I Can a Single Speaker Effectively Direct Low Frequencies?

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Directing low frequencies (30-60Hz) with a single speaker poses significant challenges due to the large wavelengths involved, requiring reflectors that are comparably large. A parabolic reflector must be several wavelengths across to effectively direct sound, making smaller designs (like half or quarter wavelengths) ineffective. Using multiple speakers in a phased array could enhance directivity and mitigate issues like reflections from nearby objects. While there is curiosity about potential applications, such as in concerts or exhibits, practical implementation remains complex and costly. Overall, achieving effective low-frequency directionality with a single speaker is unlikely without substantial equipment modifications.
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Hey everyone.
I have a couple of questions in regards to the direction of sound. I am wanting to direct lower frequencies (30-60Hz). When I say direct, I mean more of a beam rather than radiating out from the front of the speaker in all directions like a traditional wave.

I have been looking at placing the speaker in the focal point of a reflector, however to do this with lower frequencies you need a fairly large reflector from what I have read. I am trying to do this with a single speaker.

So my first question is in regards to the size of reflector for these lower frequencies, can it be half or quarter wave length? Is there a way to get around this limitation of the size of the reflector?

My second question is what is the ideal size of speaker for lower frequencies? Is there a relationship between the size/diameter of the speaker and a specific wavelength?

Does anyone else have ideas for directing low frequencies with single speakers?

Any thoughts or input would be greatly appreciated.

Cheers
 
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newaqua said:
Hey everyone.
I have a couple of questions in regards to the direction of sound. I am wanting to direct lower frequencies (30-60Hz). When I say direct, I mean more of a beam rather than radiating out from the front of the speaker in all directions like a traditional wave.

I have been looking at placing the speaker in the focal point of a reflector, however to do this with lower frequencies you need a fairly large reflector from what I have read. I am trying to do this with a single speaker.

So my first question is in regards to the size of reflector for these lower frequencies, can it be half or quarter wave length? Is there a way to get around this limitation of the size of the reflector?

My second question is what is the ideal size of speaker for lower frequencies? Is there a relationship between the size/diameter of the speaker and a specific wavelength?

Does anyone else have ideas for directing low frequencies with single speakers?

Any thoughts or input would be greatly appreciated.

Cheers
Welcome to the PF.

Yeah, I would use a single speaker at the focus of a large parabolic reflector that is steerable, or maybe several speakers driven as a phased array. What is the application?
 
I still remember this exhibit at the San Francisco Exploratorium -- I first saw it with my kids on a trip about 15 years ago...

https://s-media-cache-ak0.pinimg.com/736x/76/84/b7/7684b78d03849c317d47c57d48f8413d.jpg
7684b78d03849c317d47c57d48f8413d.jpg
 
newaqua said:
Does anyone else have ideas for directing low frequencies with single speakers?
The size of reflector needed to direct 30-60Hz sound effectively would be pretty big. (The wavelength is around 10m so the aperture would need to be comparable with (significantly bigger than) that.
That would be a bulky arrangement and you could produce simple directivity (a 'doughnut' pattern) by using two speakers with anti phase connection. It would give a good null in a direction at right angles to the line between them. Unfortunately, any directive sound emitter can suffer from reflections from nearby objects. 30Hz would be very hard.
 
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sophiecentaur said:
Unfortunately, any directive sound emitter can suffer from reflections from nearby objects
Good point!
 
Horn tube .

Horn tube loudspeakers are commercially available .
 
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I forgot to add, that I was wondering if you could use a 1/2 or 1/4 wavelength width parabolic reflector which would reduce the size. Are there any rules or theory's around sound waves and reflectors?
 
newaqua said:
I forgot to add, that I was wondering if you could use a 1/2 or 1/4 wavelength width parabolic reflector which would reduce the size.

yes, you already asked that ... did you read the responses ?
you didn't acknowledge any of them

you also didn't answer berkeman's question as to what it is you are trying to achieve

Do you realize that sound at 30 - 60 Hz is just a buzz ?

here is an example of 30 Hz ... the signal from the crab nebula pulsar


wavelength of a sound at 30Hz is 11.5 metres ... at 60 Hz = 5.7 metres
again ... knowing what you are trying to do will determine how well a 1/4 or 1/2 wave diameter dish will performDave
 
newaqua said:
I forgot to add, that I was wondering if you could use a 1/2 or 1/4 wavelength width parabolic reflector which would reduce the size. Are there any rules or theory's around sound waves and reflectors?
This is a diffraction problem. To produce a 'fair' directivity, your 'aperture' (reflector in this case) needs to be at least several wavelengths across or the launched wave will turn up in all directions. Such a small dish is virtually 'hardly there', as far as the waves are concerned. You can do the experiment by standing behind a wall and judging whether it makes any difference to the rumble of traffic going past. The wall may cut down the high frequencies a bit but not the low frequencies.
 
  • #10
I remember there was a company making a special kind of speaker that used nonlinear phenomena in air to produce sound at the listener's ear. I think it had a higher frequency carrier wave (which could be directed easily), and I guess it used some kind of amplitude modulation to generate lower frequency waves. I think it was intended for stuff like museum exhibits where only the person in front of the exhibit could hear the sound. I can't remember what it was called though.
 
  • #11
Firstly, thank you everyone who has replied here.
The other day when I tried to see the thread all that would load was the 'Something to add box', and I couldn't see my original post, hence why i have mentioned the same thing twice! I also couldn't see any replies, hence not acknowledging anyone. So thank you.

In regards to what we are doing with it or its application, we don't have a specific application in mind, more curiosity than anything.
We are trying to see if we could mount the arrangement on a bearing that is standing straight up, allowing the contraption to turn in a full 360 degree circle. Which would allow you to have a beam that you could 'wash' over people if you know what I mean.

Sorry I could not be more specific, this is literally just curiosity and extra time were filling in.

Essentially I am reading here that for a frequency that low we would need a reflector that is massive, too massive for what we are doing. Half or quarter wavelengths won't work?
 
  • #12
newaqua said:
Which would allow you to have a beam that you could 'wash' over people if you know what I mean.
For an effect at a concert or something? Why?
 
  • #13
As I said, we don't really have a purpose in mind at the moment, more of a if we could do it, then I am sure we could find something to use it for. As you mentioned, in a concert or theatre could potentially be a use, if we could get it to work.
 
  • #14
newaqua said:
As I said, we don't really have a purpose in mind at the moment, more of a if we could do it, then I am sure we could find something to use it for. As you mentioned, in a concert or theatre could potentially be a use, if we could get it to work.
A lot of the problems would be solved if you could use multiple sources. Not a problem, these days with wireless networking. Just expensive! :frown:
 
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