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In Reply to: RE: What's Enough Watts? posted by thetubeguy1954 on May 25, 2007 at 05:35:44
Hi Tubeguy
Your question goes down two familiar roads.
What is needed to be satisfying to the ear VS what is needed to reproduce the signal accurately.
On one hand you have most modern recordings, TV, FM, MP3 formats which are intentionally highly compressed in order to “sound louder” and on the other hand, you have very very few recordings which are in their native dynamic range.
Sounds all around us can have a very high peak to average ratio and instantaneous peak level. Most people are fully unaware of this factor and our ears never suffer damage, as these are very short peaks.
Using a B&K 2204 “peak hold” sound level meter, one finds that tossing a set of keys on a tile floor produced 120-130 dB peaks and sitting in a car when the door was slammed produced 140dB peaks, a “wimpy” .22cal pistol with a “short” was over 155dB at 8 ft.
As Dolby Labs had concluded about realistic Bass, reproduction of many natural sounds
is well beyond what a home system can produce.
What happens when you remove these large (but short) peaks?
In a comparison of two good power amplifiers I got to hear this, the smaller amplifier reached instantaneous clipping and while THAT was inaudible (being so short), one could still hear the difference when one A-B’d with a much larger amplifier.
The larger amp simply sounded more “dynamic”.
Clipping when short enough is inaudible as “clipping” but still a difference is heard comparing “with and without”.
Lets say one wanted to reproduce the car keys on a tile floor at the lowest level.
Lets say you are two meters from the speaker.
Lets say your speaker was 90dB 1W 1M sensitivity, had no power compression or dynamic non linearity.
Now, to reach 120dB peaks at 2 meters, means the speaker was putting out 126 dB peak at 1 meter. 126 dB is 36 dB over the 90 dB sensitivity rating, meaning that that the peak input power is also 36 dB over 1 Watt which is 4000 Watts.
Sadly, in reality, dynamic non-linearity begins at between 1/10 and 1/8 of the drivers rated power typically and even at a few Watts home speakers are generally distorting badly (ever see any speaker measurements at say 10 Watts?).
You can see that even with unlimited power a “home” style speaker simply has no chance of reproducing much of what you hear around you and this includes many musical instruments, average levels yes, peaks no.
At first it was technology limited but now this is an intentional direction too.
I think the fact that real dynamic range WAS a goal earlier in “hifi” is why many still gravitate towards the higher efficiency speakers made for larger spaces from “that” era.
Some of these “ancient” speakers can dynamically beat the pants off of modern “home” speakers (while they may have other flaws) and because of the high sensitivity, can do it in the home at low power levels (with low dynamic distortion / harmonic distortion)
With the move towards smaller more “SAF” happy designs all the way to “sugar cube” speakers has quietly brought with it, even less dynamic capacity than the old larger speakers. This is why (partly) the main musical formats are SO DAM COMPRESSED, to have an acceptable loudness on sugar cube speakers or in a car with the windows down, with no peaks that would instantly destroy the speaker with real dynamic range.
So the answer to your question is entirely different depending on the criteria.
Having had lower efficiency, lower power speakers some of my life, I couldn’t possibly “go back” now. I guess digital recording too has opened my eyes about how hard but satisfying dynamics, going the opposite direction, can be.
On the other hand, I have stopped what I was doing in my workshop in order to listen to a song coming out of the 4 inch speaker in my cordless drill’s battery charger / radio.
Fortunately for the makers of compressed music and sugar cube speakers, one can be satisfied with much much much less than actual reality.
Best,
Tom
PS: if you have an analogue volt meter like a Simpson 260 etc, monitor the amplifier Voltage, this will be a moving average of the “average level” from moment to moment.
If you have an oscilloscope, you can look for the levels of instantaneous peaks.
Follow Ups:
TS - Sadly, in reality, dynamic non-linearity begins at between 1/10 and 1/8 of the drivers rated power typically and even at a few Watts home speakers are generally distorting badly (ever see any speaker measurements at say 10 Watts?).
Actually Soundstage does show measurements at increased levels (SPL rather than power input), highlighting exactly what you have said about power compression in home audio speakers (don't want to over generalize as there are "home" line arrays, etc. which will behave much better with higher input).
There is no reason to think that clipping can't be added to the laundry list of sonic colorations that audiophiles crave.
cheers,
AJ
The threshold for disproving something is higher than the threshold for saying it, which is a recipe for the accumulation of bullshit - Softky
> tossing a set of keys on a tile floor produced 120-130 dB peaks...
I have little doubt that these and the other examples you gave are a good representation of the peaks that one hears from live sounds but the question in playing recorded music is what type of dynamic range made it onto the recording? That is the limiting factor in looking at the power needed for our speakers.
Ignoring the zero dynamic range recordings made in honor of the "loudness wars" even good quality recordings don't have a ton of headroom above their average recorded level. If your typical LP on a good system has a 60ish dB dynamic range and an CD has a 90ish dB range, it is rare to see average recorded levels that allow much more than perhaps 20 dB or so of headroom. Once the max recording level is reached, things get clipped, though hopefully with some grace.
Even on those recordings I have which have passages recorded at very low levels, these portions are meant to be played softly. If you are rocking along with an average room loudness of 90 or 100 dB, there almost certainly isn't 20 or 30 dB of headroom left on the recording.
In that sense, the issue of a zillion available watts to power a speaker to some live peak that doesn't actually exist on a recording is overkill. Whether analog or digital, the recording process limits dynamic range even before any additional processing is added.
Hi
Again it is a “depends” kind of answer.
First, if cost and effort were nothing, then one can make a broad statement about loudspeakers. All of dynamic problems get worst the greater the level.
It is logical then to use a speaker, which can go MUCH louder than it will be used at so that it is always in a more or less linear region. Like they say “Headroom is your friend”
I believe this is partly why older theater and commercial speakers have a following in hifi, other problems aside, they have headroom in a livingroom.
Second, in say “home theater” a goal is to be able to reach 120 dB (or more) at the seats.
I had the pleasure of attending an outdoor cinema at the home of a Home theater installer who uses our products in his large jobs. Being outside, it was a large room but he was able to reach the needed levels.
http://www.keithyates.com/news.htm
Some pictures of the cinema
http://www.danleysoundlabs.com/forum/photos/photo-thumbnails.asp?albumid=2
Anyway, most of his presentation was live music clips like Diana Krull etc and it was really cool watching / hearing it at comfortable concert level..
Part B, what is on CD’s?
Your right, there is a practical limit and what you see when you dissect music is a trend like this.
FM pop music, rolled off at 50Hz and 15KHz, brick wall dynamic limit by law, generally compressed at broadcast to the point of stationary VU meters.
By measure, this often has a peak to average ratio of 6dB to 10dB, peaks are 4 to 10 times the average power, much like pink noise.
The same Pop CD’s are often spectrally “flat” even approaching 20K but are compressed to about a 10 dB peak to average. These often sound hot or bright and glaring on good speakers but fine on FM or lesser speakers.
Good “hifi” CD’s are more like 20-30 dB peak to average about 100:1 to 1000:1 in peak to average power. These would likely be un listenable able in a moving car because of the noise floor.
On our website I posted a recording I made of our Town’s fireworks as heard from my backyard. It has NO compression and has a peak to average of 40 dB or 10,000:1 and occupies a total dynamic span of 70 dB or 10,000,000,000:1 in power
http://www.danleysoundlabs.com/knowledge%20baSE.htm
Part C, what is practical?
Lets say you lived in a quiet neighborhood and had a quiet house special construction, your noise floor might be 10- 20dB spl without the wind blowing outside .
A more normal house might be in the 30 or even 40dB noise floor range.
Lets say you had speakers that were 100dB sensitive and you sat 3.3 meters away from them. Lets say you wanted to reach an instantaneous peak of 120dB at your chair.
Now, 3.3m is –10 dB from 1 m so the speakers must produce a peak level of 130dB at 1 m and so with 100dB 1w1m, it requires a peak of 1000 Watts and average power of 1/10 Watt..
Yes, below some frequency you will have room gain and the reverberant field which helps SPL but it is desirable NOT to have or be in the reverberant field if you can and room gain only helps at the very low end. Also, the idea is each channel is independently capable.
So, is this realistic?
Take the fireworks recording, it has a difference of 40 dB between the average level and peak levels and 70dB between the loudest and quietest signals.
Playing this recording at this level makes the average level 80dB and the quietest parts about 50dB, which is well above the room noise floor.
With an average level of 80dB, this would not sound that loud, like being outside although the bangs make you flinch.
If one had a real quiet room (specially constructed, special air handling room isolation etc), say 20dB noise floor, then on could listen to the entire dynamic range with a peak level as low as about (20dBnf+ 70dB dnr) 90dB although ones frequency response has shifted at that lower level.
In this case one could use a 90 dB sensitive speaker with a peak power of 10 Watts.
At the far other extreme, take FM rok, with the same peak SPL of 120dB, the average would be 114dB and you probably wouldn’t even hear the po po as the swatty boys bust in, eager to face the enemy (you the obviously dangerous audio terrorist), only the concussion grenades (superb transient response although messy indoors) alert you to the impending tear gas attack. Rumors behind the headlines at 5.
So what is needed?
It depends what you want to do.
Some of the most cherished and loved music of all times was recorded on a format which only had about 35- 40 dB between 0dB and the noise floor.
The key to so many things in audio is making compromises in an audibly graceful way, historically there has never been a way to capture all of what you can experience dynamically.
It is I suppose ironic that as the recording technology has evolved to the point it has while much of what is done with it has gone the other direction.
One can only shake there head at what has happened.
Now the science of persuasion has been honed to such a degree that the average person on the street thinks the “tinycubes” and other Nose brand things are “the good stuff”.
We are always told what ever they are trying to sell, it is better than what was before.
“With that superior MP3 sound” the add said. Yep, you need to really compress and process the hell out of music to make it satisfying coming out of a 1 inch speaker.
I should just stop, this whole situation pisses me off.
Sorry for the rant.
Tom Danley
"Now, 3.3m is –10 dB from 1 m so the speakers must produce a peak level of 130dB at 1 m and so with 100dB 1w1m, it requires a peak of 1000 Watts and average power of 1/10 Watt.."
No Tom the real drop in a normal sized room is less than this at this distance with wall reflections and such. Not sure about the math you are producing here. If we assume your 10db drop then the speaker at 3.3 meters is BEHAVING like a 90db speaker at 1 meter, right. However; you have two to them (stereo) so that adds another 6db so what we really have is 96 db sensitivity (approx) at that distance. To reach 120db then would be the following:
96 db = 1 watt
99 db = 2 watts
102 db = 4 watts
105 db = 8 watts
108 db = 16 watts
111 db = 32 watts
114 db = 64 watts
117 db = 128 watts
120 db = 256 watts
I am pretty sure that 10db is an excessive drop in a normal sized room. I would think 6 db would be more likely or even less if the speaker is a line source. Assuming 4 db more sensitivity would drop the power requirements to around 100 watts with your speaker example... 1/10th what you suggested is necessary.
Now while this is a lot of watts one would assume this peak would last only a few ms and if the amp clips then the question is how fast does it recover and is that instantaneous clipping actually audible?
Hi
The “real drop” for a point source is set by the inverse square law which is as described.
It is true if you’re in a room you unavoidably have reflected sound, to what ever degree this reverberant field can be reduced, the larger the speaker’s nearfield region is (where direct sound dominates). In reality, due to reverberant field, if you were in a large enough room, you would find the SPL eventually stops falling VS distance when your dominated by reverberant sound.
Of course at that point, it is also fully unintelligible, incoherent sound.
With a TEF machine (gated window which see’s direct sound) even in a room, one see’s the inverse square law on normal speakers.
Also, coherent addition such as you mention where two speakers raise the level 6dB, only applies when the speakers are less than ¼ wl apart (only low bass).
For what its worth, it is assumed that ideally each channel is independently capable.
In my experience, very short clipping is not audible as “clipping” or anything wrong BUT when compared to say an amplifier that had more headroom, it was audible as a difference between them with the un-clipped sounding a little more dynamic.
Most minor dynamic issues are not audible “stand alone” )like what speakers do) but become audible when you A/B “with and without”.
Best,
Tom Danley
Great post Tom. So many really don't understand the real problem.
Now personally I just buy (older) records. I am often surprised how good some of the stuff from the 50's is. But I am curious if you favor some of the remastered/re-engineered and/or stuff like mapleshade? In short where do you look for "quality" recordings and what is your usual format?
Russ
Hi
I have a short ton of old records and my trusty old turntable and Ortofon but most of my favorite stuff I re-bought on CD or transcribed to CD.
I have loved music since my Grandfather played his recordings on his mono / tube / heathkit hifi. A later experience in the pipe loft at church (when I was helping him clean up after service) when the organist was playing, stuck with me and lead to a love of low frequency sound in particular (poop in link below if interested)
http://systemscontractor.com/articles/publish/article_977.shtml
Anyway, later jobs were mixing bands, doing some recording (which I have picked back up in the digital world now) and trying to get my kids interested in music.
For the last 25 years I have pretty much worked on new types of transducers, electronics for Space Shuttle experiments and loudspeakers full time.
The last 15 years I have spent a lot of time on full range speakers and systems with the last 10 on various horn arrangements.
I have found many old recordings have come to life on the new speakers.
Albums (some) I have heard since I was a teen, were literally reborn into a wonderful recordings, once some speaker issues were gone.
Led Zeplin 1 was the first “re-discovery” like that.
Other recordings were revealed as being even uglier than before but I have to say, many of them were very good. Dark side of the Moon, basically anything Alan Parsons mastered seems good.
Some of these guys were truly artists, they didn’t think of what the y had as limited, they sought to do as much as they could with what the “state of the art” provided.
I think partly what is wrong now is the pallet of tools is so vast, the nube mixer has to approach it by getting told what to do, copying what everyone else does.
Part B is music is so much more corporatized and monolithic that there is much less room for anything that is too far off the text book target.
I also have a collection of what I think of as hifi demo recordings, ones that are sonically impressive. I have a couple Maple shade discs but the one I have used (Kendra Shank) in demo, also has a noticeable distortion in one channel in a few places (like in Paris Bossa) but is otherwise very “live”.
My real dream is to figure out how to capture a real stereo image of live things.
The 24/96 digital format would have been to give a right arm for in the old days, it offers real possibilities for small scale recording.
I started back into this using my Daughters Korg D1200 and was just stunned, tape died right then and there for me anyway..
That fireworks’ recording is one made with a microphone invention I’m working on.
I have sent some other recordings to the web dudes but they have not put them up yet.
Anyway, sounds like your from the same era, we probably have some of the same music.
Best,
Tom Danley
You might try to run down a copy of the Cheryl Porter CD "These Foolish Things." It was an Italian recording done for Nagra by Marco Lincetto. It is one of the least processed commercial recordings I've heard and gives an excellent insight into the dynamic range missing from most recordings. The music is excellent. Cheryl Porter has a wonderful, powerful, expressive voice that is a very interesting combination of gospel spiritual and classic opera training that is now mostly devoted to jazz. Not an easy CD to find, but certainly worth a search.
> Now personally I just buy (older) records. I am often surprised how good
> some of the stuff from the 50's is...
That's great if all of the music you wish to listen to is on old LP records, but there is plenty of new music I like. The Waifs, Thea Gilmore, Karl Jenkins, etc. who are only on CD (or have just have perhaps one album on a difficult-to-find LP.)
As Tom noted, the entire world of recorded music, regardless of format, is a series of compromises from the studio to the final release you play on your stereo. Ultimately we need to remember that it is the music we are after and not just a sound demo to impress our friends. Our brains are quite capable of filling in missing detail and helping us compensate for the technical compromises of recorded music. At some point, no matter how fancy or meager our stereo, we need to "turn over" our listening experience and just enjoy the pleasure that music brings us.
Part of the problem is most don't take into account what the actual SPL is where your seated with 1 watt. You need to have enough power avialable for "realistic" levels there not at 1 meter. You also need speakers that will remain linear in both the frequency and dynamic domains for any hope of pulling off a realistic presentation through that entire power range. No easy task.
"If you are rocking along with an average room loudness of 90 or 100 dB, there almost certainly isn't 20 or 30 dB of headroom left on the recording."
That's the extreme. You want as much dynamic range over above your average level as you can get. Ideally a system capable of a clean 115Db level where your seated would not be out of line. The key is to keep it clean with no clipping.
> That's the extreme. You want as much dynamic range over above your average
> level as you can get. Ideally a system capable of a clean 115DbExtreme? I'd like to see a recording that has you listening at an average level of 90+ dB that has 20 or 25 dB of headroom left on the recording.
If it is not on the recording, the amp can't be asked to deliver it to the speaker. Do you have an example? I do a lot of work in Adobe Audition with recordings and don't think I've ever seen an example that would support this.
While we do not listen at 1 meter, our rooms are also reverberant and not anechoic chambers, so the increase in power needed for a normal listening position isn't as much as an anechoic test would suggest.
I certainly am not anti-power and would agree that it is certainly a good thing to have plenty of headroom. All other things equal, if you can get some extra power without sacrificing other parameters, go for it. But we rarely have an "all things are equal" scenario, and I think it can be a mistake to elevate this one issue over all others to top priority.
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