DIY microphone blimp and dead cat

High sensitivity microphones in the field need protection from both shocks and wind. After building my own shock mounts, I wanted better wind protection. A blimp and dead cat delivers good signal levels, fidelity and wind resistance.

Building a blimp

A microphone blimp (or zeppelin) looks like an airship. When covered with fur, it looks like a dead cat. The blimp creates a volume of still air around the microphone. Fur provides a better wind barrier than cloth because the fibres move and absorb wind energy.

I made my blimp from 83 mm diameter PVC plastic pipe and push-on PVC vented caps. These can be purchased from hardware and plumbing stores. Larger diameters and dead air space will better attenuate wind noise but larger, heavier blimps are increasingly difficult to handle. I have also used 55 mm diameter PVC for a smaller microphone, but installation of the mic into that narrow tube was more difficult.

Naked and partly assembled blimp with my Sennheiser ME66 microphone inside.

Naked and partly assembled blimp with my Sennheiser ME66 microphone inside.

I cut the PVC to length and drilled it nearly full of holes with a 16 mm diameter hole saw. Round hole saws are necessary, because large drill bits make a mess in thin plastic. I made a hole guide out of a thin steel sheet.

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Hole guide. The large holes are aligned with a row of holes on the PVC tube. The smaller holes guide pilot holes for the next row.

I used another hole saw to drill out the ends of the caps. I also sawed off the base of the caps, leaving about 10 mm to grip the tube. Cutting away more plastic makes the blimp lighter and the tube acoustically transparent. If you put the “unholy” tube to your ear, it sounds like a seashell. As more holes are drilled you will no longer hear any effect.

I left some plastic at the bottom of the tube for the grip. My pistol grip is secured with a wing nut (the bolt is threaded into the tube). I contact-glued some rubber (recycled bicyle inner tube) to the base to prevent slipping and squeaking. See my earlier shock mount post for a simpler, fixed pistol grip handle.

The microphone suspension is made from rubber bands. The bands pass through the tube and are secured with “H” pieces at both ends. I used a permanent marker to mark the tube where the rubber bands pass, for whenever they have to be replaced. The “H” pieces were cut from PVC tube. I contact-glued some rubber (recycled bicycle inner tube) to the inside of the “H” pieces to prevent slipping and squeaking. The microphone is inserted through the gaps between each rubber band, then the “H” pieces are lifted and rotated to twist the rubber bands and secure the microphone.

The microphone cable passes outside the rear cap. It is secured with two rubber bands to stop transmission of shocks through the cable. I have also slotted the pistol grip handle, so that the cable can be tucked away. Underneath the rear of the tube I have made a large hole where I can access the switch on my microphone.

The dead cat skin is made from fake fur that I purchased in a fabric shop. It has a single pile and a stretchy, open-weave backing material. Beware of denser furs, that can strongly attenuate the acoustic signal. It is easy to hand sew the dead cat by turning the fur inside out. Use a thread that contrasts with the fur. The fur will hide bad sewing.

Blimp with fur covering. The forward half is slipped over the blimp and the rear half has a zipper.

Blimp with fur covering. The forward half is slipped over the blimp and the rear half has a zipper.

My home-made blimp and dead cat is lightweight and cost about AUD$30 in materials. Commercial dead cats are heavier and often cost more than the microphone!

Model Length (cm) Diam. (mm) Mass (g) Cost Remarks
My dead cat 44 83 370 AUD 20
Rode blimp 49 125 550 AUD 225 Mass excludes fur.
Rycote Super-Shield 40 100 694 USD 359 Mass includes cable.
Sennheiser SEBS2 USD 926 No detailed specs.
Proaim BMP40R 40 USD 132 No detailed specs.
A comparison of blimps and dead cats that will fit a Sennheiser ME66 microphone. My home made blimp is the lightest and cheapest. The best price was selected from three sites: ebay, BHphotovideo USA, Video and VideoGuys Australia. Shipping costs are not included.

The (optional) cloth is made from leftover material from a light diffuser project. The material was light, stretchy and difficult to sew (this was the first time I’ve done machine sewing). Perhaps there are other acoustically transparent cloths that are easier to work with.

Blimp with cloth covering. It is secured with velcro (hook-and-loop) after stretching the material tight. This is a prototype and the sewing is a mess! An easier solution is to wrap the cloth around the blimp and secure it with rubber bands.

Blimp with cloth covering. It is secured with velcro (hook-and-loop) after stretching the material tight. This is a prototype and the sewing is a mess! An easier solution is to wrap the cloth around the blimp and secure it with rubber bands.

Blimp testing

For all tests, the naked mic is the reference response. A good wind protection system will have a frequency response and signal level close to the naked mic and much lower wind noise levels.

To compare frequency responses, I created broad spectrum noise by crumpling dry sheets of newspaper. The microphone was indoors (no wind), the distance to the source was fixed at about two metres (I didn’t write down the exact distance) and all recordings were made with a fixed manual gain. I made three recordings for each set-up and compared median spectra and third-quartile (Q3) frequencies. Q3 frequency is the frequency at 75% of the power spectrum.

The first graph compares frequency responses. Wind protection set-ups ordered from widest (best) to narrowest (worst) bandwidth are:

  1. Foam windscreen and microphone in shock mount. Q3 frequency = -258 Hz relative to naked mic.
  2. Cloth-covered blimp. Q3 frequency = -345 Hz.
  3. Fur-covered blimp (dead cat). Q3 frequency = -904 Hz.
  4. Fur over foam windscreen and microphone in shock mount. Q3 frequency = -1637 Hz.
Frequency response for different wind protection setups and dry newspaper sheets source. The spectra are aligned at 1–2 kHz to account for different signal levels. This comparison shows that fur coverings more strongly absorb higher frequencies (up to -1637 Hz reduced bandwidth). Measurements were made using Raven Pro 1.3 from 16 bit, 44.1 kHz recordings. The graph is zoomed to 0–11 kHz.

Frequency responses for different wind protection setups and dry newspaper sheets source. The spectra are aligned at 1–2 kHz to account for different signal levels. This comparison shows that fur coverings more strongly absorb higher frequencies. Measurements were made using Raven Pro 1.3 from 16 bit, 44.1 kHz recordings. The graph is zoomed to 0–11 kHz.

To compare signal levels I played back white noise through a small speaker. I made the white noise signal using Audacity 2.0.6. The frequency response spectra were rough, but signal levels were more repeatable than for the newspaper sheets. I compared mean levels averaged over about 60 seconds of playback.

The second graph compares signal levels. A difference of -3 dB corresponds to half the power. Wind protection set-ups ordered from strongest to weakest signal levels are:

  1. Foam windscreen and microphone in shock mount = -1 dB relative to naked mic.
  2. Cloth-covered blimp = -2 dB.
  3. Fur-covered blimp (dead cat) = -3 dB.
  4. Fur over foam windscreen and microphone in shock mount = -4 dB.
Signal levels for white noise source and different wind protection setups. The fur over foam windscreen gave a substantially weaker signal. Measurements were made using Raven Pro 1.3 from 16 bit, 44.1 kHz recordings.

Signal levels for white noise source and different wind protection setups. The fur over foam windscreen gave a substantially weaker signal. Measurements were made using Raven Pro 1.3 from 16 bit, 44.1 kHz recordings.

To compare wind noise levels, I simulated wind using a pedestal fan. I compared mean levels averaged over about 60 seconds of wind noise.

The third graph compares wind noise levels. Wind protection set-ups ordered from weakest wind noise level (best) to strongest (worst) are:

  1. Fur-covered blimp (dead cat) = -25 dB relative to naked mic.
  2. Cloth-covered blimp = -20 dB.
  3. Fur over foam windscreen and microphone in shock mount = -20 dB.
  4. Foam windscreen and microphone in shock mount = -6 dB.
Wind noise waveforms for fan source and different wind protection set-ups. This comparison  shows very poor wind protection from the foam windshield. Waveforms from Audactiy 2.0.6.

Wind noise waveforms for fan source and different wind protection set-ups. This comparison shows very poor wind protection from this foam windshield. Waveforms from Audactiy 2.0.6.

The final graph compares signal-to-noise amplitude ratios from the above two tests. Wind protection set-ups ordered from highest (best) to lowest (worst) are:

  1. Fur-covered blimp (dead cat).
  2. Cloth-covered blimp.
  3. Fur over foam windscreen and microphone in shock mount.
  4. Foam windscreen and microphone in shock mount.
Signal-to-noise ratios for different wind protection set set-ups and the experimental conditions in the preceding two graphs. The fur over foam system performed surprisingly well, however the Q3 frequency was substantially lower than for the cloth-covered blimp (see the first graph).

Signal-to-noise ratios for different wind protection set set-ups and the conditions in the preceding two graphs. The fur over foam system performed surprisingly well, however the Q3 frequency was substantially lower than for the cloth-covered blimp (see the frequency response spectra).

Blimp is best

These tests illustrate the trade-off between signal strength and fidelity versus wind noise reduction. The light foam windshield is best for indoors, but hopeless for wind. The cloth-covered blimp is best for “light breezes”. The fur-covered blimp is best for “strong wind”. For high fidelity recording, I suggest to have all three wind protection systems in the field bag and to select the one appropriate to the conditions.

I always see professionals using the dead cat outdoors. For news recording and like, there is no second chance. For nature recording, we choose to avoid windy conditions and I would recommend lighter wind protection (i.e. cloth-covered blimp) for higher signal levels and wider bandwidth.

I will not use the fur over foam system because the signal level and bandwidth were lower than for other set-ups. Some manufacturers claim that their expensive fur is acoustically transparent. I invite them to send me a sample product (to fit a Sennheiser ME66) so that I can test it myself.

Disadvantages for the blimp/dead cat are the bulkier size and slower microphone installation. Installing the microphone actually only takes a couple of minutes because I leave the rubber bands on the blimp.

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