Permanent install SPL meter

[adessmith]

Does anyone know of a sound pressure level meter which can be permanently installed with a large external display, and an external microphone?

I had this idea, if there is such a thing, to mount a display in our sound booth that shows the SPL at all times, with a sign mounted next to it showing the different measurement ranges, and what they are suitible for (i.e. Speaking, slow soft music, energetic upbeat music, and dangerously loud) as well as OSHA'S recomended maximum exposure times for each measurement.

We have a radio shack, portable SPL meter, but our sound people rarely get out of the booth to measure at the appropriate locations, and they get confused by the settings on it.

[Brad Weber]

Originally Posted by adessmith

Does anyone know of a sound pressure level meter which can be permanently installed with a large external display, and an external microphone?

I had this idea, if there is such a thing, to mount a display in our sound booth that shows the SPL at all times, with a sign mounted next to it showing the different measurement ranges, and what they are suitible for (i.e. Speaking, slow soft music, energetic upbeat music, and dangerously loud) as well as OSHA'S recomended maximum exposure times for each measurement.

Let me start by addressing the second point and that is that OSHA guidelines are indeed exposures, they factor in both both the level and and the time exposure to that level and relate that back to a total exposure or 'dose' over a standard 8 hour based time period. Since OSHA applies to occupational health and thus to employees, that results in the noise aspects being based on long term exposure over 8 hour daily periods. This is an important factor, especially as many the numbers and values referenced in OSHA, even those referencing shorter time periods, actually relate to the total noise exposure over an 8 hour period.

Thus for the chart that is often referenced, Table G-16 of http://www.osha.gov/pls/oshaweb/owad...ards&p_id=9735, it is important to read Footnote 1 and understand that the chart is addressing exposure over the total 8 hour daily period. For example, the chart indicates that the Permissible Noise Exposure for a 2 hour period is 100dBA, however that is not actually saying the 100dBA for 2 hours is acceptable, it is actually indicating that exposure to 100dBA for 2 hours represents the entire allowable exposure for an 8 hour period and is acceptable only if the other 6 hours of that 8 hour daily period do not include any exposure to noise levels that would add to the overall exposure.

You also have to realize that Table G-16 relates to having to apply "administrative and engineering controls" to reduce the exposure, in other words physically reducing the levels received and/or time of exposure. However, OSHA also address that a hearing conservation program must be established if the 8 hour Time Weighted Average (TWA) level equals or exceed 85dBA, which is 5dB below any of the levels in Table G-16. So OSHA can require monitoring hearing and hearing loss even if the noise exposure does not require active measures to reduce the exposure.

So while the OSHA guidelines may be useful, they are easy to take out of context and difficult to directly apply to many worship applications.


Okay, all that being said, an important consideration is whether you want to measure real time sound pressure levels, some sort of time averaged level or exposure. The latter requires a special device called a dosimeter and is impractical, and inapplicable, for most worship use and especially for volunteers. Some sound analyzers provide various forms of time based analysis or averaging, which can be useful and more relevant to hearing loss and noise exposure but can also be confusing unless you know how to interpret it and may not address the issues that concern you. Basic Sound Level Meters usually provide only real time values, which is good for addressing maximum levels that are often the relevant factor, but will not provide information regarding the average levels or overall exposure if that is the goal.

If what you want is real time measurements with a large external display, then you might look at http://www.gold-line.com/splsign.htm. Extech offers http://www.extech.com/instruments/pr...=18&prodid=231, which may take a little effort to set up but lets you define a limit sound pressure level and then has red and green LEDs to show when the levels are within or over that defined limit. You could also use an iPod or iPad with http://www.studiosixdigital.com/audiotools/spl/ and one of their audio interfaces. The SPL Pro version shows current levels and also has a peak hold function.

[adessmith]

Wow, those two devices are really good options.
The goldline is pretty expensive, but the exact sort of thing I had in mind, however using an ipod touch as the display seems like the better option.

You bring up some good points reguarding the OSHA info. Although I intended that this info would only be provided for "reference", maybe I shouldnt even post it at all. I dont want an irresponsible volunteer to use it to argue that 110dBa is acceptable because our worship sets are less than 1/2 an hour. I know that is an extreeme example, and I would hope no would try to justify that, but my point is (and if I understood you, your point was) that, taking the info at face value, it downplays the dangers of high SPL's.

I'm just trying to find a way to create a consistancy to the levels durring our services. When we have different sound people each week it varrys widely.
Sometimes peak levels are anywhere from the low 80's to right at 100dBa.
It seems if we can keep it around the low to mid 90's everyone is happy. Any lower and it feels dead... any higher and it is uncomfortable for some people.

We are supposed to be "intentional" in everything we do, and I feel like it is irresponsible to not have some way to continually measure this and have a "standard" to stick to.

[petereit]

Originally Posted by adessmith

Does anyone know of a sound pressure level meter which can be permanently installed with a large external display, and an external microphone?

What problem are you trying to solve?

[Brad Weber]

Originally Posted by adessmith

I dont want an irresponsible volunteer to use it to argue that 110dBa is acceptable because our worship sets are less than 1/2 an hour. I know that is an extreeme example, and I would hope no would try to justify that, but my point is (and if I understood you, your point was) that, taking the info at face value, it downplays the dangers of high SPL's.

This is where the OSHA guidelines can work for or against you when applied other than specifically intended. It is impractical for a church to monitor most members for an 8 hour exposure period, thus the guidelines are difficult to apply directly and it is very difficult to imply that you are in compliance with OSHA.

At the same time, the permissible levels in that chart are based on continuous noise levels for that exposure period and most worship services do not have continuous levels, even with louder music there can be significant dynamics. OSHA actually allows momentary peaks of up to 140dBA(SPL) if the sound levels for the rest of an 8 hour period do not add to the overall exposure. If you followed the OSHA chart and apply those numbers as maximum rather than average levels then you are just about guaranteed of not causing an exceedance (at least from the service, what someone does at outside of that you cannot control).

Also remember that the levels measured at the mix position may not be the same levels everyone hears, so it can often help to know how the levels at the mix position related to tthe levels throughout the listener area.

In the end what really matters is what works for and is accepted and supported by your leadership and membership.

[wogster]

Originally Posted by adessmith

Wow, those two devices are really good options.
The goldline is pretty expensive, but the exact sort of thing I had in mind, however using an ipod touch as the display seems like the better option.

You bring up some good points reguarding the OSHA info. Although I intended that this info would only be provided for "reference", maybe I shouldnt even post it at all. I dont want an irresponsible volunteer to use it to argue that 110dBa is acceptable because our worship sets are less than 1/2 an hour. I know that is an extreeme example, and I would hope no would try to justify that, but my point is (and if I understood you, your point was) that, taking the info at face value, it downplays the dangers of high SPL's.

I'm just trying to find a way to create a consistancy to the levels durring our services. When we have different sound people each week it varrys widely.
Sometimes peak levels are anywhere from the low 80's to right at 100dBa.
It seems if we can keep it around the low to mid 90's everyone is happy. Any lower and it feels dead... any higher and it is uncomfortable for some people.

We are supposed to be "intentional" in everything we do, and I feel like it is irresponsible to not have some way to continually measure this and have a "standard" to stick to.

How about a Limiter, you set the limiter so it kicks in right around 95dBa. A limiter is like an electronic volume control, it doesn't allow the sound to exceed the set value for more then the set period of time, before it turns down the volume, when the volume drops it turns it back up, again after a set period of time, these periods of time can be very short. Nice thing is, once it's set you can forget about it. Just make sure that you get a cover plate for it, so that people can't monkey with it. Becomes one less thing for the sound guy to need to keep an eye on.

[Brad Weber]

Originally Posted by wogster

How about a Limiter, you set the limiter so it kicks in right around 95dBa. A limiter is like an electronic volume control, it doesn't allow the sound to exceed the set value for more then the set period of time, before it turns down the volume, when the volume drops it turns it back up, again after a set period of time, these periods of time can be very short. Nice thing is, once it's set you can forget about it. Just make sure that you get a cover plate for it, so that people can't monkey with it. Becomes one less thing for the sound guy to need to keep an eye on.

I think there may be some difference in the definition of a "limiter". A traditional audio limiter does not work that way and to even come close would take a mic and preamp for a side chain input, that way it would be the actual sound pressure level in the room via the microphone that would trigger any compression or limiting of the audio signal.

The noise level monitoring and control systems used in major amphitheatres and such can get pretty complex with multiple sensors, multiple statistical analyses of the levels fed into various algorithms to determine what to do and so on.

[wogster]

Originally Posted by Brad Weber

I think there may be some difference in the definition of a "limiter". A traditional audio limiter does not work that way and to even come close would take a mic and preamp for a side chain input, that way it would be the actual sound pressure level in the room via the microphone that would trigger any compression or limiting of the audio signal.

The noise level monitoring and control systems used in major amphitheatres and such can get pretty complex with multiple sensors, multiple statistical analyses of the levels fed into various algorithms to determine what to do and so on.

I tried to simplify it slightly, and that may not have been successful. I still think an audio limiter could be helpful, with a fairly steady high level sound and an assistant with a walk around SPL meter, to make sure that at no point in the room you exceed a certain level, by adjusting a traditional audio limiter, so that your not exceeding the desired level.

The problem of course with an SPL meter that is fixed is that it depends on the room dynamics, it is possible to have a sound pressure of 90dB at one point, and 105dB at another point and 80dB at still another point, not only that, but the points can be different for different sources. So where do you put the meter?

[partsmanba]

Perhaps, instead of using an iPad display, you could just install the business part of a shock collar in the chair at the mix position

[pdc]

Originally Posted by wogster

I tried to simplify it slightly, and that may not have been successful. I still think an audio limiter could be helpful, with a fairly steady high level sound and an assistant with a walk around SPL meter, to make sure that at no point in the room you exceed a certain level, by adjusting a traditional audio limiter, so that your not exceeding the desired level.

The problem of course with an SPL meter that is fixed is that it depends on the room dynamics, it is possible to have a sound pressure of 90dB at one point, and 105dB at another point and 80dB at still another point, not only that, but the points can be different for different sources. So where do you put the meter?

I do not agree with this. If the calibrated mic and measurement device are at the FOH mix, that measurement is going to represent the level at the FOH mix position. There is absolutely no reason to walk around and measure. There is no reason to have multiple measurement mics connected to a matrix as some do. Why? We have the wonderful inverse square law. If you are using line arrays, you don't so much, which makes this a moot point all together. All you have to do is take your measurement, do the math, and know that if you are measuring 100.5dBA SPL at the mix, which is 60' away from the front row, and the front row is 20' away from your suspended arrays (diagonal line), then you are blowing people away with 110dBA SPL on the front row. The room itself may add some, but those low mids to low bass standing waves are going to be below the curve, because A has a filtered roll-off starting at 2kHz.

Re: OSHA, those exposure limits are not cart blanch for you to use. You must take into consideration that these exposure limits are to be managed by the individuals as well. If you have a country church, where more people tend to have a threshold shift and nerve damage because of their occupations, surroundings, equipment, etc, then you must take this into consideration and limit your SPLs accordingly. Churches have been sued for causing hearing loss. In most cases, it was not the SPLs at the church alone. The people had hearing health issues before the church rocked them silly, and they did not manage their exposure to high SPLs before or after the services.

My brother the doctor and audiologist gives me the scoop on this stuff, whether I ask for it or not. We used to tag team and provide churches with hearing health assessments while meeting with the people to determine their sound system needs. People have no problems with glasses and contact lenses. But when it comes to hearing aids, men especially refuse them, as it is a sign of old age and dependency. Old men are too proud and would rather not hear their wives, I guess.

Just remember that as people age, some frequencies are painful at moderate to high SPLs, By the time people are in their 40's, they have a moderate threshold shift and frequency loss. You have to be aware of this, even to the point of adjusting the curve on the EQ to something less than perfect in your ears. Maybe you run 4k down a bit to keep the purple haired people off of your back and out of the doctors office.

As for people not knowing how to use the meter....Do some training for heaven's sake. It is not rocket science. There are videos out there. Look up the differences in the filters on the Rane Pro Audio Reference. Get your mic calibrated, keep the thing in one position so that there is consistency, and monitor it. If your guys cannot hear a 3dB boost in SPL, then they should not mix. If they HAVE to increase to keep the mix jiving with an orchestra or some other high-output acoustic source that is not mic'd, then that is a matter you should address with the powers that be.

Do a Google for REW, a free program for your Mac or PC, that is as close to a free form of SMAART as you can get. It is not as resolute, but it has lots of tools that will make you look smart. People will perceive you are trying to manage the situation. REW has large meters and numerical displays for SPL. There are impulse, waterfall, RTA, FIR, etc graphs.

[wogster]

Originally Posted by pdc

I do not agree with this. If the calibrated mic and measurement device are at the FOH mix, that measurement is going to represent the level at the FOH mix position. There is absolutely no reason to walk around and measure. There is no reason to have multiple measurement mics connected to a matrix as some do. Why? We have the wonderful inverse square law. If you are using line arrays, you don't so much, which makes this a moot point all together. All you have to do is take your measurement, do the math, and know that if you are measuring 100.5dBA SPL at the mix, which is 60' away from the front row, and the front row is 20' away from your suspended arrays (diagonal line), then you are blowing people away with 110dBA SPL on the front row. The room itself may add some, but those low mids to low bass standing waves are going to be below the curve, because A has a filtered roll-off starting at 2kHz.

Re: OSHA, those exposure limits are not cart blanch for you to use. You must take into consideration that these exposure limits are to be managed by the individuals as well. If you have a country church, where more people tend to have a threshold shift and nerve damage because of their occupations, surroundings, equipment, etc, then you must take this into consideration and limit your SPLs accordingly. Churches have been sued for causing hearing loss. In most cases, it was not the SPLs at the church alone. The people had hearing health issues before the church rocked them silly, and they did not manage their exposure to high SPLs before or after the services.

My brother the doctor and audiologist gives me the scoop on this stuff, whether I ask for it or not. We used to tag team and provide churches with hearing health assessments while meeting with the people to determine their sound system needs. People have no problems with glasses and contact lenses. But when it comes to hearing aids, men especially refuse them, as it is a sign of old age and dependency. Old men are too proud and would rather not hear their wives, I guess.

Just remember that as people age, some frequencies are painful at moderate to high SPLs, By the time people are in their 40's, they have a moderate threshold shift and frequency loss. You have to be aware of this, even to the point of adjusting the curve on the EQ to something less than perfect in your ears. Maybe you run 4k down a bit to keep the purple haired people off of your back and out of the doctors office.

As for people not knowing how to use the meter....Do some training for heaven's sake. It is not rocket science. There are videos out there. Look up the differences in the filters on the Rane Pro Audio Reference. Get your mic calibrated, keep the thing in one position so that there is consistency, and monitor it. If your guys cannot hear a 3dB boost in SPL, then they should not mix. If they HAVE to increase to keep the mix jiving with an orchestra or some other high-output acoustic source that is not mic'd, then that is a matter you should address with the powers that be.

Do a Google for REW, a free program for your Mac or PC, that is as close to a free form of SMAART as you can get. It is not as resolute, but it has lots of tools that will make you look smart. People will perceive you are trying to manage the situation. REW has large meters and numerical displays for SPL. There are impulse, waterfall, RTA, FIR, etc graphs.

I give up

Obviously other churches have so many volunteers, they can have someone sit in the sound booth to monitor the SPL meter...... That's funny, never been in a church that had that problem.

[Brad Weber]

Originally Posted by pdc

There is absolutely no reason to walk around and measure. There is no reason to have multiple measurement mics connected to a matrix as some do. Why? We have the wonderful inverse square law. If you are using line arrays, you don't so much, which makes this a moot point all together. All you have to do is take your measurement, do the math, and know that if you are measuring 100.5dBA SPL at the mix, which is 60' away from the front row, and the front row is 20' away from your suspended arrays (diagonal line), then you are blowing people away with 110dBA SPL on the front row.

I have to disagree. If you are worshiping outdoors, have a single point source speaker and the speaker is omnidirectional then you may have inverse square law apply throughout the listener area. However, indoors with speakers that have patterns and a room affecting the sound combined with possibly multiple speakers and potential interactions between them and it can get much more complicated. A simple example is that a good system design would likely put the more distant listeners on axis and those physically closer further off axis, thus using the speaker pattern to reduce the differences in level compared to simple inverse square loss considerations. Thus while it may not be necessary to measure at multiple points, I do think it is very beneficial to have a good idea of how both the levels and frequency response actually do vary throughout your listener area and to take that into account in any limits or guidelines you establish.

Originally Posted by pdc

The room itself may add some, but those low mids to low bass standing waves are going to be below the curve, because A has a filtered roll-off starting at 2kHz.

Just a detail, the common A, B and C weighting curves do not affect the 1kHz octave band levels. So in the case of A-weighting, the levels for the 1kHz octave band are not rolled-off or decreased by the weighting, rather the levels are increased by 1.2dB for the 2kHz octave band and by 1dB for the 4kHz octave band.


The aspect of this that does not seem to yet have been addressed in this thread is that Sound Pressure Level and perceived loudness are two different things. The perceived loudness is affected by factors other than just SPL including frequency content, distortion and even subjective considerations such as personal preferences. Two sources of different perceived loudness level may actually have the same SPL while it is very common to have different sources with the same SPL be perceived as being of significantly different loudness. Thus it is difficult to compare relative perceived loudness based purely on the relative Sound Pressure Levels and why that while having SPL limits or guidelines can be beneficial, that should not be misinterpreted as representing the perceived loudness.