chiminoid

i have a phoenix gold amp from my friend that is rated for 300watts rms, bridged. i'm planning on getting an mtx sub that is 400watts rms. do you guys think that the amp is too underpowered to handle the sub. that's a 100watt deficit.
the thing is, i'm not into crazy bass and knock. if i'm looking to just get an wholesome & above-average sound for my FD, do you guys think this'll be ok?

my options are as follows
1st choice: 300watt amp + 400watt sub = 100watt underpowered sub
2nd choice: 300watt amp + 250watt sub = 50watt overpowered sub

chiminoid

^

LoveBone

No worries. If you're not into "crazy bass and knock", or even if you are, 300W into a sub that can take 400 is fine.

chiminoid

amp is 300 rms bridged
sub is 400rms and 800 peak watts?
still ok?

chiminoid

^ just want 1 more opinion

LoveBone

Yep. You won't be taking advantage of all of the sub's potential but it will work.

rynberg

Speaker wattage ratings are damn near meaningless.

You are not underpowering the speaker. 300W through even an insensitive speaker will be very loud.

chiminoid

thanks guys

theloudroom

PEAK power ratings are pretty much useless. RMS ratings are very important.

The only companies that only give peak power ratings are pretty much not worth buying from.

DamonB

Yep. I've built lots of speakers for both cars and homes. Right now I have a single 12" sub in my home theater that will shake the entire friggen house at 250 watts. Why you need so many drivers and so much power inside the small space of a car I will never understand

DamonB

I got news for you; that don't mean a hill of beans either.

First off you don't know what freq the RMS was measured at (it's never on pink noise or within a given bandwidth, they just choose wherever the biggest spike is). Second off amp power doesn't mean anything; speaker sensitivity does. Third power (watts) isn't as important as current (amperage). Nine times out of ten an amp with much less power but higher current capability will kick the snot out of something with more wattage that can't handle as much current. Again for example I have a pair of towers here at home that when running on only 10 watts of tube power will make your ears bleed. On the other hand my sub is not sensitive at all, it must have lots of power to act like I designed it too.

Car audio (even the "respected" names) is hideously out of the park in their ratings. An amp is just a power supply. You know how much power it would take from a 12V car system to generate a REAL 300 watts? Enough that your alternator would overheat and die in a matter of moments.

theloudroom

1. No, both are important figures. You can't buy a $10 speaker and hook it up to a 1000 W rms amplifier. You NEED to look at the power ratings for your speakers and your amps or you risk frying stuff.

2. He's asking if a 300W amp with a 400W speaker is "okay"? He wants to know if he's going to damage something or if it will sound bad, not if he's going to win an SPL contest.


See (2). This doesn't really have to do with the discussion at hand.


3. Yes, actually I do know how much power it takes for a 12V system to put out 300 watts. I'M A FRICKIN ELECTRICAL ENGINEER! You are calling the wrong person out to a battle of electrical knowedge. Best case for a 300W RMS amp is about 24 A @ 14V. Totally do-able without melting anything BTW, just don't turn on your headlights, power windows, AC, etc.

4. See my post in this thread about why you should upgrade your alternator.
https://www.rx7club.com/forum/showth...hreadid=239306

5. Many brands do overrate their amplifiers, but some brands underrate them. Unless you're planning to go out there and test every amplifier on the planet youself, you're going to have to use someone else's figures at some point. A good sanity check is to look at the fuse on the side of the amp and the a typical efficiency for that class of the amplifier, but I don't really want to get into that. For this discussion, the manufacturer's rating is good enough.

The point is, for the average joe shopping at Best Buy, they should be looking at RMS values on amps and speakers. It's the best information they have availible. I wish they would plot frequency responses and include Theile-Small parameters in their sales flyers but they just don't.

rynberg

You may be an electrical engineer but you are wrong in regards to speaker wattage ratings. The ratings may be somewhat useful as a comparison tool WITHIN a brand, if the brand is a high quality and honest manufacturer. Other than that, they're useless.

As to your $10 driver example, I've seen cheap *** speakers rated for 100 watts rms that I could easily blow with 10 watts. Like Damon said, the power handling of the driver will vary greatly with the signal.

Like any specification without a full description of the testing conditions, speaker wattage ratings are useless. As an electrical engineer, you should know that.....

DamonB

That is a very good rule of thumb as is shear weight. Big transformers are heavy and so are heatsinks.


Your assuming all the power into the amp also comes out the other end; that is incorrect. Notice how HOT amps get? They are not perfectly efficient. It takes much more power on the input side in order to make up for what is dissipated as heat inside the amp. Kudos on your electrical engineering.

Frying speakers rarely happens from exceeding their wattage rating, it comes from amplifier clipping of the signal when the amp runs out of headroom (current). Speakers see an ac signal from the amp but a clipped waveform from the amp is essentially dc. This quickly overheats the voicecoil and will kill a speaker much quicker than anything else. I can take a 300 watt speaker and completely fry it with only 20 watts pretty easily, and it happens all the time; especially in the car audio environment.

It was relevant as an example of amplifier power and speaker sensitivity.

theloudroom

(sarcasm)Yes, I'm oh so very wrong. No one should ever try and figure out how much power their speakers can handle before buying them. From now on I'll just buy speakers based only on size and SPL @ 1W 1m. This isn't enough information to make a sensible decision, but who cares if I blow them up ?(/sarcasm)

AHhhhhh! dammit! (insert Sam Kinison yell here)

Of course cheap speakers are crap. I'm talking about a basic rule of thumb, not treating power ratings as if they are spot on. If someone tells you their $10 speaker can handle 10,000 watts their obviously full of ****. It's the same if someone tells you their stock Jetta runs a 10 sec. 1/4 mile. Does that mean 1/4 mile times are a useless measurement?

Obviously power handling varies in certain situations, but that doesn't make spec. useless. Get it? How many watts of DC does it take to fry even a good speaker?

Guess what? Speaker sensitivity is different a different frequencies too! Does that mean it is also a useless figure? Does that make both me and DamonB idiots?


Geez people. We haven't even said anything about the box this ?400w? speaker is in! Isn't that a good enough clue that we're in "general approximation land" not "full-fledged system design mode"?

This argument is as silly as saying manufacturer's hp ratings are useless in judging a car's performance. Obviously it's not a good as a dyno chart, but that doesn't mean it's a useless figure.

theloudroom

More true with old equipment, but still useful. Most new equpiment uses toroidal transformers.


No, I'm not. I assumed 90% efficiency. This is possible for a class D amplifier. Most amps aren't class D, which is why I said "best case". Some are.

Kudos on your ability to divide 300 by 14.

This is true in some cases, but not in others. There a multiple ways to fry a speaker. Clipping transients are one way, but definately not the only way.
A given speaker can only take so much power, if you hook up a 300W RMS amp to any of the stock speakers in an RX-7, it's going to fry because you applied too much power.

DamonB

Class D= digital. "Normal" Class AB amps are happy to be 50+% efficient.

Class A amps may only be 10% efficient and can be used to heat your home

theloudroom

Actually, true class D amps aren't quite digital in the tradditional sense, they're PWM (Pulse Width Modulated).

The amp works by comparing a high frequency triangle wave (hundreds of KHz) with the incoming audio signal and using the result to switch the output transistors.

Nowadays, it seems "class D" is used as a catchall for any digital amplification scheme.

Personally, I'm going to be putting "class D" amps in my FC for the dual purpose of cutting heatsink weight, and conserving alternator power. There are a couple for sale on on this board.
As you've said, class AB amps dissipate significantly more power, this requires much larger heatsinks, more transistors, etc.

chiminoid

lol what happened to the original question here?

this discussion is very informative none-the-less

vchacon

Wow, I thought WE hijacked threads on the west forums but this is nice.