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How flat can cornerhorns be?

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Posted on July 6, 2015 at 09:08:57
mdg
Audiophile

Posts: 51
Location: Gilze-Rijen (Holland)
Joined: November 27, 2004
 Hello,

After building 2 labsubs in the early years i never forget
the impact of a hornloaded design, with all the dynamics it had.

This time i have to build a subwoofer for a home theater room and
would like to go back to the hornloaded approached.

The design has to be a special horn that can be placed in the corner, what already have some benefits.

I was wondering or anyone has some experience with it and how low can the in room response be made flat with eq?

gr. Marcel

 

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RE: How flat can cornerhorns be?, posted on July 6, 2015 at 09:45:41
tomservo
Manufacturer

Posts: 8211
Joined: July 4, 2002
 Hi
In a normal room there is a room gain slope which can be from +12dB per octave in a sealed concrete bunker to more like +3 to +9 dB per octave in a normal house.
This (with a flat a flat response speaker in half space or outdoors) produces a rising response once one is below the lowest room mode which is often associated with the 1/2 wavelength frequency of the largest room dimension.

In an automobile where this effect is easier to see, one can take a sealed box which rolls off around 50Hz at -12dB/oct and when you place it in the car, you can (with windows rolled up) get flat response down an octave or a lot more below the normal corner due to the room gain or cabin gain slope as they often call it in the auto world.
In a sealed car, the +12dB cabin gain slope cancels out the -12dB slope from the speakers roll LF off, perhaps the closest thing to a free lunch in audio

Hope that helps
Tom Danley
Danley Sound Labs


So, since a sealed back horn (including a lab sub) eventually has a -12dB /oct roll off, one might figure out approximately where your lowest room mode would be and then shoot for a horn that has a response knee around that same point.

 

RE: How flat can cornerhorns be?, posted on July 6, 2015 at 09:50:12
weltersys
Industry Professional

Posts: 685
Location: FL
Joined: September 28, 2004
 Generally a horn can be equalized down to the low cutoff (FC).
The FC is determined by the horn's path length and flare rate, generally the path length is 1/4 the wavelength of the lowest frequency that can be effectively reproduced. As an example a 30 Hz FC would require a 9.4 foot path length, the corner can be part of the path length.

 

RE: How flat can cornerhorns be?, posted on July 6, 2015 at 10:47:51
Bill Fitzmaurice
Industry Professional

Posts: 5371
Location: New England
Joined: October 20, 2002
 >The design has to be a special horn that can be placed in the corner

Any horn can be placed in a corner. You'll get 1/8 space loading so long as the mouth is less than 1/4 wavelength from the three boundaries. You may build the horn along the lines of the KHorn, which in effect made two of the room walls part of the enclosure, but you don't have to. As alluded to by Tom in-room response can actually go lower than the horn corner frequency when cabin gain is factored into the equation.

 

RE: How flat can cornerhorns be?, posted on July 6, 2015 at 12:18:18
Cask05
Audiophile

Posts: 80
Location: N. Central Texas
Joined: November 11, 2007
 Under certain circumstances you can EQ a little below Fc, but I've found that it takes a well-designed bass horn with closed box back volume behind the woofers to do it--not vented.

For instance, the Klipsch Jubilee bass bin will easily load to flat response down to 32 Hz from its nominal 40 Hz Fc by adding one PEQ boost filter. The increase in distortion is typically much less than adding TH or even typical front-loaded horn subwoofers. The added LF response has been popular among those owners that do not own or employ horn-loaded subwoofers.

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

 

RE: How flat can cornerhorns be?, posted on July 7, 2015 at 10:01:28
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 My listening room has a concrete floor and long wall. The room is also thickly paneled on all 4 walls. The volume setting on my subwoofer tells me that their is a lot off room gain. Very satisfying base is achieved at a very low volume setting in relation to the satellites.

Dave

 

RE: How flat can cornerhorns be?, posted on July 7, 2015 at 13:14:40
mdg
Audiophile

Posts: 51
Location: Gilze-Rijen (Holland)
Joined: November 27, 2004
 Hi thnx all for the reply.

I also read, from archived post, that the corner has also
a hornloading effect an the radiator.

Would it be possible to extract the adding resistive and reactance load of a measurements and intergrate this in my model, for the last final flare?

I had a tought about measuring a simple sealed radiator outside (free from reflection) and then measuring it in the room, placing the radiator where the mouth off the horn would normally be.
The difference in resistive and reactance load would be presenting the extra hornloading of the corner. I dont know it this would be represantative.

I want to come as close as possible to the 20hz corner.

gr. Marcel

 

Not Very, posted on July 8, 2015 at 10:24:02
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 They are shaped like a triangle.....sorry couldn't resist

E
T

ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: How flat can cornerhorns be?, posted on July 8, 2015 at 18:44:53
John Sheerin
Audiophile

Posts: 524
Location: PA
Joined: July 28, 2003
 Below the horn's cutoff the system reverts to being a sealed box (assuming the back of the driver is sealed). So you can model and EQ it the same way you can a sealed box. It just depends on how much power, power handling and excursion you have to work with as to how low you can get it to go for a certain output level.

I know in my room I get a +10dB shelf below about 40Hz that almost exactly compensates for my sealed sub's rolloff. I figured this out by doing basically what you suggest - measuring outside, then inside. Although really at low frequencies, I was just measuring inside to see what EQ I needed to apply. But knowing the room gain did tell me how much output I could get at the listening position relative to the max output I measured outside.

 

RE: How flat can cornerhorns be?, posted on July 11, 2015 at 15:48:28
hollowboy
Audiophile

Posts: 263
Location: Melbourne
Joined: June 26, 2007
 I once looked up "room gain" and found some good articles and discussion at the data-bass website.

The short version (as others, like Geddes, have noted) is that the room effects will make ANY speaker non smooth in the bass. Using more sources helps even it out - by a substantial amount. Room gain is real, but is only smooth and predictable below 10Hz.

Are you free to modify the room itself (manifolds, wall treatment etc)?

 

RE: How flat can cornerhorns be?, posted on July 13, 2015 at 09:27:15
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 Not much is going on in most recordings at 10Hz.

Dave

 

RE: How flat can cornerhorns be?, posted on August 27, 2015 at 17:06:29
claudej1@aol.com
Audiophile

Posts: 817
Location: Detroit
Joined: August 17, 2007
 you just described a Klipsch LaScala, which depends on it.

 

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