Stated output of amps compared to actual

[Vincent]

Didier you mention the TDA 2050-do these ever need repacing? it is bolted onto an alimunium heatsink block-which obviously gets warm.I wonder if that affects the thing in time. It's important to fit the correct shim-or washer which is a transparent material as well as heat paste( I believe it's known as Mica).

[Vincent]

Does the TDA 2050 module ever need replacing? This is bolted to a heat sink and you need the correct thermal shim or pad to go with it plus heat paste. I wondered if in time the heat affects the thing.

[Didier]

Does the TDA 2050 module ever need replacing? This is bolted to a heat sink and you need the correct thermal shim or pad to go with it plus heat paste. I wondered if in time the heat affects the thing.

Replacing the TDA2050 power chip on a Cambridge 30 amp is is a subject which has been much discussed on the net, and I have some documentation about it, but I have not yet attempted to do it myself, and I am not completly sure about isolation and heat sink issues.
There is another problem : is the Cambridge 30 power supply strong enough to make a LM3875 power chip deliver all of its rated power ? I don't have the answer.

Didier

[Graylion]

In a similar vein here's a question for an expert (i.e. Didier!) Amplifier output power and actual volume are on a logarithmic scale whereby the apparent volume, for instance, only doubles when the power is increased by a factor of 10. Meaning that, all things being equal in the speaker department, a 1000 Watt amp will only sound twice as loud as a 100 Watt amp.

The question: will two 100 watt amps sound twice as loud as one?

Logic says they will, but what has that got to do with anything?
Cheers, Lionel

[Didier]

In a similar vein here's a question for an expert (i.e. Didier!) Amplifier output power and actual volume are on a logarithmic scale whereby the apparent volume, for instance, only doubles when the power is increased by a factor of 10. Meaning that, all things being equal in the speaker department, a 1000 Watt amp will only sound twice as loud as a 100 Watt amp.

The question: will two 100 watt amps sound twice as loud as one?

Logic says they will, but what has that got to do with anything?
Cheers, Lionel

No, two 100 Watt amp will sound like a 200 Watt amp, not like a 1000 Watt amp !

Loudness level are generally expressed in dB, which is a logarithmic unit. You need to double the electric power to gain 3dB.

This is why the speaker sensivity is an important matter. Speaker sensivity is genrally measured for 1 watt at 1 meter. A speaker with 100 dB sensivity will sound as loud with a 15 watt amp than a speaker with 97 dB sensivity with a 30 watt amp.
This is why changing the speaker by one with higher sensivity may improve a lot a budget amp (which are generaly fitted with low sensivity cheap speakers).
I tested a Celestion G10 vintage speaker which has a 97 dB sensivity on a Cambridge 30 amp with excellent results. I don't know the sensivity of the original Bulldog speaker, but it's likely to be around 94 dB at best.
The replacement was easy, as the speakers have the same basket, so no mechanical modifications were needed.



Bottom left : the original 10" Bulldog speaker (with blue basket) from the Cambridge 30 amp.
Bottom right : the G10 Vinage speaker, with a much bigger magnet, hence the higher sensivity.
Up center : a 8" Bulldog speaker from a Vox Pathfinder 15R amp (I cheked if a 10" speaker could fit inside the Pathfinder 15R cabinet, but it wasn't the case).

Didier

[peter roest]

Maybe this is more easy to understand.
Suppose an amp gives 10 Watt electrical output into a 100 dB rated speaker. The speaker would give a certain sound level.
To get the same sound level out of a 97 dB speaker, you need 20 Watt electrical output, a 94dB speaker needs 40 watt, a 91 dB speaker needs 80 Watt out of the amp.

Peter

[Graylion]

Thanks Didier - yes, I know about speaker sensitivity but the question is simply about comparative volume using two identical combo amps with identical speakers - as I said, logic tells you that two seperate amps will sound twice as loud as one!

I picked 2 x 100dB speakers (Eminence 1058 Legend) to give the maximum volume from my 'pseudo' Watkins Dominator, 18 Watt, V-front amp, knowing that it will be louder than using 97dB speakers.
Cheers, Lionel

[JimN]

Thanks Didier - yes, I know about speaker sensitivity but the question is simply about comparative volume using two identical combo amps with identical speakers - as I said, logic tells you that two seperate amps will sound twice as loud as one!
Cheers, Lionel

There truth in that. If it were not so, there'd be no difference between the sound of a single-speaker amp (like the 1x12 AC30 combo) and the two-speaker version. And that's even without the extra amplification.

JN

[Bob Dore]

If you have two speakers next to each other they are said to be close coupled. If each one is generating a level of xdB(SPL) then the result is x+3dB(SPL).

To sound twice as loud requires an increase of 10dB so you would need just over 8 speakers close coupled to get this.

Bob.

[Didier]

If you have two speakers next to each other they are said to be close coupled. If each one is generating a level of xdB(SPL) then the result is x+3dB(SPL).

But if they are powered by the same amp, each speaker will receive only half of the electrical power, so no 3dB gain...

But when several speakers are close to each other and fed with the same signal, interferences between them will result in directional effects. With several speakers side by side, the sound will be focused horizontally, with several speakers one above the other the sound will be focused vertically. This was first described by Harry F Olson in 1957 (also called "line array").
Vertical speaker columns are often used in PA, the sound if focused vertically, so reducing reflections on ground and ceiling. Another result of focusing the sound is to give a slightly louder sound for listeners in front of the "beam".
Two speakers have been used on AC30 only because the speakers could only handle 15W. Dick Denney obviously didn't know about the Olson effect, otherwise the two speakers would have been set one above the other !...
More details about line array here : http://www.performing-musician.com/pm/f ... hnotes.htm

Didier