Car stereo amps

Factual Questions
1

I’m probably going to be upgrading my car stereo soon, and by what some audio snobs say, you’d think your car was a ticking time bomb if you didn’t get a seperate/dedicated amp for your stereo system.

I want to buy a good head unit, with midrange speakers - 2 5.25s, and 2 3x9s. I don’t plan on blasting music too loud, and don’t plan on getting a sub. Do I really need an amp? What difference would it really make? Less distortion at extreme volumes, I know, and easier on the speakers in that case - but I plan on keeping the volume reasonable, so is there a benefit to an amp? Am I risking my speakers if I don’t?

Assuming I don’t go with an amp, what’s the minimum acceptable wattage you’d expect out of a decent to good head unit?

2

4x25 watt head units are common and IMHO plenty loud. If you get a good one, there should be no more distortion than a good amp at the levels you describe.

Save your money and get better speakers.

3

Bump.

4

Wattage isn’t just about volume. It’s about dynamic range–the ability to go from very soft sound to very loud without distortion. Exactly how much power you need for the cleanest audio depends greatly upon the speakers you have installed, but as a very rough rule of thumb, a car audio system should be at least 50 watts total power for good, clean audio, IMO.

5

A 4x25 head unit would be 100 watts total, and therefore more than adequate? Dumb question, I realize - but I was thinking that perhaps “total wattage” was calculated in an odd fashion.

6

Yes, that’s it exactly. 4x25 is just saying 4 channels at 25 watts each. No fancy math required.

7

I have a sony CDX L-300 (4 45w channels) head unit with 6x8s in the rear mounts and the OEM 5"s in the front… unless you’re planning on providing the music for a beach party from your car, you won’t need much more. The head was cheap… something like $150 I think.

DO install bass blockers or you will blow anything under 6 inches pretty fast, but an amp shouldn’t be necessary.

8

A receiver rated at 4x25 is generally quoting MAX output, which most companies will do with an unacceptable amount of distortion.

Realistically it is probably 4x10 or 4x12 actual power.

If you spend any amount of money at all on the speakers, I would get the amp to protect them. You are going to overdrive the head unit’s small amp pretty easily, which will introduce clipping into the signal and will damage the speakers.

If you are talking about spending 100$ a pair for the speakers, or something inexpensive in that range…then it’s a judgment call…over time you will probably degrade their performance, but at such a low cost, it’s not a big deal.

9

power usage does have some goofy math…but basically–
in order to hear an increase in volume of 2x…you have to add 10 decibels, or increase power 10x.

so 100w is 2x as loud as 10x
1000w is 2x as loud at 100x

there is a noticeable gain in volume at 3dB though. you gain 3dB by doubling power

an actual 4x25 amp is going to be noticeably louder than your receiver

to further cloud the issue, all companies rate their power different ways(at different power voltages, or at different distortion levels)

10

I believe JaxBeachBoy was being generous with the 10-12w/ch rating for a head unit. However, I have had some good results without an external amp.

I also believe the best item for car sound is sub woofers. There are some cheap self powered subs out there. Just block the bass to the full-range speakers and let the sub do the heavy work. It will make a big difference - better than just using an external amp to power the speakers.

11

I noticed amps are often rated for “RMS” wattage - what does that mean?

12

root mean square

13

RMS = Sample the wattages over a certain period, add up the squares of the samples, average them, then take the square root of that.

14

Could someone tell me what that means in practical terms?

15

RMS is a measure of average power output and is a much more useful figure than “peak”. Cheap gear can put out huge amounts of peak power but it is only momentary, when you see a stereo saying it puts out 1000W or something ridiculous like that then it will be peak power and essentially meaningless. To compare amps you should use the RMS output and you should also take note of the distortion level this power is measured at. 100W RMS at 10% total harmonic distortion will not be as loud as 100W RMS at .07% THD.

16

Good information, but what about folks who aren’t into loud music at all and do not want a sub? (Like the OP)

Best Buy has a Kenwood CD deck rated at 45 watts x 4 channels for only $129 installed. Nothing “small” (as you say) about this head unit’s amp.

If I’m listening to jazz or classical at a rather low volume (low enough to allow easy conversation and not offend other passengers), what’s the point in getting a separate amp?

17

Something to note… and I offer this knowledge in the kindest of intentions…

If you’re really into hi-fi, let alone if you’re a professional recording engineer, the human hearing is so precise that when doing mixdowns in the studio, changing just one track by as little as 1.5db is a noticeable influence. Such is the degree of “black art” involved in doing a good mixdown.

However, equally true is the human ears ability to “ignore” noise which is louder than that which we need to hear. It actually takes a long time to train your hearing to recognise such noise - because our brains have an astonisihing ability to filter noise which isn’t important to our immediate survival.

Sadly, the honest truth is that very few automobiles, very, very few actually qualify as an ideal listening environment. Even at idle, most road cars hover at 60+db of background noise. Now this is way, way louder than an ideal hi-fi listening lounge. But it gets worse. The moment you’re under way and your engine is under strain and your gearbox and differentials are working away, and your have wheel and axle noise and body rumble, hardly any cars at all are capable of driving at 30mph at less than 75db of background noise.

Certainly, it’s true that Lexus recognised this problem and invested incredible amounts of research and development into noise suppression. Indeed, I seem to recall they hold at least 35 world wide patents on noise suppression building techniques therein.

But the bad news is this, unless you’re driving a Lexus or a Bentley, or a Jaguar, or some similar car which actively strives for road going noise suppression, the reality is that most folks simply go for sheer decibels to overcome the innate background noise which exists in cars so as to enjoy a certain sense of “decent car stereo”.

Well, this is, quite frankly, really really bad for your hearing… really bad. To achieve even 30db of dynamic range in a typical car, you have to be listening to your music at least at 90db or more sound pressure level.

When you consider that a Greyhound bus pulling away from a bus stop at 10 meters creates 88db of spl, you’ve got an idea now of the sort of bombardment you’re giving your ears.

Alternatively, you can lower your average listening volume, which in turn, reduces the inherent dynamic range in the music you’re listening too. And what does this mean? All of the subtlety which exists in a decent album will be getting lost in amongst your car’s road noise.

So, in short, before ANYONE invests money into a car stereo, I always like to point out such realities. It’s not my goal to rain on anyone’s parade or ruin anyone’s day - merely my goal is to inform people that “good hi fi” and “car stereos” are actually mutually exclusive. Something has to give… either your hearing gets pounded because you have to listen to it so loud to get a decent sound, or the qulity suffers because there’s too much background noise at lower volumes.

In this context, often it’s good money after bad, to be perfectly frank.

18

The last reply deserves a TTT.

I am so damn tired of saying WHAT?

BTW, I was never the one to crank it at gas stations or in traffic… but when the right song was on I sure got heavy on the throttle.

Country Squire:

I mentioned a sub because it can make such a huge difference sound, does not mean it must be loud or boomy, a simple self powered sub is a fantastic bang for the buck - I believe it is the best add on for car stereo ever - even more so than CD players.

19

Professional mobile electronics installer here.

There are many different ways to rate amplifier power, and most of them are used to lie to the consumer.

Ignore any power rating that says “peak,” “max,” or anything like that. We often jokingly call this the ILS rating----the amplifier may actually produce that much power if lightning strikes it.

RMS is generally regarded as the more honest rating, but even there, each manufacturer tests by a slightly different standard, so it can be difficult to compare brands.

In any event, most name-brand head units produce about the same power, and its usually plenty enough for most people’s everyday listening. There are some no-name brands that are lacking in power…but if you stick with a name brand and spend around $125+, power output will be about the same.

What is it you don’t like about the system you have now? If you can be specific, including what kind of car and what you have now, and what your goal is, I may be able to offer some suggestions.

20

Oh, my system now is just terrible. The rear speakers are salvagable, perhaps, but that’s it. It’s an old tape deck/radio in which the tape deck and radio are shot. The tape deck just sounds way off and the radio has reception that inexplicably goes in and out all the time.

So I was gonna overhaul the whole system… I just wanted to get an idea of what I was looking at. I want to put a cd/mp3 head unit in there, some new dash speakers (they’re 5", but I can carve the dash out to put 5.25" or whatever the more common speakers are), and then some new rear speakers, in that order.