[THROWBACK]

I have a wonderful combination of LS-9 mains and servo subs. I am experimenting with using a Mini DSP with REW software as an external crossover instead of the one in the A370 PEQ amps to knock down a couple of peaks in the bass. The mini-DSP takes the signal from the preamp (an AtmaSphere MP-3), converts it to digital, and is programmed by REW in the digital realm.
My curve looks gorgeous, but . . . and I need to do a lot more listening with a lot more and different kinds of music to confirm . . .  I might be hearing just a bit less growl, texture and impact. Again, I have only begun to listen critically and it might be my imagination. Maybe I just got used to my peaks. But I'd like to get some feedback from those of you who have experimented the same way. Thanks.

[Tyson]

I had a mini DSP for a while running fully active speakers for a while.  I ultimately abandoned it because it robbed too much inner beauty from the music.

[DannyBadorine]

There is certainly something different when you add a D/A conversion and an A/D conversion.  I use mini DSP's in my bi-amp and tri-amped speakers.  They give many options, but when I recently converted a pair of those speakers back to a passive crossover I liked the sound of them better.  There is something more real and more alive about passive.  It is similar to the effect I find with an analog mixing console vs. a digital one. (I work as a live mixing engineer and have also mixed many records).  I use digital because it is more flexible, convenient and versatile, but every time I get back on an analog console I find them to sound purely better.  They are more real.  They have pleasing distortion.  Digital allows me to get the frequency response flatter, but as you said, it takes some of the growl out of it.  I believe it was Danny Ritchie who said that they take the life out of it. 
The crazy thing that I have experienced about analog (similar to a passive crossover) is that the inconsistencies are what sounds good.  I tried to calibrate a 40 year old mixing console and every channel was different.  When I ran a mix through the console, the mix sounded remarkably better.  It's like the circuitry is alive.
So what I like to do now, is use the mini DSP to figure out my passive crossover then use the passive crossover.  If you have some peaks in your speakers, it is likely that the room is causing these and you would be better served with some sound treatment in order to fix those, especially if you like the sound better without the digital stuff inline.

[THROWBACK]

Interesting. So it may not be my imagination. Hmmm. I thought since I'm only using the mini DSP in the bass realm - - below about 90 Hz - - that it might not have that much effect on the actual quality of the sound but only on the contour.

I'd love to have Danny Ritchie chime in. Danny, have you prepared a tutorial on the best way (step-by-step) to integrate the subs using the A370 internal PEQ?

[THROWBACK]

Deja Vu all over again. I just noticed that I raised the issue about A 370 PEQ settings 4 years ago without a completely satisfactory answer. First time I have compared it to miniDSP/REW, however.

[Endo2112]

Does anyone think that the Minidsp is state of the art??? I think/hope not, however people always sight them when comparing dsp to passives. If you want to know what current dsp can do ask HAL as he actually works with it. In my personal opinion, as i've been playing with it lately, when implemented properly is far superior with things like dynamics, spacial cues and accuracy in the lower bass region. At the end of the day, why add to the signal path if you don't have too?

My two cents,

Don

[ThePriest]

I am using a DEQX HPD5 as my preamp. Sources are both digital and analog.
The DEQX does 'the DSP stuff' for you. It corrects frequency response, phase response and room nodes. You can change your target curve and adjust.

My experience is that I have to be careful when measuring the speaker in near field (I took them outside on a calm day, to be free from reflections), and try out different correction filters/limits.
While I have not tried a passive filter on my speakers, I am absolutely thrilled with the DEQX. As Endo2112 wrote, transients, attack, natural, relaxed sound are things I notice.

The Priest

[HAL]

THROWBACK,
Likely what you are hearing is the miniDSP ADC and DAC Codec that they are using for analog conversion.  That and the analog section design are a big part of any DSP system sound. 

Bass response in systems seems sensitive to the digital filters used in the ADC/DAC's and I prefer other styles of filters than the stock linear phase (i.e. brickwall/high rolloff rates) styles used by a lot of systems.  The miniDSP documents I see on the website do not tell you what is used for the ADC/DAC inside and what filters are used. 

REW is a way to make room correction measurements.  It will create the correction data needed from the measurements that many systems can use.  As above there are other systems as well, like MathAudio, DEQX and others.

I use the Danville Signal dspNexus 2x8 in my system with Rythmik/GR-Research 6x12 servo subs and as complete speaker system crossover.  So far a prototype, but sounds great in my setup.  Hoping to see the production units this quarter.    I use the HX300 servo amps and do all the room correction in the DSP, since the amp does not have PEQ. 

Just some thoughts.

[DannyBadorine]

It is important to note that the Mini DSP stuff is much less expensive than other products.  Keeping that in mind, they do a really great job.  But they don't keep up with stuff that costs 5-10 times as much.

[THROWBACK]

Good inputs, guys: thanks. The solution might well be to get a better DSP (Danville? DEQX? Prices?). But these seem like overkill for just a subwoofer application. I'm very happy with my mains and don't want to screw them up. Rather than add anything extra between the preamp and my Rhythmik subs, it would be "purer" just to be able to program the PEQ that's already built in to the A370 sub amps. But, as I outlined in an AC post 4 years ago, there are something like 15 controls, each with several settings. It would be nice if there existed a "start-here-then-do-this" tutorial to lead me through the process. I haven't found one though.

[Tyson]

I ran a DEQX too, and I also had a chance to demo a Trinov unit.  Neither of them sounded as good as a pure analog preamp with no correction.

What I would do is run pink noise through your subs and see where the biggest spike in response occurs and then use the PEQ in the sub amp to knock down that peak. 

I actually recommend 3 measurements.  First measure just your right subs.  Then measure just your left subs.  Then measure both together.  Then make your adjustments in the PEQ and see how it affects the response.  It should let you drop at least one of the peaks very effectively. 

If you are only doing EQ on the subs, then a digial eq is not a terrible idea.  But remember you can only cut peaks, you should never try to boost the signal in places there there are gaps or nulls in the response. 

[DannyBadorine]

I second what Tyson is saying.  I didn't realize that you're only using the DSP on the subs.  This means that they are going to be delayed a bit from the mains, which is a phase issue.  Since they go through a conversion to digital then back to analog, there will be slight latency.  So definitely take some measurements in order to try and get them more phase coherent to the mains, which can be difficult since the mains might need to be delayed back to the subs to compensate, but that will depend on placement in the room, etc.

[77SunsetStrip]

My 2 cents and experience.  Switched to a Dayton Audio Subwoofer Amp with DSP.  Many measurements with REW, adjustments, and listening have yielded improvement over Subwoofer Amp with no DSP.  Have been considering a DSP unit with Dirac live.  However, skeptical introducing more signal manipulation into my system will improve overall sound quality, measurably and audibly.     

Performed full range measurements with REW then generated EQ settings.  Used those EQ recommendations to adjust a 31 band analog EQ.  No adjustable Q so not a perfect solution, but did move in positive direction.  Achieved a good REW FR curve.  After several hours of listening identified the good and bad of FR following the Harman Curve.  Made EQ adjustments until pleasing to my ear.  Will measure FR after more hours of listening just to know if my by ear EQ tweaks changed the FR much.

[HAL]

THROWBACK,
Since you are using the A370PEQ servo amp, here is the instruction sheet to work from:

http://www.rythmikaudio.com/download/PEQ_quickguide.pdf

These might be too basic instructions, but might help.

When I had one, here is what I did for use.

The amp has 3 sections that are setup.  First is the LF bass servo settings and filter extension for the high pass section.  I used 14Hz and high damping as it gave the lowest frequency extension for the OB servo subs.  If you are using a turntable, might be better to use the suggested setting with the rumble filter.  That is one set of listening checks to watch for sub driver movement on warped records. 

Second is the low pass frequency controls and Delay/Phase. The dots on Crossover control are every 10Hz in f-3dB. These are in tandom with the subwoofer control switches.  Setting the crossover f-3dB to the frequency you want and then set the subwoofer Low Pass switch to either one of the preset of 50Hz-24dB/Oct or 80Hz-24dB/Oct setting, or set it to EXT/12 to use the f-3dB control.    This is the low pass -12dB/Oct filter.  You use REW to tune the sub crossover to the mains for the smoothest response at crossover. If you are using an analog source, The switch settings for removing any TT rumble are also shown on the info sheet above.

Use the Delay/Phase control to adjust for highest bass output at your seating position. 

Here is the Rythmik description of setting the Delay/Phase control for the servo amp:

http://www.rythmikaudio.com/phase1.html

Since the description states a linear phase filter is in use for Delay/Phase adjustment, there is a DSP with ADC/DAC in use.

The Parametric EQ (PEQ) section allows setting for one room mode frequency as measured by REW.  Typically the highest peak in the frequency response below the f-3dB cutoff frequency you choose.  As stated above, typically you only want to drop a peak and not increase a dip in frequency response.  The Bandwidth control is the Q of the filter.  This is set to the width of the peak you want to cut.  You want to try matching the control so you cancel as much of the peak as possible without affecting the other frequencies around the peak.  The gain is set to the opposite value of the peak measured.  If the peak is 3dB, the Gain would be set to -3dB as a simple example.  They all interact. An easy way is to turn off the main speakers and with REW measure the response.  It will give PEQ filter settings for EQing the room.  You can use those to set the PEQ control to some extent.  Then remeasure with REW once settings are done to see if that flattens out the response.  It is an iterative process since the Bandwidth control has no calibration marks.

With a DSP, you can typically do more Parametric EQ settings than the single one on the A370PEQ.  If the main speakers are in front of the subs, then Time Delay from a DSP is useful to delay the main speaker signal to integrate the impulse response of both speakers.  If they are both at the same distance from the listening seat, then Phase setting is should work.

If you have REW measurements of the subs at the listening position, might be worth posting to see what is happening.  If you do one of the subs, mains and both for just one channel at a time, might find some ways to help with settings.

Hope that helps.

[THROWBACK]

Good stuff, guys. Thanks. I swapped out my Mini-DSP and went back to the A370PEQ. I have only an old Stereophile (1990) test CD with pink noise and warble tones to 200Hz and an old Radio Shack LS meter. But even with the crude settings (I had to guess a lot), the sound is much more coherent, alive, natural and juicy than it was with with the DSP. I'm going to get ahold of some better measuring equipment so that (maybe) I can refine my settings, but already I can more than live with what I have.