Open-baffle with the miniDSP

I've put up an article/tutorial on HifiZine on using the 4-way PEQ plugin for an open baffle speaker. I'd be happy to respond to comments, suggestions, or questions either here or there. This is the first part of what is most likely going to be a three-part tutorial:

http://www.hifizine.com/2010/12/prototyping-4-way-open-baffle-speaker-with-the-minidsp-2x4/

Parts 2 and 3 will be a bit more advanced. Thanks, please feel free to let me know what you think ;)

JohnR
 

otto88

Member
2007-12-05 10:39 am
Hi John

Thank you for your excellent tutorial!

Very timely for me:
A small question re the DC power supply: I also will use an external supply
The power supply wiring picture shows (apparently) one supply, with 2 sets of leads to the screw terminals of the two miniDSP units.
While 5 -24 V works, what is the optimum voltage, and in particular, what off-the-shelf unit did you use (I'm also in Oz), that has 2 sets of leads?
 
Hi, you're welcome, thanks for the feedback :) The power supply voltage is not critical, as it is regulated down again on the board. I'd suggest a 12V DC supply, although it doesn't really matter. I'm just using a simple unregulated supply I made a few years ago with the two leads soldered to a DC socket. You could do something like that, or connect the second DC jack up from the first - actually now I think about it perhaps I should have shown that arrangement.

Good question on local availability. Here is the kind of thing available in the US (I haven't used one but I'm told they're fine) :

Amazon.com: Pyramid PS3KX 3-Amp 12-Volt Power Supply: Electronics

I'm not really finding anything equivalent locally yet. But you can use almost anything, I've used a cellphone charger too - just cut the connector on the end off and wire it up. Just be sure to check the polarity with a multimeter.
 

minidsp

Member
2009-12-15 12:15 am
Indeed, a very nice tutorial John! Great stuff...

You're covering a lot of the basics and step by step procedure... A lot of good info for those who want to start twinkering with miniDSP and learn its full potential...

Looking forward to part 2! :)

DevTeam
 

2skunks

Member
2010-02-17 3:17 pm
Hello:

I am in the same boat: Trying to use two amps for a 2-way OB speaker.

The mid/high driver (one per side) will run full range and be powered by an SET amp.

The 15in bass section (one driver per side) will be powered by a SS amp.

I am still researching but think I can get away with one MiniDSP with the 2-way PEQ plugin so I have some parametric adjustments to the low end.

Still learning this MiniDSP unit so any advice would be greatly appreciated.

HL
 

minidsp

Member
2009-12-15 12:15 am
@ Scrappydoo & 2skunks,

1 x miniDSP kit/2x4 + 1 x 2way Advanced (integration with REW) is indeed all you will need for a 2 way stereo configuration. Another advantage of the Advanced plug-in would be the capability to program custom filters like a linkwitz transform.

Hope this info helps.
 

minidsp

Member
2009-12-15 12:15 am
REW stands for Room EQ Wizard. A free measurement and tuning software provided online for free. Type REW on google for more info. The advantage being the ability to let REW calculate EQ settings for you (autoEQ mode) or tune EQ/filter settings and export them to miniDSP.

There is an app note that will give you a lot more information on our website. MiniDSP - Auto-EQ tuning with REW

Hope this clarifies.
 
Is it possible to use one dsp per channel with 4 way horn set up. I am concerned about power supply based separation issues of these units. Off board dacs might be another option. I had in mind a preamp using these(the balanced version for higher output) battery powered to use with PC based home theater (channel) Austar is bleeding me dry$$$. I think I can find as much content on free to air and internet these days
 

minidsp

Member
2009-12-15 12:15 am
@ Fatbattery,

As already answered by keyboad123, one miniDSP kit/2x4 will indeed be required to provide processing power for each 4way speaker. In total 2 miniDSP kit for a stereo configuration.

miniDSP been running on batteries fine on other designs from our community members.

Hope this info helps,
 
Are horns fullrange huh? are what I am referring to is using one dsp per channel left right rather then frequency channel Sorry if I wasn't clear on that. I am worried about the lack of separation these little dsp's may have. So digitally you have to split the left right Chanel's. I don't think that will happen hey? I realize you can daisy chain them up for as many frequency channels as you want. Anyway how is the sound quality? Are they as good as say better then a ipod even after you mess with the time domain's. I could live with them I think if they where as good as a ipod. I am not saying a ipod is supa but that would be my minimum hopes. I think having the freedom to do what they can do would make up for there short comings Fidelity wise then. I will always keep a passive system to compare. Just poor seperation really bugs me. And modern dual op amps seem to suffer that problem.
 
Hi Fatbattery,
The way i would use the DSp is one per channel. So if one channel (say left)of a stereo signal is fed into it. then if say your speaker box has four speakers in it the signal is split up to the frequencies you would want to send to each via a dedicated amp for each one. Mine is not up and running yet, but users seem to say its very good.

Maybe miniDSP can give you more info , on what youre' looking for.:)
 

minidsp

Member
2009-12-15 12:15 am
In answer to your questions, I think that what you're referring to is the so called "crosstalk" between channels. In a miniDSP solution, you'll be looking at -82dB crosstalk which is already good. A signal that is -82dB is already very close to the noise floor of most products and I really doubt that it would become an issue (at least we've never heard anybody commenting/complaining about that... )

Remember that at the source (i.e. the mix by the engineer of the CD/DVD), they would indeed do some natural crosstalk of the signal to get your stereo signal to sound center stage so it will add another challenge to be able to notice that crosstalk..

Would it sound better than a passive system? I'm not sure how easy that comparison is... i.e. In the DSP world, the flexibility you will have in terms of tuning (filter/PEQ/time alignment) is just no match for a passive filter. Unless you have many months of free time to constantly change your passive filters to tune them manually... DSP processing brings up to the table ease of use where you can focus on tuning your speaker rather than changing caps and resistors.. Things like time alignment would matter a lot in our way of tuning. DSP is just a different angle to speaker design I think, hence no direct comparison possible to my mind.

Finally, note that none of our users ever used a single miniDSP per channel to prevent crosstalk, although a lot of them are doing some high end implementation... But with this said, that doesn't mean much since audio is so subjective... :)

Hoping this info helps.
 
Yea thats fine. I did not clarify either that I will be using only digital in. I want to take the digital out of my austar and PC . If the separation is OK I wont worry about it too much. I would disagree with you on the issue of separation being hard to hear. Its very easy. I love lots of stage width. Thanks for all your help folks.

When I set up my dsp I will report back with my results. I have been wanting to go digital active for years. And pretty much from what I have read the Beringer crossover was about the only budget solution. And most that used it where never happy with it so I stayed passive.

I think this product is a massive break through for the audio diyers. An absolute bargain when you consider how expensive and damaging just one inductor in the speaker path can be. It's why I have always until now stuck with full range. Even the most efficient speakers loose all there dynamics and life when a inductor is inserted between them and a low damping factor SE amp. Massively expensive large Low DCR CCcore inductors being the only half solution to the problem. I look forward to setting it up. Thanks again!