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What happens if you take some midrange horn like my EV SM120A (bi radial with straight lateral sides) and put some "wings" that prolongates the lateral sides in the same angle? Does it effectively lower the cutoff frequency?
I was playing with some thick polystyrene sheets and I heard fuller low midrange when I was putting the "wings".
It made me thinking as my horns are not really able to go down to 400qHz, they're 500Hz horns and 400Hz is pushing it a bit, even tho I'm not the first who does it.
I know Altec was using "wings" on the voice of theater but it was for low frequencies, but I suspect the theory is the same?
But then how to determine the size of the wings?
Follow Ups:
"Better" is a different issue.Again, the operative term here is "midrange horn".
Horns do multiple things. They help to manage directivity/dispersion, they load the driver, and they provide an impedance matching to the outside world. The size and shape of the horn mouth is also important.
But, if you want high quality sound, you can't just slap any horn onto your favorite driver and call it excellent.
:)
Edits: 04/26/17
It does, but not by a huge amount, when you consider to take the Fc down by an octave you'd have to at least double the horn length and quadruple the mouth area. The intent of the Altec 'wings' was to extend response by lowering the baffle step frequency. To some extent making a horn mouth larger does the same thing.
I agree with that statement.Placing any horn in a flat baffle at its mouth controls its polars by a small margin and also provides a bit better loading to the driver to a lower frequency.
A "baffle step" is actually the effect of a flat baffle acting like an 90 degree exit angle horn.
Chris
"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."; Jack Dinsdale, May 1974
Edits: 04/25/17 04/25/17
I believe that you're listening to the difference in polar control at lower frequencies in the horizontal direction (assuming the EV horn is in a horizontal orientation), but maybe not so much in terms of "cutoff frequency" which is a function of the path length for exponential and hyperbolic horn profiles (but less so for conical and other straight-sided horns).
The Klipsch K-402 horn does the same thing. It's good down to 170 Hz based on 1/4 wavelength alone, but the biggest effect of the increased size of the horn is its control of polars with frequency. It's like night/day compared to its little brother, the K-510 horn, at lower midrange and mid-bass frequencies.
Chris
"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."; Jack Dinsdale, May 1974
The Klipsch K-402 horn does the same thing. It's good down to 170 Hz based on 1/4 wavelength alone, but the biggest effect of the increased size of the horn is its control of polars with frequency. It's like night/day compared to its little brother, the K-510 horn, at lower midrange and mid-bass frequencies.>
As owner of a pair of these excellent horns by Roy Delgado of Klipsch, I concur with this observation. The 90x60 degree HxV polars are good from 600 to over 8,000 Hz. and have acceptable control above and below that, but it's 26 H x 40" wide, FYI.
Yes I understand the subtility.
But in effect, subjectively, it gives impression to load the driver better ("load " is of course not the correct term) since it sounds like low midrange is more rich.
I might try some wooden removable wings. Would be a cool DIY woodwork project.
By placing straight-sided extensions on the horn, you're strongly controlling polars in that direction to a lower frequency (the point that I believe is so important not to mix with "cut-off point" in listening trials) and weakly extending the 1/4 wavelength cut-off frequency...since the vertical direction of the horn isn't extended axially along with the sides.
I believe that most people haven't heard the effects of controlling polars to a lower frequency. It sounds just like what you describe.
If you were to extend both the vertical and horizontal mouth exit angles (which is an issue with the horn you've got because the exit angle vertically looks to be 90 degrees), then you'd be playing with both its polar control high pass point and its 1/4 wavelength horn gain high pass point.
If you want to extend the mouth on the horn you've got, note that you're going to take a bit of a hit at the 1/4 wavelength axial length point corresponding to the "cut-off frequency" as-is...in gain and in impedance bounces below the as-built cut-off frequency. You'll need to change the vertical exit angle to be significantly less than 90 degrees to measurably lower its cut-off frequency.
Chris
"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."; Jack Dinsdale, May 1974
Both horn length and mouth size = perimeter/circumference affect the horns low freq performance. A truncated horn with too small a mouth will have lower fundamental freq efficiency closer to the 2-3 harmonic in level.
Rafaro
It's more than just circumference in controlling polars.
Take the K-400 midrange horn--a so called "collapsing polar" design. It allows frequencies below ~1700 Hz to spill on the ceiling and floor of your listening room due to the short vertical dimension of the mouth, but not in the horizontal direction until you get to ~400 Hz-thus ending its horn loading/gain: the so-called "cut-off frequency" for an exponential horn expansion profile. It was designed that way to avoid having to EQ like a controlled directivity horn requires. It works extremely well doing just that - requiring no EQ from 400 Hz to ~2 kHz or higher (depending on how flat you think flat must be) using the ubiquitous K-55 driver.
You can determine the polar control loss frequency of a horn by measuring the mouth dimension in each direction and comparing to the 1/4 wavelength that corresponds to that horizontal or vertical mouth size.
Chris
"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."; Jack Dinsdale, May 1974
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