What shapes inside a wireless wooden speaker can amplify sound?

[AlfieD]

So, I need to make a wireless wooden speaker (no Bluetooth or anything, you just put the phone in and it makes it somewhat louder) for my phone (white iPhone 4 without a case if you wanted to get an idea of the dimensions and aesthetics). My design sketch as of now is a cube measuring roughly 6in by 6in by 6in (obviously, because it's a cube). On the top side of this cube, the phone will sit in an insert area (the sound comes out of the bottom of my phone so it will rest as though it were a landline or home phone). Then the part that the sound will actually exit the speaker will be on the front side of the cube. What shapes inside the cube would make the sound amplified? For instance, would spiraling the sound around miniature tunnels like you do with copper wire amplify the sound?

*NOTE* The cube is going to made out of layers (so if you look closely you would be able to see that it is just layered square wood to create a cube of wood), I haven't decided on the wood yet but was thinking of either plywood, MDF, or something dark. But I'm open for suggestions!

 

[berkeman]

So, I need to make a wireless wooden speaker (no Bluetooth or anything, you just put the phone in and it makes it somewhat louder) for my phone (white iPhone 4 without a case if you wanted to get an idea of the dimensions and aesthetics). My design sketch as of now is a cube measuring roughly 6in by 6in by 6in (obviously, because it's a cube). On the top side of this cube, the phone will sit in an insert area (the sound comes out of the bottom of my phone so it will rest as though it were a landline or home phone). Then the part that the sound will actually exit the speaker will be on the front side of the cube. What shapes inside the cube would make the sound amplified? For instance, would spiraling the sound around miniature tunnels like you do with copper wire amplify the sound?

*NOTE* The cube is going to made out of layers (so if you look closely you would be able to see that it is just layered square wood to create a cube of wood), I haven't decided on the wood yet but was thinking of either plywood, MDF, or something dark. But I'm open for suggestions!

Sounds like a fun school project. Have you looked at how the Bose speakers/radios are designed? Can you do something like that?

 

[AlfieD]

Just looked, that's pretty awesome but I kind of have my heart set on the cube, and that would be too difficult to do given the equipment etcetera, not to mention my not too fantastic expertise regarding the topic. :D

 

[Mech_Engineer]

I think you may want to read about horn loudspeakers: http://en.wikipedia.org/wiki/Horn_loudspeaker

 

[AlfieD]

I think you may want to read about horn loudspeakers: http://en.wikipedia.org/wiki/Horn_loudspeaker

Hey thanks, I got a good idea from the re-entrant (reflex) horn loudspeaker (A.K.A. Bullhorn)! Do you have any idea how I would go about building that given the contents of my original post? Just to note , I still plan to do the cube, but with the bullhorn incorporated into it (almost like making a bullhorn and then putting a solid cube around it and filling the gaps inside to form a cube which has empty space inside which forms a bullhorn). Do you know how I would do this? See the attached file for the bullhorn.

 

[Mech_Engineer]

My recommendation would be keep it simple, maybe have a long tube (around the size of a paper towel roll or so) where the phone mounts in the middle and two horns (one going left, one going right) which amplify the sound out each end of the tube.

 

[berkeman]

@AlfieD -- BTW, how do you expect this passive speaker to make your phone speaker "louder"?

 

[AlfieD]

Yeah... Haha, it only makes it a tiny bit louder but it definitely makes the sound softer; nicer to listen to. The main task is to make the speaker marketable, look nice etcetera. I'm not too concerned of it's not the loudest speaker in the world, it has to be a noticeable change though. As long as it's a good design executed well. I understand your concerns though.

 

[Travis_King]

"Do you wish you're phone speakers would be a tiny bit louder? Do you wish the moderately harsh audio quality would be slightly softer? Try the iBox! For only 29.89 you'll be able to kinda notice that the audio is different than if you had simply laid the phone on a table or in a corner!"

Not so marketable...It's a nice idea, but two things:

1) a cubic box is not a great idea for sound amplification. If you're stuck on the cube idea, at least consider adding internals to the box which allow some degree of acoustic amplification. (And, as MechEngineer said, you want the sound to go left and right, it makes the sound seem "bigger").

2) wood might not the best material for sound amplification as it has many qualities that make it more of a sound absorber than reflector...consider lining the inside of the box with some plastic.

 

[AlfieD]

1) a cubic box is not a great idea for sound amplification. If you're stuck on the cube idea, at least consider adding internals to the box which allow some degree of acoustic amplification. (And, as MechEngineer said, you want the sound to go left and right, it makes the sound seem "bigger").

Yeah, in one of my posts I said that I was incorporating the bullhorn which does bounce sound from left to right.

2) wood might not the best material for sound amplification as it has many qualities that make it more of a sound absorber than reflector...consider lining the inside of the box with some plastic.

This I hadn't considered much, thanks very much! Will put together a model in the next few weeks to get an idea of what it's going to be like. Great suggestion!

 

[Travis_King]

Yeah, in one of my posts I said that I was incorporating the bullhorn which does bounce sound from left to right.

That's good, but be careful that your bullhorn design doesn't actually turn it into a muffler design. Car mufflers use similar principals, but they work to eliminate resonance and cause destructive interference.

Be careful, as your attempts to amplify the sound might actually work to muffle it. :grumpy:

This I hadn't considered much, thanks very much! Will put together a model in the next few weeks to get an idea of what it's going to be like. Great suggestion!

Good luck with your project. If possible, I'd shy away from making it very tall, ie cubic. The benefit of these devices is that they are portable. Consider how likely it would be that someone would want to carry this thing around if it's a big 6 inch cube...

 

[AlfieD]

That's good, but be careful that your bullhorn design doesn't actually turn it into a muffler design. Car mufflers use similar principals, but they work to eliminate resonance and cause destructive interference.

Be careful, as your attempts to amplify the sound might actually work to muffle it. :grumpy:

Do you have any advice/knowledge on how I can avoid turning it into a muffler design and optimise the loudness?

Consider how likely it would be that someone would want to carry this thing around if it's a big 6 inch cube...

How about 4 inches?

 

[Travis_King]

just make sure you consider actual acoustic design and not just add a few little channels and barriers here and there. It's easy to create a lot of destructive interference if those sound waves just start bouncing off internal walls and running into each other in random directions. Study the megaphone design and be sure that you undestand why it works the way it does. Understand also that passive megaphones don't actually amplify sound. They directionalize and focus the sound. You won't actually amplify the sound itself, but you can make it louder/more intense in specific directions as the sound waves will be traveling in a determined direction, and not everywhere at once.

As for the size, just be sure that the main focus in the exterior design is ergonomics. Make it easy to carry around (it's obviously not pocket sized, so how is one to carry this from their apartment, on the train to the park, and then to their favorite picnic spot).

 

[AlfieD]

just make sure you consider actual acoustic design and not just add a few little channels and barriers here and there. It's easy to create a lot of destructive interference if those sound waves just start bouncing off internal walls and running into each other in random directions. Study the megaphone design and be sure that you undestand why it works the way it does. Understand also that passive megaphones don't actually amplify sound. They directionalize and focus the sound. You won't actually amplify the sound itself, but you can make it louder/more intense in specific directions as the sound waves will be traveling in a determined direction, and not everywhere at once.

As for the size, just be sure that the main focus in the exterior design is ergonomics. Make it easy to carry around (it's obviously not pocket sized, so how is one to carry this from their apartment, on the train to the park, and then to their favorite picnic spot).

Sounds difficult to avoid the waves bumping into each other and cancelling out. :/ I'll make sure to take your advice of lining it with plastic, that makes sense, thanks. And yeah, I'll try and make it as ergonomic as possible, and aesthetically pleasing as possible!

One thing regarding that though, do you think it would look OK or even be a good idea if I were to cover all four corners of the cube (which would probably be dark wood coloured, I don't know but you get the picture) with black rubber for protection when dropped to prevent the corners from denting or chipping?

 

[NascentOxygen]

One thing regarding that though, do you think it would look OK or even be a good idea if I were to cover all four corners of the cube (which would probably be dark wood coloured, I don't know but you get the picture) with black rubber for protection when dropped to prevent the corners from denting or chipping?

Your cube has how many corners?

 

[cjl]

@AlfieD -- BTW, how do you expect this passive speaker to make your phone speaker "louder"?

If you could effectively horn-load the driver, you could significantly improve the coupling of the driver to the air, thus improving the efficiency of the energy transfer from the driver to the sound waves. That could dramatically increase the volume, if it can be done properly (horn loaded speakers can have output sound pressure levels 10+ dB higher than non horn-loaded speakers at the same power level). That having been said, I don't know how doable that is - it would be pretty geometrically sensitive.

 

[berkeman]

If you could effectively horn-load the driver, you could significantly improve the coupling of the driver to the air, thus improving the efficiency of the energy transfer from the driver to the sound waves. That could dramatically increase the volume, if it can be done properly (horn loaded speakers can have output sound pressure levels 10+ dB higher than non horn-loaded speakers at the same power level). That having been said, I don't know how doable that is - it would be pretty geometrically sensitive.

Interesting. I don't know what the typical cell phone "speaker" piezo structure is like. Does anybody know what that output looks like acoustically? Can it benefit from a horn or other output acoustic structure?

 

[AlfieD]

Your cube has how many corners?

Haha, yeah, 8 corners. I was working with a prototype and only had one side of it so muddled it up and said 4, sorry.

 

[AlephZero]

Interesting. I don't know what the typical cell phone "speaker" piezo structure is like. Does anybody know what that output looks like acoustically? Can it benefit from a horn or other output acoustic structure?

I don't know about the transducers in cellphones, but good quality piezo loudspeakers do use a horn for acoustic impedance matching. http://www.bestgrouptechnologies.com/piezosource-technology-background.php

They are usually called "bullet" tweeters, from the shape of the central part of the horn structure (which is fixed, not connected to the piezo element). Without the "bullet", the maximum frequency would be limited not by the transducer, but the "cutoff frequency" when the radius of the horn was the same order of magnitude as the wavelength of the sound (about 15mm, to cover the full human hearing range).

http://www.bluearan.co.uk/sales/dap/images/D3115.jpg

 

[mrspeedybob]

Have you considered putting some electrical guts in your box? Microphone under the cell phone, batteries, amplifier, speakers.

 

[AlfieD]

Have you considered putting some electrical guts in your box? Microphone under the cell phone, batteries, amplifier, speakers.

We can't. :( It had to be a sustainable speaker; no electrical a whatsoever.