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Thread: DSP active crossover

  1. #1
    Join Date: Mar 2017

    Location: London N2

    Posts: 898
    I'm Edward.

    Default DSP active crossover

    So I'm mulling over doing a new project. Specifically a 3-way active DSP crossover. Was wondering if someone has done something similar or can provide any hints/warnings etc.

    I already have most of the main items, the balance are relatively cheap to get.

    Idea is to use Magnum K2s I have lurking here (given to me by Tom of this parish) driven by a Sony 7.1 AV amp (another item that is lurking). DSP will be via JRiver's parametric equaliser.

    So this 3-way digital crossover signal path will be something like this:

    Digital source (flac etc) > Windows 10 machine > JRiver > Parametric EQ > USB > multi-channel DAC (e.g. Xonar) using 6 of the available channels > Sony AV amp (6 ch. in > 6 ch. out) > Magnum K2.

    In terms of the Magnum's I would simply take the existing passive crossovers offline and connect up each driver (bass, mid and HF) to the corresponding speaker output of the AV amp. I would protect the tweeters and probably also the midrange drivers with capacitors (just in case I muck up the DSP/DAC mappings). What I'm not sure of yet is how I place such caps (serial or parallel?) and what capacity caps I should use?

    In terms of the parametric EQ I would create suitable low and high pass filters and map those to the relevant DAC ports. What I'm not clear about is where I would set the low and high pass points. I guess I could start with whatever cross over points are already used in the passive setup? Or perhaps it does not matter as long as I'm in the general area and get the roll off slopes correct?

    Later on, assuming this all works, I could do some room correction I guess. Using something like REW and implementing a filter within JRiver?

    This is just a 'fun' project. Not sure what the eventual SQ will be like, but judging from other forums could be quite nice. Certainly the Magnum K2 12 inch bass drivers can move vast amounts of air.
    Source: Tidal/Roon
    DAC: Metrum HEX NOS

    Amp: Sugden Masterclass 2018 spec, Radford Revival STA25,
    Speakers: Tannoy Eaton


  2. #2
    Join Date: Apr 2012

    Location: London

    Posts: 368
    I'm james.

    Default

    I have done similar. Best crossing points to start are the ones in the passive crossover. Then adjust as suits. It is worth working out the passive crossover schematic and modelling it to see what eq was built into it and slopes used.
    You only really need a cap on the hf unit as it is easily wrecked by bass energy, the mid and bass units will just sound rubbish if the crossovers are wrong. So saying, it would be easy to run a frequency sweep through the active crossover and check it on a 'scope before connecting up. I think a common value such as 2.2uF would be fine, depending on crossover point and impedances and placed in series with the tweeter to block bass energy.

    Sent from my BLA-L09 using Tapatalk

  3. #3
    Join Date: Mar 2017

    Location: London N2

    Posts: 898
    I'm Edward.

    Default

    Quote Originally Posted by Jazid View Post
    I have done similar. Best crossing points to start are the ones in the passive crossover. Then adjust as suits. It is worth working out the passive crossover schematic and modelling it to see what eq was built into it and slopes used.
    You only really need a cap on the hf unit as it is easily wrecked by bass energy, the mid and bass units will just sound rubbish if the crossovers are wrong. So saying, it would be easy to run a frequency sweep through the active crossover and check it on a 'scope before connecting up. I think a common value such as 2.2uF would be fine, depending on crossover point and impedances and placed in series with the tweeter to block bass energy.

    Sent from my BLA-L09 using Tapatalk

    Cheers James. Really helpful getting confirmation I'm heading in the right direction. But I hasten to add I'm not very experienced in electronic engineering. I would not know what to do with a schematic. Having said that I could not find any schematic for the Magnum K2s. The only info I found was that the crossover points appear to be at 800hz and 5khz. But perhaps 950hz and 5khz.

    At what point do I need to place the 2.2uF cap? on the +ve or -ve?

    Good idea to run a freq. sweep through the active crossover. Trouble is I don't have an oscilloscope and never used one. Would a pc based 'scope such as the pico be ok? Perhaps you have a cheaper suggestion please? Not really looking to spend lots of money on this project really.

    As mentioned I already have the main items (3 way speaker, AV amp giving me 6 channels and JRiver software). Remaining items to get is a xonar 7.1 dac (about £60) and speaker binding posts, cable etc. Down the road I may get a calibrated mic for room measurement and creation of a suitable filter. One idea is to also use some coral 10 inch bass drivers I have instead of the 12 inch drivers already in the Magnums. Just for fun.

    Come to think of it I could possibly use Roon software for the parametric EQ and room correction instead of JRiver.

    Interested to know what you did on your project.
    Source: Tidal/Roon
    DAC: Metrum HEX NOS

    Amp: Sugden Masterclass 2018 spec, Radford Revival STA25,
    Speakers: Tannoy Eaton


  4. #4
    Join Date: Mar 2016

    Location: Barnet, london UK

    Posts: 935
    I'm Adam.

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    Quote Originally Posted by Edwardlon View Post
    Come to think of it I could possibly use Roon software for the parametric EQ and room correction instead of JRiver.

    Interested to know what you did on your project.
    interesting!
    "lack of passion is fatal"

    Vinyl: Garrard 401, Russ Collinson 'shindo' plinth / Tenuto gun metal mat / SME-3012 j7 rewired / audio-technica ATP-12T - phonomac modified / Ortofon Vintage SPU GTE /Shure M3D / Ortofon Royal N / Cartridge Man Music Master with isolator / Miyajima Zero B 0.7mil mono / Vintage GE VRII mono / Amps: Radford STA25 mk3 / David Coe AD Audio 'Satchmo' pre & phono / Hashimoto HM-7 SUT / Digital: SW1X Audio Design DAC 1 signature / Roon / Tidal Speakers: Tannoy 12" MGs' in RFC custom 'Rutland' Cabinets with RFC custom crossovers / Cables: Duelund DCA16GA tinned copper / Kimber 12TC / SW1X Audio Design USB-SPdif / Duelund DCA20GA interconnects / SW1X Audio SPDIF Aero 6 / Mains Power Conditioner / Box Furniture sapele rack

  5. #5
    Join Date: Apr 2012

    Location: London

    Posts: 368
    I'm james.

    Default

    Quote Originally Posted by Edwardlon View Post
    Cheers James. Really helpful getting confirmation I'm heading in the right direction. But I hasten to add I'm not very experienced in electronic engineering. I would not know what to do with a schematic. Having said that I could not find any schematic for the Magnum K2s. The only info I found was that the crossover points appear to be at 800hz and 5khz. But perhaps 950hz and 5khz.

    At what point do I need to place the 2.2uF cap? on the +ve or -ve?

    Good idea to run a freq. sweep through the active crossover. Trouble is I don't have an oscilloscope and never used one. Would a pc based 'scope such as the pico be ok? Perhaps you have a cheaper suggestion please? Not really looking to spend lots of money on this project really.

    As mentioned I already have the main items (3 way speaker, AV amp giving me 6 channels and JRiver software). Remaining items to get is a xonar 7.1 dac (about £60) and speaker binding posts, cable etc. Down the road I may get a calibrated mic for room measurement and creation of a suitable filter. One idea is to also use some coral 10 inch bass drivers I have instead of the 12 inch drivers already in the Magnums. Just for fun.

    Come to think of it I could possibly use Roon software for the parametric EQ and room correction instead of JRiver.

    Interested to know what you did on your project.
    I'm no engineer either sadly, just a happy amateur
    I was working on a pair of Tannoys.I love everything about them except the sound in my room dammit. So I attempted a fix. It sort of worked but I came to the conclusion that it was the cone/ horn interface that I didnt like.
    Whatever, I have a DEQX 3.0 that is the only item that hasn't changed in the last 5 or 6 years, in and (occasionally) out of the system. I am becoming wedded to it. Extraordinary what it can do. Get stuck in, you won't regret it I think!

    Sent from my GT-I9195 using Tapatalk

  6. #6
    Join Date: Mar 2017

    Location: London N2

    Posts: 898
    I'm Edward.

    Default

    Yes I've heard great things about the deqx stuff. Lovely stuff, bit expensive for my tastes. I did try out their software at some point but that was a fail as I did not have a good enough mic.

    I will need a mic at some point in this project to do room correction. Was thinking of using REW for that.

    Once I start this project I may have a question or two. I'll put them up in this thread.

    Were the Tannoys dual concentrics that you tried to drive via the DEQX?



    Via Tapatalk
    Source: Tidal/Roon
    DAC: Metrum HEX NOS

    Amp: Sugden Masterclass 2018 spec, Radford Revival STA25,
    Speakers: Tannoy Eaton


  7. #7
    Join Date: Apr 2015

    Location: Central Virginia

    Posts: 1,193
    I'm Russell.

    Default

    I did some reading on this subject some time ago. From what I remember, they used a pro digital crossover, and 3 amps. Like a DBX digital crossover, you feed the output of your preamp to it, and it distributes it into 3 parts to drive 3 amps, one for each part of your speaker. Then they used a software package with calibration microphones to adjust it. Something like this maybe?
    https://www.roomeqwizard.com/
    And the DBX crossover allowed adjustment of the crossover points and individual volumes to each amp, and you used the calibration microphone and the software to adjust it to get the best looking response in your room.

    I have done (helped a guy do) this for a live performance hall, (bar) but never for a home audio system, but I assume itís about the same? Set the mic at your listening position and calibrate the system for the flattest curve. And the digital DBX even has time delays to help reduce reflections, if you are running surround sound.

    A friend has a huge Onkyo surround sound receiver that comes with a calibration mic, and a built in system to create a flat response at the listening position, it came with a book to figure it out, but he never read it, and instead just used the ďauto-adjustĒ, and let it do its thing. This doesnít adjust the levels of each speaker, but just works an internal EQ.

    This is all probably a mile from what you are trying to accomplish? But just showing there is more than one way to skin a cat.

    Russell

  8. #8
    Join Date: Mar 2017

    Location: London N2

    Posts: 898
    I'm Edward.

    Default

    Thanks Russell

    Certainly not a mile away, it is precisely what I'm trying to achieve. The big difference in my plan is it is just for fun but primarily I will be doing it on the cheap. Essentially I will take a USB feed from a computer and go into a cheap multi-channel DAC (stuff they use everyday in gaming rigs) and from there to a multi-channel amp. From there I will take 3 stereo pairs and drive the 3-way drivers in Goodmans Magnum K2s. Within the computer there will be a digital cross-over such that the feed to the DAC will have 3 stereo pairs. That is the first step.

    As a second step, assuming the first step is fine, I will do room correction via REW (as per your link) and a mic. As I understand it REW will create a FIR filter which I can inject into my software.

    Looking at my costs (I consider the computer, software, multi-channel amp, cabling and speakers free as I already have them) the biggest cost will actually be the banana plugs, binding posts and DAC. That should be about £100 - so a cheap(ish) experiment. Not sure what I will do with it all once I have done it as my main system are more than adequate.
    Source: Tidal/Roon
    DAC: Metrum HEX NOS

    Amp: Sugden Masterclass 2018 spec, Radford Revival STA25,
    Speakers: Tannoy Eaton


  9. #9
    Join Date: Apr 2012

    Location: London

    Posts: 368
    I'm james.

    Default

    You can do it on the cheap just fine. When I bought the DEQX you couldn't do it cheap. Now I would buy a mini DSP and a UMic. They aren't as feature rich but they're a damn sight cheaper, and within their limits more flexible as well.
    Capacitor best across the positive terminal of the speaker for lower PD between wiring and ground. Not essential and I suspect there's no difference in SQ.

    Sent from my BLA-L09 using Tapatalk

  10. #10
    Join Date: Apr 2015

    Location: Central Virginia

    Posts: 1,193
    I'm Russell.

    Default

    Quote Originally Posted by Edwardlon View Post
    Thanks Russell

    Certainly not a mile away, it is precisely what I'm trying to achieve. The big difference in my plan is it is just for fun but primarily I will be doing it on the cheap. Essentially I will take a USB feed from a computer and go into a cheap multi-channel DAC (stuff they use everyday in gaming rigs) and from there to a multi-channel amp. From there I will take 3 stereo pairs and drive the 3-way drivers in Goodmans Magnum K2s. Within the computer there will be a digital cross-over such that the feed to the DAC will have 3 stereo pairs. That is the first step.

    As a second step, assuming the first step is fine, I will do room correction via REW (as per your link) and a mic. As I understand it REW will create a FIR filter which I can inject into my software.

    Looking at my costs (I consider the computer, software, multi-channel amp, cabling and speakers free as I already have them) the biggest cost will actually be the banana plugs, binding posts and DAC. That should be about £100 - so a cheap(ish) experiment. Not sure what I will do with it all once I have done it as my main system are more than adequate.
    So, if youíve got the multi channel amp, and a computer, thatís a major head start!

    You could get by cheaper with my scenario by buying a Behringer digital crossover, used. And a calibration mic, you may even find one used? But Iíve seen new ones for $35. And as I was searching for the software, like the one I referred to, I see a lot of versions that were free for download. How much they will do? I guess youíd have to try a few. So, a used Behringer digital crossover may not be more than $100? These digital DSPís have 24bit processing and run exceedingly quiet. The DBX brand is more feature rich, but one of the articles I read about used the Behringer with great success.

    But you sound like youíve got a handle on it! I was not aware that there were DACís that you could control with a computer to create crossover points? It sounds very interesting!

    Of course, you will have to keep us updated as you go, with photos and listening impressions. To educate the masses!

    Russ

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