Scope powered Studio monitors - DIY possible ?

[astroman]

well, I've recently dissected my Roland DS30s and found some nice and simple bi-amp IC inside plus a general powersupply - parts worth 50 bucks per box.
The circuitry is really simple as the amp is a common part in many high end hifi units.

There have been frequency splitters designed (in SFP) by various developers which could serve as a cross-over.

Probably many here have an A16 or similiar converter and possibly don't use all it's analog outs.
You need 4 channels for 2 monitors, a 5th for a sub and another 4 if you want 5.1 surround.
First question would be what drivers ?

So far it's pretty obvious, but the more interesting application would be 2 stages to compensate non-linearities in the drivers themselves and (even better) the room acoustics.

I once found such a 'room compensator' in a high end hifi shop and it was even based on Sharcs (at least one) for about 3.5k Euros - ouch
but of course a bargain if you can spare heavy room modifications
The latter unit could also be a (rewarding) project for our suffering developers - though I don't have much knowledge about micing room anomalies.

cheers, Tom

[Immanuel]

I don't really believe in digital acoustic compensation. You can even out the frequency range - and you can do this without fase shifts, but then you get so much latency, that I don't think doing any real time adjustments will be tight enough. I do, however, not see, how such a box should be able to make 80Hz notes in the music shorter, if you have standing waves in your room at 80Hz.

My current monitor system is actually very influenced by Scope. I use the bass driver from some Epos 11 speakers for sounds up to 1600Hz. Above that, I use JBL 4411 speakers, from which I have taken out the bass drivers. The main X-over is done in M3. I use 48dB octave filters to devide the frequencies between the speakers. I found out, that you have to use to identical filters set to the same frequency in series, if you want to end up with a flat response from the x-over. That makes 8 filters all in all for a stereo 2-way x-over, and I use 4 outputs on my converter. The 4411 speakers still have their x-overs in them. Thus, they cut 12dB/oct from 1000Hz and down. I keep the filters as a life insurance for the drivers in case the amplifier makes bad things.

[Neutron]

you could easilly buld some very nice chip amps based on "gainclone" which is a clone of the 47 labs gaincard. these are very highly regarded amplifiers, even though they only use 7 or so components per amplifier.

personally i would use LM3875 chips for the mid/high and LM3885 or 2x LM3875 bridged for the bass.


you could also build an active crossover fairly easilly. or as you said use your A16/scope, the only thing about that is if you decide to make a change later you will have to build an active crossover to make them any use for anything, plus you will not be able to use them for anything when the computer with the scope board in it is turned off (or you need the DSP for something else). personally i do not like depending on anything that much for something else to work. i would design the crossover with scope, and a program that measures response, and then make it hardware with values to match what you finally decide on from listening.

the much harder part is to design some good speakers for them to work with. since you are building monitors rather than HIFI speakers the goal is quite different.

you can find much information (and silly arguments about which resistors and capacitors sound better as well) on http://www.diyaudio.com/forums/
look in "chip amps" for the amplifier portion
and loudspeakers (duh) for speakers.

ther is a nice well made circuit board avaliable from one of the members there (brianGT) i have built a few of them myself
including this one (was my first) http://www.briangt.com/gallery/nigc-neutron
the sound from these amplifiers is quite astounding if you build them well, even without exotic components. better than any mainstream commercial offerings, and my froend with brystons even liked them better for clarity ,imaging etc. they did not have quite enough oomph though for his JBL 4311s
(remember mine are just full range 50 watts, so if you have bridged for bass, and another for mid/treble, there will be PLENTY of power for any near field monitor you could think of)

oh yeah if you have an email adress that is not hotmail,AOL etc or a major ISP, (like a company one prefered) you can order "samples" from national for the LM3875, up to 5 at a time. however some whole countries are excluded from that program, i guess they have too many leechers try it anyways.

http://www.national.com/pf/LM/LM3875.html

get the isolated one, its easier to work with and "sounds better" just click on the "24hr samples" button

<font size=-1>[ This Message was edited by: Neutron on 2004-09-18 21:22 ]</font>

<font size=-1>[ This Message was edited by: Neutron on 2004-09-18 21:28 ]</font>

[garyb]

engineers...