Sub and Amplifier Question

vskid · Post by **vskid** » Sat Aug 16, 2008 4:31 pm

The 1993 Ford Explorer I drive has a 6" subwoofer (the sound system is 100% stock). It makes an acceptable amount of bass, but the surround is ripped and so it sounds like crap unless you turn the volume up enough to drown out the flutter and buzzing. I hot glued the surround back together a couple months ago and it sounded great. Now its ripped back apart, so I think it is time to replace it.
I was thinking of replacing it with an 8-12" subwoofer with the same impedance and use the same amplifier. I just don't know if the 85w the amplifier outputs could drive a larger speaker and still make the same amount of bass. My reasoning for using the bigger sub is so that it can take the full power of the amplifier and not get damaged (I don't care if it makes more bass than the 6"). So does anyone know if I could successfully use the larger subwoofer with the original 85w amp?

Post by **marshallh** » Sat Aug 16, 2008 10:37 pm

Yes, you can, be be careful turning it all the way up - as soon as you begin to hear distortion or clipping, stop! Clipping will overheat the sub coils and ruin your sub. Plus it sounds bad.

I'd just get a 8" if you were going to stick with the stock amp.

vskid · Post by **vskid** » Sat Aug 16, 2008 11:40 pm

In theory, shouldn't I be safe from overheating the coil as long as the power that my amp outputs is in the RMS power range of the speaker? I was checking on Crutchfield, and the lowest low end rating of the 8" subs was 30w, with 50w being the most common low value. The higher end of the range was 150w and up. Since my amp outputs 85w, it shouldn't be able to damage one of those subs, right? I also found that their 6.5" subs are rated up to 150w RMS, so I'm assuming old age and poor build quality is the reason the original sub ripped.
To find the impedance that my amp can handle, do I just break out the multimeter and test the resistance of the sub?
Now, to watch the classifieds for cheap 8" subs...

Porta Potty · Post by **Porta Potty** » Sun Aug 17, 2008 5:33 am

vskid wrote:In theory, shouldn't I be safe from overheating the coil as long as the power that my amp outputs is in the RMS power range of the speaker? I was checking on Crutchfield, and the lowest low end rating of the 8" subs was 30w, with 50w being the most common low value. The higher end of the range was 150w and up. Since my amp outputs 85w, it shouldn't be able to damage one of those subs, right? I also found that their 6.5" subs are rated up to 150w RMS, so I'm assuming old age and poor build quality is the reason the original sub ripped.
To find the impedance that my amp can handle, do I just break out the multimeter and test the resistance of the sub?
Now, to watch the classifieds for cheap 8" subs...

Under driving a sub is more damaging than over driving it. A 12" sub should have an RMS figure of around 250w or more, anything less and it's not really a sub just a large speaker. Subs needs huge power to move lots of air.

Post by **marshallh** » Sun Aug 17, 2008 12:55 pm

It doesn't matter if the amp is putting out less power - if you get ANY clipping/distortion that is going to eventually ruin your sub. The same goes for square waves.

The reason is that the diaphram is held at one position of the wave for too long without any movement/airflow and the coil will heat up. Enough of that, and the windings will burn out.

timmeh87 · Post by **timmeh87** » Sun Aug 17, 2008 2:34 pm

Porta Potty wrote: Under driving a sub is more damaging than over driving it. A 12" sub should have an RMS figure of around 250w or more, anything less and it's not really a sub just a large speaker. Subs needs huge power to move lots of air.

But how does that damage it? I mean, wouldn't that mean that turning the volume down is damaging to your subs?

Post by **bicostp** » Sun Aug 17, 2008 2:36 pm

No, because when the volume is down, there's less current running through the coils. Less current = less heat.

Whatever you decide on, do your ears a favor and build a proper tuned enclosure. Those pizza boxes at Best Buy suck at helping the speaker do its job.

vskid · Post by **vskid** » Sun Aug 17, 2008 2:52 pm

marshallh wrote:The reason is that the diaphram is held at one position of the wave for too long without any movement/airflow and the coil will heat up. Enough of that, and the windings will burn out.

So is there anything I could do to prevent that? It seems like something that would be caused by poor quality of the sound's source (like poor reception of a radio station). Could you find a video of it on youtube, I'm not sure if I'm understanding what it sounds like.

If I can find a 6" or 6.5" sub, I might just use the sealed enclosure the current sub is in. I was thinking of a ported enclosure if I get an 8" though, because the amp might not have enough power to drive the bigger area in a sealed enclosure.