Acoustics Beyond the Datasheet

A Good Speaker on a Datasheet doesn’t guarantee a Good-Sounding Product

Working with audio components, one thing I see pretty often is how much attention goes into selecting the right speaker or microphone, and sometimes not enough into what happens once that component is actually inside the product.

On paper, the process can look pretty straightforward. You find a speaker with the SPL and frequency response you need, or a microphone with the right sensitivity and signal-to-noise ratio. The specifications look good, the component fits and you move forward with the design.

Then you build the prototype and it doesn’t sound the way you expected.

The component itself might be perfectly fine. The problem is that once you put a speaker or microphone inside an enclosure, you’re no longer evaluating just that component. The mechanical design around it becomes part of the acoustic system.

That’s where integration starts to matter as much as component selection.

A speaker doesn’t perform the same way inside your product

A speaker datasheet gives you a useful starting point, but those measurements are taken under specific test conditions. Your product will probably give the speaker a very different environment.

The available air volume behind the speaker, for example, can have a big impact on its performance. In a compact product, that back volume can be very small. The air behind the speaker affects how the diaphragm moves, which can change the resonant frequency and low-frequency response.

Sealing matters too. Small gaps around the speaker or between mechanical parts can create acoustic leakage and change the performance you expected from the original design.

Then there is the enclosure itself. The speaker is creating vibration, and those vibrations don’t necessarily stay inside the speaker. They can transfer into the surrounding plastic, PCB or mechanical structure and create buzzing or resonances that weren’t there when the speaker was tested on its own.

So even if two products use exactly the same speaker, they can sound very different depending on how that speaker is integrated.

That’s why I don’t think speaker selection should happen independently from the mechanical design.

Microphones have a different set of problems

Microphones have the same basic challenge, but in a different way.

With a microphone, you’re trying to make sure the sound you actually want reaches the microphone while limiting everything you don’t want: vibration, wind, internal noise and sound coming directly from the device’s own speaker.

The acoustic path between the outside of the product and the microphone is important. If the microphone isn’t properly sealed to its acoustic port, sound can travel through the inside of the enclosure instead of following the intended path.

This is where things like gaskets, rubber boots and acoustic meshes become part of the design. They aren’t just mechanical details. They can directly affect how the microphone performs.

Placement matters as well, especially when a product has both speakers and microphones. If they are too close together or poorly isolated, the microphone can pick up a lot of energy from the speaker. Software can help with Acoustic Echo Cancellation, but I wouldn’t want to rely on software to solve a problem that could have been reduced mechanically in the first place.

The same applies to vibration. If the speaker transfers vibration through the structure and into the PCB where a MEMS microphone is mounted, the microphone can pick up that vibration as noise.

Again, the microphone itself may be doing exactly what it is supposed to do. The integration around it is creating the problem.

Small mechanical decisions can have a big acoustic impact

This is probably the part I find most interesting.

A gasket can look like a very minor part of the overall product. So can a piece of acoustic mesh, a vent, the position of a screw or a few millimeters of additional air volume.

From an acoustic point of view, those details can matter a lot.

If the product needs water or dust protection, for example, you may need an acoustic mesh over the speaker or microphone opening. That mesh protects the component, but it can also affect the acoustic performance, so it needs to be considered as part of the system rather than added at the end.

The way a speaker is mounted can also affect the product. Mechanical isolation using the right mounting material can help limit how much vibration transfers from the speaker into the rest of the enclosure.

And then you have the physical location of the ports themselves. A speaker or microphone can work perfectly during a test on a table and behave differently once someone actually holds the product and accidentally covers an opening with their hand.

These sound like small details until you build the product and hear the difference.

DSP helps, but it can’t fix everything

DSP is obviously a big part of modern audio products.

Equalization can help shape the response. Compression can help manage the output. Acoustic Echo Cancellation can make a big difference in products where microphones and speakers are operating at the same time.

But there is a limit to what software should be expected to fix.

If the enclosure has a mechanical resonance, the microphone isn’t properly sealed or the speaker is creating too much vibration through the structure, DSP may help compensate for some of it, but you’re starting from a much more difficult position.

That’s why I think the mechanical, electrical and software sides of an audio product need to be considered together.

You don’t want to finish the mechanical design, put the speaker and microphone inside, and then expect DSP tuning to solve whatever happens next.

Testing the complete product matters

This is also why testing the individual component only tells you part of the story.

You need to test the speaker and microphone once they are installed in something that is representative of the final product. Controlled acoustic measurements are useful for understanding frequency response, distortion and output, but real-world testing matters too.

How does it sound when someone is actually holding it? What happens if a finger partially covers the microphone port? Does the enclosure start vibrating at higher volume? What happens outdoors or around wind? Does the microphone still perform correctly when the speaker is playing?

Those are system-level questions, and you can’t answer all of them from a component datasheet.

It also means acoustic testing shouldn’t be something that only happens at the very end. If you discover an integration problem after tooling is already finished, your options become much more limited.

What I take from this

When I’m looking at an audio application now, I don’t think only about which speaker or microphone has the best specifications.

I want to understand where it is going.

How much space is available? Where is the speaker positioned? What’s behind it? How is it sealed? Where is the microphone relative to the speaker? Does the product need to be waterproof? How is someone going to hold or use it?

Those questions can change what the right component actually is.

And I think that’s the bigger point. The best component on paper isn’t necessarily the best component for the product.

A slightly different speaker that works better with the available enclosure volume may give you a better result. A microphone with great specifications won’t help much if the acoustic path around it isn’t designed correctly.

Audio performance comes from the complete system, not just the component.

One last thought

Datasheets are important. You obviously need them to compare components and understand what you’re starting with.

But a speaker doesn’t know what the datasheet says once you put it inside a small plastic enclosure.

It only knows the environment you gave it.

The same goes for the microphone.

That’s why I think good audio integration starts earlier than people sometimes expect. Speaker selection, microphone placement, enclosure design, sealing, acoustic protection and DSP shouldn’t be completely separate decisions.

They all end up affecting the same thing:

What the person using the product actually hears.