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[Chris Jensen]

Hi All,

I have a rider that wants "110dB SPL RMS at the FOH position".  I am not contracting the group, however I wanted to make sure that the person I am working with clearly understands what they are potentially agreeing too or not.  I will advise to push back a little and have that conversation with the band management so that they are aware of what I can offer.  I wanted to check my math and see what that will take.

Looking at a chart that shows dB drop over distance I see at about 100' there is 29.5dB drop.  This means that to get 110dB at FOH at 100' I would need a speaker that can output 140dB at 1W/1m.  In my case of a single K12, published at 131dB, the most I can get at 100' is 101dB.  Is my understanding correct?

I understand that this is all theoretical and there are so many other factors that it isn't this simple.  I want to be able to make sure that if there is any push back I can have some quick math done.  Let's hope there is no push back as they are out of luck if they do.

Chris

[Mark Cadwallader]

I don't think that "RMS" has anything to do with respect to an SPL level. As somebody will probably point out, there is no weighting or response time specified, so it is impossible to determine whether or not you meet the "specification in the rider."

[Steve Crump]

Hi All,

I have a rider that wants "110dB SPL RMS at the FOH position".  I am not contracting the group, however I wanted to make sure that the person I am working with clearly understands what they are potentially agreeing too or not.  I will advise to push back a little and have that conversation with the band management so that they are aware of what I can offer.  I wanted to check my math and see what that will take.

Looking at a chart that shows dB drop over distance I see at about 100' there is 29.5dB drop.  This means that to get 110dB at FOH at 100' I would need a speaker that can output 140dB at 1W/1m.  In my case of a single K12, published at 131dB, the most I can get at 100' is 91dB.  Is my understanding correct?

I understand that this is all theoretical and there are so many other factors that it isn't this simple.  I want to be able to make sure that if there is any push back I can have some quick math done.  Let's hope there is no push back as they are out of luck if they do.

Chris

QSC has a great "K" series rental guide. Look at page 8. I will attach a link.

As far as riders, every time I have contacted an artist's management about a part of a rider that we could not fulfill, I have either been told, "as long as your meet these other requirements we are good" or either, "don't worry about it".

I think the basic idea is to set a standard so the artist doesn't end up with a sub-par production. Most of the riders I have seen look like a modified copy of another artist's rider.
The groups that I have worked with that have specific dB requirements have never metered it.

I was told by one agent that they just put items in the rider to make sure you are paying attention and of course, it doesn't hurt if they can get the extras provided.
Once we did provide a fruit tray as asked in the rider and no one from the band touched it, so since then we have refused and no management or group has bucked it. The artist said they didn't know that it was in the rider.

Just talk to their management about your concerns.

https://www.qsc.com/resource-files/applicationguides/professional/q_ag_sys_spk_k_series_rental.pdf

[Art Welter]

Hi All,

1)I have a rider that wants "110dB SPL RMS at the FOH position".
2)Looking at a chart that shows dB drop over distance I see at about 100' there is 29.5dB drop.  This means that to get 110dB at FOH at 100' I would need a speaker that can output 140dB at 1W/1m.  In my case of a single K12, published at 131dB, the most I can get at 100' is 91dB.  Is my understanding correct?
3)Let's hope there is no push back as they are out of luck if they do.

Chris,

1) Since sound drops at 6 dB per doubling of distance, you can easily "meet the rider" by moving the FOH position close to the stage.
2) 131-30 is 101, not 91. One 131 dB/1 meter speaker could produce 101 dB at 32 meters, two could produce 107 dB, add room walls and it's possible to get more than 110 dB.
3) Or your K12 is "out of luck", and the show sucks when it lets out the magic smoke.

110 dB, if low frequency, is not unusually loud. If the band is expecting some real low end and you show up with one K12, expect some "push back" ;^).
Of course, bands with real expectations generally will make production calls..

Cheers,
Art

[Tim McCulloch]

Hi Chris-

Good comments and advice so far.  I'll add that when contacting artist's management the response will be "it's all good!"  And NOTHING in that conversation will make to the artist or crew... Nothing, nada, zip, zero.

If you can get a contact name and phone number for the artist's production manager or equivalent, tell them about the room size, shape, capacity, PA, monitors, etc that will be provided.  Give them a chance to say "yeah, we can make that work" or "uh... I think we need to do more regarding...." 

[Don T. Williams]

+1 for Art and Tim's replies.  In a room it will be very hard to predict the levels unless you know a whole lot about the room and can model it correctly.  I've a tech rider where they ask for 130 db 30Hz to 20KHz measured at 125 feet or, in indoors, any place in the room.  I DID NOT take the job !

[Ivan Beaver]

And now for the "technical side".

First of all, SPL RMS is a term that does not exist.  RMS is a voltage term, specific to 0.707 of the peak of the waveform.

If they are talking about "average level as read on a SPL meter", then you must add about 15dB to that number for the peak capability, due to the dynamic range of music.  Some styles are greater, some are less, 15dB is a good "starting number".

So you need to figure on at least 125-130dB peak at FOH, PLUS the SPL loss over distance.

Next, it does not say A or C weighting. fast, slow or peak.

If you ask me, and want to be "picky" then you can "assume" that an unweighted peak measurement is all they are asking for.

If they wanted it louder, they should say specifically.

What people "assume" changes over time.

Back last century, C weighting fast was pretty much the standard.

Today (wrongly of course) A weighting seems to be more popular.

But A weighting was never intended for use with loud noises (it was intended for use 80dB), so even if you get a reading, does not relate to how it is supposed to be used.

But doing it wrong doesn't stop many people.

[Ivan Beaver]

Hi Chris-

.  I'll add that when contacting artist's management the response will be "it's all good!"  And NOTHING in that conversation will make to the artist or crew... Nothing, nada, zip, zero.

Yeah, like getting a current stage plot of the ACTUAL BAND that will be performing that night, NOT, what the band looked like 4 years ago--------


I've seen that quite a few times.

[Frank Koenig]

And now for the "technical side".

First of all, SPL RMS is a term that does not exist.  RMS is a voltage term, specific to 0.707 of the peak of the waveform.

Let's try to clarify a few things. While SPL RMS is not a customary term in day-to-day sound work, it does have a useful meaning. Sound pressure and volume velocity scale as the square root of sound power. The microphone in a sound level meter produces a voltage proportional to sound pressure. To get an estimate of sound power this voltage is generally full-wave rectified and low-pass filtered. (The cutoff frequency of the low-pass determines "fast'" or "slow".) This estimate is accurate for sine waves and while good enough for most purposes it is not a good estimator of sound power for complex waveforms. It was used (and incorporated into standards, I think) because of the expense and difficulty of implementing a true RMS computation in the analog days. For complex waveforms the RMS of the sound pressure is the correct estimator of sound power. This is analogous to the measurement of electrical voltage (sound pressure), current (volume velocity), and electrical power (sound power).

On the loss of sound pressure and power with distance. For a spherical wave in a free field the sound power falls as the inverse square of the distance and the sound pressure falls as the inverse of the distance. This results in the familiar 6dB drop for each doubling, whichever way you figure it. In a room the sound pressure falls more slowly due to reverberation, the difference between the actual and free field sound pressure being referred to as room gain. This is why you need more subs outdoors.

This is not in defense of the OP's admittedly malformed rider. Just trying to keep the discussion from being "simple and wrong".

--Frank   

[Stephen Kirby]

Just put the FOH right in front of the speakers. 

Or was there a distance specified that wasn't in the original post?  110dB, even C slow at 100' out is pretty darn loud where people will be.  Outside of a rave or head banger event this is way out of line.  We're way past speakers on sticks over subs territory.

In any event, I would just tell them what you have and let them (as Tim pointed out which means the band not the event coordinator) tell you if it's adequate.  Maybe send some pics of the venue so they can get a sense of how much space what you have will be trying to fill.  If they're someone you want to work with, they'll understand.

[Ivan Beaver]

Let's try to clarify a few things. While SPL RMS is not a customary term in day-to-day sound work, it does have a useful meaning. Sound pressure and volume velocity scale as the square root of sound power. The microphone in a sound level meter produces a voltage proportional to sound pressure. To get an estimate of sound power this voltage is generally full-wave rectified and low-pass filtered. (The cutoff frequency of the low-pass determines "fast'" or "slow".) This estimate is accurate for sine waves and while good enough for most purposes it is not a good estimator of sound power for complex waveforms. It was used (and incorporated into standards, I think) because of the expense and difficulty of implementing a true RMS computation in the analog days. For complex waveforms the RMS of the sound pressure is the correct estimator of sound power. This is analogous to the measurement of electrical voltage (sound pressure), current (volume velocity), and electrical power (sound power).

On the loss of sound pressure and power with distance. For a spherical wave in a free field the sound power falls as the inverse square of the distance and the sound pressure falls as the inverse of the distance. This results in the familiar 6dB drop for each doubling, whichever way you figure it. In a room the sound pressure falls more slowly due to reverberation, the difference between the actual and free field sound pressure being referred to as room gain. This is why you need more subs outdoors.

This is not in defense of the OP's admittedly malformed rider. Just trying to keep the discussion from being "simple and wrong".

--Frank

I would "argue" that the voltage that is the result of a specific pressure on the microphone is measured as RMS.  So that is the normal "SPL voltage".  There is no reason to state it.

It starts to get cloudy when you say "peak" SPL.  Is the peak, the peak voltage of the voltage waveform?  OR is it the maximum short duration signal that is received.

I know of one SPL meter, that when you put a know sine wave (like a 1K calibrator), you will read the same SPL on all scales and weighting, EXCEPT the peak scale.  It shows 3 dB louder.

So not only is it reading the peak voltage of the sine wave, but also the maximum short duration pressure reading.


And of course, being "technically correct", the rate of falloff is less inside rooms depends on a number of factors, including the size of the room.

The boundaries of the room will cause reflections (reverberation), which can result in the sound being louder further away, in extreme cases.

A friend of mine did a gig this past weekend in "whisper room", with other whisper rooms attached to the entrances.

We were looking at some waterfall plots he took and often out in time the reflections were several dB louder than the direct sound arrival.

There are a lot of "it depends", when it to trying to predict the rate of rolloff inside, one of which is totally freq dependent.

A simple easy answer is usually wrong.

[Chris Jensen]

Hi Everyone,

Thanks for all the info.

I knew some of you would respond just as you did.  I put the quotes around what they asked for as it was directly pulled from the rider.  That was my first clue that they are not quite sure what they are asking for other than as a few of you pointed out, they just don't want to get screwed.  There was no weighting, bandwidth or FOH location requirements.  Really what I wanted to get here was the basic real world math.

Art, thanks for pointing out I subtracted 40 not 30.  I will edit so that for the rest of time I don't look too bad.  Also as you pointed out Art, FOH is not defined meaning that if closer than it's louder.  I don't intend on being that far, but again for the sake of application beyond this issue, I want to be able to have the right concept for future.  It's not often that I have to worry about contracts and requests, so I don't usually do the work to qualify the system to any given constraints.

I know I didn't give much detail as I was more interested in the math.  The event will be outside.  It is a small 2 stage festival on a college campus that is in its infancy.  I am partnering with the programmers to supply PA and labor.  The rider in question is on stage 2 and getting the QSC K12 and KW181 system.  The other stage gets the ARCSII and SB28s.  Due to how campus works with vendors I want to make sure that the rider is taken into consideration as the band contract is way nicer and simpler than what campus makes the band go through.  I don't want to be in a position where they have entered into a giant contract with campus yet we can't provide their somewhat simple requirements.

Tim, the next step is to talk to someone on their end and I'm sure as soon as we start talking they will be fine.  I just wanted to have my math confirmed so if it comes up I have some confidence.

Thanks All!

[Caleb Dueck]

Hi Everyone,

Thanks for all the info.

I knew some of you would respond just as you did.  I put the quotes around what they asked for as it was directly pulled from the rider.  That was my first clue that they are not quite sure what they are asking for other than as a few of you pointed out, they just don't want to get screwed.  There was no weighting, bandwidth or FOH location requirements.  Really what I wanted to get here was the basic real world math.

Art, thanks for pointing out I subtracted 40 not 30.  I will edit so that for the rest of time I don't look too bad.  Also as you pointed out Art, FOH is not defined meaning that if closer than it's louder.  I don't intend on being that far, but again for the sake of application beyond this issue, I want to be able to have the right concept for future.  It's not often that I have to worry about contracts and requests, so I don't usually do the work to qualify the system to any given constraints.

I know I didn't give much detail as I was more interested in the math.  The event will be outside.  It is a small 2 stage festival on a college campus that is in its infancy.  I am partnering with the programmers to supply PA and labor.  The rider in question is on stage 2 and getting the QSC K12 and KW181 system.  The other stage gets the ARCSII and SB28s.  Due to how campus works with vendors I want to make sure that the rider is taken into consideration as the band contract is way nicer and simpler than what campus makes the band go through.  I don't want to be in a position where they have entered into a giant contract with campus yet we can't provide their somewhat simple requirements.

Tim, the next step is to talk to someone on their end and I'm sure as soon as we start talking they will be fine.  I just wanted to have my math confirmed so if it comes up I have some confidence.

Thanks All!

The quick skim I took of the thread implies the band isn't into math and SPL, but weeding out cheaper systems.  I don't know about them, but if I were the BE I'd take L'Acoustics and feel shafted with KW anything.   

Sent from my VS980 4G using Tapatalk

[Patrick Cognitore]

The event will be outside. 

Ouch. How far out are you putting FOH? I suggest as close as possible. I can't imagine K12's sounding very good if you're trying to get 110db out of them at a great distance from the stage.

Maybe you need to clarify with the festival programmers how large of an area you'll be expected to cover with sound with each system. I'd imagine an event of this type probably has DB limits, I doubt 110dB at 100' is going to be an acceptable volume, particularly if there is another stage playing nearby.

As someone else mentioned, I would be supremely disappointed to be playing on a stage equipped with k12's when there is L'Acoustic right next door. But I'm sure there are budgetary considerations here too.

[Stephen Kirby]

Outdoors a pair of K12s over single 18s would be okay for folk music in the park for a couple hundred people, just.  Maybe a blues band at nice comfortable old folks volume.  80-85dBC at 100' out.  No way will such a system carry an entire band at 110dBC even 50' out in front.  Good reliable stuff that sounds good at moderate volumes, not your pretender pile-o-cheap boxes.  But not rock and roll either.  Tell the acts on that stage what they're going to get.  Let them decide if they want to complain to the promoter and get someone to pony up for more.

[John L Nobile]

I've gotten riders with SPL requirements. None have had any reference (A, C etc) and only a few have stated at FOH. The most common one I've seen is "capable of 110db". My phone probably does that if I put it up to my ear.

What I've always done is contact the sound tech and tell him what's in the room and the bands that have played on that system. SPL has never come up in conversation.

[Tim McCulloch]

Outdoors a pair of K12s over single 18s would be okay for folk music in the park for a couple hundred people, just.  Maybe a blues band at nice comfortable old folks volume.  80-85dBC at 100' out.  No way will such a system carry an entire band at 110dBC even 50' out in front.  Good reliable stuff that sounds good at moderate volumes, not your pretender pile-o-cheap boxes.  But not rock and roll either.  Tell the acts on that stage what they're going to get.  Let them decide if they want to complain to the promoter and get someone to pony up for more.

Sure you can rock and roll them... just don't expect it to sound good.

I "stuffed" an entire 5 piece band mix through a pair of Mackid Thuds® with companion subs for a songwriter showcase where everything else was 2 acoustic guitars and 1 or 2 singers.  It's where I learned to hate on the Thuds® (before I stuffed that mix in these shitty boxes).  It can be done but it sure won't be pretty.

Again the best bet is to advance the show with performers and see if, perhaps, the PA for the B stage need to be butched up a little/lot.

[Ivan Beaver]

I've gotten riders with SPL requirements. None have had any reference (A, C etc) and only a few have stated at FOH. The most common one I've seen is "capable of 110db". My phone probably does that if I put it up to my ear.

.

What many don't realize is how much the "little numbers" matter.

I just retested this, with my peak reading meter.

At 1M, a single hand clap was around 126dB peak.  A slow was 89dB, A fast was 98dB  (give or take a couple of tenths)

I could snap my fingers at 1meter and get a little over 103dB peak, A slow was 68dB, A fast was 74dB (give or take a couple of tenths)

[Ivan Beaver]

The most common one I've seen is "capable of 110db". My phone probably does that if I put it up to my ear.

I just tried the phone measurement.

With "pop" video playing, on speaker phone, mic close to speaker (in the phone), I got 103 A slow, 106A fast and 124dB peak.

YES, details matter.

[Scott Holtzman]

Ouch. How far out are you putting FOH? I suggest as close as possible. I can't imagine K12's sounding very good if you're trying to get 110db out of them at a great distance from the stage.

Maybe you need to clarify with the festival programmers how large of an area you'll be expected to cover with sound with each system. I'd imagine an event of this type probably has DB limits, I doubt 110dB at 100' is going to be an acceptable volume, particularly if there is another stage playing nearby.

As someone else mentioned, I would be supremely disappointed to be playing on a stage equipped with k12's when there is L'Acoustic right next door. But I'm sure there are budgetary considerations here too.

Numbers aside, except for a small gathering of spectators around an acoustic performance outside K12's are completely inadequate. 

Honestly for any type of amplified music I get a little cringe at folks that only want to rent KW153's and 4 KW181's (still speaking about outside).

On a warm day we stacked 3 aside FBT Muse 210's over two STX828s (on 4kw Powerlights each) and I would call that adequate.

Ditto for a texas swing band on the pool deck of a cruise (probably 150' to the back) with 4 Kara and two SB28's aside.  That got the job done, well.  But if a rock band or possibly even a DJ and a rowdy crowd we would have been wishing for more rig.

Small powered suspension speakers just don't cut it outside. 

Maybe you could rent something for the B stage?  Even a pair of VRX on poles (something cheaply rented) would be no sonic masterpiece but it would enough headroom. 

[John L Nobile]

I just tried the phone measurement.

With "pop" video playing, on speaker phone, mic close to speaker (in the phone), I got 103 A slow, 106A fast and 124dB peak.

YES, details matter.

The ring tone seems to go much louder in the middle of the night.

[Ivan Beaver]

The ring tone seems to go much louder in the middle of the night.

I didn't try that.

Maybe tomorrow

[Chris Jensen]

Thanks for all the conversation about this!  I didn't expect this much activity.

Unfortunately for the band this is a B stage.  It's always fun to look at things from a purely gear related point of view.  I love to do that.  I am in what I think is a somewhat unique situation that many of you do not deal with.  Being on a university is like another world!  For example, I am required to provide a weekly Noontime concert on campus.  There are SPL policies, however none of that really matters as Ivan points out that it's all about how you measure.  For us it is all about disturbance.  If I had a complaint I would have a hard time telling campus police that they are wrong and don't know what they are doing because my measurements are better than the measurement of my class is being disturbed.  It's more of a how many units of SPL = 1 unit of "turn that down". 

I am not a K12 lover, however it is hard to beat as a tool for the jobs I must complete.  You would be surprised at how much volume a K12 over 2 KW181s can do in *the right space*.  No it's not gonna rock the house, but if I do that then I get complaints from admin buildings.  I am against a wall for much of what I do.  Anything else is wasteful.  I have gotten my students to the point where from rolling gear to power distro to making noise takes about 35 mins for two people.  I could go bigger for daily gigs, but I must find a balance of speed to quality.  Plus I did have an opportunity to look into a small array package, but can you imagine the look I would get from a school admin when I need a few hours to rig arrays for an hour a week?  Another great outcome is the students learn how to use the gear effectively instead of blame the tool.  They get decent results without resorting to something top of the line.

As far as this show goes, the ARCS are way too much but it is what I have.  Again, I am against a wall that we will be shut down fast if I am disturbing neighbors or any other building on campus.  To be honest in some ways I wish I had enough of the small powered gear for both stages.  I have a lot of extra setup for a system that is way too big compared to the daily system setup.  I will actually need to set up more stage so that the sight lines of the ARCS are dealt with instead of a nice small speaker over some subs.

My 100' for FOH was a number out of the air for the sake of comparison.  In all the examples that have been used what if FOH is off to the side of stage and an Ipad is used?  My point in asking was to make sure that I did my math correctly for SPL loss over distance.  This rider made me think.  The question was not as much for this event and its unique specifics and requirements, but more so to take a look at the document and requirements that this band asks for for EVERY event without knowing any details about the unique show.  Art broke down the math exactly for what I was asking.

The last thing in my head is that when we contract a band from my end, we are contracting with the same weight and requirements that the state requires.  From my point of view we have a ton of power in what is agreed to.  The band must go through pages of paperwork that is many times irrelevant to what they are doing to get paid.  From their point of view their contract is we show up, maybe on time, play some music, get paid and go home.  The last thing I want is to be on the side of might and not be able to make good for what they ask as long as it is in reason.

The reason I didn't share too many details is that they are irrelevant to "110dB SPL RMS at the FOH position" and what the output of a speaker must be to make that in theory at 100'.  Having the 100' as a reference 50' and 25' can be predicted.  As I said this event is in its infancy and hopefully grows to something that becomes a big hit for years to come with money to go bigger.  At this point my students are super happy to get to do more than just another talking head event and apply some of their skills at a higher level.

I have valued each and every one of your comments.  Thank you for staying positive and constructive in your assessment of the event details instead of just telling me I am stupid or crazy for trying to do it at all.  Luckily the expectations are set low for this year.

Thanks,
Chris 

[Ivan Beaver]

The ring tone seems to go much louder in the middle of the night.

I use the "old style phone" ring tone.

I got 130dB peak, 116 A slow, 119 A Fast

This was right near the speaker

[ProSoundWeb Community]