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My boombox (of sorts)

billybob

Member
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Here's a two foot speaker box I made Its got midrange on the sides Sub on the front and the two tweeters on top. Im using A boat stereo amp to power it Later I would like to make It battery powered with a recharge port, but It takes up a lot of Amps right now. It also has Led strips next to the sub to be in sync with the music, but I haven't figured out a way of using a transistor switch to work them yet without shorting the amp.
Hope you find it somewhat interesting.
 

audioguru

Well-Known Member
Most Helpful Member
The tiny photo is hard to see but your tweeters look like the shrieker in a cheap clock radio. A good tweeter has a dome, not a cone.
Two speakers beside each other produce cancellation of some frequencies when heard a little to the side instead of straight ahead, due to the change of phase caused by different distances to your ears.

Some amplifiers waste a lot of battery power making heat, even when not playing. Some modern amplifiers do not get hot because they do not waste battery power.

A transistor switch does not short anything. It is simply located in series between the battery and the LEDs and connects the battery to the LEDs when sounds turn it on.
 

billybob

Member
I know it’s not the best design, I was just going for fast and somewhat efficient. I’ll send you the diagram of what I did for the led light thing and maybe you can see what went wrong.
 

billybob

Member
448FD764-D147-40B7-9894-A42CEFC01A10.jpeg Here is what I did and it shorted. I was thinking of doing a mic design, but it wouldn’t be very effective when the volume was down
 

audioguru

Well-Known Member
Most Helpful Member
Yes, you have the collector of the transistor at the + of the battery and its emitter connected to the ground side of the battery. Then when the transistor turns on it shorts the battery.

The transistor will provide about 11V to the LED strips when the amplifier output is maximum then when the volume is turned down only a little less than maximum, the LEDs will be VERY dim or not produce any light.

You have the transistor as a linear emitter-follower instead of as an on-off switch that can be very sensitive.
Since you want the LED strips to light in sync with the music then you should use a low frequencies-only filter so that the LEDs only light for bass beats and drum beats.
 

billybob

Member
thank you! I thought for sure I had it right. can you describe how the circuit should look? I‘m still trying to learn how to use npn and pnp transistors as switches. From what I gathered I thought (for an npn transistor the base has the positive input voltage that triggers the Emiter negative to flow to the positive collector. Please correct me if I’m wrong.
 

billybob

Member
If I place the Led between the Collector and The positive 12 from the amp, and the emitter connected to grd would that work?
 

audioguru

Well-Known Member
Most Helpful Member
If I place the Led between the Collector and The positive 12 from the amp, and the emitter connected to grd would that work?
Yes, then the transistor will be a switch and will turn on fully and light the Leds whenever current flows in the series base resistor. But as I said earlier, the transistor will turn on only when the music level is exactly at the correct voltage (the loudest peaks), or the LEDs will be on all the time or off most of the time.

To show sound levels, I made a "VU" meter with 10 LEDs and an IC that detects different levels and lights them. The levels are 3dB apart in a logarithmic sequence so that the 1st LED lights when the sound power is maximum, the 2nd LED lights when the sound power is half, the third LED lights when the sound power is 1/4, the 4th LED lights when the sound power is 1/8th, the 5th LED lights when the sound power is 1/16th etc and each LED lights when the sound level is at and below its assigned switching level. The 10th LED lights when the sound power is only 1/512th which is far from almost quietness.
A logarithmic sequence is used to match the logarithmic sensitivity to loudness of our hearing.
 

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