A sound pressure level meter (or SPL meter for short) is a commonly used accessory in the house of worship environment.
If you’re like me, you always have one sitting on or around the console to keep you honest. It is the first line of defense against fader creep. And when someone asks you if it’s louder than normal, you can smile, point to the meter, and say no.
Each week I turn the knob to my reference point of 90, set it on the console, and then forget about it until I turn it off at the end of the service. But how exactly does it work? What’s the best way to utilize its functions? Let’s have a look under the hood.
Overview
There are many SPL meters on the market, but most of them have the same basic features. The meter has a small microphone mounted to the body with either a digital or analog readout. Depending on the model, the display might include a dB reading, response setting, and/or weight setting. There is also a range setting that tells the meter the general level you think you’re running within 10dB.
Basically the meter works by converting the electrical energy created by the sound source coming in contact with the microphone into a decibel reading by using log tables and mathematic formulas. Since this is just a basic article, I won’t go into that much detail.
But if you want to go deeper check out the wikipedia article here.
Setting Up Your Meter
First set the range. If you’re not sure where to start, begin with the loudest setting and then move down until you get a reading. I run our services around 90-92 dB, so I set my range to 90. Remember the meter will show a readout as long as you are within 10 dB of your selected range.
After setting the range, choose the weighting. There are usually two options here: A and C.
“A” weighting is responsive to frequencies between 500 and 10,000 Hz. Using this mode there is a drastic cutoff of low and high frequencies. It is also most accurate at low levels. Given it’s low frequency cutoff and inaccuracy at higher SPLs, I wouldn’t recommend using “A” weighting to measure the SPL in worship services. Even though you might have your subs pumping out frequencies around 50 Hz, they won’t be included in the meter’s measurements. This weighting is normally used to measure industrial and environmental noise levels.
“C” weighting measures frequencies between 32 and 10,000 Hz, making it much more applicable to a house of worship. By setting the meter to “C” weighting, you are including more frequencies into the reading, producing a more accurate representation of the actual loudness of the service. Unlike “A” weighting, it is also more accurate at higher levels, such as the levels used by rock concerts and worship services. When you want to know how loud your services are, set your SPL meter to “C” weighting.
After you set the weighting, adjust the response time to either fast or slow. When set to slow, the meter updates every .5 seconds. When set to fast it updates every .2 seconds. I don’t have a personal preference between fast or slow. Experiment with both settings for your particular situation.
Taking Measurements
Now that you have your SPL meter set up, it’s time to take some measurements. While at the sound board, point the meter toward your speakers. Hold the meter away from you to reduce sound wave reflections from your body from reaching the meter. After you get your reading, take a walk around the auditorium and test the level at different spots in the auditorium. You may be surprised at how the SPL can change depending on your location in the room.
Take a reading from the seats closest to the speakers. If you are trying to keep the maximum loudness of your services at a certain level, compare this reading to the one you took at the sound board. Let’s say you measured 90dB at the sound board and 95dB at the seats closest to the speakers. If you want your maximum loudness to be 92dB, then you will need to run your system no higher than 87dB at the sound board.
Continue walking around and measure the quietest spots of your auditorium. Usually these spots are located in the corners of the room, off axis from the throw of the speakers. Knowing where the quieter sections are will help appease those who feel that the service is too loud. Kindly point them in the direction of the quiet seats.
Do you use an SPL meter during your services? If so, how loud do you consider acceptable?
Yep. We keep it at 85dB – small room, so it sounds very full at that level.
Great post, we mix a few dB hotter, usually peaking around 95-96 dB.
I train our sound team to measure using the “slow” setting when setting up the meter. When set to fast, I find many meters are very sensitive to hard transients (like snare drums). Since our ears respond to transients differently than the meter, I find that when they are set to fast, they can often give a reading on transients that is “louder” than what we are actually perceiving.
Personally, it drives me a little nuts to have to use these things. Most often I tell our guys to use these as guidelines while “feeling” the room during a mix. However, it is handy to have a “standard” level when the odd negative nancy comes strolling by the sound booth.
Thanks for expounding on the fast/slow setting. Good point about the transients.
Negative Nancy …
I have to say that is an extremely dismissive attitude and one only too common amongst a lot of sound techs (and I’ve bene ther done that with sound though it’s no longer my day to day thing).
Please see my comments below regarding what is too loud – as the parent of a profoundly deaf child (now 20) I have studied sound and seriously looked into the consequences of it or even the lack of it in my son’s case. I don’t lightly proclaim that 85db is too loud – it’s an accepted fact, so why do we caring christians insist on pushing beyond accepted guidelines and dismissing the very people we are meant to be serving as negative?
BTW – I’m sure you don’t mean to be dismissive but that’s how it has come across to me. And for teh record I don’t know you so am not having a personal go at you but am aiming at the seemingly generalised opinion that just because someone isn’t a sound tech then they don’t have an opinion.
We like to keep it around 95dB too. We tell our sound people we want it loud enough that someone can sing and not worry about everyone around them hearing their (possibly bad) voice.
The hard part is getting people to use it. The meter is a great tool but our sound people just won’t/don’t remember to use it.
We meet in a movie theater, and we run a peak level of 100db.
SPL’s should be mandatory in any sound based environment but I don’t know of any church in my locale that uses one – it’s all based on subjective (=the sound tech) feeling as to what is the right level.
Consequently sound levels are actually all over the place and thus the complaint that “it’s a bit loud this week” is usually right and appropriate. I frequently find of the sound techs I know, that they’ve grown a selective or actual deafness to how loud stuff really is – and take it from the father of a profoundly deaf child who tells me “its loud this week” that it is LOUD!
As to how loud is loud – well for that we need to understand what level certain day to day items come in at. However, various deaf and medical societies state that anything over 85Db can and does cause permanent damage to your hearing. So IMO 90db is too loud.
And lets face it – do we actually need our worship to be that loud? No we don’t. After all, God hears us whether we whisper or shout so why do we need loud worship?
What about all the missing freq above 10k what if those are really loud? The slp meter does not pick them up. I ask because I use inears and I measure how loud the sound coming out is. On the in ear it seems to have more of the higher freq