W-frame Dipole Construction Q

[weinstro]

Hi,

I've searched the archives, but cannot seem to find an answer....

1. Does it matter if the drivers are installed pointing in the same direction, but wired out of phase, as shown on

"standard" Linkwitz W-frame

or with the drivers facing each other, but wired in phase, as shown on (see image at bottom of page)

"stacked" Linkwitz w-frame?

2. Is there a benefit to offsetting the drivers towards the front edge of the cabinet? For example, in the last image, the 1.75" offset could go to zero in the front, and change to 3.50" in the rear.

3. Is there any requirement to match the chamber openings of the cabinet to the effective driver area? For example, a Peerless 830500 has an Sd of approximately 100 sq. in., but the chamber opening is 14" x 4.5", or 63 sq. in. Seems a little small....

[gtforme00]

1. The drivers should be arranged and wired such that one motor is pushing, while the other is pulling. This ensures that you will have symmetric output capability on both the front and back of the enclosure. This also helps to mitigate some of the distortion associated with non symmetric force products as the voice coil changes position in the magnetic gap.

2. I suspect that the offsets in Linkwitz's designs are more for the visual effect than for any acoustic benefits. Note that any change in the acoustic path length of the front wave compared to the back wave will have some (likely small) effect on the dipole radiation pattern. I don't think that 1.75" offset would cause the design to be invalid.

3. The chamber opening is often recommended to be no smaller than the driver area. This is simply a generic recommendation and is not a strict rule. I do not think that Linkwitz would recommend a design which was deficient in performance, and would not hesitate to build the W frame to which you refer.

One certain aspect that you will have to deal if you alter the geometry from Linkwitz's designs is the correction filter. Linkwitz's filter corrects for the specific response anomalies associated with the exact geometry he constructed. If you deviate significantly from the dimensions in the plan or change the drivers chosen, you will have to measure the response of your particular setup and customize your own filters.

Best of luck and feel free to ask more questions!

Regards,
David

[Jonasz]

I can recommend his W-design with the 830500 as described. I've had it for several years and I'm still to hear something better. I've listened to the Orion and I can say that the Phoenix W-baffle is at least as good as the Orion bass and it plays more effortless too.

[weinstro]

Originally posted by Jonasz
I can recommend his W-design with the 830500 as described. I've had it for several years and I'm still to hear something better. I've listened to the Orion and I can say that the Phoenix W-baffle is at least as good as the Orion bass and it plays more effortless too.

How did you finish the cabinets?

Thanks,

Rob

[Calvin]

Hi,

I prefer the ´stacked´style.
Not only does it give better optics as to my taste, but both drivers work under identical conditions, which is often not the case with the standard frame. If the chambers are not of equal volumes (at least 2 of them) the drivers work under different conditions, which -in my opinion- renders the possible advantage of distortion reduction obsolete.
The offset looks rather like a method to me to flush mount a piece of cloth.

The opening -aka chamber volume- and its effects can be calculated/simulated.
The design rules are:
- the smaller the dimensions the more will the freeair resonance of the drivers sink. In conjunction with a passive Notch and LP, You can reduce the Fs up to ~15-20Hz! Which is a nice feature, since You can use drivers with a rather stiff suspension, which will lead to an improved behaviour under high stress conditions and/or You can find many 15" or 18" PA-drivers with suitable parameters.
- there is a kind of treshold down to which the reduced volume just reduces the Fs of the driver. Reducing even further the efficiency drops drastically and even noise (similar to too small BR-channels) may be generated with elevated excursions.
- the larger the excursion capabilities of the driver, the larger should be the opening.

jauu
Calvin

[theAnonymous1]

What should the area be for two 15" drivers sharing the same opening. I understand it's 25-30% of Sd for one driver, but I can't find any info for using two drivers.

[Jonasz]

Weinstro: Here's a pic of my system, it's 3/4" MDF painted black, nothing fancy but it looks pretty nice to me...

[weinstro]

Originally posted by Calvin
I prefer the ´stacked´style.
Not only does it give better optics as to my taste, but both drivers work under identical conditions, which is often not the case with the standard frame.

That's kind of what I was thinking, too.

Originally posted by Calvin
The opening -aka chamber volume- and its effects can be calculated/simulated.
The design rules are:
- the smaller the dimensions the more will the freeair resonance of the drivers sink. In conjunction with a passive Notch and LP, You can reduce the Fs up to ~15-20Hz! Which is a nice feature, since You can use drivers with a rather stiff suspension, which will lead to an improved behaviour under high stress conditions

I've selected a driver with Fs = 23 Hz, and Qts = 0.45. It shouldn't require much shift in Fs.

Thanks and regards,

Rob

[weinstro]

Originally posted by Jonasz
Weinstro: Here's a pic of my system, it's 3/4" MDF painted black, nothing fancy but it looks pretty nice to me...

Looks pretty nice!

Regards,

Rob

[weinstro]

Originally posted by Calvin
The offset looks rather like a method to me to flush mount a piece of cloth.

Actually, I was thinking back to what another member had said about cardioid responses and U vs. H frame. I found this post to be interesting:

Post on U frames