So. I don't exactly understand this.

[fwb_1234 10+ year member]

I recently set my gains using the official gain setting tutorial, and I set it to the RMS of my amp and subs (same - 400W). I realized that I could have set them to whatever the heck I wanted.

When I first got started, I was told my amp would not actually produce the wattage stated, but I could have set them to whatever I wanted to anyway.

I understand that at one point, my amp will start sending a distorted/clipped signal to my subs, which I can check with test tones, or, better yet, an O-scope. Another tutorial I read told me how to set gains by ear, by listening to tones and turning up the gain until the signal distorted, which makes much more sense, because you could adjust it to the exact point at which it started to distort, not the stated wattage proved by the manufacturer.

Does this mean that anyone with an O-scope (or good ears) can perform benchmark tests? If not, why?

Who creates the ratings that are incorrect (in cases where an amp is under/over rated)? Why are they off?

I'm just really confused how some amps are under/over rated, or even rated at all. Subs I understand; it's based upon how much heat they can handle before they burn up. It's amps that make me //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif ...

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[skadude016 5,000+ posts]

they probably round up on wattage to make it look better. and some under rate for competitors. Also subs can fail mechanically too //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif not just thermally

 

[grizzly 10+ year member]

most companies that over rate so that they can sell mroe to ppl that dont know any better. ones that under rate are usually better companies.

 

[fwb_1234 10+ year member]

So, the BEST way to set gains is with an O-scope/less-reliable-listening-method? Right?

Why would a company ever underrate a sub?

Edit: When I asked an audio-shop guy about my amp (bahn a8002t), he said that they would "probably" put out what they say. What does that mean? It'll put out whatever I say it puts out.....?

 

[patrick1202 10+ year member]

so people will prolly stick to that so they know less chance of sub failer

 

[Immacomputer 10+ year member]

Does this mean that anyone with an O-scope (or good ears) can perform benchmark tests? If not, why?Who creates the ratings that are incorrect (in cases where an amp is under/over rated)? Why are they off?

Just because you have a scope and good ears does not mean you can perform a proper benchmark test (I'm assuming you mean to find actual power). To perform this, you will need a scope, reliable and accurate meters, and a purely resistive load (no, speakers are no where near purely resistive).

Amp ratings are going to vary due to components. Components all have a % of accuracy for their claimed ratings. When you put all these components together to make an amp, you have a wide range of possible performance for each amp. The better the components used, the lower the variation and closer to rated power. Most decent companies will rate their amps at the low end of the variation to keep the chance of having an amp that doesn't meet their requirements to a minimum. Shitty companies will rate their amps for the chance that it is possible to get one that will perform on the higher end of the spectrum.

So, the BEST way to set gains is with an O-scope/less-reliable-listening-method? Right?
Why would a company ever underrate a sub?

Edit: When I asked an audio-shop guy about my amp (bahn a8002t), he said that they would "probably" put out what they say. What does that mean? It'll put out whatever I say it puts out.....?

Setting gains with a scope is by far the best way to set your gains. Ear is my second choice although I would use my eyes and ears when setting my gains with a scope as well. Just because your speakers are OK thermally does not mean they're fine mechanically with the power you're planning on sending it.

Companies would underrate a sub to reduce the amount of returns on warranty. Also, people may not use their recommended enclosures and that will change the mechanical power handling of the sub. A good company will realize that this will not only decrease returns and increase profit but it will also build the company's name as a company that has "well built" products.

What he is saying is that the amp may not put out the power that it's rated it. It may or it may not and there is no way to tell just by listening to it. You could get an idea with a scope and multi meter but you're going to get numbers higher than you expect.

 

[fwb_1234 10+ year member]

Thanks. I mistyped this sentence: "Why would a company ever underrate a sub?" I meant, "amp," but you answered that as well.

You could get an idea with a scope and multi meter but you're going to get numbers higher than you expect.

You would need the multimeter to see what voltage the amp is putting out when it starts to distort? (and with the voltage, find the power...)

Edit: And, by failing mechanically, you mean like ripping apart, right?

 

[Kriszilla 10+ year member]

Why would a company ever underrate a sub?

Sometimes it's a holdover from the old IASCA RMS classes, most of the time it's due to design. They may have made a board that will average between 1100 - 1250 watts RMS on a bell curve, but *always* does at least 1000. So, it gets labelled a 1000 watt amplifier.

Why make the design less efficient (especially once it's been done and the templates are in place for production) to only do rated when you can sell it as a 1000 and earn even better reputation points for having an underrated amp?//content.invisioncic.com/y282845/emoticons/naughty.gif.94359f346c0f1259df8038d60b41863e.gif

 

[Immacomputer 10+ year member]

You would need the multimeter to see what voltage the amp is putting out when it starts to distort? (and with the voltage, find the power...)

Edit: And, by failing mechanically, you mean like ripping apart, right?

You would need to measure the voltage and the current. The scope will tell you the voltage and if it's a nice scope (read: over $5k), it will be pretty accurate. You will also need to measure the current. From those two figures, you will have apparent power, which is measured in volt amps or VA. This is NOT the power the amp is putting out. From there, you will be able to calculate the impedance of your load (speaker and wires) and then you can find the phase angle of the impedance given DCR and this resistance. This phase angle can then be used to find the actual power, measured in watts. If you had a purely resistive load, you could just use the voltage and current to find the actual power of the amp. This also needs to be done with no clipping of the signal to be accurate. After clipping occurs, measuring actual power changes... especially when we're talking how you calculate it.

My mechanically failing, I mean a number of things: voice coiling leaving the gap permanently, the cone shattering/ripping, the spider separating, the voice coil becoming jammed due to being bent, the voice coil unwinding, and many other ways.

 

[fwb_1234 10+ year member]

I'm still a wee confused. I have just read about ten FS threads with people dumping on other people's stuff about how that 1000W amp will only put out 500W, etc? What's that supposed to mean? If you set the gains with a multimeter, it'll produce what you calculated....right?

So with amps that are "underrrated," how do you guys set the gains? Do you just pick a ballpark number and set it there?

 

[fwb_1234 10+ year member]

help?

 

[spoonraker 10+ year member]

Matching an amp to a sub is not an exact science. Giving a sub that is rated at 1000W RMS 1046W RMS will not blow it up. So you simply pick an amp that is rated at or maybe slightly above that power that you are shooting for, and then using the method of your choice (o-scope, multimeter, ear), you set the gain on the amp so that just before maximum volume on your head unit is when your amp will start to distort.

Without a lot of expensive equipment you probably will never know exactly how much power your amp is putting out. It depends on so many things, your wiring, your alternator, your car, the temperature, god, aliens, the color of your eyes, etc....

Setting your gain is simply the process of adjusting your amplifier so that the signal coming from it will not distort until maximum volume on your head unit. The only reason a lot of people confuse setting the gain with figuring out exactly how much power you are putting out is because when you use the multimeter method you have to use the amount of power you are shooting for in your calculations for voltage.

 

[req 5,000+ posts]

listen man, you are nuking it. taking this whole 'benchmarking' thing way too far.

all you need to know, is that your amp is rated for XXXX wattage. do your research, make sure it can put out the power its rated for, or close to it, and then make sure its a little more than what your sub is thermally\mechanically rated for. headroom on power from your amp over what your sub is rated for, means that the amp will not have to be driven to its maximum in order to make the system sound normal. we all have cars that can go 100mph+ but you never get there often do you, so dont expect your amp to live long if it has to eaither. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

so another little thing, there is something called impedance. or the characteristic of a speaker being a resistor. since speakers are nothing more than electro-magnets placed inside a static ceramic\exotic magnet, this means that the coil inside generates a magnetic field when voltage is put though it. since we listen to music, in our case AC voltage. when you put electricity through a wire, a few things are generated. heat, a magnetic field, and more resistance for the electrons flowing through. this resistance is caused by the magnetic field "pushing back" on the electrons flowing through the wire. the amount of this resistance changes depending on what frequency is played.

here is something neat i bet you didnt know. an inductor is a coil of wire. we use inductors inside crossovers to limit high frequency signals. so your subwoofer is a big giant low pass filter. this is caused by impedance changes of the magnetic field due to frequency modulation.

so, this relates to your dillema because not only is your amplifier not going to put out the power that the company states due to mechanical\electrical tolerances on the components inside the amplifier, or due to overrating\underrating, BUT - the SPEAKER itself will change its resistance based on the frequency you play, AND the amplifier will put out different power levels because of the constant change of coil resistance.

this is called an impedance curve. since we listen to AC voltage (ie: music) and music is a bunch of frequencies, its going to constantly change the frequencies and resistance of the speaker.

meaning your amplifer will not produce its rated power no matter what pretty much //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

here is an example of an impedance curve. can you see on the right hand side? as impedance goes up, Db goes down? this is the inherant factor in what i was talking about above, that speakers are giant low pass filters //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

how many watts do you think your amplifier produces at 40ohms? i will venture to guess, almost nothing. can you hear that change? no.

in retrospect? dont worry about all that shit. set your gain with a multimeter - not your freggin ears, because you cant hear clipping when it starts and stops. and get a more powerful amp than your sub can take.

thats all you need to know. i bet most of what i wrote does not make too much sense //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[fwb_1234 10+ year member]

No it makes sense, and it helps.

However, it doesn't answer this question.

If you have the SA (sh1tty amp) 1000D, which does 1000W @ 1ohm, and the AA (awesome amp) 1000D, which also does 1000W @ 1ohm, according to manufacturer's specs.

The SA 1000D is "underrated" and generates comments like: "Man, it'll probably only put out 500-600W." On the other hand the AA 1000D generates comments like "Yeah, dude, that amp probably puts out 1300-1400W, hommie."

OK?

So I get both amps, side by side in my car. I plan to run 950W to a sub, so I set the gains for 950W @ 1ohm. Doing the math, that means I need to set my voltage to 30.8 V. Math: [sqrt(950 x 1)]

So, I do this and put them to the same sub. Will they perform differently? If so, how?

 

[Flipx99 5,000+ posts]

No it makes sense, and it helps.
However, it doesn't answer this question.

If you have the SA (sh1tty amp) 1000D, which does 1000W @ 1ohm, and the AA (awesome amp) 1000D, which also does 1000W @ 1ohm, according to manufacturer's specs.

The SA 1000D is "underrated" and generates comments like: "Man, it'll probably only put out 500-600W." On the other hand the AA 1000D generates comments like "Yeah, dude, that amp probably puts out 1300-1400W, hommie."

OK?

So I get both amps, side by side in my car. I plan to run 950W to a sub, so I set the gains for 950W @ 1ohm. Doing the math, that means I need to set my voltage to 30.8 V. Math: [sqrt(950 x 1)]

So, I do this and put them to the same sub. Will they perform differently? If so, how?

Just because the voltage is the same doesn't mean the signal isn't affected. There is more to it than just the voltage. Shitty equipment can degrade the signal, thus the sub performs differently.