48db/oct crossovers causing listening fatigue? - diyAudio
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Old 15th January 2013, 07:53 PM   #1
Bazukaz is offline Bazukaz  Lithuania
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Default 48db/oct crossovers causing listening fatigue?

Hi,

For a while I have been trying miniDSP with various configuration of active filters on a couple of my DIY systems.
What I have noticed is subjective listening fatigue when 48db/oct filters are used vs lower order ones like 24db/oct.
The sound is subjectively "cleaner" with these high order filters but after a while it becomes very uncomfortable to listen. The feeling is like the sound is "strange" to me. I have tried to use them both as a subwoofer filter and also between bass/mid/treble in various configurations in a 3-way with the same result. Frequency response analysis did not reveal any problems.

I have some possible explanations for this:
a) Very abrupt change in polar pattern causing sharp changes in power response.
b) Significant phase shift so harmonics of instruments are shifted too much
c) Psycho acoustics
d) Something specific to my systems or electronics

Am I lone there or someone else has similar experience?

Regards,
Lukas.
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Old 15th January 2013, 08:03 PM   #2
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Steeper slope improves IMD performance and breakup rejection, but level matching and fine tuned timing is needed to get best performance. Deep symmetrical notch with polarity reversal of driver leads/miniDSP is great indicator of alignment.
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Old 15th January 2013, 08:12 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

You should use the lowest electrical order you can get away with for
good real acoustic slopes, the latter depends on the drivers, anymore
and your just making it worse, for phase and transient wise.

rgds, sreten.
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Old 15th January 2013, 10:36 PM   #4
a.wayne is offline a.wayne  United States
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Agree, 6db is too little, 12db is too much ......
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Old 15th January 2013, 10:48 PM   #5
ra7 is offline ra7  United States
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Have you checked off-axis response? Ideally, you'd want both drivers to have wide dispersion near the crossover for steep slopes to work. Without it, there may be abrupt change in off-axis response, causing poor timbre and ultimately inaccurate sound.

There is nothing wrong with steep slopes... depends on implementation and design.
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Old 15th January 2013, 11:05 PM   #6
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Try overlaping them a bit. Say if you cross over at 200hz
Cross your woofer at 210! Try it you'll like it
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Old 16th January 2013, 12:42 AM   #7
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Same experience for me. I don't pretend to know why, but the lower order filter sounds more 'relaxed'.

When I have a free afternoon I need to try switching from LR24 to B18.

Bill

Quote:
Originally Posted by Bazukaz View Post
Hi,

For a while I have been trying miniDSP with various configuration of active filters on a couple of my DIY systems.
What I have noticed is subjective listening fatigue when 48db/oct filters are used vs lower order ones like 24db/oct.
The sound is subjectively "cleaner" with these high order filters but after a while it becomes very uncomfortable to listen. The feeling is like the sound is "strange" to me. I have tried to use them both as a subwoofer filter and also between bass/mid/treble in various configurations in a 3-way with the same result. Frequency response analysis did not reveal any problems.
...
Am I lone there or someone else has similar experience?

Regards,
Lukas.
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Old 16th January 2013, 01:44 AM   #8
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Quote:
Originally Posted by Bazukaz View Post
Hi,
Frequency response analysis did not reveal any problems.
It wouldn't but phase and impulse response probably would as higher order filters screw both of them up and this may be what you're hearing.

Measure at the output of the board for each filter type from 1st to 8th order and you'll see what I mean.

I always used higher order filters but currently running a 4 way + subs with 1st and 2nd order filters.

Never sounded better.
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Old 16th January 2013, 02:15 AM   #9
GoatGuy is offline GoatGuy  United States
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Sigh...

Its like people forget what they're trying to accomplish, it seems to me. So many people just "run after the numbers".

The ONLY purpose of a crossover, yes ... the SINGLE incontrovertible purpose, is to "steer" power at the various drivers in frequency ranges that corresponds to their reasonably efficient and accurate sound-reproduction range. Period. Truly, the whole story in a nutshell.

So, let's look at drivers. Its not like they have 48 dB/octave rolloffs outside their sweet-spot range! Most tend to ROLL off first at 2-3 dB/octave for an octave, then 6 for another one or one and a half, then another 10 for another, and so on... a complex roll-off that is very hard to model with either single-stage single-pole filters, or double pole, or even multipole in Chebychev, Bessel, Butterworth and all the other configurations.

But again - what are these drivers doing, outside their sweet (relatively flat) range? Well, they're making sound, but not doing so especially efficiently. And way outside, they're doing so especially inefficiently. Moreover, usually when they're in their "inefficient" sidebands, they're also likely to be distorting the sound, and causing all sort of spurious sonic effects that are ... generally non-musically interesting. [he puts up kevlar shield to deflect tomatoes lobbed by electric-guitar rockers!]

Anyway, the idea was/is: "well then, why not put together some filters, either passive, or active that confine the frequency spectrum applied to each speaker, more or less in its sweet (relatively linear) frequency band!"

Passive crossovers, active ones, makes no difference - this is the goal. So... the next (and by far hardest) thing to do is to figure out then what the response of the drivers are, in the enclosure that has been engineered for them, in a "normal" listening situation that is statistically likely to represent the average consumer use of the speakers ... and when that's figured out, to tailor a set of filters that splits up the signal power into bands that allow the smoothest transition between the drivers' responses ... across the whole band.

As I said, this edges toward the mythically-hard science and art. Purists will rail endlessly on their soapboxes about phase distortion, transient delays, responsiveness, energy storage and so on ... but in truth, that which seems most apparently important over the years of designing and listening to these things is the gentleness of the transition between frequency ranges.

In other words, I am entirely unsurprised that a lower dB/octave roll-off would sound better. This is because the transition between the drivers overlaps more, and allows their specific 'speed' and 'attenuation' to mix into a more interesting (complex phase, yet relatively flat power) far field.

And its not like with modern amplifiers, that one can't afford to "waste" a bit of power overdriving the skirts of each driver's cross-over frequency band, in order to achieve "sweet" and "musical" and all the rest of the words of cherished nature we use to describe perfect systems.

So... using near-50 years of experience: Choose a the lowest order filters that accomplish the cross-over, and moreover, if using multipole, choose non-ringing filters, such as subcritical Butterworth or even Bessel filters. Space the poles out in a chain, to further unsharpen the cutover frequencies. The result WILL be musically pleasing.

This advice can be followed whether one is bi/tri amping, or whether one is simply making passive cross-overs with low Q within the speakers themselves.

GoatGuy
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Old 16th January 2013, 02:45 AM   #10
pos is offline pos  Europe
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Bazukaz,

You can try to isolate the amplitude slope issue (your "a" explanation) from the phase shift issue ("b") by using rePhase to linearize the phase of the crossover (or maybe just linearizing some of it, like 360°, to end up with a 24dB/oct-like phase shift)

But of course before going any further in your investigations (and whereas you choose to linearize the phase or not) you should make sure that your crossover is properly setup: symmetrical acoustical slopes, and phase coherency between drivers around the crossover point. The phase coherency is the most important (and most overlooked) part IMHO, and if messed up it can have an impact on the slopes you will prefer: shallower slopes might typically become more "acceptable" in such situations, as it will tend to "blur" any phase issue...
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