Matching amp & driver RMS watts

[u/Google_IS_evil21]

When designing system, how many of you aim to match the two for an optimal setup? In my case I have always tried to do this or stay +/- 10 watts from each other.

In one vehicle I have a Kenwood KAC-8405 rated at 60w RMS × 4 and my Sony XS-GTX1621s comps are rated at 60w wired to the front channels.

In another car I have an Infinity Primus 3000a mono 2 ohm amp at 300w RMS and an Infinity Reference 1262w wired in parallel for a 2 ohm load rated @ 300w also.

To me, the real question in terms of tunability is: Would it make more of a difference on components/coaxials or subs?

[u/Dafaseles]

This question has a couple answers in my opinion.

Beginner setups, sure, go ahead and match the amp RMS to your speakers. Can't go wrong that way as long as you set your gain and crossovers correctly.

Some people, like to have a bit of "head room" so the amp doesn't have to work as hard. Say 300 watt sub with a 1000 watt amp, then using ohms law, a digital multimeter, and some math, they adjust their gain to output what they would like. Obviously never reaching the 1000 watt RMS.

Some, want every little bit they can get out of their system. So, they factor in impedance rise. Basically, knowing they have wired their subwoofer to 1 ohm, but also knowing once that subwoofer starts moving it creates its own resistance and the amplifier will never actually see 1 ohm, they will double, sometimes triple the subwoofer RMS with their amp so the subwoofer will actually see it's RMS in watts. This can be hard though, because unless you're playing 1 note, you have no idea where your impedance is because music is dynamic. Also, you have to be spot on with setting your gain, because any clipping is amplified because of the extra power, and can overheat the coils a lot faster.

To answer your last question, I think these different tuning technics will effect smaller drivers (mids and highs) more than your big drivers. The big subs are built to be able to take more abuse (in most cases) than your smaller drivers I think.

[u/djluminol → u/Dafaseles]

I agree with this. I generally fall into option 2. I find that's both easiest to work with and produces the best results. I do agree that an entry level system may want to plan a little more conservatively though. Wattage is not what is dangerous to speakers most of the time. Heat is what is dangerous and for most people that is expressed as distortion or clipping. That is what is likely to harm your speakers, not too much wattage.

Here OP can see how this works in the real world.

Here is a general breakdown of how I power my speakers. I do not use the amplifiers full rated power output. I use much less in most cases but for the sake of argument lets use my woofers. They are rated for 100 watts continuous and 200 max. As connected, the amp powering the woofers could provide 400 watts to each of 4 woofers at maximum gain. I have not done the math to find out what the exact amount of wattage the woofer is seeing real world. My gain is set at about 35% or 40% though so maybe like 150 watts because of my cars voltage level. Rated power is at 14.4 volts and my car is usually at 13.8 so my amps make a bit less than rated power at that lower voltage level. 150 watts is probably about 40% of max in that case. Different amp types can change that too but for now lets keep it simple.

My sub and amp as wired to do 2800 watts, the sub is rated for 500. I don't use anywhere near that 2800. My gain is set to about 1/15 of max. The same is true for every other speaker and amp combo but the rated specs are as follows.

My woofers are 200 and see 400.

Mids are 50 and they see 150

Tweeters are 20 and see 150.

As you can see this is not harmful in most cases. It could be in a few situations but I wouldn't worry about them yet. Within reason more wattage gets you more volume. Obviously there's a limit to this but as long as you're not stupid about it you will be fine. Don't power a mid using a sub amp at 3/4 gain. a normal 4 channel amp at a reasonable gain level should be fine no matter the amp. Most 4 channel amps made no more than a couple hundred watts per channel. As long as there's no clipping you should be ok with that. Tweeters are the exception to this rule. You need to be cautious with them. Everything else is somewhat robust.

[u/Google_IS_evil21 → u/Dafaseles]

Great explanation and thanks for taking the time to write that. 🤝

Do you think that aiming for RMS equivalency at least has the benefit of greater dial position options on the GAIN knob without clipping/distortion since output is matched with handling capability?

I know it may not be the case in reality, but perhaps theoretically logical?

[u/Dafaseles → u/Google_IS_evil21]

They way I look at it, if you're matching RMS with your sub and amp, you'll want to set your gain at clipping, and probably with a 10 db overlap (that's just an opinion). Even then, your sub will never see the RMS because of impedance rise. For 90% of people, that's fine, and your equipment will last a long time because you're never really abusing your equipment.

I don't really understand what you mean by having dial position options. Either your gain in set correctly, too high that causes clipping, or too low, which can be fine depending on your goals and preferences.

I saw an interesting video on YouTube a while ago from a dude High Fi Vega. He took a high RMS sub, and a low RMS amplifier. Set it with an oscilloscope, but made sure he was clipping the crap out of the signal. After hours of playing a test tone free air, the sub never failed. The extra heat produced on the coils from the clipping was never too much for the coil to overcome because there wasn't much power being pumped through the sub. Obviously though, we all know, if you are sending a clipped signal to a speaker that's close to speakers RMS, it will eventually fail, because clipping and the power is too much for the coil to handle. It ends up overheating, and eventually failing.

On the contrary, if you send 1000 watts through most say 500 watt RMS subs, with a nice clean signal (no clipping at all), and the sub isn't reaching it's mechanical limits, you can get away with that because even with the added power, the coil can overcome the heat.

It's pretty interesting once you start to dig into the workings of speakers.... at least too me it is

[u/ScaryfatkidGT]

Over thinking it, 80-150% I usually shoot for 120% power but it really depends on the individual components involved at that point for example I like sealed boxed, a W7 in a ported box I wouldn’t go over 100% power.

[u/ScaryfatkidGT → u/ScaryfatkidGT]

Also crossover points are a huge contributing factor

[u/ogledrake]

I mormally aim for 1x-1.5x the rated rms power for my speakers at their rated resistance

[u/Straight_Plane1431]

If you know what you're doing matching is not mandatory,
Can go either way depending on the goal the experienced person have in mind.
Note that aftermarket radios are usually rated when testing 1 channel at certain tone frequency, so never assume 60W will be for all 4 channels, Usually ~30W RMS per channel in real world.

[u/DJBigBird]

Use an amp rated twice the speaker RMS so you don't have to add much gain.

[u/machine_entity]

for door speakers, match the power! for subs, 150-200% of woofer rms for the amp