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

[JinMTVT]

ok
i have to admit that i do not understand or grasps half of what you guys are talking about ..


if we summarize ...


W-Frame advantages and H-Frame advatages

inconvenient and prerequisites of the drivers for both also


Then design wise,
do the drivers need to be at 90degree perfectly for a W-Frame magic to happen ?
is there any other design rules to follow when constructing a W or an H baffle

i also didn't find the Linkwitz paper you guys are all refering to .

and both needs to be seriously braised enclosures because of obvious vibrations/resonnance?


I would like to know wich design gives the best quality wise performance ( sonically )
also wich drawbacks/solutions need to be adressed when using this design

super high spl at low hz aren't my concern with this project, but super high quality is

with 4 12 or 15" drivers in a small room i should'n't have much trouble making up for the lack of efficience in lower octaves i guess

[Rudolf]

Originally posted by JinMTVT
ok, i have to admit that i do not understand or grasps half of what you guys are talking about ..

That´s exactly how I started into dipoles. So your premises are perfect.

Then design wise, do the drivers need to be at 90degree perfectly for a W-Frame magic to happen ?
is there any other design rules to follow when constructing a W or an H baffle

I don´t think there is a special W-frame magic. Any configuration from plain flat baffle to a compact "ripole" might work. Driver requirements would be almost identical for all applications. But please don´t mix different drivers in one baffle.

i also didn't find the Linkwitz paper you guys are all refering to .

www.linkwitzlab.com A MUST read (at least a big part of it) if you are seriously into designing your individual dipole frame. And you will find those design rules too.

and both needs to be seriously braised enclosures because of obvious vibrations/resonance?

Indeed. It was my fault to show my W-baffle without the final bracing in the middle of the front . JohninCR is definitely right in putting some emphasis on this.

I would like to know which design gives the best quality wise performance (sonically )
also which drawbacks/solutions need to be adressed when using this design

Impulse compensation: Full for 180° W-baffle a la Linkwitz, half for 90° W-baffle, none for H-baffle.

Efficiency: Best for H-baffle, worst for ripole. The more you fold the baffle, the more efficiency you will loose.

Usable upper frequency limit: Highest for H-Baffle, lowest for a sqeezed ripole

For overall sonic quality the driver quality will be more important than the baffle geometry IMHO. I believe that most geometry decicions are done for reasons regarding volume, apppearance or geometry and not for sound quality in the first place.

I hope this keeps you busy for some time.

Rudolf

[Retsel]

I don't know if you have investigated infinite baffle subwoofers, but I thought that I would at least mention them as an alternative to open baffle designs.

Infinite baffle subwoofers have similar sound qualities to open baffle subs, although they MAY have more room node issues (but I am not convinced at that), but don't suffer the gross inefficiencies that open baffle designs suffer from. An infinite baffle design uses a crawl space, an attic or a second room as the "box" for the backwave Thus there is very little backpressure on the driver and has a similar sound quality to an open baffle design, but because there is no sound cancellation from front to back, the deep bass extension is much better.

With my open baffle system (right now), I am only flat down to 60 hz (I don't have an electronic crossover), although I will get quite a bit lower when I add my rectangular box to the back of the W open baffle box. However, with an infinite baffle system, which enjoys the benefits of room gain, it is normal to achieve flat frequency response down to 20 hz, and some are even flat down to under 10 hz.

If I am able to convert a backroom, which has a crawlspace, to an audio room, I will most likely design an infinite baffle subwoofer into the room design.

Are you in the position to consider an infinite baffle subwoofer?

Retsel

[JinMTVT]

ahahha
that is funny

i've "looked at" and not completly read
linktwitz' site a few times...almost always looking at it's sub analysis without ever noticing that his double compound subwoofer was a 180 folded baffle


this is a seriously compact design though

i still wonder a few things

what exactly is :Impulse compensation

and then is this more important than mechanical distortion wich W frame permits to cancel ??

i'd guess that all those designs have a compromise over all the positive and negatives ...


and i still don't get what i a "U" frame ?
is it a sort of short TL with the driver at the end of the enclosure?

what is called the woofer arangement on linkwitz Orion ?
is this an H-frame type ?


So W is more compact and offers impulse compensation
AND mechanical cancellation ?

i'll have to think about all that and seriously READ linkwitz papers ..

thanks again Rud

[johninCR]

You should also read JohnK's tech studies at www.MusicAndDesign.com

I consider anything with more baffle to the rear a U-baffle. A pure U would be a driver on the end of a short pipe with damping to eliminate the 1/4 wave resonances. If you took the Linkwitz W-dipole woofer, not subwoofer (it rolls off too early), and slid the driver manifold the 2.25" to the front, you'd pick up 4.5" of extra rear wave travel distance. This brings the Fequal point, where 6db/oct roll off starts down from 121hz in the Linkwitz cab to only 97hz with exactly the same size enclosure, and negible, if any, sonic difference. It does shift away from pure dipole, and this W/U hybrid would have a slight shift rearward in the area of greatest null. The "U" part is the rearward extension that isn't equal in the front.

Above is a perfect example of why I would never again build a pure dipole to handle the bass region. If you want the response of an H, cut the front off of it and eliminate the potential on the front side for resonances. The only time I can see any justification for any panel to extend toward the front past the driver mounting baffle is be able to hide the magnet in a push/pull alignment. There's always room on the backside of any U for damping, if necessary. Small changes can have big benefits, but change the polar response pattern very little, so room problems aren't a concern. Your net imput into the room is still 0, so your bass stays in the room very well (louder listening without disturbing others). Plus you can always get the same response in a smaller enclosure, plus you avoid the dipole bottom extension limit in small rooms. There aren't too many win-win compromises in audio, but I see using U hybrids in the bass region as one of them.

[Calvin]

Hi,

"For overall sonic quality the driver quality will be more important than the baffle geometry IMHO"
That is soo true! imho
Design-aims as optics and size may play and do play a great role in the dipole design, because technically the differences don´t make much sonic difference as long as You plan to use the thing as a subwoofer below 100Hz. But for the good feel, symmetry and small size are the sexiest. (btw. the Linkwitz-W is rather big and ugly to my eyes and not symmetrical as a ripole). And I fear that the advantages of the distortion cancellation by mounting the drivers as SL does will be swamped by the inherent asymmetry of the construction.

jauu
Calvin

[Davey]

Uh...John, I think you might want to re-read both Siegfried's and John K's excellent technical explanations of the various woofer configurations and how the "D", "D/2", "Fequal", etc, etc, parameters are related in the three configs.

Cheers,

Davey.

[johninCR]

Davey,

If you have a point then state it. It sounds like you're the one who needs go back and re-read that great work. Most do misunderstand how D is measured and and it's impact on Fequal once you fold a baffle. This is due in part because of the way SL displays D graphically in the H configuration. In an H dipole, the distance differential is from the back of the driver baffle around the rear edge back to the front to the plane of the driver baffle. SL displays it as the side panel depth, which is only correct because they happen to be equal. John K also has the tendency to explain things in a technical manner, and as a result very simple explanations are sometimes not spelled out.

The very simple explanation of why a U-baffle has 6db greater output at the bottom than a similarly dimensioned dipole H-baffle is because D is doubled in a U configuration. Doubling D moves the Fequal point down exactly 1 octave, which is exactly a +6db increase.

The D that I am talking about is not Diameter. It is the Differential in travel distance for the rear wave vs the front wave. I believe at some point SL uses D as diameter, then later as the Differential in travel distance, which leads to confusion.

[Davey]

Okay, sorry to bother you John.

Cheers,

Davey.

[moray james]

http://web.telia.com/~u82608519/WF8.ppt