Matching amps to speakers: Basic "overpowering" theory

[Snail 10+ year member]

To preface, I come from the professional audio field doing installations in facilities like churches and such. The commonly understood method to matching amps and speakers is to use an amp to deliver twice the power that the speaker is rated at. In car-audio speak you would give a 40watt speaker an 80watt amp (and all of this is, of course, relating to average or "RMS" power). What I'm trying to create discussion on here is efficiency; really driving a speaker for all that it is safely worth, without straining the amplifier. I'm talking about everything from tweets to subs BTW.

Generally, from what I've read and using this and other boards search function, car audio doesn't work the same way (or does it and it's just not common knowledge?). It seems as though the consensus is to give a 40watt speaker 40watts of amplification. My dilemma is that I've seen tidbits leaning very much to the "double it" idea in referance to mobile audio, and for the same reasons it is the norm for professional audio installs: "Doubling It" results in cleaner sound and amps that don't clip if done correctly. Of couse if you actually use 100% of the amp and put double continuous power to a speaker over a given period of time (depending on the quality of the speaker build, among other things) the power will physically overdrive and damage it.

So I'm wondering: The major difference I see here is the "professional" aspect of the professional sound reinforcement realm. For the most part, the system is set up by people who know what they're doing. The person behind the sound-board controlling the output, if they have any idea what they're doing with the gains on the board, would have a difficult time damaging the speakers.

This is of couse very different when you have Joe-Schmo throwing a car system together. All the online guides have to account for the lowest common denomenator right? Especially in our sue-happy society, I'm not going to take something like the Crutchfield matching guide as gosphel.

Bottom line: I'm sure we can all agree that, generally, matching a speakers technical handling capability very closely to what an amp actually delivers is a can't-go-wrong recepie. Of course if the user doesn't set up the system correctly or constantly drives the system into distortion, even the most perfectly matched system would have a dramatically shorter life span.

Please submit links to help me see the application of (or recommendation against) "doubling-it". Setting me straight, other theories and whatnot are welcome, but to the best service of the intention of the thread, please use real-world proof of what you believe to be true. Again, the general concensus is to match power desired to power given.

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[snoopdan 5,000+ posts]

There are different modes of car audio use of equipment....daily beating, SQ, and SPL....there are applications for all three that have bounderies of use for what they're trying to accomplish. Perhaps you can just narrow down a topic...because what your asking is way to broad.

 

[lostdaytomorrow 10+ year member]

I'd also like to add a small thing here:

In car audio, electric current isn't "infinite" (for lack of a better word) as it is in large buildings. Basically if you don't need a memphis 4kw, then get the Sundown 1500.1 if you catch my drift. It's important to be more conservative with current in a car because it doesn't come from the transformer down the street; it comes from the car's elec. system (batt., alt. etc.)

 

[hoodkid 10+ year member]

I'd also like to add a small thing here: In car audio, electric current isn't "infinite" (for lack of a better word) as it is in large buildings. Basically if you don't need a memphis 4kw, then get the Sundown 1500.1 if you catch my drift. It's important to be more conservative with current in a car because it doesn't come from the transformer down the street; it comes from the car's elec. system (batt., alt. etc.)

^ i agree with you, but i think i understand what he is saying, like for my setup my speakers combined are about 1500 watt rms but i will have like 3000+ watts on them //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif , not only for headroom but for competition also

 

[squeak9798 5,000+ posts]

I think the main difference between the two examples is that in car audio, the desired result is much more specific to the individual user.

Take your church example. You have pretty defined goals with not a whole lot of variability in those goals. The sound needs to adequately fill the space without being too loud or too quiet. There are a relatively finite limits there, and the system typically won't be pushed beyond very far beyond them.

In a car, on the other hand, the listening conditions are going to be specific to each individual. Some just want something "a little better than stock", while others want to wake people in the neighboring time zone. This larger variability in listening habits and conditions is going to change the power demands for each specific scenario, and hence defining a rule such as "double it" doesn't really apply. Some people are perfectly happy with a set of co-axials (~40w RMS) running off of headunit power (~10w RMS). On the other extreme, some people want either maximum output or sound quality, and hence their power requirements are going to dramatically different from the previous example.

There is, ofcourse, the DAF (dumbass factor) that needs to be taken into consideration as you mentioned. Most of the people asking the question aren't experienced or knowledeable enough to keep from damaging their equipment if given the opportunity to overpower their speakers. Heck, even when we recommend they match power output to power handling (rather than "doubling it") we have a hard time keeping people from damaging equipment due to clipping from improper gain setting/etc. Just imagine what it would be if we recommended everyone have the ability to really overpower their speakers //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

If someone is looking to upgrade to something more than what headunit power offers, but want less than the loudest setup on the block and just want it more for casual listening....there's no point in them spending money on power they'll never ever use. If they only need a 50w x 2 amp to get the speakers (of whatever reasonable power handling) to their desired listening level....then there's no value in adding higher power capabilities. They won't be using any of that extra power and it's unlikely they'll hear any sonic benefits.

But you'll find that in general, people pushing their systems towards the higher extreme of sound quality or output will have more power on tap than their speakers are "rated" to handle. There are some SQ competitors that have 2kw worth of amplifiers on their frontstage. I have a 285w x 2 amplifier on my front speakers which are rated for...60w RMS I believe.

The main "rule of thumb" I suggest when someone is looking for an amplifier (and have the knowledge to handle it) is to purchase the most power they can for their money (while keeping product quality in mind).

 

[joetama 5,000+ posts]

Well basically there are several reason for the difference.

First of all as you push an amplifier harder and harder the THD% gets higher and higher. So, if you were to only use half of an amplifier's power to drive a speaker system then you have much less distortion and noise than you do at full power. So it is always favorable to do this and have plenty of headroom, in Pro/Home/ and Car. However, many reasons in car audio don't let you do this. Amps with more power are usually much more expensive than amps with less. So, most people go for the "best" fit instead of having that extra overhead power.

You also have less 'gain' noise, that 'hissss' sound, when you go with a more powerful amp and have to drive less pre-amp gain in a console. In a car that hiss usually isn't noticeable because of road noise and or other car sounds. In a quite church this hiss of gain noise is very noticeable. Also, the least about of pre-amp gain you can have is very favorable for live microphones.

Furthermore, you have a much greater distance to the speakers from the amplifier than you do in a car. In a car you might have 12 ft max speaker cable, in a chuch or club you might have 30, 40, or even more distance. In this cable you loose a lot of power.

Also, the human factor is a big thing. Most people in car audio haven't been dealing with audio long enough to know exactly what they are doing. Overdriving and damaging a speaker is very easy. So, for most people getting a amp that is = to the speakers RMS is probably the best.

I personally have lots of overhead on my system. But, I know how to set gains and know when I hear distortion.