# How to calculate TRUE amplifier output (watts)

## Car Audio, Video, & GPS

#### How to calculate TRUE amplifier output (watts)

How can i calculate how many watts my amp is actually putting out? Just to verify what the manufacturer is saying on the box. IE to be able to tell if your amp which is rated at 600w rms is actually putting out about 600w rms.

I heard something about a volt meter and a couple of equations?

If you look at a lot of youtube videos about a person's subwoofers the person who created the video will say ive got this amp and its doing 1200w rms and then you'll look down at the comments and some basshead will be talking about how they seriously doubt that amp has that much output and that the rms is actually much lower than that... so that makes me curious of how to calculate what mine is doing

Thanks!

• TigerHeli

(Also - make sure the amp RCA's are plugged into the sub and not the front or rear pre-outs).

Got the RCA in the subwoofer outputs now and everything sounds like it should. Thanks for the help!

All Replies
• the only true way to know is to use an ocilloscope :) .. also state us the amps brand and model and we can give you a range of the power its putting out :)

JVC KD-AVX44, 2 Massive Audio Hippo 8's , Hifonics Colossus going back in soon, MB Quart ONX216, Fli audio FL450S-F2, Energy ENC693x2 in rear deck, 6 gauge kit plus a huge 3 gauge kit. Custom built box for my 8's :)

• In a previous post, you mentioned the Cadence TXA-1000D, which is 650W@2-ohms.

You can get close by playing a 50Hz test tone with the sub disconnected and the HU near full volume - measure the AC voltage at the amp outputs and you should get something around 36.05 V  (sqrt(650*2) or Sqrt(Watts*ohms) or third equation here.

That test tells you the amp is putting out the power it claims, but it doesn't tell you the distortion it is putting out - i.e. it might be a terrible sounding amp, but it makes it's rated power.  To account for distortion, you need an oscilloscope like Shak said.

As far as the comments - you can usually tell from the context.  If someone says "I bought this 1000W RMS amp and it is putting out 1285W" they probably ran it on at least a meter if not an O-scope.  If they say "I'm running a 2500W Boss amp to these subs" - they probably just read the box top.

As far as the YouTube comments - a great example is my old friend, the Vibe 286.  Lanzar markets this as 4000W and most YouTube'rs would claim that, but the real specs on the web page are 2x1000W RMS at 4-ohms and the real specs in the manual are 2x300W RMS@4-ohms (and that might be generous).

Hope This Helps!!!

2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

• Thanks guys, i know i can always come here when i need a good answers.

One of my friends was actually talking up his 2000w rms lanzar system so I took the time to listen to it and it was terrible. He had them in a plexi-glass box he made that was probably 1/4" thick and i asked him what the volume was of each enclosure and he was like "uhh i dont know.. doesnt it look cool though?!" as the box continued to rattle, squeak and crack lol

• Oh and Tiger you mentioned to test the AC voltage on my speaker terminals. Can i just go to Home Depot and just pick up a digital volt meter and make sure it has a positive and negative lead?

• Yep - I got mine on sale at Harbor Freight, but if you pay more than \$15, you paid too much.

The digital ones are better with electronics and it has to have an AC voltage scale.

Also - you want to disconnect the subs when you test the amp output.

Hope This Helps!!!

2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

• Okay we have an issue i ran to menards and picked up the correct multimeter, i ran the test tone of 50hz, disconnected my subwoofer and tested the volts i was getting less than 10V when i was looking for about 35?

This was with my HU settings on flat, 0 everything (HU), at about 70% volume. I didnt want to turn my HU up any more because that is my normal listening level.

The amp's gain was turned very close to all the way up and the bass boost was on zero. So to reiterate i was getting a reading of about 8-10V so that translates to about 32 watts if my calculations were correct (I used 8 volts) And that SERIOUSLY doesnt sound right to me. But, (sqrt(32*2)) does equal 8.

I decided to play around with the bass boost and the highest I saw was about 50V. When i had the bass boost at just under half way turned up it was about 35V.

So, any ideas on what is wrong?

This is my first dvc sub (4 ohm DVC, SHOULD be wired in parallel @ 2 ohms) and maybe i wired it wrong? (If it was wired wrong at 8 Ohms it would read 16V and at 70% HU volume would read about 11V on a multimeter which i close enough to 8-10 for me.)

Could a bad ground do this, assuming it is wired at 2 ohms?

• You were using the VAC and not the VDC scale on the DMM?

You did have the subs disconnected?

You are using the same terminals as the sub?  (i.e. bridged if the sub is bridged to the amp)?

I wouldn't expect a bad ground.

I picked 50 Hz, but I've seen 40 Hz recommended, but it shouldn't make much difference.

That calculated voltage is without the subs hooked up - so if the sub was wired for 8-ohms instead of 2-ohms, it would get less power and not be as loud, but the DMM readings would NOT change.

I have a hard time believing that a 600W amp is only putting out 32W to your sub and the sub still sounds okay to you, so I'm thinking something else must be wrong.

That said - if the gain is near max and the amp is only putting out 32W, the only real possibility would be low RCA pre-out voltage, but that is not likely either.

What HU, amp, and sub are you working with?

Thanks!

2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

• AS far as the multimeter, I followed the instructions on how to test for AC Voltage so the dial is turned to ACV 200. Near the positive lead it says VΩmA and something about 750VAC. The negative lead says COM. Im not sure what any of that means but it should be correct.

The subs are indeed disconnected. I disconnected the wire at the subs instead of disconnecting the wires at the amp but i doubt that makes a difference.

Same terminals, One Sub, mono amp.

The sub is not as loud as i would want to be. Sometimes it sounds decent but i keep telling myself that the box is the problem. The type r came in the mail the day before i moved to college so i just threw it in a 1.2cu/ft3 sealed box but i havent had a chance to buy/make a ported box for it. It just doesnt seem to be as loud as my previous sonys, probably because i had 2 subs instead of one. The type R is actually in the old sealed box i used to have the sonys in. It still shakes the mirror a little and it sounds nice and low but its not the pounding bass i used to have.

My HU is a Pioneer Deh-4000UB and is probably two and a half years old.

The amp is the Cadence TXA-1000D that you referred to me.

The sub is a 2010 Alpine Type-R (4 Ohm)

Just a final note: Previously i had a separate line out cable but when i upgraded to the cadence amp i got a new wiring kit I used the RCA cables which had a line out built in with the two RCA cables. There is a setting on my HU that i used to use all the time to make the subs louder/quieter. It had the subwoofer high pass filter (i think thats what it is) and a setting to that would go from -24 to 6. Also, if you hit the same button again you could change the subwoofer to normal, reverse, and off. Since the wiring upgrade and new amp, these settings have not been working. I change the high pass filter around to 50hz, 62hz, 80hz etc nothing happens. I can set it to off which on my last system would turn the subs off. Nothing happens now. Same goes for the -24 to 6 feature.

My roommate who i sold my system to used the same type RCA cable with the line out built in. He  has a pioneer deck too and these settings dont work for him either. But his system is still just as loud as it was before so im not sure if this could be my problem.

• DMM settings and procedure seem correct.

Burkem10
The type R is actually in the old sealed box i used to have the sonys in.

Dumb question, but I assume the box is chambered - ie, there isn't a big hole for the other 12 (10?) that is open to the rear of the new sub, is there?

I think I found the problem - I think you somehow turned off the subwoofer output in the head unit - no output - very little voltage at the amp - although it should be a lot less than 32W if it is off.

Burkem10
Previously i had a separate line out cable but when i upgraded to the cadence amp i got a new wiring kit I used the RCA cables which had a line out built in with the two RCA cables.

You mean the remote turn-on wire, correct?  The line-out cable IS the RCA cable.  Having the remote wire with the RCA shouldn't make any difference.

Burkem10
There is a setting on my HU that i used to use all the time to make the subs louder/quieter. It had the subwoofer high pass filter (i think thats what it is) and a setting to that would go from -24 to 6.

Low pass filter for a subwoofer - there is an HPF setting for the main speakers with that HU.  Look at page 25 and make sure SUB SW1 is set to ON.  That setting only shows up with the SUB output turned on.  (Also - make sure the amp RCA's are plugged into the sub and not the front or rear pre-outs).

Burkem10
My roommate who i sold my system to used the same type RCA cable with the line out built in. He  has a pioneer deck too and these settings dont work for him either. But his system is still just as loud as it was before so im not sure if this could be my problem.

The remote wire attached to the RCA should have no effect on the deck - I'm really puzzled by that.

Hope This Helps!!!

Anyone else have suggestions?

2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

• Yes the box is chambered, thats why i said it was 1.2cu/ft3 lol. It would be tough to fit two 12's in a box that small!

Sorry about the line-out, remote turn on wire mix up, you are correct it is the remote turn on wire.

I think the problem is where i placed the rca cables on my HU. I debated on this for a while when i was doing the initial install and decided that the middle rca outputs were for the subwoofer, but the manual shows that the bottom rca outputs are for the subwoofer.

This would explain why the subwoofer specific setting would not work. The middle RCA outputs are for the front output....

Thanks for the help again Tiger. I'll go home tonight and get things how they should be, if it works which it should ill verify your answer and be back to bumpin'

-Matt

• Burkem10
Yes the box is chambered, thats why i said it was 1.2cu/ft3 lol. It would be tough to fit two 12's in a box that small!

Touche!!!

Burkem10
I debated on this for a while when i was doing the initial install and decided that the middle rca outputs were for the subwoofer, but the manual shows that the bottom rca outputs are for the subwoofer.

That would do it!!!

Let us know how it works out!!!

2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

• TigerHeli

(Also - make sure the amp RCA's are plugged into the sub and not the front or rear pre-outs).

Got the RCA in the subwoofer outputs now and everything sounds like it should. Thanks for the help!

• Glad you got it sorted out!

2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

• Me too. I was on the edge of my seat. Lol not sarcastic