HiFiBerryOS – Room equalisation

Even with the best DACs, amplifiers and speakers music reproduction in living rooms won’t be optimal. As you’re not living an a concert hall, your listening room is probably not optimized for optimal acoustic performance. One major problem are so-called room modes. These are basically resonances that are caused by your room. Have a look here to learn more about room modes.

In an ideal world, you would first design your room in a way that its room modes are well-distributed and you would use tools like diffusors and absorbers to improve the situation. That’s definitely the best way to go and we strongly recommend you to lern more about these tools first. However, we’re aware that you may not be able to add lots of absorbers to your room – because you still want to live in it. In general, we recommend to learn more about room acoustics before going on. Unfortunately it’s not a topic that can be dealt with in a few chapters. However, if you’re eager to learn more, Floyd Tools book “Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms” is worth reading.

If you think you did everything possible to improve the characteristics of your room, that’s where room equalisation starts. It uses equalizer rules specifically designed for your speaker/room combination to help with bigger problems. It’s not a replacement for acoustic treatment of your listening room, but a complementary tool to improve acoustics.

How does it work?

First, you need a measurement microphone. HiFiBerryOS supports the following USB Microphones:

Check out this page for a comparison of different models. Using the microphone, HiFiBerryOS measures the frequency response at your listening position.

One important thing now: Turn the volume as high as you can! This might hurt your ears, but you can simply leave the room and start the measurement from outside as you control it via the web interface. Also turn off other devices that might emit sounds. Computers often use fans that can impact measurements.

When the measurement is finished, you can see the result and it might look like this:

In this example we see some large spikes in the low-frequency region. Some are caused by the speaker itself, others are cause by room modes. From the frequency response you can’t easily distinguish. A good rule of thumb is that room acoustics issues are small spikes as they occur at specific frequencies.

Now let’s run the optimizer:

You now see that the peaks in the low freqency have been removed by the optimizer.

BTW: While it says “Tannoy D300” the frequency response shown here isn’t a “plain” Tannoy D300, but some equalisation had been implemented here.

Tuning the optimizer

At this stage, you can only select different pre-defined sound profiles. We might introduce tuning options in the future, but we won’t commit on specific features or options.

Even more control

Our design goal was it to bring optimisations to people that don’t have a lot of experience at this topic. Therefore if you’re an advanced user or even acoustics professional you may look for something more advanced. In this case, we recommend tools like REW that support much more measurements and tuning of the optimisation parameters.

Feedback

The room equalisation optimizer is brand-new and hasn’t been tested a lot. If might not always work perfectly. If you feel some optimisations could be improved, please post in our community area.

FAQ

Q: What’s the correct target curve?
A: There is no “right” or “wrong”. However, we recommend to start with the “bass only” curve. This will only touch the frequency range that is mostly affected by the room.

Q: The frequency response isn’t fully linear after the optimizsation.
A: Yes, and that’s fine. The frequency response doesn’t have to be perfectly linear. Equalisation isn’t “for free”. Each equaliser will also impact other parameters as the phase response that will have an impact on sound quality. Therefore our optimizer isn’t working very aggressively.

Q: Why doesn’t it fill gaps in the frequency response.
A: Large “gaps” (frequencies where the sound level is very low) are cause by destructive room modes. Basically the room cancels sound coming from the speaker. Equalisation can’t fix these problems. Our optimizer won’t aggressively try to linearise the frequency response as this would create more acoustics problems than it would fix them.

Q: Why are the data pushed to your cloud server?
A: The optimisation requires quite a lot of CPU resources. Handling this on a cloud server allows us to run optimisations that the Raspberry Pi wouldn’t be able to handle, because it lacks processing power. We also use these data to improve the optimizer.

Q: After the optimisation my system lacks low frequencies.
A: That’s possible as you’re probably not used to a more linear frequency response. Feel free to add some additional equalisation by yourself. Start with an additional “Peak” filter at 100Hz. Adjust frequency, width and gain that it matches your personal .

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