alpine pdx 8 ohm rating
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=126878
Printed Date: May 17, 2024 at 8:33 PM
Topic: alpine pdx 8 ohm rating
Posted By: soundnsecurity
Subject: alpine pdx 8 ohm rating
Date Posted: April 07, 2011 at 6:44 PM
does anyone know the 8 ohm rating on the PDX-F6?
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Replies:
Posted By: i am an idiot
Date Posted: April 07, 2011 at 10:09 PM
Do you know the 2 ohm and the 4 ohm rating?
Posted By: soundnsecurity
Date Posted: April 08, 2011 at 7:37 AM
ok so it is the same as the 2 and 4 ohm rating. i was afraid of that, but ok thanks.
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Posted By: haemphyst
Date Posted: April 08, 2011 at 11:10 AM
That's not what he asked...
Into 8-ohms, those amps will possibly make a bit less than their 4/2-ohm rating. I'm guessing between 50 and 75% of it. That's a guess. This being said, why would you afraid of the amp making the same power into 8-ohms as it would into 4-ohms? It's normal for EVERY amplifier to make less power into a higher impedance, and more power into a lower impedance.
The PDX amplifiers are (though not COMPLETELY) unique, in that they make the same rated power into 4-ohms and 2-ohms. This is due to the smart power supply that limits the current into 2-ohms. Because it doesn't have to limit the current into a higher impedance, it will probably make about the same current into an 8-ohm load as it does into a 4-ohm load, with roughly the same output voltage. If it doesn't change the output voltage or current into an 8-ohm load, relative to a 4-ohm load, the power would be half. Having never done any testing or experiments on these amps into higher impedances, I can't say... It's all guesses.
Posted By: i am an idiot
Date Posted: April 08, 2011 at 3:32 PM
They are all guesses, but probably pretty accurate guesses.
Posted By: soundnsecurity
Date Posted: April 08, 2011 at 8:11 PM
well i wanted to bi-amp my components. the woofers are 4 ohm and the tweeters are 8 ohm. the rms rating on the woofers is 200W and the rms on the tweeters is 75W. so i was going to use two channels for my woofers and send them 150W and use the other set of outputs for the tweeters and give them potentially about 90 to 100W. but that is only if the amp will lower its output on a higher ohm load. im not worried about blowing the woofers but i dont want to overpower the tweeters by that much. all in all i need a 4ch amp that will give me close to or above 200W into 4 ohms and about 100W into 8 ohms.
i really wanted the PDX mainly because its probably one of the cleanest amps out there(spec wise anyway) and its small enough to fit where i need it to, and its not ridiculously expensive.
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Posted By: i am an idiot
Date Posted: April 08, 2011 at 8:31 PM
Do you know the 4 ohm and the 2 ohm rating of the amp? If it does 200 per channel into a 4 ohm load, theoretically it will produce 100 watts into an 8 ohm load.
Posted By: soundnsecurity
Date Posted: April 08, 2011 at 8:44 PM
the 2 ohm and 4 ohm rating are the same at 150W/channel. i know that normally an amp roughly doubles or halves its output depending on the ohm load it sees. the PDX outputs the same power into either load but it wont give me an 8 ohm spec. my woofers call for 200W but im willing to make the sacrifice so that i can use just one amp to bi-amp my highs and go completely active.
any other amp i look at that gives me 200W/ch into 4 ohms, that is not regulated like the PDX, costs way too much. these amps are all rated by their 2 ohm load specs which means that in the end i would need a 1600W RMS 4 channel amp. i know that doesnt seem like a challenge to some people but im looking for a very clean SQ amp, not boss or hifonics. a good clean 1600W 4 channel amp is generally pretty expensive and also physically larger than i have space for.
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Posted By: i am an idiot
Date Posted: April 08, 2011 at 8:50 PM
If it does the same power into 2 or 4, as Haem stated they are regulating something when it runs into a 2 ohm load. The power supply in the amp will only produce + and - X voltage. The voltage will not go any higher if you run it into a lighter load. So if it does 150 into 4, it may do as much as 90 or so into 8. Reason being is the supply may not be able to maintain X voltage when driving all channels into a 4 ohm load. I know it should be able to keep it up into an 8 ohm load. Example, with no load or 8 ohm per channel, the supply may stay at + and - 30 volts. When driving a 4 ohm load the supply may not be able to stay at 30, it may drop a volt or 2. So it may produce a bit more than half of the 4 ohm rating, but not much more than half.
Posted By: soundnsecurity
Date Posted: April 08, 2011 at 8:56 PM
i am an idiot wrote:
If it does the same power into 2 or 4, as Haem stated they are regulating something when it runs into a 2 ohm load. The power supply in the amp will only produce + and - X voltage. The voltage will not go any higher if you run it into a lighter load. So if it does 150 into 4, it will do 75 into 8.
yay, normally if it were any other idiot saying that, then i wouldn't trust them but i know you know your stuff. ill probably order the amp sometime this weekend. thanks for all your help guys. -------------
Posted By: i am an idiot
Date Posted: April 08, 2011 at 9:00 PM
I edited my last post after you quoted me. Read it again.
Posted By: soundnsecurity
Date Posted: April 08, 2011 at 9:06 PM
ok yeah, thats still just fine. 80 - 90 watts is still right in the happy zone for my tweeters, even 100 watts is ok, just not 150.
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Posted By: DYohn
Date Posted: April 09, 2011 at 10:36 AM
What crossover frequency are you using for the tweeters? They are unlikely to use more than 15 watts or so depending on the Xover frequency. ------------- Support the12volt.com
Posted By: soundnsecurity
Date Posted: April 09, 2011 at 7:12 PM
im not sure on what frequency what i will eventually settle on but i will be using a cache 3-way active crossover before the amp which is fully adjustable. the set of components im using are diamond D9's or Hex pro as they are now called. mine are actual D9's from before they changed the name.
first im going to try to figure out what frequency they get crossed over at from the crossover that came with the set and ill start with that and i might be happy. my best guess is that it'll be in the range or 2800hz to 3500hz. im doing this mainly to simplify my setup a bit because the passive crossovers are huge and i would rather not have to use them if i dont have to.
im confused with your statement about them only using 15 watts or so. can you explain a little bit? i understand that the amp makes more or less power depending on the frequency being played but im under the impression that the amount of power that the tweeter uses is dependent on the resistance it presents to the amp at any given frequency.
the tweeters are rated in the owners manual for 75 watts. i know this is not the rms at all frequencies within its range but im still confused. -------------
Posted By: DYohn
Date Posted: April 09, 2011 at 9:45 PM
The owner's manual rating is program power, meaning when used with their crossover. As far as how much power a tweet will actually need, that's dependent on the crossover point and on your volume control. At normal loud listening levels a woofer might be using 100 watts, a midrange 45-50 watts and a tweeter 10-12 watts. The higher the crossover point the less power that's required to play music.
Your owner's manual lists the fs of your tweeter as 850 Hz, which is quite good, and means you can safely cross it as low as 1700Hz (2X fs) with an 18 db/oct or steeper crossover. ------------- Support the12volt.com
Posted By: soundnsecurity
Date Posted: April 10, 2011 at 3:13 PM
ok thats interesting, maybe i should go with the pdx-f4 just to air on the side of caution. i really really want to avoid having to find a place to put both of those humongous crossovers. i have an extended cab ford ranger and im already short on places to put things.
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