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TOPIC: Re: Building a 2 way crossover with minisharc

Building a 2 way crossover with minisharc 7 years 1 month ago #9182

  • orangeart
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Hi I have just bought a mini sharc to use with my latest 2-way active speaker project and just want to try and understand the workflow of tools I need to get there. Firstly I was going to get RAW inbox measurements of the drivers in either REW, HOLM or ARTA. Never used REW before, but as it seems to be compatible with the UMIK-1 I've also bought it seems sensible to use that. It's after that I'm stuck really. I'd like to use the FIR function of the mini sharc to implement the crossovers, hopefully linearising the phase (at least at the cross over points) while I am at it. I wonder if there is anyone out there who has done similar who can give me a heads up or point me to a tutorial?

These speakers are currently passive and as I designed the crossovers for them (similar to zaph audio ZRT revelators)i know the parameters and could at least get a cross over set up, using the 'crossover' tab and 'PEQ' tab but would much rather leverage the FIR ability of the minisharc.

Maybe I'm barking up the wrong tree, maybe I need to set the crossover up and then use FIR the linearise phase and EQ using some software.

It seems using a steep crossover is the best way to avoid some of the overlap problems the passive version uses but with the FIR giving the ability to also correct the phase related impulse problems.


Regards

Stefan
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Re: Building a 2 way crossover with minisharc 7 years 1 month ago #9201

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Anyone?

Pretty please.
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Building a 2 way crossover with minisharc 7 years 1 month ago #9209

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Hi Stefan

Here is one way to do it (among many others)

For each driver:
- measure your driver using REW or HOLM (with you mic correction file installed)
- choose the appropriate gating and/or smoothing
- export the resulting frequency response as a txt file (3 columns: frequency; amplitude, phase)
- import the measurement into rePhase (0.9.6 or up) and dial the measurement (polarity as well as, phase and amplitude offsets) to ease the correction (avoid positive gains in the resulting correction impulse, which you can check using the bypass button)
- dial your corrections and filters (minimum-phase EQ + phase linearization + linear phase filters). Try to target complementary slopes. Symmetrical acoustical LR filters are the most common target. Try to avoid too steep slopes as they might cause problems off axis (preringing being one of them).
- generate your correction/filtering impulse (2048taps, 48kHz, ".bin" format, blackman or nuttal window), and check the ripples level outside the passband (if you see ripples to high in level, even with the nuttal window, that means that you do not have enough taps for the slopes and frequency you are targetting, and that means you will probably have to resort to IIR filters in the miniSHARC, which you will be able to simply linearize using rePhase)
- take note of the offset delay implied by the impulse (you can discard fractional samples)
- load the impulse in the miniSHARC plugin (set to 2048taps, which is the current maximum, and which can be maintained for the 4 channels you need for a stereo 2-way like you wants to achieve)
- set the delays so that all the offsets are compensated (you can of course deduce the larger delay) so the impulse are time aligned
- add the delay implied by the geometrical distance differences of the diaphragms (not voice coils, but radiating surfaces) from your listening positions (not necessarily parallel to the baffle...) so the drivers are time aligned

Of course you can (and should) to several measurements (and/or smoothings/gating) for each driver, and load them in turn into rephase (simply drag and drop each txt file on the rephase window, in turn) to see the effect of your correction at different distances and position (you typically do not want to correct problems that only occur at a specific position, such as diffraction or modes, as this will cause problems at all other positions).

good luck :)
https//wavetracing.com | rephase.org
Last Edit: 7 years 1 month ago by pos.
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Building a 2 way crossover with minisharc 7 years 1 month ago #9210

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Hi Pos,

Thanks for that. I must admit that rePhase looks way beyond me, and with no supporting doc I don't think I've got much chance. I can do measurements no problem (ish) But when I had a quick fiddle with rePhase I couldn't even see how to add more than one driver measurement!!

Stefan
Last Edit: 7 years 1 month ago by orangeart.
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Building a 2 way crossover with minisharc 7 years 1 month ago #9211

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Yes it is clearly lacking some user manual... :dry:
Writing that sort of things take time tho :pinch:

If you open a thread in the rePhase section I could help you step by step with your project, and that could help other people too.
I couldn't even see how to add more than one driver measurement!!
That is because you can't (yet) : you can only use (and save in .rephase file toghether with correction settings) one measurement at a time, so you have to load them one by one (using drag and drop it should not be too painful, except if the time/amplitude/polarity parameters are different than the previous measurement, but this can be taken care of in the measurement software, before exporting the measurement...) and see the effect your current correction has on each of them.
In a future version you should be able to load several measurements (and save them in the .rephase file), and possibly average them...
https//wavetracing.com | rephase.org
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Building a 2 way crossover with minisharc 7 years 1 month ago #9214

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Sounds like a plan Pos, I've only just realised that this is your software, Thanks for getting involved.

I've had a bit of a read around and with reference to your post above, understand it all a little better now :laugh:

I'm a little way off yet, I need to get another pair of amps and build this lot into a box with my buffaloes and I'll run a basic XO with the kit until I get up to speed.

I'll happily get screen Shots along the way when the time comes and do a proper step by step tutorial in PDF that you can keep a link to in the re-phase section.

Stefan
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Building a 2 way crossover with minisharc 7 years 1 month ago #9215

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orangeart wrote:
I'll happily get screen Shots along the way when the time comes and do a proper step by step tutorial in PDF that you can keep a link to in the re-phase section.
That would be great! :cheer:

I also have the project to interface a miniSHARC to my Buffalo (8 channels), but have not committed to start it just yet.
I am waiting for miniDSP to release the I2S adapters first :P
And then I will also have to figure out a good way to built 8 I/V stages (I will probably just use the buffalo in voltage mode as a start...).
My electronic skills are lacking to say the least, so this is going to be a loooong journey :)
https//wavetracing.com | rephase.org
Last Edit: 7 years 1 month ago by pos.
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Building a 2 way crossover with minisharc 7 years 1 month ago #9216

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I've not got the buffalo 3, I'm going to be using 2 buffalo 2's. Main reason being I had one already and couldn't bear the thought of losing dynamic range by dropping the number of DAC channels available per audio channel. This obviously works out expensive, but as I'm 2 way, it's not to bad. Building at the moment,

2 buffalo II
2 legato I/V stages
1 mini sharc
1 vol-FP
1 AN-FP
1 wave/io async USB
9 salas shunt regs with custom voltage references
1 big box

oh and then

2 hypex ucd 400 HG with HXR
2 hypex ucd 180 HG with HXR

feeding

2 scanspeak illuminator D3004/662001 tweeters
2 scanspeak revelator 18W/8531G00 mid-woofers

Sounds amazing in passive already but nice to tweak it that little bit further :woohoo:
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Building a 2 way crossover with minisharc 7 years 1 month ago #9252

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@ orangeart,

Souns like an amazing system indeed! :-)
Looking forward to hearing from it.

@ pos,
We did build 2 adaptor to the Buffalo3, we just didn't get a chance to send it to manufacturing yet and most important to the TwistedPear team for a quick review.
Hoping we can push it on our todo list when things become a bit more sane... :-) Thanks for the reminder though!
DevTeam
miniDSP, building a DSP community one board at a time.
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Building a 2 way crossover with minisharc 6 years 8 months ago #10712

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devteam wrote:
@ pos,
We did build 2 adaptor to the Buffalo3, we just didn't get a chance to send it to manufacturing yet and most important to the TwistedPear team for a quick review.
Hoping we can push it on our todo list when things become a bit more sane... :-) Thanks for the reminder though!
DevTeam

Any update about the adaptors?

Best regards
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Building a 2 way crossover with minisharc 6 years 7 months ago #11182

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Well I've not really got that much further with this, I sort of stumbled when I realised I couldn't connect the i2s of my waveio to the minisharc. I've got over myself and am just going to go with the spdif until the dev team sort out the ASRC and slave mode (SOON PLEASE DEVTEAM IT'S BEEN A LONG TIME NOW ;)

I've made a little progress so thought I'd share here.

I've got all the salas regs built and powering all of the modules which was a massive feat in itself. I can input a test signal at the wave io and get the vu meters moving on the set up screen of the minisharc so have made some progress. Next I need to get it connected to the buffaloes whcih will be via i2s and test that I get a signal out of the end of that chain. I can move onto boxing up then and reinstall in my system in pass through mode so I can just get back to using one of the DACS for listening again. From there I can set about doing the measurements and documenting my steps in REW and Rephase as I promised POS I would 5 months ago!



@POS if you are reading this, once I have got the measurements and done the crossover as you described above, what would be the best way to then use further room measurements to do a bit of further EQ in rephase given that I can't apply a further level of FIR? Would I maybe better using IIR filters for the drivers and then linearising the phase and eq for room using your tools?

Lastly @DEVTEAM I have digi-AN as well, when the digi-an is linked to the minisharck 5v must be used not the 12v that the minisharc can handle.
Would the minisharc be happier with a 12v PSU ? if so I have enough regs and windings spare that I could feed them both separately.
Realise we are talking small optimizations here but if it's better it's better!

Stefan
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Building a 2 way crossover with minisharc 6 years 7 months ago #11186

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Wow, impressive setup ;)

All those salas shunts will keep your house warm during winter :)

I doubt that there will be a difference between 12V and 5V supply of miniSHARC (there is a 3.3V reg onboard anyway) but I know your situation - it keeps running through your brain once you know there could be an improvement ;)

regards, Daniel
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Building a 2 way crossover with minisharc 6 years 7 months ago #11188

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It'll only be impressive if I manage to make it all work!! There has been lots of giving in going on with mini-sharcs so I hope I can get it all working :)

The Salas's don't actually produce to much heat, I spent a lot of time getting the shunts and references correct and using windings that had as little voltage overhead as possible. When I first built them some of them were operating at about 140 deg c !! now I'm down to around 80 ish.

OK, so the operating voltage is fine for the mini-sharc but I guess I'll benefit from some separation for the boards anyway. I've got a spare winding and got a placid shunt kicking around somewhere......

BTW kudos for linking up with @devteam with your dacboard, I'll give one of them a go sometime, ahs the 9023 got the same async input as the 9018 so that we can go i2s in without fear of sample rate and master/slave?

Stefan
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Building a 2 way crossover with minisharc 6 years 7 months ago #11534

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Another little update.

I've finally managed to get a signal into and back out of the minisharc so over the weekend my intention is to get it boxed up and neatly cabled then I'll just use it as a DAC for the time being, maybe take some in room measurements and fanny around a bit.

The next step really is to get the amp re-boxed so I have all 4 channels available and the re-wire the speaker without the passive crossover. When I hook up the active system initially it'll just be with very basic crossover parameters set in the plugin and as I find time I'll work my way toward an FIR implementation.

I'll post more pictures as I go.

Stefan
Last Edit: 6 years 7 months ago by orangeart.
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Building a 2 way crossover with minisharc 6 years 7 months ago #11560

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Hi Stefan,

Nice build!
My BIII is still in its box :P
orangeart wrote:
@POS if you are reading this, once I have got the measurements and done the crossover as you described above, what would be the best way to then use further room measurements to do a bit of further EQ in rephase given that I can't apply a further level of FIR? Would I maybe better using IIR filters for the drivers and then linearising the phase and eq for room using your tools?

If you only need minimal-phase EQ (which *should* be the case), then you could use the IIR eq on the input section.
Another possibility is to measure you loudspeaker, load hte measurement in a fresh rephase instance, do your corrections, and then replicate them in each of your crossover rephase file. You can also use the IIR section to do these EQs (you need to use proportional-Q minimum-phase EQs, and limit your gain setting to +/-12dB).
https//wavetracing.com | rephase.org
Last Edit: 6 years 7 months ago by pos.
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