Any Tips for Making Spherical Speakers Sound Even Cooler with SPAT?

tslclab · November 19, 2024, 3:46am

Hi, friends of the forum,

I’ve recently developed a strong interest in the beamforming of spherical speakers. Using open-source resources, I attempted a DIY project to create a 393-speaker array. With SPAT’s recent updates providing a more complete approach for IKO tuto, I’m particularly curious: if I use the 393-speaker array, can I employ spat5.iko.decoder~ as the final decoder and adjust the original output to 15?

Since my knowledge and experience with spherical speakers are still quite limited, I’d also like to ask about the differences between two approaches:

Using hoa.encoder~ to transform a stereo or mono source into a 3rd-order HOA stream.
Using beam control to encode into a 3rd-order HOA stream.
What are the practical differences between these two methods?

I’d also like to share the patch I’m currently experimenting with!

393FIR.maxpat (146.8 KB)

tcarpent · November 19, 2024, 10:00am

Hello,

Wow, a 393-speaker, that’s an impressive DIY project ! Curious to know more about it !

As the name suggests, spat5.iko.decoder~ is designed for the IKO and cannot be used for other spherical arrays.
Also, decoding an HOA stream to a compact loudspeaker array requires a set of decoding filters. There’s (currently) no tools in the Spat package to calculate these filters.
(for the IKO, pre-calculated filters are included in the package, as wav files)
You’d have to compute these filters on your own. Then you can use Spat tools (such as spat5.hoa.slaconv~) to render (i.e. convolve) the decoding filters.

Also, be aware that decoding to IKO is extremely CPU-intensive; it involves 16 x 20 x 2048 filters
(where 16 == 3rd order HOA, 20 = number of speakers in IKO, and 2048 is the typical FIR filter length)
In the case of a 393-array, I doubt this can operate in real-time.

as the final decoder and adjust the original output to 15?

why 15 ??

the differences between two approaches

spat5.hoa.encoder~ encodes a mono signal to 3rd order HOA.
This is equivalent to creating a beampattern with “hypercardioid” shape.
See the attached patcher.

Hope this helps,
T.


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tslclab · November 20, 2024, 2:28am

Hi tcarpent,

Thank you for your detailed explanation! It gave me a clearer understanding of the IKO tutorial and how it’s specifically designed for compact loudspeaker arrays like the IKO. I’m curious about the decoding filters you mentioned—what tools are typically used to obtain accurate measurement data for spherical arrays like these?

The reason I attempted a DIY 393-speaker project is my fascination with how spherical speakers create what’s called a phantom source in a space. It’s that surreal experience where there’s no visible speaker, yet sound seems to originate from a specific direction. Through this project, I want to explore whether the decoding logic from the IKO tutorial can be applied to the 393-speaker array.

As for adjusting the output to 15, it’s because my 393-speaker array currently has only 15 drivers arranged in a spherical layout.

Perhaps my first step now is to use spat5.hoa.slaconv~ to render decoding filters for the 393 array.

Thanks again for your insights,
Xan

tcarpent · November 20, 2024, 2:09pm

For the IKO, we typically use decoding filters provided by the vendor (Sonible).
I’m not aware of (open source) tools to generate decoding filters for your own array, but admittedly I havent searched recently.
As for measurement data for spherical arrays, this typically needs to be done in an anechoic chamber… so not exactly DIY !
Good luck with your project !
Best,
T.