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High sensitivity/low sensitivity. ξ = Ø


RichP714

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After I acquired my V20 I needed a speaker that would work in concert with my rig.  After months of exhaustive research I purchased my Spatial M3s. They are a 4 ohm(nominal) impedence speaker that’s provides 94dB on axis/1m/1watt that got absolute rave reviews from the M3 fan base. The M3s have been a special purchase and a great addition to my rig’s synergy.

 

I’ve also owned very hard to drive speakers. They require big power to be revealing and that means big $$. I ran Alex Sauter’s ALllls vertically bi-amped with a pair of Lightstar 2.0s years back that was revealing, musical and dynamic. 

 

There is a case for both methodology types but it ultimately comes down to implementation and synergies.  

 

And $$$$$

 

ray

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Steve's a very soft spoken guy, that's for sure.  It would have been nice if he gave a couple of examples though:

 

Consider two loudspeaker systems with 8Ω nominal impedance and copper voice coils

A has a speaker efficiency of roughly 0.4% (99.8% of incoming energy is wasted as heat)

B has a speaker efficiency of roughly 2% (98% of incoming energy is wasted as heat)

 

Spoiler

A transducer is always a horribly inefficient device, and many people might not think much about this disparity, a slight bump of the volume knob should account for a 2% difference right?

 

Let's now convert that spec to transducer sensitivity

 

A speaker has a sensitivity of 85 dB/w/1m

B speaker has a sensitivity of  95 dB/s/1m

 

A 2% (rather minuscule) change in efficiency has provided a 10 dB sound pressure difference (about twice as loud)

 

At first blush, the less sensitive speaker has thrown away 10dB of acoustic pressure, lost as heat in the transduction

 

But can't you 'get it back' with the volume knob?  Yes and No

 

In the case of a static signal (e.g. 1Khz sinusoidal at a steady amplitude) yes, you can bump the volume of speaker A to match level with speaker B

 

In a dynamic case (music), however, things change a bit.  First .....

 

Spoiler

considering the thermal coefficient of resistance of Cu wire to be 4.1-3 per °C, the DCresistance of a 6Ω voice coil at ambient(25°C) will increase to 10.3Ω @200°C

This increases Speaker A impedance (Z) to 13.7Ω  (Z to DCr ratio = 1.33:1) when hot @200°C

 

Now, lets throw 50V at speaker A(85dB/w/m): about 300W dissipated (P = V2/Z)

when hot (less than a minute): about 180W dissipated(almost half the power lost)

speaker A has a thermal compression factor of 2.3dB (effective sensitivity now 82.7dB/w/m)(Gdb=10log10(P2/P1))

 

Let's aim for an SPL of 100dB at 3m distance (assuming 6dB SPL loss per doubling of distance)

 

Speaker A(85dB/w/m) requires about 300W for 100dB SPL@3m

hot speaker A (Z=13.7Ω) will only reach 97.7dB

hot speaker A now requires about 500W to reach 100dB SPL@3m

Thermal compression is 2.3dB

 

by contrast

 

Speaker B(95dB/w/m) requires only 30W for 100dB SPL@3m

much less hot B (Z=8.5Ω) will only reach 99.5dB

warm speaker B now requires only 32W to reach 100dB SPL @3m

Thermal compression is only 0.5dB

 

 

Higher sensitivity means less thermal compression, always

 

Spoiler

Consider that an excellent peak to average (minimal dynamic range compression) ratio is 20dB.  A highly compressed musical signal may have a peak to average ratio of 5dB or less.  I'm going to take 10dB as 'average'

 

We're still aiming for that 100dB SPL@ 3m level.

 

Speaker A (85dB/w/m) requires 300W and only reaches 98dB averages when hot

Speaker A would require 3000W to reach 110dB peaks (not going to tolerate the heat)

 

Speaker B (95dB/w/m) requires 30W and reaches 99.5dB on averages when hot

Speaker B only requires 300W to reach peaks

 

 

In the case of dynamics, therefore, the higher sensitivity speaker will always be superior (JBL has measured the average thermal compression of a high power loudspeaker system to range between 5 and 7 dB)

 

 

 

 

Edited by RichP714
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2 hours ago, Nahash5150 said:

Just another reason to keep turning up the volume during a party. :D

 

 

That would recover the SPL (until the voice coil adhesive melted), but the dynamic thermal compression would get worse and worse

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1 hour ago, RichP714 said:

 

That would recover the SPL (until the voice coil adhesive melted), but the dynamic thermal compression would get worse and worse

 

Yeah, I meant that there are several pressures which cause the the volume to keep climbing at a party:

 

1) room ambiance, louder music, louder ambiance, louder music...

2) intoxication dulls the senses, turn it up a little more...

3) thermal compression reduces SPL output, turn it up more...

:D

 

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37 minutes ago, Nahash5150 said:

 

Yeah, I meant that there are several pressures which cause the the volume to keep climbing at a party:

 

1) room ambiance, louder music, louder ambiance, louder music...

2) intoxication dulls the senses, turn it up a little more...

3) thermal compression reduces SPL output, turn it up more...

:D

 

 

Oh sure, I guess, I thought I covered that in the first part; a static loss of volume can be overcome, but the dynamic losses cannot

 

The example I gave had only about 3dB of loss, but JBL has measured on average 6dB in large powered systems; there is more than thermal dynamic compression going on, there's also thermal bl compression et al.

 

Partygoers may not be a good example, in that they probably aren't listening for dynamic losses.  In fact, I would bet $100 that many people, listening to their low sensitivity system,  are unaware of the dynamic losses that are happening.  I'd also bet that these same people lament the 'loudness wars' trend of dynamic compression of music and are unaware that their system is responsible for 'built in' compression

Edited by RichP714
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2 hours ago, RichP714 said:

The example I gave had only about 3dB of loss, but JBL has measured on average 6dB in large powered systems; there is more than thermal dynamic compression going on, there's also thermal bl compression et al.

 

Do have access or link to their study/article?

 

The party-goers was tongue-in-cheek, but I see your point.

 

 

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16 hours ago, Nahash5150 said:

 

Do have access or link to their study/article?

 

The party-goers was tongue-in-cheek, but I see your point.

 

 

 

https://www.jblpro.com/ProductAttachments/tn_v1n18.pdf

Here's an article on flux compression:  https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_11_Flux_Modulation.pdf

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