stupid polarity question.

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Learnincurve

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Joined 2004
#1
I'm building an active sub and still planning the electronics to go in front of the bridged power amp. I know this is a really stupid question for those who know the answer, but:

What is the point of a 180 deg. phase switch circuit? won't simply reversing the polarity of the speaker dp the same thing? Yes, I did search.

OK! SHOOT ME NOW!
 
#2
Yes, just changing the cable to speaker will do the same thing BUT, many subs have a continous setting that can be used to alter phase anything between 0 and 180 degrees. But if it´s only a simple switch it´s only to make it a little easier than having to unscrew the cable.

/Peter
 
#3
thanks

Thanks for the reply. The consensus about continuous adjustment seems to be that it's a waste of time as it's only correct at one frequency. The (limited) modelling I've done suggests that I'll be around 160deg. out at crossover frequency (40Hz), so 180 deg is probably near enough.
 
#5
You only need for it to be correct at one frequency, and that's the crossover frequency between the sub and the mains. The phase switch allows the sub and mains to be in phase in the overlap zone of their outputs, and you adjust it simply by using whichever position delivers the higher system bass output. If you can't hear the difference don't worry about it, it only matters if you can hear the difference.
 
#8
Bill you make me laugh...

I dont know exactly how variable phase controls all work, but I'd imagine most dont perform ideally. Phase and polarity are related, but in audio they are often considered to be the same thing. They are not!

For a function F(x)= sinX

a function with reverse polarity is written
F(x)= -sinX
A function out of phase is written
F(X)= sin(X+pi)
 
#10
Try changing the frequency.

instead of using sinX use sin2X as this represents a double in frequency.


I believe the standard form of a sin function is written

Asin(B(x+c))
where A determines amplitude. B determines frequency and C determines phase shift.

for sinx A=1 B=1 and C=0
For sin(x+pi) A=1 B=1 and C=pi
for -sinx A=-1 B=1 and C=0

Now if we go to the equation Sin2X and reverse the polarity we get -Sin2X... An equivilant equation would be Sin(2(x+pi/2))
Now this could be simplified into Sin(2x+pi), but the phase change is still pi/2 and NOT pi
 
#11
BillFitzmaurice said:


I have no idea what he means by that either. Sounds like a line from 'Star Trek' to me: "More power to the shields, Scotty, and modulate the phase frequency!"
Click to expand...


ok. no problem. 🙂 should you understand what means "phase" control on the picture - let me know, I'll be able to show you some more scheme.
however, if you can't hear effect of phase - something wrong.
An externally hosted image should be here but it was not working when we last tested it.
 
#12
Hey, Nice schematic! Do you have a .pdf of that, or an eagle project or whatever. Would be good for the coillection.

I see you maths folks were kept busy last night. It makes me wish I'd paid attention in school. I can just about follow it on paper, but how to actually apply it is, and will remain a mystery, I'm glad some of you know what it means.

I'd like to thank yopu all for your time and patience. Unfortunately a combination of SAF and finance are putting a stop to this entire project. In order to do what I want I need a driver (drivers) that will work at under Fc in a tiny box (around 1 cu.ft.). They just cost too much. So despite having the silicon and the will it will just have to wait. I may pass the time by building the electronics to control the signal and hope for better econoimy later.

Cheers!
 
#13
🙂
ok. forget it Learnincurve.
it's just nuance. DIY user have lot of it

but formulas: money- quality cut down our desire often... it's pity.

I'm always produced just what you want. subwoofers 27 litres inside. see the picture in my homepage.
should you need some consult - I'm always ready for you.
sorry my English 🙂
 
#15
I'm not sure about passive version. do you mean wothout ampl and crossover?
I think it is.
unfortunately - it's won't work...
I'm meaningly cut of range of waves about 80Hz. couse that sub have to work with front loudspeakers, you can see it too there and they have 60-20000 range as well.
marble - for the best damping factor and for silent box.
I have MDF version, wich I use for modelling difference design of sub box. it's working almost the same like marble one.....
almost..... it's "almost" take lot of money for my customers 🙂
but they are happy. they get nice, exclusive element of interior.

so, you can make it easy, using wood, or MDF of course, but in that case you need calculate box according the driver.
port system make easy way for small box and low resonanse of system. therefore - I make it ported.
 
#16
I understand. The reason I say passive is that I already have amp. Up to about 800 watts into 4 Ohms (seen because of bridge mode), and acoustic correction circuit: http://www.marchandelec.com/wm8.html. I will of-course cross over at a good frequency (posssibly 40 Hz = -6dB of main pair) possibly 60 with matching high pass for main pair. I wil never have the money for "exclusive finishes" and anyway they wouldn't look right in our old-fashioned house, so ordinary MDF is better. I was staying away from ported designs because of chuffing. How do you avoid this?

Cheers!
 
#17
I see. it's ok.
let's make MDF box.
I use simple formulas for port system:
L=(2354*D^2/VF^2)-0.85D
L - port length (cm)
D -port diam (mm)
V - box capacity (litres)
F - tuning frequency (Hz)
and make more exact then. it's very depend of driver.
I consider "Onken" design are very interesting. do you know it?
probably you'll get result easy. hardly made a mistake
 
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