calibrating speakers

[Disasster]

Should two speakers at 79dBSPL read 85dBSPL when played together?

[boingoman]

Not necessarily. At certain points in space, at certain frequencies, maybe. It depends on a lot of variables. But you will probably not see a broadband increase of 6db no matter what.

[acegunn]

Originally Posted by Disasster

Should two speakers at 79dBSPL read 85dBSPL when played together?

FYI, doubling power gives a 3 dB increase. Doubling voltage gives a 6 dB increase. This is the power case.

[Disasster]

thanks guys,

Im just trying to calibrate my speakers using the k system. http://www.aes.org/technical/documen...s.cfm?docID=65

What would be the best way to do this? I was told to make each speaker at 79dBSPL...but thats only 82dBSPL. So would you suggest upping each speaker equally untill i reach 85dbSPL?


P.S - Im calibrating it by using a -20dBFS Pink noise

[Rod Gervais]

Originally Posted by Disasster

thanks guys,

Im just trying to calibrate my speakers using the k system. http://www.aes.org/technical/documen...s.cfm?docID=65

What would be the best way to do this? I was told to make each speaker at 79dBSPL...but thats only 82dBSPL. So would you suggest upping each speaker equally untill i reach 85dbSPL?

Each speaker individually set at 82 dB (Side by each) would produce 85dB IN A FREE FIELD.....

however - inside a small room - depending on where you were micing the speakers - you could easily have swings from that +/- 30dB depending on frequency..........

Everything begins with to what degree your room is treated and to what extent it colors your signals.....

You can't calibrate your speakers until you are able to take the room out of the equation.

Sincerely,

Rod

[Disasster]

Originally Posted by Rod Gervais

Each speaker individually set at 82 dB (Side by each) would produce 85dB IN A FREE FIELD.....

however - inside a small room - depending on where you were micing the speakers - you could easily have swings from that +/- 30dB depending on frequency..........

Everything begins with to what degree your room is treated and to what extent it colors your signals.....

You can't calibrate your speakers until you are able to take the room out of the equation.

Sincerely,

Rod

Alright thanks,

My room is treated, have around 12 bass traps and 12 Broadband absorbers.
But yes, my room is pritty bad, its 10feet wide, 11feet long and 7 and a half high.

Im using my SPL meter in my listening position, around 4 feet away from the wall.

[boingoman]

Originally Posted by Disasster

I was told to make each speaker at 79dBSPL...but thats only 82dBSPL. So would you suggest upping each speaker equally untill i reach 85dbSPL?

Ah. OK. Here's why they said that.

Double the speakers= +3db
Double the power = +3db

When you hook up both speakers on a stereo amp, you have both doubled your speaker area and doubled the power, for a 6db increase.

The key is that you have to be in the area where all the acoustic energy is focused and coherent to realize the full 6db. Outside a very small listening area, the total SPL increase will be more like 3-4db and the response will be uneven.


If this is for monitoring in a studio, where you will essentially be sitting in the "sweet spot" then if you set each speaker to be 79db you should be around 85db in the listening position when both are hooked up.

[Rod Gervais]

Originally Posted by boingoman

Ah. OK. Here's why they said that.

Double the speakers= +3db
Double the power = +3db

When you hook up both speakers on a stereo amp, you have both doubled your speaker area and doubled the power, for a 6db increase.

Boingoman,

nope,

it doesn't work that way.....

if I have 1 speaker putting out 80dB and sit a 2nd speaker by it putting out 80dB - the total output will be 83dB......... it doesn't matter if it's the same channel - a different channel - a different power amp........ 2 80dB signals side by each will add 3db....... add another 2 for another 3db - then 4 more - then 8 more- then 16 more - so a total of 32 speakers @ 80 dB will provide 95dB of output.......

The company's instructions contain an error........

Sincerely,

Rod

[boingoman]

Originally Posted by Rod Gervais

Boingoman,

nope,

it doesn't work that way....

Rod- you're right, of course, my bad. Up to a point. Or down to a point, really. Speakers only couple below frequencies determined by the distance between drivers. On a set of studio monitors on five foot centers, that means below about 110Hz. And since they wouldn't be a point source, there will be uneven response with a +6db peak in the centerline between the speakers and areas of severe cancellation off to the side. In the live sound world we call the centerline the "power alley".

Your speaker numbers vs. spl work if the speakers do not couple. If they do, then they are considered to be a point source, and either doubling it's area or doubling it's power will give you +3db. Doing both gives you +6 db.

For instance, a bass player with one 4X10 cab and a 200W amp. Since the drivers in the cab are coupled in the frequencies of interest, they are considered to be one point-source driver. If he stacks another 4X10 and uses the same amp, he gets +3db because now the two stacked cabs are considered to be one driver with double the area of the single cab. If he doubles the power to this system, he will see +6db total.

[acegunn]

That doesn't seem to make sense. Using that logic, a 1 W amplifier could have infinite SPL by having an infinite number of drivers.

Originally Posted by boingoman

Rod- you're right, of course, my bad. Up to a point. Or down to a point, really. Speakers only couple below frequencies determined by the distance between drivers. On a set of studio monitors on five foot centers, that means below about 110Hz. And since they wouldn't be a point source, there will be uneven response with a +6db peak in the centerline between the speakers and areas of severe cancellation off to the side. In the live sound world we call the centerline the "power alley".

Your speaker numbers vs. spl work if the speakers do not couple. If they do, then they are considered to be a point source, and either doubling it's area or doubling it's power will give you +3db. Doing both gives you +6 db.

For instance, a bass player with one 4X10 cab and a 200W amp. Since the drivers in the cab are coupled in the frequencies of interest, they are considered to be one point-source driver. If he stacks another 4X10 and uses the same amp, he gets +3db because now the two stacked cabs are considered to be one driver with double the area of the single cab. If he doubles the power to this system, he will see +6db total.

[Rod Gervais]

Originally Posted by boingoman

For instance, a bass player with one 4X10 cab and a 200W amp. Since the drivers in the cab are coupled in the frequencies of interest, they are considered to be one point-source driver. If he stacks another 4X10 and uses the same amp, he gets +3db because now the two stacked cabs are considered to be one driver with double the area of the single cab. If he doubles the power to this system, he will see +6db total.

Sorry buddy - but still not right......

OK - first off - we aren't concerned with cancellation or boosting here - just pure theory.... as I stated above - you could get 30 db boosts or dips depending on the room - and 2 speakers 6' apart (in a free field) would actually get a 3dB reduction - because you loose 6dB in the first 3 feet of transmission - and the the remaining signal would get a 3 dB boost.

But doubling the power to his system - or tripling it - or increasing it a hundred fold - only has to do with the capacity of total output -

The world doesn't know - nor does physics care - how much power a speaker has pushing it - it can only measure the actual output of the speaker itself.......

If a speaker has an 80dB signal - and you set an identical speaker next to it - with an 80dB signal - the sum of the 2 speakers will be 83dB (not allowing for cancellation or coupling - just calculating the pure energy itself).

It doesn't matter what the power source is capable of - all that matters is the signal....... this is a doubling of power (intensity)

you are confusing power with amplitude -

it takes 4 speakers at that same 80 dB to increase the amplitude by 6dB (which is double the SPL ) and this (6dB) is 4 times the intensity........

You can argue this all day long if you want - but you can't change the laws of physics..........

By your reasoning - 83 dB is louder or sofer depending upon the source...... and that's impossible......

Read this from Indinana Edu.

http://www.indiana.edu/~emusic/etext...plitude4.shtml

That should clear it up for you.......

Sincerely,

Rod

[mshilarious]

Originally Posted by acegunn

That doesn't seem to make sense. Using that logic, a 1 W amplifier could have infinite SPL by having an infinite number of drivers.

The output of the amp is dependent upon its load. It so happens for most amps when you double the load (going from say 8 ohm to 4 ohm by adding another cabinet), you can double the total power the amp puts out. Thus you have 2W total power rather than 1W. But you've split that power to two cabinets, thus each cabinet only has 1W, and total increase in SPL is only 3dB, not 6dB.

Adding cabinets only works until you cause the amp to melt by dropping its load too low

Alternatively, you could wire the added cabinets in series-parallel such that the load stays constant. In that case, the amplifier's output is constant, and you no longer are driving each cabinet to the same SPL as before. That is, your 1W output at 8 ohms is still 1W, just now split between 2 or 4 or 8 cabinets. In that case, SPL is theoretically unchanged, however if you spread them out on a stage, for a given listening position it might be louder because the listener is closer to the cabinet.

[Disasster]

right, so 1+1=2=+3dBSPL

So are you telling me that i need to set each speaker at 82dBSPL to get 85dBSPL?

[Rod Gervais]

Disasster,

again - this is all perfect in theory - as far s what you'll get - it is room dependant - so that all depends on just ow flat your room is........

Rod

[mshilarious]

Originally Posted by Rod Gervais

Disasster,

again - this is all perfect in theory - as far s what you'll get - it is room dependant - so that all depends on just ow flat your room is........

Rod

If you are measuring using a handheld SPL meter, it shouldn't be hugely different for pink noise, especially if you are on A weighting, which will ignore all those pesky bass frequencies where you may have nodes. That method won't work as well if you are trying to calibrate a sub, but for setting relative levels of two mains, and overall mix level you should be fine.

[acegunn]

Yeah, I guess I was ignoring the impedance change w/ 2 speakers (I assumed a constant 1 W amplifier output). It seemed that the implication was 3 dB for doubling the power + 3 dB because of proximity = 6 dB for two speakers.

Originally Posted by mshilarious

The output of the amp is dependent upon its load. It so happens for most amps when you double the load (going from say 8 ohm to 4 ohm by adding another cabinet), you can double the total power the amp puts out. Thus you have 2W total power rather than 1W. But you've split that power to two cabinets, thus each cabinet only has 1W, and total increase in SPL is only 3dB, not 6dB.

Adding cabinets only works until you cause the amp to melt by dropping its load too low

Alternatively, you could wire the added cabinets in series-parallel such that the load stays constant. In that case, the amplifier's output is constant, and you no longer are driving each cabinet to the same SPL as before. That is, your 1W output at 8 ohms is still 1W, just now split between 2 or 4 or 8 cabinets. In that case, SPL is theoretically unchanged, however if you spread them out on a stage, for a given listening position it might be louder because the listener is closer to the cabinet.