By: Ken Humphreys

Speaker Engineer

After a sound wave reaches your eardrum, the real magic begins. When you’re aware of a sound, your ear and brain are working together on the difficult task of selecting which sound to pay attention to, what might be making it, where it’s located and much more. Here are a few of the important “processing” jobs you routinely but unconsciously accomplish:

Determining Loudness

You can hear a sound at 0 dB (but just barely) yet handle sounds with a trillion times the energy at 120 dB! The price you pay to be able pull off this remarkable feat is that you’re fairly insensitive to changes in sound energy levels. For example, a speaker receiving 100 watts of energy will sound only four times as loud as when it’s receiving 1 watt. One side-effect of this phenomenon is that you don’t need to concern yourself with amplifier power nearly as much as you might think. 70 watts—100 watts—what’s the difference? Only about 1½ dB. Not much, right?

This graph shows the sound intensity range that you’re able to make sense of. Each 10dB increase represents 10 times the energy, but only twice the loudness.

Another neat loudness related trick your ear performs is that it becomes increasingly sensitive to bass when the sound is loud and sensitive to the midrange when everything quiets down. The “loudness” button on your receiver is designed to compensate for this by boosting the bass at lower listening levels. This context-sensitivity was probably quite useful for cavemen by allowing them to derive useful bass information when encountering stampeding wooly mammoths — yet be able to tune into the slight rustle of a skulking saber-toothed tiger. Dinner is served!

Locating sound

When you hear a sound, you can immediately turn your head and face it. You probably take this for granted, but you might not if you knew the number of hard-to-believe calculations your brain just performed. Scientists are discovering that you construct a spatial model in your brain that updates constantly and uses sound as well as sight. Yes, very similar to bats.

To locate sounds in this model you constantly gather information from a variety of sources:

What kind of space are you in? When you hear a sound it has a “signature” that is unique. It arrives at your ear and gets “fingerprinted,” and a few milliseconds later a family of other sounds that bear the same signature arrive in the form of reflections. First, they are associated with the first arrival that created the signature so that the cacophony of other sounds around you can be ignored. Then, by calculating the direction of these delayed arrivals, how long they were delayed and the way that their signature has been “smeared” (whew!) you are able to tell a lot about what kind of environment you are in. For example, you may now know that you are in a small room with large, hard surfaces. In order to do this you had to determine the directions of the original sound and the way it echoed around the room. This was not simply done. Your brain just took into consideration at least three different kinds of information to calculate the direction. First, one ear heard the sound as louder simply because your head created a “sound shadow” and blocked the sound to the ear furthest away. Secondly, the part of your ear that sticks out from your head modified the sound in ways that clue you in regarding the direction the sound came from. And lastly, your brain calculated the phase thing: How much was the delay between the wave arriving at the left ear versus the right ear? Your brain then unconsciously applies this formula to what you just experienced.

And you thought you were bad at math! Your brain is a whiz.

For speaker designers, some of the important points are:

1. For familiar sounds, you are very sensitive to “tonal balance,” that is, are the treble, bass and midrange parts in the right proportion to one another? If a speaker’s frequency response graph is “flat”, that tells you that it’s reproducing the sound with the right balance (at least for the position of the measuring microphone). This has been shown to be the most important thing perceived as “accuracy” in the entire audio system.
2. How much of a time-delay does there need to be for an arriving sound to be identified as a reflection rather than part of the original sound’s signature? Jury’s out on this one, but if the “delayed arrival” is soon enough, say from reflections off of the grill frame or speakers that aren’t mounted flush, it is heard as part of the signature and you will hear it as a distortion to the tonal balance.
3. Your brain mostly ignores reflected signals when evaluating the balance of sound. Bass reflections get treated a little differently.
4. You cannot locate bass sounds unless you correctly associate a bass note’s overtones and then locate them in space. This allows for speakers that specialize in low bass—subwoofers—to be placed away from the main speakers and successfully fool you into believing that the bass is coming from the small speakers that reproduce the overtones.
5. Here is a neat little experiment you can try at home: Put your amp in “mono’ mode and notice that if you are just slightly off-center, the sound will appear to be coming completely from the speaker closest to you. This is because your brain is a detective, and the sound coming from this speaker gets “fingerprinted”, identified as the first arrival of sound and then used as the sole source of information as to the sound’s location. You are still hearing the other speaker, (try unplugging it) your brain just isn’t using it for location information.

In Conclusion

The study of how the brain processes sound – psychoacoustics — is a huge and very interesting body of information. If you’d like to read more, there’s a lot to dig into. You may want to bring a good shovel and start at this wikipedia article. Have fun exploring science!

Calibrating your home theater system is critical to an awesome home entertainment center, and only takes about 10 minutes to accomplish. The SPL meter measures the level of sound coming out of your speakers and it will help you fine-tune your system for the best possible sound.

To start, you’ll need to turn on your receiver and have the receiver’s remote handy. Now grab your Sound Pressure Level (SPL) meter and take a seat in your favorite chair.  It’s time to calibrate!

System Setup

1. Are your speakers placed where they will live for years to come?  If not, please check out our Aperion University course on Multi-channel Speaker Placement or make sure they’re in their final positions.
2. Verify that the speaker wiring is correctly attached, that positive is connected to positive and that negative is connected to negative.  If they’re wired incorrectly, the sound will be diffuse and hard to locate.  So be sure everything is wired up properly before you start calibrating.
3. Verify that your receiver has been configured properly.
   • Speaker distance to the listening area is set to the correct distance.
   • That the “Speaker Size” is correctly selected in the menu.
   • If your receiver has a selectable crossover setting for your subwoofer, verify that is its set to manufacturer’s recommendation.

Testing with the Aperion SPL Meter

1. SPL Meter Setup: Remove the SPL meter from the box and pull the clear plastic battery protector from the slot on the right side. Turn the switch to the “BATT” position to ensure the meter is working properly. Next, switch the weighting to “C” and the response to “slow”. For most receivers, you will set the volume dial to 70 but if your receiver’s test tone is loud enough to “peg the meter,” set it to 80.
2. SPL Meter Placement: Your SPL meter’s built-in microphone works best when it is pointed directly at the sound source and it should be placed as close as possible to where the primary listener’s ears will be. It’s best to use a tripod for placing the meter but if you don’t have a tripod, you can use other household items like a stepladder. Be sure the front of the meter extends a few inches beyond the support because you don’t want the microphone near anything that will reflect or absorb the sound.Stand off to the side of the SPL meter when making sound measurements. Because YOU absorb sound, standing behind the meter can produce an error of several decibels.
3. Playing Test Tones: The test tone volume in your pre/pro or AV receiver will be set at a predetermined reference level. To play these test tones, enter the speaker setup menu and find the level calibration feature.  Once you find that, enjoy the lush sound of test tone static.  Try to disregard any unusual looks you get when someone catches you intently listening to static.  They won’t understand.
4. Speaker Level Calibration: Although many new receivers have an auto-calibration feature, using your SPL meter for calibration will result in much more accurate settings. To calibrate with your SPL meter, follow these steps:<
   • Within your receiver’s setup menu, go to the level calibration function. This function is usually found under the speaker setup menu. If not, consult your receiver’s owner’s manual to find the level calibration feature.
   • Using the SPL meter to measure each speaker’s volume level, adjust the volume of each speaker to get a uniform level. Depending on your circumstances there is a wide range of adjustments may be needed. Some will require very little adjustment and others may require significant volume changes.
   • If your subwoofer is powered, it is recommended that you leave the subwoofer level set to the manufacturer’s recommended setting. Use the level control on the receiver to adjust your subwoofer volume to the uniform SPL of your system. Please note your SPL meter is accurate from 32Hz – 10 kHz using C weighting. If your receiver produces a 20 Hz test tone, you will need to add approximately 7 dB to the actual meter reading to correct for the SPL meter’s lower sensitivity at the lower frequencies.

Advanced Calibration

If you would like to optimize your system more fully, you can use one of the popular calibration discs like AVIA or Digital Video Essentials. They offer advanced audio and video calibration and walk you through a step-by-step process of optimizing your entire system.

As always, if you have any questions call us at 1-888-880-8992, start a live chat, or email us at customerservices@aperionaudio.com.

By: Ken Humphreys

Speaker Engineer

The cornerstone of every home theater and many music audio systems is the subwoofer, and home theater owners want to shake every corner of their home theater to its foundation. This course will help you do just that, in the highest possible fidelity. (Note, we are not responsible for noise complaints or neighborhood association ordinances.)After you’ve selected your subwoofer, optimizing its performance actually comes down to just two things: its placement in your home theater and your setting adjustments.

Your Room vs. Your Subwoofer

This sounds simple, but when it comes to placing your subwoofer(s), four competing objectives will be vying for attention to the point where you’ll probably need to live with some sort of compromise. Where your subwoofer eventually ends up will affect how evenly the bass gets spread throughout the listening area, how much bass is produced per watt of power, how well its sound waves integrate with those from the rest of your speakers and, of course, whether you like its placement in your home theater. Of course you want the best possible sound. But your wife is right: your subwoofer isn’t making sound most of the time – usually it’s furniture. So unless you want to sleep in your home theater, you may want to take room aesthetics into account. You may also want to consider things like where you can plug it in and how hard it will be to run the wire from your receiver. Subwoofers are supposed to make life easier, not harder.

Getting the Bass Distributed Evenly Through the Listening Area

Subwoofers are bass specialists. If they could wear a hardhat and carry a clipboard, they would. All sound, of course, is made of waves – with bass being the longest. For example, subwoofers typically output waves that are longer than 12’. The physics of what happens with long waves in rooms is complicated – reflected waves arriving later than non-reflected waves, reinforcing or canceling each other out, other waves doing funny things just because they happen to neatly fit in the room, and more. The result is a pattern of bass-loud and quiet zones distributed throughout your room that will differ for every bass frequency.

Fortunately, there are a few things you can do that will help:

1. Place your subwoofer in a corner. By making the three closest reflected paths close in length to the non-reflected path, they all arrive at your ear at pretty much the same time and reinforcing one-another. If a corner is impractical, the next best place is near one wall, the floor and an open area (like a hall) for the same reason except that one of the reflected paths is taken out of the equation. Whew. Just place your subwoofer as close to a corner or wall as you can, and you’ll be fine.
2. Use more than one subwoofer. This way, the pattern of bass from one subwoofer will be different than from the other and likely to even-out the combined bass distribution. This will fill your room with bass and hopefully even out the “dead zones.”
3. If you use more than one subwoofer and they both can’t go in corners, put them in non-similar places relative to walls and open areas. Non-symmetry is good for bass. Not as good as corners, mind you — but still good.

Getting the Most Bass With the Least Power

Let’s check out the corners again. Each room boundary (wall, floor or ceiling) you get your subwoofer close to will be equivalent to four times the power going to the same woofer. Close to three room boundaries results in (theoretically) 64 times the bass energy when compared to a subwoofer suspended in the middle of the room! So put your subwoofer in the corner.  It will sound better and shake-shake-shake your foundation.

Getting Your Subwoofer to Work With Your Other Speakers

Because of the way frequency filters divvy-up what goes where, a range of frequencies end up getting shared by the subwoofer and front speakers. In this overlap-zone, the waves from all these speakers need to add together to produce the proper loudness. They can all be positive contributors to the sound level or, if the peak of one wave meets the trough of another, they can actually end up canceling each other out. Thankfully, you won’t need a calculator, a tape measure or a tenured physics professor to get things right if you follow these two simple recommendations:

1. Make sure the subwoofer has a “phase switch” or knob. The use of this feature will be explained in “Setting the controls” below.
2. It’s best is to keep the subwoofer(s) in the same general area as your front speakers. It’s a-okay to put a subwoofer to the side of the listening area, and very much not okay to place it behind the listening area.

Hooking Up Your Subwoofer

If your receiver has a subwoofer output:

1. Run a cable with the appropriate plugs on each end (sometimes called RCA plugs) from the receiver’s subwoofer output to the subwoofer input labeled something like “sub input”, “line in” or “low-level in”. It is best to use a shielded cable for your subwoofer so other pesky signals don’t worm their way into your precious bass.
2. If this cable encounters household wiring, have it cross at a 90-degree angle.
3. Most subwoofers have both a left & right input. It usually doesn’t matter which one you use. Some people will buy a “Y adapter” or “splitter” so that a single cable can feed both subwoofer inputs. There’s no harm in doing this, the reason subwoofers have L & R inputs is so that if you have a stereo pre-amplifier, you can use both “pre-outs” to the subwoofer without losing anything.
4. If you are using more than one subwoofer, you can run the same kind of cable from the subwoofer’s “line out” or “low level out” to the next subwoofer.

If your receiver does not have a subwoofer output, you will need a subwoofer with inputs (usually called “high-level inputs” or “speaker level inputs.”)

1. Run speaker wires from your receiver (or your front left & right speakers) to the subwoofer’s high-level inputs. Don’t worry about speaker wire quality (the subwoofer’s amplifier is a resistive load meaning that, unlike speakers, all frequencies will be treated the same.) These high level inputs are not a lower quality input but they will not allow you to use the really cool crossover feature that’s built into most home theater receivers.
2. Since speaker wire is typically unshielded, it’s best to steer clear of household wiring. If it does need to encounter household wiring, have it cross at a 90-degree angle. If your subwoofer emits a buzz or a hum, this may be the culprit.
3. When using more than one subwoofer, its input wires can originate from the receiver, front left & right speakers or the inputs of the first subwoofer. Do not use the “high level outputs” to connect to other subwoofers. We recommend that these high level outputs not be used.

Setting the Amp Controls

230V – 115V: In America, this will usually be set to 115V. Many parts of the world use 230V for their household power.

On – Auto – Off: Most listeners like this switch set to “Auto” so that your sub will turn itself on when it receives a signal and fall asleep when not in use. The small light that tells you if the amp is on or not usually takes awhile to confirm when the subwoofer has stopped receiving a signal. Also, just to be safe, turn the knob labeled “volume”, “level”, or “gain” down before turning your subwoofer on.

Crossover frequency / bypass

1. If you’ll be using the crossover built into your receiver (recommended): Use the “bypass” switch if your subwoofer has this feature. Otherwise, turn the “crossover frequency” to the highest possible setting.
2. If your receiver does not have a built-in crossover (or you’re not using it): Your front left & right speakers extend down into the bass but begin to peter-out at some point. This frequency should be specified in the speaker’s owner’s manual or on their website as the lower limit of the speaker’s range. Set the subwoofer’s “crossover frequency” to this frequency (or maybe a little higher since a lot of liberties are taken with this specification). Later, you can fiddle with this control to hone in on the best setting.

Volume (aka Level or Gain) : For starters, turn this to a comfortable level. Final adjustments will be made later.

Phase: The easiest way to set the phase switch (or knob) is with a steady bass tone. Best is if you have a special test CD or DVD that has “pink noise” or, better, a constant bass tone around the crossover frequency (usually 80 Hz if you’re using a home theater receiver). If you don’t have anything that can produce pink noise, pick a favorite music track that has a constant, prominent bass line. Now, hire an assistant or have a friend move the phase control back and forth while you’re evaluating the sound in your listening area. Settle on the control position with the most bass. For now, don’t worry about which setting has the best bass, just the most. If this control is a 2-position switch, it’s possible that there will be no difference between the two positions (expected when the sub is about 3’ closer or further from you than the front speakers), in which case either position is fine.

Finally : Re-adjust the subwoofer’s crossover frequency (if you’re using it instead of the preferred crossover built into most receivers) and volume settings to where you think the sound is best. Listen for a solid, robust bass that is tight, well controlled and clear without “tubbiness” or “muddiness”. To get the subwoofer’s output at the same level as the front speakers you can use your ear or a sound level meter and test CD. You’ll probably find yourself making additional fine adjustments over the next few weeks as you listen to a variety of material.

Room treatment : This is a big topic. We could spend weeks addressing this important and often overlooked subject. The main thing to know is that normal rooms can be made to work well using ordinary furniture, like couches, rugs and bookcases that effectively absorb and scatter the sound.

In Conclusion

With a little patience and attentive listening, you can make your bass performance rival the most expensive systems. Refer back to this document, trust your ears and above all, have fun!

By Oliver Amnuayphol

Home Theater Guru

It’s hard to believe there was a time when using physical storage media, like CDs and Blu-rays, were the only way we could enjoy our music and movies whenever—and almost wherever—we wanted. Nowadays, using disc media is becoming the exception rather than the norm: The popularity of digital entertainment downloads, and streaming media in particular, is growing so fast it will soon outpace disc playback. But with the myriad of online content providers offering downloadable media—and the multitude of options for playing it back—it’s easy to get confused as to how to enjoy what you want when and where you want it. That’s why we here at Aperion Audio have put together this two part primer to help you navigate the new frontier that is the digital streaming media world, so that you can get back to what’s important: Enjoying your favorite music and movies!

In part 1 of How to Enjoy Streaming Media, we’ll tell you everything you need to know about what it is, where to get it, and what equipment you’ll need to get started.

First of all, what is Streaming Media?

Nearly all of the music and movies we enjoy today were at some point converted into digital packets of information via compression algorithms, or “CODECs” (Compression/DECompression). These digital packets can then can be stored, transmitted, and played back in various ways, including via traditional physical media like CDs, DVDs or Blu-ray discs: It’s up to the components receiving the signals, or playing back the discs, to take these digital files and convert them back into the sights and sounds we know as movies, TV shows, and music. No doubt you’ve heard of some of these file types before, such MP3, WAV, or Apple Lossless for music, or MP4, AVCHD for video. And since what we’re talking about are in fact digitized and formatted files, these music and movie files can be stored on or downloaded to any device compatible with said file types for repeated playback. Most importantly, they can also be transmitted, or “streamed,” the same way other computerized files can: Via the internet, from one computer (or server) to another computer—hence the phrase streaming media.

Where can I Download or Stream Media?

So by now it should be obvious: Since the internet is what made downloadable and streaming media possible, the internet is where ye shall find all kinds of movies and music to enjoy. As such, there are also a variety of ways to purchase media: Certain content providers, like Amazon.com and Apple’s iTunes, offer both downloadable music and movies; others choose to focus on one or the other, like HD Tracks (music) or Vudu (movies). For streaming only services, Netflix is one of the oldest, offering their entire streaming catalog of movies for a monthly fee, while others like Pandora and Spotify offer tiered streaming or cloud-based services: You can use the free, ad-supported service, or pay a monthly fee for premium benefits, such as unlimited music, mobile phone access, and no advertising. (Note: Since there are a wide variety of streaming services and options available, we’ll cover these in a later Aperion U article).

What Equipment Do I Need?

1) A Fast Internet Connection

Of course, the very first thing you’ll need is a high-speed internet connection to enjoy streaming media in any form: You simply won’t get smooth streaming quality from high resolution files unless you have a quality connection (consider 3 Mbps the bare minimum you should have in terms of bandwidth). Next, you’ll need to setup some sort of home network to transmit your audio and video signals, which means getting a router so that you can have more than one internet-connected device in your home. Better still, make sure you have a Wi-Fi capable router; this will enable setting up a private and secure wireless transmission network in your home to take advantage of equipment featuring Wi-Fi capability (more on this later). Oh, one more thing: If you have a newer construction home, check to see if you have Ethernet/Cat 5 cable already running through your walls, which will make streaming to multiple rooms throughout the house much easier.

2) Computer, Media Server, or Distribution Platform

After that, decide what kind of access you’d like to have to your music and movies and where you’d like to enjoy it; figuring this out will determine what kind of hardware you’ll require and in which rooms (for example, streaming Netflix in the living room and the kids’ room? etc.). In most cases, having at least one computer or media server (such as a Sooloos or an Olive Media server) where your media files are stored and/or played back will be enough to get started: You can use this to stream and watch Netflix movies, for example, or stream music to other devices connected to your home network, such as a networked A/V receiver or whole-house audio distribution platform, like Sonos or Logitech Squeezebox (We’ll get into the ins and outs of how you can enjoy streaming throughout the house in part two).

4) Media Players, TVs, and A/V Receivers

If you want to experience streaming media in all its home theater glory, get an internet capable media player or gaming console such as a PlayStation 3 or Xbox 360. Current owners of these gaming consoles already know that there are a multitude of streaming applications right at their fingertips—including Netflix, Pandora, Hulu Plus, ESPN, Last.fm, and a host of others. If gaming isn’t your thing, then a current generation Blu-ray/media player or newer TV should do the trick; more and more Blu-ray players and flat-panel TVs feature built-in Netflix, and Vudu apps with simple and streamlined interfaces at lower prices than ever before. This way, you don’t have to be anywhere near a computer to instantly stream HD-quality movies to your TV, and routing the audio directly to your A/V receiver (and Aperion Audio speakers!) will yield the best possible sound quality (many Vudu movies, for example, feature 1080p picture and 5.1, Dolby Digital Plus sound). Speaking of A/V receivers, many of today’s receivers include built-in networking capabilities and streaming applications such as HD/internet radio and Pandora. And remember that Wi-Fi router I mentioned earlier? More and more components with streaming apps are Wi-Fi ready, meaning you won’t have to worry about running additional Ethernet cables—especially useful if your HT rig is most definitely not located next to your internet router.

But Wait—There Will Be More!

So now that we’ve covered the basics of how to stream media in your home, hopefully you have a good idea of where to start; you should now know:

• What streaming media is, and what kind you’d like to start enjoying.
•  Where to start looking for streaming media content and service providers.
• Where in your home you’d like to stream media and what equipment you’ll need.

So now that you have all the info to start setting up your own streaming media network, get your gear ready, pop some popcorn, then sit back, relax, and take a breather: In part 2, we’ll cover the different types of streaming media services available, how to stream music you already own, and how to distribute it throughout your home—wirelessly, even!

By: Ken Humphreys
Speaker Engineer

The Lowest Of Lows

Subwoofers boom the thunder, the rumbles, the explosions and the guttural lows that bring music and DVDs to life. Reproducing low frequencies from 20-100 Hz, subwoofers let other speakers be diminutive and unassuming. In other words, your other speakers’ cabinetry doesn’t have to be as large because they’re not being asked to produce the really low bass waves.

Subwoofers come in a variety of designs. All of them can work fine if they’re well designed and well made (with the exception of passive subs which we’ll get to in a moment).

Powered vs. Passive-Powered Wins

A powered sub is a woofer in a box with its own amplifier/pre-amp. The amp drives the woofer and the pre-amp does a host of useful chores:

• It lets you adjust the loudness of the sub so that it works seamlessly with the rest of the system.
• It filters out unwanted frequencies so that it receives just what it’s designed for: low bass.
• It equalizes its output to compensate for some of the possible loss of bass due to a smaller box.
• It accepts LFE.

Some subwoofers give you the option to adjust the phase, which means the phase can match your front speakers regardless of their placement.

Passive subwoofers, instead of having their own amplifier/pre-amp, borrow power from the receiver to move the woofer. Another shortcoming is all the features you’ll love so much about a power sub are absent except for only one: the filtering of unwanted frequencies. Yet, even this isn’t done with much skill.

Designs-Thinking Inside The Box

Sealed Box: A sealed box design is exactly what it sounds like. If well built, it provides a tight, well-defined bass.

Ported Box: You have probably noticed that most subwoofer boxes have a hole in them. This hole is referred to as a port. The advantage is that a ported sub can usually produce lower bass tones, per watt input, than a non-ported sub.

Isobaric Designs: There are several nifty things that can be done when using two woofers per box:

1. Isobaric designs do just that. Imagine two woofers mounted at both ends of a tube. Now, place this tube into a box so that all you actually see is one woofer. Because the air pressure in the tube will be half that of the enclosure, this fools the front woofer into thinking it’s in a box twice as big. The end result is half the box size. Unfortunately you also get half the efficiency.
2. One woofer backwards. This design reduces harmonic distortion. The main cause of harmonic distortion in woofers is the difference between the out-stroke and the in-stroke of the woofer. This difference is caused by magnetic anomalies around the voice coil, manufacturing errors and suspensions that are stiffer moving in than out. When you mount one woofer backwards, but wire them up so that they both move in the same direction, the sound from the two woofers reinforce each other (in phase) while the distortions cancel each other out (out of phase). Clever, but the value is less than one might think. Not only are humans insensitive to harmonic distortion in the bass region, harmonic distortion by nature is, you guessed it, harmonious. So not that unpleasant.

For additional technical information go to:

http://www.thx.com/mod/techlib/crossover.html

http://www.dolby.com/ht/Guide.HomeTheater.0110.html

http://diyaudiocorner.tripod.com/software.htm