Amplifier power regarding speakers, room, ears (Newbie question)

[TasKitas]

Hello everyone,

A while ago I slowly started to learn about electronics and especially audio. So far, I've made LM3886 (powered by 24-0-24 toroidal) (still without case) and it is powering some old Magnat 20cm (8") car speakers.

I don't know how exactly the quality should sound but so far it seems not bad for me.
For fun I've tested TDA7377 amp which I got from old car stereo, connected it to 12V toroid (~16VDC) and at my usual listening levels I could barely feel the difference and it even reached quite high volume.
I've measured the RMS Voltage across the 4ohm load, the max power before distortion was about 4W. To compare, my LM3886 can give up to 65W.

For my future goal, I’d like to make audio system in living room, 2 speakers neat TV (probably towers, powered by LM3886) and 2 at the back, still wondering what driver should it be, but I'd like to use my 12-0-12 toroidal. And by how I hear it, I feels like I could just slap 4 more powerful 4 channel car audio amp and it will be enough.

Now the question, since such low power can power these speakers pretty well how much power would the living room (size 5 meters x 4 meters) would need? Also, since most speakers have more than one driver, I should consider this fact as well. And furthermore, there are some very sensitive speakers, some people even use high quality low power amplifiers and are happy.

This seems like there are too many variables and how can one solve it? I would like to hear how people of this forum solved this problem and how you did it in your beginning of audio electronics.

TL'DR I have LM3886 and recently tested TDA7377, used 20cm (8”) car speaker, TDA which is much lower power compared to LM and it sounds loud enough for room. So how do you set the audio system in your room and how to calculate how much power do you need? How the power gets distributed to proper multi driver speakers and how to include the sensitivity and size of the room into calculation?

Eddit: Applied bold

[ubergeeknz]

Generally, there's no need to make any precise calculations.

For an average size room, and normal efficiency speakers, about 15W should be enough for normal listening levels. The rest is additional headroom, which is a good thing and you can't really have too much, tradeoffs such as increased noise (due to higher gain), expense, power consumption and physical size aside.

If you do want to figure it out; take the efficiency of the speaker at 1W/1m and adjust based on the sound level you want to achieve at a certain distance.

Sound pressure level will increase 3dB for each time you double the power, and decrease 6dB for each time you double the distance.

So to achieve the specified SPL at 1m from a 2m distance requires 4x as much power from the amplifier.

A stereo system has 2 x speakers. This also increases output by 3dB as it is effectively doubling the input power, so you can take that into account or treat as one speaker with twice the input power.

The size of the room shouldn't make a *huge* difference in the calculation aside from how far the listener will be from the speakers. In reality it will affect frequency response the effective speaker efficiency, someone might be able to provide formulas or a table to help with that.

I've attached a chart to give a reference for how loud things are in dB SPL. As you can see, over 100dB you're getting into discomfort and hearing loss territory, but a rock concert might be as loud as 120dB so if that's what you're looking for you're going to need either a lot of power, or very efficient speakers.Attachment 895014

[chermann]

Hi
good explanation.thank you.
your link is not working....
chris

[ubergeeknz]

Sorry about the attachment, here you go.images%20(27).jpg

[brig001]

Try this:
A Test. How much Voltage (power) do your speakers need?
A Test. How much Voltage (power) do your speakers need?

Brian

[ubergeeknz]

I also found this article, goes into some detail on the topic.
The Decibel (dB) Scale & Audio Rules 101 | Audioholics

[TasKitas]

Thank you for your answers

Originally Posted by ubergeeknz

A stereo system has 2 x speakers. This also increases output by 3dB as it is effectively doubling the input power, so you can take that into account or treat as one speaker with twice the input power.
Attachment 895014

I wouldn't have thought of that. After raeding what you say, i've tried to measure how loud do I listen to music and measure it.

brig001 this is a really good piece of information as well. Actually i've did something similar myself, using music, then switching to 1khz tone on youtube, the voltage was about 5V, so I guess that's enough, but in future I plan to use different speakers, so these test tones should be just perfect!

ubergeeknz Thank you for this informative article. It helps to put things into perspective.

I've measured the sound using mobile app, as far as I can consider it accurate, the normal sound levels for me are 70-75DB and if I want really loud 80-85 so that's more than enough.

So I guess I shouldn't put that much attention when, for example, speakers say 100W RMS, it should for as fine with 50 just not as loud? Or there are other things to consider that I'm not aware at?

[MAAC0]

So I guess I shouldn't put that much attention when, for example, speakers say 100W RMS,

Speaker Wattage doesn't mean anything. It only give You a relation between Your amp & speakers. It is more or less powerful than You amp. It Blows or not blows faster.

A poor 90dB 100 W speaker is quieter than a 100dB one with the same amp when placed side by side.

Efficiency is what really matters when comparing speakers & of course quality & frequency response.

how much power would the living room (size 5 meters x 4 meters) would need?

It depends on how much pain You want to feel in Your ears, but bear in mind all speakers need a minimum power applied in order to overcome inherent mechanical resistance.
For example, PA speakers like to be played loud.

[Richard Ellis]

Historically, loud music reproduction had to "make due" with just a few Watts of power for a whole auditorium. case in point, the vintage 1970s large 43XX JBL far-field monitors were rated about at 120 Watts...todays far-field monitors are half the size & consume well over 1000 Watts of power.
Wattage is horrifically cheap now a days, so loudspeakers are now getting less & less efficient.
Watch "Silbatone, Western Electric, Joe Roberts describes the system, Highend Munich", on Youtube...listen with your decent headphones.





----------------------------------------------------------------------Rick........

[ubergeeknz]

Yes, 85dB is already quite loud. 95 is clutch-your-ears loud. So generally, power levels need not be high. Although some specialised high end speakers are very low efficiency and do need a lot of power.