OK, so both "Xlim -7dB for continue power" and "Xlim -4dB for max power" need to be calculated WITH power compression numbers to know the true wattage of "continuous" and "max" power, right?
Nope, the power compression you need to be subtracted from the true wattage (AES power rating or Xlim -7dB) to calculate the true SPL outcome. So for instance if you calculated with HornResp a driver needs 1000watt to generate 130dB you need to calculate the power compression figure and distract it from the 130dB.
You can calculate the figure of power compression with HornResp. By using the concept I gave you earlier -> AES power = Xmax.
So to calculate power compression you look to the difference between HornResp prediction and the fact AES power = Xmax.
I'll give you an example in my next post...
How to calculate pwr compression figures in TH’s:
We know that a well engineered balanced PA drivers should reach its Xmax at AES power rating. So in case of the 18Sound 18LW2400 with a Xmax of 9,5mm should be reached at 1200Watt (AES power rating). Lucky for us 18Sound (is the only brand who) shares power compression figures for their drivers. In case of the 18LW2400 it suffers from 2,2dB at AES full power (1200W).
We also know the Re of the driver which is 5 Ohm. If you use this calculator you can calculate Eg (HornResp Voltage Input parameter) 1200W at 5Ohm = 77,46V for this driver.
If you use Xoc1’s TH18 HornResp input as an example you will see at 1200 watt (77,46V) the excursion reaches 12,3482mm at 48Hz.
The real Xmax is however 9,5mm so we need to lower the excursion with 2.8482mm in the HornResp excursion Graph. With trial and error you can find out Eg needs to be set at approx 59,6V to reach 9,5mm. Use the same calculator again to find out that 59,6V and 5 Ohm means 710W
Now we can calculate how many dB’s the difference is between 710W and 1200W.
1200 : 760 = Factor 1,69
Use the following calculator to calculate the factor of 1,69 into dB's.
You will read 2,28dB. If you compare that to the factory specs given for power compression (2,2dB) you can see how close it is.
I know I'm a terrible teacher but I tried to make it as simple as possible without using difficult formula's...
We know that a well engineered balanced PA drivers should reach its Xmax at AES power rating. So in case of the 18Sound 18LW2400 with a Xmax of 9,5mm should be reached at 1200Watt (AES power rating). Lucky for us 18Sound (is the only brand who) shares power compression figures for their drivers. In case of the 18LW2400 it suffers from 2,2dB at AES full power (1200W).
We also know the Re of the driver which is 5 Ohm. If you use this calculator you can calculate Eg (HornResp Voltage Input parameter) 1200W at 5Ohm = 77,46V for this driver.
If you use Xoc1’s TH18 HornResp input as an example you will see at 1200 watt (77,46V) the excursion reaches 12,3482mm at 48Hz.
The real Xmax is however 9,5mm so we need to lower the excursion with 2.8482mm in the HornResp excursion Graph. With trial and error you can find out Eg needs to be set at approx 59,6V to reach 9,5mm. Use the same calculator again to find out that 59,6V and 5 Ohm means 710W
Now we can calculate how many dB’s the difference is between 710W and 1200W.
1200 : 760 = Factor 1,69
Use the following calculator to calculate the factor of 1,69 into dB's.
You will read 2,28dB. If you compare that to the factory specs given for power compression (2,2dB) you can see how close it is.
I know I'm a terrible teacher but I tried to make it as simple as possible without using difficult formula's...
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school is now in session
THis is some good information.
Tell me more.
We know that a well engineered balanced PA drivers should reach its Xmax at AES power rating. So in case of the 18Sound 18LW2400 with a Xmax of 9,5mm should be reached at 1200Watt (AES power rating). Lucky for us 18Sound (is the only brand who) shares power compression figures for their drivers. In case of the 18LW2400 it suffers from 2,2dB at AES full power (1200W).
We also know the Re of the driver which is 5 Ohm. If you use this calculator you can calculate Eg (HornResp Voltage Input parameter) 1200W at 5Ohm = 77,46V for this driver.
If you use Xoc1’s TH18 HornResp input as an example you will see at 1200 watt (77,46V) the excursion reaches 12,3482mm at 48Hz.
The real Xmax is however 9,5mm so we need to lower the excursion with 2.8482mm in the HornResp excursion Graph. With trial and error you can find out Eg needs to be set at approx 59,6V to reach 9,5mm. Use the same calculator again to find out that 59,6V and 5 Ohm means 710W
Now we can calculate how many dB’s the difference is between 710W and 1200W.
1200 : 760 = Factor 1,69
Use the following calculator to calculate the factor of 1,69 into dB's.
You will read 2,28dB. If you compare that to the factory specs given for power compression (2,2dB) you can see how close it is.
I know I'm a terrible teacher but I tried to make it as simple as possible without using difficult formula's...
THis is some good information.
Tell me more.
How to calculate pwr compression figures in TH’s:
Second example:
Now I’ll take the RCF LF18N451 as example. The Xmax is 8,8mm and should be reached with 1500W (AES power rating). Use the first calculator to calculate the Eg Voltage for 1500 watt at 5 Ohm (Re driver). The outcome is Eg = 86,60V.
The excursion at 86,6V of the LF18N451 in Xoc1’s TH18-2 = 12,0918mm
So, again we lower the voltage until we reach 8,8mm. You will see it will need approx 63,05V.
Use the calculator again to find out 63,05V and a Re of 5Ohm = 795W.
500 : 795 = Factor 1,89.
Use the second calculator and you’ll find out this RCF suffers from 2,76dB at 1500 watts at 48Hz in Xoc1’s cab.
And you can use this for every driver that works in the corresponding TH, basreflex or 6th order bandpass. The only rules are the Fs of the driver needs to be lower than the Fb of the system and power rating should be given in AES standards...
Second example:
Now I’ll take the RCF LF18N451 as example. The Xmax is 8,8mm and should be reached with 1500W (AES power rating). Use the first calculator to calculate the Eg Voltage for 1500 watt at 5 Ohm (Re driver). The outcome is Eg = 86,60V.
The excursion at 86,6V of the LF18N451 in Xoc1’s TH18-2 = 12,0918mm
So, again we lower the voltage until we reach 8,8mm. You will see it will need approx 63,05V.
Use the calculator again to find out 63,05V and a Re of 5Ohm = 795W.
500 : 795 = Factor 1,89.
Use the second calculator and you’ll find out this RCF suffers from 2,76dB at 1500 watts at 48Hz in Xoc1’s cab.
And you can use this for every driver that works in the corresponding TH, basreflex or 6th order bandpass. The only rules are the Fs of the driver needs to be lower than the Fb of the system and power rating should be given in AES standards...
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Power Compression data
@ Djim
Hi, actually more manufactures than in previous years are, & have been providing PC data for some time now 🙂 Here's several more that do.
Beyma/Fane/Precision Devices/Selenium
Thats just a quick list i put together, so expect to see more from other manufactures as well.
PC is often overlooked, or not known about, by a lot of people, which more times than not, leads to them wondering why their system doesn't sound as loud as they thought it would, even when throwing lots of power into it. And that's one of the reasons they blow them up !
So it's nice to see you providing some good info etc on the subject for folks.
@ Djim
Hi, actually more manufactures than in previous years are, & have been providing PC data for some time now 🙂 Here's several more that do.
Beyma/Fane/Precision Devices/Selenium
Thats just a quick list i put together, so expect to see more from other manufactures as well.
PC is often overlooked, or not known about, by a lot of people, which more times than not, leads to them wondering why their system doesn't sound as loud as they thought it would, even when throwing lots of power into it. And that's one of the reasons they blow them up !
So it's nice to see you providing some good info etc on the subject for folks.
Thanks Zero D and I didn't know the other brands you mentioned also released these numbers for 'public domain use'.
I gave you a complete worked out method and the calculating tools, so now its your turn Olsound!
Sorry at this moment I am not near a computer
Also I have to read this about ten times before I get it
Slow processor
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My turn 🙂
I’ll attempt the B&C 18SW115.
The Xmax is 14mm and should be reached with 1700W (AES power rating). I'll use the first calculator to calculate the Eg Voltage for 1700 watts at 5.3 Ohms (Re driver). The outcome is Eg = 94.92V.
The excursion at 94.92V of the 18SW115 in Xoc1’s TH18 = 13.1353mm
So, again we lower the voltage until we reach...wait, we're already below xmax. What now?
Note: I'm wondering if my HR inputs are slightly different that Djim's - my plots for the RCF and 18 Sound examples were a couple tenths off (so, very slight difference).
Also note: I used 18 Sound's xmax calculation for this B&C driver which is actually the listed xmax by B&C.
I’ll attempt the B&C 18SW115.
The Xmax is 14mm and should be reached with 1700W (AES power rating). I'll use the first calculator to calculate the Eg Voltage for 1700 watts at 5.3 Ohms (Re driver). The outcome is Eg = 94.92V.
The excursion at 94.92V of the 18SW115 in Xoc1’s TH18 = 13.1353mm
So, again we lower the voltage until we reach...wait, we're already below xmax. What now?
Note: I'm wondering if my HR inputs are slightly different that Djim's - my plots for the RCF and 18 Sound examples were a couple tenths off (so, very slight difference).
Also note: I used 18 Sound's xmax calculation for this B&C driver which is actually the listed xmax by B&C.
Can you show me the HornResp input and responses from the B&C 18SW115, cause we seem to use different data and somehow I don't get a nice response from that driver in the Xoc1's TH18-2...
B&C's Xmax = 13,5mm if you use RCF's method. But I need to model a basreflex to see if that method works.
B&C's Xmax = 13,5mm if you use RCF's method. But I need to model a basreflex to see if that method works.
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