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Speaker crossover before versus after bi-amplification

milezone

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#1
With the multitude of high quality multi-channel dacs available today -- eg the Motu 8A with 8 outputs -- I'm curious if there's an advantage to establishing LF/MF+HF crossover frequencies pre-amplification versus post. An example scenario in a two way system would be sending low frequency content 20hz-300hz to an amp powering a subwoofer, and applying a high pass filter at ~300hz and sending the remainder of the spectrum to an amplifier driving the mid+hf driver. Would this implementation result in an easier load for the amplifiers, then if crossing were done post amplification?
 

Julf

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#2
"Easier load" only so far as that the amp driving mid+hf would typically have to produce much less power. There are additional advantages - damping factor is much better if you don't have to go through the passive filter components between amp and speaker, and digital filters can be much steeper than passive analog ones.
 

milezone

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#3
Okay thanks. When I mention easier load, I'm thinking in terms of the impedance response curve of a driver. I'm not certain it makes a difference where the crossover occurs in the chain, though perhaps it does.
 

Julf

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#4
Okay thanks. When I mention easier load, I'm thinking in terms of the impedance response curve of a driver. I'm not certain it makes a difference where the crossover occurs in the chain, though perhaps it does.
Well, yes, sort of, of course. Typically the lowest impedance point is at low frequencies, so the mid+high amp doesn't see it.
 

Juhazi

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#6
Xo between pre and power amps is definitely better in many ways. The problem is that xo must be specifically designed for the loudspeaker used.
DSP-crossover is the modern way, much more versatile than analog circuits. The designer of an active speaker can set eq and delay freely to achieve practically perfect acoustic matching response and phase curves, and amplifiers can have different optimized gain. Also xo and delay between subwoofer and main speakers can be handled better, if both are controlled by same dsp. Several different presets can be saved and switched easily.

For DIYers dsp-xo like minidsp, Hypex, Behringer, DEQX etc. have opened a new world where one don't need to understand and master so much physics and electronics plus soldering skills.

https://www.minidsp.com/applications/digital-crossovers/digital-crossover-basics
 

milezone

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#7
Thank you for the product references. Ideally I'd like to establish the crossover points pre dac preferably in a software interface of some sort. That would be the cleanest solution audiowise and otherwise. Does such a thing exist? I'm using a Motu 8A right now which in my understanding features two ESS chips for balanced operation. These dacs can provide up to 8 balanced output channels and in my experience using the Motu as an interface with a DAW, those channels can be totally independent audio streams. Does anyone know of a crossover // dsp software that complements these hardware advances?
 
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#10
You can use Equalizer APO in Windows. While the built-in filters are IIR, it also supports convolution. REW, rePhase and DRC-FIR are the popular options to prepare the impulses.

For Linux, find Charlie Laub's threads at diyAudio.
 

g29

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#11
JRMC also has some basic digital XO functionality, but not as diverse as the aforementioned Audiolense and Acourate.

Danville Signal Processing is coming out with a new modular product called dspNexus which combines digital XO/mixing functionality in a multi-channel AKM AK4499 DAC with phantom power mic input, analog and digital inputs. DSP Concepts Audio Weaver software is used to design/implement the digital XOs.
 
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#12
I took a 'studied' approach towards bi-amping when trying to tame some less than perfect woofer response.
What I found was that bi-amping by itself (using original passive xovers) made just a slight improvement (say, 5%); barely noticeable - frankly, given all the hype about it, I was expecting more.
Adding adjustable (DSP) electronic crossovers gained another, 10%? improvement, and implementing roomEQ (REW) made the most notable improvement, perhaps another 20%?
But, it wasn't until I found the proper woofer upgrade that I was able to achieve an acceptable 'end-state'.
The point is that all of the above will help - even quite a bit - but cannot make up for under performing drivers (or, presumably, really
'bad' rooms).
 

milezone

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#13

g29

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#14
I took a 'studied' approach towards bi-amping when trying to tame some less than perfect woofer response.
What I found was that bi-amping by itself (using original passive xovers) made just a slight improvement (say, 5%); barely noticeable - frankly, given all the hype about it, I was expecting more.
The gains of biamping are achieved by removing the passive XO components and padding from the signal chain as well as limiting the frequency range/workload each amp sees and amplifies (i.e. each amp only does a fraction of the work, 4 hands/20 fingers covering 88 keys on a keyboard versus 2 hands/10 fingers). By using the same passive XO, you are missing these benifits so little is to be gained unless each existing amp can not handle the whole load by itself.

Rod Elliott - Biamping part 1
Rod Elliott - Biamping part 2
 

Juhazi

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#15
Thanks. The speaker system I intend to build is a Linkwitz sub // electrostatic hybrid. The woofer I'm considering is the Seas L26RO4Y in an open baffle enclosure https://www.madisoundspeakerstore.c...-kits/open-baffle-subwoofer-flat-pack-lxsub2/ which seem perfect for the application. The panels are a pair of http://www.eraudio.com.au/Mini_Panels/mini_panels.html preferably suspended above the woofers in some way. With the right adjustments I think it should be a pretty good setup.
Sounds familiar! You might find this thread interesting... https://www.diyaudio.com/forums/multi-way/231353-aino-gradient-collaborative-speaker-project.html Feel free to PM me or eemail juha.sirkka(around)fimnet.fi
 

Julf

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#16
What I found was that bi-amping by itself (using original passive xovers) made just a slight improvement (say, 5%); barely noticeable - frankly, given all the hype about it, I was expecting more.
Adding adjustable (DSP) electronic crossovers gained another, 10%? improvement, and implementing roomEQ (REW) made the most notable improvement, perhaps another 20%?
5% and 10% of what? How did you determine that?
 
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#17
:) Figured I'd get busted for saying that here. Mostly subjective, and meant as % gain towards the objective, namely +/-2db, 20hz-600hz. The final objective was met, and actually measured with REW. The first two step, of just bi-amping, made no measurable difference.
The Rod Elliot articles were a tremendous help when I did mine.
 
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