where to take power for subwoofer
 

I will install a powered subwoofer in my 86 Targa under the passenger seat. Found some threads about it, but none that showed where the power source was taken from. I will pull the power-on sense lead from my dash radio, there should be plenty of 12V available under the seat given they are powered. But these are 'always on', which in principle is not a problem given that the real power-up happens through the sense signal. Correct? Anyone can clarify ?

When installing an amplifier, you typically pull power directly from the battery positive (+) post with a dedicated fuse. For a powered subwoofer I would recommend doing the same. I would not recommend taking power from the seat harness.

alexander: correct? >> I don't think so > if I were you I would perform a much more through analysis of where to draw the power... as sub woofers - stero amps in general draw ALOT of power - frequently independent wiring is run to satisfy component requirements.

Gold plated studs and crimp connectors with # 4 wire is the Car Stereo "Gold Standard"

Suggest VU meters in dash also:D

Had not given thought to the power consumption, assuming the circuits for the electric seat were heavy duty. I'll check. It's not that I want to have kick-in-the-stomach type of bass, just adding some roundness to the chilly sound is all I need.
If I were to pull new power leads, where would I lead them to?

Are you thinking about an amp + subwoofer or powered subwoofer?

It depends on what kind of power you intend to draw. As a general rule, the greater the distance from the battery, the larger the wire gauge required. Most stereo installers will tell you to put the amp as close to the battery as possible.

You might want to also think about weight. Putting amps under the seats is great from a weight distribution standpoint but you’ll need to run a larger wire gauge from the battery.

It’s all about trade-offs.

I have a great system in my 911. By far the best sound quality I’ve ever owned. But there are times I want to go back to basics just to simplify things.

I checked out the wiring diagram, the electrical seats are powered from a 25Amps fused line, and the cushion heating elements from a separate 25Amps fused line. That should be plenty enough for this modest subwoofer. It's rated at 150Watts max, which is in electrical load terms closer to 75 Watt continuous. That is 6 amps on 12V and still only 12 amps at peak (which I will never use). Have not taken out the seat yet to verify the gauge of the wires. If those inspire confidence, I'll give them a try;)

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I would also recommend you take power directly from the battery. Previous owner installed an amp to power just speakers, no subwoofer, but took power from the ignition harness. You can see how well that turned out from the photos...

You have to run the power to the powered sub or sub amp directly from the battery. I have a 100amp reset-able fuse on my 800 watt sub's power wire and the wire is as thick as my index finger. Subs pull a lot of amps, so much so that people regularly install a second battery to provide the amperage they require.

setting aside power (amperage) requirements for a second, the other advantage of running a wire directly to the battery is avoiding the noise/hum that frequently results from tapping into an existing circuit. It's been years since I did my under seat power amp install, but I recall that it was pretty simple to run the 14 gauge wire I used to power my a/d/s power plate through the firewall to the battery.

I'll definitely will be careful not to under-dimension the install. That being said I checked the manual, and specs say that power consumption is max 8 1/2 amps. It comes with a 10A fuse. I appreciate the replies, still I am far away from the 100amp fuse and 800 Watt woofer that Steve has (post 9). Steve, you still hear the engine when the radio is on? ;)

Humming/noise is a genuine concern, I'll look into that.

I would think it would be easier to pull power off the starter lug for an underseat installation. Route the wire through the tunnel and exit under the seat.

I would not pull power from factory wiring. Too old.

Despite having a 25A fuse the derating factor to get to the fuse means the current is much lower. Possibly half. Often these factory wires power multiple systems in the same location and this decreases margin for your amp install.

I would pull a dedicated power lead for the amp.

150W is the output power rating. Depending on the type of amplifier (Class A or Class D), the efficiency can range from 40% for a Class A to 85% for a Class D.

Meaning, for every watt of output, you will need to divide the output by the amplifier efficiency rating to get the real input value which determines the fuse and cable sizing.

Class A:
150W/40% = 375W input power requirements at 12V = 31A of current draw at peak output.

Class D:
150W/85% = 175W input power requirement at 12V = 15A of current draw at peak output.

Put in a fresh wire straight to the battery with a fuse and run it to your under seat location. you can route along your existing wiring harness path to get it in the cabin.

The power sensing you talk about is the switched lead to power the sub on. It can either sense power and fire up, or you can use your amp (or power antenna) lead out of your head unit.

Correct, but as I wrote earlier this amp never goes over 8 1/2 amps. as stated by the manufacturer himself. ;)

What is the make/model of the amp? Is it a 75W output unit?

It's a Kenwood KSC SW11

I am not unfamiliar with the laws in electrics (I am a university degree engineer in electronics), I am familiar too with the laws of marketing ;) . Power ratings of majority of manufacturers are the most optimistic they can put forward without the risk of being accused of lying. Even if they don't make sense to what reaches your ears (as you rightly explained)

One can read on the specs max current is 8.5 amps, and they define acceptable voltage range between 11 en 16V. That's how they come to the '150Watt' max: they multiply 16V times 8.5 amps. And even that is only 136 watt INPUT. The missing 14 Watts are marketing watts, I assume by multiplying with the 10 Amp fuse that comes with it (and not the 8.5A) hence rating everything at 160watt , so they can say 150 Watts is 'safe'. How much of those 150 end up to the speaker is not relevant to dimensioning the wiring.

Anyway, thanks for all the input, I know what to do!

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I call the max output the WLS rating..... When Lightning Strikes.

directly from the battery only!
you can ground the sub right to the seat mounts.

also run your RCA or speaker wires ( depending on how you are sending it signal) along the other side. my power wires go on the right side of the passenger seat and my signal wires go up the left side of the passenger seat

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I finally went for a dedicated power lead from the battery and a dedicated passage through the firewall.
I noticed that there is some free space available where the battery grounding bolt goes. The cabin side comes out directly at the top of the footwell, so from there it's easy to choose an appropriate routing.

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The bright spot is the 12mm hole I drilled from inside the cabin, then put a rubber grommet

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Wire is protected with a sleeve from battery to woofer amp.

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This is the amp as installed. Sound is exactly how I wanted it ;)

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