durwood

Not quite.

I can think of a few times this idea could be violated. Drivers have natural roll of points acoustically. If you run your crossover point near this roll off, then the slope changes. You have to factor in acoustic + electrical. Running drivers off axis can also change this natural roll off behavior, acoustic loading, etc etc...

You will rarely ever see a speaker designer just select 24dB L/R passive or active crossover and claim it to be perfect every time. Hell, even Linkwitz himself uses different types of crossovers when needed.

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netchris

but that sounds like an issue with EQing out a dip in frequency response around a crossover point rather than a phase issue.. right?

durwood

Example:What causes a woofer to roll of in higher frequencies?

Clue: Inductance

When you have reactive components they form a filter, IIR filters are nothing more than analog models done in the digital world.

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netchris

i'm still learning here.. but is it right to say that a fixed amount of inductance is present in an active circuit, and in the case of a speaker that inductance is constantly affecting the voice coil of a speaker, but that it does not audibly manifest itself until the "stroke" (if that's the right term) of the voice coil/magnet assembly is sufficiently short to cause audibly perceptible distortion? (ie further shortening of the "stroke" and thus reduced frequency response -- as in rolloff?)

still, that doesn't sound like anything that would affect the phase... unless the magnetic field produced by the electricity's flow through the circuit was enough to entirely overpower the voice coil at higher frequencies in which case there would be a lot of breakup, which i can see could affect phase.. so i guess the ideal would be to cross the speakers before that breakup would occur, and one would remain in-phase? (given a fir or 360* [or multiple therof] l/r [or any iir?] filter)

i'm still getting a grasp on this -- so am i right about anything? lol.. just trying to get an idea of what's going on.

[edit]

maybe oscillation would be a more appropriate term than stroke.

durwood

A voicecoil is nothing more than an inductor.

Capacitors and inductors introduce phase shifts with AC signals.

When I speak of roll-off I'm talking about the response graphs of the individual drivers. Woofer top, tweeter bottom graph.





I know you really want to understand all of this, but to be honest with you, this doesn't need to be complicated. There is no such thing as a "perfect" crossover. Butterworth, Linkwitz riley, bessel, epiliptical....all have their uses.

or in the digital realm Infinite Impluse Response, Finite Impluse Response.

Each one has their tradeoffs and people select different ones based on design goals.

The whole phase smearing (I would not call it distortion) at the crossover point is hard to detect, especially in a car.

BTW, EQ is nothing more than tight filter bands. Everytime you use a typical band of EQ you are introducing more phase shift at each band as you adjust. So now ask yourself, are you going to concern yourself with sticking only to L/R filters or 24dB/oct? FIR filters are linear phase but can introduce "ringing" if overdone. Not to mention it's very CPU intensive especially in lower frequencies. Everything is a tradeoff.

The environment of a car is going to wreck more havok on everything than the processing algorithms, unless you really don't know what you are doing during tuning. Use whatever you need to get the job done.

If you really want indepth stuff start with the first link then move on to the second one. Then read the last one and see it the whole "phase distortion" (I prefer phase smearing) is a moot point.

http://www.bcae1.com/xoorder.htm
http://sound.westhost.com/ptd.htm
http://www.audioholics.com/education...ibility-part-2

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Cris

Any new developments in this field?
I'm new at this game, I have the Audiotrak card, but I don't seem to understand how the plugins work, or wich ones are the best suitable...

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durwood

I've been adding to the list as people post new stuff they find. The list of useful plugins has grown substantially since what was available over a year ago. BTW, anyone can add to that list if you find something. Please place it in it's appropriate a category.

http://www.mp3car.com/wiki/index.php...g_via_Software

netchris found some good ones recently. For an alternative to Frequency Allocator, you can use multiple instances of Rubber Filter, or the LS Filter plugin is a 4way filter plugin that allows you to select Butterworth, Linkwitz riley, or Bessel filters up to 24db/octave. It also has phase flipping. There is also a 4way FIR filter (linear phase)-it requires the use of the convolver VST as well in order to work. That is for advanced users.

Voxengo has updated their delay plugin, I prefered the simpler older one since the new one is a bit trickier to setup, however all they have available for download is the new one now.

Lots of cool plugins for emerging technologies such as ambiophonics and ambisonics have been included as well.

Recently I came across this site
http://acousmodules.free.fr/acousmodules_en.htm

There are some crazy things in there to do "surround sound" I think using ambisonics and possibly VBAP, but since the guy is French and his English is just ok, there is not much info on HOW to use them. He has some that will do up to 10.2, 17.2 and 22.2 surround sound setups, but it's all graphical based.

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durwood

Interesting plugin pack. I found the Analyser plugin useful for some experiments I have been working on. Not free but they have a demo though.

http://www.pspaudioware.com/plugins/stereopack.html

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