Reference Calibration Question and Confusion (1 Viewer)

[CollinMorphew]

I know there are a lot of threads with SPL calibration but I haven't seen anything with respect to the after results. I calibrated all speakers (7.1) with an SPL at 75db per channel using the Sound and Vision disk. Started at -40 on my receiver since it said a comfortable level to listen to cd's. I ended up up raising my channel levels anywhere from +4 (SB, SL/R) to +10 (FL/FR) to get each channel to the 75db. Then I put in a couple of discs (audio/video) and the SPL was measuring at approx 90-95 db at the same -40 mark. This means to get to the 75db calibration level I was at -60. My question is two parts. With the above information did I do this correctly and is this somewhat consistent with what others have seen/done and what would be my "reference level" volume setting with this type of calibration.

 

[Yogi]

I think you are confusing two different things. a) calibration at 75 db from internal test tones or a CD and b) Actual SPL levels during music/movies. The calibration is done at 75 db from your receivers internal test tones (or a CD). For that you set your SPL meter on slow C weighted response and turn up the volume until you read 75 db from one of your test speakers (say the FL speaker) then you go and adjust all the other speakers to match the output of this speaker. So you shouldn't have to turn all speakers up in order to attain 75 db. One of the speakers i.e., your reference speaker will be at 0 db setting (preferably FL/FR speaker) and the rest of them will be calibrated in reference to that speaker.

The next thing is when you calibrate at 75 db internal tones you will be hearing a headroom of 30 db (20 db if you used VE/Avia) in your musical and movie scores. So you could get peaks of 105 db from your channel. The Sub is supposed to touch 115 db!!!. So dont worry what you are hearing is normal. You calibrated your system to 75 db reference and when you listened to some music you heard 95 db levels. So dont worry about it. Just do another calibration like I said and you'll be all set (not that your calibration is wrong).

Hope that helps.

 

[CollinMorphew]

Thanks for the response--I never knew one speaker was to be set at 0 and then calibrate off that. Now, (if I'm understanding) my volume level on my receiver will change to approximately -35--this still means I will be running everything at 95db. The -40 with all speakers +'d was consistent 95 db--not spikes. Now at -35 I'll be at 95 db consistent. With this type of calibration, does that mean pushing ref level will be approx -25 on the receiver based on a calibration at -35?

 

[CollinMorphew]

I guess I don't understand headroom-I was very surprised at the 75 db calibration on test tones and then everything audio/video playing at 95db with the receiver on the same volume--I'm using S&V's disk which says to do this at 75db.

 

[Yogi]

The -40 with all speakers +'d was consistent 95 db--not spikes

Turn your SPL meter to A weighted Fast response and see if this gives your instantaneous SPL. This should give you a rapidly changing reading. With the slow response you are sort of averaging the SPL levels over a wider time interval, which could result in a constant SPL level.

If it is calibrated properly with the S&V disk to 75 db, that should be reference level right there. So in your case if it turns out that the master volume level of your receiver is -35 for a 75 db calibration. Then your reference level is at -35 db setting.

 

[jeff lam]

75dB isn't reference level, 75dB is used to measure because 105dB test tones would tear your ears to shreds. On the disc, the test tones are attenuated 30dB or 20dB to spare your ears the discomfort. That is the only reason. Some people get confused and think that 75dB is reference level. Reference level is peeks of 105dB, like I said before, nobody can comfortably play test tones at 105dB to take measurements.
Look here for more info on calibration and reference level:
http://www.hometheaterforum.com/htfo...highlight=avia

 

[CollinMorphew]

Thanks for all the input. I read everything on the calibration before doing it so I understood the reasoning and the levels of reference. I needed this to make sure I was understanding it correctly. I totally agree on the test tones--they were annoying enough at 75db. So, once all speakers are calibrated at 75db with test tones I am hitting 95 with spikes to 105db at the given -35 receiver setting. This means that after this calibration the -35 receiver setting is "reference level" in my particular environment? And--is this going to get really interesting, challenging and/or confusing when I start to install my 4 seperate amps I just got???

 

[Yogi]

Reference level in not one discreet level. It a range. Its when the softest passages in your movies are at 85 db and the loudest are at 115 db (from the sub). So when you have your receiver set at -35 db you are watching the movie at Reference Levels (that is if it is mastered at the right levels but lets not go there). For example if you watched LOTR at -35 db setting on your system you will be running for cover all through the movie.

When you install your four amps in your system recalibrate the same way you did now. As long as everything is calibrated to the same level you wont have a problem. The receiver master volume setting might be different depending on your amp sensitivity. But you dont have to worry about that. Just connect your amps and repeat the procedure and you should be fine.

 

[altan]

Please help me understand.

Lets assume I calibrate with VE for 75dB. Also, lets assume that to reach 75dB I'm using all my receiver/amp's power.

Does this mean that I can obtain reference levels OR do I really need an amp/receiver that can put out enough juice to make up for the 30dB (= 105dB - 75dB)?

Logically it would seem to be the latter... that (for 75dB) an amp/receiver better be able to juice out the additional 30dB.

Let me add one more thing. I realize that reference level means I'm setting up my system so the loudest that it can achieve is 105dB (through the mains) when volume is "set to reference". However, I'm interesting in understanding whether my receiver/amp can output 105dB given where 75dB ended up on the volume knob. I believe my receiver/amp must be capable of this additional 30dB or else it will clip... ie, if I get reference level at full output, then I will not get 105dB without clipping. Right?

Thanks in advance!

... Altan

 

[BrianJ>Y]

That's right Altan, you're receiver may not be capable of outputting 105db peaks CLEANLY. It could be heavily distorted or start slipping if you're reaching it's power limits. To reach "reference" levels of 105db peaks, you generally need 70-80 watts of clean power from your receiver. Whether or not you're receiver will do that is difficult to know for sure, btw, what receiver are you using?

-Brian

 

[altan]

I'm darn confused...

I've got the HK525, apparently 70watts of "clean power" per channel.

However, with my Paradigm Studio 60's, I need to have the HK525 at 0dB (on the volume knob) to get 75dB SPL via VE.

The darn volume knob only goes to +9. I would expect to be able to get +30 dB on the volume since I need +30 dB over the reference level of 75dB SPL to ensure I reach the 105 dB SPL peaks.

As you can image, I'm concerned this 70 watts is not enough. However, my calculations show I should get about 94 to 98 dB SPL with 70 watts. Assuming I listen at 10 dB below reference (-10dB on my volume knob), it's still hard to believe I'll even reach 95 dB SPL (105 dB - 10 dB) at peaks when (again) the volume knob only goes up to +9 dB (so from a volume knob point of view there is only 19 dB of headroom when I apparently need 30 dB --- and I've always been under the impression that you should turn the knob all the way up anyway).

So either I'm calculating something wrong, the HK525 isn't really 70watts, or I'm relying on the volume knob dB rating to much. (I do have an email from HK saying 0dB means 70watts output, but it's hard to know whether or not to trust support folks).

... Altan

 

[BrianJ>Y]

Altan,

If you calibrate using the VE disc and it turns out that setting your receiver to the 0db mark gets you to 75db then the 0db mark will NOW be your reference point. Meaning at the 0db mark on your receiver, you will hear 105db peaks, which is 'reference' level, when playing back an actual DVD.

I hope that clears things up for you, the most common misunderstanding with this whole calibration process is that people confuse the fact that when calibrating to 75db or 85db using either the VE,avia,or S&V disc, that same level will result in 105db peaks when playing back ACTUAL DVD's, not 75db.

In short, 75db using VE = 105db peaks with an actual DVD at the identical db setting on your receiver, in your case at the 0db mark.

-Brian

 

[altan]

Brian, Thanks for the response. I agree with you, however, I'm still concerned that things do not "add up".

Any HK525 users out there? What is your reference level on the volume knob?

... Altan

 

[AaronBatiuk]

with my Paradigm Studio 60's, I need to have the HK525 at 0dB (on the volume knob) to get 75dB SPL via VE.
The darn volume knob only goes to +9. I would expect to be able to get +30 dB on the volume since I need +30 dB over the reference level of 75dB SPL to ensure I reach the 105 dB SPL peaks.

NO!
You are confusing the volume dial with the amount of power that the receiver has available. One has nothing to do with the other.
Here's one way that you can estimate how much SPL you can put out with your speakers:
1. Get a good voltmeter (multimeter) that can read true RMS for AC+DC voltages at up to 20 kHz or more. My B+K unit will do this; many will not. Acutally, a cheapy analog meter should work great for this, if it has a very low voltage range (10 V or 5 V or less, so you can take an accurate reading!), just because the mechanical nature of the meter needle enables it to take nice average RMS readings. This is difficult with digital meters.
2. Play reference level through your speakers (75 dB SPL). Measure the RMS voltage at the speaker terminals. It may jump all over the place. Take an average. That is the average voltage that the receiver requires to put out an average SPL of 75 dB. Call this voltage Vref.
3. Calculate the (approximate) maximum voltage (RMS) your receiver can deliver using it's rating wattage (RMS).
P=(V^2)/R --> 70=(V^2)/8 --> V ~= 24 V
Call this voltage Vmax
4. Divide Vmax/Vref.
5. Calculate headroom by:
hearoom(dB) = 20 * log(Vmax/Vref)
For example, if your amp was delivering an average of 2.00 VRMS to your speakers at 75 dB, then you have 20*log(24/2)= 21.6 dB of headroom. The amp will begin to clip somewhere around the 75 + 21.6 = 96.6 dB SPL mark. Let's hope your speakers don't require 2.00 V to reach 75 dB.

 

[altan]

Aaron,

Awesome post! Thanks... I'll look into doing exactly what you said.

Not to belabor the point, but why is the amount of power the receiver has available unrelated to the volume dial? I've commonly heard people say a receiver outputs (in general) full wattage at 1 o'clock on the dial. Are you saying that there is no specific or guaranteed relationship? But they might "in general" be related?

Finally, is the output on the speaker wire AC or DC? (You wrote ...true RMS for AC+DC", which made me think of this)

Thanks again

... Altan

 

[AaronBatiuk]

Finally, is the output on the speaker wire AC or DC? (You wrote ...true RMS for AC+DC", which made me think of this)

Definitely AC. But most meters will "AC couple" or "DC decouple" their input when put in a normal AC range. This is done with a capacitor, which by it's nature acts as a low pass filter. So if you have an AD+DC function available, use that. If not, use the AC range. The capacitor shouldn't present a problem since any AC voltmeter is desinged to measure 50 or 60 Hz (quite low frequency) AV voltages, so you won't be losing much through that unintentional low pass filter. Another thing to watch out for: many cheap analog meters just use a rectifier diode at the input; this can cause a fairly significant voltage drop (around 0.6 V), which is why many don't have a low voltage AC range. Find a good digital unit or and analog one with a very low AC range (around 5 V or less full-scale).

 

[Jack_Geo]

Wait! Now I'm confused.

Should I:

1. Set my receiver volume to 0, then adjust the front left channel level to get 75db on the SPL meter? (then calibrate the rest of the speakers)?

OR

2. Turn my receiver volume up (or down) till I hit 75db on the SPL meter for the front left channel, then calibrate based upon that volume level reading on the receiver...adjusting the other channels up / down? (the volume level may be -27 or -14 or +3 or whatever in this scenario)

I've been doing #1...but after reading this thread I've got some second thoughts...

Thanks

Jack

 

[altan]

Jack,

Either #1 or #2 --- it does not matter. In either case you have a specific place on your volume knob that causes the SPL meter to read 75dB. And this specific place is where you woudld listen to achieve reference (105dB main) peaks.

My concern is that once I find this "specific place" on my volume knob, does my amp/receiver have enough power to reach 105dB peaks without clipping.

... Altan

 

[altan]

Aaron,

Ok... my voltmeter only had an AC setting. I used this setting (please let me know if this is not ok). However, the volt reading was too low to read when driving the speakers at 75dB SPL.

I changed the SPL to be 84dB SPL and got 1.5V on the meter.

So is the following correct

vMAX / vREF = 24/1.5 = 16
headroom dB = 20 * log(16) = 20 * 1.20 = 24.08

so in my setup I will clip around 84dB + 24dB = 108dB?

Thanks again!

... Altan

 

[LanceJ]

Just out of curiosity, what if a person were to simply turn up the volume on the front mains to their normal movie listening level when setting the other channel's levels? I.e., where explosions don't cause discomfort, etc.
Thanks.
LJ