<![CDATA[Tech]]> http://velodyne.com/tech/ Sat, 18 May 2013 05:25:35 +0000 Zend_Feed http://blogs.law.harvard.edu/tech/rss <![CDATA[Connecting Subwoofers to Music and Home Cinema systems]]> http://velodyne.com/tech/connecting-subwoofers-to-music-and-home/ There are several ways to connect subwoofers to home music and cinema systems. The information you need is a bit different for Home Theater (multi-channel) systems than for two-channel, or stereo, systems. Here we discuss many aspects of subwoofer connection that we at Velodyne have encountered:

1. Defining some key terms
2. Crossover networks and how they work
3. Home theater receivers: multichannel amplifier hook-up
4. Stereo receivers: two-channel amplifier hook-up.
5. Subwoofer placement

Defining some key terms:

What is a subwoofer? Subwoofers are dedicated low-frequency speaker cabinets that fill in the deep, rich bass that is missing from most main speakers. Subwoofers are specialized, and don't reproduce midrange or high frequencies. See our article on "What Is a Subwoofer, and Why Do I Need One" for more information.



What does LFE mean? LFE refers to the Low-Frequency Effects channel that is a part of the specification for five channel and seven channel home theater receivers and processors. The LFE signal is a filtered connection, encompassing the LFE channel signal along with the bass content of any channel that is designated as "Small" in the receiver or preamp/processor. Line Level connections are

What is a speaker-level connection? Older stereo receivers (and some current stereo receivers) do not have RCA-connector based line level or LFE connectors. Those receivers can still be used with a subwoofer via speaker cables. The speaker level connection is a full-range, amplified signal connection, so the subwoofer's crossover network will remove the high frequency content and reproduce the low-frequencies only.

What is a subwoofer input? This refers to the RCA signal connection on the back of the subwoofer. It accepts the signal from your receiver or preamp/processor, which in multi-channel receivers has usually already been filtered, or processed, by the receiver's crossover network.

Crossover networks and how they work:

Crossover networks in subwoofers: A loudspeaker's crossover network is a set of components designed to act as a "traffic cop", directing the full-range audio signal to where it can provide the best sound. The tiny tweeters in a speaker would be quickly destroyed if asked to handle the long wavelengths involved in reproducing deep bass frequencies. Large woofers don't really move fast enough to reproduce clearly the high frequency notes that tweeters handle. Crossover networks divide the frequency range between speakers (bass to the woofers, most of the music to the midrange driver in a three-way speaker, and high frequencies to the tweeter). Most crossover networks are analog devices, using a combination of inductors, capacitors, and resistors to filter the signal. Digital crossover networks are becoming more common in our products. They handle the signal-processing functions even more precisely, via computer-chip technology that is programmed by our engineers.

Velodyne subwoofers include a crossover network. The low-pass crossover is set at a specific level, often 80 Hz, allowing the sub to reproduce frequencies below this level, while filtering out higher frequencies. Most subwoofer crossovers are user-adjustable (i.e., from 40 Hz to 120 Hz), so that you can determine the sub's upper frequency limit.

Crossover adjustment involves attaining a seamless blend between the main speakers and subwoofer, so bass sounds cannot easily be localized. If you listen to the music and can clearly hear bass notes coming directly from the subwoofer's location, something is wrong! Some main speakers are very bass-capable (i.e., large, costly floor-standing speakers). Others are less bass-capable (i.e., compact satellite speakers, and most in-wall or in-ceiling speakers). Try a crossover point below 80 Hz for large speakers (perhaps 60 Hz) or above 80 Hz for compact or inexpensive speakers (perhaps 100 Hz). This may give a better blend with your main speakers than the 80 Hz starting point. A little experimentation with some bass-heavy music can go a long way toward adjusting this setting so that you are very happy with your subwoofer purchase.

Crossover networks inside a multi-channel receiver: Modern home theater receivers and preamp-processors have crossover networks built into them. Stereo receivers generally do not. When using a home theater receiver, many people prefer to use its crossover, especially if it is of the "continuously variable" type. In such cases, we suggest deactivating the subwoofer's crossover network. Using both crossovers poses no risk of damage, but if the crossover networks compete with each other, distortion can result. Many Velodyne subs have a crossover-bypass switch, usually labeled on the amplifier as "Direct", "Subwoofer Direct" or "Subwoofer By-Pass". This switch de-activates the internal crossover for use with an already filtered signal from a home theater receiver.

Home theater receiver connections:

LFE Input: Home theater (multi-channel) receivers have an LFE (Low Frequency Effects) channel as a part of the 5.1 or 7.1 specification. The most common way to connect a subwoofer to an HT receiver is to use a single audio cable with RCA connections on both ends. Hook the cable from the LFE Out connection on the receiver (often labeled "SW" for subwoofer; "Sub Out"; or "LFE") to the LFE input on the subwoofer. The receiver sends an unamplified, bass-managed signal to the subwoofer. Set the sub for "Subwoofer Direct" (as above).

Velodyne Digital Drive subs also have a balanced XLR input for LFE. Over long signal runs, XLR connections are less prone to noise than standard RCA cables.

Line-level Input: Some older receivers don't have a bass-managed LFE output. In that case, line-level outputs can be used. This sends the sub an unamplified, low level signal down the same type of audio cable used for LFE output. You will need a stereo pair of such cables. This signal is not filtered, so you will use the sub's crossover network to manage the signal. Do not use Subwoofer Direct.



Stereo system (aka two-channel) connection:

Line level: Many modern stereo receivers have a sub-out connection, an unfiltered, single RCA line level connection dedicated for the subwoofer. If there is no sub-out, standard line level connections work fine. If the receiver has no sub-out or line level connection, but has jacks marked "Pre-out", those work too.

Connect an RCA cable from the sub-out (or a pair of RCA cables from the line-out or pre-out) connection on the receiver to the LFE or line-in connection on the subwoofer. The subwoofer's crossover network will manage the signal, so do not use Subwoofer Direct.



Speaker level: If the receiver has no sub out, line out or pre-out connections, you can connect the subwoofer using speaker level inputs. This sends a full-range, amplified signal to the subwoofer. The subwoofer's crossover will manage the signal, so do not use Subwoofer Direct.

We suggest using speaker cable of 16-gauge or lower. Connect the speaker cables to the receiver's left and right speaker outputs, and run those cables to the subwoofer's speaker level input connections. Make sure to that you are consisten with positive and negative connections. In other words, make sure that the wire connected to the positive (+) terminal on the receiver is also connected to the (+) terminal on the sub. The wire connected to the negative (-) terminal on the amp must also be connected to the (-) terminal on the sub.

Then connect your main left and right speakers to the sub. Simply run another set of speaker wires from the subwoofer's speaker level outputs to the left and right speakers. You now have a stereo system with a wonderful addition: a subwoofer dedicated to handling the lowest frequencies, which removes quite a bit of the load that the speakers, and receiver, would otherwise have to handle.

Subwoofer placement:

The quality of bass that we hear depends on how the subwoofer is placed in a room. The room itself has a far greater effect on the bass than most people realize, and is one of many factors that determine the sound quality of bass:

  • Of what quality is the subwoofer?
  • Is the subwoofer integrated optimally with your system?
  • Where in the room is the subwoofer located?
  • Where is your listening position, relative to the sub's location?
  • Are multiple subwoofers being used?
  • What is the room configuration: large, small, rectangular, square?
  • How resonant, or absorptive, are the room's surfaces?


Change any one of these elements, and the quality and quantity of the bass will change. It is common that listeners who are seated in different spots of the room will report vastly different levels of happiness with the bass. One may hear the bass as sounding ideal, while another believes "It sounds too bass-heavy", or "Is the subwoofer even turned on? I barely hear any bass."

The key idea with subwoofer placement is to experiment! If you can, play some music that is rich in bass, and try a variety of locations in your room. If you cannot move the position of the subwoofer, you may instead be able to re-position your favorite chair or listening position. Often times they recommend and showcase the benefits of using multiple subwoofers to help enhance and even out tone, however the size of the room and factors above will help you to make the correct decision.

]]> Thu, 23 Feb 2012 00:42:07 +0000 <![CDATA[The Benefits of Using Multiple Subs]]> http://velodyne.com/tech/the-benefits-of-using-multiple-subs/ Many music and home theater enthusiasts have begun using multiple subwoofers in their systems, rather than using just one subwoofer. A home entertainment system that has weak, distorted bass sounds less than thrilling! Getting great bass in consumer-sized living rooms is a challenging topic, and a single sub may not fill the room evenly with great bass. Let's investigate the reasons why multiple subs make sense.

Many consumers know that a large listening area may require a second sub. What is sometimes missed is that every listening room, large or small, suffers from standing wave issues. When excited by deep bass, the room itself resonates, storing and re-releasing bass energy, somewhat like a water glass hit by a fork. The slowly-decaying bass notes can lead to muddy-sounding bass, even from a quality subwoofer.

The subwoofer and the room work together, creating the bass sounds that we hear.

Bass wavelengths are long (over 50 feet in the deepest bass), and most home listening rooms are smaller in comparison. The deep bass wavelengths are reflected off walls, ceilings and floors, colliding with each other. This sets up areas in the room where bass energy is too prominent, which sounds boomy to listeners in those areas. It also creates cancellation points, or "nulls", where bass energy is lacking. In single-sub systems, depending on where you are seated, the bass sounds may be satisfying or far from it.

Twin subs, strategically placed, can help balance these room resonances. Twin subs are far more capable than one at filling in the null spots where bass cancellations occur, and smoothing out overloaded, boomy areas. The whole family is more apt to get clear, rich bass. Much research suggests that four subs is the optimum number, but two sub systems are nearly as effective as four subs (and far better than a single sub). Twin subs are also more practical, cost-effective, and easier to position in the room than four. Here are three reasons why multiple subwoofer systems make sense:

1. Decreased distortion and greater bass headroom: Even a solo listener will enjoy lower-distortion bass. Twin subs offer greater headroom and minimize compression, so neither sub works as hard to fill the space with bass. The climactic scenes in movie soundtracks, and big passages in musical pieces (such as the 1812 Overture), are more easily handled by double the power and twice the subwoofer radiating surface. Clean beats "overloaded" every time!

2. A wider "sweet spot": Well-placed twin subwoofers recreate bass that is more evenly distributed throughout the room, minimizing areas where bass seems either weak or boomy. Multiple listeners can have a great Home Theater and music experience.

3. Longevity: Heat is the enemy of electronic longevity. As neither sub is working as hard as one sub would, heat build-up is minimized, prolonging subwoofer life.

]]> Wed, 22 Feb 2012 23:24:06 +0000 <![CDATA[What is a Subwoofer, and Why do I Need One?]]> http://velodyne.com/tech/what-is-a-subwoofer-why-do/ The trend toward small, easily concealed main speakers has fueled an increase in the use of subwoofers. Compact main speakers, and in-wall or in-ceiling speakers, are often bass-shy. Large, costly floor-standing speakers often have plenty of bass, but they may be cosmetically unacceptable. Also, the speaker room placement that results in the best stereo imaging is almost never the best placement area for reproducing deep bass.

A subwoofer is a dedicated low-frequency speaker cabinet, usually self-amplified, that fills in the deep, rich bass that is missing from most main speakers. Subwoofers are specialized, and don't reproduce midrange or high frequencies. They are designed to reproduce the deepest notes in the musical spectrum, and low frequency energy provided by home theater soundtracks. Most main speakers are passive (unamplified). But most subwoofers include a power amplifier, creating the raw power needed to cleanly generate deep bass, without robbing excessive amplifier power from your receiver. Subwoofers usually handle frequencies below 150 Hz or so.

A quality subwoofer not only reproduces the thrilling deep bass notes with authority. Its presence in the system also allows the receiver / amplifier to reproduce mid-bass and mid-range notes more cleanly. The burden of reproducing deep bass, the most difficult frequencies to reproduce, is lifted. Your amplifier and main speakers work more efficiently, with less distortion. All kinds of instruments, including voices, can be heard more clearly. Why should you add at least one great subwoofer to your system?

1. Deep bass adds the emotion, the physical feeling of presence and excitement, to a good music or movie performance! One reason that inexpensive speakers sound "just OK" is that they cannot reproduce deep bass very well.

2. Subwoofers help solve problems in speaker set-up and placement. It's difficult to set the main speakers where they are able to provide realistic imaging, and set them in the best place for bass. A separate subwoofer can be placed where the bass sounds best, with the main speakers set up to provide the best image. In-wall and in-ceiling speakers can be placed where they work best cosmetically, without concern for their bass reproducing ability, when the system has at least one great subwoofer.

3. High-quality subwoofers are engineered to generate the massive cone movement required by low bass reproduction. Main speaker drivers are often taxed to their limits, and beyond, by the demands of deep bass, and audible distortion results. A good subwoofer is specifically designed to generate deep bass. Whether you like jazz, classical, pop or rock, a good system can be made better with a good subwoofer.

Regardless of your musical preference or taste in movies, a good subwoofer can make a good listening experience great. There are two main types of subwoofers:

In-room subwoofers are still the most popular choice. If a consumer doesn't need to conceal the subwoofer by hiding it in the wall, ceiling or floor, in-room subwoofers work well. The cost vs. performance ratio is very high.

Built in subwoofers are preferred by many design-conscious consumers. These subs cost a little more to build and engineer properly. But hidden subwoofers are very popular in homes where space and the look of the interior are primary concerns.

]]> Wed, 22 Feb 2012 23:18:00 +0000 <![CDATA[ Differences in Subwoofer Design ]]> http://velodyne.com/tech/differences-in-subwoofer-design/ There are many ways to design a subwoofer enclosure. In our view, there is no one "correct" way to design a subwoofer. Rather, there are many design approaches, and some designs work better at certain price points. Each design can have a good or bad result, depending on how it is implemented.

All subwoofer design involves trade-offs, and so determining at the start what result we desire is key to building a good subwoofer. What do we want this subwoofer to be? Should it be inexpensive, and sound as good as possible for the price? Is it a "cost no object" exercise in great sound? Do we want a small subwoofer that performs like a larger one?

Several key tradeoffs are involved in designing a subwoofer, as follows:

1. Cabinet Size: The larger we make the subwoofer cabinet, the more air there is to work with, so the more efficient we can make the subwoofer. However, some consumers object to a larger cabinet. So, many subwoofers are designed specifically to take up very little space. Getting great bass from a small cabinet is not an easy task.

2. Cost: How much will the product sell for at retail? The more we invest in quality materials, the better we can make the subwoofer sound, and the better its deep bass performance can be. More amplifier power can produce louder volume levels, but a big amp will likely cost more than a less powerful one.

3. Efficiency: How loudly do we want the subwoofer to play, given a specific cabinet size? With one watt of amplifier input, how much sound pressure can we measure at a one meter distance? The larger the cabinet, the less amplifier power it takes to reach a given sound pressure level. But as we know, a large cabinet may or may not be an option for the space-conscious consumer.

4. Deep Bass Accuracy: What are the lowest frequencies we want this subwoofer to reproduce? Most subwoofers aren't able to reproduce the lowest notes in the musical spectrum (20 Hz) without significant distortion… or at all, in the case of the least expensive subwoofers. Do we want deep bass extension, and the ability to play low frequencies at high volume levels?

There are actually many ways to design a subwoofer system - band-pass enclosures, isobaric designs, compound enclosures, transmission line enclosures, etc. Four design approaches are among the most popular for consumer home electronics use. Not coincidentally, Velodyne builds subwoofers using each one of the four: sealed enclosure, ported bass reflex, slotted bass reflex, and passive radiator designs.

The following is a brief discussion of some the benefits and drawbacks of each design:

1. Sealed Cabinet: One of the most popular subwoofer designs, the sealed enclosure is relatively simple. There are no ports, radiators, or other cabinet openings. Instead, a driver is mounted in a sealed enclosure that must be air-tight in order to function properly. The enclosure is often filled with some type of insulating or damping material (acoustic foam, fiberglass, etc.), which can aid in producing bass notes with a tight, clean sound. Transient response is typically very good. Many listeners feel that sealed cabinet subwoofers have the best, most accurate sound quality, often described as "tight" vs. other designs. The low frequency extension, or deep bass performance, is usually very good when compared to vented designs. If sound quality is the highest priority, sealed cabinet design is often the choice.

There are some drawbacks to sealed cabinet designs, which generally are less efficient than ported designs. More amplifier power is needed to produce a given Sound Pressure Level (SPL), so more money must be invested in the amplifier. Alternatively, the box size can be increased in order to produce higher sound pressure levels. But a larger box may not be an option if cosmetic appearance is a high priority.

2. Ported Bass Reflex: Perhaps the most popular subwoofer design on the market, ported bass reflex designs, offer a good combination of efficiency and powerful, low distortion bass. An opening in the cabinet, often a round PVC tube of a specific length, is tuned to a particular reinforcing frequency - the frequency at which the woofer begins losing the ability to create deep bass. The woofer and the tuned port work together to give significant output at this frequency. The port effectively extends the subwoofer's ability to provide low, loud bass, beyond what the woofer can do on its own. This is a very efficient design, generally resulting in at least a 3dB gain in efficiency vs. a similarly sized sealed cabinet design. The box itself can provide some free amplification, as less amplifier power is required to reach a specific SPL.

One disadvantage is that the air inside the cabinet is no longer a fixed entity, so it exerts less control over the motion of the woofer cone. Careful tuning of the enclosure - a precise calculation of the length and width of the tube - is required in order to avoid a sound quality that is sluggish or "muddy". In other words, the transient response of the system is typically not as good as the sealed cabinet design. Also, the port must be fairly large in order to prevent whistling sounds from being audible during loud bass passages. The cabinet must be big enough to accommodate the port, and a large cabinet may or may not be acceptable. Still, the performance attainable for the cost involved makes this a popular way to get ample, powerful bass.


3. Slotted Bass Reflex: These are similar to ported bass reflex designs, but instead of a PVC tube or pipe, a slotted opening of specific length is cut into the cabinet. The slot acts as a reinforcing element at the frequency at which the woofer begins losing the ability to generate low frequency information. Many of the advantages and disadvantages of tube port designs apply here, making the slotted bass reflex design a popular choice for subwoofers.


4. Passive Radiator: Known variously as "bass radiator" or "drone cone" designs, passive radiators offer an interesting combination of the benefits and drawbacks of sealed and passive designs. A passive radiator takes the place of the port or slot in vented enclosures, and looks very similar to a standard subwoofer driver - minus the heavy and powerful magnet structure on the rear of a driver. The cone or diaphragm, surround, and basket each resemble a standard woofer. But the passive radiator is not being pushed by the electromotive force of the driver's magnet structure. Rather it is incited into resonance when the active driver creates the specific frequencies that the passive has been tuned to. Tuning a passive radiator to move its resonant frequency down can be easily done by adding mass to the passive radiator. Subtracting mass will move that frequency higher.

Like a tuned port design, the passive radiator is very efficient, meaning less amplifier power is needed for a specific SPL. A passive radiator offers greater control over the tuned frequency, often resulting in better transient response, and a tighter, more accurate sound than that from a ported system. Also, there is no risk of port noise, the whistling sound that can occur with a port. This design can work well with a smaller cabinet. A port of sufficient length to reinforce the desired low frequency simply won't fit into many small cabinets. The Velodyne Impact-Mini (with its 10" x 10" x 12" deep cabinet) is a good example of a situation in which the passive radiator design works well. The result is a small cabinet, relatively inexpensive, efficient subwoofer, capable of playing quite loudly.

These advantages do come at a price. The passive radiator typically costs more than a tube port, and can be almost as expensive as a complete driver. This drives the price of the finished subwoofer up a bit, handing back some of the cost-effective advantages of a ported system.

]]> Wed, 22 Feb 2012 23:10:20 +0000 <![CDATA[Anatomy Lesson: Inside Subwoofers]]> http://velodyne.com/tech/insideasubwoofer/ By Chris Hagen, acoustical engineer at Velodyne Acoustics

Digital Drive ExplodedYOU NEED the acoustical foundation of a subwoofer to replicate an earth-rumbling movie theater or a spine-tingling concert hall—or to take home gaming sessions to the next level of realism. High-quality bass extends the frequency range of your loudspeakers, providing a more realistic and pleasing listening experience. To help you understand what’s involved in creating the low end, I’ve dissected Velodyne’s Digital DrivePLUS subwoofer. No two subwoofer models are identical, but the parts described here are included in most. Now when you go to complete your sound system by purchasing a subwoofer, you’ll understand the salesperson’s lingo.

1. WOOFER CONE/SURROUND ASSEMBLY AND DUST DOME.

Responsible for producing the bass energy from a subwoofer. The surround supports the front edge of the cone while allowing movement. The dust dome keeps foreign particles out of the voice coil area.

2. SPIDER. Responsible for supporting the neck of the cone, as well as the front edge of the voice coil. Returns the cone and voice coil to the rest position after a signal from the power amplifier moves the cone.

3. FRAME. Holds the complete speaker driver structure. It’s comparable to the frame on a car, and the build quality can have drastic effects on the performance of a subwoofer.

4. VOICE COIL. A coil of wire wrapped around a cylindrical “former” and attached to the neck of the cone of the subwoofer driver that converts the current of a signal produced by the amplifier into a mechanical force that moves the cone.

5. MOTOR TOP PLATE. A piece of steel that helps focus the field from the magnet through the voice coil windings.

6. FRONT PANEL DISPLAY AND CONTROLS. Make setup and use of the subwoofer much easier and convenient. The subwoofer must have its own power amplifier to facilitate this feature.

7. MAGNET. A piece of magnetized material that generates the constant magnetic field that interacts with the varying current in the voice coil to move the cone.

8. MOTOR BACK PLATE. A piece of steel that completes the magnetic circuit from the back side of the magnet to the inside of the top plate, helping to focus the magnetic field through the voice coil.

9. CABINET. The outer structure that houses and protects all of the internal electronics and parts. Its main purpose is to stop sound radiated by the back of the subwoofer driver from interfering with the front radiated sound. The cabinet includes the baffle, a mounting board for the driver, as well as top, bottom, sides, and rear. Gaskets are used to seal openings and eliminate rattling where parts touch. Some cabinets may include auxiliary resonating devices such as ports or passive radiators as well.

10. BRACE. Higher-quality cabinets include solid bracing of some sort to rigidify the cabinet.

11. LINING MATERIALS. Materials such as Dacron and fiberglass are frequently used to ensure the cabinet acts purely as an air volume and has no reflections inside of it that can cause distortion to the emitted sound.

12. POWER AMPLIFIER. Most subwoofers come with a power amplifier, which will include the appropriate equalization, if any, for the model, as well as all the controls and connections necessary to properly mate the subwoofer to your sound system

Important Specs

Woofer Size. All other factors being equal, a larger cone moves more air. More air movement means that your subwoofer can play louder.

Excursion. Not all woofers of the same size have the same excursion. Greater excursion allows the cone to move more air. Greater air motion equates to greater bass energy to be reproduced, whether it is in level or lower frequency.

Frequency Response. This describes how evenly a subwoofer can reproduce its range of sounds. Subwoofers are typically designed to reproduce frequencies from below 20 Hz to above 100 Hz, producing this band with more accuracy and authority than smaller satellite speakers.

Distortion. More or deeper bass doesn’t mean very much if it is produced with large quantities of distortion. Typically this will show itself as “slow” bass,” “muddy bass,” “overhang,” or even hearing a higher frequency than is intended to be reproduced.

Maximum Output. Because a powered subwoofer (one with an amplifier built in) has been designed to have a driver, cabinet and amplifier that work in concert, specifications such as sensitivity, nominal impedance, and power handling are not very important. But the end result, the maximum output capability, is very important. Most times, this needs to be experienced first-hand.

Orginal Article posted at Electronic House.

]]> Mon, 06 Feb 2012 20:14:05 +0000