would the svs pb2+ be a noticable upgrade from a vtf-3? (1 Viewer)

[Edward J M]

Hi Craig!

I've been a faithful reader of your (now defunct) AVS thread, and finally found the continuation thread over at HT-SPOT and continue to follow it there. Isn't life nice without Mar....uh I mean thread trolls?

Phew - lots of fun and what a huge thread. I liken reading it to watching all three Extended Editions of the LOTR trilogy back to back - awesome but draining at the same time.

There's a PB2-Ultra in my near future - stay tuned for that review. On other fronts, I'm working hard on convincing a friend who's in the market for a $600 12" to buy an STF-3 and a PB1-ISD so we can hear them both (easy when it's not your money - LOL). Sort of like the "little" brothers to the PB2+ and the VTF-3.

Ed

 

[Craig Chase]

Ed - If he tries both subs, see if you can get some blind tests done. It would be interesting to get the results to that !

I am also going to try to get the new Hsu Flagship due out this year... What these companies are putting out (including Adire/Acoustic Visions) in subwoofer bang for the buck is amazing ...

 

[Edward J M]

Roger that. Will be interesting to see if the results parallel yours, or if the tables get turned. It's a hot and competitive price class, that's for sure.

 

[Doug BW]

Ed, I think if you actually crunch the numbers, you'll find that a doubling of the ratio between p and p0 will give you a 6 dB increase in SPL, not 3 dB.

It's a little easier to see that this is true if you re-arrange the equation as:

L = 20 log (p/po)

(Note that p/po is no longer squared.) If p is double po, then L is 20 log(2) which is (roughly) 6.

Good thing this is true!! If 3 dBs represented a doubling in SPL, then 6 dBs would be a quadrupling. Since we know that having two subwoofers co-located gives an increase of 6 dB, it would be quite miraculous if doubling the number of subs, quadrupled the SPLs.

 

[Edward J M]

Hi Doug:

I checked the equation for sound intensity again, and the terms are not squared. They are squared for sound amplitude (that's what I get for rushing through my reference manual). I think you'll see in a minute, we're both right.

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The correct equation for sound intensity is:

dB = 10 log (p/po) where po is the reference intensity and p is the unknown.

Using a 3 dB increase and solving for p both times does indeed yield a doubling of the sound intensity.

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Sound intensity is proportional to the square of the amplitude.

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In the case of sound amplitude:

dB = 10 log (A2/Ao2) where Ao is the reference amplitude and A is the unknown amplitude. In this equation, the terms are indeed squared.
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So a 3 dB increase will provide a doubling of the sound intensity, and a 1.414 increase in sound amplitude.

And a 6 dB increase will provide a quadrupling of the sound intensity and a doubling of the sound amplitude.

So in the future, we should all (not the least of which me) be specific when discussing the difference between sound intensity and sound amplitude and how they relate to the dB scale, because the equations are indeed different.

Thanks!

Ed