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3 way DSP XO

March Audio

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#1
Its really annoying, I have had no time to post here lately :)

Wont be detailing this yet but this mass of spaghetti :eek: is a 3 way dsp crossover prototype Im playing with. Hoping to get the speakers finished this year. Ill try and post more later.

20161111_181248.jpg
 

Sal1950

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#2
I'll be very interested in following your journey when time allows.
Best of luck.
TIA
 

March Audio

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#3
Well progress is painfully slow, but just made my first PCB. A very simple one for the PSU trafos. A bit tidier than veroboard! :)

20161126_181155.jpg
 

Keith_W

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#4
Very interesting project you have there. Can you tell us more, please? What software are you going to be using for DSP? What processor? Are you going to build your own DAC's? How do you interface this to your audio system?
 

March Audio

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#5
Its been a very long time since I posted about this and things have changed a fair bit from the original intention. So, where am I? :)

The design is still a DSP xo, however I have moved away from internal DSP and DAC within the speaker. After trying Acourate correction software and being highly impressed, I discovered that there was no simple DSP platform available that was going to be powerful enough to perform the necessary number of TAPS for the FIR filtering.

So, on to plan B:

Cheap used 4 core i7 laptop from fleabay to run ROON core and Acourate convolver
Motu 8A 8 channel ADC/DAC feeding balanced to Hypex NC252MP +NC100HF 3 channel amps in each speaker

One reason for the Motu is that I still need to integrate my home theatre into the mix. As such I can feed that into the Motu ADC, process it with low latency IIR filters (think lipsync issues with FIR filters) in Acourate convolver and back out to the speakers.

Up next speaker cabinet design :)
 
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March Audio

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#6
Used Vituixcad to design the cabinet size (closed). Ill talk about drivers later. Found a great and easy to use 3D cad package called Sketchup. Used this to create the design. The output file could be imported straight into a CNC machine which a small local company used to cut out the panels from 1" MDF.

upload_2017-6-23_15-21-56.png


Ended up like this

20170605_183803.jpg


Just had the painting finished. Piano black.

IMG_0395.jpg


IMG_0396.jpg



next a bit about the drivers
 

March Audio

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#9
Thanks! :)

My descriptions are somewhat brief at the moment, but I will flesh it out over time. It will include all the measurements of course.
 

Sal1950

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#10
I give you 5 power cords up for that beautiful piece of cabinet design and build!
 

March Audio

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#11
Drivers.

Should mention I chose a closed box as I prefer the tight better transient response. I was always intending to use this design with a sub and despite its relatively large size it is only really linear down to about 50Hz (in room).

I looked at a lot of drivers and ended up a little disappointed with some of the measurements I saw on the Scandinavian usual suspects. Ended up with the following:

SB Acoustics Satori MW19P-8 7.5" Woofer
Morel EM1308 2" Midrange
Mundorf AMT23CM-1.1-C Air Motion Transformer Tweeter

XO frequencies 50Hz, 600Hz, 4.5kHz - I wanted the mid to cover the most sensitive part of the hearing range which required a small driver to retain good dispersion up to a relatively high point. However the beauty of the DSP XO is that I can play as much as I want with XO points before I settle on the final design. Initial testing and prototype (see my Avatar) was done with a passive XO at about 550Hz and 5 kHz.

Have to say there is something very beguiling about the sound of the AMT tweeter. It is very linear up to 30kHz with very good dispersion compared to some of the domes I looked at. Essentially it sounds very sweet and extended. It has low distortion and excellent transient response.
upload_2017-6-26_20-12-17.png


Some pics.

IMG_0413.JPG


IMG_0414.JPG


IMG_0406.JPG


IMG_0407.JPG
 

March Audio

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#12
So I have now got to the point where I am waiting on the amplifiers to arrive. First speaker is on test with the development passive crossover. Of course I think it sounds excellent, but I would say that :)

IMG_0411.JPG


Oh yes, missed the pics of the padding and stuffing (Mid and tweeter are separate boxes)

IMG_0398.JPG
 

March Audio

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#15
My 9 channel Nord literally arrived this morning. It comprises of the new Hypex Nc250 modules with nc100hf for the tweeters

https://www.hypex.nl/product/nc250mp-oem/74

https://www.hypex.nl/product/nc100hf-oem/78

Its against Nords oem agreement to sell the modules seperately, as you would expect, so I had to buy the complete amp. I havent fired it up yet, but the build looks great.

In theory I will take the modules out and build them into the speakers. I will re use the case for something else.

First I will do all the crossover set up and speaker linearisation.

Also just recieved an Earthworks M23 measurement mic. Im going to be busy over the next week or two :)
 
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LarsS

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#18
Drivers.

Should mention I chose a closed box as I prefer the tight better transient response. I was always intending to use this design with a sub and despite its relatively large size it is only really linear down to about 50Hz (in room).

I looked at a lot of drivers and ended up a little disappointed with some of the measurements I saw on the Scandinavian usual suspects. Ended up with the following:

SB Acoustics Satori MW19P-8 7.5" Woofer
Morel EM1308 2" Midrange
Mundorf AMT23CM-1.1-C Air Motion Transformer Tweeter

XO frequencies 50Hz, 600Hz, 4.5kHz - I wanted the mid to cover the most sensitive part of the hearing range which required a small driver to retain good dispersion up to a relatively high point. However the beauty of the DSP XO is that I can play as much as I want with XO points before I settle on the final design. Initial testing and prototype (see my Avatar) was done with a passive XO at about 550Hz and 5 kHz.

Have to say there is something very beguiling about the sound of the AMT tweeter. It is very linear up to 30kHz with very good dispersion compared to some of the domes I looked at. Essentially it sounds very sweet and extended. It has low distortion and excellent transient response.
View attachment 7625

Some pics.

View attachment 7632

View attachment 7627

View attachment 7631

View attachment 7628
Very impressive BE!

Couldn't agree more on the AMT virtues, got them in all my three systems (primary, secondary & summer house setup).
 
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