Tying a subwoofer into standard desktop speakers and electronically lowering the pitch (so that it produces deep sounds)

For fun I decided to take apart my desktop computer speakers and convert them to a portable iPod speaker. I have already found a way to convert it to DC power so that I can integrate it into a portable "boom box". I also have a subwoofer that I would also like to build into the boom box but the sound when connected is rather high in pitch. Is there any I can do electronically to lower the pitch so that the bass is more pronounced and deep? Thanks!

thegeeke gives good advice, feed the right frequencies to the speaker in order to make it work "best". Enhance the sound shape with the player's EQ and bass settings.

I would like to add some more points.

Enclosure. Low frequency drivers (woofers and subwoofers) need to be in enclosures (boxes) that are designed to enhance those low frequencies. If your "subwoofer" was in an enclosure before but is not now (or the enclosure you've made is radically different in size - especially if it is smaller), then it is not going to produce the sound you are looking for no matter how much electronic bass boosting you do to the signal. Try this: put the driver on the table by itself, no box or anything around it. Run some music through it and listen to it. Kinda tinny, huh? Now find a container to sit the driver in, a cup, plastic bowl, bucket, whatever it will rest nicely on top of while sealing the edges pretty well. Now listen to it. Sounds better, doesn't it. My suggestion would be to use the original enclosure if possible or try to make an enclosure with similar interior volume(s) even if it is a different shape. Of all things you do, this will make the most difference.

Power. The bass frequencies are where most of the power in music is used. This is because low frequencies require large amounts of air to be moved in order to be heard/felt. This requires POWER (watts). If you are seriously underpowering the woofer, the bass will be very weak while higher frequencies will seem more normal. You might need more power. See if the driver has wattage ratings labeled NOM and MAX. NOM would be the minimum power required to properly drive the woofer and obviously MAX means the maximum you can safely run through it. Check to make sure the amp you are using can supply the minimum (NOM) power required. Since you are now running the speakers from battery power, do the batteries have enough power to run everything? Using a standard 9v rectangular battery (at most 180 mA) to run something that used a 9v 1000 mA wallwart will seriously underpower things, and the first thing to go will be bass and then comes distortion.

Phase. This pertains to systems where there are more than 1 driver including dual voicecoil subwoofers. If you have a driver wired backward (180 deg. out of phase) while facing the same direction, ie. both drivers on the same side of a faceplate like a standard 2 driver sub box, then 1 driver will push while the other driver will pull. If the signal being fed to both drivers is exactly the same, most of the sound will be canceled out. I say most because the drivers are not on top of each other and some of the edge radiated sounds will escape, but not much. In the case of dual voice coil subs, you will get very little, if any at all, movement since the voice coils are overlapping in the same area. IF you have more than 1 driver/voice coil, check for phasing problems. Also, you can have phase problems between different types of drivers. The only way to truly check this is to listen and experiment.

Now to the crossover you referenced. The PREamp in this case stands for before an amp. It only serves to separate the bass and mid/treble signals. There is no amplification going on here. As a matter of fact, there will be a "slight" attenuation (loss) due to the input resistor(s) and output potentiometers, but it shouldn't be much. You can use just 2 of these, leaving out the appropriate input resistor, thereby not connecting that specific tab to the circuit. Buy or make a "Y" cable and feed each Xover from that. Feed the mid/treble outputs from the Left and Right Xovers to the appropriate "small speaker" amp inputs. How you do the bass outputs depends on how your subwoofer amp works. If it uses 2 inputs, feed the Left and Right bass outputs to the corresponding inputs and you are done. If it uses only 1 input, you'll have to combine the L + R outputs together. Just connect the + of each together and the - of each together and then feed that to the single input on the amp.

Good luck,
thegeeke5 years ago
You need a crossover. Basically, a speaker will play whatever you send at it, but not all speakers are built for playing certain frequencies. (Like a sub woofer is not built for playing high frequencies.). A crossover decides what frequencies to send to what speaker. This is the only good way of fixing your problem. The only way to boost your lower frequencies from your media player would be to adjust your eq. (If you have a graphic eq, the frequencies on the left are the lows, the frequencies on the right are the highs.) But adjusting the eq still doesn't fix the fact that you are sending the wrong signal to the woofer.
ckrupala1 (author)  thegeeke5 years ago
So I could use something such as this: https://www.instructables.com/id/monoXover-2-way-pre-amp-audio-crossover/

With this could I tie in the subwoofer as well as 2 small tweeters with the addition of an amp with a single module?
Yes, this will work. I didn't look closely, but it looks as if you need an amp on each channel since this is pre-amp.