Subwoofer output

Hi everyone,

I have a problem and hopefully someone has an idea. I recently upgraded to a sub that allegedly goes all the way down to 16hz. However after hooking it up and getting all frustrated I realized this: because it is running as an output from my Motu 24ao which stops at 20hz I’m missing the bottom 5-6 notes which is why a bought this big sub.

I’m trying to get around running the sub through my audio interface (the Motu) so I tried plugging it into my Mac’s headphone jack to see if I could make that work. But I can’t ever get any sound through the headphone jack. Will HW only play audio out through the Audio interface OR headphone jack nut not both?

If anyone has found a way to make a situation like this work I would LOVE to know.

Many thanks!

Jonathan

[mdyde]

Hello Jonathan,

You can only have one audio 'device' selected at once in Hauptwerk (to ensure that all channels are perfectly synchronised, otherwise audio glitches could occur). However, you could use macOS's "Applications/Utilities/Audio MIDI Setup" to create 'aggregate' devices, for which macOS handles synchronisation and presents the channels of each aggregated real device as channels on the single virtual 'aggregate device':

https://support.apple.com/en-us/102171

Then you could select that 'aggregate device' as the output device in Hauptwerk.

However, I'd be surprised if a Mac's built-in output has a bass response extending deeper than a professional audio interface (such as those from MOTU).

The MOTU 24ao has a specification that is essentially ruler flat down to 20 Hz. I would assume that the response continues well below 16 Hz as it's hard to imagine a filter that would cause such a steep cutoff. It's possible to do a quick check with a program such as REW from www.roomeqwizard.com. As an example my Scarlett 18i20 interface is flat down to below 4 Hz.

Perhaps someone already has a 24ao measurement or calibration file.

I used the 32' sine wave stop on Al Morse's calibration organ (seems to be gone from his site now) through my MOTU 24Ao to test my SVS PC12+. The lowest note sounding in air was A 27.5 Hz, but the floor carried notes below that, almost down to C 16 Hz, when the sub was turned up loud. So the low note signals are passing through to the sub. The room isn't big enough to sound in air below 26 Hz, apparently.

Have you tried playing a low note then walking round the room? OK, you might need some help for that or a way to jam a note on in some way. I was surprised when I tried it. In the middle of the room the bass note I was playing dropped right off in volume while it was much louder towards the sides.

Also, I am told that placement of the sub can make a difference as well.

Thanks very much everyone for your replies! I’ll try walking the room and doing some more careful tests.

One thing I would add is that this room also has an another digital organ subwoofer in it. Although that monster speaker is at the other end of the room it very comfortably produces 32’ low C which I compared it to. My HW setup will not, on any sample set produce anything lower than bottom E of a 32’ Bourdon for example.

I have also moved the equalizer way up on the bottom end of the sub’s range to do as Mnailor suggested. I have an SVS sub as well.

jkinkennon, could you elaborate on your statement about the Motu having some response below the spec of 20 hz? I was thinking that since in A440 32’ E is 20.6hz I kind of expected that to be the lowest note that the Motu would reproduce(?)

Thanks again everyone!

The response of systems doesn't in general have sharp edges. A system which is flat "only" to 20Hz will only be one or two dB down at 16Hz (32' C), which is scarcely noticeable.

The effect of standing waves at low frequencies is far more important. Reproduction of the lowest notes is hardest in small rooms (especially ones whose dimensions are less than the wavelengths of the notes concerned); but you'll find that if a low 32' note is held in a cathedral and you walk around you'll also get areas where the sound cancels out (or gets reinforced) - recording engineers have to consider this when placing microphones to record an organ. Of course, it's hard to get a uniform response even that way, because notes with different wavelengths will cancel or reinforce at different positions! This effect is also most pronounced with stops with few harmonics (which being at higher frequencies are less affected), so a Violone will be less affected than a Bourdon, for instance, and any reeds much less.

Paul

Thanks, Paul, for the good observation about filter behavior. I have never needed to measure the actual roll off of a MOTU 24ao output channel, but I did have a customer provide the 24ao on an install where I built the Tuba HT sub as part of the pedal division. It did work well down to 16 Hz.

It's important to understand that a 16 Hz tone output from a sub is not audible, at least not to the vast majority of people. It is felt and certainly has an impact on the sound of the rest of the pedal channel. Any sound heard from a 32' Bourdon at low C is likely due to harmonics either recorded or excited by the 16 Hz wave (picture frames). Speakers may produce doubling as well which would be audible.