|27th February 2006, 04:24 PM||#11|
diyAudio Member RIP
Join Date: Nov 2003
Location: Brighton UK
seems to me a different way of saying the same thing,
|27th February 2006, 05:42 PM||#12|
Join Date: Feb 2006
thank to everybody for all the answers, that are too techical for me, you are like Einstein trying to eplain relative theory to a child at scoo! ;-)
I'm getting confused and lost on what I have to do, so I think that what I want to achive cannot be done in a simple way, 'couse I don't want to spend more money on this projet and so I have to use what I already got. So I will say my question in another way :
-I dont need HIFI stereo, so I can have low freq only from I channel (don't say boooh!)
- wich value for capacitor/resistor/coil I have to use to connect one loudspeaker in order to cut high freq, and how I need to connect it parellal/serial.
If this is not possible I thank you again in advance for your kind help.
|27th February 2006, 06:08 PM||#13|
Join Date: Jan 2006
Read what I said earlier- get some coils and put them in series with
the big loudspeaker and 1 channel, if you like, but remember it will unbalance the system If you can find enough coils you may be able to connect the one loudspeaker to both channels but youwill need big coils or a lot of them or you will end up with MONO.
( amp +ve) -- (coil) -- (coil) -- etc -- (+ve loudspeaker-ve) -- (-ve amp)
This is how to wire it
heretics are sometimes right
|27th February 2006, 06:42 PM||#14|
Join Date: Feb 2006
Location: Boulder City, Nevada
Everyone wants you to go purist. I agree, but your question CAN be answered, and you don't always have to follow all the rules.
You must NOT connect both amp channels to the woofer if using only one woofer/voice coil with stereo source. This is where dual VC will be very handy, otherwise you have to choose a channel if not bridging, as described by others here. I hate the idea of loading 2 channels differently, but the laws of physics will allow it.
My assumption is that driver impedance is nearly resistive (in the impedance curve swoop between resonance below and inductive rise) at filter frequency of interest (I suggest 3-400Hz if driver smaller than 8 inches). Check ohms with multimeter. This will not tell you everything, but it gives the ballpark. A nominal 8-ohm driver will probably measure 4-6 ohm DCR. Add about 1 ohm to figure the impedance minimum value (roughly where driver will interact with filter). You can compensate for inductance above this point with a Zobel network to maintain filter performance, but not essential. You could probably assume 6-ohm impedance for rough guessing.
Optional: Zobel network to flatten inductive rise. Inductance could probably be guessed around 1.5 mH (L measurement at 1kHz would be helpful). If 6-ohm DCR, use 6-ohm resistor in series with capacitor where C=L/(R^2) (here would be about 40 uF). Connect these two in shunt with the woofer.
I recommend a second-order filter, as filter frequency is not a function of actual driver impedance, only Q (damping) is.
Per ohm (at 350Hz), use inductor (L) of about 0.85mH for critical damping (larger = overdamped, smaller = underdamped). and C=1/(2*pi*350Hz)/L. Connect the capacitor in shunt with the woofer and the Zobel network (3 parallel paths), and the inductor in series with the works.
To quantify the example, my component choices, assuming you have about 6 ohms DCR and 1.5 mH VC inductance;
path 1 = woofer
path 2 = 6 ohm + 40 uF
path 3 = 33 uF
and hook the whole shabang in series with 4.5 mH inductor.
If you get a dual voice coil (say, 4 ohms each) woofer, halve the resistance and inductance values, double the capacitance values, and connect two complete and equal networks, one to each voice coil and amplifier channel respectively.
Choice of frequency is inveresely linearly proportional to inductance and path 3 capacitance (filter frequency= 1/(2*pi*sqrt(L*C)).
The whole thing is more involved in truth, but my impression is this is the sort of analysis you are seeking... This is a definite finger-in-the-wind approach, but it won't blow anything up and may even sound OK.
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