Question - I see lots of high quality speaker cabinets use "wavy" insides

[wesayso]

Are you sure?
Wavelength frequency convert lambda Hz sound conversion acoustics acoustic audio radio measure speed of sound and radio typical waves wave length light vacuum equation formula for frequency speed of light color electromagnetic spectrum - sengpielaudi

 

[weltersys]

While we're at it...

This is something I can't understand: why do we care about internal wave reflections or standing waves while a 20 KHz 1/4 wavelength is 3,750 meters ? In such a limited pace, does the physical rules apply for such a long wave ?

1/4 wavelength of 20kHz is about 4.25 millimeters..

 

[planet10]

20 KHz 1/4 wavelength is 3,750 meters ?

20 KHz 1 wavelength is 0.68” = 17.22mm = 0.0172 m, divide by 4 for quarter wavelength.

dave

edit: beat to the punch.

 

[chrisb]

Um, maybe you could show the class your math on that, Sined?

 

[andy2]

Vince Bruzzese, owner of Canadian Totem acoustic, believes that veneer and lacquer inside the cabinet improves the sound. Probably has to do with reducing friction therefore improving the transient of bass.

 

[AllenB]

20 KHz 1/4 wavelength is 3,750 meters

This is correct for electro-magnetic radiation.

 

[Cableaddict]

You probably can get some answers from this similar thread: Innerchoic cabinets - should I?

I have used the wavy shaped insides myself in my build:

All you'd really need is the curves, not the waves. I dunno if that will improve the sound of a speaker or not, (I suspect it will) but if there are no parallel surfaces, that's about as good as you can get, short of making the insides a quadratic sequence.

Say - If you were mixing a record, while actually sitting inside your monitors, this could be a very good thing.

 

[PLB]

Hi Pygmy,

This article provides some logical answers to my mind, but does not negate the use of acoustically absorbent materials.

http://www.keith-snook.info/wireles...e Transmission-line loudspeaker Enclosure.pdf

Hope this helps.

Peter

 

[Sonce]

Link is not working properly. If you are referring to the Bailey TL design article in the 1972 Wireless World, I do not see how it is related to this thread.

 

[PLB]

Hi Sonce,

Here's the pdf attached. It explains in logical detail what happens to reflected sound in a loudspeakers enclosure, which directly relates to the TS's OP.

 

[wesayso]

Impedance tests with the driver in the enclosure can tell us a lot about those internal reflections.
See here: http://www.diyaudio.com/forums/full-range/242171-towers-25-driver-range-line-array-62.html#post4140167 where I start impedance tests of my wavy shaped enclosure (well, an 1/25 scaled test enclosure) to find my optimum internal damping recipe.

 

[Sined]

Most certainly wrong maths ! I used the formula l = 300/f in MHz.

 

[Sined]

Yep, this explains my misunderstanding. The formula I used is for radio waves and is based on the speed of light. The right formula must uses the speed of SOUND !!!!

Thanks for the info !

 

[Sonce]

Hi Sonce,
Here's the pdf attached. It explains in logical detail what happens to reflected sound in a loudspeakers enclosure, which directly relates to the TS's OP.

Again, no relation to "wavy" style of the inside of the cabinet.

 

[PLB]

Sonce,

"Again, no relation to "wavy" style of the inside of the cabinet."

And again I have to tell you that it does. Literally, anything you do to the inside of an enclosure will have a measureable effect, wavy or otherwise. Even the basket of a driver or its magnet has a measureable effect including the chamfering of the inside edge of the drivers cutout. However, that does not mean that a "wavy" style surface will completely eradicate standing waves, but it will help to disperse standing waves over time in the same way as Bailey's article describes, by having non parallel surfances.
But all this does not negate the use of acoustically absorbtive materials.

 

[Pygmy]

This is an interesting point - I've always understood the chamfering of the driver hole is quite important.
(I think I read a post by Troels Gravesen about this)

But yesterday I happened to find this image of Neat Motive SX1 speakers - that one of my friends has and thinks of really highly - and I noticed a lack of chamfering.?

http://www.6moons.com/audioreviews2/neat/3.png

(Or maybe it is chamfered and it's just the angle of the photo?)

 

[planet10]

Doesn’y look champhered.

dave

 

[Pygmy]

Doesn’y look champhered.

dave

For speakers costing 2300 euros / pair, that seems like a fairly big mistake if chamfering is really that important?
In the whole production process I don't think chamfering would have cost much more?

 

[Sonce]

However, that does not mean that a "wavy" style surface will completely eradicate standing waves, but it will help to disperse standing waves over time in the same way as Bailey's article describes, by having non parallel surfances.

No, it won't. Size of the non parallel surfaces (>15") and angles (45 deg.) inside the Bailey box are much, much bigger than the "waves" depicted here. One-inch "waves" have no audible effect. To be effective, dimensions of the object has to be appreciable part of the sound wavelength. 1000 Hz has over 13" wavelength. Wave with 13" wavelength do not "see" 1-inch obstacle.
Chamfering of driver hole is effective, because it is very close to the speaker cone (same with speaker basket and magnet). "Waves" are far away.

 

[bwaslo]

As far as breaking up waves, try to always think in terms of wavelengths. If the variation in the surface is ~1 inch, well, 1 inch is only 1/4 wavelength at about 3.5kHz. So the surface wobbles aren't going to do much of anything below that frequency (below 1/4 wavelength, physical features become more or less invisible). The wavelength fraction is even smaller (much!) in solid materials, btw.