20 replies to this topic

[markm1111]

I am looking at using 2 balanced miniDSPs to feed low frequency signals to the amps driving a pair of passive subwoofers. The miniDSP setup is required as I want to take both the LFE signal from an AVR, and unbalanced signal from a 2 channel pre, and switch between the 2.

On reviewing the miniDSP forum, I find that the miniDSP seems to cause somewhere betwen 1.5ms and 4ms delay. I'm not exactly sure what that means in a real world situation i.e. would this be noticeable, or is it well below human perception? It also occurred to me that any normal active subwoofer may introduce an element of delay, as they take a full range signal and cut it back to the chosen xover point, or am I misunderstanding something?

I know that no delay is the ideal, but what tolerance do we have for delay? Are there any other solutons out there that don't introduce as much delay as the miniDSP?

Thanks

Edited by markm1111, 27 March 2012 - 09:55 PM.

[Monkeyboi]

4mS time difference over a short distance (like you'd encounter in a typical listening room) is usually noticeable. To give you an idea, a reflected signal of 30mS delay is heard as a distinct echo.

Cheers,
Alan R.

Edited by Monkeyboi, 27 March 2012 - 10:05 PM.

[markm1111]

hmmm, that causes a problem then. I don't want to run everything through the miniDSP. Is there anything similar that has a lower delay?

[Arg]

I am looking at using 2 balanced miniDSPs to feed low frequency signals to the amps driving a pair of passive subwoofers. The miniDSP setup is required as I want to take both the LFE signal from an AVR, and unbalanced signal from a 2 channel pre, and switch between the 2....

Do what?

switch between.....? nah. I'm too dumb.

If you just mean you want to compare one sub runing off the AVR with another running off a miniDSP, bear in mind the AVR also causes a delay (it's a DSP too). You just don't know how much delay the AVR introduces.

[gainphile]

What is the frequency range?

You can calculate 4ms as wavelength. Then compare. 20 hz is like 17m so if it's a fraction of it, doesnt matter. Then also the room response. My gut feel it doesnt matter.

Delay is more problematic for tweeter range for example.

[markm1111]

Frequency range is likely to be about 20-25 Hz up to a maximum of 80Hz.

Arg, I will be running stereo subs. The miniDSPs are to allow me to integrate the subs for both 2.2 channel listening via dedicated 2 channel pre, and also use in HT with the source as the AVR

[Arg]

.....Arg, I will be running stereo subs. The miniDSPs are to allow me to integrate the subs for both 2.2 channel listening via dedicated 2 channel pre, and also use in HT with the source as the AVR

OK so for 2.2 you run the audio preamp into the miniDSP and its 4 outputs to L main, R main, sub 1, sub 2. No problem with delays.

And for HT you run the AVR's SW output into the miniDSP then to the subs. Calibrate the AVR speaker delays while the miniDSP is in circuit and any delay contributed by the miniDSP will be accounted for.

[Ando]

I run my mains full range ( not through my mini dsp ) but my subs are rolled off and equalised via mini dsp. I think this what you are asking about. Works fine as far as I can tell.
Cheers Mike

[markm1111]

I run my mains full range ( not through my mini dsp ) but my subs are rolled off and equalised via mini dsp. I think this what you are asking about. Works fine as far as I can tell.
Cheers Mike

Hi MIke. Yes, that is exactly what I want to do.

I don't want any extra filters between my Pre and the main speakers. I purely want to use the miniDSP to roll off the signal before it reaches the subs. The LFE output from the AVR is already rolled off at 80 Hz, with the range above that going through the HT bypass on the Pre to the mains. Any chance for some more informaiton on your setup? It sounds like it is what I am trying to acheioeve, but I keep running into conflicting or at least puzzling information.

Cheers

[Ando]

If you go to http://www.stereo.ne...o-note-at-last/ you can see a couple of pictures of my system. In the first one you can see one of the subs, sealed SEAS L26 Roy and most of the one of the mains , the 3 way not the panel with no drivers. I think there are some more pictures further down as well.
My pre has two outs. One directly drives the main power amp that runs the mains run full range, without any filtering, which means down to high 30's. The other pre out connects to the mini dsp which provides rolloff and equalisation for the subs. Roll off and equalisation vary with position of the subs in the room. The outs of the mini dsp drive the power amp that drives the subs.
This seems to work fine for me.
I think getting a smooth frequency response through the lower frequencies is probably the most important thing to consider.
Cheers Mike

[svenr]

@ markm11 - the delay of the miniDSP is not your main problem. You need to add delay to the main speakers anyway to achieve coherent summation of subs and main speakers in the 80Hz crossover region. Given that your sub has a very small bandwidth of 20..80Hz, it's groupdelay in the crossover region will be much higher than that of the main speakers. To match the phase response of the mains, you need to introduce additional delay anyway and can easily compensate for that arising from the miniDSP.

I suggest you get a software like LEAP and model the summation of the mains and subs. You will get a good feeling how much additional delay your mains need and whether your AV receiver can cover that.

[markm1111]

I am looking at almost the same setup. Thanks for the heads up.

[Arg]

Sure but the Ando setup has the delay issue you wanted to avoid - although he is not noticing a propblem. And svenr pointed out the need for delay on the mains due to group delay on the sub. So you need to be able to delay the mains. Enter miniDSP.

Edited by Arg, 28 March 2012 - 03:59 PM.

[markm1111]

@ markm11 - the delay of the miniDSP is not your main problem. You need to add delay to the main speakers anyway to achieve coherent summation of subs and main speakers in the 80Hz crossover region. Given that your sub has a very small bandwidth of 20..80Hz, it's groupdelay in the crossover region will be much higher than that of the main speakers. To match the phase response of the mains, you need to introduce additional delay anyway and can easily compensate for that arising from the miniDSP.

I suggest you get a software like LEAP and model the summation of the mains and subs. You will get a good feeling how much additional delay your mains need and whether your AV receiver can cover that.

I believe I can achieve enough delay on the mains via the AVR for the 80HZ crossover. For running 2.2, the crossover will be at 50Hz, but with no ability to delay the mains as I don't want to run them through the miniDSP. I wll check out the software you mentioned, but do you have any thoughts on the 50Hz crossover point? I am also not sure of what you mean by group delay, so I will have to investigate that as well.

Edited by markm1111, 28 March 2012 - 06:04 PM.

[Ando]

I was just idly reading a few other threads and I saw this one :http://www.stereo.net.au/forums/index.php?/topic/40542-ozmillsys-day-in-melbourne/page__hl__ozmillsy__fromsearch__1
Described there is a rather elaborate system that uses subs driven via a Behringer digital processor not in the signal path in same way as is being discussed in this thread. I would think the Behringer would have the same delay effect as the mini dsp. The system mentioned is apparently widely admired so I conclude I am not the only one who doesnt have a problem with this type of arrangement.
Also mentioned in the same thread is Keith W's system that uses DEQX to integrate subs. I wonder if the signal to his mains passes through the DEQX.
Cheers Mike

[svenr]

My experience with systems is that the deterioration caused by the presence of something like a miniDSP or DCX2496 in the signal path is widely outweighed by the benefits these devices bring once set up properly (using both simulation and measurements).

@markm1111 - 50Hz crossover needs even more delay than 80Hz, thus the situation of non-coherent bass reproduction will worsen in your 2.2 setup. If you could hand-draw a sketch showing all teh componets of the two system configurations, people could make suggestions how to use miniDSPs or other devices to allow correct system setup.

[markm1111]

My experience with systems is that the deterioration caused by the presence of something like a miniDSP or DCX2496 in the signal path is widely outweighed by the benefits these devices bring once set up properly (using both simulation and measurements).

@markm1111 - 50Hz crossover needs even more delay than 80Hz, thus the situation of non-coherent bass reproduction will worsen in your 2.2 setup. If you could hand-draw a sketch showing all teh componets of the two system configurations, people could make suggestions how to use miniDSPs or other devices to allow correct system setup.

Thanks Svenr, I will try to draw something up that shows what I am trying to achieve.

One thing does puzzle me though. The miniDSP or any similar device introduces delay, I assume because of the processing time. With any active sub, they take a full range signal and/or a LFE input, filter it, then use the filtered signal to amplify and drive the woofer. Why does separating out the filtering/crossover process all of a sudden make it harder? Or is this issue present with active subs as well, just accepted?

[svenr]

You're right - the hit & miss approach of crossover between subs and mains is the consumer industry standard. The issue exists for all so called "systems", unless they are designed based on a systems approach and include signal processing for mains and subs, prediction software that calculates the basic adjustable parameters for a given setup, and in-room measurements for placement and tuning.

[markm1111]

The devteam at miniDSP has come responded to me and have stated they believe the maximum delay is only 1.8ms, not the 4 quoted on the forum. More to think about...........

[svenr]

I assume you have basic measurement gear (ARTA or REW) if you think about using miniDSP in your setup. Its simple to measure the delay of the device once you got it.

[Nigel]

Regarding delay and bass freqs - 1 wavelength at 20 Hz is 17m and approx 50ms.
My question is..... how much of this long pressure/trough wave does the ear/brain need before it recognises the bass freq ?. Less than 1 cycle? more than 1 cycle? The answer to this may make delay corrections at low freq a moot point. Or not !
but absolute alignment of bass is probably not as important as say, room bloat. (New expression I just made up). My feeling is that time alignment is more important higher up, say mid-rage ?

Edited by Nigel, 02 April 2012 - 06:26 PM.