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HELP! My speakers and amps aren’t in the presets! What now?
Amp sensitivity....
What is amp sensitivity anyway and why do I need it? Let’s say that an amplifier has a sensitivity spec of 1.2 volts. The amp manufacturer specifies then that with a 1.2 volt input the amp will achieve full output potential. So if we apply 1.2 volts to the amp and the attenuator is @ 12 o’clock position and the amp is rated for 1000 watts, we should have 1000 watts @ the outputs. So why do they put all that extra gain capability there if we can get full voltage out of it at ½ that available on the attenuator? The problem is the equipment we drive the amp with have divergent output voltages. That is to say that all equipment isn’t created equal, or standardized. Oh there is some basic standardization, but we have “consumer levelâ€? and “pro levelâ€? gear. A common spec you might see in consumer level gear is output -10 db, and pro level gear +3db. There are math calculations available that are beyond the scope of this discussion and available here:
http://www.audiokarma.org/forums/showthread.php?t=58829
but suffice it to say that @ -10 db the consumer level gear will need more amp gain to achieve full output than a +3db pro piece would to achieve full output. So, I’m using all pro gear, why not set the amps @ the published sensitivity rating and leave it at that? Well, you can. BUT what happens if we have a top speaker that is 103 db efficient at 1 meter at 1 watt of input power, and a sub that is front loaded and 94db efficient with the same 1 watt input at the same distance, 1 meter (these are common speaker measurements) the tops would be 9db louder (with the same amp used for both), and since 6 db is a about twice as loud, the subs would not be audible. So we can either drive the amp harder, as in adding gain @ the Driverack crossover output gain control, or turn one amp up or down. As we bring different amps, and gain structure into the picture as well you start to see that in a perfect world if we had the same 103db efficient tops and an amp that was 9db less efficient than the one driving the 94db efficient subs, then 1.2volts would achieve full output for both amps and a similar output from both speakers. Folks it isn’t a perfect world. So we get a mishmash of amps and speakers in stead of a perfect world setup and we need to make compromises. Those compromises can take the form of changes to the amps attenuator, or to the gain in the Driverack. Since the level of competence here is generally newbi, or new to pro audio, or digital processing, and since we place so much emphasis on gain structure here, it is simpler to use the gain controls on the amps to balance the different components of the system. You can however do either or both. I generally do. It’s kind of like a balancing act.
Now, why aren’t my speakers listed? What do I do now?
Well, for one thing, the Driverack has a finite storage location. To add all the different speakers made by all the worlds manufacturers to the database would require a huge storage allocation, and we would have an ever changing database as well as new speakers are developed. Add to that some speaker manufacturers don’t let out their info, or wish not to provide it for what they consider aftermarket, or third party processors…JBL happens to be a Harmon company as is DBX, and the other speakers in the data base were either provided by the manufacturer, or developed by DBX. In many cases, like say the Mackie C300 provided in the menu, only a bandpass filter is provided…all the other modules are just as they were without anything in them.
If we were to choose however the JBL SR4722x from the preset menu and load it into the GUI (graphical user interface.. available here:
http://www.dbxpro.com/Download/
for setup purposes, even if you don’t have a 260 or up this makes the whole thing much more understandable) you will see, by clicking on the xover, that they have provided crossover frequencies, slopes and even gain (which is useless without amp sensitivity provided…. Note how low the xover gains are…). If you look you’ll can see that the mid is the least efficient of the components, and that the horn is the most efficient. If you click on the various PEQ’s you will see that they have provided PEQ settings. They have also supplied Delay on the mid component. These are provided so that you can Tri-amp the speakers in lieu of the passive crossovers inside the speakers. Why Tri-amp/Bi-amp instead of using the passive crossovers? It is much easier to just use the internal crossovers after all? Simple.. efficiency…and in the end sound quality since a digital processor has much better tools available to achieve the crossover with the least impact on the sound quality.
Now add to this a subwoofer and we have a potential for some serious processing, and the ability to do so with the Driverack. With the SR4722x to add a sub we would have had to mono the lo mids to output 5 and had mono subs run off output 6. This is not something you can do with the DRPA, PX since they don’t have the capability of doing 4 way and up, and the PX has only 4 outputs. This then is an exercise for the 200 series on up.
So, you want to set up a preset for your particular system. Now what? Well, using a preset that doesn’t match your system and modifying it is one option, but it’s simpler to just set up a preset from scratch. It isn’t that hard or time consuming (speaker tuning without settings can be however ... and I don’t recommend this for beginners or novices). Select the Wizard by pressing the front panel button or using the GUI for those with the 200 series and up. A series of questions will be asked about your perspective setup. Make the selections from the menu which fit closest to your equipment. A selection of something that’s “CLOSE� to what I have would be better served by selecting “CUSTOM� since in some cases PEQ, and Delay are provided which could totally screw up your sound. Remember here that if you select dual mono or stereo unlinked you will need to process each of the components individually, and the same goes for the Auto Eq and so forth. This can be a good thing when a non symmetrical room provides “obstacles� on one side or the other we need to deal with. So once you have selected all the components as either exactly, or as “custom� we can move on to the tuning portion. For this you will need to go to one of the other sections in the FAQ�s that meets your needs.
For your own edification select a number of different setups(in the GUI) that are in the presets and see what different modules are used and what they did to them. This will help you when you want to add your own setups to the preset we have just created. In many cases when you go to a manufacturer’s site there will be a section for “tunings�, where you can look up your speakers. If they are NOT in there DON�T use something “Close�. Your better off to not do that as it can start you in the wrong direction. Instead, try a forum like this or the manufactures.
I’ll keep adding info here so check back from time to time.
G
What is amp sensitivity anyway and why do I need it? Let’s say that an amplifier has a sensitivity spec of 1.2 volts. The amp manufacturer specifies then that with a 1.2 volt input the amp will achieve full output potential. So if we apply 1.2 volts to the amp and the attenuator is @ 12 o’clock position and the amp is rated for 1000 watts, we should have 1000 watts @ the outputs. So why do they put all that extra gain capability there if we can get full voltage out of it at ½ that available on the attenuator? The problem is the equipment we drive the amp with have divergent output voltages. That is to say that all equipment isn’t created equal, or standardized. Oh there is some basic standardization, but we have “consumer levelâ€? and “pro levelâ€? gear. A common spec you might see in consumer level gear is output -10 db, and pro level gear +3db. There are math calculations available that are beyond the scope of this discussion and available here:
http://www.audiokarma.org/forums/showthread.php?t=58829
but suffice it to say that @ -10 db the consumer level gear will need more amp gain to achieve full output than a +3db pro piece would to achieve full output. So, I’m using all pro gear, why not set the amps @ the published sensitivity rating and leave it at that? Well, you can. BUT what happens if we have a top speaker that is 103 db efficient at 1 meter at 1 watt of input power, and a sub that is front loaded and 94db efficient with the same 1 watt input at the same distance, 1 meter (these are common speaker measurements) the tops would be 9db louder (with the same amp used for both), and since 6 db is a about twice as loud, the subs would not be audible. So we can either drive the amp harder, as in adding gain @ the Driverack crossover output gain control, or turn one amp up or down. As we bring different amps, and gain structure into the picture as well you start to see that in a perfect world if we had the same 103db efficient tops and an amp that was 9db less efficient than the one driving the 94db efficient subs, then 1.2volts would achieve full output for both amps and a similar output from both speakers. Folks it isn’t a perfect world. So we get a mishmash of amps and speakers in stead of a perfect world setup and we need to make compromises. Those compromises can take the form of changes to the amps attenuator, or to the gain in the Driverack. Since the level of competence here is generally newbi, or new to pro audio, or digital processing, and since we place so much emphasis on gain structure here, it is simpler to use the gain controls on the amps to balance the different components of the system. You can however do either or both. I generally do. It’s kind of like a balancing act.
Now, why aren’t my speakers listed? What do I do now?
Well, for one thing, the Driverack has a finite storage location. To add all the different speakers made by all the worlds manufacturers to the database would require a huge storage allocation, and we would have an ever changing database as well as new speakers are developed. Add to that some speaker manufacturers don’t let out their info, or wish not to provide it for what they consider aftermarket, or third party processors…JBL happens to be a Harmon company as is DBX, and the other speakers in the data base were either provided by the manufacturer, or developed by DBX. In many cases, like say the Mackie C300 provided in the menu, only a bandpass filter is provided…all the other modules are just as they were without anything in them.
If we were to choose however the JBL SR4722x from the preset menu and load it into the GUI (graphical user interface.. available here:
http://www.dbxpro.com/Download/
for setup purposes, even if you don’t have a 260 or up this makes the whole thing much more understandable) you will see, by clicking on the xover, that they have provided crossover frequencies, slopes and even gain (which is useless without amp sensitivity provided…. Note how low the xover gains are…). If you look you’ll can see that the mid is the least efficient of the components, and that the horn is the most efficient. If you click on the various PEQ’s you will see that they have provided PEQ settings. They have also supplied Delay on the mid component. These are provided so that you can Tri-amp the speakers in lieu of the passive crossovers inside the speakers. Why Tri-amp/Bi-amp instead of using the passive crossovers? It is much easier to just use the internal crossovers after all? Simple.. efficiency…and in the end sound quality since a digital processor has much better tools available to achieve the crossover with the least impact on the sound quality.
Now add to this a subwoofer and we have a potential for some serious processing, and the ability to do so with the Driverack. With the SR4722x to add a sub we would have had to mono the lo mids to output 5 and had mono subs run off output 6. This is not something you can do with the DRPA, PX since they don’t have the capability of doing 4 way and up, and the PX has only 4 outputs. This then is an exercise for the 200 series on up.
So, you want to set up a preset for your particular system. Now what? Well, using a preset that doesn’t match your system and modifying it is one option, but it’s simpler to just set up a preset from scratch. It isn’t that hard or time consuming (speaker tuning without settings can be however ... and I don’t recommend this for beginners or novices). Select the Wizard by pressing the front panel button or using the GUI for those with the 200 series and up. A series of questions will be asked about your perspective setup. Make the selections from the menu which fit closest to your equipment. A selection of something that’s “CLOSE� to what I have would be better served by selecting “CUSTOM� since in some cases PEQ, and Delay are provided which could totally screw up your sound. Remember here that if you select dual mono or stereo unlinked you will need to process each of the components individually, and the same goes for the Auto Eq and so forth. This can be a good thing when a non symmetrical room provides “obstacles� on one side or the other we need to deal with. So once you have selected all the components as either exactly, or as “custom� we can move on to the tuning portion. For this you will need to go to one of the other sections in the FAQ�s that meets your needs.
For your own edification select a number of different setups(in the GUI) that are in the presets and see what different modules are used and what they did to them. This will help you when you want to add your own setups to the preset we have just created. In many cases when you go to a manufacturer’s site there will be a section for “tunings�, where you can look up your speakers. If they are NOT in there DON�T use something “Close�. Your better off to not do that as it can start you in the wrong direction. Instead, try a forum like this or the manufactures.
I’ll keep adding info here so check back from time to time.
G
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