Can a Single Speaker Direct Low Frequencies? Exploring Options and Limitations

[newaqua]

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

 

[berkeman]

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?

 

[berkeman]

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

 

[sophiecentaur]

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.

 

[berkeman]

Unfortunately, any directive sound emitter can suffer from reflections from nearby objects

Good point!

 

[Nidum]

Horn tube .

Horn tube loudspeakers are commercially available .

 

[newaqua]

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?

 

[davenn]

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

 

[sophiecentaur]

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.

 

[Khashishi]

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.

 

[newaqua]

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?

 

[berkeman]

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?

 

[newaqua]

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.

 

[sophiecentaur]

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!