| Horn mouth vs. front baffle or "speaker cone" [message #88752] |
Mon, 03 September 2018 12:53  |
johnnycamp5
Messages: 354
Registered: June 2015
Location: NJ
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Grand Master |
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When comparing horns to direct radiators.....
I have read over the years that the mouth of a horn is to be considered the same (in regards to fore/aft source location) as the surface of a direct radiator/woofer cone on a typical loudspeaker front baffle.
Is this generally correct?
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| Re: Horn mouth vs. front baffle or "speaker cone" [message #88764 is a reply to message #88752] |
Mon, 03 September 2018 19:02  |
johnnycamp5
Messages: 354
Registered: June 2015
Location: NJ
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Grand Master |
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I think I understand what you mean by "vertical nulls".
I had something like that in my living room system due to room dimensions or nulls that I attributed to a low 7.5' ceiling.
While sitting on the couch listening to my system (4pi's with flanking subs), the music sounded awesome...
nice and punchy, especially with those flaking subs...
but when you stood up, almost all the punch went away, as if you had shut off the subs and half of the woofers!!
To confirm my hunch of vertical room nulls (what else could it be?), I built a set of high flanking subs (using a pair of 2226H) with the centers about 2' below the ceiling.
I used the single bass array concept -
For my room it equals= 1/2 of the ceiling height (3.75) vertical distance between each woofer center (in my case the 4pi and flanking sub) and 1/2 of that distance (1.875') between the top woofer and the ceiling/bottom woofer and the floor.
The woofer in the 4pi was somewhat less than that, but I did not bother to raise them.
Also, the single bass array 1/2-1/4 distances are applied horizontally as well (left wall to right wall), but I could not do this in my room (but it wasn't far off).
The bottom line is it worked! The deep extension wasn't there with the JBL's.. but the mid-bass punch was back.
Stand or sit...the bass response was the same.
Every ones experience is unique...but needless to say, this got me liking the (vertical) bass array concept lol.
P.S.- The high flanking JBL's were low passed at 150Hz. 24db/octave slope.
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| Re: Horn mouth vs. front baffle or "speaker cone" [message #88768 is a reply to message #88767] |
Tue, 04 September 2018 16:18 |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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I definitely understand what you've described. Geddes suggests placing one sub high in the air like that, specifically to deal with modal smoothing in the vertical dimension.
My guess is your troublesome mode is probably in the 60-80Hz range. Partly because you've described it as "bass punch" and partly because flanking subs aren't addressing it.
Self-interference and modes above 80Hz are smoothed with flanking subs, but they can't do anything with the modes below that. They're not spaced far enough from the mains. In most rooms, the modes that flanking subs can address are axials above the second or third wave and some of the oblique and tangentials. These are the modes between about 80Hz and 160Hz, and they're sometimes pretty troublesome. Flanking subs also mitigate the self-interference from nearest boundaries, especially the wall behind the speakers, which almost always causes a deep notch between 80Hz and 120Hz. This is because the convenient place to put speakers is often against the wall or a foot or two from it, but that makes this deep notch. So flanking subs can address all those things, but they can't smooth lower frequency modes, below 80Hz or so.
So all that to say you're probably best off with a distributed multisub placed right where you suggested in addition to your flanking subs. Set a sub up high on a shelf somewhere and low-pass deep enough to prevent localization. Again, this is very much like the multisub arrangement that Geddes prefers. He likes to place one sub 2/3rds the way up the wall.
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