[Freo-1]

From what I've seen the majority of Solid State amps will give a double the power rating from 8 ohms to 4 ohms to 2 ohms.
Frank told me that Tube amps have the same output regardless of the ohm load.

It seems to me that I read somewhere on some circle that there are SS amps with the same output on all ohm loads. I can't remember
what this is a result of. Can some of you more knowledgeable folks elaborate on this?

Thanks

James

Many McIntosh SS amps are the same power at 8 or 4 ohms.  That is because of the autoformer (same as a output transformer for a tube amp.)

[pansixt]

Thanks Freo, That may have been what I read about previously.

[Letitroll98]

And with many tube amps you can use the 4 ohm tap with Maggies, making them a perfect match for the current delivery they want.

[/mp]

I'm starting research for my first dedicated room.  I have nothing right now but a 9x11 1/2 empty room.... 

I listen....never more than moderately loud, and rarely even that....
John

Hi John,

The amount of sound a speaker generates is typically described as number of db produced for 1 watt input at 1 meter distance. We generally listen from a greater distance but stereo uses 2 speakers. The extra sound from the extra speaker roughly equals the sound lost from listening further away.

The efficiency with which different speaker design principals convert electrical energy to sound energy vary considerably. A very rough rule of thumb say horns produce 100 db for 1 watt input, cones produce 90 db for 1 watt input & planers produce 85 db for 1 watt input. These numbers are based on anechoic measurements. In the real world room volume matters a lot. Sound waves reflecting of room boundaries reinforce (in some cases, cancelling) the sound waves heard directly from the speaker making speakers sound louder. I do not recall a rule of thumb. All other things being equal, bigger rooms require more powerful amps, smaller rooms allow less powerful amps. 

I googled decibel chart and compared several sites. Most examples are too vague for precise work but illustrative examples include: Quiet bedroom at night, 30 db; Conversational speech, 1 m distance,  60 db; Kerbside of busy road, 5 m distance, 80 db & Chainsaw, 1 m distance,   110 db.

Power required to increase sound pressure level (db) increases logarithmically. Doubling power adds 3 db. 10x power adds 10 db. 100x power adds 20 db.

How powerful do amplifiers need to be? 2 extreme & 1 hopefully more practical example: 1) Music played louder than loudest rock concert (120 db, 130 db peak) on ultra inefficient speakers (80 db @1 m) requires 100,000 watts; 2) Music listened at quiet levels (70 db avg, 80 db peak) on ultra efficient speakers (110 db @1 m) requires 0.001 watts/ch; 3) Music mostly played quietishly (65 db) with the occasional orchestral climax (105 db) on inefficient speakers (85 db @ 1 m) requires 0.01 watts for the average passage and 100 watts at the loudest peaks.

Your trusty NAD 3020 puts out 30 watts continuously which is plenty most of the time. 30 watts into an 85 db efficient speaker becomes c. 98 db at your chair. The NAD also has 3 db dynamic headroom (IIRC, I sold mine ~30 years ago.) For short bursts the hypothetical speakers will produce just over 100 db.

N.B. These amplifier produced watts are at specified distortion levels (typically ~1% for tubes & ~.01% for solid state but that's a whole other lecture) Amplifiers almost always can increase their outputs somewhat but with more (often much, much more) distortion.

Bass is more difficult in smaller spaces. The length of low frequency sound waves exceed the length of the room.

Hope this is useful and enjoyable,
/mp

[Johnaki]

Thanks /mp,

It was very helpful and I'm enjoying the entire discussion.

John

[josh358]

I googled decibel chart and compared several sites. Most examples are too vague for precise work but illustrative examples include: Quiet bedroom at night, 30 db; Conversational speech, 1 m distance,  60 db; Kerbside of busy road, 5 m distance, 80 db & Chainsaw, 1 m distance,   110 db.
/mp

The best info I've ever seen on peak SPL's is here, see Figure 2:

http://www.zainea.com/Dynamic%20range.htm

[Rocket_Ronny]

When I would mix an album for our small indie Christian label ScriptureSongs.com I would allow for 8-12 db peaks over the average music volume. Modern, highly compressed, songs would be less as I was fairly soft with the compressors. 6 - 8 db max compression on vocals typically. Vocals can really spike in volume.

So I would advise figure your average volume in chair and allow for peaks of 10 db.

Rocket_Ronny

[/mp]

I stumbled across this interesting web page.
Music and The Human Ear
http://www.silcom.com/~aludwig/EARS.htm
It includes among other things:

A full orchestra can also hit a sound level of 110 dB and more, and then play a quiet passage at 20-30 dB. To reproduce this faithfully requires a recorded sound source capable of covering this 80+ dB dynamic range. (Everest quotes one researcher who claims a 118 dB range is required). A vinyl record is good for about 50-70 dB; a standard compact disc with 16-bit encoding can cover a 96 dB range, and the 24-bit DVD disk format a 144 dB range - in theory. Real D/A converters tend to be noise limited to a somewhat lower range.

Popular music has considerably less dynamic range especially the by product of the loudness wars in which the music is intentionally compressed to achieve less dynamic range and a louder average volume for any given maximum volume.

FWIW, I crunched hundreds or thousands of hours of spoken material down to 6-9 db b/c that's what work best for the particular application. 12 db sounds entirely plausible for most popular music.

[satie]

The main variable in amplification is you. You have a preference for listening at particular  loudness levels on average and at peak. Beyond that, the dynamic range of the music you listen to also determines what you require from your speakers and amps.

You need to find out what you like first. Once you have quantified it via an SPL meter then you can make a more certain choice in amplifiers with less of a chance of you wasting your time on an underpowered amp or paying too much for power you won't ever use. So buy or borrow an SPL meter and go to someone with a large full range system with ample power (dealer or friend) and find the level at which you like listening to a recording you would normally want to hear louder than others among your favorites.  Once you are acclimated and have a solid preference for a given volume then measure the average SPL levels on loud passages, then set the meter to peak hold and fast response and measure the peak levels on the loud passages. I usually use the C weighting, which is what most SPL tables contain.

As others have said, you want to match up power with your music. If you are playing pop you will rarely have peaks 10 db over the average, if you are playing large scale orchestral works then you will have up to 20 db bigger peaks than the average. The peak level you need should match up with the peak output of your amps - e.g. a 20ms peak specification of 600 w/ch into 4 ohms is telling you that you that on an 87 db @1m sensitive MMG you will get 114 db theoretical peaks which is enough for a full orchestra. That same amp would typically rate 400 w/ch into 4 ohms and 250 w/ch into 8 ohms. It would provide you with an average output capacity of 112 db theoretically.

Your Maggie is not going to put out the theoretical amount of acoustic power. It will compress heavily well before that, particularly if you have not braced the speaker with Mye stands or a DIY equivalent. Also, compression is not even throughout the frequency range. Low tones will compress at lower output levels, and midrange tones compress at higher levels, so the theoretical 114 db peak will actually give you something like 104-5 db actual peak output at 60 hz, 108 db at 200 hz, and 110 db at 1khz out of an MMG or MG1. And this will be reduced at least 3db if the speakers are not braced. The quality of the high output sound will be substantially compromised by compression, which is a distortion.

The larger maggies 3.x will give you 3 db more peak output, but are 2 db less sensitive (85), the bigger 20.x and Tympani will give you even more peak output - especially at low frequencies (about 6 db more than an MMg - which is alot), and are as (in)sensitive as the 3.x models. Which means also that they will need higher peak output power from the amps - by 3 db and 5 db respectively for the 3.x and big maggies (since the onset of compression is 3 db and 6 db higher, you need less additional power to get the same output from the speakers). So the high current 250 w/ch @8 amp that will take the MMG beyond its limits, is not going to be enough to take the 3.x to its peak potential (assuming you need it - many if not most will never want to listen that loud even on peaks) will need an amp specified for nearly 1 kw into 4 ohms.

Once you know how loud you want to listen and how loud your speakers can go you need to size the amp to the room and listening distance.

Subwoofers: the maggies will not give you the bottom octave bass in a big way, even when braced. You can use a subwoofer to take the bottom one or two octaves off the maggie's hands and lower the amplifier power requirement substantially. You can even drive the maggie with a 50 watt tube amp or class A SS amp if you cross over to a subwoofer at 80hz, and still obtain good peak power output.

[twitch54]

are you talking 'Planar Watts' or 'Voice Coil Watts'.........sorry I couldn't resist.....why is this in the 'Planar forum' ??

[SteveFord]

Why Planar Watts, of course.
They clip differently - instead of the voice coil popping out and falling on the floor the mylar catches fire and stinks up your house.

The OP is looking at some Magnepans or similar and is trying to figure out what to get.