Reference SPL's 'VS' All Channels Driven...

[Trevor Schell]

Hi!,,

When we calibrate our systems to reference level, we are running pink noise to each channel seperately to do the calibrations..No problem here.

Now when an amplifier is playing back material with all 5 or 7 channels driven, the wattage output per channel normally drops and in some cases can be a very significant drop.

With this,,would it mean that even though your system was calibrated to refernce per channel,,are you really experiencing reference level volumes when the 'Volume' level on the receiver is set on the Calibrated reference location(Usually '0')when all channels are driven simultaniously?
Maybe it would depend on the power supply and quality of the particular receiver?

Any thoughts on this.?

Thanks,




Trevor
My HomeTheater S.E.
Sonically Enhanced
C5

[Crimson]

Trevor,
I would have to agree with you in that the amplification section of receivers may be put to the test when reproducing soundtracks at reference levels with all channels driven. On the other hand, higher efficency speakers may pose no problem to such a setup. IMO, the only way to tell is to hear for oneself. If it tends to sound strained, compressed, with a lack of dynamics before actually distorting, then you are probably right.




Q.

[Andrew Pratt]

well yes and no..try taking an SPL reading when all channels are being given a signal. Remember that adding two signals are playing the same tone they will increase the over all volume by 3 db...now play all five and it should be well above reference level...BUT this is playing the same tone through all 5 speakers at once..this doesn't happen in movies etc since each speaker is mixed independantly. So to answer your question calibrating each channel to ref level should mean that you're still at ref level during movies...unless of course your amp can't handle that much current in which case you need a larger amp with more head room to hit ref level cleanly.

[Bob Santos]

Wow Andrew, I'm impressed.
One question though. If all channels are calibrated seperately at 75db, then you play the same tone through all of them at the volume position that you calibrated each to 75db at why would each additional channel above just one add 3db?

[John Holmes]

If a given power supply is anything like those in the television industry, only god knows what it will do under given situations.

And I would venture to say that, most people have miss match speakers (some of different impedence) which I'm sure will make the same amp perform aleast slightly different. So, I would not be surprised that many of us may not know the answer to this...or have been lucky enough to hear it cleanly.




"I came here, to chew bubble gum and kickass. And I'm all out of bubble gum!!!" My DVD's

[Andrew Pratt]

well we have to assume this is a perfect world since you're right each speaker would have to produce the same signal and in the same phase with no cancelation effections or room gain etc. Also when all channels are driven there won't be enough current in a receiver to drive the speakers as loud as when driving a single channel. But assuming all that were true when you double the volume you increase the SPL by 3dB. Remember that dB is a log scale not linear so adding volume doesnt mean the numeric value doubles.

for example...

1 watt into a 90 db/watt effiecent speakers will give you a 90dB reading on your SPL meter. in ordre to get the volume twice as loud you need 10 times the power so you're now sending 10 watts into the same speaker and getting a reading of 93 dB.

[GregoriusM]

Andrew: Unless I'm right out to lunch, a 3 db increase is not doubling the volume.

I agree that you need 10 times the power to double the volume. Known that for a long time, but when I was calibrating my system with a "friend's" SPL meter, a 3 db increase around the 85 db level was certainly not DOUBLE the volume.

Or am I outside in winter wearing only shorts?

... Greg

P.S. Like I said in another post, ALWAYS borrow calibrating equipment, never buy it yourself! ;-)

[Trevor Schell]

It makes sense that all channels would never be driven simultaniously during a HomeTheater application so they drop may not occur.

The reason I posted this was for the fact that when I had the NAD,,it was calibrated to reference levels and I always watched/listened to DVD's at the reference level. I did not find this too loud at all. Many times I would wonder why people would say that reference was too loud and thought we were crazy to listen at those levels.
Now with the Denon 5800 it is a total different Story as reference is very loud,,In fact I have found -10 to -8 as the level that i enjoy the most and rarely turn it up to reference at all. ,,So my NAD was never really acheiving a true reference Volume as I had thought that it was...but why..The Nad was 70 watts per channel while the Denon is 170 watts per channel.,,The NAD must have been maxed out and just did not have enough oomph to drive the Paradigm Studio's..




Trevor
My HomeTheater S.E.
Sonically Enhanced
C5

[John Kotches]

Gregorius,

I'm a little late replying to your post, but here goes.

There are two items at work here, physics and your perception. From a physics perspective, doubling the volume is a 3dB increase (10^ delta dB/10)
[10 raised to 1/10th of the change in dB].

Calculating the dBs for a change in power is done as the inverse [10 x log(10) delta Power].

So Andrew is absolutely correct.

However, as Andrew also pointed out, our perception is logarithmic and as such it takes a 10dB change, which equates to a 10-fold power increase for us to perceive a doubling in apparent volume.

Regards,




---
Editor, PC/Home Theater
Secrets of Home Theater and High Fidelity
My Home Theater
NEC LT-150 specific page.

[Lexman]

Trevor, it really sounds like maybe you weren't reaching reference levels previously. Or your just experiencing better dynamics with this setup, maybe...

Good thread,

Lex

[Andrew Pratt]

phew thanks john I figured that was right but wasn't 100 percent sure...

[GregoriusM]

Hmmmmmmmmm...... Okay, I get the 10 db change required to "perceive" a doubling in volume, to the user.

In physics, a 3 db change is a doubling in volume, to what?

Now, I guess, I need to ask what the term "volume" means? Is that not to "the user"?

Or is this kind of along the lines of "if a tree falls in the forest, does it make any sound"?


... Greg

P.S. I appreciate your patience with this one! ;-)

[Tom Vodhanel]

>>>for example...

1 watt into a 90 db/watt effiecent speakers will give you a 90dB reading on your SPL meter. in ordre to get the volume twice as loud you need 10 times the power so you're now sending 10 watts into the same speaker and getting a reading of 93 dB<<<

every time you 2x the input voltage, the dB will increase about 3dB until something starts to fry.

if

1w=90dB

then

2w=93
4w=96
8w=99
16w=102

ect.


Good topic too...underscores another reason to let *bass management* reroute all the real low bass(which sucks a TON of amp headroom) to a dedicated woof or 2.

TV

[Andrew Pratt]

Thanks for chiming in Tom and welcome to the guide. Hope to see you around more frequently

[Trevor Schell]

Welcome aboard Tom!!,,

Now you are probably correct that the small settings may help to provide more Headroom, but I find setting to large expands my front soundstage significantly..maybe because I experience slightly higher DB outputs from the mains at this setting VS the small setting,,Not sure!.




Trevor
My HomeTheater S.E.
Sonically Enhanced
C5