MartinC

Speaker Correction with miniDSP 2x4 HD

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As it came up elsewhere today I thought I'd share the speaker correction possibilities of my miniDSP, that I've just started experimenting with. Id be grateful for any feedback/advice from others who have tried something similar.

First up here was the rough measurement geometry, with the speaker being measured on a chair to get the drivers roughly equidistant between the floor and ceiling and so maximise the length of the time window that could be used before the first reflection reached the microphone. The setup in the photo had the microphone at a height about mid-way between the two drivers but the results below were made with the microphone raised up to the height of the tweeter.

Shearwater Calibration

With no correction this is what I measured (with the frequency range shown being about the meaningful range for the 2.7 ms gated range):

image.thumb.png.5607a3b1de8b1c7571af8ea344352d79.png

Adding filters to aim for a flat response centred around 78 dB I was then able to achieve the following (measured) response:

image.thumb.png.c0b1e3c26006bd318ce53e9c22e55b56.png

The correction has taken the variation from about +/- 4 dB to +/- 1.2 dB. I have fairly recently replaced the mid/bass driver on the right speaker (red traces) which may be a factor in the initial differences, although as this is only something like 1.5 dB I don't think this is too bad/atypical?

I only did this last night and so haven't done much listening but initial impressions are good. I'm enjoying Radio 2's folk show as I type this :).

I have various thoughts/questions that need further work, including:

1) The above measurements were at 138 cm from the tweeter, at the height of the tweeter. I initially made measurements at 1 m but then moved further away as it would be closer to the listening distance (of currently about 2.4 m). What I measure understandably varies a bit with this distance, so what is best to use to generate correction filters?

2) I picked the 78 dB target level as it looked like a sensible one to enable filtering to achieve a similar response for both channels, which worked pretty well. I'm conscious I don't know if I've introduced a disparity with the output levels below 400 Hz though.

3) I used the REW default Tukey window but I'm conscious that the window selection has an impact on the measured spectra.

4) All of the above used the basic REW filters. I will go on to explore using rePhase to experiment with both FIR filtering to not change the phase response, and then to try linearising the phase too.

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Do things sound different , and importantly , better to your ears , i am interested , i have a lovely set of really old prehaps 35 years , sony ss G4 heritage three way speakers , that sound perfectly usable to me but i have been wondering recently about replacing cross over components etc to see if i can improve on the performance of the speakers , but i am fortuante to also have a second pair of simelar era sony ss s51 speakers again 3 way but with a 12 inch bass unit, lovely things need very little power to get things very loud but also , lots of propper bass slam, mid clarity and even it seems to me extendd nicely top end from a  nice looking top end tweeter,  honestly as working speakers in a modest system both sets of sony speakers seem to do the job of playing back compressed 16 bit disks nicely. Any one got a input. 

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On 22/04/2018 at 21:22, lowendall said:

Do things sound different , and importantly , better to your ears , i am interested ,

Sorry, just seen your reply. I've been busy with other things recently and so view this as a work in progress and so won't commit to whether it enables things to sound 'better'. It can obviously make changes to the sound though.

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Really good comparison. I my experience window selection does have an impact on the measured spectra, but it's not that significant.

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I've just come across the miniDSP site and only just starting to understand it all, and REW, or is it Dirac Live...?

I followed their Applications link to the Room correction 101 page, which referenced the DDRC-24 box. I wasn't entirely sure but so that all of my sources would be covered I think this can plug-in between my pre-outs and power amp...?

Is doing the measurements very tricky? It looked a little bit daunting TBH but I guess you can do it, and re-do it, as many times as you like. I guess the generated correction data file is downloaded into the DDRC-24 box via the USB...?

I am tempted to give it a go but it's making a commitment with the money - I assume you ordered from the US...?

Thanks

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Super Wammer

It's a bit daunting but easier with help. 

Getting your head around the system is the first thing. I think the following is something like correct...

*There's a box called a mini dsp. It has a stereo input via 2 phonos, or usb, or optical. There's 4 outputs (phonos). The bit in between the inputs and the outputs where all the magic happens is digital.

*A piece of software called a plug-in can be installed that converts it to a DDRC-24. Allows you to do filters, EQ, crossovers for each of the 4 output channels. You don't need to use all 4. Maybe just 2 for stereo, or 3 for 2.1 stereo, or all 4 for 2 mains and 2 subs. Or all 4 for a pair of two way speakers using the box as a crossover. Any of the 4 outputs can receive either of the 2 inputs.

*A piece of software called Dirac Live Calibration Tool runs on your laptop. This sends audio sweeps to the box via a usb lead and listens with a usb microphone. It can therefore "hear" what your room sounds like and compare it to what it "should" sound like. It then programs the box with this correction data - but not before taking into account your opinion of how you would like it to sound.

You can also install REW (free!) on your laptop as an addition, and this will show you a graph of the speaker/room response curve and you can manually tweak the magic box to give you the curve you want.

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Ed,

How did you find the improvement? Was it a worthwhile upgrade?

Looks like the DDRC-24 version with Dirac Live is in the region of ~£300 plus a microphone. Seems that both Arcam and NAD have bought in to this technology with their AV amps.

Thanks

Nigel

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Super Wammer
1 hour ago, v1nn1e said:

Ed,

How did you find the improvement? Was it a worthwhile upgrade?

Looks like the DDRC-24 version with Dirac Live is in the region of ~£300 plus a microphone. Seems that both Arcam and NAD have bought in to this technology with their AV amps.

Thanks

Nigel

Was it worthwhile? Yes, totally, 100%, staggering improvement. Because I have an asymmetrical room with 3 walls of glass, bass control is a problem and the stereo stage is weird. But no longer - I can point at instruments and there's a crispness to everything. The room has, to all intents and purposes, disappeared.

I had a DSPeaker Antimode2 previously and that was good. Very easy to set up in its self contained, do everything box, whereas the DDRC24 etc etc is not easy, although much wider in scope and there's much more to play with.    

The title of the thread is Speaker Correction. I think it should really be Room Correction. The room is the single most influential component. And has been said before, often overlooked. 

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@MartinC
I note the measurements.

They look flat to 15kHz, then go down seemingly steep.

Does the box try to EQ flat or can it do the Bruel & Kjaer target curve?

I'm probably getting the miniDSP SHD Studio unit next, but I would be concerned if it only EQs flat to 20kHz.

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Super Wammer

Can I just add a little extra to this as I have used both the MiniDSP HD2-4 and the DDRC 24 . The HD 2-4  is the basic unit and with this you get a full software package that allows you to make measurements using REW software and from REW create FIlters to correct the output tpo your speakers. As aunit you can input your signal via two Analogue RCA sockets , a Toslink Digital or a usb Digital . You can then use the unit to either provide the Active Crossover and Equalisation for your speakers and out put this to either two or four RCA sockets as an analogue out signal .

DIRAC Live is a DSP correction software and in the case of the DDRC 24 it is an additional firmware plug in for the HD 2-4 . With this added you are then able to do all of your measurements and filter creations on the DDRC 24 Software and the DIRAC Live Software which you download to your PC . DIRAC live offers a more complete and comprehensive set of correction filters that also covers time delay and phase in your room . Because of the supplied software and on screen prompts doing a complete measurement is very simple and requires you to make 10 separate measurements from designated points . The system will tell you if the sound is too loud or not loud enough and will confirm after each measurement that it was acceptable . Once all of these are completed it will then show the spectrum graph and an autometed Target graph of what it suggests you apply to achieve correction .

All of the above sounds more complicated  than it is . Using REW takes a bit of practice while the DIRAC Live gives in my view better and more musical results and is simpler to use. You can either purchase a DDRC 24 outright which will come with DIRAC Live installed , or you can buy a HD 2-4 and give that a try and then upgrade the unit to a DDRC 24 at a later date.

MiniDSP are based in Hong Kong and you can buy form them direct but you will need to factor in the additional costs of VAT and Customs on top of the online price. Please note that if you buy the HD 2-4 unit and then buy the DURAC Live plug in you do not have to pay any VAT on this as it is a straight download.  They also have two UK Dealers and you can check them out for prices. While we are still in EU they have some European Agents as well and they can be cheaper is some cases . Blue Planet were selling the HD 2-4 for 199 EUR which is a good saving , Tony J had a very good experience with them mine was not as good but could have been a one off .

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Quick reply...

The 2x4 HD gives you full control over everything but will take more thought/work as a result. Is does not inherently work to a target room curve but actually Floyd Toole would argue that any system that does (like Dirac Live) is a BAD idea, and so is not something I'd personally want.

The high frequency roll-off in my graphs is inherent to my speakers rather than something I've sought to achieve. In fact by reducing some of the lower frequency peaks I have in practice increased the frequency range a little.

Edit: I will just add that I've not heard a Dirac live system but the theoretical argument against it seemed pretty strong to me.

Edited by MartinC

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5 minutes ago, MartinC said:

The 2x4 HD gives you full control over everything but will take more thought/work as a result. Is does not inherently work to a target room curve but actually Floyd Toole would argue that any system that does (like Dirac Live) is a BAD idea, and so is not something I'd personally want.

Each to their own, I guess. All I can say is that my experience so far with the 2X4 HD and more recently with the DDRC-24 (==2X4HD plus Dirac) is that the results I am getting with the latter produce a much more enjoyable end result. I have great difficulty considering that in any way to be a bad idea!

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3 hours ago, Tony_J said:

Each to their own, I guess. All I can say is that my experience so far with the 2X4 HD and more recently with the DDRC-24 (==2X4HD plus Dirac) is that the results I am getting with the latter produce a much more enjoyable end result. I have great difficulty considering that in any way to be a bad idea!

If you enjoy it then it obviously isn't 🙂.

I'll try to dig out a link later but the general problem with room-curve based correction methods is that they corrupt the direct signal in favour of getting the desired response for the sum of direct and reflected signals. This makes some sense for the very lowest frequencies but not elsewhere. I realise that Dirac is 'smarter' than some other systems but from memory I thought it still had this fundamental flaw? I'd like it not to be as I know the measurements on ASR show the new SHD should be a good step up from the 2x4HD on the DAC front.

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This excellent talk covers the issue I referred to, plus much more. (I'm guessing you've seen this before though @Tony_J.)

Edit: there's a section from 37 minutes  in that covers the particular issue I raised but it only really makes sense with an understanding of the material that preceded it.

Edited by MartinC

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On 28/01/2019 at 21:16, Metatron said:

@MartinC
I note the measurements.

They look flat to 15kHz, then go down seemingly steep.

Does the box try to EQ flat or can it do the Bruel & Kjaer target curve?

I'm probably getting the miniDSP SHD Studio unit next, but I would be concerned if it only EQs flat to 20kHz.

I should perhaps add that my measurements were time windowed to give just the speaker output (direct signal), rather than being a measurement of the combination of the speaker and the room which is what 'room curve' targets are used for.

In case it's of interest there are some Stereophile measurements of my (rather old) loudspeakers here:

https://www.stereophile.com/content/meadowlark-hotrod-shearwater-loudspeaker-measurements

(In the long run I'd definitely like some better speakers, possibly some ATC actives, but right now I have other financial priorities. Which is also why I've rarely posted here recently.)

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