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Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
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Old 8th February 2014, 05:21 PM   #1
bwaslo is offline bwaslo  United States
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Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
Default Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho

I'll be moving to a smaller house in around a year, and will have to make the basement my music room. Which should be do-able, but its ceiling is much lower than in my current room. And I think that means I should be more concerned about ceiling bounce.

My homemade Synergy ("CoSyne") has a nominal 90 degree horizontal which I want to keep, and a 60 degree vertical which you'd think would help minimize the floor and ceiling bounce. But the problem is that the pattern control frequency for vertical on that horn is much higher than for horizontal. so at not-very-low frequencies, the vertical essentially goes omnidirectional, the opposite of what is wanted!

As has been mentioned in other threads, going to a narrower pattern needs a larger mouth dimension and a longer horn to keep the same pattern control frequency, neither of which happens when the vertical coverage angle is simply changed and the horn stays the same length as for horizontal. In fact, the vertical mouth size actually gets smaller than for the wider angle horizontal coverage, the wrong direction!

What I'd want would be to have the vertical control angle be narrower than the horizontal, while getting the same pattern control frequency for both. So, the horn will have to longer for the vertical part, and the mouth has to be larger for vertical also. Here's what I've been thinking of:

Click the image to open in full size.
(The offset drivers aren't shown since this is just a horn concept. But there should be plenty of room for mids and woofers on the horn's larger top and bottom walls)

One nice thing is that the width of the cabinet remains the same (the Horizontal doesn't have to grow to meet with the Vertical). The extra dimensional growth is mostly within the height of the current cabinet, which only has to grow a little vertically since the cabinet is already high to place it's center axis at ear height. The overall depth of the cabinet has to grow substantially, though. Which should be ok for a basement listening room, not so great for most living rooms though.

It may look a little funny from the side, with the odd cutout, unless you're a form-follows-function sort of guy. I think it would certainly be unique.

Now to see whether I'll have a decent place to try to build such a thing after the move!

Any comments, suggestions?

Last edited by bwaslo; 8th February 2014 at 05:23 PM.
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Old 8th February 2014, 05:33 PM   #2
CharlieLaub is offline CharlieLaub  United States
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If the ceiling reflection will be a problem only for higher frequencies, why not just put up a 2" thick 4x8 rockwool panel or two?
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Old 8th February 2014, 05:58 PM   #3
bwaslo is offline bwaslo  United States
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Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
Charlie,

It's the other way around. The reflection is a problem at lower frequencies where the horn loses vertical pattern control.

Besides, 2" thick anything up there and I may be dragging my head through it when I walk!
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Old 8th February 2014, 06:37 PM   #4
weltersys is offline weltersys  United States
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Quote:
Originally Posted by bwaslo View Post
The reflection is a problem at lower frequencies where the horn loses vertical pattern control.
To have 60 degree control down to 400 Hz the point in the horn before the break (where your diagram shows the horn going from 60 to around 90 degrees) would require it to be around 34 inches. That would be a deep horn.

Most people would think of "low frequencies" as below 250 Hz, which in a small room the modal response will dominate.

Even if you had a 54" tall horn (pattern control down to around 250 Hz) the room modes would render the pattern control moot.

If the ceiling reflections bother you, you may want to consider mounting the cabinet at the ceiling.

Your new lower listening room will have different modal problems than your current room.

There are on-line calculators which calculate room modes based on dimensions, check them out and look up "Schroeder frequency", I think you are experiencing problems that are not going to be solved by a horn that will an acceptable size.

Art
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Old 8th February 2014, 07:31 PM   #5
bwaslo is offline bwaslo  United States
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Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
Art, I think you're maybe misinterpreting my (admittedly crude) sketch? The horn doesn't ever go from 60 to 90 degrees. In the vertical, it's a 60degree horn only, the break in slope I think you mean (seen from the side view) is where the second expansion starts for reduction of waistbanding per Keele. The entire depth of the cabinet is for the vertical horn length (which, yeah, will be kind of deep, but what other options are there?).

Ceiling mount would make it sound like its coming from the ceiling, and then make floor bounce worse unless the vertical pattern is made still narrower.

The dotted line hidden view from the side shows the entire horizontal 90 degree horn section and it's second expansion. The side of the cabinet is open as shown in that view to clear horizontal radiation over the 90 degree angle. On the view from the front, it's the bow-tie looking part (essentially the same horizontally as what I have now in my current room).

"Lower frequencies" relative to such a horn design is down to around the Shroeder frequency, maybe ~450Hz, below which pattern control doesn't have much meaning. Below that the speaker goes omni.

I'm not actually experiencing any problems with that room yet, just anticipating them. Haven't moved in yet!

Bill

Last edited by bwaslo; 8th February 2014 at 07:44 PM. Reason: typos, rewording
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Old 8th February 2014, 07:56 PM   #6
weltersys is offline weltersys  United States
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Quote:
Originally Posted by bwaslo View Post
Art, I think you're maybe misinterpreting my (admittedly crude) sketch? The horn doesn't ever go from 60 to 90 degrees. In the vertical, it's a 60degree horn only, the break in slope I think you mean (seen from the side view) is where the second expansion starts for reduction of waistbanding per Keele.
The entire depth of the cabinet is for the vertical horn length (which, yeah, will be kind of deep, but what other options are there?).

"Lower frequencies" relative to such a horn design is down to around the Shroeder frequency, maybe ~450H, below which pattern control doesn't have much meaning. Below that it all goes omni.
l
Bill,

I did not misinterpret your picture, for a -6 dB coverage angle at 450 Hz the horn height at the end of the 60 degree horn portion needs to be about 30 inches. From your drawing I took it your horn is a fraction of that size.
With the Keele break (the 90 degree vertical wall angle portion) the horn would be around 30"+ deep and 40"+ tall.
"Kinda" big, but as you point out, no other smaller (horn) options if you want pattern control to 450 Hz.

Art

Last edited by weltersys; 8th February 2014 at 07:59 PM.
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Old 8th February 2014, 08:07 PM   #7
bwaslo is offline bwaslo  United States
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Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
Ah, I get you now -- 60deg +0.5*60deg = 90deg, the keele expansion angle vertically.

Well, seeing as my current cabinets are already 24"w x 48"h x12"d (it uses the rest of the volume for porting of the woofers and holding the horn up at ear height), the size change in the front profile isn't too bad. The depth change will be about 3x, though. Fortunately, I don't have to worry about living room aesthetics, and the basement has about as much volume as I care to box in, It's just vertically challenged.

afterthought: I suppose another option would be to try to drive a tall 90degree H horn with a tall narrow BG planar driver to try to get 90deg H x linesource vertical down to 450Hz. Any idea how well those kinds of drivers (RD75?) would do pushing a horn? Not exactly high BL product drivers. Also, the driver wouldn't be in the right horizontal expansion point to drive the horn at below tweeter frequencies...

Last edited by bwaslo; 8th February 2014 at 08:26 PM. Reason: clean up wording
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Old 8th February 2014, 08:27 PM   #8
weltersys is offline weltersys  United States
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Quote:
Originally Posted by bwaslo View Post
on would be to try to drive a tall 90degree horn with a tall thin BG planar driver to try to get 90deg H x linesource vertical down to 450Hz. Any idea how well those kinds of drivers (RD75?) would do pushing a horn? Not exactly high BL product drivers.
They would work fine with a 90 degree waveguide, but still would require 40+ height for pattern control to 450 Hz.

DSL's new SBH-10, a 60" vertical stack of 8 Paralines has a nominal dispersion of 140 x 10, yet widens to 30 vertical at 800 Hz, and almost 90 degrees at 250 Hz.
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Old 8th February 2014, 09:05 PM   #9
weltersys is offline weltersys  United States
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Actually, the SBH-10 is more than 90 degrees at 250 Hz.
Attached Images
File Type: png SBH10 LF polars.png (184.7 KB, 319 views)
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Old 8th February 2014, 09:13 PM   #10
bwaslo is offline bwaslo  United States
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Another Home Synergy Concept - matching pattern control frequencies for asymmetric ho
The RD75 is 75" high, so height isn't an issue for drivers with that one. Except for maybe the 75" cabinet that would need to go with it.

I think that getting a "normal" (non-Synergy multiway) horn like that to go 450 to 20k from one driving point could be troublesome. The expansion rate at the throat wouldn't be so good for driving much below 1kHz, I don't think (not from experience, just from reading Tom's commentary on how the Unity horn works).

If the line source reached near floor-to-ceiling and both were left or made reflective, then the acoustic image should make it act like an infinite line.

Paraline performance (flatness) hasn't appeared wonderful from what I've seen, pretty ugly in fact. And in a home, I certainly don't need 8 HF compression drivers to reach usable levels.
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