How exactly to set the RMS going from amp?
Thread Starter
On The Tree
Joined: Apr 2007
Posts: 187
Likes: 0
From: Fruit City, TX
How exactly to set the RMS going from amp? /boggle
Basically, the amp i want runs 325 rms @ 4 ohm and the sub i have is 250 rms @ 4 ohm...
I definitely dont want to blow the sub..
Does the gain **** represent wattage going from amp?
ie, the amp is 975 watts peak, so putting the **** at 1/3rd = 325 RMS, therefore i would have to put it around 1/4th to get around 240 RMS???
Basically, the amp i want runs 325 rms @ 4 ohm and the sub i have is 250 rms @ 4 ohm...
I definitely dont want to blow the sub..
Does the gain **** represent wattage going from amp?
ie, the amp is 975 watts peak, so putting the **** at 1/3rd = 325 RMS, therefore i would have to put it around 1/4th to get around 240 RMS???
its not like that. the gain **** is the level of amplification of the sound. in a sense, it can be called the volume ****.
the calculation isnt easy for RMS power since RMS is an average, not a constant number. if the power is clean then your sub will take it, but also remember that you only get the rated power when your amp is all the way up AND your deck puts out the voltage that the amp is rated at AND the deck is all the way up.
my suggestion, never go over 2/3 gain on an amp, and depending on deck, dont go over 2/3 on that either.
to tune the amp, basically, you turn the amp gain all the way down, turn your deck volume up as high as 2/3, then slowly turn your amp gain up until you get the desired sound level. you dont want to hear any distortion, and you dont want to go over 2/3 gain. beyond that, the numbers game is all arbitrary more or less.
the calculation isnt easy for RMS power since RMS is an average, not a constant number. if the power is clean then your sub will take it, but also remember that you only get the rated power when your amp is all the way up AND your deck puts out the voltage that the amp is rated at AND the deck is all the way up.
my suggestion, never go over 2/3 gain on an amp, and depending on deck, dont go over 2/3 on that either.
to tune the amp, basically, you turn the amp gain all the way down, turn your deck volume up as high as 2/3, then slowly turn your amp gain up until you get the desired sound level. you dont want to hear any distortion, and you dont want to go over 2/3 gain. beyond that, the numbers game is all arbitrary more or less.
The simpliest way is to use a DVM and a test tone CD. I use a 45 Hz 0dB Sine Wave for my subs. This is what you do:
1. Disconnect the the sub(s) from the amp. Disconnect the RCA's from all the other amps, if necessary
2. Turn the amp gain all the way down.
3. Insert the test tone CD and make sure the bass, bass boost, loudness, etc is set to flat.
4. Set the playback to repeat and I set the volume to 70% of full scale. At this point you should not hear anything.
5. If you want to target a certain RMS output, use Ohm's Law to calculate the output voltage.
So, you have a 4 ohm load and you are targeting 250 Watts RMS. What we are going to use is Voltage = Sqrt (250x4) and that equals ~31.6 VAC. Now, put the DVM on the output of the amp and turn up the gain to 31.6 VAC.
1. Disconnect the the sub(s) from the amp. Disconnect the RCA's from all the other amps, if necessary
2. Turn the amp gain all the way down.
3. Insert the test tone CD and make sure the bass, bass boost, loudness, etc is set to flat.
4. Set the playback to repeat and I set the volume to 70% of full scale. At this point you should not hear anything.
5. If you want to target a certain RMS output, use Ohm's Law to calculate the output voltage.
So, you have a 4 ohm load and you are targeting 250 Watts RMS. What we are going to use is Voltage = Sqrt (250x4) and that equals ~31.6 VAC. Now, put the DVM on the output of the amp and turn up the gain to 31.6 VAC.
Blacker, that would only work if you are burping the system at that frequency, its not practical for everday use. Also, it is not safe to assume that everyone is as familiar with ohms law as some of us are. this stuff is WAY more complicated than 99% of the people even care to know about.
This is the way I have set my systems up and works like a champ. I actually use this for my highs and lows. For the highs, I use a 1KHz 0dB Sine Wave test tone. Using this method is more scientific that listening for distortion, which sound different to each person. BTW, I use the test tones from http://realmofexcursion.com/
There is a tutorial on jlaudio.com
http://mobile.jlaudio.com/support_pages.php?page_id=143
That is pretty much what Blacker was talking about.
http://mobile.jlaudio.com/support_pages.php?page_id=143
That is pretty much what Blacker was talking about.
I have to agree with Blacker here. That is the recommended (and conservative) way to set amp gain. With that method you are pretty much guaranteed that you won't be sending too much power to the sub. I used 30 and 40hz tones to set my gain based on the rated output of my amp. Then I found the gain was way too low for most music and just cranked it back up!
I then used a scope to find out when my amp would start clipping and set the gain based on that. My amp puts out a lot more than rated power. Most subs can handle more than rated RMS power also... I have run 400W RMS to a 250W sub w/o a problem, a lot of people run way more power than their sub is rated for. The rating is to ensure you don't overheat the sub, you can also bottom out the sub with too much power also, but you can hear that.
Brian
I then used a scope to find out when my amp would start clipping and set the gain based on that. My amp puts out a lot more than rated power. Most subs can handle more than rated RMS power also... I have run 400W RMS to a 250W sub w/o a problem, a lot of people run way more power than their sub is rated for. The rating is to ensure you don't overheat the sub, you can also bottom out the sub with too much power also, but you can hear that.
Brian
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Verdad Gallardo Thread Starter
On The Tree
Joined: Apr 2007
Posts: 187
Likes: 0
From: Fruit City, TX
Ok the rockford sub is 250 RMS @ 4 ohm (2 ohm DVC)
The amp i just purchased was a Rockford 200 watt 2 channel, heres the specs
* 2 Channel amplifier desighn
* 200 Watts RMS x 1 @ 4 ohms
* 100 Watts RMS x 2 @ 2 ohms
* 50 Watts RMS x 2 @ 4 ohms
* 600 watts max power
* Variable high / low pass crossovers 40-400Hz 12 DB
* NOMAD- Internal analog-computer output protection circuitry.
* Thermal switch- Shuts amp off in case of over load.
* New focused mass heatsink
* Removable connector cover
* Improved TO-247 Mosfet transisters
* RCA preamp input and output
* 30 Amp inline fuse rating
* 30 amp on board fuse
* S/N rating: 80 dB
I dont have that crap to test the wattage or w/e..
Does the gain **** all the way up indicate max power, 600 in this case? If so ill turn it to a little less than half. My stereo goes up to at least 25 volume, but i usually run it at 10-12.
So my guess is that the gain **** a little less than halfway would be a good estimation?
Also.. how important is the wiring? Will you notice a difference between the wal mart wiring kits and the $60 shipped rockford wiring?
The amp i just purchased was a Rockford 200 watt 2 channel, heres the specs
* 2 Channel amplifier desighn
* 200 Watts RMS x 1 @ 4 ohms
* 100 Watts RMS x 2 @ 2 ohms
* 50 Watts RMS x 2 @ 4 ohms
* 600 watts max power
* Variable high / low pass crossovers 40-400Hz 12 DB
* NOMAD- Internal analog-computer output protection circuitry.
* Thermal switch- Shuts amp off in case of over load.
* New focused mass heatsink
* Removable connector cover
* Improved TO-247 Mosfet transisters
* RCA preamp input and output
* 30 Amp inline fuse rating
* 30 amp on board fuse
* S/N rating: 80 dB
I dont have that crap to test the wattage or w/e..
Does the gain **** all the way up indicate max power, 600 in this case? If so ill turn it to a little less than half. My stereo goes up to at least 25 volume, but i usually run it at 10-12.
So my guess is that the gain **** a little less than halfway would be a good estimation?
Also.. how important is the wiring? Will you notice a difference between the wal mart wiring kits and the $60 shipped rockford wiring?
you are completely misunderstanding the function of the gain ***.
It does not work like a throttle for amp power. Infact, a 200 watt amp installed in your car, may make it's 200 watts with the gain *** at 3/4. Put that same amp in my car, and it may make it's 200 watts with the gain all the way down.
The gain is used to match the input of the amp, to the output of whatever is feeding it (head unit, eq, etc ...). A high voltage head unit (4v and up) will requre less gain then a head unit with only 2 volts.
The problem with all of these measurements techniques discussed, is they don't take into account that speakers are not static loads. Your 4 ohm sub is only 4 ohms at certain frequencies, and the load changes very dynamicly while the system is playing.
Short of using expensive test gear, there is no way for you to set your amp to max out at a paticular wattage number. These methods are about as accurate as guessing a systems SPL by looking at it.
Just use common sense while listening. If you turn up the gain, and it sounds distorted, bottoming out, and generally bad, then back off some.
mike
It does not work like a throttle for amp power. Infact, a 200 watt amp installed in your car, may make it's 200 watts with the gain *** at 3/4. Put that same amp in my car, and it may make it's 200 watts with the gain all the way down.
The gain is used to match the input of the amp, to the output of whatever is feeding it (head unit, eq, etc ...). A high voltage head unit (4v and up) will requre less gain then a head unit with only 2 volts.
The problem with all of these measurements techniques discussed, is they don't take into account that speakers are not static loads. Your 4 ohm sub is only 4 ohms at certain frequencies, and the load changes very dynamicly while the system is playing.
Short of using expensive test gear, there is no way for you to set your amp to max out at a paticular wattage number. These methods are about as accurate as guessing a systems SPL by looking at it.
Just use common sense while listening. If you turn up the gain, and it sounds distorted, bottoming out, and generally bad, then back off some.
mike
Originally Posted by 95bat
Sorry Mike, but I trust the engineers at JL audio more than you 
JL is assuming that your speaker is going to be a nominal 4 ohm load. There method is ok for estimating, but not an exact science. Like I said, it's like guessing SPL by looking at a system. Someone who is knowledgable may guess within 6db or so, but a meter is still the only way to be 100% accurate.
