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Old 20th July 2004, 06:17 AM   #1
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Default Baffle step correction circuit - how to design?

My question is: how to design the baffle step correction circuit from the graphs in the Baffle Diffraction Simulator? I have used Passive Crossover Designer (http://www.pvconsultants.com/audio/crossover/pcdc.htm) to simulate the results of the BSC I designed but I don't know if my strategy of choosing the correction curve is correct. I have used 100 Hz as minimum attenuation point (because that is the the more attenuated frequency by the baffle diffraction that I can see in the graph!) and 1000 Hz as maximum attenuation, at that frequency is where the highest peak is found. I believe that's not 100% correct, the values suggested by "The Edge" differ by large amounts.
And one thing I don't understand in BDS: why isn't the response below 100 Hz shown? Doesn't it count in designing the correction circuit?
And the last question: what program do you recommend using for baffle diffraction simulation: the Excel Baffle Diffraction Simulator or "The Edge" The results given by these two programs are pretty different, especially for high frequencies.
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Old 20th July 2004, 06:36 AM   #2
Mark25 is offline Mark25  United Kingdom
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here's a basic one by Rod Elliot of ESP, change the values to suit your needs, it's line level though:


http://sound.westhost.com/bafflestep.htm
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Old 20th July 2004, 08:33 AM   #3
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Thank you for that link, but that page explains active equalization, which I don't preffer, because as long as the baffle step is a phenomenon that occurs at the speaker, the BSC circuit should also be part of the speaker, not something belonging to the amp (anyway, active correction can be achieved with a multiband equalizer, isn't it)?
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Old 20th July 2004, 09:11 AM   #4
Mark25 is offline Mark25  United Kingdom
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Quote:
Originally posted by mr_push_pull
Thank you for that link, but that page explains active equalization, which I don't preffer, because as long as the baffle step is a phenomenon that occurs at the speaker, the BSC circuit should also be part of the speaker, not something belonging to the amp
so you would passivly EQ a subwoofer then?

Quote:
Originally posted by mr_push_pull
(anyway, active correction can be achieved with a multiband equalizer, isn't it)?
if....
you can stand the SQ loss
one of the equalizer f's coincides with your BS freq'


then yes
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Old 20th July 2004, 10:25 AM   #5
Jennice is offline Jennice  Denmark
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Now I'm curious!

If Baffle Step correction is such a hassle for DIY'ers to implement at the speaker end (after the power amp), then how does every manufacturer do it?
After all, a speaker manufacturer can't send a line-level filter with the box and hope that everybody has a seperate pre- and opwer-amp!?

Jennice
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Old 20th July 2004, 11:15 AM   #6
Svante is offline Svante  Sweden
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Default Re: Baffle step correction circuit - how to design?

Quote:
Originally posted by mr_push_pull
My question is: how to design the baffle step correction circuit from the graphs in the Baffle Diffraction Simulator? I have used Passive Crossover Designer (http://www.pvconsultants.com/audio/crossover/pcdc.htm) to simulate the results of the BSC I designed but I don't know if my strategy of choosing the correction curve is correct. I have used 100 Hz as minimum attenuation point (because that is the the more attenuated frequency by the baffle diffraction that I can see in the graph!) and 1000 Hz as maximum attenuation, at that frequency is where the highest peak is found. I believe that's not 100% correct, the values suggested by "The Edge" differ by large amounts.
And one thing I don't understand in BDS: why isn't the response below 100 Hz shown? Doesn't it count in designing the correction circuit?
And the last question: what program do you recommend using for baffle diffraction simulation: the Excel Baffle Diffraction Simulator or "The Edge" The results given by these two programs are pretty different, especially for high frequencies.
Edge calculates the compensation circuit from the actual baffle step response as in the simulation. It assumes that there is a full 6 dB step, the load is resistive (ie R1 really is a resistor). In Edge, the compensation is always a smooth transition consisting of a single pole and zero. The frequencies are found from the +2 dB frequency of the simulated response.

There are a few reasons why this compensation is not an ultimate or exact solution. First, the load in the passive filter case is not a resistance, but the loudspeaker and other filter components. Second, most baffle geometries does not produce a smooth baffle step, so there will be a residual ripple even after compensation.

Also, another reason that Edge may produce different results than other software is that there is a rule of thumb that circulates on the web, which is based on the early work of Olson. He demonstrated the baffle step for a sphere, consecutively others have assumed that this is applicable to a baffle of the same width. In my view, this is an assumption that leads to errors in the compensation, and this would lead to a difference between Edge and others (that use this assumption). I don't think BDS falls in this cathegory, however.

HTH
/Svante
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Old 20th July 2004, 11:36 AM   #7
rabbitz is offline rabbitz  Australia
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I find it easier to use a 0.5 woofer for BSC at the back of the box as suggested by planet10. Works a treat but a bit more expensive as you need additional woofers. You do gain SPL and less components in the crossover.

Do a search and there's some info in the Wiki.
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Old 20th July 2004, 11:38 AM   #8
Mark25 is offline Mark25  United Kingdom
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Quote:
Originally posted by Jennice
Now I'm curious!

If Baffle Step correction is such a hassle for DIY'ers to implement at the speaker end (after the power amp), then how does every manufacturer do it?
After all, a speaker manufacturer can't send a line-level filter with the box and hope that everybody has a seperate pre- and opwer-amp!?

Jennice
the answer in a lot of case's is that they don't! There are many ways to achieve BSC though;

a .5 way bass driver, with low pass at the BS
a seperate bass driver on the rear of the box, a la sonus faber electa amator.......just a few......
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Old 20th July 2004, 11:39 AM   #9
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Default Re: Re: Baffle step correction circuit - how to design?

Quote:
Originally posted by Svante There are a few reasons why this compensation is not an ultimate or exact solution. First, the load in the passive filter case is not a resistance, but the loudspeaker and other filter components.[/B]
But if one uses impedance equalization?

So, how do I design the BSC? I mean, how do I derive the values of the inductor and the resistor (or the capacitor and the resistor, depending on what type of correction circuit I use), by looking at the diffraction "response" (if I can call it like that)?
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Old 20th July 2004, 12:27 PM   #10
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The first thing you do is ignore trying to accurately predict the baffle step; you must actually measure your woofer response. There are too many variables to arrive at a correct solution otherwise.

Once you have plotted the actual woofer response you'll be able to see the frequency where the response begins to rise. At that frequency you calculate from your usual source (http://www.lalena.com/audio/calculator/xover/ if you don't have another favorite) the value for a first order low pass filter; that will compensate for the rising response.

Having done that you then add additional stages at your crossover frequency to achieve the desired final acoustic and electrical slopes. To do so involves repeated measuring of response and substitution of component values until the desired result is attained.

This, by the way, is the process used by most professional crossover designers, including the best there is in the business, Joe D'Appolito.
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