H Frame Open Baffle

irishpatrick33 · « **on:** 7 Sep 2019, 08:15 am »

Is there any reason to stagger the widths on sides of an H-frame open baffle (literally and H as looking from above)? To give an idea, I plan on having an 18" wide panel sandwiched between 9" and/or 10" wide sides. So the question is, do I make the sides equal lengths? Or slightly different (like one 9" and on 10")? Thanks.

gab · « **Reply #1 on:** 7 Sep 2019, 04:33 pm »

http://www.linkwitzlab.com/models.htm#B1

http://www.linkwitzlab.com/proto.htm

irishpatrick33 · « **Reply #2 on:** 8 Sep 2019, 09:12 pm »

I read as much as I could from the website. It's pretty technical from my perspective.

If I am understanding correctly, the H-frame is better than a U-frame (cardioid)? An H-frame should be a symmetrical design? Which would go against my preconception that you want your driver mounted slightly off center.

Openly Baffled · « **Reply #3 on:** 9 Sep 2019, 05:20 am »

Linkwitz achieved what you are talking about in his LX521 speakers with a W (or V or M) Frame.
The Woofers are effectively in an H but are mounted so that the edge length is effectively variable.
You could achieve the same result with a single woofer as shown below.

Maybe consider this to be an H frame in the mid cross section and U frames facing backwards and forwards at the extreme top and bottom.

I am currently experimenting with something similar.

gab · « **Reply #4 on:** 9 Sep 2019, 02:10 pm »

deleted

irishpatrick33 · « **Reply #5 on:** 9 Sep 2019, 09:58 pm »

The driver is a Wild Burro Betsy. It will be a single driver design.

Wild Burro has a speaker plan on their website, but the design would be way too big of a horizontal footprint for my application. Essentially I was thinking about folding their 37" of panel width into an H-frame or U-frame.

Based off the readings, I can infer a few things. A flat baffle delivers the best frequency response at the cost of bass. The H-frame is the other end of the spectrum, offering better bass but produces larger peaks as a result. The U-frame is the middle ground between them.

I've attached images of what I meant by staggered sides on an H-frame. I'm not sure any of those articles addressed such a concept. Again, I thought that would satisfy a preconception that you want your driver mounted off center. Judging by the reading, doing something like this would alter the way it radiates, almost creating a pre-toed-in effect.

The thing I wonder about is the U-frame producing a cadioid pattern. That might actually be something of value, as I also have limited space between speakers and back wall.

Openly Baffled · « **Reply #6 on:** 11 Sep 2019, 05:27 am »

Quote from: irishpatrick33 on 9 Sep 2019, 09:58 pm

I've attached images of what I meant by staggered sides on an H-frame. I'm not sure any of those articles addressed such a concept. Again, I thought that would satisfy a preconception that you want your driver mounted off center. Judging by the reading, doing something like this would alter the way it radiates, almost creating a pre-toed-in effect.

I don't believe this will alter the radiation pattern at all. If either side is considered they both remain symmetrical dipoles with equal front and rear radiation and the null would then remain at 90deg to the orthogonal axis on both sides.

There will however be a difference in the resonant air mass on each side. If the H width is similar to the driver width, this will have little effect as the air moves as one in front of the piston. I think it would require either FEA or a build and test comparison with a symmetrical H to discern the impact.

One aspect that concerns me in building asymmetrical H (or U) loading is the variable air mass in front of different regions of the woofer cone. I am concerned that the uneven pressure loading could cause distortion of the cone at high Xmax. I have not yet thought of a way to measure or verify this... any ideas?

MarvinTheMartian · « **Reply #7 on:** 12 Sep 2019, 01:20 am »

Irish, You were correct in one respect.
Take asymmetry to the extreme, place an OB woofer tight against left the side wall and you will change the bass polar response.
The predicted figure "8" becomes a more of a "B" , your toe in analogy.

Unfortunately all "H" frames also have an upper frequency limit, review the Linkwitz website bumpy H frame plots.
It is almost impossible to put a full range whizzer driver into a simple H frame.

Stick to a "U" frame if you need single driver full range coverage.
You can still play with the "U" frame asymmetry.

Shawn The Leprechaun