< Back to IRCAM Forum

Dealing with subs in HOA

Spat
#1

Salut,

Sometimes, in live situations, we have to feed multi sub woofers, additionally of feeding the dome. Until now, or we used to export sub channels in studio and play HOA stream and subs stream together. Or we did it in the mixer by splitting the dome in pizza slices and feed the subs (with pizza).

With the great improvements of Panoramix, and specially the player integration allowing us to have a plug and play tool, it’s attractive to have a global solution wish treats HOA and sub streams at the same time. Without needed a mixer (or at least keeping a straight routing). So I guess a (the ?) solution is to create a bus 1 hoa3d(x order) for the regular speakers and an other one, also in hoa3d(x order), for the subs outputs.

In our studio we only have a single sub, and we can’t test what happens in low frequencies. I guess the question is really pertinent if we think about the number of sources we have and the number of sources we need in theory. In our case, we use to mix in 4th order 3d so we need at least 25 speakers. It could be the case for the dome but we are really far from this number with 4 or 8 sub speakers.

So, theoretically, is this way of doing is pertinent ? And what method and/or type of decoding is/are the best to deal with low frequencies and the lack of speakers ? I guess the rendering of low frequencies on a large sweat spot is more important than the location of sounds.

Thanks a lot
Christophe

#2

Hi Christophe,

Well, dealing with multiple subwoofers, I mostly think of two approaches :
if tracks are not (hoa) encoded, then create e.g. a vbap (2D) bus, with reverb muted, and send all your tracks to this bus. Then apply a low-pass filter for proper “bass” management.
if the input tracks are hoa-encoded, then you indeed need a (1st order?) decoder. As the location of (subwoofers) sounds in space is not that important, the settings of the decoder should not matter much. Maybe try in-phase decoding (?) as this is optimal for low-frequency content. Just a guess.

Cheers,
T.

#3

Hello,

Thanks for your answer (again). The vbap solution doesn’t work this time because the stream is encoded. I give a try again before answer to your post (to be sure) and I notice something… Generally I use to create an input track “direct to bus” 25 channel and feed a 4o HOA bus (an habit from the time when HAO stream input didn’t exist) But I just can’t feed a 1st order HOA bus.

I just tried again with a HOA stream input and, in this case, it’s possible to send the signal in many HOA bus no matter the order. So, problem solve… Just as you said.

As a sound engineer, the words “subwoofer” and “in-phase” look good together. :slightly_smiling_face: I’ll do this !

Tschüss
Christophe