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help using an SPL meter


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14 replies to this topic

#1 of 15 OFFLINE   david*mt

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Posted December 27 2004 - 04:02 AM

I just picked up the analog SPL meter at Radioshack. It says on the box that I should use it with an equalizer. What exactly is an equalizer and do I really need one? And can someone tell me in a nutshell how I use the SPL meter to calibrate my speaker volumes? I already have the DVE disc but am not exactly sure how to use it.

#2 of 15 OFFLINE   Jeff Gatie

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Posted December 27 2004 - 04:11 AM

A Quick Overview of Home Theater Calibration

No, you do not need an equalizer for this level of calibration. DVE also has a guide to using the SPL meter in it's presentation on calibration.

#3 of 15 OFFLINE   Eric C D

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Posted December 27 2004 - 04:14 AM

There's two things to do with the SPL meter. The first you can do with the items you have: balance the volumes from all your speakers. Run pink noise through each channel and get the volume at your sitting location to be equal. Let's see: set the meter to SLOW C weighting. For a little nuance, put the meter about where your ears are, and point it up at about a 45 to 60 degree angle (so that all the speakers it the mike at about an equal angle).

The second thing is to measure the frequency response using a frequency sweep. Then you can correct for humps or dips using an equalizer. For now, you can figure out if you want one by running the test with your SPL meter, but you won't be able to fix it unless you buy the additional gear.

have fun,

#4 of 15 OFFLINE   david*mt

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Posted December 27 2004 - 04:56 AM

My receiver is the Yamaha HTR-5560 and one thing that I have noticed is that I cannot adjust the volume of the main speakers, only the center and the rears. There is, however, a way to adjust the left-right balance between the main speakers. So am I supposed to get the main speakers equal in volume first, and then adjust the center and rears? I still am not sure how to adjust the subwoofer. My sub is the Onkyo SKW-210. It doesn't have a way to adjust the crossover frequency only a knob in the back that changes the volume. How exactly do I calibrate my sub?

#5 of 15 OFFLINE   Ronneil Camara

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Posted December 27 2004 - 05:30 AM

Hi Eric,

This is interesting. I have an AVIA disc. I think it's in Chapter 7 that you can really start audio calibration. Anyways, I just use the selection in the main menu such as Left Front channel, Right Front channel and so on. I use the test sound included in those buttons. Is this pink noise? Anyways, I also set my radio shack spl to 80 in the dial. I also changed my receiver main volume to 0. Turned off all bass and treble setting. Brought back each channel's volume setting back to 0. Then I started the calibration. I set my Left front to 85db and the remaining speakers to 85db too.

I also got very interested when you mentioned "frequency response using a frequency sweep." Where can I find this in the disc? And you mentioned that I won't be able to correct this unless I buy another gear. What's that gear?

Thanks. Posted Image

#6 of 15 OFFLINE   Eric C D

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Posted December 27 2004 - 05:51 AM

Cavat emptor: I'm not a pro at this - there's a lot better people around here. I do have the Avia disk, and I believe you'll find the noise listed as "pink."

From "Sounds Like? An Audio Glossary" by J. Gordon Holt, July 1993

Pink Noise - Random noise (hiss) that has equal energy in each octave.

White Noise - Similar to pink noise, except that white noise contains equal energy at each frequency point.

Re audio calibration: Don't worry about setting everything so that the 0dB setting for your receiver is 85 dB. Disks vary in volume anyway. Use whatever overall volume you like to listen to and even out all the speakers. A good pink noise input is the only way you'll be able to level-match the subwoofer because the sound out of the sub is nothing like the other speakers.

You should be able to find a LF Sweep for each channel (200 down to 20 or maybe even 10 - I forget). If you have that channel set as small, then the output will go to the subwoofer. You can't correct unless you have an equalizer. Let me take that back - you can make some changes by moving the subwoofer around the room as well, or by changing some of the contents of the room or treating the room for acoustics. But in home-sized rooms there is usually a frequency hump where the wavelength of the sound is the same as the room dimensions - length, width, and height.

Some subs come with an equalizer built in and some processors have equalization. But lots of people use an additional piece of hardware - either a band equalizer where you set each specific frequency band, or a parametric, where you set the frequency, bandwidth, and correction.

If you run the sweep, you'll know if you have a room mode. It can jump over 10dB louder or more. If you do, then I recommend getting an eq. Flattening out the response will allow you to both hear the other parts of the LF octave from your sub and (surprisingly!) to turn UP your subwoofer louder because that one frequency isn't overpowering the room. You'll really start to like those 20-30 hz effects once you can hear them over the 40-60 hz humps and you can turn it up enough to pressurize the room. (I was watching ROTK EE Part I last night. Posted Image)

enjoy!

#7 of 15 OFFLINE   Eric C D

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Posted December 27 2004 - 05:54 AM

David, Yes, I'd set the balance before doing the center and surrounds. Then try to keep from touching the balance setting after you adjust everything else.

good luck,

#8 of 15 OFFLINE   Eric C D

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Posted December 27 2004 - 05:57 AM

P.S. to all - read the link Jeff suggested!

#9 of 15 OFFLINE   Jeff Gatie

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Posted December 27 2004 - 06:27 AM

Quote:
Re audio calibration: Don't worry about setting everything so that the 0dB setting for your receiver is 85 dB. Disks vary in volume anyway. Use whatever overall volume you like to listen to and even out all the speakers. A good pink noise input is the only way you'll be able to level-match the subwoofer because the sound out of the sub is nothing like the other speakers.


This is true, unless you want to calibrate to true reference level. If you want to establish a reference volume level, you would calibrate to 85dB (Avia) or 75dB (VE or most receiver tones) and note the master volume level after calibration. This would be your "reference level" volume setting, i.e. the volume level that produces a reference level tone from each speaker. Some receivers (Denon for one) make it convenient to calibrate reference level to "00dB", making it easier to calibrate and easier to remember reference level. Denon does this by allowing you to enter "calibration mode", wherein the volume is frozen at "00dB" and the speaker level adjustments are toggled on the screen, thus combining "00dB", reference level calibration and speaker level adjustments into one easy to follow setup mode. This is the method I use on my Denon.

#10 of 15 OFFLINE   Ronneil Camara

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Posted December 27 2004 - 06:46 AM

Likewise in my Yamaha, main volume is frozen at 0db. But I can still toggle each channel's volume. I'm very happy to have that feature. Posted Image

I actually placed my sub behind my rear sitting position, left corner. That's where I found where the sub is really nice. But as I move closer to my television, the sound on the sub is decreasing. Is this normal? And as I go back to my listening position again, I start to hear the sub back to normal again.

#11 of 15 OFFLINE   Jeff Gatie

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Posted December 27 2004 - 07:58 AM

Quote:
I actually placed my sub behind my rear sitting position, left corner. That's where I found where the sub is really nice. But as I move closer to my television, the sound on the sub is decreasing. Is this normal? And as I go back to my listening position again, I start to hear the sub back to normal again.


Physics states that as you get farther away from a sound source, the apparent volume decreases. As you move closer towards it, apparent volume increases. This is why we calibrate from the optimum listening position, often called the "sweet spot". Mine is directly in front of the display and sitting right between the surrounds, on my main couch. Move away from the sweet spot and the apparent volume of each speaker changes (as does the viewing angle/apparent resolution of the display). All viewing positions that are not directly inside the sweet spot will see slight changes in volume and image. The farther away, the greater the differences.

#12 of 15 OFFLINE   Ronneil Camara

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Posted December 27 2004 - 05:28 PM

Ok, but what about in movie theaters with big screens, such as the once we pay for $7-$9 per movie? How come, we got plenty of chairs there and I think that even if we sit on different location, the sound will still remain the same. How do they do it?

#13 of 15 OFFLINE   Jeff Gatie

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Posted December 28 2004 - 06:33 AM

Quote:
Ok, but what about in movie theaters with big screens, such as the once we pay for $7-$9 per movie? How come, we got plenty of chairs there and I think that even if we sit on different location, the sound will still remain the same. How do they do it?


It really does not sound the same. The further you sit from the front, the lower the volume is for the center, mains and sub. Theaters do utilize multple surround speakers, though. Take a look at the Dolby website, it explains it.


Dolby Theater layout.

#14 of 15 OFFLINE   Eric C D

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Posted December 28 2004 - 09:04 AM

Another note: the sound drops in relationship to the *ratio* of how far you move. Is your rear sub placement near to your seat? If you are normally 2 feet away from your sub, moving 2 feet more means you're twice as far away from the speaker. Of course, room reinforcement changes this effect, but I'm talking nearfield only.

The movie theater speakers are actually quite a distance away from your seat, so moving a few seats doesn't change the volume very much.

But sit in the front of a theater, and the front speakers will definitely be louder in proportion to the surrounds, and vice versa.

Take care,

#15 of 15 OFFLINE   Edward J M

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Posted December 28 2004 - 12:33 PM

The DVE disc has a flaw in the subwoofer calibration tone. See the hotlink in my signature block for details.

Long story short - depending on your sub and room, DVE will show anywhere from 10-15 dB hot on the sub calibration tone. So if you go 75 dB for the speaker channels, go 85-90 dB for the subwoofer. It will sound crazy during calibration, but it will work out OK with music and movies.

Alternatively, you could use Avia or the AVR test tones instead.
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