r/CarAV • u/LowVoltCharlie • 1d ago
Discussion Power-matching fronts & subs
I've been into car audio for a while but I haven't ever heard any rule of thumb for the power rating of a front stage VS the power rating of your subs when designing a system. Is there any such rule at all?
I've had many audiophile headphones, demoed a bunch of home audio systems more expensive than my house, but never heard a car audio system with anything more than 100W front stage and 500W sub amp. Is there a clear benefit with going with higher wattage front stage if the driver quality is about the same? And how would you take power into account when selecting a sub amp?
Photo for attention
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u/East-Paramedic6846 1d ago
I don’t believe such rule exists as most front stage component speakers don’t handle nearly as much power as subwoofers. I’m currently running 1800 watts to my subs and 100 each to 3 way front components running active. All high end Focal Utopia M series.
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u/roby8159 1d ago
If you’re going for an actual SQ setup power only kind of matters. When you tune the system you would level match the subs to the front stage. They said you would want overhead in power because all cars and enclosures vary drastically in frequency reproduction so you in theory could need a lot more power to get 35hz and 45hz to have similar db output to match the front stage.
Edit to say this is oversimplifying things but I hope makes the point.
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u/alphuscorp 1d ago
Higher wattage front systems biggest benefits for higher than subwoofer frequencies are more dynamic range (speakers have full power to properly produce sound at all frequencies both in bursts and sustained notes), pushing the amp less to reduce output distortion (matters more as you go up frequency), as well as opening headroom to add multiple component systems such as two way or more component systems which all improve clarity And perceived quality.
The lower frequencies you go, yes there’s more power needed to produce it, but it’s also a function of the speaker design and its sensitivity (dB/w). Tweeters are very efficient for their size output, but standard cone woofers are much less so at smaller sizes like what we see in car doors and smaller speakers need more power to produce the same output as a larger cone. Most passive crossovers have resistors to cut the tweeter output down to balance out the response so it isn’t too bright. This is all to say there isn’t easy rules of thumb for power per component as it changes based how the components are set to crossover one another on top of the preferences of the system as sound is still very subjective. Typically though tweeters will be “assigned” 1/4-1/3 of the power handling of the smaller woofers with the tweeter handling more if it’s crossed over at lower frequencies. Subs are multiple times the mid systems with a lot of 5 channel amps providing 5-7x the power of the speakers channels.
Mid-low frequencies are usually the missing link in factory systems for quality as most boost the two ends of the spectrum with the highs being most of the intelligibility of a sound to distinguish instruments or lyrics and the lower tones providing a lot more of the volume.
With car audio systems typically not having ideal placements of each speaker component, there are more benefits in a dsp setup to improve phasing, time alignment, and good frequency eq, over just adding more watts.
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u/Monster_Grundle 1d ago
Why is there a subwoofer in the passenger seat footwell??
The benefit is it’s going to be louder. Every doubling of wattage theoretically increases the volume 3db. Personally I’ve found 100w per speaker front stages to be satisfyingly loud and able to keep up with very loud subwoofers. In many competition vehicles you’ll see both higher number and wattage front stage speakers to keep up with the absurd subwoofer installations. For most casual enthusiasts I believe one set of properly installed 100w rms speakers in front will be sufficient for their listening needs. If you want to absolutely crank the hell out of it you might consider more cone area or wattage.
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u/LowVoltCharlie 1d ago
I had space constraints and needed the trunk for storage, it actually measured decently well in that location! Now I have two 10's in the trunk instead, same model.
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u/MeepMeeps88 1d ago
I run 190 each to my front comps and rear co axials with my sub running 700. More than enough power
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u/scooterfrog 1d ago
No rule of thumb. Measure to a house curve you like with out clipping.
But people undersetimate efficiency's impact. My midranges are not sensitive. I run them to clipping its a 4 inch inch hi passed around 350. On 125 watts. Everything else is set lower on the dsp. 50 watts to tweets 125 to midbassas 500to sub. Its a lot of power but sq oriennted.
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u/Otherwise_Stretch_74 14h ago
Really depends on the equipment and spl level desired.
To reproduce a 200hz signal requires more power than a 20,000hz signal. And that depends on target level 100db is easier to do than 120db.
Most tweeters don't need 150 watts of power.
My helix ci7 t20fm-sc tweeters maybe using 9.5w of power to get a fairly flat response from around 3.5khz to 21.5khz. My amplifier is capable of 75w per channel.
The problem you are trying to fix with a front subwoofer is from 40hz to 95ish hz. And fixing the null that is common in vehicles from 60hz to 90hz from rear subwoofers. Allowing the rear subwoofer to focus on playing from 10hz to 40hz.
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u/LowVoltCharlie 11h ago
Good explanation! This photo was my old system when I needed the trunk for storage, I've since gone with a 2x10" trunk sub setup and it's a lot nicer. It's purely a question that's bouncing around in my head for my next system when I get a newer car
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u/ifixtheinternet 80PRS|HELIX P SIX|SB17-6|KARMA-3|TB-TW|MRD500|2X JL-12W3V3 1d ago edited 1d ago
I don't think you can have a rule of thumb for this because there are so many variables.
Driver sensitivity. 2 way vs 3 way vs Coaxials. Where the sub is located. Type of sub enclosure. Type of vehicle. Front stage on axis? In the dash?
Then the big one of preference, how much bass do you like? The lower you go in frequency, The more power is required. I think that's about the only rule of thumb you're going to get.
Right now I have roughly 700 w available to my front stage through six channels, but only 500w for my subwoofers. Mainly because the subs are JL 12W3s which can do quite a lot with a mediocre amount of power. That is plenty to keep up with the front stage if tuned for any common house curve.
Would I enjoy dual 13W7s on 2k watts, or something similar? hell yes. But I would mainly benefit from the clarity. sure, I could put on some hip hop and absolutely crank the bass, but that blows any kind of rule of thumb out of the water.