Folded Dipole Dimensions

[Victoria]

I would like to build a dipole speaker system in which the woofer portion uses two drivers and is folded.
There is no mention of this type of speaker in the 1981 edition of David Weems book. I am waiting for the 7th edition of the Cookbook I have ordered the but the online Table of Contents for it does not show anything either.
My questions are: How do you size the width and height of the openings, front and rear, of this arrangement? And are the dimensions a function of the T/S parameters of the drivers? Thanks, Vic

[Rudolf]

Originally posted by Victoria
How do you size the width and height of the openings, front and rear, of this arrangement? And are the dimensions a function of the T/S parameters of the drivers?

There are different kinds of folded dipoles known as H baffle and W baffle. Lesser known types are Z baffle and N baffle. If you could give us a more precise description of the construction you are talking about, help would be easy.

While a certain set of T/S parameters gives better results in dipole drivers the dimensions of the "box" are not a function of the T/S parameters, but of the desired bass extension. The bigger the lower.

[Victoria]

The one which set me off had the drivers on horizontal boards. The front of one driver faced into the front facing cavity and the rear of the other driver protruded into this cavity. The rear facing cavities were
formed by horizontal boards above and below each driver. Each side was closed in by a vertical board. Which baffle is this?
I need to know how to size the output area of these cavities. Obviously, the width is somewhat set by the driver that is used. So how do you size the height?
I propose to build a 3way using an ESS AMT, a fairly decent 5 or 6" midrange, and 10 or 12" woofers.
But I'm not really up to speed on the current speaker technologies so I am open to your suggestions and help. Thanks, Vic

[JohnL]

Hello Victoria,

I think you are referring to a W-baffle woofer. Linkwitz Labs website has some info on how to design such a thing.

Linkwitz Lab Phoenix Woofer

Those things do develop a cavity resonance based on the size of the thing that might make it difficult to cross to a 5-6" dipole woofer. Mr Linkwitz crosses his to a pair of 8" in the Phoenix. Again, the site gives you all the math to figure it out.

I am interested in your design, I've got something very similar in the planning stages now (AMT, single 6-7", a pair of 12-15") Because of the AMT, I'm looking at trying to keep the efficiency up. Mid choices I'm currently entertaining are Audax PR170, PHL 1120, or maybe something else. For woofers I'm thinking Lambda dipoles or perhaps something from JBL Pro (2225H?). If you do a search for a user named Ultrachrome on this forum, I like the direction he has gone with his project. In any event good luck, and keep us up on your progress.

John

[Rudolf]

OK Vic,
if the dipole you saw looks somehow like the one in the picture, its a W baffle. Heigth H needs not be larger than the woofer dimensions demand. Most people decide to let Depth D be the same as "H". "D" is forming the length of a lambda/4 transmission line being responsible for a resonance peak of up to 15 dB (cavity resonance). You want that peak to be as far away from your usable passband as possible. So it makes sense to have "D" as short as possible, i.e. the same as "H". The width of the 3 chambers is a matter of dispute. The area of the outer openings may be from 1/2-1/4 cone area. The area of the "inner" opening should be about double that of each outer opening.

As John said, try to get some more insight from the Linkwitz site. It doesn´t get more precise than there.

Rudolf