Subwoofer Integration

Volumio Version: v3
Hardware: Raspberry zero 2 - two pieces.

Hi , I am looking for a way to add a Subwoofer. I read somewhere about synchronized multi room playback, so the question is:

Can I use one raspberry with Volumio for stereo and a second raspberry, with a second Volumio, for a Subwoofer?
It would be used together within one room, so there has to be no timming issues between signals.

Sounds like an elegant solution when your amp has no sub out. If the new Volumio 3.x indeed synchronises the signal 100% this should be possible.

How is that supposed to work? One volumio does all the work and then just sends the signal to the other, who’s doing DSP for the second Volumio?

why don’t you connect your subwoofer to the speaker outputs of your amplifier? Doesn’t the sub have high level inputs? You could easily solve that with a so called voltage divider, it’s just two resistors per channel, which will set you back less than a dollar or euro. No need for extra RPi or a myvolumio subscription, no latency issues etc. Only benefits.

I have such a setup with my stereo system (including RPi0/volumio). My Cambridge Audio S90 sub doesn’t have speaker level inputs, but using the voltage divider is is hooked up to my amp’s speaker outputs anyway.

Because main speakers need a lot of gain towards the lower frequencies. If a Subwoofer would be fed the same signal, it will output quite a bit more SPL than needed.

I don’t get it. Are you saying you eq your main speakers for more bass? Why? Isn’t your subwoofer supposed to make up for lack of bass of your main speakers?

It might work, but it’s a very strange way to integrate a subwoofer.
A specific solution will depend on the plugs on your particular subwoofer, but commercial subwoofers are almost always designed to take a) a one channel signal from a dedicated subwoofer channel, and b) in addition can use the same signal you would send to your speakers. I suggest you probably want b), most people do if they aren’t looking to get fancy.
The vast majority of them also have independent volume controls, because that’s how you generally do simple sub integration. Many subs also have a passthrough so you can either plug your 2-channel amp into the sub and plug the sub into your speakers, or have the outputs from your amp split to both sub and main speakers.

The advantage of this is that you only need a few extra cables, which is far more elegant and more cost effective than trying to run two players in sync.

It’s a great idea to get a sub, I thoroughly recommend the general idea, but you need to work out the wiring, ideally before you even buy the sub. You will struggle to buy one that doesn’t have its own volume control.

Subs will almost always have a crossover too, which means all the controls you need for integrating a sub are generally part of the sub itself. Unless you have something more exotic, the usual method is to buy a sub and plug it into your amp, and then play with the cutoff frequency and volume knobs. Once you get something reasonable sounding, then start tuning the overall frequency response if you need to.

Hi, thanks for answering. I should explain a reason for this unusual sub integration.

I’ve built open baffle speakers that can reach down to 45 Hz. I went with an open baffle to minimise the room effects upon low frequency reproduction. You trade significant low end extension, but you get a figure 8 bass dispersion, that forms less room interference at your listening spot.
That’s the reason I don’t want to limit their bass output, but just to add something below. I can alter the signal with DSP, add a 30 Hz crossover, manage the EQ and FR, but I need another way to implement a separate signal.

The solutions I found are:

  1. Add a DAC hat to the main raspberry. Send one signal through USB to an external D/A converter and use a DAC hat to output a second signal.
    I do not know if volumio can play two separate streams with two separate DSPs on a single device. CPU performanse will also be an issue, since everything is to be done on a signal chip.
  2. Make another volumio device and sync it to the other one. Possible problems could be timing of the two signals, but I do get two separate CPUs for DSP.

OK. Why not set the cutoff on the sub to roughly 45Hz and plug it all into one set of amp outputs?

It’s easy enough to try if you already own a sub, just a re-cabling job. The best/only way to overcome uneven sub distribution is to get a second sub and play with the respective phase settings on the sub, so I can see why you might want such a low cutoff if you like the open baffle bass, even though your speakers will be eating a lot of power at 45Hz and there’s no real directional component to sound much below 100Hz anyway.

But if you are only concerned with a single listening position, one sub connected normally should be fine, then play with sub volume and cutoff frequency to taste. It doesn’t have to be complicated in my opinion, and it’s way cheaper and easier to try it the easy way first, you lose nothing much.

That would be by far the easiest option. However, open baffle requirers more than 6-8 dB of gain at around 50 Hz. I can’t get a Subwoofer crossover slope steep enough, in order not to get influenced by such a large gain. Plus, common subwoofers don’t offers 4th order slope, especially not at only 30 Hz.
If I could find a sub that can get 24 dB per octave or more, I might EQ everything with parametric at the end. However, a digital crossover would make for a far more practical solution.

Yes, a crossover would work.

My sub, for instance, already contains a crossover/passthrough set to about 100Hz, so my main speakers aren’t eating so much amp power trying to reach their absolute low end, the sub takes it off their hands (not that they have hands). I suggest you might want to avoid the 50Hz area and assign it to the sub since that is part of the job description of a sub.

The reason for that gain requirement is that your speakers are on the bleeding edge of what they can do. If you give, say, up to 80Hz to the sub with a crossover, you will not have to correct so drastically at 50Hz since the sub isn’t straining to deliver at 50Hz at all.

True, they are limited to moderately loud listening at 45 Hz, even though they are dual 12 inches per speaker. I was trying to get away with one sub, and not to invest in two of them.

Is it possible for one volumio to play two signals at the same time, through two separate outputs (eg. One usb out and one analogue RCA)?

For a single listening position one sub (suitably powerful wrt to your main speakers) is sufficient, you just move it around the room a bit to make sure the local maximum is roughly where your listening chair is. Look up ‘the subwoofer crawl’.

Perhaps what you describe will be possible with the new Volumio 3 sound architecture and the right hardware, I don’t know about that. Some sort of crossover would be a better solution than two synced Volumio instances I believe, but it’s still not simple. Good luck.

1 Like

What kind of music are you playing that would require a frequency response below 45Hz? Organ works bij J.S. Bach perhaps?

I don’t know if these exist, but perhaps using an optical TOSLINK splitter would allow you to connect two DACs to one streaming device, and avoid latency differences. If needed, you could also filter in the analog domain.
If these don’t exist, you could also use coax, but that might introduce unwanted jitter.

1 Like

I can answer that.
Subs add both low frequency reproduction as well as additional power in that range which most full range speakers either struggle to provide, or struggle to provide without eating amplifier power, as mid range speaker cones are designed for mid range reproduction.

An active (separately amplified) sub adds a number things - more power at low frequencies to match what is usually available in the midrange, a way to relieve midrange speakers of the burden of reproducing frequencies at the limit of their range, a way to use a main amplifier to drive the mid and upper frequencies only, making the whole system effectively more powerful if you care about that. And if you plug your music system into your telly you have an instant home theatre system.

Dance music benefits since is designed to have low frequency components below 45Hz, but most other forms, particularly those containing percussion like kick drums, gain a definite feeling of presence with a sub, it seems to fill the room more convincingly.

If my sub broke tomorrow, I would go straight out and buy a new one. When someone plays me their fantastic newfangled music system, my most regular comment is ‘When are you getting a sub for it?’

The only exception would be vinyl based nostalgia music systems, since there is less need for low frequency sound that vinyl doesn’t reproduce well anyway.

Your scepticism is understandable. If you’ve never had a sub maybe you don’t notice the difference, but if you’ve ever had one you won’t want to be without one in my view.

1 Like

Also, if you hate your neighbours you can use a sub to really punish them.

Actually, I did punish the neighbors two doors away once, after asking them to keep down the volume several times, so that I wouldn’t have to enjoy their musical tastes as well. I then demonstrated what a Denon PMA-720A and a pair of B&W DM220 speakers are capable of when playing some bass-heavy progressive metal. They probably were able to hear me at the other end of Amsterdam. no more problems after that :wink:

Verdomme was jij dat?

1 Like

I have plans to do some negative re-enforcement training for my neighbours above.
Mount some 12" subs to the roof and then
Sample sounds they make → Delay by 2 seconds → Amplify → Replay

Ahahahaha, I’m sure that will end up well!