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Topic: The Decibel (dB) Scale & Audio Rules 101 |
b0b
From:
Cloverdale, CA, USA
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Posted 11 Feb 2018 10:07 am |
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I ran across this very informative article about amplifier power and loudness. It's geared towards home audio, but the science is the same for live music.
www.audioholics.com/room-acoustics/the-decibel-db
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Every doubling of power is another +3dB of loudness. So:
2 w = 89 dB
4 w = 92 dB
8 w = 95 dB
16 w = 98 dB
32 w = 101 dB
64 w = 104 dB
128 w = 107 dB
256 w = 110 dB |
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Billy Easton
From:
Nashville, TN USA
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Posted 11 Feb 2018 10:52 am
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So Bob...
what does the "w" refer to in their explanation?
Billy
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Billy & Meriul Easton
Nashville, TN |
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Ian Rae
From:
Redditch, England
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Posted 11 Feb 2018 11:01 am
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Watts, the unit of power. Should be in capitals.
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Georg SĆørtun
From:
Mandal, Agder, Norway
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Posted 11 Feb 2018 12:05 pm Re: The Decibel (dB) Scale & Audio Rules 101
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| Quote: |
| Every doubling of power is another +3dB of loudness. |
That's what makes me relax when it comes to available power (how many Watt an amplifier can deliver), as an 160 Watt amp is barely louder than an 80 Watt amp when all else is equal - speaker/cab with same efficiency etc.
It takes four times the power to get twice the loudness (+6db), so although it is nice to have a little extra headroom at times, a few Watt difference in available power makes no difference in loudness. A lot more to gain by putting a more sensitive speaker in a better cabinet. |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 11 Feb 2018 12:32 pm
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| b0b, I've been enjoying your most recent posts, you may have to put an E/I warning that the post is educational/informative! |
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Ken Fox
From:
Nashville GA USA
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Posted 11 Feb 2018 12:55 pm
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George is right on. A more efficient speaker is much cheaper than buying more power.
For years I played a 1965 Deluxe, non reverb with a D120F speaker. It was so efficient I could keep up with most a Twin a Reverb amps that used stock, inefficient speakers
I now play guitar with a 1967 Princeton Reverb with a 12" Jenson Neo. Fact is I got two them. I hardly ever need the second one. Little amp us around 12-14 watts |
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Jim Sliff
From:
Lawndale California, USA
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Posted 11 Feb 2018 2:18 pm
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It's important to note that this is *theoretical*, though.
Perceived "loudness" is not a function of power (watts). Speaker sensitivity can change the loudness level of an amp - easily [cut it in half in the case of low-efficiency speakers.
And total square inches of speaker cone; cabinet size, material, construction style, open/closed back; cabinet placement in the room (or on thes tage...and stage type/height etc if any); room size/shape; ceiling height/shape/construction; wall coverings/construction (drywall, glass, wood, carpeted, shelved etc) and so on....
PLUS the frequencies reproduced and distortion level/type....
...ALL change how the human ear hears sound, and all cause changes in what we consider to be "loud" or "soft". Regardless of what an SPL meter might read.
Nevertheless, it's useful stuff. One additional point is that 3db (if everything else is equal) is generally the minimum difference the human ear notices.
From a practical standpoint - what Ken said. Most players still use "too much amp" and can't turn it up enough to drive the speaker(s) to full frequency response. I can't gig any longer due to some physical problems but when I did I rarely used anything larger than a Deluxe Reverb for pedal steel, and often a '55 tweed 5D3 Deluxe that pushed all of 12 watts through an original Jensen P12Q. Unmic'd and perfectly clean in clubs.
Amp power - no matter the type - just isn't a good indicator of volume. Ken's example was excellent; another is the relative volume of a Twin Reverb - an 80 watt amp - and a Vox AC30 - a 30 watt-ish amp. If both are the stock 2x12 versions (the Twin with CTS or equivalent stock speakers), in good repair (serviced and with good tubes) they're on pretty much equal footing!
One quick qualifier, especially regarding tube amps - they HAVE to be serviced periodically. Filter capacitors have an effective service life of around 15 years, other parts can wear out, tubes need to be replaced (especially those made in the last 25 years - vintage RCA, GE, Sylvania, Mullard, Tung-Sol and so on...not the so-called "reissues" - are often still good), and when power tubes are replaced in "fixed bias" amps the bias needs to be checked and usually adjusted.
Manufacturers don't publish this information anywhere and most used amp sellers have no clue, so I recommend ALL newly purchased, used tube amps over 10 years old go directly to a tech for examination/service (unless there's documentation of qualified, recent service).
Before even turning them on.
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1921 Weissenborn Style 2; Hilo&Schireson hollownecks
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1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Scott Duckworth
From:
Etowah, TN Western Foothills of the Smokies
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Posted 12 Feb 2018 3:39 am
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| Ken Fox wrote: |
George is right on. A more efficient speaker is much cheaper than buying more power.
For years I played a 1965 Deluxe, non reverb with a D120F speaker. It was so efficient I could keep up with most a Twin a Reverb amps that used stock, inefficient speakers
I now play guitar with a 1967 Princeton Reverb with a 12" Jenson Neo. Fact is I got two them. I hardly ever need the second one. Little amp us around 12-14 watts |
Same is true in amateur radio (or any radio service). If you don't have a good antenna, throwing more power at it doesn't help.
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ajm
From:
Los Angeles
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Posted 12 Feb 2018 8:56 am
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Jim Sliff: "Amp power - no matter the type - just isn't a good indicator of volume."
I've often found it to be a good indicator on if the guitar player is going to be too loud. ;>)) |
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ajm
From:
Los Angeles
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Posted 12 Feb 2018 9:09 am
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Georg brings up another point or topic: What is the difference between headroom versus input sensitivity?
I always equated them as being the same, but either I'm wrong or most of the internet is. ;>))
It seems that most people equate headroom with the maximum volume available from an amp. But input sensitivity and the signal level you're feeding the amp are just as important.
I always thought that headroom equated to the largest signal you could feed into an amp before the preamp stage(s) clipped. It has nothing to do with the volume knob or power available.
If you feed a cheap Strat into a (for example) Deluxe Reverb you'll have lots of room on the amp volume knob before you get any clipping.
Turn on a CLEAN boost pedal set to max and you're probably going to get distortion regardless of how the volume knob is set.
Your "head" has just hit the ceiling of the preamp and you have no more "room".
Like I said, I'm probably wrong but that is how I always envisioned things. |
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Georg SĆørtun
From:
Mandal, Agder, Norway
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Posted 12 Feb 2018 10:01 am
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Every amp-stage has a ceiling. If the headroom is used up to the point of clip/distortion in an early or intermediate stage, headroom in following stages doesn't matter much since they cannot fix what's "broken".
If all amp-stages are well balanced with regard to headroom, the last stage will have slightly lower headroom than the ones before it. In practice that is rarely ever the case, as just a little boost on the equalizer to get the right tone, or increasing sensitivity on the input-stage to reduce amp-noise, lower the headroom on those stages. Chances are those pre-stages don't have all that much extra headroom to go on compared to the output stage, and having an output-stage with more headroom than the preceding stages is of little use. |
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b0b
From:
Cloverdale, CA, USA
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 12 Feb 2018 9:07 pm
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'Nother fun fact:
The Merriam Webster dictionary references to "first known use" can be extraordinarily inaccurate. I don't know where they get their data, but it is often quite deficient. Consider that their "first known use" of the term pedal steel guitar was in 1965!  |
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Dustin Rigsby
From:
Parts Unknown, Ohio
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Posted 15 Feb 2018 12:23 pm
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And this is how a 65 W musicman head became my preferred amp for everything ! Celestion loaded Marshall 410 for guitar and a Jensen Neo 15 for steel. More than enough amp for any situation. Good thread b0b !
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