Using a Nintendo adaptor

[ChesterFuzzin']

I currently taking a public speaking course at school right now..For my last speech, I wanted to give a brief primer on subwoofers and stuff... One thing I wanted to incorporate was some sort of demonstration, however bringing in an amp was something i was not going to do. Bringing in a boxed sub, however was no prob. I eventually began thinking, and thought to use a Nintendo as a pseudo amp, in that basically all it is, is a AC step down transformer that outputs a 60 hz signal.

the specs on the adaptor were 9 volts and 1.3 amps... using regular ohm' 9 / 1.3 ~= 7 ohms.

basically my question is this. could use the adaptor on a 4 ohm sub, would this cause any damage/problems. i've tried the adaptor on a 8 ohm sub, worked fine...

[454Casull]

You mean you want to power a subwoofer using the 120V mains?

[moving_electron]

I think he would like to use the 9V AC 60Hz output of a "wall wart" transformer (happens to be from a Nintendo) as a speaker level 60Hz sine wave "tone" to demo a passive sub.

It worked on a 8 ohm sub but he wants to know if it will work on a 4 ohm one he wants to demo.

[ChesterFuzzin']

I think he would like to use the 9V AC 60Hz output of a "wall wart" transformer (happens to be from a Nintendo) as a speaker level 60Hz sine wave "tone" to demo a passive sub.

that's my exact question..

the reason i want to use the 4 ohm sub in the box i got is it just so happens to peak +5 dB's @ 60 hz...according to WinISD that is...

[AudioFreak]

a 5-10W 5-6ohm resistor in series with one of the speaker leads would minimize the chance of things getting nasty.

[ChesterFuzzin']

no 120v mains!!

last time i checked they run at like 1800+ watts..

hrm.. i wonder though??? pumping 1800+watt, 60 hz signal into a woofer....besides the voice coil circuit, would i fry a house circuit...would the voice coil burn my a$$.. would it be like a bomb ..?

[moving_electron]

a 5-10W 5-6ohm resistor in series with one of the speaker leads would minimize the chance of things getting nasty.

Yes it would seem like resistance would have to be added because:

This may not be right because it is AC and RMS [or not?] but I am sure someone will correct me )

Here is my thinking.
I=V/R
I= 9volts/4 Ohm = 2.25 Amps exceeding the rating the transformer, blowing the fuse or if it has one or worse, overheating the transformer with potentially disasterous results.

But with 5 Ohms added in series
I=9volts/9 Ohms = 1 Amp which is within the spec of the transformer

1 amp through the 5 Ohm resistor would be 5 Watts (if it was DC, so is it less at AC? If so by how much?)

[moving_electron]

1 amp through the 5 Ohm resistor would be 5 Watts (if it was DC, so is it less at AC? If so by how much?)

Putting 5 watts through a 5 Watt resistor would be providing no margin. Even though you presumably will only be connecting it only for a short time.

A 10 watt resistor would provide more margin. Or you could could use two 10 Ohm 5 watt resistors connected to each other in parallel then connected in series between the transformer and the speaker.

Or if only connected for a short time you could attach the resistor to a hunk of metal as heatsink. For example, you could attach it temporarily via a spring clip to a large wrench or other tool you might have. Any way to remove the heat will help. Make sure the resistor leads are prevented from shorting via the metal heatsink. Blowing the fuse (if it has one) or triggering the thermal protection in the transformer will end the live sound demo.

9v seems benign but follow good electrical safety practices none the less.

[sreten]

It simply depends on the impedance of the
sub at 60Hz, not its nominal impedance.

Personally I can't see how a single frequency
will demonstrate anything to onlookers.

Certainly not its +5dB peak.

sreten.

[moving_electron]

It simply depends on the impedance of the sub at 60Hz, not its nominal impedance.

Without calculating or measuring the impedence, if one was planning on the worst case it would be unlikely that the impedance would be less than 3 Ohms would it?

Personally I can't see how a single frequency will demonstrate anything to onlookers.

Pretty good demo of what an amp sounds like when the power supply filter caps fail?

Hooking it up to 60Hz tone would show that it worked. It could easily be a 90dB or greater tone which would be pretty noticable. If it is ported near that frequency, perhaps one could show the difference between the port being active and when it is covered. I suppose it is not to likely the port frequency is that high though.

Certainly not its +5dB peak.

I was thinking that he wanted to try the sub that had a peak at 60 Hz because it would potentially be louder in the presentation room. No info on the efficiency etc. of the 4 Ohm sub vs. the other but it a possible thing to try.