Confused about dB's, Sensitivity....

[joel2762]

He should find it very good like I find mine!

[chimera128]

This was a really good thread. I agree that the question does not get asked enough. Something you might want to do if you are searching for amps is to go look at a couple of McIntosh amps with wattage meters on them. That way you can get an idea of the wattage it takes to drive speakers even if you don't want or can't afford McIntosh products. Also, a lot of the higher power/quality amps seem to have more control over the speakers production of sound. In terms of SONY, I just wanted to say I liked my STR-V333ES, when it worked !! I tried out their new STR-DA3000ES in my home for about a month and took it back to the dealer. It only put out about 110 constant wattage and 120-130 watt peaks. There was also a little hiss in the backround at ALL volumes. If you are considering this model line you may want to stay away till they iron out the Digital Amps

[Chuck]

I was recently looking at a Decibel level chart. I tried to upload but it was too big. This chart states that 90 Db can be dangerous under constant exposure. Okay. So my speakers are rated at 89 dB/1 watt. Does this mean that at one watt from my reciever my speakers can almost damage my hearing!? What's all the extra power there for then?? I don't get this...There must be something more to it that I don't get here but i'd like to know what it is. Thanks in advance!

When a loudspeaker has a rating of 89 dB/watt/meter (which is probably the specification you're looking at) it means that the speaker will produce an output of 89 dB when one watt is applied and the SPL is measured at a distance of one meter.

Each time you double the distance you loose 3dB, so if you sit 2-meters from your speakers the output with one watt in would only be 86 dB.

Peak levels for an orchestra can exceed 102 dB, and for rock music peak levels can be much higher. "Spectaculars" like performances of the 1812 that use real cannons have even higher levels.

Each 3dB more output requires us to multiply the amplifier power by two. The following table applies.

86 dB = 1 watt
89 dB = 2 watts
92 dB = 4 watts
95 dB = 8 watts
98 dB = 16 watts
101 dB = 32 watts
104 dB = 34 watts

Classical music with peaks of 100+dB rarely have an average an level in excess of 80 to 85 dB, and it is the high averages that do the damage (in this range). At extremely high levels (like some live rock music) hearing damage happens very quickly. Keep the average as measured using an SPL meter below 90dB long term, but expect the musical peaks to require substantially more than one watt.

Hope this helps.

[jack70]

A couple of points that aren't being made clear here... (perhaps missed by some?):

Electrical Watts (amp power) and Audio Watts (acoustic energy that hits yer ears), are 2 different things.

Acoustic (perceived by our ears) energy is an "absolute thing". If you went into the quietest room in your house, you'd find the background sound level was around 30-40 db. That's an Absolute figure.

The Electrical energy of the amp is totally dependent on the efficiency of the speakers. You could have an amp that puts out 100 electrical watts through an 8-ohm speaker... this would be equal to 28 volts across it (sq rt of 100x8). If the speaker is very efficient it'll "sound" loud (acoustic energy). If it's very ineficient, it'll sound much quieter for the same input going into the amp. The amp-speaker interaction is the key here.

You could have a 10 watt amp conected to a speaker with 115db "efficiency" that puts out 125 db of acoustic energy (loudness to your ears). You could have a 500 watt amp connected to a low effiecient speaker (70db) that sounds much quieter in comparison.

Its' true that perceived "loudness" is a logrithmic (power) function... it requires "more & more" power to hear "a small amount" of loudness increase.

The other issues discussed (frequency aberations) and (peak power) are both more complex issues, because they depend on more variables. Generally, audiophiles use high power amps because they have the reserve electrical power to reproduce the kind of (very-small) peaks in reproduction that make music sound more real... these are instantaneous (fast) pulses of power... the kind you'd hear from the sound of a hammer or a gun. It's not a constant acoustic output, but of a short duration. It's impossible to reproduce that "reality", through any speaker with a smaller amp (all things considered). But having that extra "power reserve" of a big amp isn't valuable unless the speaker system is matched well to the electrical circuitry of that particular amp.

Speakers are VERY inefficient devices. They waste 90% (more or less) of the amps energy in mechanical ways. The acoustic power they put out is but a fraction of the electrical power coming into them. They also have dozens of times the distortion of the electrical signal coming into them. That's also why speakers are such a neat thing to play around with for most audiophiles -- they all have inherent defects and a "ways to go" to reach perfection.

[Chuck]

A couple of points that aren't being made clear here... (perhaps missed by some?):

Electrical Watts (amp power) and Audio Watts (acoustic energy that hits yer ears), are 2 different things.

Acoustic (perceived by our ears) energy is an "absolute thing". If you went into the quietest room in your house, you'd find the background sound level was around 30-40 db. That's an Absolute figure.

The Electrical energy of the amp is totally dependent on the efficiency of the speakers. You could have an amp that puts out 100 electrical watts through an 8-ohm speaker... this would be equal to 28 volts across it (sq rt of 100x8). If the speaker is very efficient it'll "sound" loud (acoustic energy). If it's very ineficient, it'll sound much quieter for the same input going into the amp. The amp-speaker interaction is the key here.

You could have a 10 watt amp conected to a speaker with 115db "efficiency" that puts out 125 db of acoustic energy (loudness to your ears). You could have a 500 watt amp connected to a low effiecient speaker (70db) that sounds much quieter in comparison.


Its' true that perceived "loudness" is a logrithmic (power) function... it requires "more & more" power to hear "a small amount" of loudness increase.

The other issues discussed (frequency aberations) and (peak power) are both more complex issues, because they depend on more variables. Generally, audiophiles use high power amps because they have the reserve electrical power to reproduce the kind of (very-small) peaks in reproduction that make music sound more real... these are instantaneous (fast) pulses of power... the kind you'd hear from the sound of a hammer or a gun. It's not a constant acoustic output, but of a short duration. It's impossible to reproduce that "reality", through any speaker with a smaller amp (all things considered). But having that extra "power reserve" of a big amp isn't valuable unless the speaker system is matched well to the electrical circuitry of that particular amp.

Speakers are VERY inefficient devices. They waste 90% (more or less) of the amps energy in mechanical ways. The acoustic power they put out is but a fraction of the electrical power coming into them. They also have dozens of times the distortion of the electrical signal coming into them. That's also why speakers are such a neat thing to play around with for most audiophiles -- they all have inherent defects and a "ways to go" to reach perfection.

Hi Jack,

You are correct in concluding that the loudspeaker and amp are key factors, but the size of the room and listening distances are equally important factors. You are also confusing "sensitivity" and "efficiency." Efficiency is always rated as a percentage. Sensitivity is a measure of pressure-level at a given distance using a specified input . The two are related, but VERY different.

Using acoustic watts as a measure of power needs isn't going to work very well. A 36-inch bass drum can produce a peak power of around 25 acoustic watts. Speaker efficiency is typically between 1% and 10% (can be lower or higher, but this is typical) so we'd need from 10 to 100 times that 25-watts just to produce the power of the 36-inch bass drum. That would be from 250 to 2500 watts! However, if you put that drum in your living room, along with the rest of the orchestra, and then have them play at peak levels, you'll be deaf in short order. In a huge performance hall the power is needed, but not in your home. If you take a sound system that can reach 100dB at Row M in Radio City Music Hall and put it in your bathroom it will produce a high enough pressure level (SPL) to exceed the pain threshold.

The industry settled on sensitivity measurements years ago because they are far more useful than efficiency numbers. As a system designer they allow us to *estimate* the output we can expect, and by applying a few "rules of thumb" we can easily insure that we'll be able to produce the target SPL levels.

Working with watts and efficiency really falls apart when we look at something like an ESL, as they are driven by voltage, and could be said to be "wattless speakers." Working with sensitivity allows consistency even with odd driver types. Your numbers (70dB and 115dB) for sensitivity aren't at all typical, but your point is valid. More commonly we might end up comparing a loudspeaker that has a sensitivity of 82dB/w/m with one that has a sensitivity of 97dB/w/m (the latter being the sensitivity of my ESL's). The former loudspeaker will only reach 102dB *peak* at one meter when driven by a 100 watt amplifier, but the latter will reach 107dB with only a 10 watt amplifier. If the goal is to produce 110dB peaks then the 82dB/w/m speaker will need well over that 100 watts, but the second will reach that level with only 20 watts.

Of course the above example also shows the danger in any over-simplification, because if you try to drive my stats with any commercial 20-watt amplifier it will most likely shut down instantly. ESL's present a nasty load to the amp, and the load is yet another factor to consider when determining amplifier requirements.

Rod Elliott, and others (most notably Bob Carver) have written extensively on amplifier requirements and works like the "Handbook for Sound Engineers" are full of info on determining the power requirements for almost any situation, and it is a topic that is far to complex to discuss on an audio forum. It takes chapters, and anybody with the level of interest to tackle all the reading and the math simply needs to get a few good books. Nobody want's to read an entire course on the topic in a string of forum posts.

Crest factor hasn't even been mentioned.

Without going into too many details, some of the important factors to consider are:

* Room size.
* Room acoustics (dead, live, etc.)
* Distance from source to listener.
* Loudspeaker sensitivity.
* Loudspeaker load (as seen by the amplifier).
* Types of music to be reproduced.
* Listener preferences (some like it louder than others).

Other things that most seem to overlook:

* Distortion levels - Sound can seem "ear splitting" at modest levels if there are objectionable distortion products. When someone says "my 30 watt amp is already WAY TOO LOUD when the volume control is at 3:00" it is almost always distortion giving them the impression of "TOO LOUD."

* Crest factor - This is a complex-signal issue. With even a slightly complex signal we have to consider crest factor. Two tones are enough. Assume we record 100 Hz. and 2000 Hz., and that each is originally produced by a 10 watt source. We have two 10 watt sources, but to reproduce the two tones with a single speaker and amplifier we need more than 20 watts. In fact, we need 40 watts, due to the crest factor of the two signals when they are mixed (the 2k signal rides on top of the 100 Hz. signal producing twice the voltage swing, and twice the voltage swing means four times the power. This is one of the reasons so many people go to bi-amping with their flagship loudspeaker designs, and why most pro loudspeakers are powered and bi-amped, but it is probably too complex to cover in forum posts. Check the literature (Rod has some good info on his site).

So, Jack, you are right even if a little confused over terms; A LOT has been glossed over here, but the basics still hold. If you take the sensitivity of a loudspeaker, adjust for the listening distance, ignore room support, and then use the desired peak SPL desired, you can calculate the amplifier power required. Good engineering practice requires that you add in a margin for error (at least 3dB) and I'd add a little more for other factors (like the crest factor). THEN I'd add a little more with an SS amp to make sure that protective circuits were either never partially triggered, or simply weren't needed.

I think the original post discussed 89dB/w/m. Here's how I'd *estimate* the amplifier requirements for my situation. I sit four meters from my speakers. With one watt I can expect a little over 83dB at the listening position (a little over due to room support) with one watt applied. There are times (RARE), when playing music with lots of bass, and showing off the system, that I've seen 112dB in my room, and I want at least 3dB margin, so I want to shoot for a peak output of 115dB. Assuming single amp and passive xovers we can now calculate the power we need to reach (about) 115dB.

1w = 83dB
10w = 93dB
100w = 103dB
1000w = 113dB
2000w = 116dB

(note that we have two speakers and two channels, so it would take almost 1000 wpc to reach that 115dB mark. AND, we still haven't considered the crest factor issue. How many speakers will even handle 1000 watts? If we add in 3dB more for to handle worse case crest factor issues, and another 3dB to alow a margin of error or to avoid partial protective circuit triggering, we're talking 4000 watts per channel!!!

Increasing the speaker sensitivity 10dB would reduce that by a factor of 10, to only 400 watts, so the speaker sensitivity is obviously a key factor.

Note that when the bass peaks are reaching 112dB, the average level is right around 90dB, and that the bulk of the high-energy is at the lower frequencies. If that weren't the case this level would be ear-splitting (and if the sound is distorted it will be ear-splitting at much lower levels). I use ESL panels that have a sensitivity of 97dB/w/m, and drive them with an amp that can deliver over 1000 watts to the load without working up a sweat. That's JUST for the mid-tweeter. The mid-woofer has it's own 600 wpc amp and the sub-woofer has it's own 1000+ watt amplifier. The system reproduces highly dynamic music at any desired level as effortlessly and with as much impact as any high-efficiency horn system (but with a much flatter response). Does ANYONE actually NEED that much power and output capability?
IMHO, ABSOLUTELY NOT.

However, 200wpc was NOT enough to drive my mid-woofers, and 400 watts was NOT enough to drive my sub, even at more normal (and common) "audiophile" listening levels (averages approaching 90dB). With the smaller amps the sound was LOUD but distorted due to all the momentary clipping on peaks. Not obvious to anyone who has never heard a system that is free of such problems, but very obvious when compared to the same drivers with larger amps.

Velodyne upped their sub drives from 400 watts to over 1000 watts, because 400 just wasn't enough. Ask them if you don't believe me.

InnerSound upped the power of the amp driving their mid-woofers from 200 watts to 600 watts, because 200 just wasn't enough. Ask them if you don't believe me.

Kilpsch Corner Horns can be driven to INSANE levels with a 10 watt amplifier, so the speaker certainly can make all the difference.

I use to sacrifice efficiency (as well as sensitivity and high output capability) to get lower distortion, wider bandwidth, and excellent transient characteristics, but that is no longer necessary. Today we can have our cake and eat it too (as long as money and floor space isn't an issue).

Yea, Jack, we glossed over a BUNCH of stuff, but I don't think any thing that was missed was actually relevant to the original question.

If I understood it properly, the original question could be rephrased this way: "If my speakers have a sensitivity of 89dB/watt/meter and 90dB will damage my hearing, then why would I want an amplifier larger than 2 watts per channel?" I think I answered that question in my response. If he's putting the system in a bathroom he'll need less power, in Radio City Music Hall he'll need a lot more, but in general, if he takes the sensitivity and adjusts for distance and desired SPL he'll see why he needs more than 1-watt. That's all he asked. Why more than a watt or two? Didn't I answer that fully enough?

(I could have just said "crest factor, distance, and a bunch of other stuff" but the explanation of sensitivity and distance seemed most appropriate. Do you think I was mistaken?

See ya,

Chuck

[jackz4000]

will kill your hearing. No doubt about it. I know my hearing would be a little better if I had not been a recording engineer...even though I was careful with the dbs. Most sound mixers need increasingly higher volumes to mix tracks. Many times the client needs to be wowed. So you pump it up. Met alot of senior engineers who mixed by the #'s and experience because their hearing was shot. Continually high sound pressure will make you progressively...deaf.

[jack70]

You are also confusing "sensitivity" and "efficiency."...

...So, Jack, you are right even if a little confused over terms; A LOT has been glossed over here, but the basics still hold.

Hi Chuck...
Yeah, you're right about sensitivity vs efficiency... but I was trying to avoid getting too deep into that for fear of losing some people. When I said: "The Electrical energy of the amp is totally dependent on the "efficiency" of the speakers, I was using the term "efficiency" generically & rather loosely, to explain a more general point to a whole thread of listeners who seemed to have overlooked the point (on DB's). "Technically" they're quite different, but in non-technical jargon, they're addressing the same issue.

You're absolutely right to clarify it though. For time limitations (& so as not to confuse some), I just tried to shed some light on the apparent "inconsistencies" between Amplifier specs (db's), and speaker/load specs (db's) that many were "mixing up." The primary (of many) reasons is the fact that different speaker systems have different unique transfer functions (call it efficiency...as a general-type-term here)....LOL.

You're also right about the room and other aspects which effect real-life acoustical input to our ears. I totally avoided getting into that, and other issues of impedance and frequency anomalies (what you called "crest factor"), etc... would have been a little too long for me.

Your explanation of peak power demands for speaker playback is better explained than what I did... it's something many people should appreciate when thinking about what an amp is theoretically called upon when reproducing real life (demanding/difficult) sounds, and why high power amps are needed for that (generally). This aspect of sound, transient response and dynamic range, are the most important things that makes amplified sound appear "real". It's a primary reason why we can hear the difference between a live sound in the next room, and a recorded one. I'm not saying other aspects aren't important, but dynamic range is the hardest to master, simply as a technical "problem".

In fact your whole post should be edited a bit and bookmarked so that newbies could get some insight into some of these issues. It's explained rather well.

BTW, I often use my (very efficient) JBL-15" drivers (low end) together with very inefficent mids + tws. Tri-amped, etc... lots of "problems" and issues trying to get things balanced.

Too Much Sound Pressure=Semi-Deaf
will kill your hearing. No doubt about it. I know my hearing would be a little better if I had not been a recording engineer...even though I was careful with the dbs. Most sound mixers need increasingly higher volumes to mix tracks. Many times the client needs to be wowed. So you pump it up. Met alot of senior engineers who mixed by the #'s and experience because their hearing was shot. Continually high sound pressure will make you progressively...deaf.

My uncle spent years around jets... this was back before they spent a lot of care about those things. You think your SPL's were high in the studio? LOL. His hearing was shot.

Even worse than continual high levels of sound are impact sounds (machinery or guns). I try to put in earplugs when even hammering nails... the sound profiles are very narrow... but the levels are VERY loud. You can hear your ears twitch if you pay close attention. Nerve damage is permanent. I remember one private party were we played in a small basement (I played bass in a cheesy R&R band)... my ears were ringing for hours... but I was young... and stupid.

[Chuck]

Hi Jack,

I had only read the original post, not all the responses and sub-threads, but since you posted your reply in this sub-thread, I read some more of the posts. All of them either made good points or asked good questions, but it's clear that there is a lot of confusion. You seem to have a good understanding, but since you're the only person I've been chatting with in this topic-thread, You probably already know most if not all of what follows, but it seems appropriate to tie some of the information together for those who are still confused.

Sensitivity Ratings:

These ratings specify the sound pressure level a driver or loudspeaker will produce at a standard distance and input level. I won't go into the credability of manufacturers specifications other than to say that sometimes they are unreliable. Even so, they are rarely exaggerated so much that they can't be used as a guideline.

Measurements:

It's not enough to know that someone fed a loudspeaker 1 watt and measured 87dB SPL at one meter. All loudspeakers have peaks and dips in their response, as do all rooms. If I put a loudspeaker in a room, and find the largest peak in the frequency response, I can then feed one watt to the speaker and get a nice high "sensitivity number" to impress people. Anyone can spin measurements (and claims) to make products look more appealing. Still, I don't know of any loudspeakers that are so over-rated (in terms of sensitivity) as to make the number meaningless.

Distance and Room Size:

Sound intensity decreases with increasing distance. Unless you sit one meter from your loudspeakers, one watt will not actually produce the pressure level given in the sensitivity rating. At the same time, a loudspeaker that can reach a given output level outdoors will be able to reach a much higher output level once it is placed in a room. This is due to what is called "room support," and in general, the smaller the room (and all else being equal), the less power we need to reach a given output level.

Dynamics and Complex Waveforms:

For all of the reasons given above, the sensitivity ratings are ONLY a guideline. Loudspeakers with a sensitivity rating of 87dB/w/m across it's useful bandwidth might actually produce 87dB, more or less, at the listening position in a given room with only one watt available, but it is important to realize that this is the PEAK output we'll ever see if we drive the speaker with a one watt amplifier. The typical SPL meter doesn't actually measure the signal peaks, even when set in "peak mode." Most actually average the signal over a very short period of time, and the "peak" setting just reduces that time period. Music and natural sound can produce signal peaks that are only 1/2 cycle long, and the SPL meter will just average that big peak into the measurement. When using an SPL meter it becomes readily apparent that the dynamic range of music varies greatly from one recording to the next, in spite of the fact that the meter isn't really showing us the absolute signal peaks. Some recordings will show as little as 10dB difference between the loudest and softest passages, while others can show 20dB or more. 30dB is probably a reasonable amount of overhead (above the long-term average level) to take care of most if not all recordings. However, if we want to be sure that the transients that the SPL meter doesn't show us don't cause clipping issues. The effect of clipping on these momentary peaks varies widely depending on the amplifier design, and can range from hardly noticable in a tube amp to adding grain or brightness to the sound. In many cases it won't be recognized as distortion, but the sound may get irritating after a long listening session ("listener fatigue"). I could not even guess what the largest momentary peak ever recorded might be, but if one is after the highest fidelity they can manage, they have to allow for these peaks. If we are conservative and allow 10dB more for momentary peaks we're looking at a total of 40dB to allow for dynamics and crest factor.

Listening Levels and Preferences:

If audiophile A is listening to very dynamic music at an average level of 80dB, the peak demands will be at least 15dB higher, and as noted above, might require as much as 40dB above the average level. Given a typical recording though, 15dB is pretty common. Audiophile B, listening to rock music with limited dynamic range might be listening at an average level of 85dB, but the music might only demand only 10dB for the peak levels. In both cases the peak SPL requirement would be 95dB SPL, even though the average levels vary by 5dB (80dB vs 85dB). For many, 80 to 85dB averages seem pretty loud, even when the performance is live. For others, it doesn't "get real" until the peak levels exceed 100dB SPL. Given all of the above it is clear that power requirements vary greatly from person to person, room to room, loudspeaker to loudspeaker, and so on. When we are involved in "active listening" here, the average SPL is typically between 80 and 85 dB SPL. At those levels I turn on the SPL meter and keep an eye on the levels, becuase as our ears clamp, it is all too easy to end up listening at levels that are too high, for too long. With some rock music the averages here can exceed 90dB, but that's never going to happen for very long, because everyone here is paranoid about damaging their hearing. Those who want to reproduce both rock and classical music totally free of any clipping issues under any curcumstances should probably allow 40dB over the average level at which they listen to highly dynamic music, so for us that would mean that we need to reach momentary peak levels of 85dB plus 40dB, or 125dB. Most of that peak energy will be at lower frequencies, and all of the momentary peaks will be momentary, so it's not as loud as it might sound (and rarely will you actually find a recording that will make such extreme demands). A system that can reproduce peaks of 100 to 103dB is actually enough for most people. Use that number and the sensitivity rating to get a (very) rough estimate of power requirements. If the speaker is rated at 83dB at one watt, we need to reach a level 20dB higher to reach the 103dB peak target. Since one watt will produce about 83dB we know that 10 watts will produce 93dB and 100 watts will get us to our 103dB goal.

Power Demands:

Given all the variables it is impossible to make any blanket statements that cover every situation. In general it is not going to make much difference if we go from an 80 watt amp to a 100 watt amp (all else being equal). Depending on how we listen, both will be clipping on some momentary peaks unless we are using speakers with very high sensitivity, listening near-field, or have a very small room. In most cases the clipping won't be at all obvious, depending on the way the amp is designed. If it's a tube amp it is unlikely that the momentary clipping will do anything that anyone would notice without direct comparison to an amp that is free of clipping issues. With an SS amp there may be grain or veils that aren't noticable except in direct comparison to a tube amp or an amp with anough power to avoid the clipping issues. At higher average listening levels with peaks approaching or exceeding 100dB, and typical speaker sensitivity, there will be a difference between a 50 watt SS amp that is clipping every major transient and a 200 watt amp that rarely if ever clipps a transient, but since the momentary clipping almost always goes unnoticed (or unidentified) it is often hard to see where more power might be needed (usually this only becomes readily apparent when one upgrades from something like a 60wpc amp to a 200-250wpc amp (again, all else being equal). One reason tubes get such high marks with so many audiophiles is because they handle this momentary clipping in a far less objectionable way than most SS amps. Basically I'd have to say that if one's system plays loud enough, at an acceptable level of distortion, then a bigger amp probably isn't a must. However, increasing the power by a factor of four or more can often (if not always) yield some benefits. Increasing it by 50% is not likely to make much of a difference (though in some cases it might).

Bi/Tri-amping and Sub-woofers:

When a powered sub with a crossover is used, the system is technically bi-amped. This reduces the crest factor demands on both amps, and most subs have pretty strong amps. Even little subs tend to have 100 watts or more, and are often high sensitivity ported designs. Big high-performance subs often have over 1000 watts behind them. With HT we run the sub below 80 Hz., and may drop the crossover point to 60Hz. or less in a stereo "music only" system. A LOT of the high-energy bass now totally bypasses our main amp and gets handled by the sub amp, so the main amp can be smaller. A system with a 400 watt subwoofer, and a 200wpc amp driving the mains, if of any decent sensitivity at all, can produce a LOT of sound in most rooms (assuming that the drivers can handle the power well). Even cutting those numbers in half will probably provide enough output for most people, but the perfectionist audiophle wanting to get the cleanest possible sound is likely to want a little more power. The benefits might be small (or not), but for the perfectionist audiophile it's all about small benefits and incremental improvements. That's not the case with most people though.

DANGER LEVELS:

A constant level of 87dB (or less) at the wrong frequency over a long period of time will damage our hearing. Listening to any kind of music, long term, and levels above 90dB SPL will damage our hearing. Jack hammers, chain saws, leaf blowers, jet engines, and trips to the shooting range WILL damage our hearing if we don't use proper ear protection, and limiting exposure is prudent. Lower frequencies at high levels are less damaging than middle frequencies (where the ear is most sensitive) but it's always best to be cautious (IMO).

In General:

A speaker that can reach a peak output of 90dB with one watt in is not going to approach dangerous level when driven with only one watt, without being obvously overdriven (likely to sound very nasty, even with tubes). 10 watts MIGHT allow momentary peaks of 100dB, but the amp is not likely to handle this well, especially if it is an SS amp. Even the shortest transient demanding a little more will result in momentary clipping. Yes, if you listen at 90+dB average levels, long term, using a 10 watt amp and high sensitivity speakers, you could damage your hearing, but I doubt that you'd be able to tolerate the distortion products of the setup (unless you use tubes and tolerate dynamic compression well). At 100 watts the speaker with a sensitivity of 90dB/w/m will go pretty darn loud in an average room, and for many this may well be at or above the point of diminishing returns. Given all the variables and preferential issues it's just not possible to make blanket statements about power requirements.

Case In Point:

InnerSound's Eros is bi-amped. The original design came with a seperate bass-amp/crossover, and the bass amp produced 200 watts per channel. They sold a ton of the original design and I've never heard anyone complain about the bass performance. However, starting with their Series II Eros they changed upped the bass-amp output to 600 watts per channel (three times the original power). Owners (I know several) reported an improvement, and attributed it to improved dynamics. "The music has more impact now." In point of fact, the bigger bass amp does give the system more impact, beacuse it clips fewer (perhaps none) of the momentary peaks that the older/smaller amp couldn't handle. That's the only difference anyone reported when upgrading to the new more powerful amp/crossover, but the few who tried switching back to the older crossover after a few months were SHOCKED at what they heard. Going back to the smaller amp makes the mid-bass and bass both downright muddy in comparison, and it gets noticed instantly. The newer amp/crossover always goes right back into the system and people are left wondering how it was that they actually liked the bass before the upgrade. The difference is jaw-dropping, but it's most apparent when going back to the old amp/crossover after getting use to the bigger, improved amp/crossover. I thnk that this example shows that a lot depends on one's experiences and expectations. The 200 watt amp seemed to be sufficient, but in hindsight there was clearly room for improvement. Those who have never upgraded their crossover/amp are probably still perfectly satisfied with their setups and the bass performance, so for them, the 200wpc amp is obviously quite good enough.

It's All Relative:

Anyone who thinks they can drive my 97dB/w/m stats to "concert hall" levels in my (large) room with a 10 watt amplifier is simply wrong. A tube amp with less than 20 watts can generate "satisfying levels" at the expense of substantial dynamic compression (at higher levels), but a 20wpc SS amp would sound nasty due to the fact that it won't like the load it has to drive. Lots of people drive similar speakers to satisfying levels with amps in the 100wpc range, but they are in fact clipping the signal at times (current clipping due to the load rather than voltage clipping due to the output demands). That would drive me nuts, becuase I'm use to the sound of systems that never approach clipping, and really dynamic recordings played at higher levels just won't deliver what I've come to expect. It may be a subtle difference, but it's noticable, so to me, it matters. Past the point of diminishing returns? Absolutely! Excessive? I think that depends on so many factors that it's impossible to say for sure.

You Can Never Have Too Much Power:

Come on guys, this is a man thing. Fast cars, fast bikes, and audio systems can never really have too much power. They can all three easily hurt you if they have lots of power and you push them too hard. I've dinged more than one high-performance car in my day because I've been stupid and let the power get the best of me. Never anything serious, but I have dinged a few really nice cars because I've mismanaged the power (and been stupid). I'll probably do that again too, because I'm not so crazy as to totally throw away a high-performance vehicle, but I love to push the envelope, and sometimes unexpected things happen. In this area deer are a major danger, and we've had two minor dings as the result of deer and driving just a little too fast to deal with the sudden appearance. If you play, sometimes you have to pay, so never play with anything that might do irreversable damage. A ding in the car can be fixed, but once the ears go, they're gone. Guys, don't let our love of power in all things lead you to do anything that will do perminent damage to any part of your body. When you do things that involve risk, take sufficient precautions so that you don't do any perminent damage.

See ya,

Chuck

[Jimrod]

Hi, just a thought, in skimming over these comments I didn't see anyone mention the actual current output of amps as a factor, the reason a Sony 100watt amp will not drive speakers as well as most "high-end" 100watt amps is down to it's current limitations. Most people seem to think distortion = loud as in many demo's I have performed with speakers people keep saying "go louder" and don't realise they are having to shout very loudly to get their message across then the speaker hit's it's end-stops and they are all disappointed because they think the speaker was feeble because it didn't go all harsh and crappy sounding. This is where good amps (such as class-a and valves) outperform lower quality ones because they don't distort with their high current keeping the speaker under control. Next time you look at an amps power rating bear this in mind as this is usually the reason some 250watt amps dont work as well as some 50watt ones (liken it to torque and horsepower in cars... a Honda with a 2 litre engine pumping out 200hp and a car of a similar weight and hp but with a 5.7 V8 will both have advantages but you can bet the big V8 will cruise at 90mph a lot better than the Honda if the gearing was the same...)

So sometimes an amp with a low wattage will go much louder without distortion than a high wattage model, I know this is a little off topic but it is an often overlooked point that should be considered more often. You can have a speaker pumping out 90 decibels of horrible distortion which will not be pleasant to listen to at all or you could have one putting out a pure and clean 100 decibels which you could probably listen to for much longer...

[bfalls]

You're learning! All that extra wattage makes for great marketing print, even if in reality the capability is never used. Also, keep in mind that those wattage figures,especially for multichannel amps is rarely if ever expressed with all channels driven. So, that 100 watt x 7 channel receiver you see advertised at most stores is not really a 700 watt receiver (the power consumption stat on the back of the unit is usually a dead giveaway that it's a physical impossibility for the unit to output 700 watts). In addition, there are myriad ways for stat sheets to distort the actual output figures, like posting output levels with high distortion or using low impedance tests. The thing to look for is a 20 Hz-20 kHz test done at 8 ohms impedance -- that's the standard FTC test used for mono and stereo amps.

I'm not positive, but I don't think the power consumption of the receiver is rated the same as power provided to the speakers. Usually the receiver's power consumption is rated at it's input voltage (120VAC). The last I checked, output transistors (SS) and speakers don't run at 120V. Sensitivity is usually a decibel rating at 1W, 1M, 2.83V at either 1KHz or 20Hz-20KHz. Although the voltage won't remain constant 700W @120V is much different than 700W @ 2.83V.

Using a simple power formula (P=EI) a very rough calculation can be made for demonstration purposes I know it doesn't take into account speaker impedance, change due to frequency, or phase angle. Rated consumption power of 700W @ 120V results is 5.833A over the seven amp modules or .833A/ch. Well within the reach of an receiver's power supply to perform.

Using your assumption that the rating is the speaker power, 770W @ 2.83V results in 272A or 38.9A/ch. Within the reach of some higher-end amp capable of delivering 60+A to the output, but far from the norm.

I agree most HT receiver don't/can't output what their reported specs. It's been proven over and over. I just don't think the power consumption of the unit is all that telling of its performance.

What the "fuzz" MoviesOnlineTR? Is the TR short for TROLL?