I'm done with the SMS-1, it limits the output of my Submersives - Page 2

Wrong calculator. "Summing up to ten non-coherent or uncorrelated noise sources"

All bass sent to the subwoofer is coherent for all practical purposes.

Read the notes for that calculator.

"For beginners: non-coherent means the signals of the overdubbed channels are irrelative like a violin and a trumpet,
that means having no correlative relationship. Sometimes we say uncorrelated when we mean non-coherent."

Yes, but THX assumes you have 5 or 7 speakers capable of 105dB covering the entire frequency range. People who run their speakers as small require the subwoofer to pick up the redirected bass. That means the subwoofer must utimately be capable of something greater than 115dB.

If we were adding up 40Hz sine waves from every channel I'd agree that they're coherent, but how is a 40Hz and 65Hz sine wave coherent?

Further, 7 coherent channels at 105dB + a coherent sub at 115dB still doesn't equal 121dB. It's 125.14dB
5 coherent channels 105dB + a coherent sub at 115dB also doesn't equal 121dB. It's 123.236dB.
Edited by Stereodude - 1/3/13 at 11:20am

You only need three channels at 105 dB and one channel at 115 dB to get 121 dB via bass management (AKA electrical addition).


http://www.sengpielaudio.com/calculator-coherentsources.htm

The above makes the assumption that even the surrounds are cranking out 105dB. I realize this is all in the hypothetical but that's some crescendo.

Coherent means in phase.

Peaks of 40 Hz and 65 Hz sine waves will be 100% in phase at certain times even thought they are different frequencies.

So, that only means the calculated "coherent" SPL is correct what 1/25 of the time? The other 24/25th of the time the non-coherent SPL is correct.

That means if you use a signal generator with a simultaneous -5 dB FS 40 Hz sine wave and a - 5 dB FS 65 Hz sine wave, you will clip on a digital basis due to coherent signal addition of 6 dB.
Edited by J_Palmer_Cass - 1/3/13 at 11:51am

With 20 subs I would say I could barely manage those levels Pretty much he room felt like it was going to crumble, both with the SMS-1 in and out of the system

Man I really wish I knew what y'all were talking about here.
Makes me wonder how much more potential my system could be if I took the time to learn all this verbage.

Did you try raising the Volume past 15? It could be that, in your particular unit, Unity Gain is higher than 15. You might want to pose your questions/issues in the Official Velodyne Support Thread. http://www.avsforum.com/t/304306/offical-velodyne-support-thread There are some factory support guys who post there. They may be able to shed some light on the issue.

I no longer have my SMS-1. I took it out when I moved to Submersives and Audyssey XT32. It was no longer necessary. I probably never saw the limits of the SMS-1 because, at the time, I had a pair of JL Audio F112's. They were the limiting factor in that system, not the SMS-1.

Craig

I'd like to hear more about you clipping the SW ouput, call me curious.

Well, curious... I found all of my receivers will clip the SW output if you turn up the volume enough and have a sufficiently "hot" signal. I tested my Pioneer Elite SC-05, Onkyo TX-NR809, and Pioneer Elite VSX-84TXSi. Here's the output of a -0.01dBFS 40Hz signal DTS encoded into all 6 channels. The SC-05's master volume is at 0dB and the SW trim is at 0dB.

Don't bother fixing the SMS....Just sell it to me :D:D

Can you stop the clipping by lowering the master volume to any specific level while leaving the SW trim @ 0 dB?

Can you stop the clipping by lowering the subwoofer output trim to any specific trim level while leaving the MVC @ 0 dB?

Haha does the mbm really add to the experience?

On the SC-05, yes to both. On the VSX-84TXSi, no not with this particular worst case test tone.

I'm not sure on the Onkyo. I didn't test it as closely. I only checked it for maximum output before clipping with a different test tone (-0.01dBFS 40Hz sine wave DTS encoded in the LFE channel only).

Hmmm, you would be badly clipping the input of the SMS-1 with the use of those AVR subwoofer output jack voltage readings. Around 9 V RMS maximum readings if your chart is calibrated.

According to the thread below, the SMS-1 can only take an input of around 400 mV RMS when clipping starts.

http://www.hometheatershack.com/forums/electronic-processing-equalization-devices/6346-behringer-fbq2496-velodyne-sms-1-distortion.html#axzz2H0snJSms


"So for those owning the SMS-1, I would definitely set the subwoofer output on the receiver as low as it goes. Typically the subwoofer output can easily give a couple volts, and as you can see, it doesn't need much more than 0.4 volts to clip the input stage of the SMS-1."

I'm finding this interesting even though I don't have the knowledge to read Stereodude's graph. If i'm following correctly, the suggestion being made is to reduce the sub trim level on the avr and bump the lvl on the SMS-1? I think some or all AVRs go +10/-10 on the trim level so bringing it down to -10 and raising it on the SMS-1 will solve the clipping?

In the simple, equipment likes dome tops not flat tops and when one gets the hair on their dome cut, they get clipped.

Square wave, vs modified square wave vs full sine wave.

Well, it depends on how loudly you listen. If you listen at reference (0dB) even a setting of -10 on the SW channel trim will only reduce the voltage of a worst case amplitude signal like this to 4.48Vrms, which is still way beyond what the SMS-1 can reportedly handle.

Calibrated at 75db, the highest I would ever run the MV at would be -5

The scope plot is accurate. The SC-05 can output a clean peak to peak voltage of ~22.6V, which ~8Vrms with a sine wave. My 84TXSi has the same output capability. My Onkyo NR809 is pretty much the same also.

FWIW, the RMS voltage of that signal is listed on the plot. Keep in mind that RMS voltage is really not the right thing to discuss when talking about clipping since the RMS voltage changes depending on the shape of the waveform (it's effectively related to area under the curve). The measured RMS voltage keeps increase even as the waveform becomes more and more clipped. On the other hand, peak to peak voltage is always peak to peak voltage regardless of the waveform's shape and it doesn't increase as the waveform gets more and more clipped.

At least the balanced 2x4 MiniDSP clips at ~4.6Vrms [with sine waves] / 13.5Vpp and IMHO it should accept and output even high amplitude signals since they clearly can exist in the SW output. If the SMS-1 really clips at 400mVrms it's completely and utterly useless for SW equalization in any serious HT system and highly questionable for a 2.1 music setup.

Of course it's dependent on what receiver you have, but in the case of the Pioneer Elite SC-05, -5dB on the MV with -10dB on the SW level trim (as low as it goes) can still output a SW voltage of ~2.5Vrms (sine waves). The Onkyo 809 would fare a little better since the SW trim can be reduced to -12dB and its SW output isn't quite as "hot". It would be somewhere around 1.4Vrms (sine waves) This assumes you don't use some of the other LFE reduction options in the receiver.

Thanks Carp, interesting thread. I am almost positive I tested for this when I got my SMS years ago and was hitting the same max with or without the SMS in the chain, but I am curious to retest this now. I am also curious to test it with my multiple sub configuration since the first time I tested was with a single which should not matter in theory I would not think, but you never know.

Question...........I have one Y-cable coming out of my sub out on my pre-pro now, one end goes to my SMS and the other to my BK amp. Can I just unplug the BK from one end of this Y-cable and then use 2 more Y-cables attached to each end of the Y coming out of the sub out so I have 4 sub outputs? Any issues doing this? I would like to test this now after reading this thread to confirm (I hope!) my original findings and to see if going from 1 to 4 subs has caused this to change for any reason.

Thx