Here's the setup...
HU - Sony CDX GT920U - Max 52w x4 @4ohms
Front Speakers - Infinity Kappa Series 52.9i (2ohm) 55w RMS/165w Max
Deck Speakers - Infinity Kappa Series 63.9i (2ohm) 75w RMS/225w Max
Possibly adding Infinity Kappa Series 32.cf (2ohm) to dash at a later date.
I need an amp to power the front, deck, and possibly future dash speakers. Ignoring the dash speakers, the lowest RMS for the above speakers is 55W for the 52.9i @ 2ohms.
The question is... Is it possible to run a 100W x4 amp at 50% power and the HU at 100% without risk of damaging the speakers? Or possibly the 100w x4 amp at 75% with the HU at no more than 75%? I'm trying to determine how to get maximum RMS without max'ing either the HU or amp.
Also, if you run a 4ohms amp and connect two speakers to the same output does that decrease the ohms to 2? This is confusing me as I am only slightly electrically inclined.
Short answer - I would recommend getting a 60-80W RMS amp and running the Front and rear speakers off it, and the dash speakers off the head unit, which should be around 17W RMS.
SireArthur:The question is... Is it possible to run a 100W x4 amp at 50% power and the HU at 100% without risk of damaging the speakers?
It's not linear and it's not that simple either. It is probably possibly to run the 100W amp at maybe 30-40% gain and not turn the HU all the way up and be okay, but I don't recommend it.
SireArthur:Also, if you run a 4ohms amp and connect two speakers to the same output does that decrease the ohms to 2? This is confusing me as I am only slightly electrically inclined.
Not that simple either. Two 4-ohm resistors can be wired to present EITHER a 2-ohm or 8-ohm load on an amp. With speakers and impedance, that varies with frequency, so with 2-ohm full-range speakers, it would be 1-ohm or 4-ohms at the amp, except that 3.5's (essentially tweeters) have less effect on this - I don't recommend combining them, though.
Hope This Helps!!!
2002 Ford Focus Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs
Welcome to the Crutchfield forum! From this day forward, you can disregard any wattage rating that says Max. It is of no consequence whatsoever, and only creates confusion. Continuous power or Root Means Squared(RMS) is the wattage rating you can use when comparing speakers and amplifiers.
SireArthur: The question is... Is it possible to run a 100W x4 amp at 50% power and the HU at 100% without risk of damaging the speakers?
The question is... Is it possible to run a 100W x4 amp at 50% power and the HU at 100% without risk of damaging the speakers?
Your first question... the simple answer is yes. You can't power a single speaker from both the HU and an amplifier at the same time.
A 100 watt RMS x 4-channel amp can produce clean power anywhere from 1 watt to 100 watts at 4 ohms. The amount of watts it produces depends on 4 key factors. The first one is the RCA input voltage. This is determined by the pre-amp voltage of the HU. The second factor is the volume on the HU. Thirdly, the impedance load seen by the amplifier, measured in Ohms. The last is the gain setting on the amp itself. If you want less power, you can rotate the gain setting counter-clockwise. If you connect speakers that are lower than 4 ohms impedance, the amp will be capable of producing more power to that speaker. When choosing an amplifier for your Infinity Kappa's, the specification that you should consider is the RMS watts @ 2 ohms, since all the speakers you listed are basically 2 ohms. Having more amplifier than your speakers can handle is really not a bad thing. You have to be more careful when setting the gains, but if they are properly set the amp itself will run cooler and last longer.
SireArthur: Also, if you run a 4ohms amp and connect two speakers to the same output does that decrease the ohms to 2? This is confusing me as I am only slightly electrically inclined.
Two 4 ohm speakers wired in parallel will let the amp see a 2 ohm load. Two 2 ohm speakers wired in parallel will make the amp see a 1 ohm load. Fewer amps are stable at this impedance. There is another way of wiring two speakers which will double the impedance rather than half it, called series wiring.
**@TigerHeli**
you beat me this time
J Ro makes a valid point - I assumed SireArthur meant the amp at 50% gain and the HU at 100% volume, but no, you can't connect them BOTH to the same speaker directly.
J Ro:Having more amplifier than your speakers can handle is really not a bad thing. You have to be more careful when setting the gains, but if they are properly set the amp itself will run cooler and last longer.
A fifth parameter is the level of the source being played - i.e. a loud rap song compared to a violin quartet chamber piece.
There are some misconceptions about the gain control - it is not a limit on amplifier power - it merely sets the limit on WHEN the amplifer reaches maximum power.
Let's assume your HU volume control goes from 1-100 and your amp is 100W RMS.
If you have 4V pre-outs, your amp might make 100W RMS (with a given test tone) with the volume at 75. If you turn the gain higher, the amp might reach 100W at volume 50. With the gain lower, the amp might reach 100W at volume 100. With a radio with 2V pre-outs, you could do the same thing, but the gain settings would have to be higher to compensate.
Now the key point is - there is no way to set the amp so it only produces 50W. You may be able to limit the gain to a low enough setting that it only makes 50W at Volume 100, but if your source material is significantly loud enough, the amp will put out more than the 50W setting.
Great info... Thanks to both of you for such detailed info.
I'm considering a Pioneer Premier PRS-D4200F using the two sets of RCA outputs from the HU. In your opinions, does this sound about right?
Thanks in advance
Nope - that amp is 150Wx4@4-ohms.
I'm generally not a fan of Pioneer amps, but the Premier's seem pretty nice.
The MRP-F300 would be a great pick, and any of these would be good - but most are higher than I would recommend on the wattage, but probably okay.
Any plans to add a subwoofer down the line?
Possibly moving the amp/subs from my other car but more than likely I'll be adding a BassLink or a mono amp with single sub in the future.
The MRP-F300 looks like a good choice but I have a lot of respect for Sony's electronics and the SM-4S is the perfect size.
Actually, you've got three sets of RCA's available so you are covered for adding a subwoofer.
The Sony is really only about 1-inch smaller all around, but that might be enough to make a difference. It should work fine for your application.
a little word of advice.. find the loudest song you will ever play!.. then use a DMM to set the gains to where is puts out the power you need.. i did this myself just yesterday while setting up my sub amp.. but people say use a tone at 0DB.. personally i disagree as i set it up with a test tone first.. then played music.. and my amp only put out about 150RMS with my loudest song when it actually should put out 300RMS!.. just use the loudest level recorded song you will play and set from there! :D i hope this helps.. tell me if you need help with this method. the calcuations are simple.. grab a dmm hook up to amp with the speakers disconnected. do your calcuations. so say... 60rms at 2 ohms.. multiply 60 times 2.. so 120 then square root 120 so you get 10.95 volts. thats what you set the gains at with a dmm. works well and you know your safe.. as ive owned 2 pairs of subs that wouldn't distort even with extra power!.. after doing that set the gains by ear.. but only turn them down if needed to match everything else! :D enjoy :D getting an amp too powerful isnt a concern but rather sending too much power is the consern :D
edit: keep your HU's volume at about 75% volume when doing this procedure :D sorry if this is too long or complicated.. its alot easier then it seems. :D
JVC KD-AVX44, jl audio 12 inch W1v2, alpine mrp-m500 , JBL GT5-652 fronts, audiobahn dub269's in rear deck, 4 gauge kit, voltage displaying fused distribution block:D .. all wired on my own. :D
shak - that works if you know that is the loudest source data you will ever own. If you buy a new album and it is recorded much higher than your test file, you could have some bad results ....
yea.true :D.. thus why i kinda stated the loudest you will ever play.. so a song that reaches its peak recording level :D .. or has many peaks at 0DB with various frequencies. im pretty sure that would work?
So much information... This is great. Thanks to both of you. I'll try to remember to post how everything works out. Thanks again for your extensive knowledge and assistance.
shak:yea.true :D.. thus why i kinda stated the loudest you will ever play.. so a song that reaches its peak recording level :D .. or has many peaks at 0DB with various frequencies. im pretty sure that would work?
It will work, but you are somewhat walking a fine line on it.
Look at it this way - the 0 db test tone (or white noise) is essentially what you are asking for above - if you set your gains with that, you essentially NEVER have to worry about damaging your subs - of course, if you normalize your MP3's to 89 db with MP3Gain as I do - then you could turn the amp gain up quite a bit and still be safe. But if someone else asks you to play a track, you could be in trouble.
(Now all of this assumes that you can't hear distortion very well and you crank the volume up even though the signal is audibly distorting, but that is possible).
In the end, it is whatever you feel comfortable with ...