I recently decided it was time to own my own home theatre and stop mooching our display models over the weekends. This seemed like a good idea because not only would I have my own dream setup, but I would be able to test other equipment against a known baseline for my reviews.
All I needed was a well-matched speaker and an amp. No problem right? Wrong!
Lucky for me I feel in love with Yamaha’s A-S501 amplifier the moment I met it. Ooooh, that sexy retro simplicity. This amplifier peaks at 120Watts per channel and has a RMS of 85Watts per channel. This means that in short bursts it can reach 120W but it can sustain 85W all day long. This is an important distinction that I will need you to remember. If you care about this stuff you may want to start taking notes now. It’s about to get messy.
85W RMS in hand, I went hunting for speakers. The obvious choice for my small space would be bookshelves. I started with the Prestige 15B because I am a fool for a pretty lady and you can’t beat the Prestige series for being pretty. The 15B has an amplifier rating from 15W to 150W with a max input of 90W. This means it will play with as few as 15W. It can also handle amplifier up to 150W (if you are careful not to turn it up too high). The 15B will play all day long on up to 90W. More than 90W will damage these speakers.
I took the 15B’s home for a test drive and was shocked how far up I had to dial my amplifier to get decent volume. Numbers alone, the AS501 should have had no problem working these speakers to their very edge, but I wasn’t really getting comfortable until 2/3rds volume. This seemed too close to the limits to me. What if I wanted to dial them up for a movie or a party?
The next morning I went in to talk to my product expert Rick. Rick explained that although the speakers are rated at 90W Max the Prestige series uses that power inefficiently. Basically, it takes a whole pile of Watts to get the heavy-duty cones moving. This helps iron out unwanted artifacts in the music. It also means that the speaker will not play as loud at the same power level because it needs more force to vibrate. (This is actually a good thing, and a common trait of premium speakers.)
Rick suggested I try Paradigm’s Mini Monitors for comparison. Mini Monitors are rated for 15-100W 80W Max. I figured they would react similarly given the similar numbers but Rick explained that the Monitor line is far more efficient than the Prestige line. I went home not expecting much, but remembering his cautions to be careful.
The Mini monitors exploded to life, and by the time I reached a 1/3 volume they were exceptionally loud. By 1/2 volume the speakers were bouncing of the limits of their surrounds and I had to back down.
I was shocked. By the numbers alone I would have assumed that I could have driven these speakers almost to full volume without risking damage. There I sat; listening comfortably at 25% volume, and limited somewhere under 50%. The AS501 could clearly drive a much larger speaker in the Monitor line because they use the power more efficiently.
The next day I was back at Ricks’ counter looking to see how far I could push the AS501. I wanted to test the big daddies of the Monitor line. A pair of speakers that I happen to really love; the giant Monitor 11’s!
I asked Rick if he thought they would run on my moderately sized amp. Monitor 11’s are rated for 15-250W 180W Max. Because my amp peaks way below this, I expected Rick to laugh me out of the office. To my surprise, he did not. Instead he explained that though I would probably need to dial my volume up a bit, they would likely be closer to the levels of the Mini Monitors.
I would have assumed that I would need twice the volume to achieve the same amount of noise with the Monitor 11’s. Rick explained that though the max power rating is 2.24 times higher I was missing a critical consideration. Speakers have crossover switches that control power to the different cones and tweeters. These switches cause power to be used differently than I expected.
Rick explained that as I dial my amplifier up, I am actually not increasing the power output directly. I am increasing the desired volume. The amplifier then sends Watts to the speaker tower. Once the power enters the tower a switching block, like a sorting machine breaks the power down into separate streams in order to fire different cones. Tweeters only need a little power for the high notes, then the middles need a little more, and finally the bass speakers need a bunch.
Compared to my volume, which remains steady, my power usage will jump up and down depending on the music. A big crashing rock number will need big surges of Watts to punch those woofers in time to the bass and drums. An equally loud solo on a flute will only need a little bit of power because it does not need to fire the woofers at all. (If you have an amplifier with analogue sweep gauges on the face, it is these surges of power that make them dance at a set volume.)
In fact, Rick explained, I might experience the same loudness with the towers and with the bookshelves, at the same volume level on the knob. The difference in power usage will be hidden inside the amplifier.
Because the tweeters and mids on both the Mini Monitors and 11’s are similarly efficient they will come up to volume easily and quickly. However, the amplifier will have to send more power to the towers when the crossover switch sends Watts to the woofers for low notes. The kick of a drum at a certain volume on the bookshelves might take 20Watts while the same kick on the towers takes 60Watts. This is because the crossover-switch fires 6 woofers on the towers instead of only the two mids on the bookshelves.
Will my A-S501 be able to achieve the same maximum volume on the equally efficient towers and bookshelves? No. The limiting factor is no longer the speakers themselves but the power of the amplifier during certain listening conditions.
Symphonic music that forces the towers to fire every cone throughout the range will take a pile of watts. As I turn this music up, the amplifier will eventually run out of power to kick the bass drivers. This condition is called clipping.
Clipping also known as “popping” or “farting out” is how you know that the amplifier has reached its limits for the song you are enjoying. YOU NEED TO DIAL IT DOWN FAST. Sustained clipping will either burn out a speaker by heating the coils until they melt, or you will torch the amplifier as the circuits heat up from the massive flow of electricity.
Lucky for us, we don’t need special tools to diagnose clipping. Just listen for a pops, clicks, and weird farty sounding bass in heavier sections of music. If you hear it, back off the volume until it stops. Brighter songs will be able to play louder, but turn down that heavy metal.
So how do you know what a particular amplifier and speaker will sound like together? Well it’s not in the numbers. For general advice, you should deal with person you trust; like Rick. Ultimately, the best thing to do is, find a store where they will let you demo the pieces you want with your music. The numbers can say almost anything, but your ears will know right away.
P.S. I’m not bringing the Monitor 11’s back. They like it here in my living room.
