View Full Version : how to aim SPL
12-14-2002, 01:37 AM
i have the SPL and the instructions. What i don't know is how to point the meter. I will mount it on a tripod should it be pointed at each speaker in turn? Or should it be left stationary? And if stationary pointed forward toward the front or cealing?
12-14-2002, 08:33 AM
1) toward the front
2) halfway between the mains
3) at head height when seated
4) angled 45 degrees up from the horizontal
5) distance from the mains should be at the key listening position
A tripod is very good. Use C-weighted slow response setting. If it is a Rat Shack model, it will read 2 dB low on the subwoofer test tone - keep that in mind when calibrating.
BTW - welcome to the forum!
PS - Damn nice system ya got going here!
12-15-2002, 04:25 AM
This worked FINE
The amp in one main died, CC maintenance and POLK parts we are as good as new. The controls on the speakers are NOT very accurate. The meter helps in getting them setup. I don't know how anyone can setup a system without a meter.
12-15-2002, 12:05 PM
WTF IS A SPL!??! and WTF is a SPL meter?
12-15-2002, 01:13 PM
SPL..........Sound Pressure Level
SPL Meter ....Measures SPL from usually a fixed position, usually in our needs from the sweet spot.
Not all speakers are created equal...Or....are from the the same distance from their location to your ear. Like setting a delay....helps ensure you are getting similar volume..or pressure levels from each speaker reaching your ear all at the same time.
That's my meager understanding of the whole gig...anyone want to add...
12-15-2002, 01:14 PM
SPL meter = Sound Pressure Level meter
This device allows you to calibrate your individual speaker decibel levels to properly match. I got a SPL meter and it made a huge difference. My center channel had to go +2 db, and my surrounds +5 db. The sound field in my HT setup is now HUGE and impressive, it seems like the room is one large speaker and you can't localize where the sound comes from. :D
All I did was buy the Radio Shack $35 analog meter and use the sound calibration mode in my receiver -- it was more than worth it.
12-15-2002, 02:28 PM
I was not aware of the sub being 2dbs low. Can you please clarify. Do I want to increase the sub to make them match or should the sub be -2db.
i.e. If the speakers level out at 0 should the sub be +2db or -2db to match.
I thank you in advance for any advice.
12-15-2002, 02:52 PM
It's impossible to properly set-up and calibrate a Home Theater without using an SPL meter.
I proved this Mantis and our Head Tech when I came to PA because they were all using there ears to set-up them up and I showed Dan that you couldn't.
We did a test at his house first I let him calibrate his system with his ears and he raised and lowered speakers and when he was finished I showed him that he was off 2-3 db on every channel. So then we properly calibrated his theater system using my meter and now the whole company uses SPL's.
What you need to do is stand behind your main seating position and slightly off center and hold the SPL at arms length and at the same height as the listeners ears and tilt the meter at a 45 degree angle at calibrate each speaker to a DB level of 75 DB and I have found that putting the sub at 70 DB works best in most applications. Some people swear by setting the sub to 80 DB but I always seem to think the sub is overpowering.
Keep in mind to that everytime you move a speaker or add furnishings to your room or even unplug a speaker wire or interconnect you really should meter the room again. I tend to meter my system at least every two weeks.
12-15-2002, 04:51 PM
Just curious, how accurate is the little Rat Shack analog meter?
12-15-2002, 06:09 PM
Hey Russman, I had a buddy of mine that had a big fancy Digital version.(I don't remember the brand)..told me ( with a big puffy chest) that there was no way that I could setup my rig accurrately with the RatShack analog SPL. So I had him bring his Digital over ...and Lo and Behold my cheap-o analog WAS pretty much on the money....I think the rear right was +1-+.5 off or somthing like that depending exactly where you had tha meter.
So in my experience...more isn't always better...but i've said that before....
My 2 Cents StuffMD
12-15-2002, 10:37 PM
I have both the Rat Shack meter, and a professional grade Bruel & Kjaer meter with the calibration test tone generator. The B&K is factory certified accurate, and I calibrate it regularly.
Russ - the Rat Shack meter is actually pretty accurate above about 50 Hz. Below that, it's pretty whacked.
Add the following dB at the noted frequencies to get the actual output.
So, Schumach - to answer your question - the meter reads about 2 dB LOW on the typical sub test tone (around 40 Hz), so 75 dB on the meter is actually 77 dB.
Liv4Fam - a tripod is better than standing. It has better repeatability, and it allows you to not block the rear surrounds with your body. Experts actually recommend crouching next to the meter (or lying on the couch) while it is mounted on the tripod.
Test tones on the receiver are good, and a calibration DVD, like Avia or Video Essentials is even better since it processes the signal through the DVD player. ALL channels (including LFE) should be set to the SAME volume.
Many prefer the sub a tad hot (i.e., a bit louder than the other channels) for moderate volume HT playback and that's fine - I run mine about 2 dB hot. At very high volume HT playback, this can overstress the sub, though, so be careful.
In addition to properly calibrating your system, the Avia or VE DVD also allows you to determine what master volume setting will provide you actual reference level playback in your HT room.
As defined by Dolby Labs, "Reference Level" is 105 dB peaks from any surround channel and 115 dB peaks from the LFE channel. If you set your speaks to small, this becomes 121 dB peaks from the LFE channel.
The Avia disc is mastered 20 dB below reference, so at the correct master volume level, the test tones will be 85 dB at the listening position. The VE disc is mastered 30 dB below reference, so at the correct master volume level, the test tones will be 75 dB at the listening position.
Be aware that most (nearly all) systems cannot safely play back at the true reference master volume setting, so don't try it. I recommend 10-15 clicks below the reference master volume setting for actual comfortable playback that won't ruin your ears or your sub.
12-16-2002, 03:51 AM
Thanks Doc! I hope to find a RatShack SPL meter in my stocking for X-mas. I knew the bottom fell off on those and you saved me some research.
I'd always been a "do it by ear" kinda guy, but have been bitten by the DIY bug and need to do some testing. I also have my hearing tested on a regular basis and can throw the results into the mix. Damn the guests.
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