dB/watts Logic Check For Me Please

[vertigo]

Hey guys,

So I'm trying to see if my logic here makes sense. I ran MCACC on my Pioneer Elite and it made me think... If it set the volume to be 105dB at my listening position as "0" and set my front speakers to -3dB at my listening position 11ft away (it gives quarter inches as well but whatever)

So is my logic correct that with the Vistas being 90dB speakers if I typically listen to my system at around -26dB does that theoretically mean I'm using roughly .84watts?

'Cause that's just silly if it's true.

 

[tsv_1]

I'm not sure I totally follow you here... but I'll take a flailing stab in the dark. First a massive disclaimer: Speaker sensitivity, impedance, power, perceived listening levels, magical receiver correction algorithms, phase lag, damping factors, atmospheric pressure, etc etc... it can all get a bit intense to parse if you really dig into it. Also, having no idea what your engineering background may be, I apologize in advance if the next part is either too light or too heavy.

With that said, a decent starting point, first order anyway, is to note that a 90db efficient speaker will produce 90dB SPL (sound pressure level) at 1KHz with 1 watt of power applied. So if you listen to your speakers at 90dB SPL on average (at about a meter away), then you're burning about 1 watt. Simple enough.

If your receiver is REALLY accurately reflecting SPL dBs and you're saying that you listen on average to about 79dB (105dB - 26dB... if I followed you right on that??). Then you are burning way less than 1 watt on average (keeping in mind that the power halves for every 3dB drop). Of course we would need to correct for your actual listening distance from the primary radiation lobe, etc.

I won't go into any further specifics because I'm not sure I really understand/follow your question :think:... but hopefully this hasn't been a complete waste of your time (or mine )

Cheers

 

[amey01]

I don't follow you either. Please state the question clearly, with complete information and correct grammar/punctuation.

However, I will say that for regular listening levels, an amplifier running at about 1w is pretty average. Music is dynamic in nature though, and that figure is always changing. One bass drum hit could spike it to 10-20w or more - but only for a split second.

How marketing can make you believe that you need something which you don't need (watts). Watts are important - but not as important as they make you think. As they say - the first watt is the one that counts. But that doesn't look impressive on paper, does it?

 

[tsv_1]

As they say - the first watt is the one that counts. But that doesn't look impressive on paper, does it?

Ya gotta love Nelson... http://www.firstwatt.com/ :bowdown:

 

[Peter_Klim]

I'm confused....is that .84 watts as in watts total or as in watts per channel?

 

[vertigo]

Still trying to sort it out

tsv_1 - You're pickin' up what I'm puttin' down.

Basically, my question was geared to figure out how much watts total AND per channel is my "average" listening consuming. The point of it all for me is so that I can better understand how much amplification I need.

The ultimate goal being do I need a 500watts per channel amp or should I spend my money on a lower powered tube etc.

- I am 11 feet from the speaker
- My front speakers were corrected by MCACC to -3dB for front right and -3.5dB for front left (let's just call them both -3dB) to have a reference level of 105dB at my listening position.
- Reference being "0"
- My crossover to sub is at 80

The question is:

Roughly how much power am I consuming at my listening position with the volume set to -26dB AND how much power am I consuming at 105dB (reference) so that I can have enough overhead to cover the swings.

Does that make more sense?

 

[Speedskater]

"tsv's" math exercise is for one channel with one speaker. With two channels and two speakers, things get real complicated real quick!
Like position of the speakers (and test frequency), position of the mic, mono or stereo signal and so on.

 

[tsv_1]

"tsv's" math exercise is for one channel with one speaker. With two channels and two speakers, things get real complicated real quick!
Like position of the speakers (and test frequency), position of the mic, mono or stereo signal and so on.

correctamundo, the deeper one digs, the murkier it all gets.

 

[tsv_1]

tsv_1 - You're pickin' up what I'm puttin' down.

Basically, my question was geared to figure out how much watts total AND per channel is my "average" listening consuming. The point of it all for me is so that I can better understand how much amplification I need.

The ultimate goal being do I need a 500watts per channel amp or should I spend my money on a lower powered tube etc.

- I am 11 feet from the speaker
- My front speakers were corrected by MCACC to -3dB for front right and -3.5dB for front left (let's just call them both -3dB) to have a reference level of 105dB at my listening position.
- Reference being "0"
- My crossover to sub is at 80

The question is:

Roughly how much power am I consuming at my listening position with the volume set to -26dB AND how much power am I consuming at 105dB (reference) so that I can have enough overhead to cover the swings.

Does that make more sense?

Frankly, I don't think it's worth sweating over. Any deep analysis is subject to too many variables.

Given fairly decent speaker efficiency of 90dB, and given the average listening levels you seem to normally enjoy (which are probably around or below 1 watt per channel based on the data provided), and given that you need 10 times the power to get twice the loudness (because human hearing is essentially logarithmic), and given that it's late and I'm ready for beddy... I'm gonna say you would be absolutely fine with 120W/ch in your system - assuming you have solid amplification that truly delivers undistorted 120W/ch power upon peak demand.

This will provide you with 4X perceived loudness during peaks - relative to your average listening level, plus a little extra headroom on top of that. Frankly, I just don't think you need much more. Few people really do. Also, most people use a powered subwoofer as well which significantly helps to offload your 5.1 or 7.1 amplification requirements.

Now, if your system looks, feels, and smells like an IMAX theater, then you may want a few more electrons flowing... but my guess is your room is probably more livingroomish in size, so we're likely in the right ballpark, er, livingroom.

Now, folks can (and probably will) argue this opinion because hey, that's what makes forums fun... and you are certainly free to completely dismiss my input (Lord knows it won't be the first time).

Cheers and good luck with your system... and most of all, have fun!

 

[amey01]

Roughly how much power am I consuming at my listening position

Yes - this makes more sense. But it is not really answerable.

It is a constantly changing thing - based on the music (of course), but also the frequency, length of time, level, impedance curve of your speakers, etc.

As I said earlier - most amps are mostly giving very, VERY low output when playing quite loudly. But it is the transients that can really push it out.

And remember - sound level/watts is not linear either - if there is a passage in your music that is twice as loud, that will demand 10x power from the amplifier.

Most amps with most speakers are running at about 0.2 - 1.5 watts when listening at moderate levels. But as above, this will blow out to 15 watts in a louder passage if the loudness doubles. 150 watts if it doubles again. Add a kick drum at the same time and you could be up to 300 watts.

Also worth noting - most amps are quite happy to deliver this sort of thing for a short time due to power in reserve. But not continually.

So, as before, the first watt is what counts as that is what you are listening to most of the time. But more power is always beneficial as it ensures the transients are handled correctly and without distortion. To a lesser extent it will also allow you to turn it up louder, but remember doubling the amplifier power is hardly going to give you a noticible difference in perceived sound level (3dB). If you want to double the loudness generated by a 100w amp, you're going to need 1kW.

 

[Sambob2]

As a few other posters have mentioned, this is more complicated than the simple math. However this will get us close enough for what it is intended for. First we will compute what is called the acoustic level change and work from there. My disclaimer, I am not an expert at this but have some knowledge and reference books from a 2 year technical audio engineering course I went thru back in the late 70’s. So here’s my go at it, if anyone sees something incorrect, please speak up. I have not done this in a while but lets give it a whirl...

Acoustic level change is given as: 20 log D1/D2

Where:
D1 is the listening distance in meters. In your case 11 feet which equals 3.35m (meters)
D2 is the distance the speaker sensitivity, typically 1 meter

Using the acoustic loss equation above:
20 log 3.35/1 = 10.51dB

10.51dB is the acoustic level change for your distance of 3.35m (11 ft).

105dB is fairly loud. I am going to work this in two ways. First I am going to work this problem backwards. That is, I am going to assume the 105dB level as including the additional 10dB to cover the “overhead to cover the swings” as you put it. (For your information, 10 dB is typical (standard) for covering the extra power to cover any program peaks). So I will first work with 105dB – 10dB for a 95dB steady state signal at your listening position. Second, I will provide the increased level of 105dB + 10dB = 115dB at your listening position. 115dB is very loud!

In order to obtain 105dB at your listening position we have to take your desired sound pressure level (SPL) of 105Db and add the acoustic level change to it. So we have, 105dB + 10.51dB or 115.51dB at 1 meter from the speaker in order to obtain 105dB at 11feet.

Side note: typical acoustic loss is reduced by 6db for every doubling of distance from the source. Example: If we measure 90dB at 1 meter, then we will get 84 db at 2 meters, 78db at 4 meters, 72 db at 8 meters, and so on. The physical reason for this is as the distance away from the source doubles, the area surrounding the source quadruples.

First:
Using 1 watt of electrical power to obtain the speakers 90dB efficiency at 1 meter, 115.51dB – 90dB = 25.51dB. So the power required is:
10 raised to 25.51dB/10= 355.63 watts

You would need an amplifier capable of 355.63 Watts into your speaker impedance to provide 105dB on peak material at 11 feet.


Second:
If you want to go the route of obtaining enough electrical power to obtain 115 db at your listening position; 105dB of steady state program material plus the extra 10dB to cover peak program material, then:
105dB + 10dB =115dB desired at the listening position. To this we add the acoustic loss of 10.51db. So, 115dB + 10.51db = 125.51db 1 meter from the speaker.

Using 1 watt of electrical power to obtain the speakers 90dB efficiency at 1 meter, then 125.51 – 90 = 35.51Db. So the power required is:
10 raised to 35.51dB/10= 3556.3 watts

If you turn your system down 26 dB, you are using about 1 watt of power.

Hope this helps some…
Sam

 

[tsv_1]

Nice analysis Sam... is your analysis for a single transducer source, or did I miss something?

It sounds like Vertigo may be talking about a 5.1 or maybe 7.1 system... multiple sources surrounding the listener (highly dependent on source material, obviously). Also, and I could be all wet here, but I was under the impression that acoustical loss factors are different for point-source versus line source (or panel source).

Regardless... it all goes back to the first point: this topic gets complicated fast. Heck, we haven't even considered elevation or humidity factors yet

Vertigo, I can tell you from experience that I get no perceived dynamic compression or clipping at VERY HIGH levels in my 7.1 HT. (see my link for details on my setup if interested). From a practical standpoint, I just don't think you need anything more than 120W/ch assuming 90dB transducers. But that's just me

Cheers

 

[Spike]

Sam,
Your analysis is for a single point source speaker. The Logans are line source and they behave differently than point source. In my experiment, I measured a difference of 4db at 12 feet away from my ReQuest speaker. Here's the link to my analysis: Dynamic Range and Power Claims In my analysis, 50 watt per channel suffice for my needs.

Spike

 

[Speedskater]

And then we have not yet begun to consider what a somewhat reverberant room will do to the equations.

 

[tsv_1]

And then we have not yet begun to consider what a somewhat reverberant room will do to the equations.

quite right... nor room cavity resonances or speaker radiation patterns (on and off axis)... nor for that matter, inebriation levels