3-way....Where's the gain coming from?!

Psychobiker · 21st April 2010, 11:58 PM

Guys,

Funnily, even with impedance smoothing circuits in place and an accurate model of the mid and low drivers, there appears to be an enormous gain peak there...surely with Butterworth's there aren't! I can't spot anything other than a first-order crossover anywhere there...unless I'm blind!

godfrey · 22nd April 2010, 01:24 AM

I think your graph is showing dB re 1 volt, so your input is about +9db.
Set the input to 1volt and it should make more sense.

Psychobiker · 01:51 AM

Godfrey...!

I cannot believe this. Someone come along, hit me with a stick. Please.
Brain-fart?! I'm going to hide my head in shame now. That fixed it!

That said, dB is a 'relative' scale and hence input voltage should make little difference...maybe the dB markers are set incorrectly in pSpsice.

20Log(Pout/Pin) is the formula...nowhere is there a 1V level for it to be 'relative' to. It should know that 2.83V is the input and hence, what it ought to be relative to. Apparently not!

godfrey · 22nd April 2010, 02:04 AM

Well it can be: 20Log(Vout/Vin) or 10Log(Pout/Pin),
but often also used is: 20Log(Vmeasured/Vreference),
in which case the "reference" is normally 1 volt.
Sim software tends to work like that anyway.

Psychobiker · 22nd April 2010, 02:23 AM

Ah! That makes sense...if they set the reference to a default 1V and didn't take ACMag into account! Godfrey, FYI, I was born and brought up in Durban! Family are still there and in Paarl.

It's late at night here, explains the oversight. But - for those using PSSPICE again in the future, hopefully this thread will be of use and stop many's a headscratching!
Forgive me, but to the uninitiated (EE here) such an error in software could cause a serious amount of confusion.

21st April 2010, 11:58 PM	#1
Psychobiker diyAudio Member Join Date: Jul 2005 Location: Montréal QC	3-way....Where's the gain coming from?! Guys, Funnily, even with impedance smoothing circuits in place and an accurate model of the mid and low drivers, there appears to be an enormous gain peak there...surely with Butterworth's there aren't! I can't spot anything other than a first-order crossover anywhere there...unless I'm blind!

22nd April 2010, 01:46 AM	#3
Psychobiker diyAudio Member Join Date: Jul 2005 Location: Montréal QC	Godfrey...! I cannot believe this. Someone come along, hit me with a stick. Please. Brain-fart?! I'm going to hide my head in shame now. That fixed it! That said, dB is a 'relative' scale and hence input voltage should make little difference...maybe the dB markers are set incorrectly in pSpsice. 20Log(Pout/Pin) is the formula...nowhere is there a 1V level for it to be 'relative' to. It should know that 2.83V is the input and hence, what it ought to be relative to. Apparently not! Last edited by Psychobiker; 22nd April 2010 at 01:51 AM.

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22nd April 2010, 01:24 AM	#2
godfrey diyAudio Member Join Date: Nov 2009 Location: Cape Town	I think your graph is showing dB re 1 volt, so your input is about +9db. Set the input to 1volt and it should make more sense.

22nd April 2010, 02:04 AM	#4
godfrey diyAudio Member Join Date: Nov 2009 Location: Cape Town	Well it can be: 20Log(Vout/Vin) or 10Log(Pout/Pin), but often also used is: 20Log(Vmeasured/Vreference), in which case the "reference" is normally 1 volt. Sim software tends to work like that anyway.

22nd April 2010, 02:23 AM	#5
Psychobiker diyAudio Member Join Date: Jul 2005 Location: Montréal QC	Ah! That makes sense...if they set the reference to a default 1V and didn't take ACMag into account! Godfrey, FYI, I was born and brought up in Durban! Family are still there and in Paarl. It's late at night here, explains the oversight. But - for those using PSSPICE again in the future, hopefully this thread will be of use and stop many's a headscratching! Forgive me, but to the uninitiated (EE here) such an error in software could cause a serious amount of confusion.

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