It just happens that I have been making a bunch of electrical measurements as I design and set up my greatly revised system.
1. SUBWOOFERS...I have three subwoofers, each consisting of a 15" JBL LF Driver and a 12" Dayton Titanic Subwoofer sharing an 8 cubic foot sealed enclosure. (They are about half way between floor and ceiling, and they back up my three Magnepan 1.6). The two drivers in each SW are in parallel, which gives a 2.7 ohm load. Each of the SW sets is driven by an amp rated for 250 watts at 4 ohms, but they seem to handle the 2.7 ohm load without any problem. Using either a warble test signal, or organ music, the maximum voltage that I see from the amplifiers is about 3.5 volts, and since it is 90 Hz or lower I don't think we need to worry about brief voltage spikes that my meter wouldn't see.
I = E/R so I = 1.3 amps.
Power = E * I = 4.55 watts.
Of course I have three of these things going, 13.65 watts all together, but it absolutely shakes the house. With all that cone area (like the Magneplanars) none of the SW drivers is working hard, and the amps don't even get warm.
2. MAIN SPEAKERS...They are three MG 1.6, driven by ADCOM 5503, rated at 350 watts into 4 ohms. These are much less efficient and go to 12-16 volts on the voltmeter, and I am sure that an oscilloscope would show higher peaks.
16 volts would yield 4 amps, with power at 64 watts.
Remember this is 90 Hz and up, and a full range drive of the Magneplanars would be more.
However, I have driven these Magneplanars (90 Hz and up) using a smaller ADCOM amp rated at 100 watts into 4 ohms, and there is no doubt that the big amp sounds a lot better.
The most dramatic difference was noted with a set of Dynaudio Gemini small MTM speakers that measure 3.1 ohm. I never realized how good these little boxes are until I hooked them up, full range, to the 350 watt ADCOM.
I don't think it is power (watts) that does the trick. The ability to deliver lots of power (more than you ever use) IMPLIES other characteristics of the amplifier that enhance its audio performance in the low voltage range (nowhere near clipping) where it actually operates. |
Thanks Sean. I'll see if I can audition some stuff in my area. |
None taken,Sean;I enjoy reading your posts,really. |
Pragmatist: I hope you understand the point that i was trying to make as my post was not meant as an attack on you personally or the information that you provided. I thought that the effort that you put forth in responding was very kind and covered the basics quite well. What i was getting at is that math and various formulas can be very helpful in predicting accurate results, but only when you factor all of the variables into the equation.
Busaganashi: I think that most people would find a quality 250 wpc amp with 90 dB speakers to be plenty of power and capable of attaining SPL levels that are more than enough in the size room that you mentioned. On top of being a bit of a nut, i also tend to push things noticeably harder than most folks. As such, i try to figure for worst case scenario, which pretty has one covered under any circumstances.
If you have the opportunity to audition the amps that you were considering in the confines of your system in your listening room, i would by all means do so. Otherwise, i would be relatively confident that a well built 250 wpc SS amp was up to the task at hand for someone that was slightly more sane than myself. You might be able to get away with a slightly smaller tube amp due to the differences in sound quality that they produce under stress. Most SS amps tend to get hard and grainy if pushing them whereas many tube products remain musical, but get a little sloppier. The fact that your speakers are of reasonable impedance and not highly reactive also helps things out a bit : ) Sean
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So it sounds like tubes are not the best for these speakers then? Sounds like a tube preamp and something like the Bryston 14BST is the better choice? I was thinking about getting the Theta Dreadnaught II as well, but that is only 250w. I don't plan on getting rid of these speakers. In fact, I think I'd buy the 802's to replace them.
My speakers are about 7 feet apart and I'm about 8 to 9 feet back. |
I would beg to differ with the conclusion that Pragmatist came up with regarding the B&W's. The figures that he quotes are for a listening distance of one meter from the speakers AND do not take into account speaker compression. I don't know of a speaker made that is linear in terms of input vs output, especially when one starts hitting them with some juice. This has to do with thermal losses in the drivers and crossover components and is pretty much unavoidable to one extent or another.
As such, one should not expect to hear anywhere near the spl's quoted at their seated listening position unless one sits very near their speakers and has a very small room. To achieve the figures quoted at a typical listening distance, i would count on needing at least twice the power ( and more realistically four times that amount ) in order to keep the amp from getting nasty due to being pushed too hard. This is especially true if running a typical SS design.
My experience with speakers rated at 96 dB's and an amplifier rated at 120 wpc in a similarly sized room supports the above statements that i made. I kept popping tweeter diaphragms from driving the amp into hard clipping. Given that these speakers are four times as sensitive as the B&W's in question, i would not count on having enough muscle and doing it cleanly unless you had quite a bit of power. Sean
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So it sounds like the Rogue 120's or perhaps a CJ Premier 12 or 8 is what I need then. Thanks. |
Busaganashi:
To double check my facts,I looked up the B&W Nautalis 803s on their web site;they are rated 90db into 8 ohms.
So 90db would require 1 watt,93db-2 watts,96db-4 watts,99db-8 watts,102db-16 watts,105db-32 watts,108db-64 watts,and 111 db-128 watts.
Sounds to me as if 110-120 Clean watts would fill the bill-with headroom to spare. |
Ok, I've got a question. I've got a pair of B&W 803's in a 12x20ft room. Moderately furnished. I play classical, jazz and hard rock almost about evenly. I like my music at concert levels some of the time and others loud enough so I have to say "what" when someone interrupts me. I rarely listen to music below that, but on occasion.
I am interested in buy a CJ MW60 or Premier 11a. Enough power? How about a Rogue 120 Magnum? |
Weiserb:
This is antectdotal;guys with physics degrees,please cut me some slack.
The softest sound,at the softest pitch,(a flute)is about 50 decibels. On a music score,that is notated pp. Each time you double the loudness,add 10 decibels. That is p is 60db,mp is 70db,mf is 80db,f is 90db,and ff is 100 db. A modern orchestra with everybody playing as loudly as they can at the same time is 100 decibels. Some rock bands play at 110db.
If your speaker is rated at 8 ohms resitance, count 1,2,4,8,etc. If your speakers is rated at 4 ohms,count 2,4,8,16,etc. If it's rated at 6 ohms,count 1 1/2,3,6,12,etc. Everytime you move up a "Counting step" add three decibel watts.
Say your speaker is rated 90db at 8 ohms. At one meter,the speaker will have a loundness of 90 decibels being fed one watt. At 2 watts,93 db;at 4 watts,96 db;and so forth. At 90 db into 4 ohms,it would be 90db at 2 watts;93db at 4,and so forth.
It's true,as Sean says, that different speakers have different rates of change at different distances,but anecdotaly,I'd allow 6 db'ds of headroom. |
Personally, i think that a system built for Classical music should be able to sustain a peak of at least 110 dB's at your seated listening position. Obviously, different radiation patterns from various speakers, how far you sit from them and the size of the room will vary how much power you need.
For a "jammin" system that is built for hard rock / metal, the system should be capable of sustaining 110 dB's average at the seated listening position. All of the variables above apply here just like they did above.
As you can see, there is a BIG difference as to what "loud" is in both circumstances. While both systems should be capable of doing 110 dB's at your seated listening position, one of those figures is peak while the other is average. Obviously, a "rock & roll" system that someone tries to achieve "concert level" spl's with will take a HELLUVA lot more of a beating on an average basis. This is NOT to say that everyone listens at these levels, but that the systems should be capable of doing so if one desired. At lesser levels, the systems will be coasting and should sound like it.
I would think that average listening levels at the seated listening position would be somewhere between 70 and 95 dB's on an average for most all types of music. It is only when one really wants to "let loose" or has highly in-efficient speakers that one needs a gob of power. Most of the time, an amp will be producing under 10 watts RMS with peaks below 50 - 100 watts ( depends on the type of music and amount of compression ). Some large scale bass peaks may require hundreds upon hundreds of watts though, so system requirements and what you want to achieve with your specific system and its' limitations will dictate how much power you really need. Look for quality first and "big numbers" later. Sean
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As I ponder my next amp, this is a very helpfull post. Special thanks to Sean and Twl. Would like to know what are 'average' listening levels for classical, rock, acoustical guitar, etc.
If this is too broad a question, would it help if I narrowed it down to a 10' x 14' room? I sit in the near field, a little over 5' from each speaker.
Really don't crank my music.
I do listen, though ;)
Thanks! |
Look at this site from Welbornelabs.com/recomendspeaks.htm |
Twl's response of "it depends" is about as accurate as you can get. Given the massive amount of variables involved ( speakers being used, their radiation and compression characteristics, the type of music being listened to, the individual recording being used, the size and acoustics of the room, your listening distance, etc...), it would be way too hard to be specific.
Having said all of that, i will make one generalization: The more efficient your speakers are, the smaller your room is and the closer you sit to the speakers, the less power that you will need. Kind of makes sense, huh ??? : )
If we look at this strictly from an amplifier to speaker power transfer point of view and use Classical music as a source, we find that the standard for peak to average listening ratios as recorded is appr 15 dB's. Using "old school" sealed speakers of the low efficiency variety, average power levels of 5 watts or less would be required for all but the largest rooms on an average basis. The power required to generate full peaks without compressing the amplifier would be ( theoretically speaking under ideal conditions ) about 160 watts to achieve 15 dB's of dynamic range. If we reduced the peak to average ratio to appr 10 dB's, which is probably more common in most recordings, 50 to 55 watts would be all that you would need. That is, so long as the amp was fast enough to respond to the demands placed upon it. Otherwise, you would run into problems with slewing induced distortion ( SID, which is a form of "clipping" ) from an amp with a slow slew rate.
Bare in mind that these figures are based on a speaker that is both steady in impedance and presents minimal amounts of reactance. In plain English, we are counting on having an 8 ohm load ( for example ) that stays very close to 8 ohms and does not produce a lot of reflected EMF or sharp phase angles. This would be considered "heaven" as far as a speaker load goes and very few speakers of this nature tend to exist.
In other words, the above "theory" only works on paper as the dynamic conditions of a speaker / amplifier are continually changing as power and spl are varied. In most cases, the changes are NOT very linear and can change quite a bit from low spl's to high spl's. In effect, i would count on needing quite a bit more "muscle" than the above figured 160 watts to deal with the "less than perfect" situations that one encounters in real world operation with less than "ultra high" efficiency speakers. How much more one needs would depend on ALL of the above criteria that i mentioned in the 1st paragraph.
Obviously, Twl's situation is a little different due to using highly efficient speakers. While his figures are all correct for a "theoretical" installation under ideal conditions, i've yet to see a speaker that actually transfers input power to output SPL's in a completely linear fashion. This is due to thermal losses within the driver itself and compression that takes place on longer excursions. Once again, that brings us back to needing ( or should i say "wanting" ) more power on hand so that one could more easily overcome deficiencies / lack of linearity in the system.
To throw a BIG wrench into the above works, let's try looking at the same system with the same peak SPL level using hard rock as a music source. The accepted norm of dynamic range for a rock recording is appr 5 dB's. Obviously, this is due to the use of large amounts of compression and the much more consistent "drive" or playing of notes associated with "harder & faster" music.
On the surface, it would appear that we would need a lot LESS power to play rock due to the greatly reduced amount of dynamic range. That is simply not the case when you look at the big picture. Remember, we are comparing apples to apples here i.e. peak SPL's with Classical to the same peak SPL with "rock". We are not comparing the average listening levels between the two, otherwise rock would require a lot less power. After all, how many people do you know that like to "jam" to rock music at the same level that one listens to Classical music at ??? Most would consider listening to "rock" music at that level as being "elevator music".
Since we used 15 dB's as a reference for peak to average ratios on Classical music and "rock" music typically only displays appr 5 dB's of dynamic range, the average listening level would have to be appr 10 dB's higher for rock than that of Classical music in order to obtain the same appr peak readings. With that in mind, the 5 watts that sufficed to power the speakers for Classical music is now required to sustain 50 watts on an average basis for rock music. While the peaks would still be hovering around 160 watts, the continual heat dissipated by the amp and speakers on an average basis would be 10 times as high. Needless to say, this is MUCH harder on the speakers and the amplifier and explains why "rock" music is much more demanding ( in terms of ruggedness and reliability ) when building a system.
To further confuse the issue as to how much power one needs, different speakers "spray" sound or pressurize the room in different manners. Danner touched on this subject in his post. While the sound coming out of all speakers "falls off" as it gets further away from the speakers, this effects some designs more than others. If listening at 10' from the speakers, a 90 dB 8 ohm "line array" ( like the Pipe Dreams ) will need less power to produce the same volume that a 90 dB 8 ohm "conventional" woofer / mid / tweeter type system would require at the same distance. This has to do with the dispersion pattern i.e. far and near-field radiation. As such, a 90 dB speaker can actually play louder into the distance than a speaker with slightly higher sensitivity due to differences in radiation patterns. SPL's from line arrays do not fall off as fast as a "conventional" design as listening distance is increased.
While there are formulas to figure out the exact distances that spl's will start to diminish at a given frequency, the typical results are that line arrays and other "acoustically coupled" designs will produce more sound per watt in a large room than a conventionally designed speaker would. Needless to say, comparing speaker sensitivities at face value is only useful if listening at 1 meter from the speakers. Otherwise, you have to take a lot of other factors into consideration.
My personal thoughts are that the quality of wattage used is more important than the quantity ( under most conditions ). As such, one would want to strive for a high level of linearity ( Class A ) for as high of a wattage as possible. This amp should also be fast enough to respond to large changes in amplitude ( fast rise time and slew rate ) to accomodate the pulsed and highly dynamic changes found in some types of music. That is, if you want to retain all of the speed and attack that instruments have when listening to them live. On top of this, if one had a huge reserve of power available, the system would tend to sound much cleaner when driven hard due to the system never being "pushed" AND easily control the speaker even if it were considered a "highly reactive" design. Both Bigtee and Gs5556 touched on this in their posts from slightly different perspectives but with the same goal in mind. As far as DrDiamond goes, i'm with him. So long as quality does not suffer, i'd rather have a LOT more power than not enough.
Obviously, not everyone has the same listening tastes, speakers and rooms. As such, what one "needs" and what one "wants" can be very different things. Each situation is independent of another and needs to be assessed individually. That is the reason that most of us stress the importance of in-home auditions when possible. After all, what works "good" for you might seem "dynamically challenged" for someone else in their system and vice-versa due to all of the variables mentioned.
I hope that this helps explain a few different aspects of what we hear and why in an understandable manner. I'd also like to say thanks to Pbb for having faith in me to be able to possibly explain such things. I'll try to extend the same amount of courtesy back to him in the future : )
As to JCB's comments, i basically agree with what he had to say, especially about the wealth of info that we have available to us here and on a few select other forums. I learn from others every day. As proven by this thread, everyone can contribute a little bit with it all ending up to make for a well rounded yet diverse perspective on any given subject. Sean
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Pbb- Sean is certainly not the only person on this forum with useful knowledge, as I'm sure he'd agree, and Twl is quite right. The nominal power required for a nominal speaker in an average room for at a nominal spl is quite low, < 5 watts, many at only 1 watt. Much of the subtle inner detail heard during a listening session would be at 1/10 watt or lower. This is why so many experienced audio-lovers claim that the first watt is the most important! As has been stated, it is the dynamic peaks that necessitate greater power reserves. Of course, not all watts are created equal. The ability for an amplifier to gracefully handle these transient conditions can greatly effect the perception of the relative power between amps.
I seem to recall having read about a demonstration that utilized 10,000 watts (ss, of course) in an attempt to reproduce the sound of scissors cutting a piece of paper, and there was still distortion/clipping of the signal. Certainly, if there is no compromise in the quality of power, then more is better. However, given practical limitations in packaging, layout and component power handling, higher power normally requires significant sonic tradeoffs compared to their smaller siblings. This is typically true of both ss and tube designs.
The approach chosen by Twl and many others offers some unique advantages over the more traditional approach of the last 30 years (low impedance, moderate to low efficient speakers with high power amps). Very high efficiency speakers coupled with a couple or a few very high quality watts is in many ways a far more elegant approach, and allows the user greater choice of amplification to match his/her preferences. Fewer compromises in the amplification topology in low power designs can yield amazing detail and musicality at the same time. Most who have followed this approach strongly embrace SET or OTL topologies, but there are some that use low power ss amps as well.
At the other end, if one works on the assumption that an amplifier is routinely asked to reproduce peaks that produce higher levels of distortion up to clipping, it often comes down to how gracefully the amplifier clips and recovers from these conditions. Fast recovery and harmonic distortion products -softening or rounding of the waveform during clipping with minimal ringing- are often far less annoying in tube amplification than the behavior of some ss amplifiers in this region.
I've heard 12wpc amps produce far better, and more dynamic sound than highly touted 350wpc behemoths. I've also heard 75wpc amps sucked dry by low efficient and difficult speaker loads. In the end, use your ears to determine if an amplifier is appropriate for you in the context of your system and listening habits. Just one man's opinion. |
Let's say you have two amps - one at 50 wpc and another at 5,000 wpc - with identical speakers and listening rooms. If you play both at a certain volume level, say 80 db SPL, both amps will provide the same power. However, during transient peaks, BOTH amps will clip. The 50w amp may distort at clipping while the 5,000w amp will recover much quicker where you would not notice the discontinuity. That's one rationale for mfr's pumping up the amp power - to tackle clipping.
So, the best way I can answer the questions is just how much quality you want for a particular listening level. You can get there with a 2 wpc SET as well as a 600w monoblock; "depends" is the answer - because a particular SPL level is dependent on room size, speaker sensitivity and physical comfort, etc. but the quality comes from both the electronics and the power capability. The SET uses its ability to produce a symmetrical waveform to recover from clipping while the SS beast uses brute force. |
All of it!
I have compared the Cello Grand Masters (96db sensitivity) driven by one of their Performance amps which puts out about 1500 watts into this speaker, vs. a bridged pair that puts out about 6000 watts (per Cello). The difference was quite impressive.
You can NEVER have too much power!
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For most applications...a quality 40 or 60w amp will suffice...and be able to drive even difficult loads to surprising levels of volume...I heard Maggies on a 40w Rega at my local dealer...and it sounded good....granted...if you want to "rock the house" or get evicted...you might need more juice...Im no expert...but even doubling your power is a marginal improvement...to really hear a gain...a factor of 3 or 4 is necessary...others will provide more technical answers...but unless you have a very large room with very inefficient speakers...I wouldnt worry about... |
Though the following is oversimplified, it's what I use when thinking about this issue.
I use a speaker with an 89dB/w sensitivity (and ignore how it was measured). I assume that peaks on the order of 15dB must be accommodated (a figure I remember for the human voice, one of the most demanding instruments). One watt will provide a listening level of 89dB and the peaks will require 32w (with a doubling of power as 3dB). Therefore these speakers require the following:
dB---w------peak w
80---.125---4
89---1------32
98---8------256
Using this as a ballpark, my 8w SET into 89dB/w speakers should be capable of about 83dB (.25w with 8w peaks) at one meter. My listening position is twice that, so somewhere around 80dB would be right (neglecting room effects - and my system is in a really small room). Since I listen exclusively to classical music and nearly always to small ensembles and solo instruments, this level suites my listening habits just fine. YMMV |
Pbb, my statement was applicable to any system of any power level, as it did not state any defined number of watts. Even high power amps are not played beyond a few watts nominal at moderate listening levels. At peaks, they use more. At higher listening levels with medium efficiency speakers, even high power amps can clip during dynamics, due to the nature of the db scale. If the speaker is around 90db efficient, and you listen around 90db, then you are only using one or two watts nominal, whether your amp is rated at ten watts or 200 watts. The rest depends on the ability of the amp to handle the dynamic peaks into the speaker load provided. In a situation where the dynamic peaks are 15db higher than that 90db average listening level, you require 32 watts above the average power required for that. That is for the 90db efficient speaker that I described above, and listening at the 1 watt level. If you have that 90db speaker and are averaging 8 watts listening level(~99db) then to handle a 15db peak, you would have to supply 256 watts to handle it. If you had a 18db peak, you'd need 512 watts.
Regarding my personal system performance values, I specified that it was my system, not theirs. My system can handle a 90db average listening level with less than 1/10 watt, and can achieve 15db peaks with about 3.2 watts. |
At modest levels, you will only average a few watts. However, those peaks can get up there. If you crank the volume a little and average maybe 10-15 watts(or are using inefficient speakers), the peaks are in the 200+ range. If the amp can't deliver that, then it clips, which compresses the music. This is the primary reason for a big amp, to reproduce high level peaks cleanly, not so much for the steady state power.
As for the big power supplies, etc., it takes a large current supply to allow sustained low bass notes to be reproduced cleanly. Larger caps provide storage for the power supply to draw upon during heavy demands. If you listen at low levels, then this would be a moot point.
Since transformers are rated in VA (voltamps) which is actually watts (volts x amps) it is easy to see how a larger VA transformer can benefit heavy bass loads(since that is where most of the power is used.) The filters (power supply caps) help eliminate ripple (AC that slips through the diode bridge) but also store electrical energy, Try discharging one of those large 40,000uf caps by shorting the terminal to ground after the power has been off a while!
Unless your amp has some sort of mute circuit, the larger the power supply, the longer the amp will play after the power is off. This will attest to a big power supply.
This is a simplistic explanation but I hope you get the picture.
Power supplies have regulation which can be loose or tight. Tight power supplies have low headroom values where loose power supplies can supply substantial peaks. Most amps use loosely regulated power supplies. What this means is, how much current the supply can sustain before it runs out of juice or can it supply demand on a instant basis only.
This translates into amps that can supply higher wattage for a brief moment(peak) but can't sustain steady power. A good example of this is NAD which might rate an amp at 40 watts continuous but can deliver momentary power output of maybe 3 times that. It makes a cheaper amp sound more powerful than it really is. |
Maybe Sean could give a more standard answer to the original poster. To indicate that TWL's experience is representative of what is normally encountered in the field is much like saying that a human can survive on five stalks of celery a day, fifty when he is doing physical work. You will not be building a railway on such a diet. While very true that background listening levels require a tiny amount of power, anything resembling reality requires substantially more. Now if you appreciate that music is dynamic in its nature, not clipping peaks requires multiples of what is required for the average level, in the order certainly of ten and sometimes way more. So the "depends" answer given by TWL is somewhat disingenuous in the normal scheme of things. Issues of speaker efficiency, room size, normal listening volume, type of music being reproduced are all pertinent. The one point to realise is that an amp when pushed will produce much greater distortion than when used within its capacity. How it reacts when pushed is another sub-topic here: some are more graceful than others in how they clip. More power is never a bad thing. Too much may be wasteful of resources. Now let the debate of the "good watt/bad watt" brigade begin. |
It's the usual "it depend" answer. It depends on how loud it is playing, how efficient the speaker is, how dynamic the music is - especially the bass dynamic content. Also other factors. For many people, there is a listening level that is comfortable, that generally would likely only use a few watts nominally, and peak at some higher values.
On my particular system, I generally listen at about one-tenth of a watt, and peak around 2 watts. |
