Baffle Step Absorption

[dcathro]

I am just wondering how much of the baffle step it is possible to absorb with something like 1" (and maybe thicker in spots) felt?

I notice that Avalon do it on their speaker - especially the Sentinal, and Wilson also. Is it possible to absorb more than a db or two? Or ist it just cosmetic?

I am thinking of trying this on an open baffle.

Thanks

David

[PKNJ]

I don't think its baffle step they're absorbing. The felt is for diffraction absorbtion/supression, not baffle step.

I run out of brains at this point, so I'll leave it to others for a more enlightening explanation.

[Brett]

Originally Posted by PKNJ

I don't think its baffle step they're absorbing. The felt is for diffraction absorbtion/supression, not baffle step.

I agree. Dunlavy, VAF and others have been doing this for a long time.

[dcathro]

Originally Posted by PKNJ

I don't think its baffle step they're absorbing. The felt is for diffraction absorbtion/supression, not baffle step.

I don't understand the distinction.

I understand baffle step to be the boosting of frequecies with a wavelength less than the baffle width/height from the reflection off the baffle.

irregular surfaces and sharp edges can cause problems in high frequency imaging, espescially when they are close to the tweeter.

If the felt were just around the tweeter, I would agree that it is for supression of defraction. However they seem to be doing some fairly broad absorption even around the bass drivers. It may take many inches to to absorb all the baffle reflection at 250Hz, but they may be reducing it.

On my midrange open baffle, I am looking to smooth out the frequency response by absorbing some of the baffle reflection between 250Hz and 3K. I would have thought that with 1" to 3" (in a recess) of felt would reduce baffle reflection. No?

[planet10]

But it is all on the baffle, absorbing only the energy at 90 degrees to the on-axis energy. The absorbtion would need to be in front of the tweeter/mid to accomplish anything like baffle step compensation.

dave

[dcathro]

Originally Posted by planet10

But it is all on the baffle, absorbing only the energy at 90 degrees to the on-axis energy. The absorbtion would need to be in front of the tweeter/mid to accomplish anything like baffle step compensation.

dave

Sorry, my understanding is that the 6db baffle step gain is from energy from the cone folding back and hitting the baffle and then reflecting as forward firing energy.

If it has to go through thick felt twice, surely this energy is reduced to some degree.

[el`Ol]

But strongly frequency dependent, in contrast to the reflection.

[dcathro]

Originally Posted by el`Ol

But strongly frequency dependent, in contrast to the reflection.

Yes understood, anything under 200 Hz is going to be hardly affected. But I would have thought from 500 Hz to 3+ KHz could be reduced significantly, with less down to 250 Hz

The driver going in the baffle is a Suprafox FR 215, so the high frequencies above 3K tend to beam. I am hoping that there will be little reduction of these from the felt.

Obviously, I need to try it, and measure it.

[markus76]

I think about the baffle step not as some sort of gain but a loss because of waves "bending" around the enclosure. It's obvious that the room will have a great influence on the frequency response. It needs to be measured in situ.

My take on absorption as part of a loudspeaker's design would look more like this:



Best, Markus

[dlr]

Originally Posted by dcathro

I don't understand the distinction.

I understand baffle step to be the boosting of frequecies with a wavelength less than the baffle width/height from the reflection off the baffle.

irregular surfaces and sharp edges can cause problems in high frequency imaging, espescially when they are close to the tweeter.

If the felt were just around the tweeter, I would agree that it is for supression of defraction. However they seem to be doing some fairly broad absorption even around the bass drivers. It may take many inches to to absorb all the baffle reflection at 250Hz, but they may be reducing it.

On my midrange open baffle, I am looking to smooth out the frequency response by absorbing some of the baffle reflection between 250Hz and 3K. I would have thought that with 1" to 3" (in a recess) of felt would reduce baffle reflection. No?

You're correct for the most part.

First, there is no distinction insofar as step and diffraction are concerned. Step is simply one part of diffraction, they are the same phenomonon.

Second, diffraction results in peaks and valleys, constructive and destructive interference. It's really a continuum.

Third, the step portion of diffraction can be reduced in some cases. Theoretically even woofer diffraction could be nearly fully controlled, but the baffle dimensions and felt required are simply not realistic.

1" of felt is usually good for most cases of tweeters and even midranges, but as you make it thicker, to some degree it will be more effective, but more so in the lower frequencies. The extremes used by Dunlavy and some others was necessary for their purposes and was certainly effective. Even 1" inch of felt can reduce the step by 1db or even more, for tweeters and for some smaller midranges. Woofers would take a considerable amount.

Dunlavy most likely applied felt to woofers as much to reduce their impact on the other drivers. I've found through testing that a nearby woofer can be more detrimental than a somewhat distant baffle edge. Every driver/baffle combination is unique.

You may find at article at my site by Andy Unruh to be helpful. I've got some tests and measurements of felt there as well. If you have back issues of audioXpress, see June 2005. You'll see among the measurements there an example of how a midrange can be affected.

Dave