H Frame designer

[perceval]

Been looking for a while on the net, but I just can't seem to find it.

Is there a program, online or standalone, that would help designing H frame or U frame for Woofers in a FAST configuration?

Mostly it's: how do I find the length of the "wings" around the woofer?

 

[chris661]

Hornresp will do it, though positioning the system close to a back wall will change things dramatically.

Chris

 

[perceval]

Thanks, I'll look it up.

I'm about 1m (3') off the back wall.

Not as much as I'd want but I have space constraints...

 

[scottjoplin]

That distance should be just about enough. U Frame can go a bit closer to wall than H frame

 

[adason]

U Frame can go a bit closer to wall than H frame

Ha? Why?

 

[adason]

Thanks, I'll look it up.

I'm about 1m (3') off the back wall.

Not as much as I'd want but I have space constraints...

You do not have to have woofer facing you. Remember Gradient Helsinki 1.5 speaker?

 

[scottjoplin]

Ha? Why?

It exhibits more of a cardioid polar response, so there is less radiation from the rear than an H frame which gives a true dipole response.

 

[adason]

U frame a cardioid? I think you are wrong...

 

[scottjoplin]

No not saying it is true cardioid. I am interested to know more about this set up as it is similar to what I have.... I am learning, and I sense from your response that you could help me with that, I would be grateful

 

[DaveCan]

Here's some info that might be of help:

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

I built a pair of the Goldwood H-Frames as mentioned in this article below.. Surprisingly nice for the money.. I use them crossed at approx 70Hz 24db slope.. Really nice sq. Using bookshelf 2 way cabs on top..

http://www.quarter-wave.com/Project08/Jordan.pdf

 

[adason]

H and U frame may have slightly different side cancelation, but to the front and back, they are completely unrestricted

If you want to learn about cardioid bass, study kimmo saunisto web pages

 

[scottjoplin]

Thanks Dave, yes I've read those. That's very interesting that you built that sub as I have the Jordan Eikona in open baffle at present. I was also torn between H frame and U frame sub, I still am. I built U frame in the end for a couple of reasons. 1- I had a couple of old speaker cabinets that were easily adapted and 2- I believed I may be able to get away with them closer to the wall. Ideally though I'd like to experiment with H frame as it seems the best solution except for the extra space they'd occupy and maybe need. I'm still not clear on that last point though

 

[scottjoplin]

Thank you adason, I think you might have cleared up that last point for me. I shall look at the web pages you suggest

 

[perceval]

Oh, I missed (or forgot) the Geometry part last time I read MJK's paper on H and U frames...

Ok, this looks easier than Hornresp, but what is r effective in the first equation?

The internal cross-sectional area is 16” wide and 16” tall. The depth of the cavity
was defined as 7.5”. The depth was selected to push the first quarter wavelength
resonance above the desired crossover frequency of approximately 200 Hz.

L effective = 7.5” + 0.6 x r effective
L effective = 7.5” + 0.6 x 9.0”
L effective = 12.9” = 0.328 m
f1/4 = c / (4 x L effective)
f1/4 = 344 m/sec / (4 x 0.328 m)
f1/4 = 262 Hz

 

[TBTL]

It appears to be some kind of end correction on the cavity making it longer, similar to that on ports of ported boxes. I think r is the equivalent radius of the opening, so approximately half the cabinet width.

 

[perceval]

Wouldn't that be 8" then?

Why would MJK use 9"?

 

[DaveCan]

Thanks Dave, yes I've read those. That's very interesting that you built that sub as I have the Jordan Eikona in open baffle at present. I was also torn between H frame and U frame sub, I still am. I built U frame in the end for a couple of reasons. 1- I had a couple of old speaker cabinets that were easily adapted and 2- I believed I may be able to get away with them closer to the wall. Ideally though I'd like to experiment with H frame as it seems the best solution except for the extra space they'd occupy and maybe need. I'm still not clear on that last point though

I use mine right up against the side walls on both sides of the living room. There's 7' of open space behind them and 12' open in the front.. On top are two bookshelf cabs towed in towards the listening couch.. They reach pretty low and sound really nice sq wise using a Dayton sub amp to power them.. Not a bad project and price for a couple of 18's to get some decent sq low end etc..

 

[CharlieLaub]

H and U frame may have slightly different side cancelation, but to the front and back, they are completely unrestricted

If you want to learn about cardioid bass, study kimmo saunisto web pages

You will find how a U-frame can produce a cardioid-like pattern here:
DIY-dipole-1

 

[adason]

I am familiar with John's pages, I am an open baffle guy...
You will notice its only cardiod-like at very low frequencies, 20 Hz and lower, which, considering cancelation has almost no output...starting 50Hz and up, it has plenty otput towards back, at 100Hz and up its like H frame...and that is only theory...

 

[TBTL]

Wouldn't that be 8" then?

Why would MJK use 9"?

With approximately I meant something like +- 30%. The effective radius of a square is somewhere in between half the diagonal (11" in this case) and half the width (8").