soundiconI recently had a JL Audio amp and subwoofer installed in my 2009 Volvo S60. The radio and other speakers are still stock. My problem is a loud thump from the subwoofer every time I start the car. I have taken it back to the installer, but he tells me I will have to change out the radio to correct it. I would prefer not to do that since the factory radio is also a navigation unit, so I’m wondering if you have any suggestions on how to get rid of the thump?

Signed, Patrick B.

Sure Patrick… it’s simple. Don’t start the car.

But seriously, it sounds to me like the problem you’re having is caused by the way the subwoofer amplifier is getting turned on. In cars like your Volvo, there isn’t usually a remote turn-on wire from the radio to an amplifier as there would be with an aftermarket head unit. So, some installers simply wire the  remote on for the amplifier to the car’s ignition. The problem with that approach is that the amplifier will actually be turned on and waiting for a signal before the radio is fully initialized. When the radio comes on, it can emit some trash signal voltage that you hear as a thump.

Rather than replace your radio, I can suggest two solutions. You can either have a module installed that provides a few additional seconds of delay before your amplifier turns on, or you can buy a signal sensing product that can sense when the radio turns on, and then send a turn on signal to your amplifier. Your dealer should have information on both solutions. Either should get rid of the thump, and be cheaper than replacing the radio. Thanks for the question.

I want to build a badass subwoofer system for my Scion tC. I have heard that sealed woofer systems sound better, but ported ones play louder. I want both. The system needs to sound awesome and be very loud. What woofers do I need and what kind of box? I have a GDN 5000 amp for it. Oh, and I like the mag, you guys give me tons of whack ideas for my ride. Plus the models rock! Peace!
Signed, Syck1

Well Syck1, we’re glad you enjoy the magazine. Your question is a bit tough to answer, since what you think sounds “awesome” may be totally different from what I or someone else thinks sounds awesome. You also didn’t mention how much space you were willing to give up for the enclosure, or how much power a GDN 5000 is. We’ve honestly never heard of your amp. But, in a small car like the tC, getting it loud is easy. If it was mine, and I wanted tight bass and plenty of volume, I would use a pair of 12-inch woofers in a sealed enclosure. There are many great brands to choose from, so the brand you buy is a personal decision, but you can always go to the store and do some listening to help decide. Just choose a quality, recognized brand and follow the manufacturer’s enclosure recommendations carefully. If you run into a specific question, all quality brands have full time tech support people who can help you resolve any technical hurdles along the way. Make sure your amplifier power is a good match for the woofers power handling, and you should be a happy camper. Peace out, indeed.

Hi. I have never written to a magazine before, but I have a question that I can’t find an answer to. I am working on a subwoofer system for my 2011 Mustang, and I thought it would be a good idea to protect the woofers from overpowering (my teenage daughter likes to borrow the car) by using fuses in the speaker wires. So, I have several questions. The subwoofer has two sets of terminals. Do I need to fuse them both or just one? Do I need fuses in both positive and negative wires? The mono amp is rated at 600Watts, and the woofer is rated for 500Watts, so what size fuses do I need? Thanks in advance for any suggestions.
Colin W.

Hi Colin, I understand your motivation for wanting to protect the woofer, I have been through the teenager borrowing Dad’s car too. Your idea is valid, but mostly effective only when things are grossly overdriven which can happen, I know…

Short of turning the amps gain to minimum every time she drives the car, you could use fuses to interrupt the current to the woofer, but keep in mind that fuses won’t protect the woofer from thermal damage incurred over a long period of time.

Okay, so how to fuse a speaker… only one fuse is required if there is only one positive and one negative speaker connection. The fuse can go in either, it makes no electrical difference. If you are running four separate conductors from the amp to the woofers voice coils, then you would need to put a fuse in one of the leads going to each coil.

When it comes to selecting a fuse value, things get trickier, since you didn’t mention what the speakers impedance was. Fuses are rated in amperes of current, and the current a speaker receives changes depending on the impedance. You did say that the woofer was 500 watts, so at least we have something to go on.

Ohm’s Law tells us that power equals I2R, or current squared times resistance. Working the math backwards, that means the current will be equal to the square root of the power divided by the resistance. So, if we know the power is 500Watts, and your woofer is a 2-Ohm load, the current at 500Watts will be or 15.81Amps. You could use a 15Amps or even a 10Amps fuse to begin with, and see how things go. Bear in mind that fuses typically will withstand 200% of their rated current for 2-seconds before opening. It’s better to start with small values and if they blow, work your way up. Good luck with the project, and your daughter.