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Bluethunder
Dodge Dakota
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2/21/2002
08:51:31
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 Subject: Head Unit Power
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Message:
Quick question for you guys.
Im running a Kenwood 47x4 head unit. (which delivers about 22 rms to each channel)...If Im only utilizing the rear speaker outputs and not the fronts, would that bump up the power on those two? I was always under the impression that it would. Can anyone enlighten me on this?
Thanks in advance
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R/Truck
Dodge Dakota
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2/21/2002
11:09:26
| RE: Head Unit Power
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With all four channels being used your probably seeing 17 watts x 4. But this amounts to 1-2 dB difference and you really can't detect that small of a difference. Remember the human ear at it's most sensitive state can only detect a 1 dB change, but it really takes 3dB to be of any notice.
Don't worry about it, 99% of the time your only using 1-5 watts of power anyway (not considering subs).
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Bluethunder
Dodge Dakota
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2/21/2002
13:07:45
| RE: Head Unit Power
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Thanks for the reply R/Truck, but that wasnt really my question....Im wondering if Im only using 2 channels am I increasing the power to those 2 channels? Like say a 47 x 4 only using 2 channels would produce 94x2 (Im sure its not double and I know im talking peak numbers...just using that as an example)
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R/Truck
Dodge Dakota
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2/21/2002
13:09:51
| RE: Head Unit Power
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I also wanted to point out that in order to increase your SPL by just 3dB, you need to double the power (watts). So when your talking head unit watts they all produce sound levels close to one another and upgrading 15 watts to 30 watts is only 3db increase.
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R/Truck
Dodge Dakota
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2/21/2002
13:35:51
| RE: Head Unit Power
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Yes you are using more power with just 2 channels driven (about 5-10 watts more)
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R/Truck
Dodge Dakota
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2/21/2002
13:39:23
| RE: Head Unit Power
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That's what I was trying to say originally:
22 x 2
17 x 4
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Bluethunder
Dodge Dakota
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2/21/2002
14:02:34
| RE: Head Unit Power
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thanks for the clarication
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DodgedogJB
Dodge Dakota
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2/22/2002
04:08:24
| RE: Head Unit Power
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I'm not sure which model Kenwood you have but all the ones currently on their site have at least 22x4 RMS (which you stated) and 50watts peak. I'm not sure where the 47x4 rating comes from though? I also don't know where R/T Truck got 17watts? (RMS = Continuous power).
And NO...You won't get more power by just using 2 channels instead of four. If that were the case, a 4-channel amp would work the same way...and it certainly doesn't. The front channels and the rear channels are separate. However, with the modest power a head unit has, 2 channels rather than 4 sucking on the power supply will strain the unit less so it will sound better during intense musical sections (especially ones with lots of bass).
SIDE NOTE:
One thing you might not realize R/T when you state “Twice as much power to only gets a 3db increase in SPL”: This is true if you were only talking about a specific frequency within a speaker’s optimum range and not the entire spectrum. This is because any given speaker produces sounds in certain frequency range better than it does outside that range. Obviously a subwoofer produces bass much better than tweeters do. For example, a speaker fed only a 1500hz signal will produce a 3db increase in SPL when power is increased from 15 to 30 watts assuming that 1500hz is within this speakers optimum range. Now that same speaker fed a signal ranging from 50hz to 22khz (similar to what the stock rear speaker in your truck is fed) may see a higher increase in SPL towards the speakers limits with the power doubling due to a better ability to control the speaker without distortion. For example, using an SPL measuring system on this full range example, you may see a 3db gain at 1500hz but the graph of SPL vs. Hz may be much flatter with the higher power. So lets say at 100hz you have 15db with 15 watts you may (I stress may) see 20db(+/-) with 30 watts, which would be more than a 3db gain. That being said, a power increase less than double may increase volume significantly due to the increased SPL’s across the entire frequency range even though the midrange SPL may not increase much. This would also sound much better because of the increased sound depth. This would be much easier to demonstrate with graphs. Obviously this doesn’t apply as much to component systems because each speaker operates more so within its ideal range.
Additionally, due to the better sound quality throughout the entire frequency range, especially with the lower frequencies, you may be able to turn it up farther before it sounds bad (distortion). So from a usability standpoint...you are getting more volume. That’s why just upgrading a head unit from factory usually makes a system sounds worlds better in terms of sound depth and clarity but the actual power increase may be minimal (true the power is usually much cleaner as well).
But this whole discussion may be pointless because in a system that’s set up properly the rear speakers only offer fill and the majority of the sound comes from the front soundstage. And if you are only planning on using the rear channels of the head unit I’ll assume you are using an amp for the front speakers. So just hook up the rears to the head unit and don’t worry about the power.
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Bluethunder
Dodge Dakota
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2/22/2002
08:39:00
| RE: Head Unit Power
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Yes Dodgedog, that is what Im doing, Im feeding the rears with the headunit and powering my front componants with an amp...thanks for the help.
BTW, Im running a kenwood 6017 (last yrs model) and it states right on the faceplate 47x4
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R/Truck
Dodge Dakota
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2/22/2002
10:51:22
| RE: Head Unit Power
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Oh man, thats a long post....
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DodgedogJB
Dodge Dakota
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2/22/2002
17:17:14
| RE: Head Unit Power
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I looked up the specs of that....the 47x4 comes from the peak power...The new models have 50x4 peak which is why I couldn't figure out where the 47 came from....but they both have 22watts of continuous power. Either way...sounds like you are already rocking.
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