High Quality Greeting Card

Hello, I’m trying to make a special greeting card with a song, I previously tried sd card and TMRpcm library with a doorbell speaker, but the quality was so low. Is there any better solution?

You need a good amplifier and a good speaker for good audio quality.

The two problems are the speaker and the size of the electronics & battery. There might be a way to couple the card to the speaker so the whole card acts as a speaker but that's not going to give "great" sound.

In general, for "good sound quality" I'd use an audio shield (with a proper DAC, etc.), plus an amplifier if the shield doesn't have one built-in. And, a regular 4 or 8-Ohm speaker. But, that's NEVER going to fit into a greeting card. (Professional electronics designers/manufactures could probably build custom electronics small enough but "microelectronics" is not so easy "at home".)

…How about a little "gift box" instead of a flat card? ...Except they might be disappointed if there isn't jewelry inside. :wink:

Until recently, I felt the same way as jremington & DVDdoug, that you can't get good sound quality without a large speaker, and without an enclosure trapping a substantial volume of air behind it.

Recently I've been working with a new chip from Maxim Semi, part number MAX98390, which does really amazing tricks to get the most from tiny speakers. The results are really quite incredible. But the tech comes with many caveats, the hardest being an almost impossible to solder wafer-scale BGA package. I've been working with a contract manufacturer to try to get shields made with this amazing chip. They've managed to solder a few prototypes, but getting it to be reliable for production volume is still quite a challenge.

If you're skeptical, and believe me I was quite skeptical before I started working with this chip, it senses the actual real-time current flow to the speaker, so it knows both the voltage it applied and the resulting current. Inside it has a small DSP engine that does many tricks. But that alone isn't the whole story. The DSP engine requires a pretty extensive set of calibration results from testing done with the actual speaker, mounted to the actual enclosure or frame. Some of the calibration stuff is proprietary "secret sauce" that Maxim won't disclose.

But one of the parts I understand involve measuring the speaker+enclosure resonance frequency. I believe the DSP engine is implementing a deep, narrow notch filter, and then allows bass notes 2 octaves below the resonance to play. It make an incredibly tiny speaker sounds like a much larger one, with 2 octaves lower response.

Another trick the chip does is computing the temperature of the copper wires inside the speaker. Again, this relies on an initial calibration measurement of the speaker, which has to be done also with a temperature sensor (that's assumed to be the same as the speaker before heavy use). The temp sensor isn't used while playing sound, only during calibration. The amplifier is capable of about 5 watts peak, which could burn up many tiny speakers. But this real-time temperature measurement of the winding (which is inferred by the current measurement compared to the original calibration) allows the chip to safely drive tiny speakers much harder for short peaks than you could safely do with a normal amplifier. For ordinary music, it makes a pretty amazing improvement in loudness.

That chip has many other neat tricks, like a boost power supply that dynamically adjusts the power supply voltage (up to 10V with 3.6V battery power) only as needed by the actual audio. It delays the sound about 100 us, so it can look ahead and know how much voltage is needed.

Of course, all this amazing tech doesn't turn a tiny 1 inch speaker into a 12 inch sub-woofer. But it does sound like a 3 inch speaker with a more powerful amp.

The bass enhancement also does not work unless you have reasonably good acoustic pressure isolation between the front and back of the speaker, which usually means making a tiny sealed enclosure around the speaker, or mounting it to it a large & sturdy flat surface... which might work for a greeting card if you can use heavier card stock.

You need a good amplifier and a good speaker for good audio quality.

And if you want full bass the speaker has to be big.