What's the optimal baffle width?

[HwaLF]

I've read several articles, and I'm getting confused about what the best baffle width and design would be. Some conclude that narrow baffles are better for imaging, while others claim that a wide enough baffle (around 45 cm, or depending on the tweeter) could push the diffraction outside the tweeter's bandwidth. I also read a comment stating that if you make a baffle wide enough so it has no significant diffraction at high frequencies, the wide baffle can actually provide better overall imaging due to an improved direct-to-reflected ratio in the low-midrange frequencies.

Would mounting the tweeter on a bottom plate on top of the enclosure be a viable solution?

What would be the optimal design for full sound with great imaging and soundstage? Any advice or insight would be greatly appreciated.

(PS: I'd rather not do an infinite baffle design due to space limitations)

 

[TurtlePaul]

While there is good science on the preference for linearity of flat on-axis frequency response and smooth off-axis response, there is more disagreement regarding if narrow or wide directivity designs are preferred in general if the preference score is the same.

Wide baffles fit right in there with cardioid vents in regards to being a preference thing that some people have. In addition to the high frequency defraction issues, don’t underestimate how good wide baffles (especially when paired with big bass drivers) are at lowering the Schroeder frequency and baffle step frequency in the bass. Look at the difference between small bookshelf speakers which are omnidirectional at 500 hz while big floorstanders generate some directivity at 200 hz.

If you are just looking to reduce diffraction, consider a faceted baffle like the DXT-Mon or Directiva DIY designs.

 

[Keith_W]

I presume you understand what a baffle diffraction step (BDS) is? In case you don't the BDS is a volume loss of about 6dB that occurs over four octaves. If you were to take an omnidirectional driver and mount it on a flat surface (infinite baffle), it radiates into a hemispherical space. On a loudspeaker surface, at some point, it will transition from hemispherical radiation to spherical radiation. The centre frequency f3 can be calculated with the formula f3 = 115824/W (W = baffle width in mm), or f3 = 4560/W (W = baffle width in inches).

The above shows the effect of the BDS on a woofer mounted on a 500mm non-rounded baffle. In green is a simulation measurement at 10cm, in brown at 3m.

The wider W is, the higher the centre frequency. Is it possible to make the baffle so narrow that you can push the BDS above the tweeter's operating range and make it omnidirectional, as you asked? Working backwards, the f3 has to be two octaves above the hearing range of 20kHz, meaning f3 = 80kHz. Rearranging the math, the baffle width would have to be 1.45mm or 0.057". Complicating matters, most tweeters are not omnidirectional. So in theory, the answer should be "no", since the baffle width is an order of magnitude smaller than the tweeter itself. And even if it was, the tweeter itself is directional.

So if we want the smoothest on axis frequency response, the solution is to make the baffle wide enough so that the BDS is too low to matter (as far as the tweeter is concerned), or to implement some kind of BDS compensation in the XO. Suppose you want to high pass the tweeter at 2kHz. Two octaves below that is 500Hz, which means the baffle width has to be 231mm (9") minimum.

The wavy lines in that graph is due to the squared-off baffle. You can reduce this by rounding over the baffle.

However this does not do anything for directivity matching between drivers. That is another long discussion!

As for wider directivity/narrower directivity as a design goal for better imaging, I think the answer is "nobody knows". Wider directivity = more reflections, and that is a huge can of worms on ASR. Some people believe it provides ambience, some people think it worsens imaging. I certainly don't have an opinion either way, and these kinds of discussions have been done to death on ASR. Being able to design a speaker with smooth directivity is said to be a solved problem with modern modelling software. The big question is what your design goal is going to be, and I don't think any of us can help you there.

 

[Duke]

I just now saw this thread; here is the reply I posted in your similar thread on another forum, in case it might be of interest to anyone here:

My understanding is that the edge reflection (diffraction) generates false azimuth (horizontal arrival angle) cues. This is because this reflection arrives later in time by an interval similar to the arrival time difference between the two ears for a sound arriving from somewhat off to either side. These false azimuth cues degrade the imaging precision.

My understanding is that the imaging superiority of a narrow baffle is because said false azimuth cue is not as big of an angular error as would be the case with a wider baffle because the arrival time of the edge reflection is not as late in time as with a wider baffle.

My understanding is that a sufficiently large round-over (or bevel, which is like a first approximation of a round-over) greatly weakens that edge reflection such that cabinet width is no longer a major factor in imaging. The round-over radius should be at least 1/4 wavelength of the lowest frequency you are concerned about.

So if you plan in advance to use a large bevel or large-radius round-over, you can make the cabinet wider for the sake of pushing the baffle step frequency lower without degrading the imaging. The Snell Type A was an imo excellent example of this approach:

http://www.troelsgravesen.dk/SnellA3i.htm

The round-over does reduce the effective baffle width, from a baffle-step standpoint. If you have a 2" round-over on each side of the front baffle, the effective cabinet width is about 2" less than its physical width. So the effective width of the Snell Type A's mid/tweet baffle is a lot less than its actual physical width.

 

[HwaLF]

I presume you understand what a baffle diffraction step (BDS) is? In case you don't the BDS is a volume loss of about 6dB that occurs over four octaves. If you were to take an omnidirectional driver and mount it on a flat surface (infinite baffle), it radiates into a hemispherical space. On a loudspeaker surface, at some point, it will transition from hemispherical radiation to spherical radiation. The centre frequency f3 can be calculated with the formula f3 = 115824/W (W = baffle width in mm), or f3 = 4560/W (W = baffle width in inches).

View attachment 499658

The above shows the effect of the BDS on a woofer mounted on a 500mm non-rounded baffle. In green is a simulation measurement at 10cm, in brown at 3m.

The wider W is, the higher the centre frequency. Is it possible to make the baffle so narrow that you can push the BDS above the tweeter's operating range and make it omnidirectional, as you asked? Working backwards, the f3 has to be two octaves above the hearing range of 20kHz, meaning f3 = 80kHz. Rearranging the math, the baffle width would have to be 1.45mm or 0.057". Complicating matters, most tweeters are not omnidirectional. So in theory, the answer should be "no", since the baffle width is an order of magnitude smaller than the tweeter itself. And even if it was, the tweeter itself is directional.

So if we want the smoothest on axis frequency response, the solution is to make the baffle wide enough so that the BDS is too low to matter (as far as the tweeter is concerned), or to implement some kind of BDS compensation in the XO. Suppose you want to high pass the tweeter at 2kHz. Two octaves below that is 500Hz, which means the baffle width has to be 231mm (9") minimum.

The wavy lines in that graph is due to the squared-off baffle. You can reduce this by rounding over the baffle.

However this does not do anything for directivity matching between drivers. That is another long discussion!

As for wider directivity/narrower directivity as a design goal for better imaging, I think the answer is "nobody knows". Wider directivity = more reflections, and that is a huge can of worms on ASR. Some people believe it provides ambience, some people think it worsens imaging. I certainly don't have an opinion either way, and these kinds of discussions have been done to death on ASR. Being able to design a speaker with smooth directivity is said to be a solved problem with modern modelling software. The big question is what your design goal is going to be, and I don't think any of us can help you there.

I see! Thank you for the response. I really appreciate the info!

 

[Digital_Thor]

I really enjoy KEF's approach. They have made something that made me listen to music and forget the speakers - IME.
Try and read white papers from both KEF and Grimm Audio... They are easy to find online, and definitely show how you can both have a wide and narrow design, as long as drivers, filters and layout fits with the baffle.
Here on ASR you can also find plenty of tests of these speakers.
Into DIY? Then Heissmannacoustics is a good place... With several options.

Heissmann Acoustics | Kits | Speaker developments

Speaker kits and construction plans. Best sound from self-made speakers. Magazine on speaker construction and DIY-Audio.

heissmann-acoustics.de

 

[Waxx]

both small and wide baffles have advantages and disadvantages, and a lot depends also on the other factors in the design. So there is no "best bafflewith", there is only a best one for your goal. And to know it, you need to know your goal and what drivers and layout you want to use. Baffle roundings and crossover can all make things worse or better depending on the case.

 

[Head_Unit]

I think a related interesting topic would be how about absorptive materials on the front baffle, as has sometimes been done, and their effectiveness or lack thereof. Hmmm spinning in my head now is that reducing the effects or worsening, can't quite think it out.

 

[Waxx]

That has been done, and is still done by some like wilson audio arround the tweeter. But better measuring is not the result. A waveguide or horn does it better (when executed right) and also deals with dispertion.

 

[Waveform Fidelity]

Responding to the original OP question. …my suggestion is either narrow as possible or as wide as possible (infinite baffle)

 

[Arindal]

Try and read white papers from both KEF and Grimm Audio... They are easy to find online, and definitely show how you can both have a wide and narrow design, as long as drivers, filters and layout fits with the baffle.

Would put it other way ´round: you have to know the directivity, geometry and transitional behavior of your drivers, and a clear goal which should be the resulting directivity and listening window over a broad frequency range, in order to choose the ideal baffle width.

Of the few general rules that are always applicable it is useful to keep in mind that very narrow baffles tend to result in a higher baffle step and usually wide midrange/lower midrange dispersion due to perfect diffraction at smaller wavelengths. When combined with higher directivity tweeter (like in many KEF models), I find this to be very disadvantageous in terms of overall directivity and colorated reverb tonality.

A very broad (or something resembling an infinite) baffle, on the other hand, is shifting the baffle step to a lower band which is a good thing for reverb tonality. If not combined with clever strategies of achieving higher directivity (such as horn, coaxial or waveguide), it comes at the price, though, of accumulating lots of energy to the sides, as an infinite baffle can also be viewed as a +-95deg waveguide, resulting in strong side wall reflections. Not ideal for home listening, having reflective walls nearby.

I would assume that neither KEF nor Grimm have chosen a good overall compromise when it comes to directivity and listening window. If you employ other measures to control directivity, such as dipoles, horns, line sources or cardioids, baffle width is less important.

My understanding is that the imaging superiority of a narrow baffle is because said false azimuth cue is not as big of an angular error as would be the case with a wider baffle because the arrival time of the edge reflection is not as late in time as with a wider baffle.

Would say your observation is absolutely correct, but I am not sure the delay is the main root cause, as it is usually very small. My understanding is that edge diffraction leads to narrow-banded cancellation issues which occur only in a very limited angle, so this degrades localization precision both by inducing interaural differences and tonal differences, making the additional mirrored sources at the edges localizable, hence blurring the overall imaging.

As a matter of consequence, except from concept strictly avoiding edge diffraction by controlling dispersion, such as large horns, I would assume the best solution from localization perspective is: no baffle. A theory made popular by companies like B&W and Vandersteen.

It comes at the price of lower directivity index and increased risk of early reflections (particularly from side walls), which is a known issue to degrade localization.

 

[Digital_Thor]

As a matter of consequence, except from concept strictly avoiding edge diffraction by controlling dispersion, such as large horns, I would assume the best solution from localization perspective is: no baffle. A theory made popular by companies like B&W and Vandersteen.

I agree on the no or minimum baffle, which I think KEF usually aim for too - IMO, I would choose any modern KEF over any modern B&W speaker - any day! For now I like the "compromise" of KEF coaxial, and rarely hear something that sounds much better - mostly just different somehow.
Besides, I think the OP should get out there and try and listen to both versions, and see if he even likes the different versions. Then slowly you have a trend and you can more easily hone in on your actual preference.
We could try and tell him what is theoretically better or worse - but he has to like it - long term.

Out of couriosity - what is a really good speaker in your experience?

 

[Arindal]

I agree on the no or minimum baffle, which I think KEF usually aim for too

Minimum or no baffle concept for a tweeter cannot be achieved with a conventional coaxial driver at the same time, as the midrange cone and surround act as a waveguide/baffle for the tweeter´s soundwaves.

I would choose any modern KEF over any modern B&W speaker - any day! For now I like the "compromise" of KEF coaxial, and rarely hear something that sounds much better

Don´t mean to say that the B&W concept is flawless, it has severe shortcomings, particularly with chosen crossover points and bigger midrange cone diameter. But is is a baffle-less concept.

The KEF ´compromise´ is indeed achieving pretty smooth behavior in the transitional band and in general in the typical listening window (no lobing whatsoever), but it leads to pretty uneven directivity to the sides and the rear half-sphere. Take a look at the side-wall and rear calculations in the spin data, and you know what I mean:

Recommend to take a closer look at the green (rear) and green (side) window calculations above 2K. With side walls or rear wall closeby, one could expect a pretty colorated reverb field in the room.

To me, any cheap but well-engineered 3-way concept with a broad baffle and small midrange driver (like a Wharfedale Linton) sounds more balanced in terms of reverb timbre.

what is a really good speaker in your experience?

Really depends on the application and environment, but if we are talking about the integration of a compact coaxial driver into a 3-way concept, I found Genelec 8341A, Elac Uni BR-62 and some TAD models to deliver a much more balanced reverb.