W-Frame or H-Frame dipoles? performace issues?

[JinMTVT]

is there any difference in the two designs performance wise ??

i am ( again ) slowly planning winter projects,

and i am considreing all dipole system
( manger on top and 2 15" on bottom...stereo )

I've seen alot of people using Linkwitz H frame design
and only a few talk about W Frame

Then, would a W frame work correctly if on the side??
( ie the 2 drivers on top of each other ...like having it rotate 90deg
on the Z axis )


Also beeing there, how high QTS should i look for in dipole woofers? is long excursion desirable? ( should be crossed at 150-250hz ..to be determined )

Was looking at either McCauley or Belisle Accoustics subs
( the mcCauley 18" are very very very very tempting again .. )

thanks again all for your time!

[DougL]

and i am considreing all dipole system

You should like that.

I've seen alot of people using Linkwitz H frame design
and only a few talk about W Frame

Both are more compact than a flat baffle. They trade cavity resonances that limit their upper frequency response for compactness. The W is more compact, somewhat harder to build and may be somewhat more high frequency challenged.

Also beeing there, how high QTS should i look for in dipole woofers? is long excursion desirable? ( should be crossed at 150-250hz ..to be determined )

IME Qts of .5 is Ideal. Lower than .5 requires additional equalization. Higher can compensate for OB roll off and should be considered an engineering decision. I have seen woofers of Qts as low as .3 used successfully, and I would consider a Qts of .8 as my personal maximum. If you have reasonable H or W enclosures, you are going to require Equalization. As long as this is true, you need as much excursion as practical. At this point, you are balancing distortion, cost, efficiency, size and excursion.

Good luck;

Doug

[Rudolf]

I second Doug in all his arguments,

and dare to give a rule of thumb:
Up to 150 Hz x-over W-frames may be fine. For anything above that you should build an H-Frame (while this will need more EQ bass-wise). Since taking a dipole bass up to 200 Hz is a good idea in every respect , I would vote for the H-frame.

Rudolf

[JinMTVT]

i thank you both for your sharing ..

is the only advantage of the W frame compactness compared to the H ??


i am still unsure as to QTS
when a driver has a higher QTS, does that means
trade offs on other parameters/performance??

Can the cavity resonnance be predicted?

i also wonder if there would be any benefit in using rounded off sides for the enclosure? ( round ends on each side of the enclosure where the wave meets ... )

i will do both type in 3d later on and see what i can get off the feeling of it!

[Davey]

Another characteristic of the "W"-frame construction is force cancellation. The two cones are always moving in opposite directions so vibrations imparted to surfaces...like the floor...are minimized.

A typical W-frame construction would be somewhat "squareish" when viewed from the front so I don't see any reason to orientate the drivers horizontally. Cone sag could become an issue in that case.

You can make a fairly good estimation on the cavity resonance based on the depth, but you need to confirm it with a close-up measurement once constructed.

Cheers,

Davey.

[Rudolf]

Originally posted by JinMTVT
i am still unsure as to QTS
when a driver has a higher QTS, does that means
trade offs on other parameters/performance?

Not necessarily, but:
High Ots can be had for less money than low Qts. So many cheap drivers "feature" high Qts values along with other money-saving " attributes".

Can the cavity resonance be predicted?

For the Phoenix W-baffle Linkwitz reports very different cavity resonances (190/270 Hz) for two different drivers (Peerless XLS 12 / Madisound 1252 DVC) in the same baffle. So I believe there is no really easy way to predict it.

i also wonder if there would be any benefit in using rounded off sides for the enclosure? (round ends on each side of the enclosure where the wave meets ... )

It´s still not clear to me, what exactly you mean. May be a drawing would help.

[JinMTVT]

fig.1a demonstrates what i talked about,
using rounded off enclosure edge
would there be any benefits to doing that?

would there be any benefits in rounding all the edges inside the enclosure also ?


fig.1b shows different enclose side angles
would that have any benefit in the resonnance department ?

i have learned from experiment that using never perfect and paralell angles for construction almost always pays off somehwere in the audio !!

please excuse the humble drawings
hope you see what i mean !!

[mcgsxr]

I am using a pair of these 12's, sourced from a great guy in Western Canada, in open baffle.

Each 12 is located at the bottom of a 36w x 48h baffle, in which lives a Visaton b200 full ranger.

By running the 12 on only 1 of the two voice coils, you double the effective QTS from 0.38, to a very nice (for OB) 0.76... good XMAX, good FS, good for OB!

http://www.mach5audio.com/product_in...a425a028ed2259

under $65 each, shipped, in Canada, and great performance in OB...

Well worth a look,

[JinMTVT]

i am not sure that i get your point
else than pointing out to this driver and website

where are those drivers manufactured ?

i'd like to buy from TRA if possible,
as their drivers are all manufactured here in Quebec!!
and they seem to have seriously good quality
second choice was 18" from McCauley
but 18" will have a huge footprint and i can't really afford that in my room

( the 18" will have to wait for the new house theater room )

thanks neway for pointing this site out !!

[Rudolf]

Originally posted by JinMTVT
please excuse the humble drawings, hope you see what i mean !!

Certainly I get it now. And no - rounding the enclosure edge will have no benefit. The length of a 100 Hz wave is 3.14 m, so it doesn´t "see" such a small extension. This is even more true for any edges inside. Rounding them off is only for aesthetical reasons.

A W-frame like yours will have a quarter wave resonance almost at lambda/4 = depth of W. A H-frame would have its resonance at double that frequency. So you will be pushed hard to get that W-frame up to 250 Hz. Have a look at mine:
http://www.diyaudio.com/forums/attac...amp=1159221400
And this is the nearfield frequency response: