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Old 11th June 2003, 01:49 AM   #1
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Default sub crossover fq as function of res freq of mid driver?

Help! I am trying to design a good subwoofer system with a knowledgable friend for my project studio - producing mostly orchestral music for film and tv. I am currently using a pair of high-end full range drivers as near field monitors. I prefer them greatly to the crossed over reference monitors that I have used, except I need to include low frequencies to get the full 20 to 20k well covered. My friend insists that I need to locate the crossover from mids to sub at two octaves above the free air resonance of the mid drivers - 45hz - or 180 hz. The problem is that in this range supposedly stereo information exists and it might therefore be better to use a pair of subs, one for each monitor, using more space (at a premium), more money, and less accurate and/or extended low freq. Can anyone tell me if there is good reason for this - what's the real skinny? Any help appreciated.
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Old 11th June 2003, 08:20 AM   #2
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Default Re: sub crossover fq as function of res freq of mid driver?

Quote:
Originally posted by kcreeger
My friend insists that I need to locate the crossover from mids to sub at two octaves above the free air resonance of the mid drivers - 45hz - or 180 hz. The problem is that in this range supposedly stereo information exists and it might therefore be better to use a pair of subs, one for each monitor, using more space (at a premium), more money, and less accurate and/or extended low freq.
I don't know which mid drivers you're using so can't comment with any certainty. However, I have used my new Seventh Veil Nonsuch 4 full-range speakers with a passive line-level crossover at 100Hz and without any crossover at all. I prefer the latter for clarity. The resonant frequency of the drive units that I'm using is about 65Hz.

I agree that crossing over at 180Hz could compromise your stereo imagery and my guess is that you'd be safe driving the mids down to 100Hz, provided you use a steep enough slope on the filter.

Why not post the details of the drive units and then hope that someone with experience of these units will give a definitive answer?

Steve
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Old 11th June 2003, 02:06 PM   #3
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Thanks - the drivers are Jordan JX92s - specs attached.
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Old 11th June 2003, 09:37 PM   #4
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Well, I can't offer a foolproof solution, but I can offer some opinions.

1) If I cross the subwoofer on my HT system at 100 Hz, 2nd order LP, I find it to be VERY localizable, especially on music. This is not an audiophile caliber system (Outlaw 1050, Mission M70, Adire AVA250 & Tempest ), and what distortion there is makes the imaging poor. Be forewarned that depending on the rest of your chain, you may see the same result.

2) Those Jordan's are very well thought of drivers.

So, I would say (1) go stereo if at all possible (2) if not, crossover absolutely as low as possible with the Jordans, below 100 Hz.
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Old 11th June 2003, 11:24 PM   #5
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Quote:
1) If I cross the subwoofer on my HT system at 100 Hz, 2nd order LP, I find it to be VERY localizable, especially on music. This is not an audiophile caliber system (Outlaw 1050, Mission M70, Adire AVA250 & Tempest ), and what distortion there is makes the imaging poor. Be forewarned that depending on the rest of your chain, you may see the same result.

2) Those Jordan's are very well thought of drivers.

So, I would say (1) go stereo if at all possible (2) if not, crossover absolutely as low as possible with the Jordans, below 100 Hz.
I can only second that. With a single subwoofer IMO You should not cross any higher than 80Hz and nothing less steep than 4th order LR/BT for the sub lowpass in order to avoid sub localization completly. The recommendations I see sometimes to cross a single sub as high as 150Hz is a mistake IMO - no matter how steep the filter is.

In a sub/sat setup to prevent the "satellites" (Jordan) from high excursions due to low frequencies, usually itīs good practise to make an overall 4th order highpass while putting a second-order electrical high-pass in series with them but in this case of the Jordan`s I believe it`s difficult because of it`s comparatively high Q which would yield to a very low crossover point - probably too low to protect this rather small driver from high low-frequency displacement sufficiently.

OTOH crossing 2 octaves above fbox of Your Jordan`s with a single sub bring the problems You mentioned.

I would cross higher and go for a stereo sub therefore .

I donīt see any point why a pair of subwoofers should be less accurate or give less extended low freq. - quite the opposite.
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