# Amp sensitivity setting question.



## tspence73 (Oct 14, 2008)

Okay,

My Planet Audio amp will be delivered on Wednesday. I am preparing for it now. I would like to get a few suggestions on how to set the input sesitivity.

Here are the parameters I am faced with:

Amp output = 4 x 175 @ 4-ohms RMS

Speaker input specs = 90-watts RMS / 270-watts peak

My JVC head unit has a 2v pre-out.

I will be using the 2v - 8v adjustment choice the amplifier provides.

Here is an image of what the Planet audio BB175.4b amp's gain controls will most likely look like:










What would be the best setting for the input sensitivity to keep the amp at a safe RMS output of about 125-watts or so? I'm guesstimating 2 o'clock on the dial at the most with any higher being risky to my comps' health. What are you guys' thoughts?


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## benny (Apr 7, 2008)

So what were you running your components and 6x9s with in your '6x9 enclosure' thread?

Do you have a DMM? 

http://www.bcae1.com/ <--great spot to learn stuff...


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## 60ndown (Feb 8, 2007)

tspence73 said:


> Okay,
> 
> My Planet Audio amp will be delivered on Wednesday. I am preparing for it now. I would like to get a few suggestions on how to set the input sesitivity.
> 
> ...


best thing to do is close all the doors and the trunk, seats up (while your in the trunk with the amp) play some music as loud as possible until the trunk lid moves violently, then get your buddy who is outside the car to call you on your cell phone (which you have in the trunk) to tell you when the trunk lid is moving just violently enough.


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## elvisjer (May 13, 2008)

Wait wait wait, you're saying lock yourself in the trunk with the music at full blast. I think this is a horrible idea although i did hysterically laugh out loud when i read it. I would really like to convince someone i don't like to try this though.


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## Jimi77 (Jul 4, 2005)

Nice looking amp. I'd give you some advise, but since you'd just tell me how wrong I am, etc - just set the gain at 8v and see what happens.


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## tspence73 (Oct 14, 2008)

benny said:


> So what were you running your components and 6x9s with in your '6x9 enclosure' thread?
> 
> Do you have a DMM?
> 
> http://www.bcae1.com/ <--great spot to learn stuff...


Well, I've been running them with less power. About 60w x 4 RMS. When I get the new amp I want to set it safely for my speakers.

Yeah, I've read that site a long time ago. I haven't had an amp more powerful on it's RMS than my speakers before, so I'm just seeking some advice, just in case. Aren't DMMs sometimes inaccurate? They don't detect clipping, right? Not that it should matter. This amp should put out more clean power than my speakers can handle.


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## tspence73 (Oct 14, 2008)

Jimi77 said:


> Nice looking amp. I'd give you some advise, but since you'd just tell me how wrong I am, etc - just set the gain at 8v and see what happens.


Actually the 8v part of the gain would be the minimum. Did you mean for me to switch it to the micro volt setting? That might have been funnier.


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## tspence73 (Oct 14, 2008)

Oh, I edited. I forgot to add my HU has a 2-volt pre-out. :blush:


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## tspence73 (Oct 14, 2008)

Hey, 

Nobody has any good input? Is a DMM the only good method here?


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## Mooble (Oct 21, 2007)

Really, a DMM is the most accurate way to tell. Anything else is completely subjective.


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## tspence73 (Oct 14, 2008)

Mooble said:


> Really, a DMM is the most accurate way to tell. Anything else is completely subjective.


Ok, just so my rusty math checks out. 

Using the rule: Volts x (Volts/Ohms) = watts

21.5 x (21.5/4 = 5.5) = 118.25

Considering that 110-watts is the point where you get double the volume after the 10-watt doubling point, anymore wattage applied is not only inaudible (according to the rules of watts and human ear perception) but greatly exceeds this speaker's designed input RMS. So, I figure a comfortable 118 watts RMS will serve my needs neatly and give a bit of headroom for any wattage loss on the speaker cables.

Does everyone agree with my assessment? I believe I'm right, but I'm rusty at all this math stuff. What test tone is the best to use for these comps? Will any impedance curve at certain frequencies effect the numbers? I figure with these having an fs of 95Hz, the best test tone should be around maybe 110Hz just to stay safe?

I emailed Infinity with the question if the 6010cs & 9613i speakers are truly 4-ohm, or if they are more like 3.8 or 3.2 ohms. I also asked what test tone would be the best to avoid any impedance curves that throw off the readings.


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## ChrisB (Jul 3, 2008)

60ndown said:


> best thing to do is close all the doors and the trunk, seats up (while your in the trunk with the amp) play some music as loud as possible until the trunk lid moves violently, then get your buddy who is outside the car to call you on your cell phone (which you have in the trunk) to tell you when the trunk lid is moving just violently enough.


Dammit, now I have to clean Dr. Pepper off of my LCD!

ETA: Your amplifier output voltage forumula should be the SQRT(Power X ohms). So if you want to see to it that the max your speakers will ever get is 118.25 watts @ 4 ohms, you will need to use a DMM, preferably on a 1,000 Hz signal (for comps) and have a voltage output of 21.74856 per channel! See how simple that is? Naturally, this is just a starting point as you will need to use your ear to blend your highs and sub together.

An even better method would be to use an oscilloscope. I am still thinking about buying an oscilloscope just to have another toy!


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## tspence73 (Oct 14, 2008)

06BLMUSTANGGT said:


> Dammit, now I have to clean Dr. Pepper off of my LCD!
> 
> ETA: Your amplifier output voltage forumula should be the SQRT(Power X ohms). So if you want to see to it that the max your speakers will ever get is 118.25 watts @ 4 ohms, you will need to use a DMM, preferably on a 1,000 Hz signal (for comps) and have a voltage output of 21.74856 per channel! See how simple that is? Naturally, this is just a starting point as you will need to use your ear to blend your highs and sub together.
> 
> An even better method would be to use an oscilloscope. I am still thinking about buying an oscilloscope just to have another toy!


So, my numbers were really close then. Thanks for the confirmation. Now, I'm waiting to hear from Infinity on any impedance differences than the listed 4-ohms. Some speaker manufacturers don't give an exact number but a ballpark. I also hope to know what impedence curves to expect based on the frequency used.

Would a 1,000Hz tone be the best idea? Would it be possible that the lower frequencies would be causing clipping while 1,000Hz wouldn't? Just curious. Or is clipping universal accross the frequency range at the same output voltage?


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## tspence73 (Oct 14, 2008)

Interesting find,

I wish searching for a how-to video on the DMM gain setting. I found this:
http://www.youtube.com/watch?v=SmkWY1e68P8

This video is too short to know for sure, but the final premise he was getting at was not to set gains by a multimeter. Any comments on this one?


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## ChrisB (Jul 3, 2008)

A dmm is just a starting point for your gains. You still need to rely on your ear for the final tuning as well as some common sense. I really want an oscilloscope now!

OTOH, some amps are under rated, some are over rated, and when will you ever play a test tone at 3/4 volume to drive your amp into clipping? I am just trying to point out that there are many other external factors that you need to take into consideration in addition to just trying to use a DMM to set your gains!


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## tspence73 (Oct 14, 2008)

06BLMUSTANGGT said:


> A dmm is just a starting point for your gains. You still need to rely on your ear for the final tuning as well as some common sense. I really want an oscilloscope now!
> 
> OTOH, some amps are under rated, some are over rated, and when will you ever play a test tone at 3/4 volume to drive your amp into clipping? I am just trying to point out that there are many other external factors that you need to take into consideration in addition to just trying to use a DMM to set your gains!


I wonder if there is a place locally that can run an o-scope on a device for a fee to tell you at what point it clips. That would be cool.


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## Jimi77 (Jul 4, 2005)

tspence73 said:


> I wonder if there is a place locally that can run an o-scope on a device for a fee to tell you at what point it clips. That would be cool.



Much like a DMM, anO-scope is a luxary. Your ear will suffice.


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## ChrisB (Jul 3, 2008)

Jimi77 said:


> Much like a DMM, anO-scope is a luxary. Your ear will suffice.


Yeah, but I want an O-scope just to say that I have one


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## 14642 (May 19, 2008)

I just got an email from one of our Customer Service reps about this--must be the email form Infinity you're waiting for. 

First: You should disconnect the speaker from the amplifier when you do this. Amplifiers are constant voltage sources, and there's no reason to subject the speaker to 15 minutes of sine waves to set the gains. 

Second: Input sensitivity controls are intended to be used to maximize the signal to noise ratio of the system--basically, to match the input sensitivity of the amplifier to the output level of the radio. 

Third: Speakers aren't resistors and they have an impedance "curve". The impedance will be high at the speaker's resonance and will be at it's lowest point below that frequency and above that frequency. The inductance of the voice coil causes a rise in the impedance at high frequencies, but a 2- or 3-way system that includes passive crossovers will have additional impedance peaks at the resonance frequencies of the additional speakers. Unsing the nominal impedance is sufficient. The actual impedance of a 4-ohm speaker varies between 3-or-so-ohms and as much as 50 or60, depending on the Q of the woofer. The difference between 120 watts and 140 watts is less than 1dB--doesn't matter.

Fourth: Setting your amplifier gains so that the most power you can ever get from your amplifier is the speaker's RMS power will limit the headroom available forpeaks in the music. Depending on the recording and the amount of dynamic range compression used by the engineer, those peaks can be require as much as 16x the average power of the music. Your amp isn't going to make 16x its rated power. In fact, it isn't going to make 2x its rated power, but why add some artifical limit?

Fifth: Some dynamic range compression provided by the amplifier clipping is useful. cars are noisy and recordings vary greatly from disc to disc. Good recordings that include very little dynamic range compression won't sound very loud, but they will sound "punchy". Recordings that include lots of dynamic range compression will sound loud, but the impact of music peaks may sound "mushy" or simply won't sound much like peaks. For an example of this, compare any track on Van Morrison's Too Long in Exile to any track on Green Day's American Idiot. 

Sixth: While using a DMM is better than setting controls by ear, the best way is with an oscilloscope. 

Seventh: Speakers can handle MUCH more power during instantaneous peaks than they can continuously. There's no need to limit the peaks, when your amp will, most of the time, be delivering far less than its RMS.

So, what should you do? IF you don't have an O-scope and don't want to buy one, you'll have to assume that the head unit doesn't clip. This is a pretty safe bet. Instead of using a sine wave at 0dB, use one recorded at -10dB. Set the amplifier so its output voltage is at a maximum (your formula is correct, thanks to the associative property of multiplication), but use the maximum RMS rating for your calculation and assume 4 ohms. This method will give you 10dB of "gain overlap", which you'll find that you like, compared to setting your system so that it will never clip. Humans have a difficult time hearing distortion on transients before it approaches about 20%, so don't worry about a little clipping. 

Set your system this way and just turn the volume down if the sound is distorted. You'll find that you may have to do this on some modern recordings, but if you have lots of well recorded music, you'll appreciate the additional gain, especially when the car is running and there's plenty of ambient noise.


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## 14642 (May 19, 2008)

Oh, and if you really want a scope on the cheap, go to a military surplus store.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> I just got an email from one of our Customer Service reps about this--must be the email form Infinity you're waiting for.
> 
> First: You should disconnect the speaker from the amplifier when you do this. Amplifiers are constant voltage sources, and there's no reason to subject the speaker to 15 minutes of sine waves to set the gains.
> 
> ...


Based on the DMM method of setting the amp, some of what you've said doesn't make total sense:

First: When using a highpass of like 110Hz at 18db/octave, the 6010cs comps can take 120-140 RMS watts? (Remember, my amp puts out 175-watts RMS to each channel.) I just want to be sure the 6010cs can take that. I was trying to play it safe by going to just a tad more than I needed with 118-watts RMS. Anymore wattage would arguably be barely heard.

Second: Also, without some kind of resistance on the amp (ie connected speakers), how will I know what voltage to set it at with the DMM? 

Third: You say the speaker ohm load will vary based on the frequency that the speaker is playing. I figured that. We come back to my original question, Could you let me know what the best frequency tone (to get the best ohm resistance) to set my amp's speaker output voltage with? I figured it would be a lower frequency to simulate the lowest ohm-load (3.x ohms) to avoid amp clipping and the speakers getting too much wattage. 

I don't mind following your directions but I want to do the DMM procedure correctly and get the best results. I just want to be clear on how I should set the voltage on the DMM without a resistance load on the amp?


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## 14642 (May 19, 2008)

As I wrote, the amplifier is a constant voltage source. Of course, when it clips hard, the rails will sag and it will produce less voltage, but for the purposes of gain setting, there's no need to have the speaker connected. It puts out the same voltage at every frequency (unless there's an electronic crossover or EQ filter somewhere). The amount of power provided depends on the speaker's impedance. 

What I'm trying to tell you is that the volume control is the thing you use to prevent your speakers from being destroyed and significant distortion will be the signal to your brain that should cause you to turn that control down. The input sensitivity control on the amp is designed to match it to the output of the head unit. Ideally, amplifiers would have an input sensitivity control AND a gain control. 

The DMM method is an imprecise way to make this setting without an O-Scope using the amplifier's maximum RMS voltage as an indication of where clipping probably begins.


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## ChrisB (Jul 3, 2008)

tspence73 said:


> I don't mind following your directions but I want to do the DMM procedure correctly and get the best results. I just want to be clear on how I should set the voltage on the DMM without a resistance load on the amp?


Here in lies the hard question, with or without the speakers connected? I use the DMM method without the speakers connected just for the mere fact that I don't want to mess up my speakers. Also, most sets of instructions say to do it with the speakers disconnected from the amp, all signal processing disabled (bass/treble flat, loudness off, crossovers disabled, etc.), and you ramp up the volume to 75% of the total. I used a 50Hz test tone @ 0 db for the subwoofers and a 1,000 Hz test tone @ 0 DB for the components. I downloaded the test tones off the web (from here) and used Audacity to make them 20 minutes long (copy/paste). Rather than burning to CD, I copied the test tones to my IPOD in Apple Lossless format since that is the source I use for 99% of my recorded material.

Using the DMM method, I normally find myself having to lower the subwoofer whereas when I tune strictly by ear, I find myself not giving the subwoofer enough gain and having my mids/highs close to right from the get go.


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## 14642 (May 19, 2008)

Mid/high amp should be adjusted for best signal to noise ratio and the bass amp adjusted so it sounds good.


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## tspence73 (Oct 14, 2008)

Come on people, numbers, numbers!

If I have no speakers connected, what ohm load number should I use?

21.5v x (21.5v/***OHMS***) = y

I need the ohm load to plug into that so I can have a number to set the DMM to. The whole point of having speakers connected is to have an ohms load number to plug into that math problem.


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## falkenbd (Aug 16, 2008)

tspence73 said:


> Yeah, I've read that site a long time ago. I haven't had an amp more powerful on it's RMS than my speakers before, so I'm just seeking some advice, just in case. Aren't DMMs sometimes inaccurate? They don't detect clipping, right? Not that it should matter. This amp should put out more clean power than my speakers can handle.


Maybe you should reread that site, you could find these answers there without having to ask on the forum.

If you stay under rated power, and your deck isn't clipping - your amplifier shouldn't be clipping.

The only way to detect clipping would be to set your gains with an o-scope.

Your speakers should be able to handle more than rated power assuming you don't send them a clipped signal. Remember music is not going to be at 0db like a test tone would be.


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## 14642 (May 19, 2008)

The point, as I've tried to explain, is that since you don't have a scope, you can't determine precisely at what point the amplifier will clip and you've chosen the next best thing--determining the sensitivity setting based on the manufacturer's output power rating. 

Amplifiers make a certain amount of maximum voltage and provide current to the load according to its impedance. The voltage doesn't change no matter the load. To find the maximum output voltage, you can use any rating at its rated impedance. If your amp is rated to deliver 175 watts at 4 ohms, then use those numbers in your formula. 

The formula you want is SQRT(175*4), which is 26.45V

If you decide that you really want to limit the output of your amplifier to your speaker's RMS rating, which is only necessary if you're a hammerhead or if you can't exercise some restraint with the volume control, then just substitute the power you want for the 175 in the formula. If the speakers you're going to use have a different nominal impedance rating, substitute it also. The nominal impedance rating is close enough for what you're trying to do and your method.


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## chad (Jun 30, 2005)

An amplifier that delivers X voltage into an impedance at clipping will generally deliver less voltage to a lesser impedance before clip, not too much but indeed less. Also keep in mind that an amplifier will clip at a higher voltage playing music than with a sine wave when under load, the sine wave has a VERY HIGH duty cycle thus sags the power supply, Dynamic power can be a wonderful thing


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> The point, as I've tried to explain, is that since you don't have a scope, you can't determine precisely at what point the amplifier will clip and you've chosen the next best thing--determining the sensitivity setting based on the manufacturer's output power rating.
> 
> Amplifiers make a certain amount of maximum voltage and provide current to the load according to its impedance. The voltage doesn't change no matter the load. To find the maximum output voltage, you can use any rating at its rated impedance. If your amp is rated to deliver 175 watts at 4 ohms, then use those numbers in your formula.
> 
> ...


Okay, I need this more basic. Easy instructions. Not so much talky talk. 

You're saying that I should use 4-ohms then with no speaker load connected? SQRT(175-watts*4-ohms?), which is 26.45V. From everything I've read, this will not be accurate on the DMM if I don't have a load connected to the amp. Is this info wrong? Won't the voltage output on the DMM be wildly different without a load on the amp?

Is 4-ohms the appropriate number to put there if there is no load on the speaker output during the test tone?

I'm trying to go on the best info I've read and this seems wrong to me.


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## tspence73 (Oct 14, 2008)

Okay,

After re-reading a few times I think I may understand. You're saying that I can have no load on the amp and run the 0db tone a any frequency and I don't need a speaker load connected. Just set the amp to 26.45V to get the rated output of 175x4 without speakers?

This seems to be if I'm setting it for 175-watts. If I want it lower, you say to substitute the lower wattage. But without a 4-ohm load on the amp, how can that number be right? Is the amp already setting itself to a 4-ohm load without any speakers connected? I'm confused again.


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## 14642 (May 19, 2008)

Because the amplifier makes the same voltage with and without a speaker connected (or close enough for what you're doing). Chad is right in the absolute sense, but you keep asking for this to be dumbed down further and further.

Amp makes volts according to its design. Amp makes current according to the load. You're measuring voltage. Load doesn't matter. Ohms don't matter. 

1. disconnect speakers.
2. insert disc
3. turn up volume all the way (or 3/4) if you wish
4. set meter for AC volts
5. Attach meter to output of amp
6. turn sensitivity knob until you get 26.45V
7. come back to computer.
8. Log on to the forum
9. type a post that says "thank you."


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> Because the amplifier makes the same voltage with and without a speaker connected (or close enough for what you're doing). Chad is right in the absolute sense, but you keep asking for this to be dumbed down further and further.
> 
> Amp makes volts according to its design. Amp makes current according to the load. You're measuring voltage. Load doesn't matter. Ohms don't matter.
> 
> ...


Okay. Cool. I'll do this. Just to qualify one more thing. With the amp running at 175-watts RMS, a 110Hz highpass @ 18db/octave, will the 6010cs comps be okay? Is that too much power for them?


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## 14642 (May 19, 2008)

They'll be fine.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> They'll be fine.


Wow. Okay. I imagine I'll probably be lowering that down if the sub isn't loud enough after I apply my EQ adjustments.


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## CGG318 (Apr 9, 2007)

A couple of things.

1. If your head unit has 2v preouts, you should set your amp to the 100mV-2V setting.
2. Make sure the the test tone you use is within the frequency range of your DMM. For example, my DMM is only accurate between 40hz and 400hz.


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## tspence73 (Oct 14, 2008)

CGG318 said:


> A couple of things.
> 
> 1. If your head unit has 2v preouts, you should set your amp to the 100mV-2V setting.
> 2. Make sure the the test tone you use is within the frequency range of your DMM. For example, my DMM is only accurate between 40hz and 400hz.


The DMM measures volts, not frequencies. At least in this test it should. The test tone frequency shouldn't make any difference.


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## CGG318 (Apr 9, 2007)

tspence73 said:


> The DMM measures volts, not frequencies. At least in this test it should. The test tone frequency shouldn't make any difference.


Do you have a DMM that accurately measures all frequencies?


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## tspence73 (Oct 14, 2008)

Okay,

Now on to my subwoofer amp. Setting the classic A7HC sub amp.

Again, as usual, I'm confused when trying to apply the same principles of DMM setting, for this amp.

This amp is rated like this:
500-watts RMS @ 4-ohms
800-watts RMS @ 2-ohms.
1400-watts RMS @ 1-ohm

BUT oops! According to the rules I was given earlier, "the amp will output the voltage it was designed for".

Well, with these ratings, the voltage won't match according to the specs. For instance, look at the following:

SQRT of (500-watts x 4-ohms) = 44.7
SQRT of (800-watts x 2-ohms) = 40
SQRT of (1400-watts x 1-ohm) = 37.4

So.....which voltage setting do I use with no load connected? Do I set it according to what ohm load I intend to use? Like, if I intend a 2-ohm load, do I set it to 40-volts? But, earlier I was told to set the amp to the voltage output it was designed for. Well, which is it? 

It's these kinds of questions that I think so called "dummies" like me need explained for them. Am I slow? Or am I a smartass?  I don't know. I would like to think that sometimes I don't catch on right away, but I can ask good questions so that I can understand better. Hopefully this thread can be an amp setting tutorial for others like me. So, if you're reading this fellow head scratchers. You're not alone. I'll look dumb for you, so you don't have to.


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## CGG318 (Apr 9, 2007)

tspence73 said:


> Okay,
> 
> Now on to my subwoofer amp. Setting the classic A7HC sub amp.
> 
> ...





Andy Wehmeyer said:


> The point, as I've tried to explain, is that since you don't have a scope, you can't determine precisely at what point the amplifier will clip and you've chosen the next best thing--determining the sensitivity setting based on the manufacturer's output power rating.
> 
> Amplifiers make a certain amount of maximum voltage and provide current to the load according to its impedance. The voltage doesn't change no matter the load. To find the maximum output voltage, you can use any rating at its rated impedance. If your amp is rated to deliver 175 watts at 4 ohms, then use those numbers in your formula.
> 
> ...





chad said:


> *An amplifier that delivers X voltage into an impedance at clipping will generally deliver less voltage to a lesser impedance before clip, not too much but indeed less*. Also keep in mind that an amplifier will clip at a higher voltage playing music than with a sine wave when under load, the sine wave has a VERY HIGH duty cycle thus sags the power supply, Dynamic power can be a wonderful thing


Ritalin might help


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## t3sn4f2 (Jan 3, 2007)

tspence73 said:


> The DMM measures volts, not frequencies. At least in this test it should. The test tone frequency shouldn't make any difference.


You are measuring AC voltage, AC voltage has frequency. Your home runs at around 120 volts AC at 60Hz. A DMM has a specified frequency range that the AC voltage being measured has to fall into in order for the reading to be accurate. Don't know how off it could be or how much it matters in your situation if you are not in that range.


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## tspence73 (Oct 14, 2008)

> An amplifier that delivers X voltage into an impedance at clipping will generally deliver less voltage to a lesser impedance before clip, not too much but indeed less


Can't people just answer the question without making riddles out of it? As I asked above:



> SQRT of (500-watts x 4-ohms) = 44.7
> SQRT of (800-watts x 2-ohms) = 40
> SQRT of (1400-watts x 1-ohm) = 37.4
> 
> So.....which voltage setting do I use with no load connected? Do I set it according to what ohm load I intend to use? Like, if I intend a 2-ohm load, do I set it to 40-volts? But, earlier I was told to set the amp to the voltage output it was designed for. Well, which is it?


It's that simple. Answer the question. Do I set the voltage according to what ohm rating I intend to use or what?


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## tspence73 (Oct 14, 2008)

t3sn4f2 said:


> You are measuring AC voltage, AC voltage has frequency. Your home runs at around 120 volts AC at 60Hz. A DMM has a specified range frequency range that the AC voltage being measured has to fall into in order for the reading to be accurate. Don't know how off it could be or how much it matters in your situation if you are not in that range.


Do DMM's come with info on what frequencies they are accurate with? Is there a general range most DMMs can do accurately? I didn't figure there would be an AC voltage frequency limitation on DMMs. But then again, I'm no EE.


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## ChrisB (Jul 3, 2008)

The lower the ohms equals lower resistance which equals lower voltage to achieve a given power output. So to answer your question, you need to set the amp to the given voltage at the given impedance you plan to run it at.


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## t3sn4f2 (Jan 3, 2007)

tspence73 said:


> Do DMM's come with info on what frequencies they are accurate with? Is there a general range most DMMs can do accurately? I didn't figure there would be an AC voltage frequency limitation on DMMs. But then again, I'm no EE.


Use 40 volts for 2 ohms.

Check the manual or go with a 60Hz tone. Hopefully your amp doesn't have some unpublished built in bass EQ that will throw off your settings.


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## t3sn4f2 (Jan 3, 2007)

06BLMUSTANGGT said:


> The lower the ohms equals lower resistance which equals lower voltage to achieve a given power output. So to answer your question, you need to set the amp to the given voltage at the given impedance you plan to run it at.


Voltage is more like limited by the inability to provide the current needed. If you take a great quality 2 ohms stable amp it will have _practically_ the same voltage output at 2 ohms as it does at 4 ohms, but twice the current and thus twice the power (wattage). Same way it does from 8 to 4 ohms. 

http://www.zedaudiocorp.com/Products/Draconia-Spec.htm


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## tspence73 (Oct 14, 2008)

t3sn4f2 said:


> Use 40 volts for 2 ohms.
> 
> Check the manual or go with a 60Hz tone. Hopefully your amp doesn't have some unpublished built in bass EQ that will throw off your settings.


At 60Hz I don't think there is a boost because at 60Hz there is a huge drop in loudness in my car. So, it should work.


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## tspence73 (Oct 14, 2008)

t3sn4f2 said:


> Voltage is more like limited by the inability to provide the current needed. If you take a great quality 2 ohms stable amp it will have _practically_ the same voltage output at 2 ohms as it does at 4 ohms, but twice the current and thus twice the power (wattage). Same way it does from 8 to 4 ohms.
> 
> http://www.zedaudiocorp.com/Products/Draconia-Spec.htm


That is a rather lower wattage amp, so maybe it could be easier to provide double the wattage at half the ohms. What about an example of a powerful class-d sub amp? Are there any that meet the example you're giving?


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## t3sn4f2 (Jan 3, 2007)

tspence73 said:


> That is a rather lower wattage amp, so maybe it could be easier to provide double the wattage at half the ohms. What about an example of a powerful class-d sub amp? Are there any that meet the example you're giving?


http://www.zedaudiocorp.com/Products/Minilith-Spec.htm
http://zapco.com/prod/comp_prods/c2k90Frame.htm


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## t3sn4f2 (Jan 3, 2007)

Its not really something to consider if you know what minimum impedance and power you will be needing.


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## tspence73 (Oct 14, 2008)

t3sn4f2 said:


> http://www.zedaudiocorp.com/Products/Minilith-Spec.htm
> http://zapco.com/prod/comp_prods/c2k90Frame.htm


Those are real close to meeting the standard but even they aren't perfect at holding consistent voltage all the way to the lowest ohm rating.


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## capnxtreme (Feb 5, 2008)

tspence73 said:


> Can't people just answer the question without making riddles out of it? As I asked above:
> 
> 
> 
> It's that simple. Answer the question. Do I set the voltage according to what ohm rating I intend to use or what?


Hey dude, you know how you posted that thread saying you appreciate our help? Don't ****ing talk to us like that if you want any more, ok? You are making a fool out of yourself, and you would probably get punched in the face if you were this annoying in real life.

Your dumb ass is everything that's wrong with the new era of the forums. Every single question you ask is a couple clicks and (at worst) a couple thoughts away from an answer. You refuse to think critically, despite your diarrhea of questions that have already been answered (TO YOUR OWN PREVIOUS QUESTIONS, EVEN).

I would bet my life that you have/had to cheat to pass in school.



> It's these kinds of questions that I think so called "dummies" like me need explained for them. Am I slow? Or am I a smartass? I don't know. I would like to think that sometimes I don't catch on right away, but I can ask good questions so that I can understand better. Hopefully this thread can be an amp setting tutorial for others like me. So, if you're reading this fellow head scratchers. You're not alone. I'll look dumb for you, so you don't have to.


Definitely both. No amount of groveling will make your whines for spoon-feeding cool.

Thank you for VBA, though.


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## Lothar34 (Oct 6, 2006)

My head hurts after reading this thread


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## 14642 (May 19, 2008)

The reason the voltages aren't the same at the different impedances is because the manufacturer has ROUNDED the power ratings because a rating like 800 [email protected] ohms, 1257.6 watts @ 2 ohms and 1593.875 @ 1ohm would be too confusing for most people. 

As I've written before, SINCE YOU DON'T HAVE AN O-SCOPE, THE BEST YOU CAN DO IS TO RELY ON THE SPECS TO APPROXIMATE THE POINT OF CLIPPING. As I've also said before, the gain setting procedure is designed to maximize signal to noise performance. The only amplifiers that contribute audible noise (high frequencies) are amplifiers that drive high frequency speakers. It's sufficient to set the sub amp's gain to a level that provides a proper balance with the rest of the speakers once the high frequency amp's sensitivity settings have been made. 

I'm not making a riddle out of any of this. I'm simply trying to help you. Occasionally, in order to help you with the procedure you're trying to understand and perform, it's necessary to explain things a little further. You can accept the help or reject it, but berating your helpers because you don't like the answers isn't cool. It's kinda like giving a kid a quarter and having him ask, "Don't you have a shiny one?"


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## tspence73 (Oct 14, 2008)

capnxtreme said:


> Hey dude, you know how you posted that thread saying your appreciate our help? Don't ****ing talk to us like that if you want any more, ok? You are making a fool out of yourself, and you would probably get punched in the face if you were this annoying in real life.
> 
> Your dumb ass is everything that's wrong with the new era of the forums. Every single question you ask is a couple clicks and (at worst) a couple thoughts away from an answer. You refuse to think critically, despite your diarrhea of questions that have already been answered (TO YOUR OWN PREVIOUS QUESTIONS, EVEN).
> 
> ...


What you wrote was insulting and frankly I could care less if you answered anything. Take your arrogant and selfish attitude to another thread then.

You know, I'm no expert and I am asking pertinent questions and not making assumptions and trying to get CLEAR answers in an easy to understand way. The way many people have tried to explain some things in here have gone around a direct answer and causes someone to make assumptions. I'm not making assumptions with equipment I have to work hard to buy.

I think in school you were the guy who got the 'C' grade because he heard half the lecture and made assumptions. Remember, assumptions are RISKS, NOT critical thinking. I haven't asked for any answer in any other way than to illicit a direct response. If someone asks me to clarify an answer for them, I don't get angry at them and accuse them of being stupid. The best way is to try and change the way you're saying it so that the person you are talking to understands the concept and/or instructions.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> The reason the voltages aren't the same at the different impedances is because the manufacturer has ROUNDED the power ratings because a rating like 800 [email protected] ohms, 1257.6 watts @ 2 ohms and 1593.875 @ 1ohm would be too confusing for most people.
> 
> As I've written before, SINCE YOU DON'T HAVE AN O-SCOPE, THE BEST YOU CAN DO IS TO RELY ON THE SPECS TO APPROXIMATE THE POINT OF CLIPPING. As I've also said before, the gain setting procedure is designed to maximize signal to noise performance. The only amplifiers that contribute audible noise (high frequencies) are amplifiers that drive high frequency speakers. It's sufficient to set the sub amp's gain to a level that provides a proper balance with the rest of the speakers once the high frequency amp's sensitivity settings have been made.
> 
> I'm not making a riddle out of any of this. I'm simply trying to help you. Occasionally, in order to help you with the procedure you're trying to understand and perform, it's necessary to explain things a little further. You can accept the help or reject it, but berating your helpers because you don't like the answers isn't cool. It's kinda like giving a kid a quarter and having him ask, "Don't you have a shiny one?"


I'm not berating anyone. I hope you don't think I am. I just want to understand what I'm doing so that I don't ruin something. And I really have learned more than I did before by trying to dig for better answers. I appreciate your help. I will go back through and read this thread over again to see if I missed something and try harder to understand.

I know I am intelligent. It sometimes takes me la few repeats or a different way of saying something but when I understand something I don't forget it and can pass tests on that information without any problems. I have adult ADD, so I'm not always going to be a perfect student on certain things.


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## 14642 (May 19, 2008)

The most important thing to understand from this whole thread is that input sensitivity controls are designed to match the input of the amp to the output of the previous component in the signal chain to maximize the signal to noise ratio. 

I don't know why there seems to be some new idea that one should use the sensitivity setting to somehow govern the output power of the amplifier, but it's unnecessary and just gets you less than you've paid for. 

Finally, once you've set the sensitivity of the high frequency amp, set the low frequency amp so it sounds good. Ideally, components would have an input sensitivity control and an output level control so the signal to noise could be maximized throught the signal chain, but most car audio components don't.


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## benny (Apr 7, 2008)

Andy, you have the patience of a saint.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> The most important thing to understand from this whole thread is that input sensitivity controls are designed to match the input of the amp to the output of the previous component in the signal chain to maximize the signal to noise ratio.
> 
> I don't know why there seems to be some new idea that one should use the sensitivity setting to somehow govern the output power of the amplifier, but it's unnecessary and just gets you less than you've paid for.
> 
> Finally, once you've set the sensitivity of the high frequency amp, set the low frequency amp so it sounds good. Ideally, components would have an input sensitivity control and an output level control so the signal to noise could be maximized throught the signal chain, but most car audio components don't.


I'm not worried so much about signal to noise as I am about alternator whine and/or electrical noise/interference. The amp I'm replacing has some minor issues with electrical noise and tiny bit of alternator whine. I'll see what happens with the new amp. Some amps are more prone to these things than others I think.

I think the practice of using the DMM to set the amp is to get as much clean output as possible and to limit clipping and distortion. All too often people treat the sensitivity knob as a volume control.


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## 14642 (May 19, 2008)

tspence73 said:


> I'm not worried so much about signal to noise as I am about alternator whine and/or electrical noise/interference. The amp I'm replacing has some minor issues with electrical noise and tiny bit of alternator whine. I'll see what happens with the new amp. Some amps are more prone to these things than others I think.
> 
> I think the practice of using the DMM to set the amp is to get as much clean output as possible and to limit clipping and distortion. All too often people treat the sensitivity knob as a volume control.


 
Yes, some amps are more prone to noise than others. There a common misconception that simply grounding everything to the same spot eliminates loops, but that's also oversimplified. Ideally, we'd have balanced outputs and diffrential inputs, but the RCA-type output that everyone thinks is such high quality causes loops, unbalances differential inputs and provides a great path for noise to enter the system. 

You're treating the sensitivity knob as a volume control--or as a limit on the radio's volume control. The DMM practice by which one limits the "distortion" of the amp and limits it's output power to the RMS power handling rating of the speaker is ridiculous and unnecessary.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> You're treating the sensitivity knob as a volume control--or as a limit on the radio's volume control. The DMM practice by which one limits the "distortion" of the amp and limits it's output power to the RMS power handling rating of the speaker is ridiculous and unnecessary.


I would suppose it would depend on how audible any distortion that is produced would be to the listener. If setting it for using only linear power output and preventing clipping sounds better to the listener then it's not a bad thing. You mentioned before that a certain amount of clipping/distortion won't be audible or detectable to the listener. There are many audio enthusiasts who I know would argue with that (whether right or wrong). I for one want to go on what is scientifically valid and not waste time or money on fixing problems that don't exist or doing a tweek that will have no improvement.


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## 14642 (May 19, 2008)

Then do this simple experiment:

Set your gains your way. Listen. Set your gains my way using a tone recorded at -10dB. Listen. Listen to several different recordings each way and drive the car. 


Then you can go argue with the audio enthusiasts.


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## chad (Jun 30, 2005)

Andy Wehmeyer said:


> Yes, some amps are more prone to noise than others. There a common misconception that simply grounding everything to the same spot eliminates loops, but that's also oversimplified. Ideally, we'd have balanced outputs and diffrential inputs, but the RCA-type output that everyone thinks is such high quality causes loops, unbalances differential inputs and provides a great path for noise to enter the system.


It's about time for my quarterly posting of "My Rant" on standardization  which also includes the sensitivity labeled in Decibels, published or standardized gain figures, and other tidbits  Just like pro audio.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> Then do this simple experiment:
> 
> Set your gains your way. Listen. Set your gains my way using a tone recorded at -10dB. Listen. Listen to several different recordings each way and drive the car.
> 
> ...


How should the component woofer respond to 175-watts RMS with an 18db/octave crossover? At loud volume there is still going to be some bass frequencies pushing the cone at around 70Hz to 100Hz. I'm not so worried about 100Hz. But it's the deeper frequencies it will be pushing which make it through the filter that concern me. I've thought about buying a 6db/octave RCA-line filter at 100Hz. Would that give me a 24db/octave slope to help take the bass off? My sub amp has a 24db/octave filter. Will that 6db/octave difference effect the sound in any significant way?


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## Oliver (Jun 25, 2007)

Re: Amp sensitivity setting question.

They're as good as most care to get

Quote:
Originally Posted by Andy Wehmeyer 
Yes, some amps are more prone to noise than others. There a common misconception that simply grounding everything to the same spot eliminates loops, but that's also oversimplified. Ideally, we'd have balanced outputs and differential inputs, but the RCA-type output that everyone thinks is such high quality causes loops, unbalances differential inputs and provides a great path for noise to enter the system. 


It's about time for my quarterly posting of "My Rant" on standardization which also includes the sensitivity labeled in Decibels, published or standardized gain figures, and other tidbits Just like pro audio. 

No one will steer our hero from his path [ soon all of us will have Infinity speakers


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## tspence73 (Oct 14, 2008)

chad said:


> It's about time for my quarterly posting of "My Rant" on standardization  which also includes the sensitivity labeled in Decibels, published or standardized gain figures, and other tidbits  Just like pro audio.


YEAH!! I really like standardization too. I'm tired of looking at equipment and trying to figure out if the specs are real or inflated. 

Like with my Infinity Refs. 92db Sensitivity but that's at 2.83v, not at a true 1w/1m @ 4 ohms but rather what it would be at 8-ohms. My comp's true sensitivity is really 89db @ 4-ohms.


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## Oliver (Jun 25, 2007)

tspence73 said:


> How should the component woofer respond to 175-watts RMS with an 18db/octave crossover? At loud volume there is still going to be some bass frequencies pushing the cone at around 70Hz to 100Hz. I'm not so worried about 100Hz. But it's the deeper frequencies it will be pushing which make it through the filter that concern me. I've thought about buying a 6db/octave RCA-line filter at 100Hz. Would that give me a 24db/octave slope to help take the bass off? My sub amp has a 24db/octave filter. Will that 6db/octave difference effect the sound in any significant way?


It affects everyone else in the world like this

Just for reference:

-3dB = 50% reduction, or a factor of 2
-6dB = 75% reduction, or a factor of 4
-12dB = 93.75% reduction, or a factor 16
-18dB = 98.4375% reduction, or a factor 64
-24dB = 99.609375% reduction, or a factor 256


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## chad (Jun 30, 2005)

tspence73 said:


> How should the component woofer respond to 175-watts RMS with an 18db/octave crossover? At loud volume there is still going to be some bass frequencies pushing the cone at around 70Hz to 100Hz. I'm not so worried about 100Hz. But it's the deeper frequencies it will be pushing which make it through the filter that concern me. I've thought about buying a 6db/octave RCA-line filter at 100Hz. Would that give me a 24db/octave slope to help take the bass off? My sub amp has a 24db/octave filter. Will that 6db/octave difference effect the sound in any significant way?


I personally feel that you are just WAY over thinking this, you are afraid of something that does not exist, complete and immediate failure, and that just generally does not happen. If the speaker does not like it you will know, ignore it and it will die, heed warning and you will be just fine. It's possible to engineer a sound system, very possible but unfortunately in a car the bets are more and more off 

You are certainly a planner, that's VERY obvious, but sometimes you cannot tell what the results will be till after you get the gear in and twist a few knobs.

Chad


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## Jimi77 (Jul 4, 2005)

Gotta agree with alot of what's been said. 

You don't need a DMM to set your gains. You don't even need a test tone.

Your speakers don't implode the second they're overpowered. As a matter of fact, you'll probably experience significant distortion before reaching max RMS. You'll hear distortion if either the spearker or the amp's being pushed beyond it's abilities. 

18db @ 100hz should be fine; there is no need for additional filters.


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## qstarin (Mar 25, 2009)

Andy Wehmeyer said:


> As I wrote, the amplifier is a constant voltage source. Of course, when it clips hard, the rails will sag and it will produce less voltage, but for the purposes of gain setting, there's no need to have the speaker connected. It puts out the same voltage at every frequency (unless there's an electronic crossover or EQ filter somewhere). The amount of power provided depends on the speaker's impedance.
> 
> What I'm trying to tell you is that the volume control is the thing you use to prevent your speakers from being destroyed and significant distortion will be the signal to your brain that should cause you to turn that control down. The input sensitivity control on the amp is designed to match it to the output of the head unit. Ideally, amplifiers would have an input sensitivity control AND a gain control.
> 
> The DMM method is an imprecise way to make this setting without an O-Scope using the amplifier's maximum RMS voltage as an indication of where clipping probably begins.





Andy Wehmeyer said:


> Amplifiers make a certain amount of maximum voltage and provide current to the load according to its impedance. The voltage doesn't change no matter the load. To find the maximum output voltage, you can use any rating at its rated impedance. If your amp is rated to deliver 175 watts at 4 ohms, then use those numbers in your formula.




I get it now. I really do. Everything I had read up to this point seemed to imply that a load was necessary. Constant voltage device. I understand that. Finally, I can stop blowing tweeters trying to set gains with tones.

I even understand the simplifications involved and the direction of the trends if we start to un-simplify it.

Thank you. 

I don't think any of my amps are sensitive enough to make rated power from a -10dB source at anything less than about 97%+ HU volume. I would hope the HU wouldn't clip there (especially with a flat eq), but I'll definitely need a scope to determine that.


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## qstarin (Mar 25, 2009)

Here's a thought.

My T1500-1bd is rated:

500w @ 4ohm (44.7v)
1000w @ 2 ohm (44.7v)
1500w @ 1ohm (38.7v)


I'm kind of wondering what that says about the amp.

It seems it can handle down to 2 ohms just fine, but when going to 1 ohm it maybe suggests the amp is being severely stressed and can't maintain the same voltage it can at a higher ohm load.

Interestingly, the efficiency specs were something around 85% at 4 & 2 ohm, but under 70% for 1 ohm.


Kinda makes more sense why 1 ohm with this amp is to a degree failboat.


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## ChrisB (Jul 3, 2008)

Welcome back old thread. 

Anyhow, amplifiers generally don't magically, mythically produce more power at lower ohm loads. In order to do this, they generally draw more current in amperage, produce more heat, and produce more distortion as a side product. Also, their efficiency goes down 

Oh yeah, my point, the voltage you are referencing is only one part of the equation. Remember, no matter what, you can not violate Ohm's Law. Volts X Amps = Watts! At that lower ohm load you are no longer in the "high voltage" area but more into the "high current" area where your amp will be outputting more amperage at the lower voltage to produce 1,500 watts.


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## shadowfactory (Oct 20, 2008)

06BLMUSTANGGT said:


> Welcome back old thread.
> 
> Anyhow, amplifiers generally don't magically, mythically produce more power at lower ohm loads. In order to do this, they generally draw more current in amperage, produce more heat, and produce more distortion as a side product. Also, their efficiency goes down
> 
> Oh yeah, my point, the voltage you are referencing is only one part of the equation. Remember, no matter what, you can not violate Ohm's Law. Volts X Amps = Watts! At that lower ohm load you are no longer in the "high voltage" area but more into the "high current" area where your amp will be outputting more amperage at the lower voltage to produce 1,500 watts.


But tspence has shown us that 1 ohm loads are the bomb, right?!? :laugh::laugh:

"TWO RE SE 12's @ 1-ohm"
The choice of true champions.


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