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[Tim McCulloch]

Thanks for this article Dick. It's a big help. I have checked the specs on all my speakers and can't find mention of this all-important efficiency spec. Is this usually published or does one have to contact the manufacturer?

Sensitivity is a listed specification for every professional speaker made.

But as Ivan will say... "at what frequency?"  One well-known sub's highest SPL, 1w/1m occurs well above subwoofer frequencies, i.e. where you won't be using it.  Is it a lie?  Well, you can replicate the measurement so in that sense it's honest, but they leave it up to you to look at the graph and not just the number.

For low frequency pass bands, it's important to note if the sensitivity was measured in half-space or full space.  Most are half-space because that is the way the subs will be used.. sitting on the floor and hopefully against the wall or more than 7 or 8 feet from any side or back wall (couples mostly with the floor, but if you can't be against the wall you need to be away from it).  Free space measurement are made with speakers suspended, usually 20' or more.  The same box, measured both ways, will have a lower sensitivity when measured in free space, theoretically 6dB less.

http://www.genelec.com/learning-center/presentations-tutorials/placingloudspeakers/radiationspace/

http://www.fulcrum-acoustic.com/wordpress/wp-content/uploads/2010/11/Comments-On-Half-Space.pdf

[Mike Monte]

Hey Guys,

My relatively new little company is gaining some traction here in Vancouver and I'm seeking to understand what sizes of rigs work well in different situations.  I have never been crystal clear on this.

Currently I'm doing sound (and stage wash lighting) for events averaging around 150-200 people, mostly indoors.  These are anything from DJ events, to concerts, dance performances, weddings, etc. 

As I mentioned, things are going well and I aspire to be doing sound for music events of up to 500 people, both indoors and outdoors.  Currently my FOH rig is 2X RCF ART 715A tops and 2X RCF ART 905AS subs.  I would ideally like to stick with RCF but am also open to other brands such as EV or JBL for a larger rig.  Also, we're talking active boxes here (which are as versatile as possible) and ground stacking.  Time and budget are always issues with my clients.

So, all this being said, I'm curious as to what the best practice is for calculating what size of rig is needed for an event?  How many tops and how many subs?  And what else is an important consideration, spec wise?  Combined max SPL of the system?  15" vs 18" subs?

The factors involved are obviously the venue particulars, the genres of music being played (along with associated volume expectations), and the number of people expected.

Perhaps it would help to have some scenarios:

1) Indoors, square box venue. 500 people. Non bass-heavy music such as folk or world music.

2) Outdoors, in a field. 500 people. Non bass-heavy music such as folk or world music.

3) Indoors, square box venue. 500 people. Bass-heavy music such as EDM, rock or reggae.

4) Outdoors, in a field. 500 people. Bass-heavy music such as EDM, rock or reggae.

Thanks for your $0.02!

Oliver

I have a small sound company that I started 10 years ago and it has grown each year....not by leaps and bounds, but steady growth.
My advise: start with an adequate monitor rig (4 mixes) and a good club rig that will work for indoor and smaller outdoor events.
My club FOH rig is a yorkville tx rig: 1 or 2 tx4 boxes over 1 or 2 tx9s boxes per side.  I've never had a problem with coverage indoors... 
My largest annual gig is providing sound for a town's local July 4th fireworks display. 
For that gig I supply the speakers/amps for two scaffolds and I "subcontract" the "long throw" speakers/amps for the third scaffold.
By subcontracting some of the gear to facilitate the gig I am able to network with a local regional provider...which he appreciates. 
DJ applications: you will need twice as many subs as needed for bands....
Scalable is good to a degree....but....there is a difference between short throw and long throw cabs...
My advise: build a rig that can handle 75% of your gigs.  For the other 25%, rent-in the gear.
Nothing is worse than having gear sitting in storage only to be used once/twice per year.
Mike M

[Ivan Beaver]

Thanks for this article Dick. It's a big help. I have checked the specs on all my speakers and can't find mention of this all-important efficiency spec. Is this usually published or does one have to contact the manufacturer?

What speakers do you have?

In almost every case it is a published number on the front of the spec sheet.

However as Tim noted-it can be "manipulated" a good bit-sometimes so much as to be totally worthless.

It could be a single peak in the response giving a very high number-yet the rest of the freq response is 10dB lower.  I have seen this quite a bit in even the "upper level" of loudspeaker manufacturers.

So while the manufacturer is not lying-they are FAR from telling the truth as to the USABLE performance of the loudspeaker.

Yet some people who either do not know-or do not care-or just want to "brag" will take this false numbers and try to compare it to other loudspeakers who have more honest ratings.

It is kinda like saying you car gets 70MPG.  Sure it might-it it is coasting down a long hill-but what does it do when averaged out over normal roads over an extended distance?

The 70MPG is not wrong-for the testing conditions-but gives the user a false sense of what they can expect in the real world.

Especially in the world of loudspeakers-you REALLY have look a lot closer not only at the specs-but where the numbers come from.  This is a lot harder on some products than others.  Typically the ones with "something to hide" are the ones that don't give many usable specs.

[Randall Hyde]

I can tell you this. The profit margin is higher on niche market system providers. As mentioned earlier, the S.O.S ( speakers on sticks ) systems get a very good R.O.I. The moment you start to try and fill tech riders, the R.O.I starts to go down...... a lot. My niche market is being a high end small system provider ( for my area ) and free lancing to other larger companies. Here is what I know. The larger companies ( with all the disco stuff ) really aren't making a whole lot on a per person salary. They make enough to stay in business and certainly the owners are doing well, but as a whole they are not making bank, so to speak.

If making a whole lot of money is desired, time to leave this business.

As for what size you need to "cover an area", it is dependent upon needs. The larger the area the more you need. The basic 12" 2 way speaker will cover as much as 100-200 people indoors and outdoors can do as much as 500, or more? The issue is the total area, not the number of heads.

Not entirely true. A given system will fill a given space just fine. Stick 500 heads in there, each one of which absorbs a *lot* of HF material and that same system won't cut it.

The general estimation is 10 watts per person. But that would mean a 1000 watt speaker amp combo is only good for 100 people. I don't think that is truthful and a 1000 watt combo should be good for around 500 people. But you get more mileage indoors. Most indoor events can't hold more than 500 people. But that doesn't mean that two speakers with 1000 watts between them will cover all those people.......

Okay, you've been beaten to death on this one. I won't comment other than to give an example:

JBL SRX 712m cabinets: 95 db @ 1w/1m
Danley SH46 cabinets: 106 db @1w/1m

It takes over 10 times the power to produce the same SPL with the 712m as it does with the SH46. Therefore, the SH46 cabinets would (in theory) need only 1w/person where the  712m requires 10 watts.

So which is it then. SPACE, SPACE, SPACE. If you have a large outdoor area that needs to cover 500 people, you will need more power and or speakers to get full coverage. If that same group of people are relatively close together and the area of coverage not that big then less will get you just as far. Indoors you get more mileage, but 500 people indoors means that there will be a lot of people who are not near a speaker.

Figure outdoors, with the same rig, is going to take someone in the range of 3-4x the power (+6dB headroom) to sound as loud as indoors. At least, that's my experience.

This will mean placing a lot of speaker around the area to get coverage all the way around.

Yeah, be careful about placing a "lot of speakers around the area to get coverage." Even with appropriate delays, you're wiping out the quality of the sound by creating interference patterns. Particularly outdoors.

The watts per person factor goes out the window. 100 people indoors can be covered easily with one 12" speaker if all the people are quiet and placed close to each other ( like sitting in chairs ) and even a small 250 watt system could easily cover it. That same group spread out will require more. The general rule of 10 watts per person stands because it is a good way to factor the total number of watts that will fully cover that many people in any given situation.

The other thing you're missing from this 10 watts/person equation is the type of audio material you're reproducing. For public address it will be one value, for acoustic material, a bit more, for a jazz band, more; for a country band a lot more; for a rock band, a  whole lot more; for EDN, it goes off the charts.

The coverage pattern of your speaker is another factor to consider. Most speakers are about 90X50. That means that if you need to cover a 180 deg. area nearly directly in front of the speaker, you will need two speakers placed together and splayed in order to cover it.

Coverage is very important. Most sound providers in the range we're discussing here will rarely need 180 degrees of coverage. I do wide shows and 120-140 degrees is about what I shoot for. You don't what to be using 90-degree cabinets for that arrangement (the comb filtering will kill you). 70-degree cabinets (splayed or cross-fired) work much better in that arrangement.

If you just need to wash a large area with sound ( like a large lawn ) then you can place several speakers ( preferably within 20-22 feet of each other ) on two sides of the lawn area to provide a wash of that area.

Please look up "comb filtering" on this site to see the problem with this suggestion. Generally, if two speakers are reproducing the same material, I'd suggest putting them at least 50' apart so the audio is down many dB before the audio from one speaker interferes with the other. Obviously for stereo audio sources, you have more leeway.

Delay stacks can be your friend if you can't have a high SPL near the stage and you still need a respectable SPL at the back of the venue, but tuning a system with delay stacks (especially outdoors) is not a trivial matter.

When you do band stand, or centralized speaker placement you basically need to factor what area you want coverage to and what volume you want to get at the end of it. Then with some calculations you can figure if it's possible or not given your systems power and SPL capability.
[\quote]
Outdoors the "calculation" method can work. The number of variables for an indoor venue complicate the calculations (what is the reflectivity at given frequencies, for example) and is difficult to achieve with a one-off show when you've never been to the venue.

A note on dispersed speaker distribution: Any time you have the same sound coming from two sources there will be a delay in arrival times if you are not equidistant from any number of speakers. To optimize and reduce the effect of this occurrence, It is suggested that speakers be placed as close as practical with an outer limit of around 20-25 feet from each other.

Where did this number come from?
Either you want the speakers (subs) to be close enough to couple, or you want them far enough apart such that the SPL is *way* down by the time sound from one speaker reaches the other that interference is minimized. The numbers I've seen have been around 50' (say, 16 meters, that drops the level 4*6 dB [-6dB at 2m, 4m, 8m, 16m] by the time the sound travels from one speaker to the other).

After that arrival times are noticeable and as in any case comb filtering will be an issue.
It is best to keep all speakers in an even plane for obvious reasons. Distributed sound is a pain because it requires a lot of speakers to do the job right. So keep that in mind if you feel that your heading that direction. Any time you need low level sound projected over a large area, you are going into distributed sound. Point source and centralized systems don't work very well low level sound over a large area. Hope all this helps.

Point source systems *can* work well as long as the distance from the source to the closest listener can be extended. This is one advantage of flying speakers high in the air. Think of a Danley JH-90 (J1) way up in the sky. Of course, we're talking about a system *way* out of the range of the overall discussion here, but the fact is that flying speakers high is a good way to even out the SPL over a given range. If you can put a speaker 6-8 meters up, you've reduced the SPL by 12-16 dB at the ground level (probably more, as the listeners won't be directly under the speakers) and the inverse-square law starts to work in your favor -- that is, it's bad that the sound drops off so fast as you go a little farther away from the speakers but once you're a fair distance, you can go twice as far (say 16 meters to 32 meters) with "only" a 6 dB loss in volume.

I'd also like to address the issue of scalability of sound systems discussed throughout this thread. In my experience, scalability of sound systems will result in no more than about 2x the coverage without some serious sound quality and logistical compromising. The problem is that doubling your sound equipment basically buys you 3-6dB under perfect circumstances and this certainly doesn't take your system "to the next level." (I have copied Tim McCulloch's post on this subject at the end of this post). Scalable systems are somewhat nice when viewed from the "I can take less equipment and do a smaller job" point of view, but it very rarely works in the opposite direction of "if I buy two copies of my A rig and haul it to a gig, I can do shows that are twice as large."

Arguably, scaling down isn't a particularly good ROI for an "A" rig. If you take half your "A" rig on a "B" rig job, you're putting wear and tear on that half of your "A" rig that may not be justified by the amount you're charging for the "B" rig. Sound systems don't have an unlimited lifetime and every time you move a box around you're shortening its lifetime. Every time you run power through a speaker you're "using it up."

Now granted, if someone's "A" rig is typical MI or lower-end pro gear, this argument is moot. But it's still something to consider when building a "scalable" sound system.
Cheers,
Randy Hyde


Tim McCulloch
Pro Sound Web
9-7-2012
Response to " Business decision and best ROI" in LAB:The Classic Live Audio Board


I love the phrase "... to the next level."  I did some back-of-envelope figuring about 25 years ago when faced with a similar desire for my small PA company to see what it would cost.

What came of that was a determination that "the next level" costs you as much as EVERYTHING YOU'VE SPENT, TO DATE.  That means from the time you bought your first microphone or speaker up to the present day.  If you spent $50,000 so far, to get to that next level will cost you a minimum of $50k ALL AT ONCE.  Faced with that knowledge and the realization that I was stuck with clients that could never pay me more (and that I hadn't charged enough to allow for proper maintenance and eventual expansion), I did some serious soul searching and sold off most of my gear; doubled down on the business & accounting side and took to managing other peoples businesses.

Some of the gems of wisdom that came from the education received and from advice from others in the industry I came to several conclusions.  In no particular order -

1 - A sound system is a tool to make money.  It is not a big ass personal stereo system, so when it comes to making decisions about brands and models my personal preferences need to take a back seat to other considerations.

2 - If myself or my crew are the only people who will operate the equipment, I have more leeway in selection; if the gear is to be operated by others it is important to invest mostly in the stuff they want to use, subject to the ability to recover those costs in a reasonable amount of time.

3-  Excess capacity is infinitely expensive.  Having another 8 speakers or amps in inventory that only go out a couple times a year means those gigs have to pay a great deal more to compensate, or we should look to renting the additional capacity on an as-needed basis.

4 - Certain big ticket items like large frame consoles seldom provide a return on the investment before they are obsolete.  Why?  Because in most music/entertainment situations you can't make them a separate line item on an invoice; a console is expected to be part of the equipment package.  In a previous incarnation of PSW, Chip Self of Logic Systems had a great Study Hall article on ROI and how this happens.

5 - Spending big money on capital equipment needs to be justified by the generation of additional income above and beyond what is brought in from existing equipment, and that investment must recoup its costs in a timely manner.  If purchasing a new console or speaker system means you can get more money from existing clients; if it means you can realistically expect to get gigs you can't get now; if it provides new opportunity; then it *might* make sense.

6 - Beware of false economies.  It's just as easy to spend too little and not buy new opportunity as it is to spend too much and have either excess capacity or gear that isn't popular with clients.

Take a good hard look at the business side of your company.  Ignore the blinking lights and flashy advertising, the gleam of bright shiny objects.  Instead ask yourself how you're going to justify to your significant other the spending (and likely borrowing most of) 6 figures to the left of the decimal point.  Almost any stock index fund will return more than spending that money on audio systems.

Have fun, good luck.

Tim Mc

And a follow up to my post:  It's been about 6 or 7 years ago, but my boss and I had a conversation about this.  We looked out the office window into the warehouse and I asked him how much we had tied up in the inventory we could see from there.  "About $350,000".  "You'll need to spend at least that much, all at once, to get to the next level or even remain competitive in the industry in another 5 years."

His wife swears she heard his sphincter pucker from across town.

It took him a couple years to fully digest that brief conversation and weigh the implications of various scenarios, but in the end we're spending more than that to remain the top shop in our market area.  You have to go almost 200 miles to find a firm with greater capability, and we've got a great staff to send with our gear.

In a long, round-about way this brings me to another bullet point:

7 - Any particular amount of capability costs the same.  By that I mean that the costs of entry at a give level (bar, club, theater, arena) remain roughly the same from year to year.  Twenty-five years ago the capital equipment costs of opening a regional sound company was about $300K.  Today it still is, but the difference in output, quality, packaging and deployment is tremendous.  Someone entering the business from scratch, with no purchase legacy or history is spending his money only once (so far), whereas an owner in an upgrade cycle is re-spending.  Guess who has the advantage?  Throw in that promoters really want to see current technology to avoid hassles with artistic crew, and there is a marketing advantage as well.  This leads us to...

7(A) - The wrong piece of gear at the 'right' price is still the wrong piece of gear

7(B) - Buy once, cry once.

[Geoff Doane]

Thanks for this article Dick. It's a big help. I have checked the specs on all my speakers and can't find mention of this all-important efficiency spec. Is this usually published or does one have to contact the manufacturer?

Strictly speaking, the chart should have used the term "sensitivity", not "efficiency".  Two speakers with the same efficiency can easily have different sensitivity ratings if the dispersion pattern is different.  And that's even if you're controlling for the other factors that Tim and Ivan have mentioned.  Put a given HF driver on a nominal 60 x 40 horn, and you'll get a sound pressure level 2 dB higher than the same driver on a 90 x 40 horn, assuming you measure the sound on-axis.

With a given electrical power input, the driver puts out the same acoustic energy, but the different horns spread the sound out more or less, depending on the model.  A compression driver could have efficiency as one of its specs, but I only recall seeing that in the case of the old Peavey 22A (25% IIRC).

Maybe the reason you don't see a spec for sensitivity or efficiency is because you have powered speakers?  Since you don't have any options on how to power them, the manufacturers tend to just specify the maximum output.  And if that's just a single number, it can be subject to all the marketing games of conventional speakers.

GTD

[Tim McCulloch]

Strictly speaking, the chart should have used the term "sensitivity", not "efficiency".  Two speakers with the same efficiency can easily have different sensitivity ratings if the dispersion pattern is different.  And that's even if you're controlling for the other factors that Tim and Ivan have mentioned.  Put a given HF driver on a nominal 60 x 40 horn, and you'll get a sound pressure level 2 dB higher than the same driver on a 90 x 40 horn, assuming you measure the sound on-axis.

With a given electrical power input, the driver puts out the same acoustic energy, but the different horns spread the sound out more or less, depending on the model.  A compression driver could have efficiency as one of its specs, but I only recall seeing that in the case of the old Peavey 22A (25% IIRC).

Maybe the reason you don't see a spec for sensitivity or efficiency is because you have powered speakers?  Since you don't have any options on how to power them, the manufacturers tend to just specify the maximum output.  And if that's just a single number, it can be subject to all the marketing games of conventional speakers.

GTD

Bingo, +1, out of the ball park, etc.

Another transducer that specified an acoustic efficiency was Community's M4, around 50% IIRC.

[Luke Geis]

JBL released a book in the 50's, or 60's? that detailed a lot about distributed sound support system design. It differs from the normal method that we currently look at ( delay lines and point source ). The book prescribes that when doing sound with many speakers at low level, it is best to keep them within 20-25' of each other to minimize the effect of the time arrivals. It states that at this distance the arrival times won't be as noticeable and the downsides can be reduced.

Is there comb filtering still? Yes. Is there still a small amount of delay between speakers? Yes ( but very little to none ). I work for a company that does a lot of stuff where sound is distributed and we will fill a room with 24 or more speakers spread all about. You would be surprised that when in the room listening at low levels, the sound just seems to emanate from no real source and there isn't really any issues. Here is the beauty. Of course as you get closer to each speaker you can hear it more than the others. But because the listening level is low ( around 80db ) when you start top come into the other speakers area, you don't really notice a volume change, or delay. The idea sounds crazy, but until you actually do it, you won't believe it works.

[ProSoundWeb Community]