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 ?
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 ?
Attachments
tinitus said:
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.
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
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
Attachments
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
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
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
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
tinitus said:
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 said:
The driver specs are MOST important !
You cannot ignore the behaviour of the driver
near its resonance !
I just said, that for the fs 16 Hz Qts 0.7 driver you proposed,
you can do just an edge simulation, because differences
between an idealized driver and this driver are easy to predict.
I did NOT say that the drivers parameters can be igored.
Cheers Oliver
Rudolf said:
it is misleading to use "baffle step" in conjunction with OBs IMHO. Dipoles don´t have a BS.
Sure? Aren´t Green and Pink swapped?
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?
Hi Rudolf,
- The curves are not swapped, i checked it.
- As the hump for the 2 woofers is 2dB higher and the curve
has stonger fall i would call the hump "more accentuated"
How would you put it ?
- I know your authority concerning open baffles. But which
term would You suggest for the hump occuring in almost
every open baffle design ?
I don't mind using a different term, if it describes the thing.
Kind regards
tinitus said:Just tried EDGE and BASTA ... well, I knew I wasnt very good at computersseems I have to rely on experience(limited) ... cant be that a total of 8 x 15" woofers with Fs=16hz and Qts=0.7 wont do bass
As Rudolf recommended, for subwoofer application you
should consider a H or a U-Frame.
The behaviour of a damped U-Frame is very interesting too.
http://www.musicanddesign.com/u_frame.html
Cheers Oliver
Could be a smart move indeed.
Placement in your room is important.
If you have not much distance to the next wall,
it is better to place the dipole to radiate
parallel to the wall. You can also try placing it tightly
at the wall, so the wall makes the H-Frame longer
at one side, as the bottom does anyway.
===============================
..............===========..............................
....................... |...........................................
....................... |............................................
....................... |............................................
..............===========...............................
Is this going to be a mono sub ?
Exciting the room at more then one point can give
a more balanced excitation of room modes.
Even if efficiency drops, it may be preferable to have
2 x 2 woofers in 2 separate H-Frames. So you can choose
if you want to stack them ontop of another or place
them separately as You like. It is just 2 panels of wood
more to pay and the frames are easier to handle.
Maybe then stereo is preferable since you have
already 2 distinct subs anyway.
You can think of downsizing them a little by using a
Z shape by tilting the mounting baffle for the drivers.
=============
............ /.........
............/..........
.........../...........
........../............
=============
But making the frame's area smaller than cone area
will increase moved mass and thereby lower fs and
increase Qts . So so don't overdo it, otherwise you
are building a Ri(diculous)pol . (Sorry couldn't resist ...)
Tilting the Z for each driver in an opposite direction,
will reduce vibrational exitation of the cabinet
since both drivers tend to move in opposite directions ...
Another panel of wood more to glue.
For calculation of displaced volume needed for a
certain SPL dependent on frequency and length
of the H-Frame you can use the excel sheet on
Mr. Linkwitz' page ... the SPL will be higher as calculated,
if you use the wall placement.
To save space it may be allowed to make the H-frame
even shorter then, just tolerate 3 - 6 db less than your
desired max SPL, the wall will compensate for it.
A wall tight placement may allow to omit the side of the
H-Frame facing the wall at all ... maybe replace it by some
sealant like a soft rubber tube e.g.
Just ideas ...
Cheers
Placement in your room is important.
If you have not much distance to the next wall,
it is better to place the dipole to radiate
parallel to the wall. You can also try placing it tightly
at the wall, so the wall makes the H-Frame longer
at one side, as the bottom does anyway.
===============================
..............===========..............................
....................... |...........................................
....................... |............................................
....................... |............................................
..............===========...............................
Is this going to be a mono sub ?
Exciting the room at more then one point can give
a more balanced excitation of room modes.
Even if efficiency drops, it may be preferable to have
2 x 2 woofers in 2 separate H-Frames. So you can choose
if you want to stack them ontop of another or place
them separately as You like. It is just 2 panels of wood
more to pay and the frames are easier to handle.
Maybe then stereo is preferable since you have
already 2 distinct subs anyway.
You can think of downsizing them a little by using a
Z shape by tilting the mounting baffle for the drivers.
=============
............ /.........
............/..........
.........../...........
........../............
=============
But making the frame's area smaller than cone area
will increase moved mass and thereby lower fs and
increase Qts . So so don't overdo it, otherwise you
are building a Ri(diculous)pol . (Sorry couldn't resist ...)
Tilting the Z for each driver in an opposite direction,
will reduce vibrational exitation of the cabinet
since both drivers tend to move in opposite directions ...
Another panel of wood more to glue.
For calculation of displaced volume needed for a
certain SPL dependent on frequency and length
of the H-Frame you can use the excel sheet on
Mr. Linkwitz' page ... the SPL will be higher as calculated,
if you use the wall placement.
To save space it may be allowed to make the H-frame
even shorter then, just tolerate 3 - 6 db less than your
desired max SPL, the wall will compensate for it.
A wall tight placement may allow to omit the side of the
H-Frame facing the wall at all ... maybe replace it by some
sealant like a soft rubber tube e.g.
Just ideas ...
Cheers
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