baffle step basic question

[kneadle]

Hello,

I have been assuming that the baffle-step low frequency attenuation phenomenon was directly related to the baffle, and my designs avoided the problem by simply mounting the driver directly onto a pipe. This is a primary reason I like the transmission-line design.

However, I'm beginning to doubt my understanding of baffle-step loss. Have I been correct in assuming that by having a baffle-less design that I have avoided the 4pi to 2pi low frequency transition problem? Or have I simply gotten lucky with my designs? In other words, my designs generally do not have any baffle that is remotely parallel to the driver surface. Any sympathetic radiation from the baffle, I hope, is severely limited, and cannot be radiating forward. This, as far as I understood, would prevent the perceived attenuation.

However, I could be wrong. Is it really the baffle, or is it a function of low frequency radiation that causes this phenomenon?

My next design depends on my current assumption being correct. Would anyone like to weigh in?

Thanks,

Dave

 

[pinkmouse]

Baffle step is caused by the emitted sound wavelength being significantly smaller than the planar surround of the speaker. This causes the radiation pattern to change response as you state.

The effect is a function of frequency and baffle size, but as your speakers have no baffle, then you should have no problem, you are already radiating into 4 pi space.

However, to get into the deeper end, driver beaming at higher frequencies is also partially due to the size of the driver creating a virtual baffle for the higher frequency radiation, but unless you are using full range drivers this is usually above crossover, and thefore not important.

Check out this article by John L Murphy for more theory.

 

[kneadle]

However, to get into the deeper end, driver beaming at higher frequencies is also partially due to the size of the driver creating a virtual baffle for the higher frequency radiation, but unless you are using full range drivers this is usually above crossover, and thefore not important.

Check out this article by John L Murphy for more theory.

This is precisely what I was beginning to think, but I didn't know to what extent I should worry about it. Very little, thank goodness.

Thanks for the reference. Reading it, and several others, is what prompted my question. It is a very good article.

Dave

 

[kneadle]

Now the follow-up

The follow-up question is this:

MJK has indicated that the throat of a TL (the area directly behind the driver) should be 2Sd or greater, otherwise the bass response is choked. What does "directly behind the driver" mean, specifically? Behind the magnet or behind the mounting ring?

Dave

 

[BillFitzmaurice]

You're not eliminating the baffle step with direct mounting to a pipe, you're raising its frequency. Since you have no baffle that serves as a reflective plane the baffle step will occur where your driver/pipe outer diameter is one wavelength across, below which radiation shifts from spherical to omnidirectional.

 

[Svante]

shifts from spherical to omnidirectional.

Apart from this last part I agree. I think you mean from half space to full space.

There will be a baffle step also for the pipe monted speaker. The speaker membrane itself serves as a small baffle. You can try this in my program "edge" if you like. Just set the baffle size equal to the driver size.

 

[kneadle]

You can try this in my program "edge" if you like.

Thanks for the freeware. Every little bit helps, eh?

Dave

 

[BillFitzmaurice]

Apart from this last part I agree. I think you mean from half space to full space.

There will be a baffle step also for the pipe monted speaker. The speaker membrane itself serves as a small baffle. You can try this in my program "edge" if you like. Just set the baffle size equal to the driver size.

Hemispherical is what I meant, making it synonymous with half-space.

 

[cjd]

The only way to really eliminate baffle step influences is to have an infinite baffle, not do away with it altogether. In fact, if your speaker is round in some ways you have the worst possible scenario as far as how smooth the transition is because the radiation center is the same distance from all edges.

C

 

[kneadle]

The only way to really eliminate baffle step influences is to have an infinite baffle, not do away with it altogether. In fact, if your speaker is round in some ways you have the worst possible scenario as far as how smooth the transition is because the radiation center is the same distance from all edges.

C

More accurately, if my speaker is cylindrical, this is true. Yet, in my case, the driver is mounted directly onto a cylinder, not onto a round baffle which is mounted within the cylinder. For example, I have a 6-inch Sd speaker mounted flush onto a 6-inch (ID) PVC-tee.

Dave

 

[Svante]

Here's the difference in baffle step between a 200 mm circular baffle with a single point source in the middle (red) and the source distributed over the baffle (green) (as in the case of a driver mounted in the end of a tube).

The green curve is much smoother, but still has a baffle step.

An externally hosted image should be here but it was not working when we last tested it.

 

[kneadle]

The green curve is much smoother, but still has a baffle step.

An externally hosted image should be here but it was not working when we last tested it.

This is exceedingly helpful. Thanks.

Dave