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Multi-Way Conventional loudspeakers with crossovers

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Old 1st December 2013, 03:39 PM   #1
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Default Soundeasy measurement question

I'm following John K's SE guide and I have question regarding microphone location when measuring a multi-way (3-way, 4 driver) speaker.

It states to measure each driver on axis at a constant distance to the baffle. I would think it would be better to leave the microphone on the listening axis. It would already include the extra path length and response to the other drivers, I would think that being especially important for x-over development. I see it is accounted for in the optimization section but was curious why it is recommended this way. It just seems an actual measurement would be more accurate than a simulated one.

Just trying to understand the process, Thanks! Scott
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Old 1st December 2013, 04:51 PM   #2
Ron E is offline Ron E  United States
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Mainly because if you measure on axis at 1 meter, the final vector sum of all the drivers will only be correct at one meter. If you could measure on axis at the listening distance and still could get a long enough window, that would be ideal.
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Old 1st December 2013, 05:12 PM   #3
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Depends you what you want. If you measure it as I suggest then develop the filters for each driver it will not sum correctly in the crossover cad screen. However, if you then move to the system screen and place the drivers correctly on the baffle the summed response will be correct for the chosen mic position and the crossover can be optimized based on that position. Also, this will allow you to see the correct polar response.

If you measure all drivers at a single point and retain the differential path length info in the phase data you can develop the crossover and see the correct summed response, relative to the measurement point, in the CAD screen. But then the System screens are useless unless you make adjustment to the path lengths by adjusting the offsets (to remove the differential path length info in the measured phase data). But then, although the summed response will appear correct in the system plots, the drivers will not be positioned correctly and the polar plots and results for other simulated mic positions (other than measurement point) will not be correct.


Simply stated, if you include the differential path lengths in the measured phase data you simulations are only good for in the CAD screen and you can not effectively use the system screen and tools. If you don't want to explore simulated results for different mic positions and polar data, do as you indicate and work in the CAD screen only.
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Old 1st December 2013, 05:23 PM   #4
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Thanks Ron for the quick reply. I see the reasoning...I was somewhat assuming that 1 meter might be better than on axis but in either case I will still have to make adjustments for the final listening position. I guess it's better to capture the on axis and adjust later then be in kind of no mans land at 1 meter. I guess the part that bothers me the most is that during initial x-over development it goes on the basis that all drivers are coincident, but then you specify driver positioning on the baffle and optimize.
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Old 1st December 2013, 05:35 PM   #5
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Quote:
Originally Posted by john k... View Post
Depends you what you want. If you measure it as I suggest then develop the filters for each driver it will not sum correctly in the crossover cad screen. However, if you then move to the system screen and place the drivers correctly on the baffle the summed response will be correct for the chosen mic position and the crossover can be optimized based on that position. Also, this will allow you to see the correct polar response.

If you measure all drivers at a single point and retain the differential path length info in the phase data you can develop the crossover and see the correct summed response, relative to the measurement point, in the CAD screen. But then the System screens are useless unless you make adjustment to the path lengths by adjusting the offsets (to remove the differential path length info in the measured phase data). But then, although the summed response will appear correct in the system plots, the drivers will not be positioned correctly and the polar plots and results for other simulated mic positions (other than measurement point) will not be correct.


Simply stated, if you include the differential path lengths in the measured phase data you simulations are only good for in the CAD screen and you can not effectively use the system screen and tools. If you don't want to explore simulated results for different mic positions and polar data, do as you indicate and work in the CAD screen only.
John...thank you too for such a quick reply! I was coming to the conclusion that the system tools would no longer function properly...but that's where I was getting a little confused so I thought I would ask. Your answer is what I was hoping to hear, I'm going to proceed as you originally suggest...thx again.
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Old 1st December 2013, 10:36 PM   #6
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I am not sure what stage in development you are measuring for. I measure nearfield each driver to get a baseline I start my sims with. I then make a prototype baffle and move to the garage and measure at one meter on axis of the tweeter without the crossover and see what difference this makes. Eventually I will move outside and measure at 2 meters with the prototype crossover. When I think I am close, I have the luxury of measuring where I will use them as I only build speakers for me. Selfish, but easy.
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Old 1st December 2013, 11:37 PM   #7
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Originally Posted by tvrgeek View Post
I am not sure what stage in development you are measuring for. I measure nearfield each driver to get a baseline I start my sims with. I then make a prototype baffle and move to the garage and measure at one meter on axis of the tweeter without the crossover and see what difference this makes. Eventually I will move outside and measure at 2 meters with the prototype crossover. When I think I am close, I have the luxury of measuring where I will use them as I only build speakers for me. Selfish, but easy.
It's always good to hear how other people test...your end result is only as good as what you start with Thanks for sharing your method. I have test cabinets built that closely resemble the final shape. My house has a pretty open floor plan with 10ft and 13ft ceilings so I'm getting pretty good results so far.
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