Amplifier and Speaker Matching 101: How to Choose the Right Power for Your Sound System

The video explores loudspeaker power ratings and the importance of matching speakers with the right amplifiers. Barry, a sound engineer, debunks common myths and explains the implications of underpowering and overpowering speakers. He discusses power handling, amplifier clipping, spectral density, and distortion, offering insights into speaker protection and system optimization. Barry's nuanced approach emphasizes understanding manufacturer specifications, avoiding extremes, and ensuring adequate headroom for optimal performance.

[AT-wlyq]

I know the video was well intentioned, but there was quite a bit left out. To start with, there's no standard that manufacturers have to go by when rating an amplifiers power (or any other measurements). Each company does it as they see fit. If you take 5 or 10 different amps from different manufacturers and measured them all the same way, every one would be different. How different depends on how honest the manufacturer is.

Beyond that, when you are trying to match an amp to a speaker, the single most important factor to consider is the lowest resistance the speaker shows the amp. That's the figure that's going to tell the amp how hard it has to work. When you look at a speaker that has an 8 ohm rating, for example, that's just an average. A speakers resistance determines the power output of an amp. And a speakers resistance changes with frequency. If you look at the specs for any power amp, you get a number in watts, like 100, but they also give you a number for resistance. You would see something like100watts at 8 ohms. And since we know an 8 ohm speaker will be an average derived from frequency, the only way that amp can actually be 100 watts is at the single frequency that shows an 8 ohm load. If the speaker has to reproduce a higher note, the speakers resistance be higher, like 16 ohms. At 16 ohms, you have a 50 watt amp. Literally. And if the speaker needs to play a low bass note, resistance may now drop to something like 4 ohms, and if the amp is made well, its now a 200 watt amp. This is where the problems start with power ratings. The lower the resistance, the harder the amp has to work. 0 ohms is a dead short. If you turn your amp on and touch the speaker cables together, that's 0 ohms.

To use all this info in a practical sense, lets say you are looking a 2 pairs of speakers. Both of them have an average resistance of 8 ohms. However, one speaker may drop down to 4 ohms, and the other 2 ohms. The speaker that drops down to 2 ohms is going to be much harder to drive, Lowest resistance is the single most important number to look at.

There was one huge thing that was left out of the video. In pro audio, its very common to bridge stereo amps into 1 channel. A bridged stereo amp is not a mono amp, its a bridged stereo amp. The rules change for bridged amps. When bridged, an amp sees the speaker at half its normal resistance. Your 8 ohm speaker that drops down to 4 ohms is now a 4 ohm speaker that drops down to 2 ohms. The amp has to work twice as hard to drive the exact same speaker.

One last thing worth mentioning is extremely high wattage ratings. When you see an amp rated for 500 or 1000 watts, its just ridiculous. Those power ratings are going to be based on the lowest possible frequency its asked to reproduced. As the frequencies go up, the amps power rating goes down. Not only that, 90-95% of the amps on the market inflate their power ratings by how they take the measurements. They use test tones, not music. Its extremely easy for an amp to reproduce a constant test tone that doesn't vary. Watts are an artificial number based on something that can't happen in real world use. If you rated that same 1000 watt amp with music going through it instead of a test tone, the actual power is a small fraction of what the test tone numbers are.

[rallisdemarseille]

Barry, I honestly throw one comment on YouTube every 5 years or so, and I gotta tell you that you and your YouTube channel are absolute gems
Thanks for the knowledge sharing, thanks for the dedication
(And don’t stop doing tractor and truck videos)

[msk]

Very interesting and helpful. I learned things that I’ve been curious about for decades and you make it easy to understand.

[themixedupkid]

Glad I found your channel. I’ve learned so much in just a few short videos. Thank you for the audio advice

[adamswanson]

Hi, I have an amp I care for very much. It is a Marshall 2525C the silver jubilee studio combo I actually have all four of those studio models lol. Either way the one thing consistent is the sharpness and the trouble of course also in the 20 W amp And summon senses their areas where I wonder if a higher wattage speaker rather than using the green back which is in the combo when I cannot carry an extension speaker cab, which I have scumbag speakers in what would be the ideal speaker I thought a cream, but then I was looking at the Celestion and even considered because my Mesa boogie Fillmore 25 has the 90 W Celestion Al Nico magnet speaker, and I wondered how this would sound in my silver jubilee and would it increase the headroom in anyway 2:02 2:05 2:10 and or deepen the Sound as well there is not a deep switch for the amp thanks any other advice about ideal speakers with the best Sound clarity and death I would love to hear any advice for this amplifier truly The greenback is OK but just not really OK thanks. Also look at a couple of eminence products. Mostly the governor.

[jaycoleman]

Very cool video. My journey brought me to less (81db) efficient speakers and 100w of hybrid power. As the speakers are 3 way with a 6 inch tweeter, they sing when the amp hits about 60%. Understanding decibels was cool too. My amp & speakers are from the same manufacturer so it was a small leap of faith, which I love now. Subwoofers are a mixed breed to me. Many sound like a loud mess like the concerts from the 70s/80s. Tight bass, imho, is tough depending on the room. Such a journey. ❤

[halrichard]

Dude, who are you! You are absolutely one of the best communicators I have come across in the world of audio. No one talks like you without having a triple digit high IQ. I am grateful to have come across your channel. I hope you will continue to give us balanced truth. Thank You.

[mikehawkings]

Recently been able to upgrade piece by piece.
Matched the amp continuous wattage to the speaker max input. Whereas the previous amp had just over half the speaker max.
I was concerned of transient peaks but now i am not tempted to push things anywhere near what i did before. No need. Anything around the 10o'clock point on the volume damaging to ears let alone anything else.
Headroom, soundstage, low frequencies are in abundance at very low listening levels.
Your advice about not pushing things is very welcome Barry.
From a budget Cambridge Audio 65wpc driving some very cheap TDL 130w 6ohm.
To Fyne Audio F303 120watts being driven by (o.k its old) NAD C370 120wpc.

[AviewFromUnder]

I start by saying I agree with your point of view on this subject and thanks for posting, I hit the button! I'm just adding a little color! At the end of the day If someone is the kind of listener mixer that can destroy speakers with a small amp going DC they should introduce themselves to A lighting desk. As that is akin to saying when you drive on narrow roads you don't like how much time is spent in the ditch so I want wider roads. Slow down driving is the job, staying on the road is the first order of business. The choice to blow speakers was the person on the throttle not the amp, under sized or not (proper output impedance considered here). Before any speaker is destroyed woofers for example will sound like a cardboard box getting slapped with a tennis racket. Bigger power wont fix that kind of talent. Yes too small of a system in too loud of environment will make it less apparent that speaker abuse is going on but it remains the first order of business in progressing with amplified live content in speaker systems. Good luck to all and remember learn to keep your crayon in-between the lines!

[johnh]

Great explanation . A trough expert is easy to spot and understand.
In a sense my only real question is how much this applies to most people, surely you would have to have your volume excessively loud before you where risking your system, or at least a verry badly mis matched one.

[dimitrioskalfakis]

'sound' qualitative analysis and advice ;-)

[WhatItBeLike]

I too have learned a lot from you Barry, thank you for the content. Can I ask .. what do you run at home for your music enjoyment?

[arvidstorli]

Watt ws watt. Or what watts. It's interesting to see how the relationship between continuous power, and peak or maximum power has changed. Compare class A/B with transformer, - A/B with switchmode power / variants like EE-Engine ( Yamaha ) and class H powersupply - and now class D, also with smp. Higher peaks compared to continuous, but that makes sense, music isn't continuous levels, at least not what I listen to. And if the peaks Perhaps the subject of another video :)

[ericnortan]

I have a NAD 216 amp with a clip limiting function. Older amp I picked up because I wanted a spare that sounded good. Nice little amp, don't know how good clip limiter works. It just seems to me if you need to use that your amp is too small in the first place.

[chriscook]

I have a pair of speakers that I want to connect to a kenwood amplifier and I’m not sure the amplifier is powerful enough and how I should wire it. I’ve tried understanding parallel Wiring and if it would double the power but I’m still confused do you have a email or other way we can communicate besides these comments let me know if so

[ericnortan]

My basic rule has always been to have an amp rated higher than the speaker peak so the speaker has everything it needs when it needs it. I know that is just one part of amplifier choice, but I think it is a good starting point. I am not a pro, just talking about HiFi, and rarely do I turn up the volume so high that it stresses my amp ormy speakers. In fact never. I have big, loud speakers and a very powerful amp. Yet, I generally listen at sane levels in my living room. Though I do like to crank it up sometimes.

[brandondavis]

Sound Man Barry! I need help! I have to run sound outside for a festival. I don't want to blow up my equipment. Will a regular generator work, or should I rent one with an inverter. I found an inverter generator that's 300watts. I'm running a Peavy 400watt mixer head, into two 200watt speakers, with a passive monitor, and I'm bringing my QSC 1450 with an Ashley bass preamp into an old Sonic 2x18 2x10 cabinet. I have no idea how to calculate total power draw. I'm really just a musician that got roped into doing this. They normally hire a sound company, but they don't have the money this year. The bands are traditional Irish bands with all acoustic instruments. I just don't want anything to blow up. Please

[RustyRaceHorse]

I dont understand how you can overdrive the amp. It the volume knob goes to 11, then the amp should be able to take it. The eq too. They should make em to take it.

[lukegowest]

I am surprised that you didn't mention one of the easiest and cheap way of protecting drivers is to fuse them. Blowing a 25 cent fuse is much cheaper than replacing a driver, or a diaphram. On the subject of power ratings, I always have to shake my head and laugh whe I see a plastic stero at Walmart with big letters saying 1000 watts, and the whole thing only costs $29.99

[fedgeno]

It's also possible to launch the whole cone out and have it hanging by the leads 🤣