posted
Thanks oldtimer, I forgot to mention that the current measurement must be made with a single freq.
Bumpin' Yota, The answer is off a little because of rounding.
You can’t use a voltmeter to measure power unless you know the exact impedance and resistance of the speaker at the freq you are playing. You need to know this to determine the current and its phase, so that you can use the formula Real power = V*I*cos(angle)
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It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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What happens when you have a passive crossover btwn the amp and the speaker? Namely a third order xover. What about with a zobel network and an attenuation circuit? do these things tend to put the current farther behind the voltage, or vice versa? I wanna crunch some numbers!! Thanks, Steve
posted
Im not sure off the top of my head. I could figure it out, kinda a lot of work for a third order. My guess is that the over all, the effect of a low pass would be an inductive one. Passive crossovers are just bad for subs.
You could put a cap in parralell with the sub. It will act as a lossless 1st order passive crossover. It might be hard on the amp at high freqs though. If I determine that my peak freq doesnt occur very close to the tuning freq, I will probably try to correct the impedance with a cap so that I get more power out of my amp. I havent heard of anybody trying this, but it is very common in the power engineering industry.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
mr. dank, by adding caps to correct the impedance, this is done to keep the power factor at an acceptable level right? my instructor from circuits I (from Iraq) is a power engineer and i think he was talking aboutt that towards the end of the semester....
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posted
Thats what power engineers do. power companys add them (caps) to the power lines to increase efficiency. Our houses are basically inductive loads. in order to supply the same amount of power at a given voltage when a load becomes inductive, the current has to increase. Well the pwer lines have resistance, the more current that goes through them the more power the lines dissapate getting the power to your house. Hence, energy wasted. They add the caps to correct the phase angle of the durrent so that its in phase with the voltage. this decreases the current, and decreases the power loss.
About the adding cap thing. I just found out from richard clark (smartest person Ive talked to in car audio) that its a little more complicated but definatly possible. he's gonna think about it and get back to me. I'll try to explain it to you when I figure this out.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
Wow we got Phasors, Fortier Series, Maybe a little Laplace Transforms, Transfer functions. The only thing I remember from EE 301 (Signals systems and transforms) is is you take a impulse function and run it through a system you have your h(w). then you can do all your good ol' convolving. Ok I am done....I just think it is refreshing to see all this in practice.
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Posts: 2679 | From: unknown bowels of the underworld | Registered: Aug 2000
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posted
good lord i can't remember half of this ****, good luck trying to find the I to V relationship of a 3rd order network, if i remember anything, first you have to find the reactance of the combined Xl and Xc, the equation for series combined reactance was X= Xl-Xc and the parallel equation was X= (-Xl*Xc)/ (Xl-Xc) and i think the dominant reactive component, be it the cap or coil, which would be dependent on freq, of course would be the load that the power sees, so if Xl was greater than Xc the voltage would lead current, but by how much, don't ask me i didn't pay attention much when we did phasors and ****. then i guess you'd just use the series equation to figure out the series reactance of all three filters, god this is starting to hurt. but if you're using the resonant freq. then they would cancel each other, which would fuk everything up.
i got this book here named impedance, that's all it covers, so to actually explain it all in a post well, to hell with that idea, anybody want this thing i'll sell is for 5 buks, + shipping. 200 pages of impedance that'll keep you busy for quite a while.
posted
umm, somewhere in here I stated that a sub could be modeled as a inductor in series with a resistor. Richard clark informed me thats only true far above resonance. near resonance its more complicated and is either more capacitive or inductive depending on what side of the curve you are on. he is going to do some test to see if the power factor can be corrected enough to get more power out of your amp. I'll let you know the results.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
Hmm, something I've been thinking about for a while. Okay if you know your angle by using a scope, know your DC value etc. and you know that the impedance doesn't vary much as the sub moves through its travel. Calculate teh required cap Q=V^2/Zc or whatever, it's back in digs atm, but then if you knew that, could you wire up the cap when you play your note at dB drags, decrease the load the amp works into as the cap will provide the reactive power, and hence get more real power into your sub. Don't mention fourier series, I've got a whole examples paper to do for monday, last night I was up till two doing everything discussed above, this is after I've been helping others design ported enclosures. Ah the joys of studying engineering at uni. Colin
posted
That whole inductor and resistor modeling has to do with 2 things. One is that I sub always has a constant resistence at any frequency. Then the inductors Zth goes up with frequency because...
L(zth)=infinty @ w=infinity L(zth)=0 @ w=0(DC)
It is just a way of measuring the impedence rise as w goes to infinity due to an inductor being a open at very high frequencys.
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Posts: 2679 | From: unknown bowels of the underworld | Registered: Aug 2000
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posted
Just wondering if anyone had tried the above that I suggested, thinking about it the least it would do would be to cause the amp to heat up less. Also the FSE seems easy enough at the moment. Colin
posted
Are you talking about adding a cap to correct the power factor? that would make the amp work harder and deliver a lot more power depending on how much you correct the power factor. Im gonna start messing around with it.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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quote:Originally posted by yesterdaysyouth: ...i got this book here named impedance, that's all it covers, so to actually explain it all in a post well, to hell with that idea, anybody want this thing i'll sell is for 5 buks, + shipping. 200 pages of impedance that'll keep you busy for quite a while.
How basic is the terminology? I want something that I can understand even if it is with some bit of struggling. I initially had a hard time understanding this thread as it's been a looooong time since I took physics with calc 1 and 2... Steve
quote:Originally posted by Bumpin' Yota: Any progress with the project using the cap yet?
Im getting close to maybe having time. I came up with a new idea based on the same principle. In theory I might just gain a lot of sensitivity. I'll tell ya after I try it. Need to retune my box and do in car impeadance measurements first.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
mr.dank....did ya ever get a chance to try this?
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posted
Ya, messed with it a little in a room with a vega-vega. I think I got an increase from 2.1A to 2.7A. That’s about 2dB. I only had a few caps lying around. This was done slightly below the maximum capacitive part of the impedance curve. I’m guessing you could maybe do 3-4dB with the right setup.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
I have no need for my set up. I peak at tuning. You can defiantly gain by adding caps to the right setup, one whose SPL peaks half way up the second impedance peak. I just think that we are using the wrong types of amps. We are voltages limiting amps current capabilities.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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