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Old 3rd May 2012, 07:54 AM   #1
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Default Designing for (very) low crossover points

As I was planning my 3-way it dawned on me that the lower crossover point at 200-300hz will be very difficult to design due to the inaccuracy of indoor measurements at these frequencies. Gating canít be used and room interaction will be huge. I donít think it will be possible to get a good crossover design here without going outdoors, but thats not an option for me at the moment.

Is any other way around this? Would it be more accurate to use manufacturers graphs up to 500hz or so, splice the gated measurement on to it and model the baffle step diffraction effects in software?
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Old 3rd May 2012, 11:19 AM   #2
AllenB is offline AllenB  Australia
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The measurements will include baffle effects, but the manufacturers plot won't. Unless it's a very large baffle you'll have some of it in your measurements.
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Old 3rd May 2012, 11:36 AM   #3
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Yes but my measurements will also include room effects which will dominate the response in this region and vary greatly with small changes in mic position.

At lease the manufacturers plot will be anechoic infinite baffle which can then be modelled for an enclosure using a diffraction simulator.
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Old 3rd May 2012, 01:02 PM   #4
AllenB is offline AllenB  Australia
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It will, but maybe I wasn't clear. Your gated measurements will show a clear shot of the speaker and the baffle above your cut off frequency. If you simulate the baffle at the same angle as each measurement and combine that with the manufacturers plot, you may be able to identify that slope on the measurement and splice accordingly.
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Old 3rd May 2012, 01:26 PM   #5
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I think we are saying the same thing essentially? Splice the gated measurement above the cut-off with the manufacturers plot below the cut-off then simulate the baffle step response to the combined plot. Sounds feasible to me.
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Old 3rd May 2012, 01:57 PM   #6
AllenB is offline AllenB  Australia
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Same thing switched You wouldn't want to combine a baffle simulation with anything you have measured that is in it's box. The baffle information is already there and you'd be doubling up. You'll need to add the baffle sim to the manufacturers plot or else it won't line up when you splice them.
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Old 6th May 2012, 09:56 AM   #7
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Ah ofcourse, thats what I meant, same same but different
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Old 6th May 2012, 10:08 AM   #8
tvrgeek is offline tvrgeek  United States
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Gated bursts across about 1/3 octave will let you do a pretty good job indoors at 1M. My experience has not been that good with sim for bsc.
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Old 6th May 2012, 11:34 AM   #9
sreten is online now sreten  United Kingdom
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Hi,

The lower x/o point of a 3 way can be designed entirely by simulation,
See : FRD tools example 2

rgds, sreten.
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Old 6th May 2012, 12:30 PM   #10
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Quote:
Originally Posted by sreten View Post
Hi,

The lower x/o point of a 3 way can be designed entirely by simulation,
See : FRD tools example 2

rgds, sreten.
Do those tools simulate the effects of the difference in floor gain experienced by a woofer and midrange mounted at different heights in a 3 way ? If not you won't get the right result through simulation alone, especially on a large floor-standing 3 way.

The same problem applies to a true anechoic measurement of a 3 way floor-stander - the difference in floor effect for the two drivers is not taken into account by an anechoic measurement, thus the in-room response around the lower crossover frequency will be significantly wrong when the floor is present.

Some tweaking of the crossover would be required for optimal results if simulation or anechoic measurement are not taking the floor into account.
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