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Author Topic: SPL above ambient crowd noise, is there a general "rule of thumb"  (Read 3744 times)

Michael Cordes

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Hi all,
Just like many others I have been reading the forums for years and have learned a lot from everyone. I have searched many ways but have not found any hits on the topic besides a few on emergency announcement systems.

Is there a generally accepted rule regarding how much level is needed above the expected crowd noise to be heard reasonably well? My guess is 6-10 db SPL but would like some professional input.

Here is the situation. My church is looking at replacing some woefully inadequate 1970s vintage wall mounted 8 inch full range speakers in what we call the Fellowship hall. It is a multipurpose trapezoid shaped room ~65ft on the narrow end ~100 ft on the wide end and ~60 ft long. It has folding partition walls that can divide the room into 3 separate ~20x40ft meeting rooms. I attached a floor plan hopefully it will show up in the post. The system will be used for meetings, announcements during dinners and possibly acoustic coffeehouse style events. Room capacity is 325 people.

We just had an annual event that I suspect would be the worst case for crowd noise and I was measuring 80-85 db C weighted slow response throughout the room. I provided the announcement PA and covered the room quite well with 4 EV SX300 speakers spaced around the room. I was measuring the announcer at 85-90 db SPL C weighted slow response in the center of the room ~30 ft from the speaker. While it was not overpowering the announcements could be heard quite well which lead to my estimate of 6-10 db SPL above the ambient noise. Still I would like to know if there is a generally accepted rule?

After a little more research I will likely start another thread asking opinions on speakers etc.

Thanks in advance.
Mike Cordes
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Yes Mike Cordes (actually rhymes with tortoise not cords) is my real name and I do sound as a hobby and play in a band.

Lee Buckalew

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Re: SPL above ambient crowd noise, is there a general "rule of thumb"
« Reply #1 on: March 02, 2015, 10:17:42 pm »

Hi all,
Just like many others I have been reading the forums for years and have learned a lot from everyone. I have searched many ways but have not found any hits on the topic besides a few on emergency announcement systems.

Is there a generally accepted rule regarding how much level is needed above the expected crowd noise to be heard reasonably well? My guess is 6-10 db SPL but would like some professional input.

Here is the situation. My church is looking at replacing some woefully inadequate 1970s vintage wall mounted 8 inch full range speakers in what we call the Fellowship hall. It is a multipurpose trapezoid shaped room ~65ft on the narrow end ~100 ft on the wide end and ~60 ft long. It has folding partition walls that can divide the room into 3 separate ~20x40ft meeting rooms. I attached a floor plan hopefully it will show up in the post. The system will be used for meetings, announcements during dinners and possibly acoustic coffeehouse style events. Room capacity is 325 people.

We just had an annual event that I suspect would be the worst case for crowd noise and I was measuring 80-85 db C weighted slow response throughout the room. I provided the announcement PA and covered the room quite well with 4 EV SX300 speakers spaced around the room. I was measuring the announcer at 85-90 db SPL C weighted slow response in the center of the room ~30 ft from the speaker. While it was not overpowering the announcements could be heard quite well which lead to my estimate of 6-10 db SPL above the ambient noise. Still I would like to know if there is a generally accepted rule?

After a little more research I will likely start another thread asking opinions on speakers etc.

Thanks in advance.
Mike Cordes

The rule of thumb would be that, for the same frequency range (including the sibilant and plosives range) you need 12-15dB/SPL greater than ambient (or musical instruments) for voice/speech to be clearly understood.

Lee
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David Sturzenbecher

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Lee, can you get 12-15dB above the crowd at EJD? Depends on the season maybe? :)


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Lee Buckalew

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Lee, can you get 12-15dB above the crowd at EJD? Depends on the season maybe? :)


Sent from my iPhone using Tapatalk

Well, it is the Rams.  How big are the crowds!  Actually the largest this past season was around 55,000.
We can get an easy (and even) 115dB/SPL A but we didn't push beyond that since we had headroom left and that level more than met the spec (plus or minus 3).  We used the spec variance to allow us to tune the upper bowl down in level to reduce reflection and keep the intelligibility higher in the mid bowl.  We kept a 0.53 - 0.596 STI throughout the bowl.  Not too bad for an enclosed dome.

Lee
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Michael Cordes

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Well, it is the Rams.  How big are the crowds!  Actually the largest this past season was around 55,000.
We can get an easy (and even) 115dB/SPL A but we didn't push beyond that since we had headroom left and that level more than met the spec (plus or minus 3).  We used the spec variance to allow us to tune the upper bowl down in level to reduce reflection and keep the intelligibility higher in the mid bowl.  We kept a 0.53 - 0.596 STI throughout the bowl.  Not too bad for an enclosed dome.

Lee

Thanks Lee

FYI I did a search for STI without the word "audio" and got a bunch of "sexually transmitted infection" testing lab websites.

Mike
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Josh Millward

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Thanks Lee

FYI I did a search for STI without the word "audio" and got a bunch of "sexually transmitted infection" testing lab websites.

Mike

Try "Speech Transmission Index" instead.
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Josh Millward
Danley Sound Labs

Michael Cordes

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Try "Speech Transmission Index" instead.

Thanks Josh,

I should have specified that when I added the word audio I found the right information.

Mike
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Yes Mike Cordes (actually rhymes with tortoise not cords) is my real name and I do sound as a hobby and play in a band.

Josh Millward

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Thanks Josh,

I should have specified that when I added the word audio I found the right information.

Mike

You are welcome, Mike.

I just wanted to help you find the information you were actually looking for and not all that other stuff you were not looking for.  :D

I'm glad you were able to find it, even if it was before I posted a reply.  ;D
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Josh Millward
Danley Sound Labs

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