wide baffles and baffle step

Thank you very much, arion and twoleftears. 

Imo "wave launch" is a good description of what a wide baffle does well.  I don't know whether it is technically precise or not, but the image it conjures up in my mind is of a sound wave getting a better "push" off of a wide cabinet than off a narrow one.  

A horn can be thought of as a special case of a wide baffle, with the baffle wrapped forward to get a still more efficient "wave launch" within its angle.  Or on the other hand a flat baffle can be thought of as a 180-degree horn, effective down to the frequency where the "horn" is too short relative to the wavelengths... and that's where the "baffle step" kicks in.  

Duke

@avanti1960 wrote: " wider baffles create the need for additional crossover components and complicate the voicing recipe. "

That has not been my experience. With a sufficiently wide baffle, no dedicated baffle-step compensation circuitry is needed. If some baffle step compensation is still called for, it can be accomplished by choice of low-pass filter component values, with no increase in parts count.

To my ears, a baffle-step compensated narrow cabinet does not have the lower-end impact and articulation nor the dynamics of a wide baffle which does not need baffle step compensation.  So imo each approach has its place. 

"imaging and high frequency dispersion is handicapped as well by wider baffles."

Yes and no. If edge diffraction is minimized, baffle width isn’t an issue as far as imaging goes.

But if there is significant edge diffraction, then yes imaging is better with a narrow baffle.

What happens is, the diffraction at the edge of the enclosure sends a false angular cue to the ear, and the farther away the edge is, the longer the time delay and therefore the greater the false angle. This holds true up to the point where the baffle edge is about nine inches away (corresponding to a 19-inch baffle width, assuming a 1" dome tweeter); at that point the time delay is great enough for the "precedence effect" to kick in and at suppress the false localization cues. (This is one of the reason why high-end recording studios often flush-mount their main monitors: Doing so pushes the arrival time for the first reflection past the point of generating significant false localization cues, so that the imaging cues on the recording can dominate.)

As for high frequency dispersion, a teeny tiny baffle around the tweeter does result in wider dispersion at the bottom end of the tweeter’s range (think "eyeball" tweeter atop the cabinet). Whether or not this is desirable is debatable from a tonal balance standpoint, but I can see it being desirable from an imaging standpoint.

Duke

Tomic601, my understanding is that sound waves are longitudinal pressure fluctuations, not transverse waves (even though we tend to draw them that way), and therefore there is no phase change when they reflect or diffract.   

There is of course a time-delay built into the path length to the reflecting or diffracting discontinuity, and that time delay works against preservation of time and phase coherence.   

Imo the solution is to minimize edge diffraction effects either by having  minimal baffle dimensions or large-radius roundovers or sufficient directivity to avoid significant cabinet edge interaction in the first place.  Since I like the other benefits which come with having a wide baffle, I try to figure out ways to minimize the downsides. But it's a juggling of tradeoffs, and arguments can be made for either side.   

Duke

@avanti1960 wrote:

"With respect to baffle step compensation, unless the baffle is wide enough to impinge on the limits of room space and physical practicality there will be a 3db loss of all frequencies below the baffle step frequency. For example the baffle would need to be 33.76 in. wide for a frequency of 400 hz. With that width, frequencies below 400 hz will drop off by 3db relative to frequencies above 400 hz...

"With the loss in output of all frequencies below the baffle step frequency, some form of compensation will be required. A BSC circuit is a popular and effective method for doing so."

The baffle step happens gradually, so in practice we really don’t need 33.76" width in order to be good down to 400 Hz.

AND that baffle-stepping side-spilling wrap-around energy isn’t "lost" - it just becomes off-axis energy. It arrives after some time delay and some attenuation due to path length and some absorption at the surfaces it reflects off of.

In the meantime, the woofer’s radiation pattern is also trending towards omnidirectional at longer wavelengths. So as we go down in frequency, we are getting proportionally more reflected energy from two phenomena: Baffle-stepping and pattern-widening. Thus obviously as we go down in frequency, the room acoustic situation plays a progressively greater role in what we hear, especially with narrow speakers.

In situations where the direct sound dominates, I can definitely see an argument for baffle step compensation. As the relative contribution of the reverberant energy at the listening position increases, imo baffle step compensation becomes less necessary and/or less desirable.

I can easily see baffle step compensation being the right choice for a 9" wide speaker which is not designed to go up against the wall. I also think it’s a tradeoff, degrading the spectral balance of the reverberant sound for the sake of the first-arrival sound. And using a wide baffle is also a tradeoff. It’s a matter of picking one’s poison... or perhaps more precisely, picking the poison which is most palatable (and most practical) to the most potential buyers. And I’ll readily admit that’s NOT a 33.76" wide baffle!

Duke