Need help on my sound system

[Dirty Dee]

I recently bought a Alpine CDA-9856 head unit:

(CEA-2006 Power Rating ([email protected] V =1% THD+N), S/N 80dBA (Ref: 1W into 4Ohm): 18W x 4Max Power Output: 50W x 4)

and a pair of Alpine SPS-46C2 4x6 Coaxial 2-Way Speakers for the front and rear for my 1989 240sx hatchback:

(Power Handling Capacity (RMS): 30W Power Handling Capacity (Peak): 150W )

I was wondering if it is a smart idea to get an amplifier, or would the head unit supply enough power to the speakers for them to sound good. Do you compare the speakers peak voltage to the hu's max power or the RMS value?

If I get an amplifier, it would be either the Alpine MRP-F450 or the MRP-F250. Thanks for any help

[Notorious170]

first off, everything needs to be based off of the rms wattage.

for the speakers that you purchased, the head unit would do a decent job. if you were to get an amplifier get the f250. just know that your speakers are 30 watts and the amp is 40 watts, so dont turn your gains up too much or you will blow your speakers.

[Dirty Dee]

Ok. Thanks for the help. I think I am just going to stick with the head unit and not get an amp.

[Notorious170]

glad i could help

[PoorManQ45]

I personally would recommend a four channel amp.

The only reason for this is because the 9856 does NOT have a built in high pass filter to prevent bass from going to those speakers.

A small 30~50w x 4 amp with an adjustable highpass filter(HPF) will do fine.

Just to let you know, this will allow you to play the speakers louder, but will reduce bass output to pretty much nothing.

So a small sub is recommended

[Notorious170]

cant he just turn the bass down on the head unit and get the same effect?

[PoorManQ45]

not the same.

Turning it down at the HU does decrease the bass, but doesn't cut it off.

Setting the HPF on the amp cuts out the frequencies below that point.

Note: I have the 9856 in my car. I am getting a 4 channel amp for the exact reason I gave.

[Dirty Dee]

I just installed the four speakers in the car. They sound pretty nice. I am going to be messing with the setting a bit tomorrow. If I get a 4 channel amp for the speakers and then want a sub, wouldnt i need another 1 channel amp to run it though?

[Notorious170]

yes you would need another amp. or you could buy a 5 channel amp to ease the addition of a subwoofer later.

[carcrazyguy]

I recently bought a Alpine CDA-9856 head unit:

(CEA-2006 Power Rating ([email protected] V =1% THD+N), S/N 80dBA (Ref: 1W into 4Ohm): 18W x 4Max Power Output: 50W x 4)

and a pair of Alpine SPS-46C2 4x6 Coaxial 2-Way Speakers for the front and rear for my 1989 240sx hatchback:

(Power Handling Capacity (RMS): 30W Power Handling Capacity (Peak): 150W )

I was wondering if it is a smart idea to get an amplifier, or would the head unit supply enough power to the speakers for them to sound good. Do you compare the speakers peak voltage to the hu's max power or the RMS value?

If I get an amplifier, it would be either the Alpine MRP-F450 or the MRP-F250. Thanks for any help

You really should not focus on watts at all with typical car stereo. In reality, only IEC rated specs are accurate, and only the very expensive car audio stuff is IEC rated (yet all home stereo is by law).In other words, with car stereo, there is no governing body as to what manufacturers quote. So in other words, differences within a single brand are all the watts quotes are good for, if that. Otherwise they are for advertising.Bottom line, clean power will rarely blow a speaker, yet distortion almost always will, so focus on clean output and speaker cone control and advertised watts won't mean hardly anything.

Anyway, if your car is an SE with the Active System (still in use), it has plenty adequate amps for your regular speakers. If not, and your deck is powering all 4 speakers directly, then it will still be OK if your deck has a built in high pass option. If you have a basic head unit with straight output, you will likely want an amp that has it's own high / low pass.

You really don't need to get into any real money with amps. If you buy anything of quality, the differences are actually minor to the naked ear. I have found that used Sony amps from the mid 90's to be the best value out there. You can get a 2540, 4040, or 4045 for about $20-40 on Ebay and they were $200-300 amps new, and have (sound quality) specs that will blow any current mainstream amp in this price range away. You can also buy older Soundstream and similar from this era very reasonable and get quality that would be hard to find these days without breaking the bank. Once again, the key is if your deck has built in crossover processing...if so, simply throw $25-50 at a simple used 4 channel amp...bridge two channels into the sub, drive the front speakers with the other two, and power the rear with your deck attenuated way down...done and finished. If not, get a 4 ch amp with a 50/50 type high low pass - which usually splits at 75hz-100HZ.

Set it up right and it will do wonders. Watts and money spent mean very little.

[PoorManQ45]

Bottom line, clean power will rarely blow a speaker, yet distortion almost always will...

Incorrect. Distortion alone does not kill speakers. It is the amplifier clipping that causes that distortion that kills speakers. When an amplifier clips it sends out 2~4 times it's rated power to the speaker.

An over-exaggerated test for this is to take a sub that is truely rated for ~1000w RMS. Something like a W7. Then put a 100w RMS amp on it. You can clipped the amp all day long and it won't kill the driver. This will be pure distortion BTW

[carcrazyguy]

Incorrect. Distortion alone does not kill speakers. It is the amplifier clipping that causes that distortion that kills speakers. When an amplifier clips it sends out 2~4 times it's rated power to the speaker.

An over-exaggerated test for this is to take a sub that is truely rated for ~1000w RMS. Something like a W7. Then put a 100w RMS amp on it. You can clipped the amp all day long and it won't kill the driver. This will be pure distortion BTW

You apparently didn't get the gist of what I wrote. Sure the scenario you mention is true, but not really a typical real world situation, and if you read the original post you will see he was asking about his main speakers. Maybe my mistake (to you) was oversimplifying the way I wrote it, which is normally the best way to answer such questions on forums.

What I was speaking of was people's obsession with watts ratings for their regular door / deck speakers. What I wrote was meant to help a novice and would have (had you not felt the need to attack it and split hairs). Bottom line, if he buys any decent door / deck speakers and amplifies them cleanly, there will be no problem short of overdriving the speaker, which will still potentially burn a voice coil, distortion or not. Think about it...you can have a million watt amp, and run it normally into 20W speakers and all will be good. So if you will go back and read again, I was only oversimplifying as to not confuse the original poster, therefore there was no reason to argue, attempt to discredit, etc. Now "Dirty Dee" is surely more confused as to what to believe than he was before he even made the post.

[carcrazyguy]

You also might want to read again (slowly) and notice the words "rarely" and "almost" in my original post.

Quote »Bottom line, clean power will rarely blow a speaker, yet distortion almost always will, so focus on clean output and speaker cone control and advertised watts won't mean hardly anything.[/quote]

[PoorManQ45]

You also might want to read again (slowly) and notice the words "rarely" and "almost" in my original post.

I understand you're trying to help. I just don't like that you didn't define that the distortion that you're talking about that almost always blows speakers is actually caused by the amplifier clipping and sending and excessive amount of power to the speaker.

So just to clarify, Power kills, not distortion(alone)

[carcrazyguy]

I understand you're trying to help. I just don't like that you didn't define that the distortion that you're talking about that almost always blows speakers is actually caused by the amplifier clipping and sending and excessive amount of power to the speaker.

So just to clarify, Power kills, not distortion(alone)

Yeah, I can see why a guy asking a very simple question about 4 basic off the shelf speakers powered by a deck or potentially an entry level amp needed to know every single layer of potential information, any applicable definition, etc. Maybe I should also quote Ohms law, and a few other things to help him buy a $25 amp for 4 coaxials.

NO. All he needed to know is not to worry about all of this watts ****. He can buy four decent speakers and any amp of his choice and he will never have a problem as long as he doesn't do anything over the top.

Maybe you are just one of those people that use forums to be right, even at the expense of picking other (already completed) posts apart. In reality however, the ONLY thing forums should be for is helping people or getting info. If you want to argue, pick apart or add layers and definitions, there are other places for that .Once again, thanks to you, he now is most likely totally confused and back to the whole silly "watts worries" I am sure. "Somehow" people have been able to run small bookshelf home speakers with 100 watt home receivers since the beginning home stereo. The same principle applies to car stereo to an extent...which was the principle I was trying to explain...and not trying to make this a car stereo forum or an electrical engineers forum. Maybe you will pick apart my user name next? I am sure there is something you can find that I didn't think necessary to add.