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Discussion Starter #1
am i reading the decibel calculator correctly? is this calculator fairly accurate?

sensitivity 1w/1m - 92db
amp power - 40 watts (i'm assuming this means 40 watts per channel, 40 watts to each speaker)
number of speakers - 6
distance to speaker(s) - 20 feet
spl - 107.9 db

 

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There's one way to find out...

Got your ear protection handy?

Hook it up. Apply signal. Twist knob. Measure.

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Decibel Exposure Time Guidelines Accepted standards for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and CDC, 2002. Each 3 decibel (dB) increase above 85 decibels cuts the permissible exposure time in half. Exceeding these times will likely result in permanent hearing loss.

Continuous dB Permissible Exposure Time
85db 8 hours
88dB 4 hours
91db 2 hours
94db 1 hour
97db 30 minutes
100db 15 minutes
103db 7.5 minutes
106dB 3.75 min (< 4min)
109dB 1.875 min (< 2min)
112dB .9375 min (~1 min)
115dB .46875 min (~30 sec)
 

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i've been looking at multi-channel amps and was surprised to find that the far, far majority were rated around 40-60 watts per channel, a far cry from the 100 watts per channel (min) i needed to fill a large room according to many posts i've read at avs and other sites, posts that always seemed to confirm that more power is best, if not essential. but if this calculator is right, it appears that achieving loudness with 6 speakers rated at 92db won't be much of a problem with much lower watts per channel than 100w, even at a distance of 20 feet. and if you play around with the sensitivity number, drop it a few, the calculated decibels can still be high. so what am i missing (a lot i'm guessing because i'm not much of an audiophile, as if you can't tell).
 

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Discussion Starter #5
Try another calculator like this http://myhometheater.homestead.com/splcalculator.html

Is the result surprising to you?
well it pretty much confirms the results of the first calculator i used, again if i'm reading it correctly, which as i mentioned i did indeed find surprising. i mean it appears that very, very loud sound can be achieved with relatively modest watts per channel, given the input variables used, even at a distance of 20 feet from the source, something which runs contrary to a lot of posts i've read here and at other forums, posts that suggested 100 watts per channel (min) is what would be needed to fill a large room, to create loudness in a large room. but it seems that a 60 watts per channel amp, assuming it did in fact produce 60 watts per channel, would be plenty, no? btw thanks for the link and RayDunzl thanks for the db breakdown, albeit it's not as colorful as some of the available graphical charts showing jackhamers, car horns and jets taking off!

 

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Keep in mind the results are summed from 6 speakers at the listening position. If you want each of your speakers to be capable of a certain spl, that's a bit different. Then again some speakers even with the power just really aren't capable of high spls due to compression/distortion.
 

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Keep in mind the results are summed from 6 speakers at the listening position. If you want each of your speakers to be capable of a certain spl, that's a bit different. Then again some speakers even with the power just really aren't capable of high spls due to compression/distortion.
yes, i understand that, but even if you use 1 speaker the calculator returns 95db at 20 feet, 98db for a pair of speakers... so i guess i'm just wondering why 100+ watts per channel amps seem to be considered imperative by many, even if you're using a powered sub(s)?
 

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yes, i understand that, but even if you use 1 speaker the calculator returns 95db at 20 feet, 98db for a pair of speakers... so i guess i'm just wondering why 100+ watts per channel amps seem to be considered imperative by many, even if you're using a powered sub(s)?
A 30dB difference - not an abnormal range of soft to loud - has a power factor of 1000

The watts add up quickly for those momentary peaks.
 

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yes, i understand that, but even if you use 1 speaker the calculator returns 95db at 20 feet, 98db for a pair of speakers... so i guess i'm just wondering why 100+ watts per channel amps seem to be considered imperative by many, even if you're using a powered sub(s)?
All depends on the material you listen to, what you want for spl/peaks/headroom, and what your speakers are actually capable of.

Just because some are hyping bigger amps doesn't mean they really know why. The Emotiva/Polk forums/threads seem to have a high number of such.
 

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Most people would be shocked at how little average power they actually use... In the primordial past I've annoyed more than one 'phile by quietly bypassing their new amp, bumping the volume a hair on their receiver, and listening to the description of the vast improvement the amp made before turning off the amp to prove it wasn't in line... Not to say some do not need one for various reasons (sonic or psychotic ;) ).
 
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I always figured, a small amount of distortion may not be noticeable, but reference level sounds might require quite a bit of power. But consider you can drop volume setting by 3 dB, a small drop in loudness and HALF your power needs. In other words, you can save some money by accepting some drop in SPL which may not be too burdensome. I managed to get reasonable SPL levels with one of Yamaha's cheapest receivers and I did not hear an obvious drop in quality

Your mileage may vary, etc.
 

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yes, i understand that, but even if you use 1 speaker the calculator returns 95db at 20 feet, 98db for a pair of speakers... so i guess i'm just wondering why 100+ watts per channel amps seem to be considered imperative by many, even if you're using a powered sub(s)?
I've got good news and bad news.

Good News: "6dB double distance" isn't true in typical rooms. Figure you lose 4dB every doubling of distance between listener and speaker.

Bad News:
  • Your speaker's average sensitivity might really be lower than advertised.

  • Your speaker's nominal impedance might be over-stated.

    I find it fairly typical in reviews where they measure the impedance to find that the impedance dipped to much lower than 80% of advertised nominal impedance. Like an "8ohm speaker" that has a 3ohm dip at 160Hz.

    Thus, this speaker should've been listed more like a 4ohm speaker. Thus it'd draw twice the watts for a given voltage. It's half as efficient as you'd be led to believe. You'd need a beefier amp than you'd think, and one that is 4ohm stable at that.

  • Your speaker's sensitivity probably isn't 92dB at all frequencies.
    It was probably measured (or extrapolated) at 2.83v, which is a volume level driven by your receiver. The actual wattage drawn by the speaker will vary by the impedance curve. If you've seen such graphs, you've seen that they often vary wildly by frequency. The average wattage drawn relates to the speaker's efficiency. A 3ohm impedance dip like described above will draw 2.7x the power (and 3x the current) versus a frequency that's 8ohms.

    If you subscribe to a principle of "You're only as good as your weakest link" (like, the strength of a dam), then you care less what the system can do as an "average." You care more that your midbass would draw 3x the current and 2.7x the watts. And midbass is where most of the power of music lies. And midbass-slam is what people seek in their system...like what you'd get at a concert.

    So, taking your SPL Calc screenshot above, where you only needed 40w for 103dB peaks: For my example speaker with an impedance dip to 3ohms, you'd actually need 107w of power for that peak, and 6amps of current. Does the amp have that? If it was more honestly a 60w 8ohm amp... maybe it does, if it's stable to 4ohms. Or, maybe it doesn't, and the amp distorts.

    Or maybe the 92dB speaker is really 89dB, and it needs 214w, and it's definitely distorting.

    Or, maybe you add a beefier amp that's 300w @ 8ohm and 200w @ 4ohm, but then the speaker is distorting a lot more because it handles 40w with aplomb, 100-200w with some strain (like distortion goes up, and you don't get the dB peaks that you should be getting, so the music is less dynamic), and it breaks at 400w.

So, just like in other types of engineering: what are the needs/demands/requirements? And make a system that exceeds that in capability, so that it's loafing along.

What I wrote above is not applicable to you if you don't listen above -15 on your master volume.
 

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One can take various charts and try to calculate power required and SPL...
But why guess... :rolleyes:
SPL is based upon loudspeaker brand/model, room size/acoustics and amplifier voltage/current capability.
There are multiple SPL measurement APPs available for Android and IOs devices for no much $..

A point that many users don't grasp is that an amplifier's power output capability is largely based upon its power supply design/cost. Unfortunately, today's AVRs are puny in comparison to the earlier, quality-brand receivers now the market is more concerned with # of channels and the latest DSP surround modes.. Even though a powered subwoofer is used in >90% of the home theaters systems, along with small satellites...
These systems may satisfy the wife and expectations of a cinema sound track playback capability, however they fall far short of delivering great sonics for music.

Since we are in the product development/sourcing end of the AV biz, we have access to various brands and have (3) different systems. (1-2 channel, 1-5.1 channels, 1-9.2 channels) Though I like to watch an action-filled movie with multi-channel effects, I get the greatest pleasure out of a good music disc either in vinyl or CD on my 2-channel music system. My music system uses an older Marantz amplifier and 4-way tower loudspeakers designed by a close friend who has over 35 years of loudspeaker design experience with JBL.

IMHO...
Don't get hung up on all of the math and published electrical specifications. Sit down and listen to a quality, sonic music performance it is a great experience.. :)
Thanx for listening..

Just my $0.02... ;)
 

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I like Eyleron's thinking and it agrees with what I found after buying class A/B monoblocks as my speaker's impedance dips all the way to 2 ohms, but the manufacturer calls it an 8 ohm speaker.

To further add to the discussion:
It is crazy to think your peaks will be no higher than 103dB, especially if you watch movies.

If your room's noise floor is 55dB (takes into account you breathing at the MLP), assume playback some of the most dynamic tracks available (probably maximum dynamic range (DR) in any musical recording is 60dB), and match the quietest part of the track with the room's noise floor: that alone calls for 115dB!?!

Now, what type of amp does that require using the calculator referenced above?

Add that to what Eyleron is saying about impedance swings, and you really need a much much bigger amp to avoid any clipping than 40 watts. I don't care what anyone tells you on here.

Note that you may not even hear or notice clipping, so a lot of folks on here say you just need these low wattage amps.

On my system, I play back tracks at an average level of 85dBA, I would definitely hear the difference between a small 40 watt amp and large monoblocks (300 watt or higher) on my most dynamic tracks which I measured to have 45dB using the DR Foobar2000 plugin.

I haven't measured the DR of a movie track yet, but I'd expect it to be even greater. Nothing wrong with headroom either...

I find it fairly typical in reviews where they measure the impedance to find that the impedance dipped to much lower than 80% of advertised nominal impedance. Like an "8ohm speaker" that has a 3ohm dip at 160Hz.
 
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