20w rms amp with 150w rms sub

[Seth=L]

Don't feel like that. It wasn't directed at anyone in particular.

There is so much misinformation about power, speakers, and clipping it will make your head spin.

Under normal circumstances, with the rms output of the amplifier matching the rms input on the speaker, clipping is definitely frowned upon, big time. It will most certainly lead to failure of some kind at some point.

Clipping in and of itself is not the destructive force, it is the extra power generated along with odd order harmonic information that will push a speaker past it's mechanical limits and/or cook the voice coil.

I am just glad I learned something. I don't feel bad about not being correct, I feel bad because I was kind of being edgy with the OP's question and it was wrong of me to be that way. DARN THE MOB! just kidding.

 

[annunaki]

I have been wrong many times in my life. I always stive to keep learning more and find the truth.

 

[Nomo]

Oh wow, I have never been so wrong (wait, yes I have). Well don't a feel like a big stupid dope?

Sorry zerox61, I was really certain that is was bad for the woofers. We all make mistakes at times.

Ditto,
I can live with being wrong. I've been there before. But I feel crappy about getting testy.
Sorry zero.

 

[zerox61]

hey its ok guys no need to apologize . i wasnt too sure of the right answer anyway. anyway. thanks annunaki for clearing this issue up. u must be pretty damn knowledgeable about this stuff. hehe.

coz it kinda rang in my head. 150watts.. i think of the voice coil is like a resistor. but its load is 40 at peak. which is under its capacity. which to me sounded fine. hope i didnt make any mistake saying that.
and i know clipping sounds horrible. but it turn it down once i hear it clip. just occasionally turn it up to feel the thrill of the bass. when it clips then i turn it down.

oh btw annuaki, about the parrallel connection the guy posted b4. how do i properly connect it so it wont stuff up? i noticed when i took off one of the subs. it sounded more clean bass. i didnt notice this b4. so now im gonna leave the sub disconnected and only have one. bt just asking for info. thanks

and also. i do believe this topic is a perfect topic to go be included into this thread 'myths about subwoofers' :
http://forums.audioholics.com/forums/showthread.php?t=35455
so there wont be another confusion like this again.

soryy just one more thing annunaki. when i had both subs hooked up. one was sealed and one was ported. the ported had a REALLY light cone while the sealed sub was really heavy. only clipping came from the sealed. i didnt not hear any from the ported one. u mentioned something about this on previous posts. but i didnt really understand. thanks

 

[annunaki]

What do you mean by "light or heavy cones"?

Ported and sealed enclosures should not be used together on the same amplifier. When runnng subs in parallel they should be of the same brand, model impedance, and in the same enclosure.

As for parallel connections, if the amplifier is not designed to run a specific load it will have highly increased distortion, overheat very quickly, fail, or all of the above.

I am not sure what you mean by "stuff up" in regard to parallel connections either.

 

[zerox61]

like when i took them out of the enclosures. the sealed one was really thick on the cone. it was kinda like a paper masche on the back side of the cone when u see it. the spider and rubber sourround are thicker and more "heavy" kinda feeling when i push it down. the vented one has a thinner cone, the rubber souuound and spider is easier to push down. hope u understand what i just said.

nomo posted earlier:

__________________
zerox61,
You seem to be hearing only what you want to hear.
If you intend to use those subs for any length of time then stop powering them, especially at high volumes, with that 20 watt amp.
In the very least stop running them in parallel. Without knowing the sensitivity of the subs it's hard to tell how bad of idea you are having, but most here have told you it is a bad idea!

Sorry to come across as rude, but you ain't listening.
__________________

he said something about sensitivity. i got a slight idea what that is. but dont know why that would affect the amp

 

[annunaki]

Do you have two different brands of sub woofer? If they are the same brand are they different models that look similar from the exterior?

Sensitivity gives one an idea of how the system will respond to input power. The higher the sensitivity the less power one needs to hit a desired output level. For instance, if you have a speaker (Tweeter, woofer, crossover, etc.) with an 87db @ 1watt/1meter sensitivity rating and one with a 90db sensitivity rating, the one with the 90db @ 1watt/1meter rating will play +3db louder with the same amount of input power. It will be easier for the amplifier to drive to a certain output level.

Now, sensitivity ratings on individual drivers should not be confused with sensitivity ratings on whole speaker systems. Speaker systems meaning a tweeter and woofer in an enclosure, etc. Sensitivity on individual drivers are not an accurate indicator of which driver will get louder or will play louder. Enclosure and other variables come into play there.

 

[zerox61]

the subs, they r completely different brands.

and i think signal to noise ratio and sensitivity are the same thing??
can u pls look at this link: http://h1.ripway.com/haiiz/IMG_0759.jpg and tell me if its recommended. i kinda like building eletronic things and i think i will be able to handle that one. (4 star difficulty).

THD of 0.002%.. thats pretty darn good? at 100watts tho. is the distortion increasing exponential? or linear? so when i crank it up and uses more power. will the distortion increase exponenially? (my old sound system had 10% thd at 500watts and i didnt really hear any difference when it was nearly max volume coz it was too damn loud.) and my guess is that its exponenial.

im also considering this: http://h1.ripway.com/haiiz/IMG_0743.jpg for my car. the specs look really promising. but will i need a subsonic filter? coz i think the subwoofer im buying wont handle 5 hertz. i would be getting the $159 one only need it to power the subs. i think the head unit can handle the surround speakers with out a extra amp..

subsonic filter is a filter that filters the frequencies that are too low right? to make the subs that cant handle it not get damaged? just asking coz i kinda guessing what it is.

 

[annunaki]

Signal-to-noise ratio and sensitivity are definitely NOT the same thing. Signal-to-noise is the measurment of the signal strength above the ambient noise floor of the component in question. Speakers do not have signal-to-noise ratios, only electronic signal/source components.

Distortion comes in at different rates for different amplifiers. When an amplifier clips it ramps up distortion VERY rapidly.

Infrasonic filters are usually only recommended for ported and bandpass enclosures. If the sub will be sealed it is not necessary.

There are better car amplifiers out there than that, even at those price points. For subwoofers I recommend a class D mono amplifer. They are the most efficient and offer the biggest wattage for your dollar.

 

[yettitheman]

Actually, DC power is something that will kill speakers. When you clip your amplifier or you overdrive your speakers, it creates a DC like sine wave at the speakers and the VC becomes something similar to a stove top element.

This is why you don't want a seriously underpowered amplifier for any speaker.

 

[annunaki]

Actually, DC power is something that will kill speakers. When you clip your amplifier or you overdrive your speakers, it creates a DC like sine wave at the speakers and the VC becomes something similar to a stove top element.

This is why you don't want a seriously underpowered amplifier for any speaker.

Amplifiers do not output DC current even when clipped. This is assumed because of the flat tops and bottoms of the clipped waveform. The square wave is a result of a combination and/or sum of the fundamental frequency and its 2nd, 3rd, and 4th order harmonics. The only way for it to be DC would be to have non-zero average value over long periods of time.

Please see my other posts for reasons why speakers fail. Mechanical failure and Thermal Failure are the only two ways. Both are caused by too much input power.

 

[zerox61]

last week i was also considering a class D for subwoofer but the price is kinda up in the skies. http://www.essentialaudio.com.au/index1.html thats like 330 US$ im guessing.(im still in highschool dont have part time job) the lowest rms rating i could find is 820w rms for class D. btw 820watts at 1 ohm and 400 @ 4 ohms. why do people connect to make it 1 ohm? isit coz u get less resistance and the coils wont be hot? or something to do with the sound output levels? im also wondering what capcitor i need.

1 farrad is prob enough for most amps dont u think so? dont think im going to get a second battery because i think its gonna be a waste of money and time. second battery is only for increasing the time u play ur subwoofer without car ingition on, whereas capacitor is used when there is current drops and spikes that the amp needs power quickly, correct?

 

[zerox61]

Actually, DC power is something that will kill speakers. When you clip your amplifier or you overdrive your speakers, it creates a DC like sine wave at the speakers and the VC becomes something similar to a stove top element.

This is why you don't want a seriously underpowered amplifier for any speaker.

yes dc killing it is true to some point. but other factors also affect it. eg. current. if a sub could handle 500w rms and u apply tiny current. even with the coil not moving (bc its dc current) it wont burn out the coil.

 

[annunaki]

yes dc killing it is true to some point. but other factors also affect it. eg. current. if a sub could handle 500w rms and u apply tiny current. even with the coil not moving (bc its dc current) it wont burn out the coil.

Se my post above regarding DC current.

 

[annunaki]

last week i was also considering a class D for subwoofer but the price is kinda up in the skies. http://www.essentialaudio.com.au/index1.html thats like 330 US$ im guessing.(im still in highschool dont have part time job) the lowest rms rating i could find is 820w rms for class D. btw 820watts at 1 ohm and 400 @ 4 ohms. why do people connect to make it 1 ohm? isit coz u get less resistance and the coils wont be hot? or something to do with the sound output levels? im also wondering what capcitor i need.

1 farrad is prob enough for most amps dont u think so? dont think im going to get a second battery because i think its gonna be a waste of money and time. second battery is only for increasing the time u play ur subwoofer without car ingition on, whereas capacitor is used when there is current drops and spikes that the amp needs power quickly, correct?

The amplifier is stable down to 1 ohm that is where it outputs the most power. Plain and simple. It is done so you can run multiple subs, in parallel, on one amplifier or run a single or more DVC subs.

Capacitors in general tend to be a waste of money. First things that need to be done is to supplement the current factory wiring under the hood. Add another cable from the alternator to the battery. Preferrable 4 ga. or larger. Do the same with the ground from the battery to the chassis (ground at the same point), and the chassis to the engine block. This allows for better current flow though out the entire electrical system and can do more for your system than a single farad capacitor. I would recommend at least 2 farads per 500 watts for it to do anything for the system. Even then the benefits are debatable. Ususally they are not necessary until you get past the 800 watt rms range. An 800 watt rms class D amplifier with 75% efficiency will draw about 85 amperes of current at 12.5 volts (at full rated output).

If your sub is rated at 150 rms, you do not need a real big amplifier. The first thing you should do is purchase matching subs. Then purchase an amplifier to run them.

 

[yettitheman]

Amplifiers do not output DC current even when clipped. This is assumed because of the flat tops and bottoms of the clipped waveform. The square wave is a result of a combination and/or sum of the fundamental frequency and its 2nd, 3rd, and 4th order harmonics. The only way for it to be DC would be to have non-zero average value over long periods of time.

Please see my other posts for reasons why speakers fail. Mechanical failure and Thermal Failure are the only two ways. Both are caused by too much input power.

Sorry, I should have clarified that amps do not (that and I was a bit tired when I wrote it). But we do know a speaker moves as an AC sine wave, and when the speaker fails to move as that, then trouble usually starts.

 

[highfihoney]

Capacitors in general tend to be a waste of money. First things that need to be done is to supplement the current factory wiring under the hood. Add another cable from the alternator to the battery. Preferrable 4 ga. or larger. Do the same with the ground from the battery to the chassis (ground at the same point), and the chassis to the engine block. This allows for better current flow though out the entire electrical system and can do more for your system than a single farad capacitor. I would recommend at least 2 farads per 500 watts for it to do anything for the system. Even then the benefits are debatable. Ususally they are not necessary until you get past the 800 watt rms range. An 800 watt rms class D amplifier with 75% efficiency will draw about 85 amperes of current at 12.5 volts (at full rated output).

What he's telling you is the truth,power supply & ground are the most important factors to powering a car amp,after doing a double ground the best thing to do is to install an alternator that will give the amperage your amps need,i went from running 5 farads of capaticence with a stock alternator to no capacitors with an ambulance alternator,my amps scream now.

 

[zerox61]

yeah, my car is already grounded with extra cables. i duno the gauges of them tho. looks kinda thick. i might re wire them to make double sure it was done properly. also arnt alternators expensive..?

 

[highfihoney]

yeah, my car is already grounded with extra cables. i duno the gauges of them tho. looks kinda thick. i might re wire them to make double sure it was done properly. also arnt alternators expensive..?

Alternators are like anything else,if ya rush right out & buy the first thing you see be prepared to bend over But if you do the homework you can get a high output,depending on the model for less than $150.

I think i paid just a little over $100 (ebay)for a rebuilt 250 amp ambulance alternator for my mustang,been going strong for 2 years now