More than 25watts realy needed ?

jcx

Member
2003-02-17 7:38 pm
..
assume 2x speakers, room gain gives ~87 dB/W at the listening spot for those speakers - then 25 W clips at 101 dB SPL

now read up on live music peak values, live concert levels - no you shouldn't listen all day at those levels - but you'll never achieve "realism" without a system capable of reaching live music dynamic peaks

90 - 100 average at live jazz club for a hot set, much higher at a "dance club"

even unamplified classical orchestra's peak way over 101 dB in the audience


while Loudness War compresion now makes anything over 12 dB peak-to-average seem "dynamic" now - really good dynamic recordings can go over 20 dB peak-to-average
 
Hi Guys

jxdking, the "1/8 watt" notation is incorrect unless your speakers are about 22-ohms.

The 2v82 standard is supposed to be equal to 1W into 8R.

87db is quite loud. In my own listening room, such an SPL is what I might blast myself with rarely - but usually when this happens I am not in the same room. It is too loud to subject yourself to for any length of time. 70db is much more of a loud TV or movie watching level and requires a lot less power. Frankly, 25W for your whole system is probably quite suitable - and is likely fine for most people.

What works against low-watt systems is mostly fashion, the low cost of solid-state power, marketing, and the low efficency of tiny speakers and woofers.

So-called "subwoofers" are really just woofers in a separate box. There should be two in a stereo system.

My system has two subs that actually go down to 13Hz and two fullrange monitors, biamped with a few watts per output possible to cover peaks. I installed clip LEDs on each of the four speaker outputs. They never light up even for crazy loudness.

Because I measured the SPLs and power used in my room before building a new system, I knew that I only needed a low amount of power. This translates into a low voltage gain given the outputs of most signal sources. With that info, I decided to use Lineup's diamond-feedback buffer for each of the power amps. The active crossovers use discrete opamps and drive the buffers. There is stepped gain ahead of the crossover so that for any listening scenario, the sweep of the volume control can be better utilised for fine control.

There is a fascination with the 120db end of the loudness ranges listed. Modern live music tends to be 100dB+ with no let up. Higher is ridulous and should be criminal. Sound companies should be fined out of business and owners should do jail time for subjecting the public to such SPLs which do serious harm. This is a health factor that cannot be ignored anymore. It is so easy to just turn it down and what do you know?... the music sounds better quieter. You can actually hear everything.

Note that for the most part, designing for lower power does not necessarily mean the PA circuit will be simpler than for higher power. All the same issues of design are still present. However, you have a few more options inasmuch as pure class-A - which can for some designs result in much lower THD - can be utilised with a reasonable heat cost. Paralleling output devices is still beneficial, as is reduced loading on VAS, optimising for neutral distortion spectrum, and so on.

Have fun
Kevin O'Connor
 
what actually makes the real difference is that you cannot design big amplifiers with astronomical bandwidth, input Z of 500K ,and without real protection such is input limiting or VI limiters .

smaller amplifiers have lower risk and obviously can be designs without all the above so smaller amplifiers have chances to sound better the rest is only load depending...

Kevin... Nice to see you around How are you ??

Kind regards
Sakis
 
Hi Guys

Bandwidth limiting at the input of an amp is worthwhile regardless of the power output. There is no real point to allow a lot of ultrasonic and possibly RF signal through the amp as this can cause basic overheating apart from stability issues with the load.

Protection circuits can be eliminated if the output stage is sized to handle the full supply voltage at the full load current - a 90-degree load. To this end, and even just for the sake of easy mounting, it is best to err on the side of larger semiconductor packages: TO-247, TO-264 rather than TO-220. On the other hand, there are TO-220F devices with outstanding performance and these can easily be paralleled to meet the above condition of dissipation.

Sakis, fine, still working on the hifi book, new web site about to be launched.Nice to see you too.

Have fun
Kevin O'Connor
 

Junm

Member
2008-12-23 5:52 am
Dau
I had built a 150w/ch amp before and also a 50W/ch. using the same speaker, not commercial brand but personal built. 12 inch woofer at 350W and dome tweeter at 150W two way config.
When listening at the 150 w amp, its very clean and really detailed especially at low volume compared to 50w and commercial 70w amp, using all transistor ouputs. Also tried chip amps and a 10w class A amp but nothing close to my 150w amp, so even listening at low volume i prefer this 150w amp.

Others right, it really depends on what speakers ,listening area and type of music and maybe the amp itself.