More on Amplifier Power & Loudness

I want to double my listening level so I need an amp of double my amp’s power, right?

Wrong, you are in for a disappointment when you upgrade your 100w amp to a 200w amp… you will only hear a small increase in output level!  You need about 10x the power to double the sound level, so in fact you need a 1000w amp! And 1000w amps are unheard off in the domestic market! Luckily these sort of sound levels are seldom important for quality music listening but it can be important if you want the ‘real’ cinema experience in your dedicated Home Theatre (HT) room.

The problem is the relationship between POWER and SOUND OUTPUT LEVEL (loudness) is not linear that means if you double the power you will not get double the loudness.

Power is measured in watts (a unit of energy) and Loudness is measured in decibels (dB).  A “deci”-“bel” means  1/10  of a bel (a unit of  sound  named after the inventor of the telephone Graham Bell). The human ear can hear an amazing wide range of sound levels so wide that in fact you have to describe it in terms of a logarithmic scale. On this scale 0dB means complete silence and 140 dB means the threshold of ear pain.  For instance a whisper is about 20db where background noise in an office is about 60db, a full orchestra can go up to 100 db and a live rock concert up to 120dB. A jet engine flying over your head is about 140dB. The human ear can pick up changes of about 1dB and an increase of about 10dB is about twice as loud. So it’s interesting to note that a 200w amp can only produce about 3dB more loudness than a 100w amp and that is not much more than the 1dB possible difference detectable by your ears. So its not a surprise that you hardly hear much more sound output when you change your 100w amp for a 200w amp!! ..so if your local sales person tells you this 120w amp will go much louder than your existing 100w amp, ignore that you will hardly hear any difference.

It is interesting to note that this 3dB increase is only a drop in the ocean compared to the 0 dB to 120db you can get at a live rock concert this is why it is basically impossible to reproduce the “live sound experience” in your HT room!

So what should I do if I need more sound output level and cannot afford a 1000w amp?

Fortunately there are two other options here that you can consider:

1. You can go for 4 ohm speakers but make sure your amp can handle this.  You roughly need twice the power to drive an 8 ohm speaker to the same sound level as a 4 ohm speaker of the same sensitivity.  So with a 100w amp you will get the same sound level output from a 4 ohm speaker as a 200w amp out of a 8 ohm speaker.

2. The second option is to go for more sensitive speakers. The sensitivity of normal speakers today varies between 86 db and 92 db (horn loaded speakers can typically go to 100 db or more).  It’s generally the norm that for each 3 db increase in sound level output you have to double the amp’s power.  Say your amp is 100 w and your speaker’s sensitivity is 87 db.  If you change the speakers to 90db sensitive speakers (not expensive to get) you will get the same output level as a 200w (very expensive) amp into your old 87db speakers. 200w amps are basically non existing in the HT market except at the very high-end of $10000!  So it’s a huge cost saving by going for the 90db sensitive speakers.

So the moral of the story is:  if you are looking for HT gear for loud output levels look at a HT receiver than can drive 4 ohms speakers and go for speakers of high sensitivity of at least 90 db. Luckily these come only at a small premium in price. Avoid cheap speakers as they are generally not of high sensitivity and cheap amps cannot drive 4 ohms speakers.

This is not the place to warn you about these models. Just scan the internet forums for these issues and you will be shocked to learn that most popular  brands you see in your local shops are just that… not suitable for  even the average HT setup. Sadly once you part with your money…their is no return. I have seen so many clients burning their fingers on these popular mass market products because they are “a bargain” and “look so good on paper”.  That is the reason why you will not see those Brands on our site. Spend a little bit more and you will be satisfied.