DIY passive to active conversion with dsp

[insider9]

Having gone to Scalford I was really inspired and really amazed what can be achieved at a relatively low cost. Yes, the Linn + PMC (in Sunbeamgls's room) wasn't in the low cost category but the level of clarity I've heard haunts me  To that extent that I'm considering wholesale changes to my system. If I can at least go some of the distance at a low budget, I need to try.

In a way it's to limit perpetual box swapping with usually unknown results. But also to future proof my setup when and if I move (whether room or a house).

I'm considering a diy digitally room corrected active setup. And no, nothing that's readily available on the market so bear with me. The aim would be to achieve all of it for no more than a £1,000 source excluded. It would need to allow flexibility so I can expand if I wished. I've never undertaken anything like it so would like your input. 

Until I know this will 100% work and that I will enjoy the effects I don't want to plough money into it. So I'm considering doing it in three stages. That would allow me time to learn and slowly make changes as my ears adjust.

1) TESTING... Use a UMIK-1  (circa £100) to measure and take out a two week trial of Dirac Live to see how much can be achieved with my existing setup also have a pair of QLN Qubic 122 (floorstanders) that I'd test and use for this project. I'd be particularly interested on impact of different speakers and amplification on the end result. Would

2) EXPERIMENTATION... Buy Minidsp DDRC-24 (circa £450) as a 2 way active crossover / room correction solution. Would use both pairs of speakers. At that stage I would not remove passive crossovers. Using standmounts as mids and highs (HF) and getting bass (LF) from woofer on the floorstanders to add extension. To do that I'd need amplification. I'd probably use Sony STR-DB930 (sub £100) as one box solution. Individual drivers don't require as much power as passive speakers. I understand I could connect LF to back speaker terminals and HF to fronts.

3) IMPLEMENTATION... Depending on results above I'd either keep existing speakers and remove passive crossovers or buy and re-purpose a second hand pair of floorstanders or transmission line standmounts. Two way IPL floorstanders (sub £200) or some older PMC (max £350) but would remove passive crossovers. If I'd manage to go with cheaper speakers I could diy some acoustic panels for about £100 or if need be upgrade the amp to something like a 4/6 channel power amp. I've seen some Rotels for little money.

So once completed the chain would look like this

Preamp streamer -> (digital stereo signal) -> DDRC-24 (working as active crossover + room correction + dac) -> (2 x analogue stereo signal for HF and LF) -> at least 4 channel amp -> 2 LF channels to drivers + 2 HF channels to tweeters

Any thoughts? Are there non minidsp (similar budget) alternatives to DDRC-24? Have I missed anything or made a wrong assumption? Is there a better way to do it that's withing the budget?

Thanks in advance for all help and participation in this thread.

 

[MF 1000]

Both Serge, Colin (Greybeard) and myself use a Behringer dcx2496 active crossover ....vv good value at around £160.

If you came to the Cottesmore Room you would of seen my setup with separate LF units from stand mounts covering the mid range upwards.

Separate amps would allow better 'tuning' again behringer amps are  good value within your budget  

 

[SMEagol]

from memory the manual was only about 2 inches thick, and double dutch, so at least you seem to have the technical skills to digest this weighty tome, and sharp edged equipment! Welcome to the Wam

 

[insider9]

Both Serge, Colin (Greybeard) and myself use a Behringer dcx2496 active crossover ....vv good value at around £160.

If you came to the Cottesmore Room you would of seen my setup with separate LF units from stand mounts covering the mid range upwards.

Separate amps would allow better 'tuning' again behringer amps are  good value within your budget  

Thanks, will look into it. Yes, seen Behringer being used a couple of times from memory. It would let me use 3-way speakers which is an advantage. Don't know whether I could correct for the room though. 

The thinking behind DDRC-24 is that I would avoid additional ADC conversion and have room correction as well.

Really cool post Luke. It has given me some inspiration so watch out for the post in Scalford 2018

Thanks

 

[MF 1000]

I've not ventured into room correction (yet  :nerves: ), but the change from passive to active is a step well worth taking imho - don't go half way remove all passive crossovers or bypass them and enjoy the fun of tuning your setup.  If you need  help just ask I'm sure any of us running active will give advice etc 

 

[sunbeamgls]

I've not ventured into room correction (yet  :nerves: ), but the change from passive to active is a step well worth taking imho - don't go half way remove all passive crossovers or bypass them and enjoy the fun of tuning your setup.  If you need  help just ask I'm sure any of us running active will give advice etc 

Maybe we should've demoed room correction on and off on Sunday.  Given the bouncy floors, hollow walls and the large built in resonant chamber (ie wardrobe) in our room, it would've been a revelation to some to hear the difference the SPACE facility makes to removing room modes.  SPACE applied 3 room mode notches, the lowest of which was around 32Hz and was -25dB deep by the calculation, although we did move it up to about -23.5dB.

 

[insider9]

I've not ventured into room correction (yet  :nerves: ), but the change from passive to active is a step well worth taking imho - don't go half way remove all passive crossovers or bypass them and enjoy the fun of tuning your setup.  If you need  help just ask I'm sure any of us running active will give advice etc 

Thanks very much, Keith. I'm sure I will

Maybe we should've demoed room correction on and off on Sunday.  Given the bouncy floors, hollow walls and the large built in resonant chamber (ie wardrobe) in our room, it would've been a revelation to some to hear the difference the SPACE facility makes to removing room modes.  SPACE applied 3 room mode notches, the lowest of which was around 32Hz and was -25dB deep by the calculation, although we did move it up to about -23.5dB.

I'm sure it would've been great to hear the difference but the overall quality was just stunning. I think I mentioned to you at a time how amazed I was what you managed to achieve with the large size of speakers in such small room and at a moderate volume. I know at my modest budget I won't be able to reach such heights but at least it showed me what's achievable. I've listened to that rendition of "A Case of You" yesterday and even though not my favourite version the differences in clarity are stark.

With an open platform I can always improve the speakers/amplification as I go along and as funds permit.

 

[sunbeamgls]

^ Thanks for such kind words about what we managed in Room 237!

Another few things we did:

- we had marble slabs under the speakers to tame the floor - £5 chopping boards from Argos

- The "hot seat" in the room was in row 2 - initially we set the system up targetting this specific chair, but it made row 3 still have some boominess, so we compromised.  The actual ideal listening position was halfway between rows 2 and 3 and slightly offset to the left - so the "hot seat" was slightly compromised to make life better for row 3 and those sitting near the left wall

- We stuffed the empty built-in wardrobe with pillows and duvets in an effort to reduce its tendancy to resonate

 

[greybeard]

With the Behringer you can do DSP as well as crossover points and time delay. I use a umik1 with free REW software on my laptop, to do room correction. You just import the settings from REW into the Behringer . It is a bit of a learning curve, but google is your friend

 

[edd9000]

The Behringer will not do FIR. The DDRC will. That makes the DDRC a no brainer to me. The new 2x4HD is also looking excellent, allowing both IIR and FIR.

Minor correction, the DDRC-24 looks like the 2x4hd but with Dirac live support, Bit of a bargain, you can do similar for free but its a lot harder.

Dirac live isn't really comparable with using peq filters in a DCX.

 

[insider9]

With the Behringer you can do DSP as well as crossover points and time delay. I use a umik1 with free REW software on my laptop, to do room correction. You just import the settings from REW into the Behringer . It is a bit of a learning curve, but google is your friend

Not bad at all. Will need to look into it. It may be a viable option. Thanks, Colin

The Behringer will not do FIR. The DDRC will. That makes the DDRC a no brainer to me. The new 2x4HD is also looking excellent, allowing both IIR and FIR.

Ah ok, thanks Edd. Yes, DDRC-24 is 2x4 HD with a firmware update. Crazy value if used with REW. Might actually start with 2x4 HD and upgrade it to DDRC-24 if funds are tight. DDRC-24 has impulse correction and allows full Dirac Live integration which I think could make a big difference.

 

[edd9000]

Using something like DRC-Designer will provide the same result at Dirac live in the 2x4hd, just with a much steeper learning curve. REW only does PEQ correction right now, no phase correction like Dirac etc.

Rephase is another great tool to design FIR linear phase crossovers. I assume the 2x4hd can make use of that.

To be clear, I consider the DCX2494 outdated and inflexible and not the most cost effective option. The 2x4hd can do everything the behringer can do better (if all you need is 4 outputs) and far more.

 

[rv295]

I have to agree with Edd, I wouldn't go back to an IIR only solution although I'd consider one again when used in conjunction with convolution filters.  

The timing adjustments in the Behringer (and the IIR only minidsp products) are for adding in a small delay to a whole channel (or a driver) which allows for different driver distances.  FIR filters allow you to correct the phase, db and timing of every single frequency ensuring that all the different frequencies arrive at your ear at the same time, at the same volume and with the same phase. 

If you used a computer as the source, you could add the FIR functionality via plug-ins for free. 

Edd has a good guide on how to implement the DRC filters for a cheap DDRC alternative.

 

[insider9]

If you used a computer as the source, you could add the FIR functionality via plug-ins for free. 

Edd has a good guide on how to implement the DRC filters for a cheap DDRC alternative.

Ok, great. Seem my research was good and DDRC-24 is the way to go

Computer as a source would be an option. I've always had this at the back of my mind but building a silent pc means low power. I take it applying filters would be cpu intensive?

Where would I find Edd's guide, please?

 

[rv295]

Ok, great. Seem my research was good and DDRC-24 is the way to go

Computer as a source would be an option. I've always had this at the back of my mind but building a silent pc means low power. I take it applying filters would be cpu intensive?

Where would I find Edd's guide, please?

The filters aren't processor intensive at all.  That's something I was worried about but no - even a low spec budget processor would do.

Edd's guide is here: http://teribil-audio.com/2015/02/using-room-eq-wizard-with-drc-room-correction/ (I hope you don't mind me sharing Edd)

If you struggle following the guide let me know (it does assume some computer knowledge) and I've also found different ways of using the software - if you can follow the above it is a great cheap way to set-it up. 

The only real downside with the above method is that you have to create a filter at each resolution that you want to play back.  The minidsp Umik (usb mic) only records at 44.1 and 48k and it doesn't sound good to me if you try and play back other resolutions with a 44.1 or 48k filter. It's not an issue with the DDRC products as they are 48k I believe. 

 

[insider9]

The filters aren't processor intensive at all.  That's something I was worried about but no - even a low spec budget processor would do.

Edd's guide is here: http://teribil-audio.com/2015/02/using-room-eq-wizard-with-drc-room-correction/ (I hope you don't mind me sharing Edd)

Thank you very much, Ross! 

I can see a busy day ahead tomorrow reading

 

[oldius]

Absolutely no plans: I didn't get out of my room!

I can no longer see what I can improve so that's pretty much it for me though Henry has kindly invited me over to Birmingham for a streamer listen.

 

[edd9000]

The 2x4hd should host the for filter generated by drc, no pc needed. Other than to create the filter in the first place.

The 2x4hd runs at 96khz. I'm quite surprised the umik only runs to 48khz. I don't really see it as an issue, I haven't experienced a problem resampling Fir filters but I'm aware Ross has.

 

[insider9]

Started the ball rolling and drove to pick up Umik-1 from IdealAV just outside Wakefield. Now to order earplugs from Amazon.