Choosing an amplifier.

[dB-SPL 10+ year member]

At least 5 times a day you will see the question "Which amp should I use?". Here are the basics of matching an amp to your speakers. Maybe our lovely mods could possibly sticky this and drop that number to 2 a day? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

The first thing that just about EVERYONE looks at..

Power: How much do you need? Search for an amp that has a relatively close RMS (continuous power) wattage output to your speaker. If your speaker can handle 250W RMS, look for an amp in the 250W RMS range. Try your best to ignore Peak Power ratings. Just because the manufacturer states that your subwoofer can handle 2000Watts Peak Power does NOT mean it can take 2000Watts all day long.. Or longer than 30 seconds for that matter.

If you're not sure about an amplifers RMS power output, check to see what size fuse the amp takes. 250W output needs a 500W input (using 50% efficiency). 500W input divided by battery voltage (14.4 with car running) comes to about 35A. If that 250W amp has (or suggests) a 20A fuse, You'd better look elsewhere. 14.4v times 20A equals 280W input. 250W output divided by 280W input turns into an 89% efficiency. Impossible number for a class A/B amp. That amp will not produce 250W continuously.

- Powering component/full-range speakers:

Dependant upon how many speakers you plan to power, 2- and 4-channel amps with high-pass filters are usually in store.

- Powering subwoofers:

Subs produce low notes. Therefore, an amp that can reproduce low frequncies efficiently should come to mind. Class D mono amps were designed soley for this purpose. 2-channel amps can also be used in these applications for: A) Powering two subwoofers or B) Bridge the amp (connect the speaker leads to the positive on one channel and the negative from the other channel) and use it as you would a mono amp.

- Powering component/full-range speakers and subwoofers with one amp:

This is again dependant upon how many speakers you plan to power. If you want to run your front stage and one (or two) subwoofer(s) off of one amp, you'll need a 4-channel amp that can meet the requirements of each speaker. Front stage, rear deck and subwoofer(s) combinations should be powered by a 6-channel amp, and so on.

Where just about EVERYONE gets lost/goes wrong..

Impediance/Ohm Stability: Ohms law states that the direct current flowing in a conductor is directly propotional to the potential difference (voltage) between its ends. Loading an amp with a higher impediance means it puts out less power. Any good quality amplifier will be two ohm stable while a rare few will go as low as .25-ohm. Ideally an amplifier should double its power each time the load is halved. For example, a 100 watt amplifier (into a four ohm load) should produce 200 watts into a two ohm load and so on. This general rule does not work for ALL amplifiers as manufacturers use different degrees of regulation on power supplies, which can restrict the actual increase in output. To get the most sound out of your amp, as well as protect it from damage, wire it correctly. Read the manual or research its specifications to make sure of its stability. There's a sticky in the "Subwoofers" section with numerous subwoofer wiring diagrams.

Damping Factor: This is the amplifiers ability to control the speakers movement. More so concentrated on mid-bass and subwoofer amps. If you want better accuracy, look for an amp with a higher damping factor. Decreasing impediances means a decreased damping factor. Example - An amp running at 4-ohms will provide tighter bass than at 2-ohms.

Signal to Noise Ratio: Not so important to look for in an amp powering subwoofers as most dedicated sub amps have a terrible signal to noise ratio. However, when powering component/full-range speakers, the higher the better.

Anyone feel free to correct/edit/add anything I might have missed.

-Bill-

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[xtremebassjunky 10+ year member]

nice post.

 

[dB-SPL 10+ year member]

Eh.. I tried. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

-Bill-

 

[xtremebassjunky 10+ year member]

it covers alot of questions that are posted...

 

[dB-SPL 10+ year member]

That's what I was aimin' for. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

-Bill-

 

[xtremebassjunky 10+ year member]

yeah... people asking the same questions over and over... not searching... //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[Stem 10+ year member]

how about adding a little something about the electrical state of the car in relation to amp selection. like, what electrical upgrades to help out amps. personally i always get lost trying to figure out if i need a new battery, another battery, a ho alt, if i need the big 3. how many watts are too much for stock electrical. this is another good answer because theres always people asking will i need a new batt? etc...

just a suggestion, but besides that excellent post dude, i certainly know alot more now than i did 5 min ago //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[dB-SPL 10+ year member]

Big 3 upgrades are already in a sticky.. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

-Bill-

 

[Whitey 10+ year member]

There's a sticky in the "Subwoofers" section with numerous subwoofer wiring diagrams.
-Bill-

I believe this is in the "Wiring" sticky section...Thanks for the great info!

 

[squeak9798 5,000+ posts]

If you're not sure about an amplifers RMS power output, check to see what size fuse the amp takes. 250W output needs a 500W input (using 50% efficiency). 500W input divided by battery voltage (14.4 with car running) comes to about 35A. If that 250W amp has (or suggests) a 20A fuse, You'd better look elsewhere. 14.4v times 20A equals 280W input. 250W output divided by 280W input turns into an 89% efficiency. Impossible number for a class A/B amp. That amp will not produce 250W continuously.

Not a big fan of judging an amplifier's capabilities by fuse size alone.

Just because an amplifier has adequate fusing for it's rated power doesn't mean it's capable of that rated power.

Fuses aren't insta-blow, and music (how most people use their amplifiers) is very dynamic and transient by nature. So if an amplifier manufacturer has placed conservative fusing in their amplifier (safety net to accomodate the DAF prevalent in the consumer base, for example) it doesn't mean it isn't capable to outputting full rated power for the short, dynamic peaks in the music.

Zed Audio, for example, notes that the fuse in the Minilith "May have to be increased by 40% when driving high power into 1ohm loads"

Class D mono amps were designed soley for this purpose.

But please note that full range class D amplifiers are suitable for high frequency applications.

Some people confuse class D with "subwoofer only", which isn't the case.

Damping Factor: This is the amplifiers ability to control the speakers movement. More so concentrated on mid-bass and subwoofer amps. If you want better accuracy, look for an amp with a higher damping factor. Decreasing impediances means a decreased damping factor. Example - An amp running at 4-ohms will provide tighter bass than at 2-ohms.

Completely overrated in usefulness and importance, and most of the claims regarding "tighter bass" due to damping factor are completely unfounded.

Damping factor can essentially be completely ignored as a spec of importance with solid state amplifiers. There are less than a handful of car audio solid state amplifiers with a low enough damping factor to significantly (read: audibly) affect the response of the system....only one comes to mind at the moment. In tube amplifiers, with high output impedances, yes damping can become an issue. But almost all modern solid state amplifiers have adequate enough damping to not cause audible change.

Richard Clark on Damping Factor

Audioholics on Damping Factor

Also bear in mind that Damping Factor is not a "higher is better" spec. Once the amplifier has adequate enough damping not to cause an audible change in sound....that's it. Going any higher nets you zero benefit.

Lastly keep in mind that CEA-2006 compliant amplifiers measure/calculate their damping factor in a different manor than those typically used by manufacturers (which is typically simply load impedance/output impedance). So most will display an absurdly low DF (such as the JBL PX300.4 w/ an "Effective damping factor" of 6.383). These figures are NOT comparable to standard Damping Factors stated by other, non-CEA-2006 compliant amplifier manufacturers.

 

[Pl8er 5,000+ posts]

Perhaps I am wrong on this, but weren't some older PPI amps made with no fuse at all?

 

[squeak9798 5,000+ posts]

Perhaps I am wrong on this, but weren't some older PPI amps made with no fuse at all?

There have been many amplifiers produced with no internal fusing.

 

[dB-SPL 10+ year member]

Eh.. Just a quick 'how to' on matching amplifers to speakers with nothing more than the 'basics' for those with little to no knowledge on the subject. By no means am I stating that I'm a know-it-all (which is why I stated "feel free to edit"), just thought it might have answered 95% of the same question asked countless times a day. That's all. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

-Bill-

 

[Pl8er 5,000+ posts]

Eh.. Just a quick 'how to' on matching amplifers to speakers with nothing more than the 'basics' for those with little to no knowledge on the subject. By no means am I stating that I'm a know-it-all (which is why I stated "feel free to edit"), just thought it might have answered 95% of the same question asked countless times a day. That's all. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
-Bill-

Really good post man!

 

[dB-SPL 10+ year member]

Really good post man!

Thanks..