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TOPIC: 2x4 LFE Edition miniDSP (High Voltage IO)

2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18795

  • Stereodude
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How about a special LFE edition of the 2x4 miniDSP with higher I/O voltages? Say 8Vrms, like the bigger units.

The miniDSP has fairly unique capabilities for being used as a subwoofer EQ. It allows filters down to 10Hz (most competing units stop at 20Hz), and can work at even lower frequencies if you use the advanced biquad filters. Unfortunately, the 2x4 units don't have the voltage headroom to accept the voltages found on the LFE / subwoofer output(s) of modern receivers. The voltages are way beyond what the 2x4 unbalanced and 2x4 balanced units can accept before clipping if you listen at reference (0dB). This is mainly because by design the LFE / subwoofer output has 10dB additional output capability when compared to the other full range channels. That equates to 3.16x times the voltage, and .9Vrms or 2.0Vrms just isn't enough.
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18797

  • ejh2854
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+1 to this suggestion... I've had good luck with the standard 2x4, but this would be a lot more optimal for LFE.

Build it, and I'll buy it!
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18802

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One more thing that would be useful in a LFE Edition for some people is the ability to set longer delays. 7.5mS isn't always enough for people who are scattering subwoofers around their room when they have a large room or are using horns. I realize the max delay is dictated by the amount of RAM in the ADAU1701, and I'm not sure if there is a similar part with more RAM, but it would be nice if possible.
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18803

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While we're talking wish-list additions to this product... perhaps some additional thought given to mitigating the power-off thump; my 2x4 can be brutal in this regard, to the point that I leave it powered continuously as self-defense.
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18818

+1
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18848

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+1
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 5 months ago #18898

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+1
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 4 months ago #18961

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Sorry guys for the late reply. It's indeed a great idea.
While I understand the fact that some AVR output +10dB hotter (i.e. miniDSP input would need to be able to accept that kind of level), in a consumer audio settings, I just can't wrap my head around why you'd want to have 8Vrms out from the miniDSP? Only ProAV amps (i.e. in a configuration where you'd want to drive 100m long lines) would ever need that kind of level. Most (if not all) amps actually have input sensitivity switch where you'd be able to switch the sensitivity to a normal level (e.g. 1.4Vrms) for full rated power (check your amp). Sure you could feed 8Vrms to an amp, but it's less than idea when it comes to Signal To Noise Ratio (i.e. gain structure). So my thinking is actually, 8Vrms in makes sense, 8Vrms out, I don't get it esp that I don't believe we're talking of running LiveSound setup accross a field @ Glastonbury :-) Please clarify if I'm missing something here..

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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 4 months ago #18973

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devteam wrote:
Sorry guys for the late reply. It's indeed a great idea.
While I understand the fact that some AVR output +10dB hotter (i.e. miniDSP input would need to be able to accept that kind of level), in a consumer audio settings, I just can't wrap my head around why you'd want to have 8Vrms out from the miniDSP? Only ProAV amps (i.e. in a configuration where you'd want to drive 100m long lines) would ever need that kind of level. Most (if not all) amps actually have input sensitivity switch where you'd be able to switch the sensitivity to a normal level (e.g. 1.4Vrms) for full rated power (check your amp). Sure you could feed 8Vrms to an amp, but it's less than idea when it comes to Signal To Noise Ratio (i.e. gain structure). So my thinking is actually, 8Vrms in makes sense, 8Vrms out, I don't get it esp that I don't believe we're talking of running LiveSound setup accross a field @ Glastonbury :-) Please clarify if I'm missing something here..

DevTeam
I can't speak for all the posters, but I wouldn't see 8Vrms output as necessary. The ~4.6Vrms (measured) that the current balanced 2x4 unit does in a balanced config seems adequate. I just figured that if you increased the IO rail voltages for the input, the output would then be equally capable since it's connected to the same voltage rails.

FWIW, I've measured both Onkyo and Pioneer receivers (fairly high end units) to be able to output about 22Vpp on their SW output, where as a high end Denon unit ran out of steam about 12.3Vpp.

Also, maybe the lowering sampling frequency would be useful for a "LFE edition" to avoid overshoot on very low frequency filters?
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 4 months ago #19055

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@ Stereodude,

While at the input one can easily so called "pad" the input to support very high level, you'd need a +/-15V split rail to do 8Vrms. that's not at all the same. 8Vrms is circa 22Vpp so indeed I really wonder why in a Hifi setup one would need that kind of level.. but then again maybe I'm missing something. :-)

Low sample rate can indeed be done. That's not hard providing the right DSP is used..

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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 4 months ago #19071

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devteam wrote:
8Vrms is circa 22Vpp so indeed I really wonder why in a Hifi setup one would need that kind of level.. but then again maybe I'm missing something. :-)
It's really just simple math. The LFE channel is rated for 115dB vs. 105dB for the main channels. That's 3.16x the voltage right there. Most of the units I've measured seem to put out about 1.5Vrms from the main channels for a 0dBFS DTS signal when played back at Reference with a channel trim of 0dB. Do a little bass management of a coherent signal from a few channels to the subwoofer output and the magnitude of signal gets even higher. If someone wants to run their bass "hot" and turns up the SW channel trim, or listens above Reference you end up with a really high amplitude output from the receiver (or clipping).
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 4 months ago #19074

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To run bass hot, it's better to increase the subwoofer gain (on the subwoofer itself, that is).
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?
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2x4 LFE Edition miniDSP (High Voltage IO) 4 years 4 months ago #19075

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Stereodude wrote:
It's really just simple math.

Actually it's not the arithmetic you claim, but algebra: preout signal levels for mains at a given listening position SPL depend on amp gain, speaker sensitivity, and the "liveness" of the room. And likewise LFE line level signals depend on the sub amps' gains and efficiency of the cabs.
Last Edit: 4 years 4 months ago by DS21.
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