1st Order XO with -6dB XO frequency. Has anyone tried this? - Page 2 - diyAudio
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Old 27th May 2004, 06:18 AM   #11
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He wants to use it at a quite low crossover frequency, so lobing is of little concern (depending on driver -size and -placement).
Also a transient perfect (or phase accurate) crossover would have a 90 degrees phase-shift in the crossover area. But as said before.
What are the drivers you want to use it for ?

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Old 27th May 2004, 07:21 AM   #12
navin is offline navin  India
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ouch! I am too hoping to use 1st order filters.

my drivers are as et undecided but the top contenders are:

Fostex FX208N in ML-TL or bass reflex mated to a FF85K (or 2) in sealed or open baffle
OR
Jordan JX125 in a small TL mated to a JX 53 (or 2) open baffle

My limitations are:
cabinet must be small (bass cabinet 32"H x 10" W x 8" D), F3 of 40-45Hz, SPL of 95db at 2 m at 50Hz, and most important the speakers must be musical.

amplification will be:
SS 30W class A (see Indian Group amp Project on this forum) for bass and EL84 SE (if 1 fullrange is used and if the Fostex combo is chosen) or EL84 PP (if 2 fullranges are used forstex or jordan).

the reason of looking at 1st order is that the XO could then be PLLXO and there would be NO XO components between the drivers and amplifiers. Would such an application be suitable for 1st order?

(BTW the surround and center speakers would use Fostex F125K or Jordan JX92 with no XO at all)
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Old 27th May 2004, 07:23 AM   #13
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Quote:
Originally posted by phase_accurate
I don't see any reason for doing so !
Not applicable to this ap, but Rune uses this technique to deal with baffle step in his Phase Linear TL

dave
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Old 27th May 2004, 07:31 AM   #14
navin is offline navin  India
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BTW my proposed mid-hf amp
http://ptsoundlab.free.fr/sectubes/s...ssa20wel84.htm
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Old 27th May 2004, 07:34 AM   #15
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rune is where i got my ideas from! apart from your highness!
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Old 27th May 2004, 12:20 PM   #16
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Someone asked about drivers, they are all Seas units

Tweeter 25TNF, Mid MP14RC, Woofer P25REXDD.

The enclosure has a volume of 100 L but this is adjustable.

I didnt realise that there would be a drop in the FR if the -3db points for each XO are offset by 2 octaves - 150Hz & 600Hz. I thought the FR would sum flat.
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Old 27th May 2004, 12:23 PM   #17
SY is offline SY  United States
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Quote:
there would be NO XO components between the drivers and amplifiers. Would such an application be suitable for 1st order?
Even more suitable for multiamping.
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Old 27th May 2004, 12:32 PM   #18
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Quote:
I thought the FR would sum flat.
Only the x-over by itself will sum flat and only if the -3dB points are the same. Keep in mind that you have 90 degrees phase-shift and not 360 degrees as with LR crossovers and therefore it won't sum flat with -6dB.

For the mid you can get a 3rd order highpass function consisting of your 1st order RC highpass and the drivers natural in-box rolloff (2nd order). But this would still not be a transient-perfect crossover.
I am not familiar with this midrange so I don't know what it can take and if it is suitable for shallow rolloff at all. But there is for sure someone on this forum who knows.

If you want to have a transient perfect crossover then there are some possibilities but they won't be minimalistic in terms of component count.

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Charles
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Old 27th May 2004, 05:14 PM   #19
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Would the total responce of drivers & XO sum flat if I reverse the polarity of one of the drivers?? If this wont work for an offset of 2 octaves would it work for a greater offset. Would this counteract all the reasons why 1st order filter are liked so much if I did???

I'm not opposed to using higher order LR filters but I herd the LR 24dB/oct can make the system sound lifless. I realise this was a subjective opinion but it did come from more than one person.

I'm planning on making the active XO easily changeable from 1st order butterworth to LR 12 & 24db/oct to allow some experimentation anyway. But.. I can see that a standard 1st order XO might not work, but I have this current mind set of a longing to use one in one form or another.
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Old 27th May 2004, 08:17 PM   #20
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The greater the complexity of a passive crossover, the more resistance it will exhibit in the pass band, there's no way around that. Because of this resistance, you are robbing some of the amplifier power from the drivers, which gets dissipated in the crossover, and restricts the dynamic range.

I doubt a correctly designed active XO of higher order exhibits the same problem. It might be that you get problems with on axis and off axis response with different order crossovers though.
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