Hello all, here is a shot in the dark. Please excuse if a stupid question. This is related to my Cub Sandwich sub build
Let's say I wanted to keep the speaker passive and use if with an outboard amp. It's a very small cab in a system sealed by passive radiators. I have designed in a heatpipe to take hot air away from the motor vent. Is there a way to bleed off a lil bit of power from the speaker terminals to power a small fan to encourage air movement in the pipe?
I.e. an active fan inside a passive speaker without any other power supply for the fan
Thanks and regards
Randy
Let's say I wanted to keep the speaker passive and use if with an outboard amp. It's a very small cab in a system sealed by passive radiators. I have designed in a heatpipe to take hot air away from the motor vent. Is there a way to bleed off a lil bit of power from the speaker terminals to power a small fan to encourage air movement in the pipe?
I.e. an active fan inside a passive speaker without any other power supply for the fan
Thanks and regards
Randy
If your typical listening level is 1 watt into 8 ohms, the voltage at the speaker is a sine wave with peak +4.0 volts and trough -4.0 volts.
Most of the high efficiency, ultra quiet fans run from a 12 volt supply, so you'd need active circuitry to take a 4V sinewave in and produce 12V DC out. Not impossible but not simple either.
Most of the high efficiency, ultra quiet fans run from a 12 volt supply, so you'd need active circuitry to take a 4V sinewave in and produce 12V DC out. Not impossible but not simple either.
Try a Noctua NF-F12 5V (it draws 0,15A at 5V to run full speed), driven by a bridge rectifier. Add a resistor and a zener, or a low-drop voltage regulator, to clip the voltage to 5V. This special 5V version low-noise fan does have a 3-pin header but cannot be connected to a PC motherboard, it would be damaged. Most 12V fans also work at 5V, but they slow down.
Given the power output is highly variable I would suggest bridge-rectifier into current limiting diode into zener. A resistor-zener combination takes much more power at high level, limiting the current will keep this to sane levels.
For instance if your resistor allows 150mA at 10V rectified input, its a 33 ohm resistor (for 5V zener). At 20V rectified input that resistor has to dissipate 7W, at 40V rectified input it dissipates 35W.
Use 150mA current limiting diode (or parallel array of smaller ones), that 40V rectified input dissipates only 5W, and the fan gets full power from just over 5V rectified, not 10V, and the zener has negigible dissipation too.
Or bridge-rectifier into capacitor (with some series resistance to limit current peaks), then a DC-DC converter with a wide input voltage range down to 5V dc?
For instance if your resistor allows 150mA at 10V rectified input, its a 33 ohm resistor (for 5V zener). At 20V rectified input that resistor has to dissipate 7W, at 40V rectified input it dissipates 35W.
Use 150mA current limiting diode (or parallel array of smaller ones), that 40V rectified input dissipates only 5W, and the fan gets full power from just over 5V rectified, not 10V, and the zener has negigible dissipation too.
Or bridge-rectifier into capacitor (with some series resistance to limit current peaks), then a DC-DC converter with a wide input voltage range down to 5V dc?
Guys, many thanks for your suggestions. Honestly, I thought it would be as simple as a parallel light bulb type thing. Given the process needed to make it work, a DC line together with the speaker cable would be acceptable. If I do need power independence, I think maybe I should look a using the 5v fan and a powerbank installed into the cab. This should keep it going for the needed hours
Thanks again and much appreciated for the input. It has really been interesting to see that its not impossible
FWIW I have done it, which I guess gives me some kind of advantage in the matter 😄
I needed it to cool my Guitar attenuator box, which when driven by, say, a Marshall Plexi or Fender Twin full blast may have to dissipate up to 150W of heat, which is a lot
So I added a 4 x 1N4002 bridge, a 2200uFx50V cap, a 12V PC type fan , and DC rectified from the Audio line fed the 12V fan through TIP122 Darlington transistor, with base clamped to ground by a 15V Zener so Fan never gets more than 12V DC. (Considering Darlington losses, about 4V).
Does fan work at, say, 1W RMS?
NO, and it does not need to, at all, we are talking 1W RMS into load!
It started turning at low speed at about 8V RMS and speed stabilized with some 12-14V RMS into speaker , do the math to get Watts.
Worked like a charm.
Will post some picture when I find one.
I needed it to cool my Guitar attenuator box, which when driven by, say, a Marshall Plexi or Fender Twin full blast may have to dissipate up to 150W of heat, which is a lot
So I added a 4 x 1N4002 bridge, a 2200uFx50V cap, a 12V PC type fan , and DC rectified from the Audio line fed the 12V fan through TIP122 Darlington transistor, with base clamped to ground by a 15V Zener so Fan never gets more than 12V DC. (Considering Darlington losses, about 4V).
Does fan work at, say, 1W RMS?
NO, and it does not need to, at all, we are talking 1W RMS into load!
It started turning at low speed at about 8V RMS and speed stabilized with some 12-14V RMS into speaker , do the math to get Watts.
Worked like a charm.
Will post some picture when I find one.
