Axiom Home Page Forums General Discussion Advice from Axiom Owners Sufficient Amp for M60s - Large Bedroom

Hey all - haven't been on the forums for quite awhile. I'm looking for some advice on a new low-priced amp to drive my Axioms.

I am moving my beloved M60s to an upstairs master bedroom that's about 350 s.f. in size, roughly 17.5 x 20 feet. They'll be playing streaming digital music from my Sonos, but I know from experience that the Sonos' built-in class D 50 watt amp can't drive the M60s well. (Actually, it can't drive anything very well, but it's okay at medium volumes on my M3s and Ascend Acoustic bookshelves.) I plan on passing the Sonos signal to a separate amp.

I like the prices and products at Dayton Audion/Parts Express, and they have this APA150 Power Amp for sale at $125:
Dayton Audio - APA150 Amplifier

In stereo mode, it's 75 watts a channel. Do you think this will be enough to drive the M60s? Key point - this is a bedroom. I like to turn it up sometimes in private, but this won't be a party room where we need high volumes often. I don't want to spend too much on this amp, but I also am strictly buying it to power the M60s, so I want it to work.

I would think 75 watts should be more than plenty in a room that size. At least for safe listening levels. M60s are not that power hungry despite their intimidating size.

However, if you like it 'ear splitting' then proper amperage gets expensive quickly.

Edit:
Here is a calculator to estimate the amps required based on the speaker, distance and listening level. Plug in "91" for the sensitivity of the M60s.
Amp Calculator

For instance, at 6 meters, 75 watts would allow for brief peaks up to 95 db which is pretty loud. Some like it louder but you are hurting your ears.

Thanks - awesome calculator. According to that, with a desired sound level / dBSPL of 85, I have plenty of power - only need 13 watts to do that. (Of course it rises quickly, exponentially, as the volume goes up.)

But, if you only need 13 watts, why wouldn't the Sonos amp suffice?

The answer to that is over my head, but I can tell you the Sonos digital amp (in the current Sonos Connect: AMP) just sounds crap-ass to my ears, whether it's pushing my M3s at above average or M60s at average. The 50W amps on the original Sonos 100ZP sounded better, but they still clipped when I pushed the M60s to any above average level (85-90 ish). Why that should be, I don't know - but IMHO Sonos is great for connectivity and all-room audio solution, can't be beat. But for sound quality, they don't deliver. So I try to get the critical listening into different amps and avoid their expensive mobile boom-box devices.

PS - Also, I thought that amp calculator was a bit low-ball myself. My hunch is I certainly want more than 13 watts for good sound at 85dbs pushing M60s in a 350 s.f. room. But seems like a good 75 wpc of A/B design amp out to do it.

I hear ya. Even before I asked the question, I was speculating that the Sonos class-d amp just might not be very well designed. It seems like that Dayton amp should do the trick.

I've heard good things about the APA150, quite a robust and heavy little amp. Let us know what you think of it if you pull the trigger on it.

Birdman, although it's been pointed out several times here that the Crown calculator gives a result far too high for home listening rooms, it continues to be cited occasionally. Crown is primarily a pro amp manufacturer and the calculator is designed for use in relation to open spaces rather than enclosed rooms. This fact isn't indicated in the calculator screen but only in a separate discussion here and only rather less than prominently under "Other Considerations". They suggest a 6dB correction for use in enclosed rooms rather than anechoic outdoor venues. Without this 6dB correction the calculator result is 4 times too high.

You don't mention the key factor, listening distance, but at a typical 10 feet, your M60s use about 1 watt for a 85dB sound level. 75 watts would supply a peak of about 103dB.

Thanks, John - I'll take that as a "Go for it!"

Hello Austin,

Before you press "Buy", it's worthwhile to carefully read the specifications for the Dayton Audio amplifier:

Features and Specifications: • Measured power output: 2 x 75 watts RMS (into 4 ohms @ less than 0.01% THD) • Signal-to-noise ratio: greater than 100 dB • Class A/B design topology • Input impedance: 47k ohms • Auto-on sensitivity: 3 mV • Voltage requirement: 120/230 VAC, 60/50 Hz •

Note that the specs are misleading. The amp is rated to produce 75 watts per channel into 4 ohms, not 8 ohms. So you should expect roughly half the 75-watt rating into an 8-ohm load like the M60s. Companies rely on consumers NOT reading specs carefully, so they cheat by quoting misleading power output specs.

Regards,
Alan

Hey JohnK.

The Crown calculator is probably cited so often as it comes up as the first hit on Google. I used to cite another calculator but I couldn't find it so I was indeed lazy.

I'll consider my hands appropriately slapped.

Hmmmm, my parade is feeling rained upon - but I respect your love of power, Alan.

It's not so much a love of power, but a love of honestly stated power output ratings. To get the power you want with your M60s, you could get two of these amps, and run them in bridged mode, one per channel, which would yield 150 watts per channel, bridged, into an 8-ohm load, if we can trust the Dayton specs.

As is, run in a stereo mode, you'd be getting about 37 watts per channel into 8 ohms, which isn't a lot of power.

Slapped AND shamed on the same day?

You better consider coming up with a safe word, Murph.

just get some Outlaw amps.

Birdman, the "rain" would appear to be just a light drizzle. The APA150 is rated in compliance with the FTC power amplifier regulations. The theoretical maximum increase between an 8ohm and 4ohm rating is a doubling into 4 ohms, but this is almost never achieved in practice. More typical results are around a 50% increase, which would imply about a 50 watt 8ohm rating. 50 watts would be used for a peak of about 101dB, rather than 103dB with 75 watts.

It's unlikely that these slight power differences would be appreciable in your bedroom setup.

All the advice here encouraged me to keep looking, so I jumped on Craigslist, and lo and behold, found one of these for a mere $150, in perfect condition:

Sonamp 275 BBE

The thing sounds awesome. Fills the room just fine and I've now got a great new critical listening space with the M60s. It's got a genuine 75w per speaker at 8 ohms. There's a gimmicky sound equalizer mode for iPods, but with that off, it's great, auto/on etc. And the enhanced mode might even help some of the higher res MP3s, since this is a Sonos all-digital setup (most of the music is in Apple lossless).

Much better than owning two Dayton APA150s, and cheaper too.

Good for you. It's always fun to get cool stuff and saving money.Have fun.

I said "it" a bunch of times. Either nobody cares or "it" is a poor choice of safe words.

Birdman, the Sonos seems like an excellent buy and it's to Sonos's credit that the company honestly states the amplifier's output capabilities and gives detailed specifications on distortion and frequency response. You'll have plenty of clean power on tap.

This may also be a good candidate (it's on sale!): Emotiva mini-X a-100. It should drive the M60 with ease and it will make a great combo for a bedroom.