W Dipole (Linkwitz alignment) Sizing Q

[arc2v]

Okay, I have searched, read, searched more, and still can't find a good resource on how to size a W frame dipole sub.

Starting from these pages:
http://www.linkwitzlab.com/woofer.htm
http://www.linkwitzlab.com/woofer3.htm

I see he has a couple of designs for different drivers, but they are mostly the same principal. Drivers force air out of the front in a combined slot and out the back in two individual slots.

It seems he sized the height just to clear the drivers and I never read anything about why its depth was set.

The real confusion was how to size those individual slots. There seems to be no rhyme or reason. Originally I thought he was trying to get the output slot near the same size as the Sd of one driver (double that for the middle), but all the slots are different widths.

Also, he mentions that you can make one of the cabinets narrower by shortening one of the slots by 1.5"!!! But he never mentions trade-offs other than it will be a pain to mount the drivers.


I have 2 15" drivers that have been playing true Open Baffle (no baffle ) on my floor for few months. They sound pretty good just like that, but the wife wants a bit more aesthetics, so I need to box them in The above designs intrigued me, but I can't seem to find a design guideline.

All help appreciated!
AC

[MisterTwister]

you may try this design
http://www.mfk-projects.com/dipole_s..._series_ii.htm
I think it's more aesthetic looking than Linkwitz design.

[arc2v]

Sorry, I should have mentioned this:

The sub is going under a screen, so it can't be too tall, and it *may* end up being the stand for my DIY center speaker, if I ever get around to finishing it.

That's a nice looking sub, but too tall for my application. Thanks though.

[Rudolf]

Originally posted by arc2v
Also, he mentions that you can make one of the cabinets narrower by shortening one of the slots by 1.5"!!! But he never mentions trade-offs other than it will be a pain to mount the drivers.

You may search the forum for the "ripole" variant of the W-frame to get the lowest bass at the lowest box volume. By shortening the slot (mainly the slot in front of the cone) you lower the Fs of the driver and raise the resonance peak of the cabinet. For a front slot area of 1/4 Sd of the driver you can expect Fs lowered about 20 %. But that depends much on the driver too.
You pay with a lowered efficiency. I measured about 5 dB less SPL compared to a H-frame of equivalent dimensions.

You mention that you will position the sub under the screen. Are you aware that dipoles normally need at least 3 feet distance to the front wall?

[Empee]

Hi !


Excuse me for diggin' up this thread, but have you come up with anything as how to calculate a W-dipole ?

Cheers,

Empee

[Bierbauch2000]

Hi,
i am looking as well for a tool or everything else to calculate a w-dipol ( Ripol )

cheers

Bierbauch2000

[DAMIC]

There is something on this thread:

http://www.diyaudio.com/forums/showt...t=#post1309701

[footloose]

Do you think the following drivers would be ok for use in a open baffle subwoofer, (4 per side)?

# Nominal Diameter 380 mm
# Power Capacity 500 watts
# Sensitivity 96 dB/watt/m
# Frequency Range 30-500 Hz
# Impedance 8 ohms
# Bl Factor 19 N/A
# Voice Coil Diameter 75 mm
# Voice Coil Material Copper
# Maximum Excursion 28 mm (before damage)
# Magnet Assembly Weight 8.1 Kg
# Effective Moving Mass 0.098 Kg
# Compliance 0.00017 M/N
# Volume displaced by unit 6 litres
# Fs 39 Hz
# Qt 0.32
# Xmax 4.5 mm

[Bierbauch2000]

Hello footlose,

i think they will work fine,

but thats only my opinion

You must test the driver.

I think they will work fine in as a Ripol

http://www.verruecktedinge.de/lautsprecher/Dipol.html

have a look on my homepage (it's only in German)


Cheers Bernd

[Calvin]

Hi,

I´d say they work, but do they work fine?????
Two of the most important parameters are missing
a) does the driver work noisefree under heavy excursion condition and
b) the quality factor Qm

The excursion capabilities of the drivers are quite low, though a quad each side will lessen the stress a bit. Still though You´d build a rather big subwoofer with rather low SPL capabilities.
The Qt is ok, but since it isn´t mentioned which part of it relates to Qm resp. Qe the Qt-figure is of lower usefulness.
The Fs is quite high. You can expect a serious reduction of Fs when built into a small ripol-cabinet (because of the low excursion capabilities the dimensions can indeed be very small) but as long as You don´t know Qm You can´t estimate the degree of the resonance-lowering. It might be (quite often to find with lossy drivers) that the fs-reduction is negligible. On the other hand can a lowloss driver show reduction values of 10Hz and more in the same cabinet.
So I wouldn´t say it´s a bad drivere for this application, but I wouldn´t say its a good driver for this application either.

jauu
Calvin

(ps: this comment relates only to the ripol-topic in this thread!)