Mid Bass Horn Design 80-800 Hz

**Steve Mac** · February 3rd, 2008, 09:35 PM

Originally posted by GM:
Hmm, I can tell from the pics you didn't change the flaring to account for the 511, so there will be some anomalies in its response even with the extra mouth area and the 511 in an aero pod, though don't have a clue how audible it will be.

Sure I did and I sent ya the spreadsheet with the details.

...Danley Horn Comments
GM

I've seen his work. For 12 grand I can pick up a set. I dunno for around 2.5 grand I can build this set, learn about horn theory, brush up on my woodworking skills, pick up a few extra tools, have fun, support GPA and Todd, possibly have some success in making the duplex work, perhaps advancing the duplex design, learn the art of using my studio to tune the system afterwards and taking a shot at taming the 210 for a decent home theater setup. I can wait for the bleeding edge people to tame the tapped horn technology over time. I will finish this project and hopefully will continue to gain knowledge and help from this forum.

**bfish** · February 3rd, 2008, 11:26 PM

Originally posted by bfish:
...the point where I chunked my cardboard models...

I found the use of heavy cardboard models of various Hi-horn "shells" a big improvement over the real deal, when studying the effects they had on the big horn, regarding size, shape, and placement. You're more likely to try different approaches if they're easy to create, and effects are more noticable with no hi-horn playing.

Just don't run any homeless people out to get a reefer box to cut up, at least not until it warms up... forums

**Steve Mac** · February 4th, 2008, 12:01 AM

I think I hear what yer sayin'.
Just make a shell, set up some measuring equipment and/or clean the ear wax out and just play with placement. I can do that. That's a good idea...just simplify the test. It's halftime and the Giants are down 7 to 3. Gawd I hate the Patriots...

**bfish** · February 4th, 2008, 01:58 AM

quote:
--------------------------------------------------------------------------------
Originally posted by Steve Mac:
...Just make a shell, set up some measuring equipment and/or clean the ear wax out and just play with placement...
--------------------------------------------------------------------------------

You got it. In the process, you'll dial in your 515s to see if you need to modify their new home any (volume, damping, leaks, etc). Swap 'em around enough to see if any 515 shows an affinity for another, and pair them accordingly. It probably won't matter, but if it does, it's worth doing. Then you can play with your new cardboard creations. If you had some 1/4" rod, you could put some in the 2 top exposed driver holes, and extend them to the mouth and suspend the ends there. Then you've got a place to hang your models, and an easy way to adjust them forward or back.

I assume you'll be testing in a room, with basic RTA. Don't be overly concerned with anything unusual you see below 200Hz or so, the room and mic placement can fool you. If unsure, move the mic and try again. To dial in the 515s, I'd suggest very close (~1/4") placement from mid-cone. For modeling horn enclosures, I'd go out far, and take at least 2 off-axis readings both vert and horiz. using the acoustic center as the measure pivot. Hopefully you'll hit on a model and location that has minimal negative affect, and will closely match the polars of the intended hi-horn at XO. (let it tell you where to XO, rather than vice-versa.)

Added;
Don't be too surprised if the optimal location actually puts the HF mouth slightly forward of the LF mouth. Use absorbant material on any surface that faces the driver, even on the models.

Added later;
Why would anyone watch the bowl when Joe Walsh coulda been crankin' out "Tend my Garden"?...I'm still grinnin'!

where was I...oh yeah. The HF shell/horn flange interface is the center ring of your new bubble wand. Any semisharp edge will diffract here and send a reflected wave back down the throat. You can easily demonstrate it with some foam pipe insulation, split in half lengthwise. Stick the 1/2-round of foam around the HF mouth edge to leave a rounded transition from both directions, and an absorbent one to boot.

[ February 04, 2008 01:30 PM: Message edited by: bfish ]

**Steve Mac** · February 4th, 2008, 02:43 AM

Yer post is filled with many good things but I'm having a hard time thinking right now. I'm not a big sports nut but I have always been a Giants fan...good grief...Mother Mary....what a game!

**bfish** · February 4th, 2008, 02:52 AM

Who won?

Never mind, Google was home...

[ February 03, 2008 11:12 PM: Message edited by: bfish ]

**bfish** · February 4th, 2008, 04:23 AM

A couple of patents you may find interesting;

Blattner 1934

Patronis 1991

The citations listed in the Patronis patent lead to more.

**Steve Mac** · February 4th, 2008, 04:40 AM

Originally posted by bfish:
For some reason, my weak brain thinks having the mid horn mouth behind the big horn mouth is asking for problems. ...

[ February 03, 2008 11:52 AM: Message edited by: bfish ]

..in front of the big horn mouth....
But yeah, I hear you and it seems to be the holy grail of audio. It is not a fruitless quest. A large point source with the imaging of the 15" duplex would surely be something to behold. So there are issues, regardless of whether theoretically it is possible and it is not assumed any theory has the final word. Like you say, tinkering and experimentation are the bottom line and it either works or it doesn't. No reason to think this won't sound good out of the chute, but taking measurements and listening will be the real judge.

Still, there may be fall back positions. Consider the setup on the left side. Because the mouth dimension is increased by ~250 in^2, rotating the cab sideways, raising the horn and adding a chute to the upper wall cut through for the driver has its own issues, but may be another possibilty.

The center of the mid range horn on the left is 63"... the center on the right setup is 50". I was planning to push the mid bass horn back, raise it up 4-6" and continue the slope on the bottom mid bass horn and run to the sub's edge.

**bfish** · February 4th, 2008, 05:21 PM

Originally posted by bfish:

"For modeling horn enclosures, I'd go out far, and take at least 2 off-axis readings both vert and horiz. using the acoustic center as the measure pivot..."

Doh! I musta been "out far" when I said that... forums

, you'd wanna be outside to do it that way.

Those things aren't far from the floor OR the ceiling...not far at all. 1M might be better, at least to get a clue on vertical directivity...Geez, I really don't know, 'cause I've never measured anything that big outdoors, much less in. forums

Added;
Just curious, have you been startled anytime in the night lately, upon seeing a giant, unfamiliar shadow lurking yon? Now there's two...and...yes, they moved. (play Jaws theme here) forums

Gotta be a Hardy Boys mystery somewhere in there... yep.

[ February 04, 2008 01:43 PM: Message edited by: bfish ]

**Steve Mac** · February 8th, 2008, 03:18 AM

Originally posted by bfish:
...where was I...oh yeah. The HF shell/horn flange interface is the center ring of your new bubble wand. Any semisharp edge will diffract here and send a reflected wave back down the throat. You can easily demonstrate it with some foam pipe insulation, split in half lengthwise. Stick the 1/2-round of foam around the HF mouth edge to leave a rounded transition from both directions, and an absorbent one to boot.

From nutshellhifi where the article The Art of Speaker Design(Lynn Olson?) there is this same information:

The root of these problems, especially with cheaper PA-style horns, is the acoustic reflection from the edge of the horn-mouth. When a sound wave moves across a sharp boundary, it diffracts and re-radiates in all directions, like a separate driver located at the point of the reflection. The reflected wave from the horn-mouth then bounces back into the throat, which typically has a hard phase plug or a driver with a stiff cone. After it strikes that, it reflects right back outward again ... this succession of reflections is called a series reflection, and it is far more audible than the small ripples in the frequency response might indicate.
...
... you can line the inside of the horn with 1/8" wool felt. 1 to 3 inches extending from the lip of the mouth going inward will do the trick. The further you go back towards the throat, the better the damping, but if you overdo it, the bass response of the horn will start to droop, along with the efficiency
this was intersting too...

.... don?t forget to remove the wire mesh bug screen in the throat. The wire mesh creates a very unpleasant gritty harshness at levels above 90dB, and is only required for severe outdoor environments.)

Additionally there is apparently a camp that thinks horns should be rough so there is some randomization of reflection...any thoughts on this?

So, there could be both an inner and outer edge that re-radiates. I didn't understand why just the bass response begins to droop as more felt makes its way farther back into the horn. It seems perhaps the inner horn shell might benefit from being completely covered with something absorbent.

But overall, it appears a smooth finish is not the better sounding horn in this case?

Thread: Mid Bass Horn Design 80-800 Hz

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