How many watts is my sub getting

Fernando Lopez

Freshman
Jan 14, 2011
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0
6
Venezuela
www.runaway69.com
I have a 4ohm TH-118

My amp is an EV CP4000S

specs:
Amplifier Gain 32 dB
Continuous Rated Power
(1 kHz, THD 1%) 2Ω 2100 Watts
Continuous Rated Power
(1 kHz, THD 1%) 4Ω 1500 Watts
Continuous Rated Power
(1 kHz, THD 1%) 8Ω 900 Watts
Continuous Rated Power
(20-20 kHz, THD<0,2%) 4Ω 1200 Watts
Continuous Rated Power
(20-20 kHz, THD<0,2%) 8Ω 600 Watts
Electronics Type Amplifier
Input Impedance (Balanced) 20 kΩ
Input Sensitivity +7dBu
Intermodulation Distortion (SMPTE) 0.02 %
Maximum Bridged Output 4Ω 4500 Watts
Maximum Bridged Output 8Ω 3000 Watts
Total Harmonic Distortion 0.05 %


Usually I will connect it to the bridge output, but sometimes due to low voltage I just plug it to the A channel

So my question is:

How many watts is my sub getting from the amp?


Thanks,
 
Re: How many watts is my sub getting

The amount of power being sent to the speaker will vary with how much input you send to the amp!

You say it is a 4 ohm speaker. Your chart shows the amp is capable of 1200 watts per channel over the music frequency range. I presume you do not just send it 1kHz. The amp is also listed as max of 4500 watts when used bridged into 4 ohms.

This is information you provided. What is your real question?
 
Re: How many watts is my sub getting

The other question should be "when is my amp working hardest".

Amplifiers don't put out "power" or "watts." They produce voltage which, when meeting the resistance of a voice coil, produce "power." Power is work being done and is measured in Watts.

Exactly what are you trying to determine? Headroom? Match of amp to load?
 
Re: How many watts is my sub getting

Thanks for your help, my specific question is this:

My amp is rated 600 watts at 8 ohms and 1200 watts at 4 ohms

Is my sub being amplified with 600 watts or with 1200 watts?

Thanks

The answer is not that simple. You also have to take into account the impedance. It is NOT (nor most any other loudspeaker) 4 ohms across the freq band. You really have to look at the impedance graph to see what the impedance is at a particular freq.

At some freq it is a little below 4 ohms and at other freq quite a bit more than 4 ohms.

But if you want a "simple" answer, it is "getting" 1200 watts-give or take.

As stated by others, an amp produces a VOLTAGE, and the wattage is a RESULT of the impedance of the loudspeaker and that voltage.

http://www.danleysoundlabs.com/pdf/TH 118 spec sheet.pdf
 
Re: How many watts is my sub getting

Yes Ivan that was the simple answer that I wanted, thanks.

I usually connect the sub to the bridged output of the amp which is capable of peaks up to 4500w and then limit it a little with the dc-one processor

In this gig voltage was so low that the amp kept going into protection. This happened during setup. So we decided to plug the sub into a stereo channel so that the amp would not have to work so hard.

I know that 600 watts is not too many db's but I was really curious

Thanks for your help
 
Re: How many watts is my sub getting

I know that 600 watts is not too many db's but I was really curious

Thanks for your help

600 watts is A LOT of dB. 600 watts is VERY LITTLE dB.

Both of the above statements are correct.

What people often miss is that dB (in its simplest term-as used above) is NOT a unit of direct measure. It is a relative measure between 2 known signal levels.

If you are talking about 1 watt vs 600 watts the difference is 27dB-that is a lot.

If you are talking 1000 watts vs 600 watts, the difference is 2.2dB Not nearly as much.

You have to get used to thinking in terms of dB, NOT wattage. Wattage is just heat-like an oven.
 
Re: How many watts is my sub getting

Tim, thanks for your help,but I am not quite that advanced yet
You may be without knowing it. The "follows the program material" comment simply means that the output of the amp and the power delivered to your speakers is not constant, it varies as the signal varies. If you have no signal you have no output and thus no power delivered to the speakers.

The voltage aspect is a bit more complex but is generally addressing the fact that amplifiers do not output power, they output voltage and current. That voltage and current then result in power delivered into the load that they are driving, in this case into the speakers, so the load is an active component in determining the power. Since a typical speaker has an impedance that varies greatly with frequency (your TH-118 may be a nominal 4 Ohm impedance but the actual impedance is as low as 3 Ohms at 67Hz and over 9 Ohms at around 95Hz) and the amplifier's output voltage is varying based on the input signal, that means that the power delivered into the speaker is constantly varying.

I think the disconnect is that you were likely wanting to know the maximum that the subs could see based on the nominal amplifier and speaker ratings rather than "How many watts is my sub getting from the amp?", which is going to constantly vary. Your amp is rated at 1,200W per channel into 4 Ohms (20-20kHz, 0.1% THD) in stereo mode and 4,200W into 4 Ohms (1kHz, 1% THD) in bridge mono mode. Since your dealing with a sub and the bridge mono rating is at 1kHz, you'd realistically get less than that.
 
Re: How many watts is my sub getting

I received this answer in another forum and I think this person might be right: ( Can I get some opinions!! )

I have heard several people voice the same complaint you have.
The class of amplifier you are using is likely the culprit.
I'm going to explain what I think is happening in fairly simple terms.
Please forgive me if I get my theories wrong. I'm by no means an expert at this.

Class H amplifiers are very lightweight. That is good. The drawback to them is that they pull their power directly from the "mains". As a result, the line voltage from the plug in the wall can sag under heavy demand. If you demand lots of power from the amp, the amp pulls that power directly from the wall. That's just the way the power supply is designed.
It's a tradeoff.

Class AB amplifiers weigh more. Their power supplies are more robust, and tend to "store" power in the power supply capacitors. These are usually big, and add to the weight of the amplifier. Under heavy demand, the AB amplifier releases some of the power it stored up. This can help support the voltage on the line, and prevent the voltage sag that would be experienced with other classes of amplifier.

If your power supply (voltage from the wall) is already questionable, then any amplifier will protect itself. When the voltage from the wall dips too far, the amplifier will suspend operation. This happens with just about any class of amplifier, but AB amps tend to have less problems with that aspect, since they store some power for future use.

To say that a QSC amplifier will not be affected the way your electrovoice amplifier was, is simply not true. It's like saying that only Chryslers can climb steep hills. There will be some QSC amplifiers that will not be as badly affected as you EV amp was... There will be EV amps that will not be as badly affected as yours was, too.

The power supply to the amplifier must be adequate to support the load, regardless of the manufacturer.

I think you could run your amp in bridged mono all night long, as long as you weren't demanding all the power it had to give.
If you also had a lighting system on the same circuit, perhaps another amp... As the loads increase, the voltage drops.

Definitely setting the proper gain structure is important. I'm just suggesting that adequate power supply for your rig is also important.

I'm not sure how dependable the power grid is in Venezuela. I don't mean to disrespect your home. I'm just thinking that if you do have voltage delivery issues, perhaps the amplifier you have chosen is not the best choice for the application. If you decided to change the type of amplifier you use, you might benefit on the performance side, but you would suffer on the weight side.

It's just a theory, but I thought I'd throw it out there, in case it had some merit.

Cheers
 
Re: How many watts is my sub getting

"Amplifiers don't put out "power" or "watts." They produce voltage which, when meeting the resistance of a voice coil, produce "power." Power is work being done and is measured in Watts."

Not really. Amplifiers produce voltage and amperage. P=IE. Power equals voltage times amperage, so amps do produce power! Wattage is a measure of power, not work. The resistance of the speaker absorbs power, it does not produce it. The speaker is a machine that converts electrical energy(or "power") into mechanical energy and that machine is powered by the voltage and amperage(watts) of the amp.

Now I am not an engineer, and if I have made an incorrect statement, I welcome corrections.
 
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Re: How many watts is my sub getting

Amplifiers amplify voltage. This is the only part of P=IE that is constant regardless of load, or even with the lack of a load. The amplifier output voltage should be exactly following the input voltage waveform- the current waveform won't.

It is correct to think of the speaker as 'extracting' current, and therefore wattage, from an amplifier, based on the voltage-impedance relationship.

For most anyone that doesn't know the fundamentals of electricity, any and all theoretical discussion of what a speaker is doing when powered with an amplifier is going to be out of their realm of understanding, especially since watts are not directly related to SPL.
 
Re: How many watts is my sub getting

Timmay said:
"Amplifiers don't put out "power" or "watts." They produce voltage which, when meeting the resistance of a voice coil, produce "power." Power is work being done and is measured in Watts."

Not really. Amplifiers produce voltage and amperage.

No, really. Mr. McCulloch did not misspeak. Amplifiers (as Silas points out) are voltage amplifiers. They happen to have a current reservoir behind them.

P=IE. Power equals voltage times amperage, so amps do produce power! Wattage is a measure of power, not work. The resistance of the speaker absorbs power, it does not produce it. The speaker is a machine that converts electrical energy(or "power") into mechanical energy and that machine is powered by the voltage and amperage(watts) of the amp.

What your missing (in regards to "power amplification") is that the impedance of a speaker is not constant WRT frequency. As the frequency of a signal changes, so does the resistance of the loudspeaker. This frequency-resistance relationship is called impedance.

A speaker is not so much a machine as it is a "motor." A motor is a device that converts one form of energy into another. It does produce power and it does not "absorb" or store it either. In converts some energy to motion, and most energy to heat. The rate at which this happens is power.

The same is true of an amplifier. It could be considered a machine, as it changes the direction (phase) of the electrical energy that supplies it. Similarly, it produces power. It changes the phase and frequency of some energy and like the speaker (machine part), converts a good bit to heat (power).

Overall, you could say that a "power amplifier" is not really a power amplifier at all. It may (or may not) increase the power of a signal whose voltage it is amplifying... dependent upon the impedance of the load.
 
Re: How many watts is my sub getting

Amplifiers amplify voltage. This is the only part of P=IE that is constant regardless of load, or even with the lack of a load. The amplifier output voltage should be exactly following the input voltage waveform- the current waveform won't.
This isn't really accurate - the voltage output of the amp sags relative to its theoretical output when connected to a real load.

Ohm's law is always true - what is constant is the equation P = IV, not necessarily the absolute value of any of the components. When an amp reaches its current supply limit, the voltage starts sagging, which is the symptom felt when there's no more juice.

In other words, it's not possible to vary the current supplied to a static load separately from the voltage - if the voltage goes up, so does the current. If the load impedance drops, the current demand increases, which will pull down the supply voltage to the equlibrium of what that supply can deliver. There are various feedback circuits that can be used to increase the supply voltage to maintain a constant output current, but these only work within the capabilites of the supply.
 
Re: How many watts is my sub getting

No, really. Mr. McCulloch did not misspeak. Amplifiers (as Silas points out) are voltage amplifiers. They happen to have a current reservoir behind them.

Hi Ryan-

Thanks for the backup on this, because I hear folks use Chuck's line of reasoning on a regular basis. A little lab experiment might convince, or not...

This is the crux of the situation and it can be demonstrated with an AC voltmeter and a current meter like the Kill-a-watt. Connect a high-impedance AC voltmeter to the output of an amplifier and put the current meter inline with the amp's power cord. Do not connect a speaker or other load. Power up the amp and note the current draw, then apply a 60Hz sine wave to the amp and turn it up until you get, say, 50 volts reading on volt meter. Look at the current meter. It should read about the same as quiescent because there is no load. There will be a slight increase in current draw due to inefficiencies of the amplifier design, but we're talking about maybe an ampere above quiescent.

Leaving the meters attached, turn down the amplifier input and connect a speaker to the terminals with the voltmeter. Bring the input signal back up until you get 50v again, and note the current meter reading. It will be much higher than the previous readings, how much so depends on the nature of the load itself.

The important thing to remember is that voltage is POTENTIAL; it is neither work being done nor the current that supplies POWER.

Have fun, good luck.

Tim Mc
 
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Re: How many watts is my sub getting

Hi Ryan-

Thanks for the backup on this, because I hear folks use Chuck's line of reasoning on a regular basis. A little lab experiment might convince, or not...

This is the crux of the situation and it can be demonstrated with an AC voltmeter and a current meter like the Kill-a-watt. Connect a high-impedance AC voltmeter to the output of an amplifier and put the current meter inline with the amp's power cord. Do not connect a speaker or other load. Power up the amp and note the current draw, then apply a 60Hz sine wave to the amp and turn it up until you get, say, 50 volts reading on volt meter. Look at the current meter. It should read about the same as quiescent because there is no load. There will be a slight increase in current draw due to inefficiencies of the amplifier design, but we're talking about maybe an ampere above quiescent.

Leaving the meters attached, turn down the amplifier input and connect a speaker to the terminals with the voltmeter. Bring the input signal back up until you get 50v again, and note the current meter reading. It will be much higher than the previous readings, how much so depends on the nature of the load itself.

The important thing to remember is that voltage is POTENTIAL; it is neither work being done nor the current that supplies POWER.

Have fun, good luck.

Tim Mc

Do not try this experiment with the bass player's 300 watt SVT tube amplifier unless you have lots of money set aside for repairs :^).

Also, there are many loudspeakers that will not survive 50 volts of 60 Hz sine wave for more than a few seconds, as I have found out by mistake :^(.
However, a B&C18SW125-4 can survive a 110 volt 60 Hz sine wave for over three seconds 3 times in a row, it takes about 3 seconds for a Crest CC2800 in bridged mono to kick it's front panel breaker, as I found out in a more recent mistake when I thought I was turning down the LF level while on the HF page...

Previously, I was suprised to hear the same speaker not complain with 120 V, however it turns out the impedance at the frequency I was testing was around 18 ohms, so the speaker and amp were "only" using 800 watts, which did not trip the amp's breaker, but did rattle various stuff off the shelfs in the shop.
Art
 
Re: How many watts is my sub getting

Uh, good advice, Art! Tube amps weren't on my horizon and I didn't stop and think about what 50v. will do to many speakers.

Okay, kids... use 20v instead. The speakers will live... but DON"T do this with compression drivers.

Thanks for the cautions.

Tim Mc
 
Re: How many watts is my sub getting

What your missing (in regards to "power amplification") is that the impedance of a speaker is not constant WRT frequency. As the frequency of a signal changes said:
No, I am not missing that, I just didn't include that obvious bit of info when I was trying(rather unsuccessfully) to make my basic point.

Amplifiers DO produce power and watts, no matter how much one trys to complicate the issue. Every amp manufacturer in the world rates their amps by the amount power, or watts they produce. How can anyone state that an amplifier produces voltage but not power? Of course how that power is used to perform work is another long, complicated story.

Physics 101 - watts are NOT a measurement of work being done, they are a measurement of electrical power(I X E).

A speaker isn't a machine, it's a motor? How many angles can you fit on the head of a pin?