Axiom Home Page Forums General Discussion Technical Questions Amplification neede for the M80s & measuring WPC

Simple and quick question:

What is the recommend power output of an amplifier that will adequately run the 4 ohm M80s? I'm looking at a used NAD receiver that only has 80 WPC X 5 channels. What does Axiom recommend for these speakers to really sing?

I should also ask if someone can help educate me on watt ratings. I fully realize most manufactures give figures that represent WPC at 8 ohms. Is there a conversion for 4 ohms or is it different for each receiver. Secondly, if this NAD is 5 X 80, is that not 80 per channel, thus I'd only get 80 for each speaker?

Any help here would be greatly appreciated.

here are some basic answers to your questions:

1 - NAD will probably not power a 4ohm load. Axiom and other M80 owners such as myself recommend Harmon Kardon or Denon in the low cost receiver groups. If you are going to spend more, buy the best amp you can afford that wil offer the most clean power. I hear www.outlawaudio.com makes excellent products at a fairly good price. You can get their monoblocks, I believe they give 300wpc into 4ohm.

2 - the M80's are ridiculously efficient speakers, needing little wattage to play loud. That being said, the amount of wattage you will need will depends on your size of room, your playing levels, and if you have a sub or not.

If you have a sub to play the bass, the m80's will need less power

The larger your room size, the more power you need

The louder you listen, the more power you need

3 - if it says 5 x 80 it is claiming 80 watts per channel, which means per speaker. it likely does not give you that much power. Try the NAD website for specs on the receiver to see what it will give you at lower impedences. If it's 80 into 8, it's likely going to be something like 110 into 6, and if there's a 4 rating, it may be 120-130.

But as far as I can remember, NAD doesn't play 4ohm speakers very well. I'd go Denon or Harmon Kardon. They have models available for anywhere between $500 - $4000 CAD. I have a Denon 1602 and it plays the M80's without a sub. It's rated at 70wpc into 8, 110 into 6.

TK, specific watt recommendations aren't particularly useful. As Ravi mentioned, there are several factors which affect power required. For example, the type of music can be relevant in that classical music can sometimes have greater dynamic contrasts than most pop music and will place a greater load on the amp at peaks. During average comfortably loud moments only one or two watts are necessary for the speakers to "really sing". Split second peaks may sometimes call for 100 watts or more.

In theory(Ohm's Law) a receiver would put out twice the power when the speaker impedance is reduced by half from 8 to 4 ohms, but this is almost never obtained in practice and an increase of about half is a fair ball-park figure. Note that NAD receivers are rated with all channels driven at full rated power for at least 5 minutes continuously. This is a severe and rather unrealistic test which would never be even remotely approached in ordinary home use. The more realistic two channels driven standard used by the FTC and which most manufacturers follow would give that NAD quite a bit more than 80 watts per channel. So, although there's a tendency to exaggerate power requirements, that NAD would probably do very well with the M80s.

Hi TK,

Actually, NAD A/V receivers do drive 4-ohm loads, and I somewhat guardedly recommend them, based on our customer feedback, for the M80ti's. My reluctance with NAD is based around a somewhat iffy reliability record in the past, which I've been told has now improved.

However, my first recommendation is always Denon and H/K, because they will drive the M80ti's without problems, so long as you don't try and power them in huge rooms with insufficient power.

Consider the total volume of the room as well as your own taste in sound levels. Some enthusiasts, including several of my colleagues at Axiom, like volume levels that I find "deafening", in which case they typically use power amps with at least 150 watts per channel ratings.

In average rooms of 2,000 to 4,000 cubic feet, the M80ti's can be driven to clean, very loud listening levels by A/V receivers (note the brands I recommend) rated at 80 to 110 watts per channel into 8 ohms.

Regards,

Alan
Is there a list where a person could find out "true" WPC on any given reciever?
I'm just curious after tradeing in my H/K130 for a Denon 2805 if I actually gained much "headroom".

Alan: Thanks for the concise update. I appreciate your wisdom.

I do have a follow-up question. If my dimensions of the room are 16 by 24, with a 9 foot ceiling, wouldn’t you say the 80s are a bit much? Also, I'm worried that I can not put them 3 feet from the walls. My wife has issues with them being so out. So don't you think the 80s are too much? Also, how far must the 60s be from the wall to sound right? Overall, to me--and without having heard either--considering the size of my room, the 60s are sounding more appealing.

TK I don't think M80s are too much, but M60s are fine for your room. M60s plus a powered subwoofer would significantly unload your amp, since the sub has its own amp.

I formerly had an amp with front panel watt meters. On speakers roughly as efficient as M60s, 0.1 watts was a nice level, 1 watt was very loud. 10 watts was beyond punishing. Also bass demands most of the power. The power needles would barely move without bass activity.

Either choice will sound great, M80s or M60s plus a sub. If you plan to add a sub anyway (say for home theater), I don't see the need for M80s. For your big room consider the Axiom EP350 subwoofer or higher, or competing products from Hsu or SVS.

Regarding distance from wall, you don't necessarily need three feet. Note there will always be conflicts between optimal acoustics and aesthetics. I've put my M60s from 1 ft to 5 ft from the back wall, and 1 ft to 4 ft from side walls and I can't tell much difference.

I have seen a big difference between various acoustic surfaces. No carpet vs carpet, amount and location of furniture, presence or absence of draperies, etc can make a huge difference. However you don't always have a choice.

Any Axiom speakers you get will probably sound better than anything you've heard, whether they're 1 ft or 3 ft from the wall.

M60s normally like to be ~15-18" from the wall...

Your room sounds ideal for M60s.

Bridgman: If you don't mind me asking, how large is your room that your 60s play in?

I just (in the last few days) moved the M60s down from a 12 x 17 bedroom to a 13 x 23 rec room in the basement. In the new location they are ~4 feet from the back wall but that is for access to a patio door, not because they need that much room.

Here's a quick sketch of the layout. Having the bar and fireplace opposite from each other is bad enough for normal furniture placement but makes it REALLY hard to put an HT in without dedicating the room. I know I suck at interior decorating, any suggestions appreciated. Until a few days ago the system was set up against the right hand wall which was OK for 1-2 viewers but really looked bad.

[EDIT] Forgot the picture, must be getting late. There is a VP100 on top of the TV although I forgot to note that on the floor plan. The room is probably closer to 12 feet wide than 13...



IMO the M60s are arguably bigger than I need for the room. I bought them for two reasons :

- I wanted a pair of "truly full range" speakers I could use for stereo music playback without a sub

- moving in 6 months to a new house with larger (and fewer) rooms