Questin I could not find logical answer

[HNaga 10+ year member]

I'm enhancing my sound system, started with Alpine CDA-9887 HU.

I'm thinking about getting Alpine Type-X SPX-17REF and Alpine Type-X SPX-13REF

Alpine 4 ch amp are PDX 4.100 and PDX4.150 both are more power than comp speakers.

my question is about amp RMS and speakers RMS, the amp should be more or less power than speakers?

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[geowick07 10+ year member]

Never hurts to have more power than necessary. Room for upgrading in the future. This is called headroom.

Just set your gains correctly, and you will be fine

geo

 

[HNaga 10+ year member]

and how to set the gain to have the max speakers power without burning the speakers?

 

[geowick07 10+ year member]

What is the RMS on your speakers?

geo

 

[HNaga 10+ year member]

currently I have Infinity kappa in front which is 75 RMS and infinity reference 100 RMS

Type-X I want to buy is 75 RMS and 60 RMS

 

[geowick07 10+ year member]

These are output voltages used when setting gain with DMM:

(All assuming 4ohm final load)

75w rms = 17.32v

100w rms = 20v

60w rms = 15.49v

geo

 

[HNaga 10+ year member]

These are output voltages used when setting gain with DMM:
(All assuming 4ohm final load)

75w rms = 17.32v

100w rms = 20v

60w rms = 15.49v

geo

Thanks Geo.

Kappa is 2 ohm the rest are 4 ohm

May I know the equation you got those results from?

 

[geowick07 10+ year member]

Equation - Voltage = SqRt(Power*Resistance)

Amplifier Output Voltage Cheat Sheet

Post #6-#8

(2 ohm load) 75w rms = 12.25v

geo

 

[HNaga 10+ year member]

one more question , how to set the gain that accurate? Do I need hardware to set it?

and the mentioned number are the maximum gain within safe range - I mean they are safe even with the max volumn. right?

 

[geowick07 10+ year member]

1. Use a DMM (digital multimeter)

2. Yes

geo

 

[HNaga 10+ year member]

Thanks a lot Geo

 

[geowick07 10+ year member]

No problem. Good luck!

geo

Mods: feel free to close thread. Issue resolved.

 

[eharri3 10+ year member]

Power= loudness. You want them to get loud enough at normal listening levels that you can hear the details you're looking for. Lack of power means a higher likelihood you will crank your HU closer to the point of audible distortion to get the loudness you're looking for, which means you will loose some sound quality and degrade the life of the speaker. I ran 60 watts to comps that take 100 quite some time. For some music I just couldn't get it loud enough unless I cranked it very close to my HU's max unclipped output, or to about 27-30 out of 35. Now I have better comps that take 125 and I'm giving them 140. My HU starts clipping around 29-30, I almost never have to go past 23 or 24 anymore. I get more loudness with clarity at a lower volume without the system straining so much.

From here on in for subs and front comps Ill always try to get it a little bit more than what it's rated for . Anyway 10-20 watts or so either way makes no real difference since RMS ratings are measured using continuous test tones and in real life you only ever see them for a brief instant every now and then in your music. Power ratings are to give you a general ball park figure of where you need to be to make the speaker sound like it should.

But when you feed a speaker probably 50-60% of it's RMS rating or less you'll start to see a difference in loudness, which will affect your perception of sound quality.