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Graham Slee Power Amplifier

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Post Options Post Options   Thanks (0) Thanks(0)   Quote bakastra Quote  Post ReplyReply Direct Link To This Post Posted: 19 Dec 2014 at 7:13am

Originally posted by CageyH CageyH wrote:

I have a 2m and a 5m interconnect, and 2 x 1m speaker cables.


5m + 2m -- is it to keep the TT hidden away from the speakers??

Edited by bakastra - 19 Dec 2014 at 7:14am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CageyH Quote  Post ReplyReply Direct Link To This Post Posted: 19 Dec 2014 at 7:47am
It's the length of cable I needed from my pre-amp to the mono blocks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bakastra Quote  Post ReplyReply Direct Link To This Post Posted: 19 Dec 2014 at 7:52am
Originally posted by CageyH CageyH wrote:

It's the length of cable I needed from my pre-amp to the mono blocks.


Of course; sorry! I am still not used to the concept of monoblocks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2016 at 5:25pm
Originally posted by Graham Slee Graham Slee wrote:

"A pair of Proprius were used for a music evening in a pub venue in the Midlands a few months ago.
OK, they did use a pair of Klipschorns which are quite sensitive. I am told the event was packed but it was loud enough to get over the noise of the crowd. It was basically a disco using a disco front end with a quality mixer.

John C did comment however that on leaving the venue quite late, the sound could be heard from the car park across the road at a volume fitting for a disco.

Attendees commented on the good quality of the sound and the organisers have asked to use the pair of Proprius again. By the way, the phono preamps used were a pair of Gram Amp 2 SE which the organisers had bought.

So, are they going to be loud enough?

Just because the speakers have a rating of 300 watts does not mean they need 300 watts.

On our two own events (which we invited everybody to but only 30-40 turned up) we demonstrated that 25 watts per channel (real rms) could drive the relatively inefficient 11 Ohm LS35A speakers to a really healthy volume with excellent sound quality in hotel conference rooms much larger than the usual domestic living room.

But, even after saying all that, I guess people may not be convinced."

 Any quality-built amplifier (like the Proprius) with greater than 20 watts rms power output is sufficient enough to drive speakers available today with very pleasing results.
 (By quality-built I mean: one that has enough current and voltage "headroom" designed-in, wide enough frequency response to not hinder delicate or powerfull sound passages, and extremely low distortion measurements at loud and quiet sound levels.)

The Proprius amplifiers can produce 26 watts rms driving into an 8 ohm speaker load... rms = rout-mean-square (another mathematical term for average power).
 That same rms power can be as much as 52 watts peak power, or more, even 70 watts instantaneous. That is the solid state circuit doing it's best into 8 ohms.
When driving into 4 ohms it will be almost 2 X as much!

Note that the 11 Ohm LS35A speakers are not that low in efficiency at 88dB @ 1 watt/1.5 meters, and the Klipschorns mentioned above are very high in efficiency  at about 95+ dB @ 1 watt/1 meter ( maybe as much as 98 dB!).
 That means with the same 1 watt input the Klipschorns would be about 10 dB louder!

Your speakers own sensitivity to the power applied to it will tell you how loud that speaker will be at a given power level (not how powerful your amp is).
 If your speakers can handle 50 watts rms and you drive them with 100 watts rms, you can easily burn out your speakers! even at half volume! First to go will be the tweeters.

 I always rate my speakers to handle 2 X the RMS power or more of the amplifier I intend to connect them to.
 And then I want to get speakers with as high an efficiency as possible.

I currently have some speakers rated at 200 watts rms connected to my 60 watt rms amplifier; these speakers have an efficiency of 96 dB @ 1 watt/1 meter.
And they get very loud at just 1 watt... the neighbors complain loud!
I have to keep the volume down to less than 1/2 watt to keep the peace.

See my next post for info about decibel levels and how to approximate decibels at different power levels.



Edited by BAK - 09 Jan 2016 at 5:27pm
Bruce
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2016 at 5:28pm
Efficiency is more important than power handling for sound quality.
It is a matter of physics.
Every time a quantity of energy is transformed from one energy form to another there is a loss of energy. The loss can be quantified by measuring the efficiency of the transformation.
With a lower efficiency transformation, less of the original information from the energy source is reproduced in the end result.
 This amounts to less of the original sound energy is reproduced in lower efficiency speakers.

The dissertation below will prove that any quality-built amplifier (like the Proprius) with greater than 20 watts rms power output is sufficient enough to drive speakers available today with very pleasing results.

 (By quality-built I mean: one that has enough current and voltage "headroom" designed-in, wide enough frequency response to not hinder delicate or powerfull sound passages, and extremely low distortion measurements at loud and quiet sound levels.)

A little-known fact is:
 In old-school electronics,
less than 1 watt rms = low power,
from 1 watt to 10 watts = medium power,
greater than 10 watts rms = HIGH POWER...(100 watts rms is extra high but was not mentioned in the reference)

This rating scheme came from early radio days.
 It was found that less than 1 watt rms was all that was needed for "personal" listening; with  headphones or a pocket radio.
 1 watt to 10 watts was needed to fill the average room with sound as with a table radio (most were between 1.5 and 5 watts).
 Greater than 10 watts rms was only needed to fill large rooms.

Average commercial speaker sensitivity today is about 85 dB @ 1 watt rms measured @ 1 meter, in short form...85 dB @ 1 w/1m. That means that you get 85 dB at 1 watt when measured with a sound pressure measurement instrument with a calibrated microphone from a distance of 1 meter directly in front of the speaker, in the center of the speaker's radiating pattern...or straight in front.

 The below is a way to approximate decibel levels.
Note: An increase in Acoustic power (dBw) is ... 10 Decibels = 10 x log of 10watts / 1watts.

Now with acoustic power you add 10 dB for every multiple of 10 watts rms... or each time you multiply the power by 10.
 If with 1 watt you get 85 dB,
 then at 10 watts you get 95 dB,
 at 100 watts you will get 105 dB!
Again with acoustic power you add 3 dB for every multiple of 2
watts rms... or each time you multiply the power by 2.
 If with 1 watt you get 85 dB,
 then at 2 watts you get 88 db (+3 dB),
 at 4 watts you get 91 dB (+3 dB),
  and at 8 watts you get 94 dB (+3 dB),

 from above, at 10 watts you get 95 dB,
 then at 20 watts you get 98 dB (+3 dB).

If you have an 8 ohm speaker capable of producing 95 dB @ 1w/1m,
 you will get 105 dB @ 10 watts / 1m,
 and then 108 dB @ 20 watts / 1m,
 and about 110 dB @ 26 watts / 1m (Proprius power @ 8 ohms),
 and 115 dB @ 100 watts / 1m.

You see from above that, if you have a higher efficiency speaker, you will get more sound measured in decibels at any
acoustic power level than you will from a lower efficiency speaker.
You will also be able to drive the higher efficiency speaker with less power to get the same amount of sound!

This is why professional sound systems use very high efficiency speaker drivers.



Edited by BAK - 09 Jan 2016 at 6:50pm
Bruce
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ICL1P Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2016 at 6:11pm
Hi Bruce,

It's a good and informative read.  Could it be converted into a blog post outside this thread.  There's so much misinformation out in the big bad world about how much power is needed.  It would be good to to have the real world story to point others towards.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2016 at 9:22pm
The problem we have here Bruce is that we understand professional sound systems but professional sound systems are not taken seriously by the majority of readers.

Probably the reason for this is all the cheap rubbish being sold as professional these days.

You and I are of an age where we remember what professional meant.

I've had to work out speaker efficiencies and amplifier powers to be able to fill an auditorium to be able to quote for work, and if I'd got it wrong it would have bankrupted me, so therefore I had to get it right--and did do.

To be on-budget meant I couldn't throw in lots of excess power because watts cost money. I also had to know the equipment which delivered real watts.

In Hi-Fi none of that matters - it's all about name-dropping their favourite brand , China and a liberal sprinkling of BS.

There's no art to power amp design anymore - it's all formula design - power amps are just a commodity like gasoline! If I had my time over again I wouldn't be hitting my head against a wall on here!!
Not simple enough for Google-Bot to understand...
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