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Proprius daisy-chaining for driving RAAL SR1a

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Ash View Drop Down
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    Posted: 02 Mar 2020 at 11:31pm
Can the output terminals of Proprius monoblocks be joined together to combine their power outputs for driving highly inefficient loads? Three Proprius per channel = 150W into 4 Ohms?? Thinking of trying these earspeakers but want competent electronics to do it with.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 7:22am
The "ribbon" is rectangular piece of stainless steel foil. The signal is applied to either end. Electrically it represents a short-circuit. Its impedance is 0.2 ohms.

The adapter box houses a number of power resistors which pad-up the resistance to a value more-suited to the output of an amplifier.

The "gold" anodised colour which can be seen through the slots in the top of the adaptor box, suggests the use of finned power resistors, and that type are wire-wound. As such their inductive effect with increasing frequency can be seen from the resistance and phase curves plotted by Stereophile (below).

Stereophile Raal SR1a headphones impedance and phase plot

The low frequency end gives us the resistive value, which looks to be around 5.8 ohms, which suggests some 5.6 ohms of series resistance.

Obviously, the signal will be considerably attenuated between amplifier and ribbon, and from the above estimation it looks to be 29:1 (or 0.0345).

However, none of the above really matters because the RAAL specification gives us the sensitivity of the box plus ribbon, which is 91dB for 1 watt.

Regarding the Proprius, as we have done a number of times before, we know that 25 watts represents an SPL increase of 14dB.

I think 91dB (for 1 watt) will be quite loud, and the increase above that (25 watts), occupied by transient information, will peak at 105dB.

This is 6dB short of the maximum quoted SPL of 111dB, but I would doubt I would ever wish to apply such sound pressure to my ears.

It should also be born in mind that the Proprius will output a little more into the 5.8 ohm load than its 8 ohm rating of 25 watts. It will be nearer to 34 watts, which will take it to 106.3dB.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 7:50am
So try it from one pair of Proprius first, as it may be enough depending on ear-to-driver distance. Others suggest 150W minimum but the whole power scale in audio is absurd. Don't understand why they make devices so inefficient that much of their power generates heat instead of sound. 150 Watts is a huge amount of power...

91dB/W puts it in perspective.

MySphere 3.1/3.2 is 96dB/mW so over 1000-fold increase in available power is required. My MS3.1 with voltage divider cable makes it a roughly equivalent load to the K1000 from Proprius, which is 120 Ohm impedance and sensitivity of 74dB per mW.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 2:52pm
It only needs a 75W into 8 ohm amp to reach 111dB max. SPL.

101dB SPL sounds half as loud.

You can reach half way between these with what you already have.

You would be able to get 108.3 dB SPL from the amp resulting from my 70's Design Indulgence.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote CageyH Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 6:02pm
101 dB? I would want eat defenders on at that level.Shocked
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 7:04pm
Once I've finished my K1000/3.1 comparisons/photography, I will sell the K1000 and pursue the SR1a. A loan may be pretty expensive so might buy blind and compare them to MySphere. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote discrete badger Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 8:10pm
Some of the SPL numbers being quoted in those reviews (even as necessary!) are mind-boggling.

http://www.sengpielaudio.com/PermissibleExposureTime.htm

This is quite interesting, and aligns with other scales I have seen, and my experiences in that I get a bit uncomfortable with >90db for long periods. Great fun for short climaxes though.

There is a reason that the great romantic composers use the orchestral tutti - with brass in full flight - sparingly. They intuitively understand what the human hearing system is capable of tolerating, and that great climaxes are all the better when set in a context of a range of contrasting dynamics.

Some types of contemporary music, and "loudness wars" mastering techniques just don't get it, and so much is being lost.
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