Simple USB Speaker Project

[ParkingLotLust]

... I tried just plugging my 8Ω resistors into the headphone jack, but to no avail. Not even a whisper.

I hope this was a misprint!

 

[Frederick]

I suppose I should have been more clear. From what hero999 said, I thought he meant that there would be some sound still made if the speaker was unplugged from the wall, but stayed connected to the headphone jack. I can see now that he meant I should have tried to get power from the amp on the sound card, not just unplug the circuit.

 

[transistor495]

He told about plugging 8ohm resistors into the jack and waiting for the whisper.

I assume your power supply is able to output 12V/1A. You need to check the output current. Try LA4600 which is a 4Wx2 channel excellent audio amp that can be done with a very few external components. You need 5or10W/4ohm small size woofer+tweeter pair or wholerange speakers for this to set up well.

I found digikey/mousers doesn't carry any Japanese IC's. However let me search it for you in US availability.
LA4600 Sanyo Original IC

All depends on your pocket ..

 

[Hero999]

No, I talking about connecting 8Ω SPEAKERS directly to the soundcard.

Connecting 8Ω resistors will obviously do nothing.

 

[Frederick]

Oh dear, I misread that too. I meant speakers.

 

[transistor495]

No, I talking about connecting 8Ω SPEAKERS directly to the soundcard.

Connecting 8Ω resistors will obviously do nothing.

I was referring to the comment of ParkingLotLust.

BTW, connecting the non-amplified speakers directly into the soundcard indeed a bad and old idea though..they're designed for work with little higher impedance actually. Intel already given explanation for that and is obvious.

Problem: Sound is distorted or scratchy
Poor audio quality or low volumes may occur if you are using passive (non-amplified) speakers.

Desktop Boards — Troubleshooting audio issues

 

[Hero999]

I didn't know that.

I didn't have a problem with the sound card I used on my old 486, which I think was a Creative Labs soubdblaster.

I suppose it depends on your board/sound card, all I say is try it, if it's crap then scrap the idea and go with the amplified speakers.

 

[Frederick]

Alright, I found a schematic for a two-way passive crossover like the one I think I'll need to separate the signals for the tweeter and woofer. It looks like this:

**broken link removed**

With the inductors both being 1.8 millihenries and both capacitors having 13µF of capacitance. This looks like it will work, but is there any way to be less redundant with the filters? I believe this style is known as a parallel crossover. Does that mean there is such thing as a series crossover?

 

[transistor495]

Series crossovers have a shunt LPF at tweeter side and a shunt HPF at woofer side.

For crossover calculation you need to provide the impedance of the drivers. Assuming 8ohms for both woofer and tweeter and considering the values 13uF and 1.8mH I get 1KHz crossover freq. using Butterworth method -that is clearly not covering the voice spectrum. Using 3.5KHz, the values will be 4uF and .5mH.

 

[audioguru]

A crossover network must match the spec's for the speakers.
Most tweeters have a minimum allowed frequency of 2kHz or 3kHz. Lower frequencies will destroy them.
Most woofers have a peak at 4kHz to 5kHz. Frequencies above 1kHz should be reduced so that the peak does not mess up the sound.
Therefore the important midrange frequencies will not be produced properly with a simple inexpensive two-way speaker.

Your simple second-order filters and all even-order networks produce a deep notch at the crossover frequency due to their phase shifts cancelling. Some cheap speakers that use this type of crossover reverse the wires on the tweeter so that the crossover frequency does not cancel, instead it adds and produces a small peak at the crossover frequency. A Linkwitz-Riley crossover is similar and has values that allow for a perfectly flat frequency response.

 

[magnatro]

here's the schematic for the pc speakers :
1+1Watt RMS.

 

[Hero999]

here's the schematic for the pc speakers :
1+1Watt RMS.

The component values aren't shown and neither is the supply voltage.

Assuming the supply voltage is 6V, the TDA2822 can't output 1W RMS unless the power voltage is 6V and the outputs are bridged to drive a single speaker. With the outputs each driving a speaker, as you've shown, the maximum power will be 650mW.

You might be right about 1W, if the power supply is higher than 6V the power might be 1W into two 4Ω loads but it isn't shown on the datasheet.

https://www.electro-tech-online.com/custompdfs/2010/04/TDA2822.pdf

 

[transistor495]

Here's the circuit of LA4600(Sanyo Semicon), costs $1.29 from MCM|LA4600|SANYO IC 10-PIN SIP | Newark.com.



Lots of versatile chips are hidden out there.

 

[Frederick]

So what I was able to understand from the last few posts was that I should probably add in a midrange speaker, some people posted amplifier ICs, & Series crossovers have shunt LPFs and shunt HPFs.

More exciting questions!

• What's a shunt filter, and what does it look like?
• What cutoff frequencies should I have?
• My drivers have 8Ωs of impedance; Do the previously posted ICs work with 8Ω drivers?
• How much wattage is normal for a speaker?
• Will the TDA2822 work with computer speakers? It said it was designed for radios and cassette players.

 

[audioguru]

So what I was able to understand from the last few posts was that I should probably add in a midrange speaker

I stated what might happen since nobody has the spec's for your speakers. Try them as a two-way speaker. Add a midrange speaker if it is needed.
Maybe your speakers are so cheap and produce such bad sound that you might start again with better speakers.

What's a shunt filter, and what does it look like?

The lowpass filter has a series inductor and a shunt capacitor. The highpass filter has a series capacitor and a shunt inductor.

What cutoff frequencies should I have?

Nobody knows the spec's for your speakers. Try 3kHz.

My drivers have 8Ωs of impedance; Do the previously posted ICs work with 8Ω drivers?

The simple and cheap amplifier ICs posted produce low output power. Some produce nearly 4 times the power when two amplifiers are bridged.

How much wattage is normal for a speaker?

The same as the normal power for a car. Aren't they all different? Aren't power requirements different? Aren't speakers cheap and low power or expensive and high power? Aren't speakers made in different sizes?

Will the TDA2822 work with computer speakers? It said it was designed for radios and cassette players.

It has very low output power but you will hear the speaker if you are fairly close to it. Maybe a cheap clock radio will be louder.

 

[Frederick]

No need to be snippy. As soon as I find exactly which drivers I'll be using, I'll post the specs; then I believe I can justifiably ask complicated questions. On the question of "shunt" filters, I was mainly curious as to what the term "shunt" meant. I'm not hip to your lingo. Also, I'm making the speakers for a computer, not a car.

To your very long list of questions in a row:
Yes, Yes, Yes, and Yes. I was just wondering about a ballpark figure for commercially made desktop computer speakers.

If that amplifier IC wouldn't be very effective, do you know of one that would both be audible from a distance of at least 5 feet and costs less than $10?

 

[transistor495]

This appears to me that you're not at all qualified for the speaker project.

Shunt filters :

 

[audioguru]

The TDA2822M amplifier IC has an output power when bridged at clipping into 8 ohms and with a 6V supply of 0.95W like a cheap clock radio. Its distortion is 0.3%. It costs $1.47US each at Digikey today. Its power is too low for a computer speaker.

An LM3886 amplifier IC has an output power at clipping into 8 ohms and with a 70V supply of 50W and is used in hi-fi stereos. Its distortion is 0.003%. It costs $7.30US each at Digikey today. Its power is too high for a computer speaker.

An LM1875 amplifier IC has an output power at clipping into 8 ohms and with a 20V supply of 4W. Its distortion is 0.02%. It costs $3.98US each at Digikey today. It would be good in a computer speaker that has a good driver.

Most computer speakers use a 3" full-range driver. A cheap one sounds awful and costs about $4.00US. A good one costs about $25.00US.

 

[Frederick]

Yes, I realize that I'm not qualified to make a speaker. The whole point is to learn how.

A full-range driver would actually be a good idea, in my opinion. I wouldn't have to mess with a crossover network that way.

Let's say I wanted to use this speaker. (which I do) It's not super cheap, and it fits easily into my budget.

Do you think that the LM1875 amplifier IC would be a good amplifier circuit for this?

 

[audioguru]

The little speaker has a pretty good low frequency response for such a small speaker. It is rated at 15W which is good because it has poor sensitivity.
With an input of 15W then its loudness is 93dB at a distance of 1m. Two will have a loudness of 96dB at 1m.

Its peak at 7kHz might be tiring and can be reduced with an LCR circuit.

An LM1875 is a good amplifier for this little speaker. It can be powered by a plus and minus 20V supply.