Internal standing waves?

Printable View

03-29-2008, 11:27 PM
oznob

Internal standing waves?

I have read that some speakers are designed with angled cabinets, such as the S2600 and S3100, to reduce internal standing waves. I have done some research and can't seem to find an "understandable" description of exactly what an internal standing wave is and how it affects a particular loudspeakers performance. I would appreciate it if someone could shed some light on this for me?

Thanks,

Mark
03-30-2008, 02:19 AM
ratitifb

considering Standing waves in a rectangular, rigid room

http://www.linkwitzlab.com/rooms.htm

you have to understand there is the same behavior inside a rectangular, rigid enclosure.

So angled cabinet allows to avoid such modes.

In a rectangular cabinet design you have to choose the best ratio from the cabinet dimensions to obtain a regular spaced modes (coloration)
03-30-2008, 09:05 AM
duaneage

Alledgedly you can use the golden rule to minimize standing waves in a cabinet. The ratio of the sides should be about
.63 > 1.0 > 1.63

This produces an eye pleasing rectangle and normal looking box. Now if you go with different dimensions you can use baffles internally to break up the waves, sloped cabinets are used for looks as well as timing on the drivers. These waves are more of a problem for bass than anything else, although their effect on sound can be debated.

If you find an unexplained resonance at one note you may have standing waves. Place angled pieces at the corners inside the cabinet and retest.
03-30-2008, 09:18 AM
oznob

Quote:

Originally Posted by ratitifb

considering Standing waves in a rectangular, rigid room

http://www.linkwitzlab.com/rooms.htm

you have to understand there is the same behavior inside a rectangular, rigid enclosure.

So angled cabinet allows to avoid such modes.

In a rectangular cabinet design you have to choose the best ratio from the cabinet dimensions to obtain a regular spaced modes (coloration)

Thanks for the info ratitifb. I kind of understand the room issue but still a bit confused on how an internal standing wave is created inside a speaker cabinet and why that has an effect on what comes out of the drivers, ports etc. If we assume that most speakers are a rectangular box and would suffer these waves, why aren't more speakers designed with angled cabinets? I'm sure a lot has to do with added costs but, some of the finest speakers I have ever heard are a flat sided rectangular box. How do I know if they suffer from internal standing waves? I'm starting to think it's just some fancy design/audiophile term that only someone with a PHD in sound engineering can understand! If that's the case, I guess I won't worry about it.:confused:
03-30-2008, 09:21 AM
oznob

Quote:

Originally Posted by duaneage

Alledgedly you can use the golden rule to minimize standing waves in a cabinet. The ratio of the sides should be about
.63 > 1.0 > 1.63

This produces an eye pleasing rectangle and normal looking box. Now if you go with different dimensions you can use baffles internally to break up the waves, sloped cabinets are used for looks as well as timing on the drivers. These waves are more of a problem for bass than anything else, although their effect on sound can be debated.

If you find an unexplained resonance at one note you may have standing waves. Place angled pieces at the corners inside the cabinet and retest.

I did my last post before I read yours Duane. That does make more sense. So, I assume, a standing wave can happen in both an acoustic suspention speaker as well as a bass reflex or ported design?
03-30-2008, 10:34 AM
Mr. Widget

Quote:

Originally Posted by oznob

So, I assume, a standing wave can happen in both an acoustic suspention speaker as well as a bass reflex or ported design?

Yes.

It's also frequency dependent. A potentially horrible box would be a 24" cube where you get standing waves that add from each dimension. The rule of thumb is that the standing waves will be ratios of the wavelength that will fit in that dimension with a 1/4 wavelength being about the shortest that will be an issue. So 24" is 1/4 wavelength of an 8' sound wave (~140Hz). This will show up as a blip in the impedance curve. If your 24" cube is a subwoofer crossed over at 80Hz or below you are fine, if you are using this box as part of a full range system... not so good.

Widget
03-30-2008, 06:13 PM
oznob

Thanks for the insight Mr. Widget. A friend of mine and I are thinking of building a bass guitar cabinet with an E140 I have laying around. I know box size, damping and port size are critical to performance. The standing wave thing had me baffled, no pun intended. The light is starting to come on, albeit slowly.
04-01-2008, 06:09 PM
duaneage

There is another thread in DIY on tuning a ported E140. It's really not a bass driver and not really suited for bass work per se, there are better options. It can be beaten a lot but overall your going to be lacing bass down to 40Hz with it.
04-01-2008, 07:27 PM
oznob

:yes:

Quote:

Originally Posted by grumpy

Uh... that's pretty much what it was designed & sold for (bass guitar/SR).
Won't get a "modern" bass sound with a trebly top end or massive
b-string bottom
... but duuuude ... :D

FWIW, two in a box sounds "better" to me ... but then I'm not slogging 100lb cabs around any more.

AMEN to that! I've lugged my share of SVT's etc. We have a garage band and I have had this E140 for a few years sitting in a box. For fun, we thought we would try to put it to some good use, if nothing else for practice. I have just be reading a lot about standing waves in relation to box size, porting, port tubes, damping and the like. We don't want to build something that sounds like crap and we will certainly not be using it in the studio! It's just an almost new driver waiting to make music. If it gets a good solid tone down to 40hz or so, that would work for me.