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Title: Calculate needs given SPL
Post by: Clark Johnson on November 30, 2011, 11:18:24 am
I was contacted about putting in a sound system in a couple of gyms and a lobby at an university rec center.  I know that I would like to achieve a certain SPL, around 95dB.  I know the size of the space and I can look at the specs on speakers to determine sensitivity.  How do I go about finding how many speakers/wattage I will need for this project?  I can handle the math if someone can point me to a formula.

Title: Re: Calculate needs given SPL
Post by: Charlie Zureki on November 30, 2011, 11:28:58 am
I was contacted about putting in a sound system in a couple of gyms and a lobby at an university rec center.  I know that I would like to achieve a certain SPL, around 95dB.  I know the size of the space and I can look at the specs on speakers to determine sensitivity.  How do I go about finding how many speakers/wattage I will need for this project?  I can handle the math if someone can point me to a formula.

  Clark,

   Have you ever Designed and Installed a Sound System before? To NEC code?
   Have you taken any data/ Measurements at this facility, and in all spaces that are to be covered?
   What is this (these) Sound System (s) to be used for?...It's primary purpose?

   If the answer to these questions is either.. No... or, I don't know....then, you should kindly refer the University to a qualified System Contractor.  See the post below regarding..."Hiring a Contractor to consult"....


  Hammer
 
   
Title: Re: Calculate needs given SPL
Post by: John Roberts {JR} on November 30, 2011, 12:04:10 pm
In a highly reverberant space like a gymnasium, you can get the same SPL from a few big speakers bouncing sound all around, or a lot of smaller speakers pointed to hit the meat in the seats and not excite the room reverberation.

Same SPL, much different intelligibility and cost to implement. Are the systems just to make background music, where intelligibility is not much of a concern, or to make announcements also that the audience should understand?

 I am encouraged that you are thinking about SPL, the net result but even this needs more qualification and inspection to keep the customer happy.

JR
Title: Re: Calculate needs given SPL
Post by: Ivan Beaver on November 30, 2011, 12:55:41 pm
I was contacted about putting in a sound system in a couple of gyms and a lobby at an university rec center.  I know that I would like to achieve a certain SPL, around 95dB.  I know the size of the space and I can look at the specs on speakers to determine sensitivity.  How do I go about finding how many speakers/wattage I will need for this project?  I can handle the math if someone can point me to a formula.
It is not a simple math formula.

You have to look at coverage patterns, location they are mounted in, "throw", is these full range systems, voice only systems, what kind of directivity will be needed (especially important in reverberant spaces), is localization important?  Is zoning important? and so on and so forth.

Each case is different and could/may require a different design approach.

If all you want to do is to make some noise at 95dB (whatever scale A or C fast or slow you mean the 95dB to be at-it can vary quite a bit-say 20dB?) then that is easy.  But if you want it to be a usable system, being able to understand it and so forth, then that gets harder.

Sorry, but there is no simple answer.
Title: Re: Calculate needs given SPL
Post by: Clark Johnson on November 30, 2011, 07:15:33 pm
Clark,

   Have you ever Designed and Installed a Sound System before? To NEC code?
   Have you taken any data/ Measurements at this facility, and in all spaces that are to be covered?
   What is this (these) Sound System (s) to be used for?...It's primary purpose?

   If the answer to these questions is either.. No... or, I don't know....then, you should kindly refer the University to a qualified System Contractor.  See the post below regarding..."Hiring a Contractor to consult"....


  Hammer
 
 
Here is the background of the project.  I work for the universities audio visual department and do a lot of learning as I go.  We occasionally take some boxes on a stick (Mackie SRM350) or bigger (Mackie SA1532z, durable and cheap) for student groups to have dances or events like that.  Also, there is some announcements.  The director of the space wants to have some of her own system.  In the best case, it would be a permanent solution attached to the structural supports so that all that has to be plugged in is a mixer and some sources.

@Charlie - Yes, I've designed some sound systems before but nothing very complex.  I designed a 4 zone clubhouse, a temporary setup for a performing arts venue (a much need patch before a 27 million dollar renovation), a 36 seat cinema.  Mostly it was available equipment and or budgets that were the strongest consideration.  I've heard a lot about codes, but finding them can be difficult.  Where is a good place to locate the relevant codes? 

In terms of measurements, I'm relatively inexperienced.  The only pieces of equipment I have is a dbx reference mic and an old hardware RTA.  I don't have any software or interfaces.  I don't know the reverb time of the space.
Title: Re: Calculate needs given SPL
Post by: Clark Johnson on November 30, 2011, 07:21:30 pm
In a highly reverberant space like a gymnasium, you can get the same SPL from a few big speakers bouncing sound all around, or a lot of smaller speakers pointed to hit the meat in the seats and not excite the room reverberation.

Same SPL, much different intelligibility and cost to implement. Are the systems just to make background music, where intelligibility is not much of a concern, or to make announcements also that the audience should understand?

 I am encouraged that you are thinking about SPL, the net result but even this needs more qualification and inspection to keep the customer happy.

JR

The space does everything, from dances to athletic camps to talent shows.  I would like to avoid carting over equipment for every event.  So the applications I want to consider are dances and athletic camps.  I can bring over more equipment as needed for talent shows.  What kind of questions do I need to ask the person with the money?  What kind of inspections do I need to make?  I'm only 1 person, so I can't do everything.
Title: Re: Calculate needs given SPL
Post by: Clark Johnson on November 30, 2011, 07:34:49 pm
It is not a simple math formula.

You have to look at coverage patterns, location they are mounted in, "throw", is these full range systems, voice only systems, what kind of directivity will be needed (especially important in reverberant spaces), is localization important?  Is zoning important? and so on and so forth.

Each case is different and could/may require a different design approach.

If all you want to do is to make some noise at 95dB (whatever scale A or C fast or slow you mean the 95dB to be at-it can vary quite a bit-say 20dB?) then that is easy.  But if you want it to be a usable system, being able to understand it and so forth, then that gets harder.

Sorry, but there is no simple answer.

Ivan,
Danley sounds definitely has done it's share of installs.  That is quite a portfolio.  So I understand that you know what you are talking about where you say there is no easy answer.  The question I guess was mired in the details of the project.  I realize that the inverse square law can not be overcome.  The root question is, how can I go from "Let's throw up some speakers and see if it works" to "here is a system that has these specs" without having to use a computer to model a room?  How did sound system installers answer these type of questions before there were computers?
Title: Re: Calculate needs given SPL
Post by: Tom Young on November 30, 2011, 08:46:28 pm
The root question is, how can I go from "Let's throw up some speakers and see if it works" to "here is a system that has these specs" without having to use a computer to model a room?  How did sound system installers answer these type of questions before there were computers?

On paper and/or with slide rules. The same way that any science was "computed" before computers came along.

Having computers and software does not free any of us from knowing the physics that are behind electroacoustics (which is what we do).

You, for example, cannot go out and buy modeling or measurement software and do anything with it unless, or until, you know what you are (and it is) doing.

Back to your dilemna: you have been tasked with providing a working live sound system. Fine. Except for the fact that you cannot possibly do this. No amount of brotherly advice from us is going to even come close to providing you with an appropriate design for a loudspeaker system for the space you are dealing with.

Then there is the rest of the sound system including the wiring infrastructure and AC power, plus rigging.

And then there are code, safety and other legal and ethical issues.

I am writing all this partly to try to enlighten you and partly because I realise you have to go back to the task-master and either bluff your way through this or convince him/her that the only way to accomplish the goal is to pay an experienced designer (consultant or contractor) to do this.

No easy task.

But easier than providing a mediocre sound system that no one can use effectively.
Title: Re: Calculate needs given SPL
Post by: John Roberts {JR} on November 30, 2011, 08:49:12 pm
The space does everything, from dances to athletic camps to talent shows.  I would like to avoid carting over equipment for every event.  So the applications I want to consider are dances and athletic camps.  I can bring over more equipment as needed for talent shows.  What kind of questions do I need to ask the person with the money?  What kind of inspections do I need to make?  I'm only 1 person, so I can't do everything.

How much are they willing to spend ?

Is there an end with a stage? 

Does the audience sit everywhere?

Simple calculus is that you can fill a reverberant space with music more easily with a few large speakers, that make effecting speech reinforcement, since the reverb hurts intelligibility. If the audience area is modest you can point the speakers at it. The closer the speakers to the listener the more direct to reverberant sound ratio and better intelligibility

What works in there now?

JR

PS: The answer for how to do it before computers, is the same as after there were computers, "experience"... and remember that free advice on the Internet is worth exactly what you paid for it, even advice from me...  8)
Title: Re: Calculate needs given SPL
Post by: Brad Weber on December 01, 2011, 12:27:36 am
... and remember that free advice on the Internet is worth exactly what you paid for it..
If you are lucky, it is also possible for it to end up being very costly.

As already stated, there is much more to it than may be readily apparent.  For example, you mentioned they want 95dB.  Is that a 95dB(SPL), dBA or dBC overall level or is it the level at any frequency over some specific frequency range?  Is it the average level, absolute maximum peak level, level exceeded some percentage of the time or what?  Is 95dB the minimum level anywhere in the listener area and what variance throughout the listener area is acceptable?  Do they care about anything other than obtaining 95dB, such as the frequency response of the system or being able to understand what is said?

And that's just defining what it is you are trying to do, then you also get into assessing practical limitations such as where you can physically mount speakers, interference from lights and backboards, where equipment can be located and so on.  You may also need to consider factors such as whether you need to be able to turn on and off or independently adjust the level of the speakers covering certain areas of the room in order to support some types of events, for example turning off speakers over the stage for talent shows.

Even then, you aren't close to predicting the system performance, more getting to a point where you can start to define something that stands a chance of actually working.
Title: Re: Calculate needs given SPL
Post by: Scott Carneval on December 01, 2011, 10:44:58 am
The space does everything, from dances to athletic camps to talent shows.  I would like to avoid carting over equipment for every event.  So the applications I want to consider are dances and athletic camps.  I can bring over more equipment as needed for talent shows.  What kind of questions do I need to ask the person with the money?  What kind of inspections do I need to make?  I'm only 1 person, so I can't do everything.

There really isn't a 'one system fits all' approach that will work here.  Dances will require a different approach than athletic events, which will require a different approach than live performances (talent shows).  For athletic events you will likely want the announcements to be projected from center court, as that will be the point of the audiences attention.  For live performances you will want the sound to come from the stage, with a strong attention to vocal intelligibility.  For dances, you'll likely want the sound to come from the stage, but you will also need extended low frequency response.  It's feasible to design a solution that will work for live performances and dances, but it's unlikely that the same system will work for athletic events. 
Title: Re: Calculate needs given SPL
Post by: Brad Weber on December 01, 2011, 02:39:12 pm
It's feasible to design a solution that will work for live performances and dances, but it's unlikely that the same system will work for athletic events.
I have done it and had to also add in supporting commencements, pep rallies and chapel services, but it took creating multiple coverage zones, using multiple matrix DSP presets and using higher quality speakers throughout, neither a simple nor inexpensive option.  Most people are not willing to make that investment and end up sticking with portable/rental for the live performance type events.
Title: Re: Calculate needs given SPL
Post by: Billy Wood on January 02, 2012, 10:24:08 pm
I was contacted about putting in a sound system in a couple of gyms and a lobby at an university rec center.  I know that I would like to achieve a certain SPL, around 95dB.  I know the size of the space and I can look at the specs on speakers to determine sensitivity.  How do I go about finding how many speakers/wattage I will need for this project?  I can handle the math if someone can point me to a formula.

As a beginning installer nothing helps more than the tools the manufactures give you.  Most the data they give you are hard numbers to weed out the obvious exclusions.  After that most data is presented in EASE files.  You can build anything you desire and see how it works.  It will be very time consuming at first if you have never used EASE.  If a manufacture does not have EASE data on that product it is more than likely not something you will want to install and put your name on it.  If you are just starting out you can use Google Sketch-up 7 and earlier or AutoCAD to make your room and then import it into EASE.  You can find EASE here: http://www.renkus-heinz.com/ease/ (http://www.renkus-heinz.com/ease/)

It is the industry standard for installed sound.  Any installer that is worth his merit has EASE.


Billy Wood
www.avprogroup.com (http://www.avprogroup.com)
The Woodlands, TX
Title: Re: Calculate needs given SPL
Post by: Brad Weber on January 03, 2012, 09:25:37 am
It is the industry standard for installed sound.  Any installer that is worth his merit has EASE.
Since EASE is a design tool that might be better stated as any designer rather than installer and you might also want to add other alternatives such as CATT-Acoustic and Odeon, both of which use Common Loudspeaker Format or .clf files.  However, the usual cautions here that having such program and even using them is not necessarily the same as using them properly.  These programs offer quite a bit of flexibility in how you can calculate and present the results, which is very useful when properly applied but that intentionally or unintentionally misapplied can give misleading results.

It is unfortunate how many times I've seen parties trying to sell a particular solution provide EASE predictions where the calculation and presentation parameters appear to have been manipulated to make their proposed solution look good.  Whether that was intentional or the result of a lack of knowledge on the part of the person doing the work, neither is very reassuring.


Clark, to your original question, determining the on-axis overall level, or at least a conservative value for it, is pretty simple.  However, that is not addressing aspects of the system performance such as frequency response, coverage and intelligibility.  That also does not address practical factors related to both the system performance and installation.  Or code compliance, Owner Standards compliance, etc.  All of these, and possibly other factors, are elements in an typical installed system design and there is no single calculation to address them all.