Removing internal standing waves from speaker cabinet

HI all.

I got this idea on how to limit standing waves inside a rectangular speaker. I though you might rout out ducts in the sides internally and glue halfcircular rods between them ( see pic or the link below ).

I have a few questions I havent figured out yet though and perhaps you might help:

1. Is it worth it? I dont know.. I have little experiance with how much standing waves destroys the sound. The effect will also vary from speaker to speaker. Speaker makers tend to worry a lot about standing waves though so it could be worth it.

2. I guess that the ducts/rods would best be aligned so they are pointing away from the drivers but Im not sure.. I have a feeling that the air would flow back and forth more easy if placed like this.

3. Can you get this kind of semicircular bit for a router? Havent checked that yet.

4. How much thickness would you have to add to the sides? The rods that you glue on will compensate somewhat but I think the result will be weaker than without these changes so additonal thicknes in the material used for the sides is probably needed. In my speaker ( Ariel6 By lynn Olsson ) Im using 19mm MDF for sides. I was thinking about using 8-10 mm diameter ducts and the same for the halfcircular rods.

5. If you do this tweak to a DIY design and the original speaker is covered internally with feltmat ( for damping ) you could do this after the change as well. You could get problems as youll end up with more damping material than in the original design ( as the internal surface will be larger ).


Comments? Tips??

<P ALIGN=CENTER><IMG SRC="http://www.ariel6.dns2go.com/AntiStandingWaveBoxed%20%20medium.jpg"></P>

<P ALIGN=CENTER><EM><A HREF="http://www.ariel6.dns2go.com/StandingWaves.htm" TARGET=_top>Removing standing wave idea explained with pics</A></EM></P>
 

Digi

Member
2002-02-02 5:37 pm
USA
If you use the proposed set-up with the grooves I doubt they will reduce standing waves with positive effects. What I think it will do is spread out the standing waves over a wider frequency range with a lower amplitude, which could make the subjective sound quality worse.

Using acoustic foam with the groove design could be a worthwhile combo. The Air trapped behind the acoustic foam will help dampen the standing waves even further. I typically use acoustic foam for all of my designs (pyramid style), it sounds much better then Acousta-stuf or fiberglass IMHO. I think a slanted baffle is much easier to build then the proposed groove design.

There was a good AudioXpress article about enclosure standing waves not too long ago.

Kind Regards,

Digi
 
Thanks digi.

Thanks, you seem to know what you talk about.

I thougt the ear was very sensitive to bumps in the frequency curve. ( less sensitive to dips. ) and would thus catch standing wave amplified frequencies even if they are narrow.

A slanted baffle is easy to build but you would still have parallell sides and top/bottom. I guess standing waves could form there.

I planned to cover the waveform sides in feltmat ( absorbs sound ) and fill the interior with combed, very lightly packed long hair wool.

I also think a combination is necessary.

Thanks for your input!
 

Digi

Member
2002-02-02 5:37 pm
USA
The ear is more sensitive to low Q peaks and valleys then high Q peaks and valleys. My favorite way of building enclosures is by laminating panels vertically, like a stack of poker chips. With this construction technique the internal and external walls can be made to almost any shape. The only waves to worry about with this design is the Y axis standing waves, which aren't really a big deal. The beauty of this design is the the outside walls can have a large diameter curve to minimized diffraction. Basically, you can mitigate two problems with this design. You seem hooked on the groove design, FWIW I thought I would present my construction technique.

Good luck on your project,

Digi
 
you mean something like this?

Im thinking of building an exterior casing using your idea. See pic <P ALIGN=CENTER><IMG SRC="http://www.ariel6.dns2go.com/External%20casing,%20explode,%20Medium.jpg"></P>

Problem I have is that I havent designed the speaker ( Lynn Olson has ) and I dont want to ( cant ) change the interior.

I fully agree that your way of making a cabinett is much better for standing waves.

My idea ( if it works at all ) has the benefit of working with most current designs.

I got a warning in another forum though that my idea probably wont work so... ( http://www.madisound.com/cgi-bin/discuss.cgi?read=177806 )

to bad.. I kind of liked the look. :(