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Please! relationship between gain, RMS power and sound

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Please! relationship between gain, RMS power and sound

  • OK, here's my question. I've tried to set the gain on my system as Crutchfield suggests. (75W component speakers, 50RMS /channel amp) 

    However, It seems to my (less than golden) ear, that with the gain turned down to min, I can crank the (JVC) head units volume to max (50) and still get no noteable distortion. So then when I bring the gain up, I get it to maybe 30% before the sound level gets uncomfortable but the sound 'quality" doesn't really improve. When set like this though, it seems like the speaker components have less "depth" /are more "tinny'. If I play around and set  the gain to 60%, and the volume to 30, the speakers sound fuller and still have no noteable distortion.. ( I'm inclined to leave it set this way but... ) I know that gain  is not volume but am confused from there. So my questions are:  What is the general relationship between gain setting and amp output? Are the speakers getting the same (approx) RMS input values at these different settings? Does turning the gain down reduce AMP output at and given head unit volume setting?

    I'm guessing my goal here is to get the max RMS to those speaker components to get the best sound. 

    Lastly, would I see a noteable difference if I drove those (Infinity Ref 5010cs) components with a RMS rated amp 75W vs 50?

    Thanks in advance for any insight!



    [edited by: WeeHooker at 2:46 PM (GMT -5) on Tue, Dec 11 2007]
  • I'll take some stabs at this - someone correct me if I mess anything up ... 

    WeeHooker:
    However, It seems to my (less than golden) ear, that with the gain turned down, I can crank the head units volume to max (50) and still get no noteable distortion.

    Makes sense. 

    So then when I bring the gain up, I get it to maybe 30% before the sound level gets uncomfortable. Set like this though, it seems like the speaker components have less "depth" /are more "tinny'.

    That "lack of depth, tinnyness" sounds like clipping to me.  When you turn the gain up, eventually, the amp can't increase the signal anymore and starts sending a flat signal like that - you want to avoid that - that is what tends to really kill speakers. 

    If I play around and set  the gain to 60%, and the volume to 30, the speakers sound fuller and still have no noteable distortion.. ( I'm inclined to leave it set this way but... )

    What you should be able to do is back the gain down some, set the volume to 45 to 50, and set the gain up again until you had the sound that you had at 30.  The only reason for not setting it this way would be if you didn't want as fine a volume control (wanted a volume control between 0 and 30, but didn't want to go above that). 

    So my question is,  'waht is the relationship between gain setting and amp output? Are the speakers getting the same (approx) RMS input values at these different settings?

    Hard to explain, but I'll try to throw some examples out - all numbers made up, but it should clarify stuff.

    Both the gain and the volume on the HU have the effect of increasing the volume.

    You amp is 50W RMS.

    If you have the gain set properly - when you reach 50 on the HU volume control, the amp is putting out 50W RMS to the speakers, and the speakers are always getting a "clean" signal.  You have very little risk of blowing the speakers, you can turn the HU all the way up and the sound will still be good and you are getting all the power out of your amp.  Let's assume the amp gain is set at 50% at this settting.

    If you turn the amp gain down to 10%, then you can turn the HU all the way up to 50, but the amp may only be putting out 15-20W to the speakers.  They will sound clean, but they won't be very loud.  You might do this if you really don't like your music blaring at you, if you wanted more sensitivity to the HU volume control (with say a 100W/channel amp, you might find the volume 15 was too loud but 14 wasn't loud enough, reducing the gain would help with this), or if your speakers were rated much lower in power handling than your amp.

    Now, let's say you set the gain to 90%.  At this setting, the amp might reach 50W RMS at HU volume 30 and sound good.  Above HU volume 30, it will "clip".  I don't have a good explanation of this - Basically, the amp reaches a wall - I am not sure if it goes up to 65W or more (I don't think it would hit 150W or anything - maybe), but it starts sending 50W-60W at all frequencies, so you don't hear dynamics in the music anymore, the amp sounds strained, and eventually the speakers will blow (if the amp doesn't as well).  The only time you would want to do this is if as above you only wanted the volume to go to 30 because you didn't want have to spin the volume knob five turns to turn the system down - but again, you have the danger that if you or someone else accidentally cranks it past this you will damage your gear.  

    Does turning teh gain down limit AMP output?

    Basically, yes. 

    Lastly, would I see a noteable difference if I drove those (Infinity Ref 5010cs) components with a RMS rated amp 75W vs 50?

    Difference, yes.  Noticeable, hard to say...

    There is a law of diminishing returns with amplifier wattage.  If you have a factory HU (3-5W) and go to an aftermarket (17W) there is a big jump in sound (12-14W increase).  If you take the 17W HU and swap it for a 40W amp (23W increase), there is much less of an increase in sound.  Bumping that up to 75W (35W) increase would probably be even less noticeable.

    Also - this is harder to explain and better if you can somehow experience it - it takes 10x the power to double the volume of a system - so if you increase the power from 50W to 75W - it isn't so much that the system sounds LOUDER, as it is that it sounds CLEARER.  The amp doesn't seem like it is working as hard, the dynamic range (volume difference between loud and soft passages) is better, and the bass is present without sounding strained.

    But it's hard to say how much of a difference it would make, but it won't be nearly as much as going from a HU without an external amp to a 75W amp.

    Hope This Helps!!! (Anyone else able to explain this better?) 


    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • Thats a really good question.  I never read the CF tips on adjusting your gains.  I always set my eq flat, and my volume at 75% on the HU(for the front components), then adjusted the gains up until I heard distortion. Then adjusted the sub channel to match, sometimes I had to turn down my front speakers because I couldn't get enough out of my subs.

    I always thought, and I am probably wrong that the gain was a cut from your input voltage.  My alpine  CDA9885 says it has 4 volts,  so if the gain were all the way up it would send all 4 volts into my amp.  I am really just guessing though, I'm sure someone on here (probably tiger) knows the right answer.

    2007 Chevy Express Diesel Van Alpine CDA-9886 HU - KCA-SC100 Sirius - USB Drive - 80Gb Ipod Kenwood KAC-859 Amp Alpine SPR-17S 6.5 - front Polk DB460 - rear (off HU) 2-Soundstream SPL-10 DVC 4 ohm subs in sealed box (10 years old!)
  • forya:
    Thats a really good question.  I never read the CF tips on adjusting your gains.  I always set my eq flat, and my volume at 75% on the HU(for the front components), then adjusted the gains up until I heard distortion. Then adjusted the sub channel to match, sometimes I had to turn down my front speakers because I couldn't get enough out of my subs.

    You basically described what CF recommends - the preferred method would be with a test tape and a sound level meter and an O-scope, but most installers don't even have this.  The other method is with a test tape and a voltmeter on the outputs, but most people don't do that either.  The problem with the method you described is that a signal can be pretty distorted (overly high gain) before someone that hasn't experienced it can hear that it's distorted. 

    I always thought, and I am probably wrong that the gain was a cut from your input voltage.  My alpine  CDA9885 says it has 4 volts,  so if the gain were all the way up it would send all 4 volts into my amp.  I am really just guessing though, I'm sure someone on here (probably tiger) knows the right answer.

    I'm not positive myself, but you are on the right track, but I'm not sure it's totally right.  First off, I think the CDA-9885 is only 4 volts at full volume and at certain frequencies.  What I think the gain does is tell the amp how much to increase the RCA voltage.

    Ah - here - when in doubt, turn to www.bcae1.com and specifically this page.   

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • Thanks, thats  EXCELENT input. ( and it somewhat confirms my suspicions) . i.e. If I tune my system the first way ( @ 30% gain) , I'm actually getting little more power to my speakers ( at my comfortable /  40+/- volume setting)  than if I was running the bare 20RMS/channel head unit near max.  Hence, it sounds OK, but not much better  beacuse the speakers are starving for power in either case. (which is the reason I dropped $250 on an amp to begin with.)   Going a step further, and correct me if I've misunderstood here, speakers are going to sound their best when driven at /near rated power. So..... If I tune my gain, to give me near max power input (say 45WRMS) to the speakers at my comfortable ( say 30 vs max) volume, I should be getting the best sound out of my system at or below THAT VOLUME SETTING ( assuming I still have no distortion/clipping.) However, the price is " a) I'll have a compressed volume adjustment range and  b) risk overpowering if some hooplehead twists the volume up. Correct?

     

     

  • Really close, just a few minor points. 

    WeeHooker:
    If I tune my system the first way ( @ 30% gain) , I'm actually getting little more power to my speakers ( at my comfortable /  40+/- volume setting)  than if I was running the bare 20RMS/channel head unit near max.  Hence, it sounds OK, but not much better  beacuse the speakers are starving for power in either case. (which is the reason I dropped $250 on an amp to begin with.)

    Basically, however, your HU is probably putting out 20W RMS at 40 on the volume knob and clipping/distorting the signal above that.  And the amp may only be putting out 20W RMS at the 40 HU volume, but it is clean power and 50% of it's rated output, so it should sound cleaner with the amp, just not louder at that setting.

    Also, after reading the bcae1 page, my initial post was somewhat incorrect in that your HU is likely going to clip above 40 anyway, so you can't set the gain to a comfortable level at HU volume 50 and listen to it, you have to set the amp to 50W RMS with the gain when the HU volume is at 40 and then not turn the HU above that, b/c the HU signal will be clipped to the amp regardless of what you set the amp's gain at. 

    Going a step further, and correct me if I've misunderstood here, speakers are going to sound their best when driven at /near rated power.

    I would say speakers sound their best with "clean" power.  I.e. if you have your amp set up properly and your HU volume at 5 or 10, your speakers should sound good, even though they aren't anywhere near rated power.  OTOH, if you turn up the HU all the way, without the amp in the system, they will sound terrible (and might blow), not b/c the amp is underpowering them, but b/c it is sending a clipped/distorted signal.  And I personally am driving 25W Peak factory speakers with a 17W RMS HU and they sound fairly good (so far), although I wouldn't recommend that to anyone. 

    So..... If I tune my gain, to give me near max power input (say 45WRMS) to the speakers at my comfortable ( say 30 vs max) volume, I should be getting the best sound out of my system at or below THAT VOLUME SETTING ( assuming I still have no distortion/clipping.) However, the price is " a) I'll have a compressed volume adjustment range and  b) risk overpowering if some hooplehead twists the volume up. Correct?

    Agreed, and you could go above 45W at this setting so long as you don't get into the range where the amp or the HU is clipping. 

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • OK, pretty clear now. Thanks again for the audio 101 course.

     

    BTW: for all the help you give around here, I'm thinking we should start a collection so we can get YOU an amp and some nice component speakers!!Angel

  • yeah I learned too, now I have to go out and **** off my neighbors again, setting my gains
    2007 Chevy Express Diesel Van Alpine CDA-9886 HU - KCA-SC100 Sirius - USB Drive - 80Gb Ipod Kenwood KAC-859 Amp Alpine SPR-17S 6.5 - front Polk DB460 - rear (off HU) 2-Soundstream SPL-10 DVC 4 ohm subs in sealed box (10 years old!)
  • Very good explanation Tiger. I know I couldn't have explained it better. Another thing to consider. I have been tweeking for months because of several issues. I listen to old and new music. Old music was recorded at a much lower level than new. When I play an old disc my hu is at 36 of 40. It's really loud. With a new disc I can't go past 30. It takes a bit of patience to get to that happy medium. I also have the same problem when changing from studio recording to mp3.

    Panasonic MXE-CQC-9801U Polk Db-570's JL 10 W0's Ported box tuned to 32hz Alpine MRP-F450 Alpine-MRP-M350 Knukonceptz wiring and Dist. blocks 14.6 jammin at idle with NO CAP!!!!!!!