You can’t.

It’s almost impossible for the average person to soundproof a dog crate against low-frequency noises like thunder, or even against most higher frequency noises. Here’s why.

• Soundproofing is bulky, so you need lots of space. You essentially need to build a room around the crate. A room with walls thicker than the exterior walls of your house.
• The necessary materials are specialized, expensive, and heavy.
• You need to be willing to give up the portability of the crate.
• And even if you can do all this, you can’t soundproof it against low frequencies (e.g. thunder, fireworks displays). And this is generally the reason why people try to do it in the first place.

For even more information, check out my webinar, Sound Decisions, which goes into these matters in more detail.

If you take my word for it that you can’t soundproof a dog crate, nor can you currently buy a crate that is soundproof, skip to Section 7 about sound masking for some practical help. Otherwise, read on for the information that every acoustician and civil engineer will tell you.

How Sound Travels

The transmission of noise into a room [space] is aided by the multitude of paths sound can find to penetrate the architect’s defenses. The most prominent paths are (1) airborne noise outside the room that sets the common wall into vibration, which in turn radiates sound into the rooms, and (2) noise originating in the vibration of a solid structure that propagates along the structure and sets surfaces in the room into vibration. If the above paths are efficiently blocked by properly designed partitions and resilient mountings, then flanking paths can become important. Some flanking paths are obvious, such as the propagation through a false ceiling or crawl space and window-to-window transmission. Others are more insidious, such as porous cement block, poor seals between walls and ceiling or floor, gaps around wall penetrations, and back-to-back electrical outlets.

Kinsler et al, 1999, p. 379

In other words, sound gets into enclosures like houses, rooms, and crates in all sorts of ways.

So imagine your dog crate sitting in the middle of a room. Maybe it’s wire or plastic. It even could be wood, although that may not be any better, since wood transmits sound from the outside of the crate to the inside very well. What would it take to block all those paths into the crate? (Don’t forget the floor and the door!)

How Soundproofing Works

To soundproof a space, you need to use a combination of specialty materials, which are very dense and expensive. You need to disconnect that space from all other structures because sound can travel straight from exterior walls and the floor through to the interior via the building materials. These materials must be decoupled to break up the paths. That can mean, for instance, a double-stud or staggered stud wall setup. Normal walls, even with insulation in the air pockets, transmit sound very well. At lower frequencies, those air pockets can even become resonating boxes.

If attempting to soundproof a crate with barrier methods, you would need to isolate the walls and roof of the crate, for example, by building another structure around it. You would also need to decouple the crate and structure from the floor. The barriers would have to be heavy and vastly larger than the crate itself. For instance, a concrete bunker such as this World War II bunker from Hirtshals Beach in Denmark would not be sufficient to prevent the sound of thunder from penetrating. Engineers compute the permeability of materials with regard to sound and publish ratings. A wall of solid, densest available, 8-inch concrete blocks would have a Sound Transmission Class (how soundproofing is rated) of 57 (National Concrete Masonry Association, 2012).

Sound transmission class, or STC, provides a single-number specification of the acoustic isolation characteristics of a particular soundproofing material.

Kinsler et al, 1999, p. 380

The higher the STC, the better the soundproofing. The rating of 57 for the concrete blocks would be decent, except for the fact that the ratings don’t apply to frequencies under 125 Hz, which is smack in the middle of the frequency range of thunder. Even this bunker, with its thicker walls, would not keep out the sound of thunder. Not to mention that enclosures for living things need doors.

The highly regarded Soundproofing Company has illustrations of some typical wall soundproofing solutions. Again, even these professionally designed installations are unlikely to be effective in the low-frequency range of thunder.

Demonstration of the Failure of Absorptive Materials To Soundproof a Crate

This article on soundproofing from the Los Angeles Film School clears up some misconceptions about soundproofing. Acoustic foam, such as that shown in the photo, is not designed to prevent the transmission of sound. It is used to adjust room acoustics.

But we really want to believe that foam and blankets can protect us from sound. So I ran a home experiment to see whether covering a crate with a couple of bedspreads (a common recommendation) could prevent low-frequency noise from entering a crate in even the smallest amount. (Spoiler: no.)

I used a Sony Bluetooth XB speaker with 20 Hz–20,000 Hz bandwidth to generate brown noise from an iPhone app called White Noise. I chose brown noise because it has more low frequencies than white or pink noise. I placed the speaker approximately 2 feet from the back corner of the crate and 5 feet from the microphone placement at the front of the crate.

I used an iPad Air 2 with Studio Six Audio Tools to record and analyze the sound inside the crate. I used the Fast Fourier Transform tool to capture peak values.

This plot shows frequencies on the x-axis going across the bottom. Like a piano keyboard: the low frequencies are on the left (and have low numbers) and the high frequencies are on the right. (K stands for 1,000, so the highest number is 16,000.) Frequencies are measured in cycles per second or Hertz.

The y-axis shows sound pressure level (not technically the same as loudness or volume but we’ll informally use those terms) in decibels. But the trick is that the software I used to analyze the sound in real time computes the volume at each frequency area separately. I juxtaposed the graphs for the crate uncovered and covered. The blue line is the uncovered crate and the red line is the covered crate. You can see that there is no significant difference between the sound in the crate when covered or uncovered from the lowest frequencies to somewhere between 1,000 and 2,000 Hz. Since there is a random element to brown noise, and I made the plots at two different times, the agreement between the two lines is remarkable. It tells us that covering the crate with two bedspreads did nothing to prevent the low-frequency sound from entering.

Somewhere between 1,000 and 2,000 Hz, the lines start to separate. This is exactly what the physics of sound predicts, because the higher frequency waves are smaller and more easily absorbed (more on that in the next section). But the maximum difference of 7 dB at about 5,000 Hz is not enough to make a significant difference. The inside of the crate will not be free of higher frequency sounds. Some of these sounds will be absorbed by the bedspreads. But they will still be perfectly audible inside the crate.

Covering a crate with absorptive materials can accomplish something, though. It dampens some higher frequencies inside the crate. Some people find that to be a “cozy” feeling. Maybe dogs do, too. There are several reasons a dog might like a covered crate. Protection from the sound of thunder is not one of them.

Why Low Frequencies Can’t Be Well Controlled

Sound waves vary in size according to frequency. High-frequency waves like hummingbird song are tiny, fractions of an inch long. But low-frequency waves are huge.

Sound waves are pressure waves, and they pass through gasses, liquids, and solids. They are longitudinal waves, which means the oscillation is in the same direction of the propagation of the wave. But they are conventionally drawn as transverse waves, because longitudinal waves are hard to visualize and draw.

The diagram shows one wavelength of a 60 Hz wave. This low-frequency wave is 18 feet long. And drawn to scale, the red line represents a two-inch wide wall of a crate. That crate wall is much too small to have any soundproofing effect. In acoustics, we would say that such a wall would be “invisible” to the large low-frequency wave.

This is the problem with low-frequency waves. They are too large to be absorbed or blocked using barrier methods (Elliot & Nelson, 1993).

Crates on the Market

I am not going to link to the crates that market themselves as protecting dogs from thunder, because they make very misleading claims. Some have some good characteristics. One has a sealing thermoplastic door. Another is decoupled from the floor (but unprotected from noise traveling through the air). But no “protective” crate addresses the issue of low frequencies. It is physically impossible for them to protect your dog from low-frequency sounds. Yet that is the focus of their marketing claims.

Active noise control was originally used for dampening low-frequency sounds and is the only noise control solution for these frequencies that doesn’t depend on bulky materials (Elliot & Nelson, 1993). Ford Motor Company has put out a prototype of a dog crate that incorporates active noise control technology. If they do a good job on this, it could work. It would have to be more sophisticated than most noise-canceling headphones, and probably incorporate feedforward rather than feedback technology. (Feedforward systems are fascinating, and in acoustics they depend on the fact that electrical signals travel faster than sound. Check out my thesis on active sound cancellation for an explanation.)

There is now a company making noise-cancelling headphones for dogs, but they provide insufficient evidence that the headphones work as claimed. Here is my review of them.

If You Really Want to Give It a Go—Nope, Sorry

OK, I tried. I wanted something I could recommend. I thought about whether it would be worth it to cover a blanketed crate with a sheet of mass loaded vinyl to pick up a few decibels of protection. But that stuff isn’t designed for household use and probably not safe for chewing puppies (some products are controlled and have health warnings attached). Plus it’s heavy, probably smells, and would make the crate hot inside.

I consulted an engineer who manufactures a unique low-frequency sound absorber and designs room acoustic treatments. His units cost more than $1,000. But I definitely know people who would spend that to help their dogs. He said, essentially, that there were too many variables to be able to recommend his product across the board. And that depending on the room, a unit might end up weighing more than 1,000 pounds. I was offering a holy grail of sorts: a free link that might attract him some customers. And he didn’t even nibble.

It was great to run across an informed, ethical person who wouldn’t even consider making tenuous promises. I’m not going to link to his business here since he convinced me it just wasn’t relevant enough. But if anyone wants to talk to the right person to custom-design a home sound barrier (or a recording studio or home theater), drop me a line and I’ll put you in touch.

Sound Masking: A Better Solution

Currently, the best acoustical help we have for dogs who are afraid of thunder and low-frequency fireworks is sound masking. For some basic information, you can check out my sound masking post. You can learn more about masking, including hearing some recorded examples, by purchasing the recording of my lecture, Sound Decisions, at The Science Dog.

Conclusion

It is heartbreaking to care for a dog who panics at certain sounds. We desperately want to help them. It is no wonder to me that people buy all sorts of products that promise to “cure” sound phobia or sound reactivity.

Go ahead and cover the crate if it helps to limit visual stimuli or makes your dog feel cozy. But know that you can’t keep the thunder out that way. The high-priced crates that claim to do so can’t either. Save your money for something that will help!

The best way to help your dog is to see a veterinary behaviorist, a veterinarian who is knowledgeable in behavior, and/or a credentialed dog behavior consultant. Desensitization and counterconditioning, often with meds on board, is what the experts recommend to treat this condition. And sound masking or taking the dog away from the source of the sound entirely are the best management techniques from a physics standpoint.

Copyright 2019 Eileen Anderson

References

Elliott, S. J., & Nelson, P. A. (1993). Active noise control. IEEE signal processing magazine, 10(4), 12-35. Available at https://www.researchgate.net/profile/Philip_Nelson7/publication/3321160_Active_Noise_Control_IEEE_Signal_Process_Mag_October/links/53d2613a0cf2a7fbb2e998ff/Active-Noise-Control-IEEE-Signal-Process-Mag-October.pdf

Kinsler, L. E., Frey, A. R., Coppens, A. B., & Sanders, J. V. (1999). Fundamentals of acoustics. Fundamentals of Acoustics, 4th Edition, by Lawrence E. Kinsler, Austin R. Frey, Alan B. Coppens, James V. Sanders, pp. 560. ISBN 0-471-84789-5. Wiley-VCH, December 1999., 560.

National Concrete Masonry Association. (2012) Sound Transmission Class Ratings for Concrete Masonry Walls. TEK13 1-C. Retrieved from: http://www.ncma-br.org/pdfs/5/TEK%2013-01C.pdf

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Photo credits: WW II bunker from Wikipedia Commons taken by Tomasz Sienicki and used according to this license. Acoustic foam courtesy of CanStock photo. All other images copyright Eileen Anderson.