CAD Audio

A Poor Man’s Vocal Booth?

by Paul Strikwerda in Articles, Studio 13 Comments

Sometimes I come across a certain product and wonder:

It looks promising, but is it any good?

The CAD Audio Acousti-Shield 32 is one of those things.

Designed to “substantially reduce unwanted reflections, echo flutter and environmental unwanted acoustic interference,” does it deliver as promised?

At about $85, could it be the poor man’s vocal booth, or is it a waste of space, and money?


Before I tell you what I think, let’s briefly discuss the whole concept of soundproofing and room treatment. As I wrote in my booklet Building a Vocal Booth on a Budget:

“In this noisy world, soundproofing has become big business. I just Googled the word and got almost two million results. Buyer beware, because the same search will take you into the realm of grotesque claims and pseudo-scientific truths:

“These Soundproof windows will totally eliminate your noise problems.”

“This soundproof foam absorbs up to 66% of sound waves.”

“Our soundproof curtains offer the highest STC performance.”

Do the makers of these products assume we’re that stupid? Think about it for a moment. What does “soundproof” really mean? Most dictionaries describe it as:

impervious to, or not penetrable by sound

Going by the aforementioned claims one could argue that the minds of the makers of these products seem impervious to, or not penetrable by logic. Then again, advertising is all about making noise and not about offering sound proof.”

Gluing some acoustic panels to your wall or on to a “shield” will do nothing to block outside noise from coming in. Auralex foam and its many clones will change the characteristic of the sound inside your recording space, diminishing reflection and reverberation. It absorbs the sound but it does not reduce it.

Yet, CAD claims that their shield can substantially reduce “environmental unwanted acoustic interference.” What does that mean? Would this shield be able to diminish ambient noise? Why not find out? For the test, I purposely chose one of the worst acoustic locations in my house: my basement.


Let’s say you want to use your laptop for a quick recording and you place your microphone in the same room. Before you know it, the computer fan kicks in and starts making noise. Could CAD’s Acousti-Shield magically neutralize the noise? 

I’ll let you listen to the same script twice. You might want to put your headphones on. First you’ll hear my voice without the shield in place. The second time I read the script, the Acousti-Shield cradles the microphone. Just notice if this device is able to get rid of the noise the laptop fan makes.


That’s pretty clear, isn’t it? It confirmed my suspicion. The shield does very little to keep unwanted noise out of the recording. As expected, this thing is no substitute for a properly isolated room. But will it deliver on the second promise? Could it make a room sound more dry? 

Before I play the second soundbite, you should know that I recorded the audio with an AKG C 3000 B microphone, plugged into a Grace Design m101 preamplifier. The 16 bit, 48,000 Hz WAVE recording was converted to MP3 format for this blog.

For the next track I removed the laptop from the room. Once again, you’ll first hear me without the shield. Then I’ll read the same text with the Acousti-Shield 32 in place.


Did you hear a significant difference? A difference worth over one hundred dollars? To be honest with you, I was disappointed. The room didn’t sound dry to me at all. How could a company with such a good reputation bring such a poor product to market? It just didn’t make sense.


The next day I woke up with an idea. What if the product wasn’t the problem? Perhaps I was not using it properly.

I went on a few online forums to find out what others thought of the Acousti-Shield, and I found my answer. The recordings you just heard were made at 9 inches from the microphone. What would happen if I would come closer? 

Once again you’ll hear me read the script twice. First I’ll read it at 5 inches from the mic. Then I’ll add the shield, and keep the same distance.


Now, this is more like it! Distance makes a huge difference.

Thanks to a clever design, you can also move the microphone closer or further away from the 53mm high density micro cell foam. This obviously changes the acoustic result.

The question remains, would I recommend using such a shield for voice-over recordings? Let’s first look at the positives.


The Acousti-Shield 32 is well-made and easy to assemble. For its size it is very light, and unless you have a  cheap mic stand on which to mount it, it won’t tip over. Compared to a product like Harlan Hogan’s Porta-Booth Plus ($189), it is affordable. As long as you stay close to the mic, it manages to tame unwanted reflections.

Here’s what I like less. CAD’s Acousti-Shield is not a unique product. sE Electronics was one of the first companies to come out with such a solution. They called it the Reflexion Filter X. Although I haven’t tested it, it looks very similar.

Unlike Harlan’s porta-booths, the CAD shield isn’t very compact. It’s meant for the studio, not for the road. Even though the shield accommodates a variety of microphones, a popular voice-over shotgun such as the Sennheiser MKH 416 does not fit.

Here’s the big one: where to put the voice-over script? 

I’m usually reading my copy from the monitor in front of me. The CAD shield would block my field of vision. Even if I were to read it from a tablet or smart phone, there is no place to put them as long as the shield is mounted on a mic stand.

In the end I came up with a simple solution. I put the shield on a flat surface that was resting on an old loudspeaker stand. With the microphone on a table stand, there was room for my Nook or iPhone. 


So, is this shield a good investment?

In the end it’s all about expectations. If you get the Acousti-Shield 32 because you need a portable studio, you’re not going to be happy. If you need something to keep ambient noise out of your recordings, this is useless. 

However, if you cannot acoustically treat the room you’re in, and you’d like your recordings to sound more dry, this is an affordable solution, as long as you know how to use it. 

Paul Strikwerda ©nethervoice

PS CAD Audio kindly donated an evaluation model to the author of this blog. Though very much appreciated, this did not influence his opinion.

PS Read more on taming unwanted reflections in “Get the boom out of the room.”

Can CAD’s Cool Colored Cans Cope with VO?

by Paul Strikwerda in Articles, Gear, Studio 11 Comments

Over the years, people have commented that I have a good head on my shoulders, and they’re right. In fact, I’m rather bigheaded.

I’m also blessed with sizable ears that turn bright red when it’s hot or cold outside. And because they continue to grow as I age, there will come a time that I’ll be all ears. When that happens, I shall probably take up sailing.

My big head never really bothered me until I had to select a pair of headphones for my voice-over work. When I’m recording I prefer not to wear them (it takes me out of the moment), but when I’m doing detailed editing, I use them for hours in a row.


Searching for the perfect cans was quite an education. Just as with microphones, not everybody has the facts, but most people have an opinion:

“You must buy the Beyerdynamic DT770. They’re great.”

“Get the Sony MDR7506. Everybody in the business is using them.”

“The Sennheiser HD-280 PRO is the industry standard.”

I’m always interested in what others have to say, but I also know that what works for one person, doesn’t necessarily work for me. Part of that has to do with our individual anatomy.

All ears hear differently, and you and I may have different tastes of what sounds good. If you love listening to classical music, you probably want headphones designed for audiophiles. I needed cans that would allow me to accurately pick up breaths, mouth noises and other unwanted sounds. I wasn’t going to use them to listen to the Berliner Philharmoniker or to mix the latest Rap album. I wasn’t even going to listen in stereo!


When comparing headphones, you’ll find that many brands display a total lack of modesty. They describe their products as “world-class,” “revolutionary” and “exceptionally accurate.” While much of this lingo is just marketing hype, there are a few terms that come back again and again. Let’s take a quick look at them.

Open versus Closed

Open Headphones are designed to allow some outside noise to come in. Closed or sealed headphones isolate your ears from ambient noise. Open headphones tend to be lighter; they put less pressure on the ears, so they’re usually more comfortable. They also produce a more “open” sound, a bit more like your studio monitors. 

Closed headphones produce a more “inside the head” sound, and they’re often used in music production where critical listening is vital and outside noise should stay out of the mix.

If I were to were to use my headphones to listen to music on the train, the bus or in bed, I’d go for closed ones, so as not to bother other people. In my studio, that’s not an issue. Because I work in a very quiet environment, isolation from ambient noise is not so important either. Comfort, on the other hand, is.

My favorite pair of cans share a feature with my mind: they’re semi-open.

Frequency Response

Sound is measured in terms of frequency. Frequency response refers to the range of bass, mids and treble (highs). Let’s say the range of a pair of headphones is 15 to 25,000 Hz. What does that tell you? Well, the first number represents the bass end of the spectrum and the second number the treble end. One of the headphones I was looking at, had a range of 15 to 25 kHz. Is that any good?

Sennheiser HD280 Pro, Beyerdynamic DT770, Sony MDR-7506 & AKG K240 MK II

The audible frequency range for human beings is about 20 Hz to 20,000 Hz. Below 20 Hz, the bass frequencies are more felt than heard, but loudspeakers are much better at delivering that punch. Frequencies over 20 kHz aren’t always audible.

Because of the limitations of the human ear, a wider frequency range doesn’t necessarily lead to better sound quality. So, don’t be fooled by the numbers.

With some headphones and loudspeakers, certain frequencies are exaggerated and others are attenuated (reduced). Because headphones don’t give you the physical oomph that sound waves from a room speaker have, some makers of headphones overcompensate and build in a hyped bass response.

When listening to your voice track on these types of cans, it sounds like you’ve recorded too closely to the microphone (proximity effect). The flatter the audio response, the more accurately it reproduces the sound from the input source. Those headphones are best suitable for voice-overs.


The impedance of a headphone (measured in Ohms) refers to the headphones’ ability to resist electricity. Here’s what you should know: The lower the impedance of the headphone, the easier it is to get higher volume. Higher impedance doesn’t necessarily mean higher quality.

The higher the impedance, the more power your headphones will require. If you’d plug a high impedance headphone (e.g. 600 Ohms) into an iPhone or MP3 player, you’d definitely notice a loss in quality because the drivers can’t handle it. That’s why those models usually need an amplifier to drive the speakers inside the headphones.

Some manufacturers make different impedances for the same model (the Beyerdynamic DT880 comes in three ratings: 32 Ohms, 250 Ohms, and 600 Ohms), so be sure to look at the specs before you place your order.


Another factor influencing the loudness of the headphones is the sensitivity. Impedance determines how much power the headphones will draw, while sensitivity indicates how much of the electrical signal delivered to the headphones is converted into sound. This is measured in decibels of Sound Pressure Level per milliwatt, or dB SPL/mW.

Headphones of a higher sensitivity (and with high impedance) will sound louder than those of lower sensitivity. Be aware that the human ear may experience hearing loss if sound is sustained above 85 dB. So, if your cans are more sensitive than that, be extra careful.

Comfort and Fit

Even the best studio headphones would be pretty useless if they don’t fit right. When it comes to fit, manufacturers use fancy words to describe the two main types of studio cans:

Supra-aural headphones like the Koss porta pro, rest against the outer ear. The ear pieces can be flat pads against the ear, but can also be shallow bowl-shaped, or deeper ear cups that are too small to completely surround the ear.

Koss porta pro supra-aural headphones

Circumaural headphones like the Sony MDRXB700, have ear pads that completely surround the ear, and ear cups that completely enclose the ear.

Professional audio reviewers recommend wearing headphones for at least fifteen minutes when you test them for comfort. I’m not sure I agree. If they’re not comfortable, I can tell within seconds. Keeping them on for an extra ten minutes is not going to change that.

This is what you should ask yourself: Do the earpads exert too much pressure on the ears? Can the headband be easily adjusted? Remember that headphones that enclose or cover your ears can get uncomfortably hot. To find out, you do have to wear them for a while.

Sony MDRXB700 circumaural headphones

There’s one other thing I pay attention to: the cord. I happen to hate coiled cords. They tend to be heavier and there’s always something that gets caught in them. I also prefer the cord to be detachable from the headset, in case I need to replace it. Every studio engineer I know has messed up some cords by rolling over them with their chair. Cheaper headphones usually don’t come with a detachable cable.


You probably remember that I’m a big fan of the CAD Audio E100S microphone. Voice-over colleagues are finally catching on to this amazing, affordable mic. This American company has a lot more to offer, though. CAD recently came out with the Sessions” MH510 studio headphones, and asked me to give them a try. Would these be just as good as the E100S?

Before I share my impressions with you, you should know that I’ll judge them based on my needs as a (bigheaded) voice-over artist only. Secondly, I’ll compare them to the reasonably priced cans I have used for the past three years: the AKG K240 Studio headphones that are quite popular in my field. You can buy both the CAD and the AKG for around $99.

First off: this CAD offers more than cans. The MH510 headphones are a fashion statement. It comes in few colors: red/white, black/orange, black/chrome and pure black. Each pair of headphones comes with two detachable cables (coiled and straight) and two sets of earpads (leatherette & velveteen), as well as an 1/4″ adapter and a carrying bag.

Compared to the light-framed, self-adjustable AKG K240, the MH501 is rather bulky. There’s a lot of rubberized plastic and the leather headband is thick and cushy. The AKG weighs 8 ¼ ounces (235 g) and the CAD comes in at 11 ¼ oz. (320 g). During longer sessions, the weight of the CAD began to bother me.

AKG K240 Studio & CAD MH510

With the MH510, CAD wanted to make isolating headphones that “virtually eliminated bleed into the playback environment.” In order to do that, the earpads firmly push against the ears. CAD has reached its objective because these headphones isolate really well. However, the price you pay is comfort. My ears did not enjoy the sustained pressure. The K240 Studio headphones, on the other hand, fitted like a glove. The semi-open design offers less isolation, but there’s also much less pressure to keep the earpads in place.


And what about the sound? Would CAD’s Sessions headphones be suitable for the simple, subtle sound of voice-over?

The AKG has an impedance of 55 Ohms and a sensitivity of 91 dB. The CAD has an impedance of 26 Ohms and a sensitivity of 103 dB. Remembering what I wrote above, this should tell you that the CAD cans are definitely louder. You don’t need to turn the volume up that much, in order to get a solid sound. CAD calls the sound pressure level “rivaling a concert experience.”

If you’d like to relive your experience at a Tiësto dance party, perhaps that’s exactly what you’re looking for in a pair of headphones. As a voice talent, I want detail. Not volume. Besides, volume can be dangerous! It can lead to hearing loss.

In terms of frequency response, the MH510 can be characterized by what CAD calls “extended lows”. One Amazon-reviewer described the bass as “intense”. I wouldn’t go that far, but the low is definitely overemphasized. For certain types of music this might be just what the doctor ordered, but not for voice-over. To me, the extended lows just made my voice recordings sound muddy.

In contrast, the K240 Studio headphones are open, airy, natural and neutral. The spoken word has a realistic, uncolored clarity to it. The best way to illustrate this is by sharing an audio sample with you.

I placed my microphone in between the earpads of both headphones, and I played one of my voice-over tracks. Of course a condenser microphone can never replace the human ear, but this will give you some idea of the difference in sound coming from both headphones. You’ll notice that I alternate between the AKG and the CAD. The K240 Studio headphones are the first ones you’ll hear.



What I’ve done in this review is unfair and unscientific. Yes, both the CAD MH510 and the AKG K240 are sold as studio headphones, but comparing one to the other is a bit like comparing heavy-duty hiking boots to running shoes. Both are footwear but made for a different purpose. It might have been better to compare the K240 to CAD’s MH310 cans, which look remarkably similar.

I don’t think CAD had voice-over applications in mind when they designed the MH510. That’s where the AKG shines.

The CAD is more geared toward tracking, mixing and mastering of pop music in a recording studio. If you don’t want to have a scratch-track/click bleed through, the closed CAD is the better choice.

Secondly, reading reviews can tell you a lot about the personal preferences of the author, preferences which you don’t necessarily have to share.

And then there’s the size of my head. We must take that into account. 

It’s only fitting…

Paul Strikwerda ©nethervoice

PS CAD Audio kindly sent me a pair of MH510’s for evaluation purposes.

PPS Interested in headphone reviews? Here are a few websites I researched as I was writing this article: