watts

[niz]

how do you measure the watts you are putting out of your amp?

[ScottXGTR]

http://www.holroyd-components.co.uk/images/ohms_law1.jpg

ohms law.

you need to know 2 of 4 things.

Voltage: measureable with a multimeter at the amps outputs
Resistance: measureable on the terminals of the sub
Amps: measureable with a clamp meter on the speaker wire
Watts: since this is what you are looking for, you clearly wont know it

basically, you play a test tone and measure the voltage at the amp. pick a couple tones in the subs range to give an average. lets just say 35hz, 40hz, 45hz, and 50hz

ohms will change as the sub plays so try and use amps as your other figure. measure amps with a clamp meter on the speaker wire. plug your numbers into the formula

then you can figure in whether its clean or not with distortion figures and throw it all out the window.

use the golden rule: if it starts smelling, turn it down some.

[niz]

damn thats over my head

[ScottXGTR]

shhht. thats nothing.

you can determine tuning frequency, measure impedance rise, and all sorts of stuff with a good multimeter and ohms law.

[niz]

i know how to work a multimeter but cant do all these equations worth shit unless someone is here and shows me

[stratusrt01]

it's actually easy, but you have to have an RMS clamp meter and a Digital Multimeter to do it. Then it's simple multiplication.

[ScottXGTR]

put your DMM leads on the amp, measuring AC voltage. play a tone and lets say you get 35v
put the clamp meter on the speaker wires measuring AC amps. play a tone and lets say you get 25a

then 35v x 25a = 875w

[zach]

the best way to know is to just buy a good true amp. ill just use alphasonic as an example. alot of the crazy low grade amps these days will claim to be 4000 watts etc. and they have like a 20 or 40 amp fuse and only measure about a foot in length 10 inches in width. my alphasonic hca 1000 has no internal fuses, measures roughly 3 feet in length 9 inches in width. it only claims 1000 watts but 1000 "true" watts is much more valuble than a 50$ 4000 watt amp. take the memphis bell amp line for example. you get what you pay for and most of the high grade amp lines arent lying (most of the time).

[niz]

so how bout a kenwood 1000? thats what i got?

[zach]

not 1000 kenwood makes relitivly powerful amps, in my excperiance they dont last the longest. but i would say mabye true 500 watts what size fuses does it have, thats a dead giveaway to an amps real power capabilities.

[niz]

40amp fuse

[ScottXGTR]

what size fuses does it have, thats a dead giveaway to an amps real power capabilities.

on a quality amp, the size of the fuse is a good indication of potential power. you could expect maybe 100w per 10a of fuse. thats a rough number tho, there are lots of variables such as amp class and efficiency.

on a crappy amp tho, the fuses could be in series. 30a+30a+30a in series isnt 90a total, its still just 30a.

companies know what people look for in amps. people automatically think a large amp with lots of fuses makes tons of power. so some amp companies make the cases extra large (and only half full) and put fuses in series so people think they can handle lots of power.

funny you mentioned alphasonic, i used to own one of their recent offerings rated at 900w, (40a fuse iirc) and i think it was highly overrated.

[bigbeto]

i just usually read the owners manual.. works EVERY time....:cool:

[zach]

granted that i have never given this amp a woofer to really test its nuts, i got it on 2 L7 12s custom box 10cu feet at 35hz vented (not sure of port displacment as i didnt build box). my HCA1000 is the only alphasonic amplifier i have ever had. im happy with it, any amp that can put up with my music addiction for at least a month gets a good rating from me lol. you sill rockin that 18 you showed me in the x-terror at matts shop scotty?

[joshboogie]

Well the old school way is you can figure $1 per watt. If the amp has a 40 amp fuse then it's not kicking out 1000w.

[ScottXGTR]

Well the old school way is you can figure $1 per watt. If the amp has a 40 amp fuse then it's not kicking out 1000w.

those days are long gone. you can get 3000w for around a grand nowadays. the problem most people have is that their car cant support the current to make 3000w.

and zach, the 18s are sitting safely in their boxes. waiting for my ass to quit being lazy.

[joshboogie]

those days are long gone. you can get 3000w for around a grand nowadays. the problem most people have is that their car cant support the current to make 3000w.

Well the days of companies lying about power ratings are stronger than ever. I'm sure you'll agree with that. While the $1 per watt theory may not be as on point as it used to be it's still pretty damn close.

[ScottXGTR]

i agree, below 500w, $1 per watt does apply to a quality amp. once you get above there, the margin opens up a little. there are always exceptions tho.

there is so much bullshit hype in the industry that makes it easy for inexperienced buyers to purchase garbage equipment. and even the vets get suckered every now and then. the only thing you can do is read reviews from unbiased sources that know what they are talking about. so avoid any review that brags about their sub "blowing out their window", "setting off car alarms", or "being heard from 3 blocks away"

[joshboogie]

i agree, below 500w, $1 per watt does apply to a quality amp. once you get above there, the margin opens up a little. there are always exceptions tho.

there is so much bullshit hype in the industry that makes it easy for inexperienced buyers to purchase garbage equipment. and even the vets get suckered every now and then. the only thing you can do is read reviews from unbiased sources that know what they are talking about. so avoid any review that brags about their sub "blowing out their window", "setting off car alarms", or "being heard from 3 blocks away"

I totally agree. That's why I'm still running a Rockford Fosgate 360a2 from 98' in my Scion lol.

As far as the math on Ohms Law this might help.

http://i114.photobucket.com/albums/n277/joshboogie2/Ohmslawmath.jpg

This is straight out of the MECP Basic Study Guide.

[stratusrt01]

Scott has some good points, he knows the deal.

I just want to add. If you do decide to clamp your amp to see how much power it's putting out, don't be upset or surprised when you come out short of the amp's rated rms power. You will rarely see rated power in a car, most of them do rated on a test bench with a stable ohmload and stable power supply at 14.4 volts. Neither of these you will find in car.

Your subwoofer actually changes it's impedance through it's xmax, so it's changing constantly as you're playing it. Add to that that your box, wiring and connectors all add to what we call "impedance rise". It's not odd to measure a 1 ohm sub in a box while it's playing as 14 or 15 ohms. How much power do you think your amp is putting out at 15 ohms? Typically though, it's more like 4-9 ohms, but still, how much power does your amp put out at 4 ohms?

This brings me to owner's manuals, since they were mentioned. Those actually mean very little unless the amp is CEA rated. Companies such as U.S. Amps have openly admitted to fudging amp ratings to sell more amps to unknowing customers. Their Xterminator line is such an amp. The XT4000, a "4000 watt amp", has been measured at between 800-1000 rms wattage. Now, the case says 4000 watts, the manual says 1200 watts, but it failed to achieve either of those on a test bench multiple times.

The next thing is birth sheets. Worthless, Worthless, Worthless. Well, at least to you and me. All they are is an indication of the amp's power, too bad you and I will never see that power in our vehicles. Remember what I said about stable ohm loads and stable voltages at 14.4? That is how your birthsheets are done, and we all know now that a subwoofer isn't a stable ohmload, and a vehicle is incapable of having stable voltage.

Now, after I've said all that, let me add:

I don't get wrapped up too much in impedance rise and power output in a daily driven street vehicle that plays music. I ask myself: Is it loud for what's in there? and Am I happy with it? Because in the end that's all that really matters.

[stratusrt01]

Well the days of companies lying about power ratings are stronger than ever. I'm sure you'll agree with that. While the $1 per watt theory may not be as on point as it used to be it's still pretty damn close.

It applies well to smaller, class A/B amps, but with the technology change, and Class D technology, true rms wattage can now be had for much cheaper to power subwoofers.

1500rms can now be had from multiple companies, and actually putting out 1500rms, for around $500.

[zach]

and zach, the 18s are sitting safely in their boxes. waiting for my ass to quit being lazy.

ha ha feel free to put those up for sale ;) ;) :thumb:

[joshboogie]

It applies well to smaller, class A/B amps, but with the technology change, and Class D technology, true rms wattage can now be had for much cheaper to power subwoofers.

1500rms can now be had from multiple companies, and actually putting out 1500rms, for around $500.


I see what you are saying but I don't agree with it totally. An amp may have a rating that says 1500 watts but if it's a true clean 1500 then it will be way more than $500. When I say that I'm talking about retail. If you are looking at class D or T amps you are no longer in the $500 market and are not looking for equipment in a Best Buy or Circuit City.

[stratusrt01]

You can pick up many 1500 watts amps for $500 from the shop that I work at that actually put out over 1500 watts.

Sundown SAZ-1500 does 1800ish watts and sells for $499
U.S. Amps MD2D does 1500 watts and sells for around the same


That may not be MSRP, but that's the typical going rate in a shop for those amps, and both do rated power or more.

[ScottXGTR]

ha ha feel free to put those up for sale ;) ;) :thumb:
hahahaha No. i got some small stuff im gonna move, but not the big boys.

I ask myself: Is it loud for what's in there? and Am I happy with it? Because in the end that's all that really matters.

thanks for your input rich. this is the best point made in the thread.

[stratusrt01]

Scott, you know my 18's showed up yesterday. If mine is done before yours when you've had yours for months, I'm going to give you hell. Oh, and mine will be done by the end of next week, so you'd better get to work!!!!!

[ScottXGTR]

lol. i was one of the first people to pre-order a havoc 18. thats how long its been sitting here.

im slowly getting motivated. all you gotta do is post lots of pics about how bad ass yours are.

[stratusrt01]

I'm picking up my Mayhems in a couple weeks from Nick. But I think I'm going to put them in the Stratus and leave the Nightshade 18's in the truck.