DIY Sub Kick

The concept of a sub kick is very simple, take a large speaker and use it in reverse as a microphone specifically for picking up low frequency information, from a kick drum for instance. This can be used in the mix to reinforce the sound of the kick alongside another kick drum mic,  providing additional depth to the sound due to it’s focus on the sub 100Hz frequency range. The subkick won’t pick up much spill from other parts of the kit either, and a good trick is to use it to trigger a gate on the internal kick drum mic, to get a very tight and clean kick sound.

Various companies make them, the  Yamaha SKRM100 for example, which is essentially a 6.5″ woofer mounted in a small drum shell, with mesh either side and a built in stand. The price, £350, quite a bit for speaker on a stand! Over the years I’ve seen various DIY versions in studios around the way including an NS10 woofer clamped into an old worktop vice as a base, all these incarnations functioned well, and cost significantly less than £350 to make. Time to get the tools out I thought.

This is an easy DIY project, it involves mounting a woofer speaker into a suitable frame (in this case a tambourine shell), and then a little soldering to attach an attenuator and a male XLR connector.

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First start with a speaker, I went for an 8″ Wharfedale woofer of EBAY (approx £18), you can use anything from 6″ up, though some say it doesn’t work as well with larger speakers. I’m not sure about that, the 8″ seems to work pretty well. Most important is the speakers frequency response, it should go down to about 20Hz to get all those sub bass frequencies.

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I thought a lot about how to mount it, I wanted something that would isolate it and look good, but not cost too much. The cheapest and most elegant solution I could think of was to use elastic hairbands to suspend the speaker within the circular frame of a tambourine (without the jingles of course). So I ordered a 10″ tambourine (£7 Ebay) and removed the jingles by pulling out the nails holding them in place.

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Slip the elastic hairbands through the screw holes in the speaker, then feed each end through one of the slots in the tambourine rim and push the upper loop (the one that goes over the rim) round and under so the 2 loop ends overlap. Take the nail that used to hold the jingles in place, push it back through it’s location hole so that it pegs the 2 loop ends of the elastic in place. Push all the way in so it’s secure. That was probably the trickiest step in all of this, required a lot of patience to get the elastic and the nail to all go in the right place. Repeat this for the remaining screw holes.

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The next challenge was figuring out how to mount the the subkick using a normal mic stand. I happened to have a broken mic stand lying around so I took the pivot mount from it (the bit that screws onto the top of the vertical part of the stand and allows the boom to attach to it and swivel up and down). The advantage of using this was that it had a standard screw thread on the end which meant I could attach it to a regular mic stand (as shown in the picture above). The pivot mount itself attached to the tambourine rim with a nut, bolt and a couple of washers (through one of the existing slots in the tambourine).

Next step is connecting it up to a mic pre-amp. The output of the subkick is pretty hot, an attenuator (or pad) is recommended to bring the signal level down to the region expected by most pre-amps. You can buy an inline attenuator that connects between the subkick and the XLR cable to the pre-amp, or you can knock together a basic potential divider circuit to do the job for you. I opted for the latter as you probably guessed. Another point worth mentioning here is that I’m going to use an unbalanced connection, providing the environment isn’t to (electrically) noisy and cable runs are short, this shouldn’t be an issue. If you wanted to go for a balanced connection, you would need to wire in an audio transformer, and to get one that has good sub-sonic frequency response isn’t going to be cheap. You could also use a DI box, again, a good quality one with good bass response would be preferable.

Circuit 1

The schematic for an attenuator circuit is shown above, I used a simple potential divider, the values I chose for the resistors R1 and R2 are:

R1=680 Ohm , R2 =150 Ohm

There are many combinations you could use and they also depend on your speaker, Google “attenuator for Subkick” if you want to get lost in that world!

 

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With the resistor values chosen, I soldered them directly to the speaker terminals and covered them with heat shrink. Easiest way I found was to solder one end of R2 to the speaker – terminal, and one end of R1 to the speaker + terminal, slide a sheath of heat shrink over each resistor then twist the exposed ends together, before applying heat to shrink the insulation (see above).

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I then soldered a short length of guitar cable to the speaker – terminal and the exposed resistor ends, ensuring I had a sleeve of heat shrink in place to insulate the connection.

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Finally I soldered the male XLR connector onto the end of the cable, (Pin 1 to Speaker -, Pin 3 to the resistors, Pin 2 unconnected). I had a retaining clip lying around so I used that to secure the connector to the frame, so as not to put too much mechanical load on the soldered joints.

So there you have it, a fully functioning subkick that doesn’t cost an arm and a leg, doesn’t look to shabby, and is not to difficult.

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Here is a quick audio example of the subkick in action. The audio is as follows

Bars 1-2 : Internal kick mic only

Bars 3-4 : Subkick only

Bars 5-6 : Internal mic + Subkick

Bars 7-8 : Internal mic + Subkick (with gate on subkick)

Bars 9-10 : Full kit, no subkick

Bars 11 – end : Full kit with Subkick

https://wijproductions.files.wordpress.com/2014/10/example-subkick.mp3

A location recording case study – The Duval Project

Here’s the first of 2 videos from this superb Bristol-based Nu soul / R&B outfit. Location recorded and mixed by Wij Productions.

This was an intense job, we had a small time window to make use of the venue during the day, 5 hours in all to get in, get setup (audio and video) and capture 2 tunes plus some string section overdubs.

Upon arrival, first thing to do was to assess the space and work out the best location for recording. As this was a simultaneous video shoot, the choice of location would have to be some compromise between the best visuals and sound.  The venue is a long vault, the acoustics could have been awful but there was enough treatment and choice of position to work with. We opted for the wooden floor in front of the stage, with the band arranged in a semi circle. The video guys set up a track to allow them to slide 1 stand mounted camera back and forth into the middle of the semicircle, with another hand held camera for alternative shots. In this kind of setup, there will always be a compromise between the best setup for acoustics and separation, and the best setup for visuals.

The band line up included keys, bass, drums, flugelhorn, 2nd keys, vocal and 3 string players (cello and 2 violins). I used a Universal Audio Apollo Duo and an MOTU 828 mk3 (as an ADAT slave to the Apollo) to capture the full set up, with Universal Audio Solo 610 external preamp to give me another mic channel. The band was mainly electric so I didnt need that many mic channels, just for the flugel horn (with an EV RE20), the drum kit (Audix overheads, RE20 on the kick, Audix D5 on snare, AKG 414 on the high hat) and the voice (Oktavamod Rode NT1a running through the UA 610 preamp). I put a couple of mics on the string trio but we decided to overdub them for the final audio as there was too much spill from the band. Everyone played live through their amps, and a foldback monitor was used for the vocalist. In the end we decided to overdub the vocal as there was a bit too much spill. Part way through the recordings I noticed someone had put the ventilation on, always one of the little things you have to look out for on location recordings in these kinds of places, only becomes apparent when you have a very quiet section (as 1 of the tunes here did).

The band we’re a joy to work with, slick, tight and super well rehearsed, they banged out 5 or 6 takes of each tune just like that, which is exactly what you want when time is tight. Once the video guys were happy that they had enough footage to work with, we quickly set up the mics for a more intimate recording of the strings. Acoustically they sounded absolutely gorgeous, the space served the sound very well. I used 4 mics, two Oktavamod NT1a’s as overheads, another facing the cello from behind and to the right, and a TBone ribbon mic in front of the cello. Some may argue that that is a slightly odd setup, but it gave me good results in the mix, I had been reading about how different acoustic instruments project different frequency ranges in different directions and I wanted to explore this.

Again, the string trio being seasoned pro’s laid down a few alternative takes of their parts and then we were done and dusted, just half an hour over schedule which was fine as it turns out.

The first thing to do when I’m back in the studio is back up the session, you never know! The vocalist came by another day and recorded a couple of perfect takes for each track (I say perfect as they synced up with the original vocal track word for word), then the mix began.

I used mainly Universal Audio plugins on this, the concept was to keep it warm and acoustic. Close micing and direct sound from the electric instruments gave me good control over the overall acoustic, I had to do some careful reverb and subtle edit tricks on the overdub vocal as there was some spill from the original vocal on the drum and trumpet mics, it worked out well though. I used a bit of SPL Transient Designer on the drums to help control the ambiance and shape the individual tones.  I was really pleased with the way the strings came out to, bussed them through the Fairchild compressor plugin to smooth them out and add some of that fabled valve and transformer warmth.

The final mix was mastered by Richie Blake (the bass player in the band) before being sent to the video guy for final integration into the finished product.