Modeling Baffle Step - diyAudio
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Old 22nd March 2014, 05:18 PM   #1
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Default Modeling Baffle Step

Designing to account for baffle step remains a very elusive subject for me, particularly with regard to unconventional enclosure shapes (extremely narrow enclosures, spherical shapes, teardrop shapes, etc...). As far as I can see, we take response measurements of the design once it's been built, and try to compensate from there, post-build. However, is it not possible to accurately or somewhat accurately predict and model what the low frequency drop will be according to enclosure shape, dimensions, and mounting of the driver? I'm completely missing locating such information. Perhaps others can direct.
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Old 22nd March 2014, 06:02 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

There are tools that will predict baffle step and ripple. Narrow
certainly but I don't think too good with curves and teardrops.

http://audio.claub.net/Simple%20Loud...ign%20ver2.pdf
FRD Consortium tools guide
Designing Crossovers with Software Only

rgds, sreten.

Zaph|Audio - ZA-SR71

Baffle diffraction sim, bassmid and centered tweeter vs offset

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Old 22nd March 2014, 06:11 PM   #3
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Thank you sreten. Until software designers take it to the next level and cease to assume only box shapes are relevant, I'm thinking there must certainly be calculations around that can be made which account for how a typical low frequency loss for a given baffle size might transfer to a perfect sphere. Front mounting or recessed might also result in more dramatic changes on the sphere, I'm guessing.
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Old 22nd March 2014, 06:29 PM   #4
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I started downloading every free computer program that I could find that deals with enclosures, crossovers, baffle step calculators, T/S parameters, passive radiator calculators, etc... and didn't come close to opening half of them, let alone understand those that I did look. Keep it simple. Build a basic crossover for whatever enclosure you want/like. Then fine tune.
May not be scientific, but, you choose the shape, not a computer. Your ears can hear something good that your eyes also like. There's just no magic formula. Enjoy both senses.
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Old 22nd March 2014, 06:43 PM   #5
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Baffle step involves wavelengths, which vary with frequency, proximity to room boundaries, and the size of the front panel of the speakers. Only the latter is perdictable. Speakers placed very close to walls will have a very different need for correction than speakers placed a few feet away from walls. If you know where they will be placed in a room, you can take a guess at what correction would be optimal. It's rarely an exact science. Personally, I rely on my four section Baxandall tone circuit to help me fine tune it in by ear.
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Old 22nd March 2014, 06:55 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

The shape of a perfect sphere is well known, but it is
a small driver in a big and ugly sphere. A big driver
in a small truncated sphere is very different.

Consult the references on diffraction, and estimate.

rgds, sreten.
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Old 22nd March 2014, 07:48 PM   #7
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Originally Posted by lucadelcarlo View Post
However, is it not possible to accurately or somewhat accurately predict and model what the low frequency drop will be according to enclosure shape, dimensions, and mounting of the driver? I'm completely missing locating such information. Perhaps others can direct.
You require a program that solves the 3D acoustic wave equation for external 3D geometries. There are plenty of commercial ones and one or two freely available ones that usually require a bit of knowledge to use.
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Old 23rd March 2014, 01:37 PM   #8
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sreten, yes, if you're referring to those early diffraction studies by Harry F. Olson, then I recall the diagrams of large planetary-like orbs with relatively small drivers in comparison. Indeed I am only interested in the more 'truncated' shapes, i.e. the size of the driver relative to the enclosure size being much greater, similar to, for example, the spherical section of B&W 800 speakers. I believe here, they're using the resulting baffle step of this form to integrate the mid unit physically rather than purely through the crossover, or to assist in that somewhat.

I use minidsp, infinitely more flexible and easier than tweaking hardwired x-over units. Ideally four settings would be offered, somewhat similar to Genelic monitors: wall, corner, desk, free. Such a feature for speakers with digital crossovers might as well become a standard.

andy19191, what are these programs you refer to, even though user-friendly they may not be?

The baffle step and baffle step compensation is really not something which I find presented in an intuitive easy-to-grasp fashion anywhere really. In the designs that I'm attempting, it's particularly relevant, but for most rectangular designs, following roughly a gold ratio-esque construction, it seems to be much less of an issue, particularly with flush mounting.

A spherical design with a large driver relative to enclosure is perhaps not at all an ideal arrangement in this department. Am I seeing this correctly - more low frequency response goes omni at a higher frequency, and thus low frequency response appears to drop off dramatically in the listening position. We then try to compensate for this by choking down some of the mids and higher frequencies to restore a flatter, more balanced response in the listening position. This involves losing a great deal of total efficiency, and drawing more power.
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Old 23rd March 2014, 02:56 PM   #9
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Originally Posted by lucadelcarlo View Post
andy19191, what are these programs you refer to, even though user-friendly they may not be?
The computer programs engineers have used to simulate sound fields since the 1960s. Commercial ones tend to work smoothly. Freely available ones are mainly derived from research codes and usually require knowledge about grid generation, boundary conditions, file formats and the like. Here is an example but there are quite a few others that may be better or worse depending on your knowledge.
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Old 23rd March 2014, 03:47 PM   #10
Juhazi is offline Juhazi  Finland
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Basta is a relatively cheap simulation program. Edge is a simple freeware baffle diffraction (eg. baffle step) Simulator. Homepage here Tolvan Data
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Last edited by Juhazi; 23rd March 2014 at 03:49 PM.
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