME TOTAL CONE AREA, you will find placements for the
4 woofers with same efficiency at low frequencies
but reduced baffle step. This is one reason why i personally
prefer do distribute the needed cone area to more than
one driver.

In your baffle is no choice for placing the 4 drivers
somewhere else then near the corners. This is why
you gain only 5dB instead of 6dB IMO .

The relative effects of driver placement and the number
of drivers used are totally independent from the kind
of driver used.

Chees Oliver

[Rudolf]

Originally posted by LineArray
the advantage of the 4 woofers is a more benign baffle step.

it is misleading to use "baffle step" in conjunction with OBs IMHO. Dipoles don´t have a BS.

See attached pic for floorstanding baffle.

GREEN = 4 Woofers
PINK = 2 Woofers

Sure? Aren´t Green and Pink swapped?

So we can say, the baffle configuration with the 2 Woofers
in itself is bit more efficient at low frequencies, with the price of
a far more accentuated baffle step.

Uh? Where am I supposed to see that "far more accentuated baffle step" in the diagrams? Could it be we have different perceptions of baffle step?

[LineArray]

Originally posted by tinitus
Thanks guys,

If possible, could I please ask you to simulate with this driver

http://www.aespeakers.com/drivers.php?driver_id=8

Hi Tinitus,

the driver has fs 16Hz an Qts 0.7 right ?

So it would be only 3dB down at 16 Hz when mounted
into an infinite baffle ....

If you use EDGE, there will be very little difference between
the simulation of an ideal driver( EDGE cannot take
driver parameters into account) and a simulation taking
this drivers parameters into account.

For frequencies above 32 Hz you just can do an EDGE
simulation and the result will be nearly the same for
an ideal driver and the driver you proposed.

If you want to take the drivers parameters into account,
you can superimpose the edge output with the drivers output
in an infinite baffle. That will show an additional rollof
of 3db at 16 Hz caused by the drivers fs and Qts.

Just download EDGE if you have not done so up to now,
its free.

http://www.tolvan.com/edge/

Cheers

[tinitus]

Originally posted by LineArray

In your baffle is no choice for placing the 4 drivers
somewhere else then near the corners. This is why
you gain only 5dB instead of 6dB IMO .

The relative effects of driver placement and the number
of drivers used are totally independent from the kind
of driver used.

Chees Oliver

With 15" woofers there is a certain limit to baffle size

I would use it only below 100hz so I do think driver specs are important

With a dipole sub I thought that multiple drivers would deal with some of the OB problems ... seems not to be so simple


Thanks, I will try "EDGE"