Setting Limiter Values
rhyde
Posts: 10
Hi All,
Today I dug out my gear, a DVM, and 1/2 of a speaker cable and decided to see if I could figure out how to set the limiters for speaker protection. I'd like to find out if I'm doing the right thing or if I've gone horribly off track somewhere.
Here is the system I'm trying to set up:
1. Focusrite OctoPre MkII Dynamic Preamps and A/D converters, feeding into:
2. Software Audio Console (SAC), feeding back into the Focusrite Octopre MkII Dynamics with D/A converters feeding into:
3. DriveRack 4800 (in ChA: left FOH, in ChB: right FOH, in ChC: Aux-fed sub, in ChD: Aux-fed sub; note that C&D get the same signal).
DR4800 output 1 goes to LSub,
output 2 goes to LLow,
output 3 goes to LHigh,
output 4 goes to RSub,
output 5 goes to RLow,
output 6 goes to RHigh
(before anyone comments, I only have one channel of aux-fed subs. It gets duplicated to in channels C&D.
Someday, when I add a center-fill speaker, this will change; it's just out of laziness. There
really aren't left and right sub channels.
4. LSub goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 728s cabinets.
5. RSub goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 728s cabinets
6. LLow goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 725 cabinets (LF in bi-amp mode)
7. LHigh goes to two channels of an XTi 2000 amp (Y-input on the amp); those channels go to 2 SRX 725 cabinets (HF in bi-amp mode)
8. RLow goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 725 cabinets (LF in bi-amp mode)
9. RHigh goes to two channels of an XTi 2000 amp (Y-input on the amp); those channels go to 2 SRX 725 cabinets (HF in bi-amp mode)
Okay, somewhere on line I found out that the 2268H woofers in the SRX 725 can take 70v RMS and 140v peak; the HF driver in the 725 cabinet can take 34.6v; and the SRX 728s can take 121V. Don't know if these numbers are correct; they don't appear anywhere in JBL's documentation, so I assume an email to JBL technical support is in order. In any case, these numbers are good enough for my current purposes.
The very first thing I did was set up the gain structure for my system. I fed various sine waves into my preamps (50 Hz, 500 Hz, and 5000 Hz, depending on which amplifiers I wanted to set up) and adjusted the input gain to clipping and then turned the gain knobs down one click so there was no clipping. I then when into SAC and adjusted input and output levels to the same exact point (just below clipping). Went into the DR4800 and did the same thing on both inputs and outputs. Finally, I turned on my amps (no speakers attached) and did the same thing on all six amplifier channels. Everything is operating at just below clipping, just as we want.
Now, theoretically, the SRX 728s and the LF drivers of the SRX 725 cabinets don't actually need any peak limiters set as the amps put out less power than the peak ratings for the drivers (I'll worry about RMS limiters in a later post). So I left the limiters turned off on these channels for the time being. Eventually, I will set the limiters at the clip value (that is, the voltage that the amps were putting out when everything was set to just below clipping).
For the HF drivers in the SRX 725 cabinet (34.6V -- not sure if that number is peak or RMS, so I treat it like peak), I measure the output voltage from the XTi 2000 at just below clipping. It was somewhere around 68-70V. So I turned on the limiter for that output channel and adjusted the threshold down until I was seeing between 28-31V on my trusty DVM.
So, the question I have -- is this an appropriate way to set the limiters for each of the output channels? Or am I going about this all wrong?
And if it is, where do you get the peak (and RMS) voltage levels for drivers (beyond calling technical support for the driver's manufacturer)? I would assume that if you set thresholds by looking at voltages as I have done, this information should be available somewhere in the manufacturer's documentation. This is the part that scares me about the procedure I've just tried.
FWIW, my threshold for the JBL SRX 725 HF driver was around -7 dB (IOW, cut the input to less than 1/4). Given that the XTi 2000 amp puts out 475 watts into 8 Ohms and the JBL 2451H HF driver in the 725 has a rating of 75/150/300 watts, this actually seems like a reasonable number to have come up with (well, assuming I'm shooting for an RMS limiter rather than a peak limiter -- probably ought to add 3 dB back if I make it a peak limiter).
Cheers,
Randy Hyde
Today I dug out my gear, a DVM, and 1/2 of a speaker cable and decided to see if I could figure out how to set the limiters for speaker protection. I'd like to find out if I'm doing the right thing or if I've gone horribly off track somewhere.
Here is the system I'm trying to set up:
1. Focusrite OctoPre MkII Dynamic Preamps and A/D converters, feeding into:
2. Software Audio Console (SAC), feeding back into the Focusrite Octopre MkII Dynamics with D/A converters feeding into:
3. DriveRack 4800 (in ChA: left FOH, in ChB: right FOH, in ChC: Aux-fed sub, in ChD: Aux-fed sub; note that C&D get the same signal).
DR4800 output 1 goes to LSub,
output 2 goes to LLow,
output 3 goes to LHigh,
output 4 goes to RSub,
output 5 goes to RLow,
output 6 goes to RHigh
(before anyone comments, I only have one channel of aux-fed subs. It gets duplicated to in channels C&D.
Someday, when I add a center-fill speaker, this will change; it's just out of laziness. There
really aren't left and right sub channels.
4. LSub goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 728s cabinets.
5. RSub goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 728s cabinets
6. LLow goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 725 cabinets (LF in bi-amp mode)
7. LHigh goes to two channels of an XTi 2000 amp (Y-input on the amp); those channels go to 2 SRX 725 cabinets (HF in bi-amp mode)
8. RLow goes to two channels of an ITech 8000 amp (Y-input on the amp); those two channels go to 2 SRX 725 cabinets (LF in bi-amp mode)
9. RHigh goes to two channels of an XTi 2000 amp (Y-input on the amp); those channels go to 2 SRX 725 cabinets (HF in bi-amp mode)
Okay, somewhere on line I found out that the 2268H woofers in the SRX 725 can take 70v RMS and 140v peak; the HF driver in the 725 cabinet can take 34.6v; and the SRX 728s can take 121V. Don't know if these numbers are correct; they don't appear anywhere in JBL's documentation, so I assume an email to JBL technical support is in order. In any case, these numbers are good enough for my current purposes.
The very first thing I did was set up the gain structure for my system. I fed various sine waves into my preamps (50 Hz, 500 Hz, and 5000 Hz, depending on which amplifiers I wanted to set up) and adjusted the input gain to clipping and then turned the gain knobs down one click so there was no clipping. I then when into SAC and adjusted input and output levels to the same exact point (just below clipping). Went into the DR4800 and did the same thing on both inputs and outputs. Finally, I turned on my amps (no speakers attached) and did the same thing on all six amplifier channels. Everything is operating at just below clipping, just as we want.
Now, theoretically, the SRX 728s and the LF drivers of the SRX 725 cabinets don't actually need any peak limiters set as the amps put out less power than the peak ratings for the drivers (I'll worry about RMS limiters in a later post). So I left the limiters turned off on these channels for the time being. Eventually, I will set the limiters at the clip value (that is, the voltage that the amps were putting out when everything was set to just below clipping).
For the HF drivers in the SRX 725 cabinet (34.6V -- not sure if that number is peak or RMS, so I treat it like peak), I measure the output voltage from the XTi 2000 at just below clipping. It was somewhere around 68-70V. So I turned on the limiter for that output channel and adjusted the threshold down until I was seeing between 28-31V on my trusty DVM.
So, the question I have -- is this an appropriate way to set the limiters for each of the output channels? Or am I going about this all wrong?
And if it is, where do you get the peak (and RMS) voltage levels for drivers (beyond calling technical support for the driver's manufacturer)? I would assume that if you set thresholds by looking at voltages as I have done, this information should be available somewhere in the manufacturer's documentation. This is the part that scares me about the procedure I've just tried.
FWIW, my threshold for the JBL SRX 725 HF driver was around -7 dB (IOW, cut the input to less than 1/4). Given that the XTi 2000 amp puts out 475 watts into 8 Ohms and the JBL 2451H HF driver in the 725 has a rating of 75/150/300 watts, this actually seems like a reasonable number to have come up with (well, assuming I'm shooting for an RMS limiter rather than a peak limiter -- probably ought to add 3 dB back if I make it a peak limiter).
Cheers,
Randy Hyde
0
Comments
Sorry to tell you that other than a few of us that answer posts, there is little traffic and even less SKILLED level practitioners here. You would get a LOT more help somewhere like the PSW if you can't find what you need here... that said, does this help?
viewtopic.php?f=60&t=2242
That helps a lot.
Though I should point out that posts to PSW are generally followed up with a link to this site
Nevertheless, I've learned that if I keep asking and keep searching, sooner or later I get the answer I'm seeking.
Thanks for the help and support.
Someday, I will document this procedure and publish it so others can benefit from what I'm learning.
Cheers,
Randy Hyde