Hello, friends!
I'm planning my own project, which will have 2 full-range speakers of 20 W RMS (4 ohms) each and one subwoofer of 150 W RMS (4 ohms). I don't plan to listen to music at full volume. So I plan to use DIY 2.1 amp (25+25W and 50W). But will a 50W sub amplifier have enough power to drive 150W subwoofer? I understand that it won't play loudly. But will amp fail? Or will it cause too much distortion? Or just will play without perceptible bass?
Thanks for help!
PS. I can't purchase a less powerful subwoofer and have to work with what I have.
I'm planning my own project, which will have 2 full-range speakers of 20 W RMS (4 ohms) each and one subwoofer of 150 W RMS (4 ohms). I don't plan to listen to music at full volume. So I plan to use DIY 2.1 amp (25+25W and 50W). But will a 50W sub amplifier have enough power to drive 150W subwoofer? I understand that it won't play loudly. But will amp fail? Or will it cause too much distortion? Or just will play without perceptible bass?
Thanks for help!
PS. I can't purchase a less powerful subwoofer and have to work with what I have.
It will work and it will play loudly, but 4.77 dB less loudly than with a 150 W amplifier.
By the way, you might be interested in the first couple of posts of https://www.diyaudio.com/community/...h-voltage-power-do-your-speakers-need.204857/
By the way, you might be interested in the first couple of posts of https://www.diyaudio.com/community/...h-voltage-power-do-your-speakers-need.204857/
^^ Clipping at maximum blast levels will start 4.77dB lower (theatre level gunshots, explosions etc), but yeah. 99% of the time the exact same volume can be enjoyed when those sort of peak levels are not required.
Thanks to all for help! I understand that all be ok with my planning amp and sub. But how do you get this magic 4.77dB? How can I calculate this value for some other power values and drivers?
10 dB times the base 10 logarithm of the power ratio. That follows directly from the definition of the decibel scale, which must be covered on Wikipedia somewhere.
Ok. I understand. 10*Lg(150w/50w) = 4.77. Thanks!
And what about using 50W amp on 20W speaker? Am I right, that on max volume it will damage the speaker?
And what about using 50W amp on 20W speaker? Am I right, that on max volume it will damage the speaker?
There is no information how hard it is to drive a speaker that is specified as "150W" - this figure is how much power it can handle. A 150W driver does not need a 150W amplifier. The specification how efficient a speaker is, is stated as "Sensitivity". This figure tells you how much of the power one enters into a driver will come out as sound pressure. This is one figure to keep track of when dimensioning an audio system. 1 watt in might for some drivers output 80 dB (somewhat loud) but an other one might do 100dB (very loud) - both could be specified to handle a max of 150 watt. But it could also be that the less efficient one can only handle 50 watt and the very efficient one could take 500 watt - this can very a lot and one need to read the driver specification to know.
If the amp has lower output power than what the driver can handle it means that the amp can clip and produce a lot of high frequency trash - this HF heats up the cold and may ruing the driver quite quickly. On the other hand, having an amp that has much higher output the what the driver is specified for will start to overdrive the speaker but still with clean power - this will be very loud, if an efficient speaker was used, and will probably make you lower the level because your ear hurts. Also, when a driver is overpowered it will distort and also here, in the end, will burn out due to to much power is dissipated in the coil.
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If the amp has lower output power than what the driver can handle it means that the amp can clip and produce a lot of high frequency trash - this HF heats up the cold and may ruing the driver quite quickly. On the other hand, having an amp that has much higher output the what the driver is specified for will start to overdrive the speaker but still with clean power - this will be very loud, if an efficient speaker was used, and will probably make you lower the level because your ear hurts. Also, when a driver is overpowered it will distort and also here, in the end, will burn out due to to much power is dissipated in the coil.
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OK, one more thing to clear. I plan to listen to music in the bedroom, at a low volume, about the level of normal human conversation. According to Wikipedia, this is approximately 55-60 dB. Is it possible to somehow convert this value into the approximate required power of the amplifier? My woofer has 89.0 dB @ 2.83V and 86.0 dB @ 1W/1m. Thank you very much for the detailed explanations.
Theoretically, assuming a 1 metre reverberation radius, you would need about 0.0025 W if you only wanted to listen to sine waves at speech frequencies. 10(60 - 86)/10 W ~= 0.0025 W.
In reality, you need more because of the crest factor of music and because music can contain frequencies that are less audible than speech, such as deep bass. I would guess that anything above 1 W per channel would do, though.
In reality, you need more because of the crest factor of music and because music can contain frequencies that are less audible than speech, such as deep bass. I would guess that anything above 1 W per channel would do, though.
Sorry, but one more question. For quiet music it's clear that 2-3W would be more then enough. But what if I want (rarely!) listen something louder. Not as loud as on party, but as loud, as most people listen when doing training or something like that? Let's suppose it would be 75dB. So, 10(75 - 86)/10 W = 0.08W. If I multiply it in 400 (like you did in your post) I would get 32W. Am I right? Or something about 10-15W would still be enough for quite loud listening?
Thank you!
Thank you!
As a general rule, radio, TV, DVD, etc., is limited to +20 dB dynamic headroom (crest factor)/channel for all but (+30 dB) LFE soundtracks, so 10^(20/10) = 100 W added to however much you need @ 1 W/m, i.e. if 0.8 W/m average, then in theory 0.8*100 = 8 W/m peak and if 2m = 16 W, 4m = 32 W, 8m = 64 W, etc., i.e. MarcelvdG's decibel scale, though sound power rolls off a bit slower in typical size home rooms:
Octaves math, inverse square law:
Fh = Fl*2^n
Fl = Fh/2^n
n = ln(Fh/Fl)/ln(2)
where:
Fh = upper frequency
Fl = lower frequency
n = octave spread
Octaves math, inverse square law:
Fh = Fl*2^n
Fl = Fh/2^n
n = ln(Fh/Fl)/ln(2)
where:
Fh = upper frequency
Fl = lower frequency
n = octave spread
Typo! 
s/b your 0.08W*100 = 8 W
Sound power expands exponentially, ergo 'someone' chose to define its 2:1 ratio expansion as an 'octave', so let's say you want to use a 1st order XO (6 dB/octave) at 500 Hz/-24 dB, so 24/6 = 4 octaves away = 500*2^4 = 8000 Hz or work it backwards to prove = 8000/4000/2000/1000/500
s/b your 0.08W*100 = 8 WSound power expands exponentially, ergo 'someone' chose to define its 2:1 ratio expansion as an 'octave', so let's say you want to use a 1st order XO (6 dB/octave) at 500 Hz/-24 dB, so 24/6 = 4 octaves away = 500*2^4 = 8000 Hz or work it backwards to prove = 8000/4000/2000/1000/500
What you got is fine for what you are doing. Its not like you making a system that has to be overheard by other people playing their musical instruments at the same time.
There is a good quara post on one aspect of this
https://www.quora.com/Do-we-need-hi...eed-also-120-dB-to-hear-it-How-does-that-work
Bear in mind normal speech is about 60dB a whisper about 30. On say a film you might set the volume in that range. Then comes dynamic range - one view discussed here. There probably are others
https://sound-au.com/articles/amp-power.htm
One tricky aspect is the efficiency of the speakers that are being used. Out of curiosity I found an old nomogram on this. It suggests that for concert levels in my size of room I would need 23w RMS per channel with 1% efficiency speakers.
The low frequency end also has it's oddities. The power needed to achieve some dB level. Eg exceeding 100dB at 20Hz needs a 1kw amp. Quoting some one and not working it out. Would commercially sourced music produce something that needs that? Few could make use of it. They are far more likely to make sure that level of power just isn't needed and that their music can be played by far less capable systems,
https://www.quora.com/Do-we-need-hi...eed-also-120-dB-to-hear-it-How-does-that-work
Bear in mind normal speech is about 60dB a whisper about 30. On say a film you might set the volume in that range. Then comes dynamic range - one view discussed here. There probably are others
https://sound-au.com/articles/amp-power.htm
One tricky aspect is the efficiency of the speakers that are being used. Out of curiosity I found an old nomogram on this. It suggests that for concert levels in my size of room I would need 23w RMS per channel with 1% efficiency speakers.
The low frequency end also has it's oddities. The power needed to achieve some dB level. Eg exceeding 100dB at 20Hz needs a 1kw amp. Quoting some one and not working it out. Would commercially sourced music produce something that needs that? Few could make use of it. They are far more likely to make sure that level of power just isn't needed and that their music can be played by far less capable systems,
