Disasster said:Should two speakers at 79dBSPL read 85dBSPL when played together?
Disasster said:thanks guys,
Im just trying to calibrate my speakers using the k system. http://www.aes.org/technical/documentDownloads.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?
Rod Gervais said: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 said: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?
boingoman said: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.
Rod Gervais said:Boingoman,
nope,
it doesn't work that way....
boingoman said: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.
boingoman said: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 said: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.
Rod Gervais said: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 said: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.