Home » Audio » Speaker » Horns and Room Size
Horns and Room Size [message #17091] Wed, 20 October 2004 18:24 Go to next message
Gerald59 is currently offline  Gerald59
Messages: 2
Registered: May 2009
Esquire
How big a room is needed for a horn? Does a bass horn work in a small room, say the size of a bedroom?
Seems like there would be a size limit. How does the idea of acoustic transformer apply if the room is very small?
In that case, the horn isn't matching a small cone to a large space anymore. Does that change things?

Re: Horns and Room Size [message #17092 is a reply to message #17091] Thu, 21 October 2004 01:00 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18669
Registered: January 2001
Illuminati (33rd Degree)
The thing is that a horn is really a tapered pipe with properties determined by a handful of variables. Three of the main ones that are germane to your point are throat area, mouth area and expansion rate. The throat and mouth are terminating junctions where there is a discontinuity, so that's what distinguishes them. Even if the environment outside the horn is small, the mouth still marks a point where the expansion stops increasing by the flare rate and suddenly opens up.

There are a lot of other variables though, and the environment that the horn radiates into is certainly one of them. Another is the chamber that precedes the throat. And the back chamber and the electro-mechanical properties of the driver come into play also. But to address your specific comments about the environment, it most certainly does have an impact, and a large one.

Assuming the environment is large, then it can be described by the radiation angle set by the boundaries nearest the sound source. If sound radiates in all directions, like if a speaker is used in wide open space, high above the ground and away from everything, that's called freespace radiation (4π steradians). If the speaker sits on the ground, but there are no other boundaries around, then the radiation angle is cut in half, hence the name half-space (2π steradians). Put a wall behind it, and now this is cut in half again, called quarter-space (π steradians). And if in a corner, it's in eight-space (π/2 steradians).

There are also smaller radiating angles than this, and your very small room may be an example. There is no reason why the radiating angle cannot be made smaller than π/2 steradians. In fact, that is exactly what a horn is - It is a device that reduces the radiating pattern of a sound transducer so that it is made more directional and stronger in the field desired. There are other things in play also, such as compression before the throat and the expansion rate, but one of the main features of the flare is its radiation angle. So in a very real way, the room becomes a part of the horn and it certainly should be considered when designing or implementing a horn system. A basshorn can be made considerably smaller if used in a constrained environment than it would be if used in freespace.

Practically [message #17093 is a reply to message #17091] Thu, 21 October 2004 05:42 Go to previous messageGo to next message
Mike.e is currently offline  Mike.e
Messages: 471
Registered: May 2009
Illuminati (1st Degree)
my 40hz corner horn worked really well in a small room of 2.2m x 5m x 2m !The small room had a relatively high frequency,below which room gain started filling in the bottom end slightly

Cheers!
Mike.e


Re: Horns and Room Size [message #17095 is a reply to message #17092] Thu, 21 October 2004 06:32 Go to previous messageGo to next message
Bill Fitzmaurice is currently offline  Bill Fitzmaurice
Messages: 335
Registered: May 2009
Grand Master
'A basshorn can be made considerably smaller if used in a constrained environment than it would be if used in freespace'.

To expand on Wayne's statement any room will get both boundary loading (if the speaker is placed close to a wall or corner) and cabin gain, which kicks in at 12dB/octave where the longest room dimension is about a half wavelength. A room with the longest dimension at 12 feet will get cabin gain from about 47 Hz, which means that you don't need to build a horn with an Fc of 20 Hz to get response to 20 Hz; 45 Hz or so will do nicely. When you account for cabin gain and boundary effects in the design process you can make basshorns quite small. With the extreme amount of cabin gain available in a car trunk it actually makes it an ideal place for a relatively small basshorn.

Going to your question, what traditionally limited the use of horns in small rooms was their physical size, not their sound, but today designers like myself are coming up with horns that take advantage of both boundary and cabin gain to create bass horns small enough for even the smallest rooms, including automobile trunks.

Re: Practically [message #17097 is a reply to message #17093] Thu, 21 October 2004 08:11 Go to previous messageGo to next message
tuber is currently offline  tuber
Messages: 10
Registered: May 2009
Chancellor
what do you mean 'the small room had a relatively high frequency'?

Re: Horns and Room Size - m value, mouth size & length [message #17098 is a reply to message #17095] Thu, 21 October 2004 08:20 Go to previous messageGo to next message
tuber is currently offline  tuber
Messages: 10
Registered: May 2009
Chancellor
some say m values of .5 to .6 are best for bass horns. does this apply to all bass horns, indoors and outdoors alike? if not, what m value is best for small rooms? do you use the same flare coefficient in a small room as big? what size mouth do you use in a very small room like automobile trunks? some use 1/4 size horns inside, some 1/8 or in between like 3/8. in a car, can you use even smaller mouth and length like maybe 1/10 or 1/12? lastly, does fc make a difference in the m value you choose? i know this is a lot of questions, but it really is a very interesting topic. there is a lot to learn.

Re: Practically [message #17099 is a reply to message #17097] Thu, 21 October 2004 22:58 Go to previous messageGo to next message
Mike.e is currently offline  Mike.e
Messages: 471
Registered: May 2009
Illuminati (1st Degree)
If you read what i typed i said : the small room had a relatively high frequency where room gain starts due to its small size

Cheers!



M [message #17100 is a reply to message #17098] Thu, 21 October 2004 23:01 Go to previous messageGo to next message
Mike.e is currently offline  Mike.e
Messages: 471
Registered: May 2009
Illuminati (1st Degree)
M value affects the last part of the horn near the Mouth
- Expo being 1 and Catenoidal being 0

The M=0.5-0.6 'optimal' value is applicable for the ideal horns.

On a highly compromised conical segmented horn the differences are less apparent-but on full sized horns it makes a larger difference.

Download the Dinsdale and Edgar horn files from the link below

Cheers!

I don't use M values in my sub horns, [message #17101 is a reply to message #17100] Fri, 22 October 2004 08:01 Go to previous messageGo to next message
Bill Fitzmaurice is currently offline  Bill Fitzmaurice
Messages: 335
Registered: May 2009
Grand Master
or Hypex flares either for that matter. While the drivers of the 1930s and 40s (when most horn formulas still in use today were arrived at) prevented the use of very high throat impedances, todays small diameter long throw high Bl drivers make it possible to deviate from traditional theory with quite acceptable results.

Re: I don't use M values in my sub horns, [message #17102 is a reply to message #17101] Fri, 22 October 2004 10:05 Go to previous messageGo to previous message
pgolde is currently offline  pgolde
Messages: 21
Registered: May 2009
Chancellor
As I put the finishing touches on my Labhorns, a project I commited to a while ago, after attending the NYC sub shootout at Paul Bell's club, I have a few thoughts. The first is that I was so into building a maximum output sub with clean low extension, I kind of overlooked the size and weight issue, these things are large and heavy, and also fairly expensive to build (correctly).
Following with interest what Bill F. has done with his tubas, and what Tom Danley has done with B-Deaps, I have a feeling I am building last years model when I look into the huge mouth of this horn.
Maybe this will change when I power them up finally. I want to build a pair of Tuba 24's, and A-B them to a single Lab.

Previous Topic: Scan Speaks
Next Topic: Need Dynaudio Gemini speaker plans and suggestion?
Goto Forum:
  


Current Time: Thu Mar 28 08:47:26 CDT 2024

Sponsoring Organizations

DIY Audio Projects
DIY Audio Projects
OddWatt Audio
OddWatt Audio
Pi Speakers
Pi Speakers
Prosound Shootout
Prosound Shootout
Smith & Larson Audio
Smith & Larson Audio
Tubes For Amps
TubesForAmps.com

Lone Star Audiofest