How to mount micro speakers to a PCB?

[Cory Parsnipson]

Hi, I want to make a small design that includes a microspeaker on the PCB and I am unsure of how to "mount" it to the PCB.

The part in question is this: https://www.digikey.com/en/products/detail/cui-devices/CMS-15113-078SP/8581915 or something similar. It has two solder pads on the back of the speaker but they're inset a bit, so when the back of the speaker is flush against the PCB surface, the solder pads will be hovering a little ways into the air. Here's a picture that might demonstrate:



On the bottom half, you can see the wires are soldered to the solder pads in the corners. The corners are inset like the opposite two corners that don't have pads on them. This means when you flip the speaker over and press it to a flat surface, the corners aren't touching the surface.

I soldered wires to it for my breadboard experiments where the leads are going into a terminal block, so I didn't have to solve the problem until now. For people who have experience with these parts, what are some conventional ways they are added to a PCB?

Thanks!

[SMTech]

more likely held in place by chassis design or hot snot than fixed to the PCB.

[Cory Parsnipson]

Oh I see. So, then for the connection aspect of it the solder pads on the speaker must still be welded to throughholes or pads on the PCB with wires, I take it? Sorry if this sounds too obvious, I'm wondering if there's an easier way to do it.

[Gribo]

If you want a reliable product, Look for speakers with spring terminals. Old Nokia phones used those. The CUI part has an option for spring terminals. It requires a very specific enclosure design, but it is easier to assemble.

[Cory Parsnipson]

Hmmm ok, I've got a 3d printer so that could be a better option for me. Thanks!

[wraper]

Such speakers usually have spring contacts. They are placed into recession in enclosure with adhesive gasket in between (gasket often combined with mesh dust protector). Gasket is very important. If it does not seal completely, sound will be very silent and lacking low frequencies. Then PCB (or flex PCB reinforced by something stiff) is mounted on top. In case of wires, it's basically the same but without PCB.

[Cory Parsnipson]

Oh wow, that's illuminating. Thanks for the detailed info! You've inspired a couple of ideas that I want to experiment with:

I've whipped up a quick mounting bracket for the AS01808AO, which is a similar, but slightly bigger speaker.



The idea is that it will go over the top and then bolt into the PCB from the opposite side and hold it in place. The AS01808AO comes with solder balls pre-added to the pads, so I put into two little windows on the side in the hopes that I can tin the pcb pads and touch the soldering iron to it with the speaker mounted and hope everything bridges. (I will try to remember to post results when I get the PCB).

In the event that this doesn't work, I can buy a spring terminal version of the speaker and modify the bracket to be taller to accommodate the new dimensions of the part. Height notwithstanding, everything else about it should be able to remain the same. Then the mounting process would only require shoving the speaker into the hole and screwing it down on the PCB, no solder necessary.



For the gasket, I want to see if I can try cutting a shape out of electrical tape and fitting that inside the mounting bracket between it and the speaker. I wonder if having something slightly soft and springy will make for a nice, tight fit. Currently I have the speaker inside a very similar mount and drilled to a piece of wood for testing and the sound seems very good so even if the tape doesn't work out, I think it might sound acceptable.

I also bought a sheet of speaker mesh off Amazon. I want to try gluing a small square of it on top of the mounting bracket and see how that sits.

[wraper]

I've whipped up a quick mounting bracket for the AS01808AO, which is a similar, but slightly bigger speaker.

It will not work well. You need a chamber sealed from the outside on its backside, preferably with a space at least as large as the speaker itself, more - better (will improve low frequencies). Otherwise an acoustic short circuit happens, and as I said, it becomes very silent and lacking low frequencies. Look how laptop or speakers are built, becomes more obvious. Again, if wires are going out, they must be sealed too. If you want them on PCB, better use ones with spring contacts. However you should have gold plated pads on PCB, or even better, rectangular flat SMT contacts with hard gold plating soldered on top of pads.

[Psi]

Double sided VHB foam tape is one option that works.
It will stick to the speaker and the PCB fine.

[Cory Parsnipson]

Double sided VHB foam tape is one option that works.
It will stick to the speaker and the PCB fine.

That's good to know, thanks! I'll keep that in mind when looking for materials.

I've whipped up a quick mounting bracket for the AS01808AO, which is a similar, but slightly bigger speaker.

It will not work well. You need a chamber sealed from the outside on its backside, preferably with a space at least as large as the speaker itself, more - better (will improve low frequencies). Otherwise an acoustic short circuit happens, and as I said, it becomes very silent and lacking low frequencies. Look how laptop or speakers are built, becomes more obvious. Again, if wires are going out, they must be sealed too. If you want them on PCB, better use ones with spring contacts. However you should have gold plated pads on PCB, or even better, rectangular flat SMT contacts with hard gold plating soldered on top of pads.

Hmmm I see. CUI has a doc about designing an enclosure: https://www.cuidevices.com/blog/how-to-design-a-micro-speaker-enclosure, but I didn't understand why it needed a spacious void behind the speaker. Interesting!

My empirical observations with my breadboarded circuit show that the volume is almost comparable to my smartphone. My uneducated opinion is that the sound is conducting through the wooden backboard. Is that a thing or complete nonsense? I thought I could do the same with the PCB version.



Here's the previous bracket I made. Does this qualify as "sealed"? No caulk or insulation was used, but I feel like maybe it's 80-90% as good. I can hear the sound very clearly, but I do notice a hard attenuation of lower frequencies, though, which is probably for the reasons you described. This could be improved if I found a way to increase the size cavity underneath the speaker, it sounds like.

Maybe I could make an edge cut in the PCB that would let me push the back of the cone through and let the outer edge rest flush. This way the soldered pads could be closer to the PCB, and I won't have to worry about sealing wires. Then I could make another 3d printed part to seal the rear... 

Just thinking out loud right now. I kind of want to try this in a separate iteration to see if it works. I'll report back later with what I find out.

[Cory Parsnipson]

I made something in Fusion360, but I'm having second thoughts because it just feels overly complicated.



The middle plane is a stand-in for where the PCB would be and I marked approximately where the pads would go in green. They fall inside the enclosure. I also insisted on bolting everything down with screwholes, but the bottom could probably be mounted with a delicate application of epoxy. The top's screwholes can stay for ease of access.

I also discovered that the miniature train community has a lot of information dealing with microspeakers: https://www.caledoniancouplers.com/fitting-sound-box-sugar-cube-speaker/

Using spring terminals or just enclosing the speaker inside a sub-enclosure without trying to get cute with the PCB look like they would be a much less temperamental design.

Hmmmmmmmmmmmmmm....

[Psi]

Get the version that comes with some short wires already attached,
Solder said wires to PCB pads/holes.
Attach speaker with a speaker-sized rectangle of double-sided VHB foam tape.

Done.

You can also get them with a tiny 2pos connector on the end of the wires but then you have the cost of the other connector side. Up to you.

[Infraviolet]

I once found a nice SMD solderable speaker type (https://uk.rs-online.com/web/p/miniature-speakers/7542081) which I used in a project, the actual manufacturer appears to be called Kingstate. There are also some through hole speaker types available. I wouldn't tend to trust the mechanical survivability of those thin wire to speaker joints, or the other solder blob sorts.