Old Benchmarks to Judge Bass By.

How To Get Really Deep Bass?

Retrieving real deep bass and reproducing it in your home theater or listening room at real-life levels is not easy. In fact, there are laws of physics that dictate how deep a subwoofer will extend its bass output, and as often as not some of these work against simple physical limitations of room size and placement.

For example, other things being equal (and each of the following may be manipulated to achieve certain gains at the expense of other performance factors), the larger the subwoofer box is in relation to the diameter of the woofer, the deeper the bass output will be. (One enthusiast I know installed a huge driver in one wall of a room in his house, using the adjoining room as the enclosure! When this is fired up, the entire house resonates. Is it any surprise that this gentleman lives alone?) Put another way, the smaller the box in relation to the driver, the less deep bass output will be. Or we can get somewhat deeper bass by reducing the driver size along with the box but sacrifice maximum loudness.

How low do we need a subwoofer to go to deliver audible output? Human hearing extends to about 20 Hz, and although there are frequencies deeper than that--some huge pipe organs actually produce a fundamental tone at 16 Hz -- they are typically more felt than "heard." If you feel the vibrations in a church pew, or in the floor, you are likely feeling 16 Hz or so, but actually hearing the second harmonic at 32 Hz. To most of us, hearing a 32-Hz harmonic of a pipe organ "sounds" really low -- and it is -- but to add to its impact, a really fine subwoofer needs to add that ultra-low "felt" component, and deliver significant output in the 20-Hz region. Virtually all popular subwoofers achieve some bass output in the 20-Hz region, but they do so only through the assistance of room reinforcement and advantageous placement in the room. (And that's also how the sub's performance is measured, by advantageous placement of the measurement microphone in a area or node of bass reinforcement.) All of this works as long as the room isn't too big. In fact, many of us have experienced very deep bass in a car equipped with a good sub, because of the small volume of air in the passenger compartment.

But in a larger space like a big room, true 20-Hz subwoofer output is hard to get. And it's this content that adds the enormous wow! element to movie soundtrack effects, and furthers the realism of great orchestral music. Earthquakes, train crashes and artillery all produce frequencies in the 20-Hz region, as do orchestra bass drums, pipe organs, synthesizers and even some pianos.

Attempts have been made (not really successful) to reduce the subwoofer enclosure size and try to compensate by using very large amplifiers and huge magnet assemblies (to take the extra power) in order to produce deep bass extension and output. But ultimately, box-size-to-woofer-diameter rules! You can extract tones as low as 40 Hz from a small sub by putting it in a smaller room in a favorable location -- a room mode or corner (a node in a room can give you 6 dB of boost). Similarly, some available ultra-compact and expensive cube subwoofers do produce fairly low frequencies, but they have real limitations in maximum output. They simply won't play low frequencies at anything approaching real-life loudness. If the sub's output is 9 dB down (-9 dB) at 32 Hz (about half the output at 70 Hz), you would need eight times the power to correct for the 9-dB loss (you must double the power for every 3 dB of boost applied). If you started out using a 200-watt amplifier, you would have to increase that to a 1,600-watt amplifier and then lose most of those gains to the driver required to take the power!

If in theory you wanted to design a sub that could truly reach the 20-Hz level with no more than a 4-dB drop in output in an anechoic environment, then the laws of physics dictate that the box must be large. There is no way around this. You would also need to incorporate an efficient amplifier because true deep bass extension requires enormous output (over 400 watts) in order to achieve sufficient loudness at these frequencies. It also must have the power to drive a large woofer and move the requisite quantities of air. This can present a problem for conventional analog amplifiers that are not very efficient (50% efficiency is common; the rest is dissipated in heat). Digital amplifier technology can lend itself to this application but the design would need to overcome the inherent problems with this type of amplifier. (At the moment, digital amplifiers are not generally used this way; more often they are implemented to reduce manufacturing costs at the expense of proper dynamic head room .) Overcoming the problem of a digital amplifier's "hard ceiling" in terms of dynamic headroom is a major challenge to amplifier designers. A conventional digital amplifier goes into immediate and severe distortion at its output limits. Given the widely varying signal levels of music and movie soundtracks, it's essential that new digital amplifier designs incorporate a means of preventing the amp from sudden distortion if a loudness peak exceeds the output limits of the amplifier.

Digital amplifier design is making great strides and receiving lots of attention at the moment. Innovative approaches to solving the dynamic headroom puzzle will inevitably be forthcoming. This is a whole different topic, and your faithful writer will look at this in greater detail in a future issue, where I will present alternatives that may make digital amplification appropriate for high-quality audio applications.

Why a Trumpet Sounds Like a Trumpet
All notes from a musical instrument, deep bass included, are made up of a "fundamental" tone and harmonics, which occur at mathematical multiples of the fundamental tones and help give each instrument its tonal signature or identity. For example, even if different instruments--trumpet, sax, and piano--all play the same note of identical pitch and frequency, each instrument will sound quite different. This occurs because each instrument's harmonic makeup gives the instrument its distinctive sound. It's harmonics that make a sax sound like a sax and a piano like a piano. That's also why we are still able to "hear" a 16-Hz organ pedal tone, because we actually hear the 32-Hz harmonic, which is much louder than the 16-Hz fundamental. However, if our subwoofer doesn't reproduce any of the 16-Hz energy, then we won't feel as much and it won't seem as realistic. The same goes for soundtrack effects.

by Alan Lofft (bio), Axiom Audio (reprinted with permission)

A Word Of Caution When Buying Consumer Transistor Electronic Equipment

Due to the dawning of the age of digitalis, the usage of transistorized components has decreased somewhat, making it important to know the

integrity of the sources of components.  When most electronics are being made in foreign lands, with high pressure to innovate as well as cheat

on standards of quality, we at Kennedy Audio want to make a statement about our hand built product by showing what a standard transistor would

look like, as opposed to one of the foreign counterfeit ones.   There are indications on the housing itself, but none that could be spotted after

the component is already mounted on a circuit board.

We screen all our materials for quality and authenticity, and find suppliers often mix in attempted hoax components.

Thus, each piece must have it’s housing pried open and inspected.  One obvious give away to ‘re-engineering’ is two or even three chips inside

the transistor (FET type) instead of only one.  These chips will be smaller than the single monolithic chip that we are looking for to validate the

component. The only sign that can be seen without prying open (and often damaging) the cap, is that the insulator fill area that shows around

the two assembly lead legs is smaller on counterfeit pieces.  Shown is the bottom of a valid transistor.

After removing cap, the photo below shows a ‘good’ FET transistor.

Toshiba transistors are the most commonly counterfeited.

In regard to the article above, there are many more low efficiency speakers on the market than high efficiency or technically

‘high sensitivity’ speakers.  The Kennedy power amplifier has a sensitivity control that greatly aids in adjusting room size and

speaker response to the required line input.  This is why the Kennedy bass amp is not a microphone level input device or other

low signal level input such as guitar itself..  Because bass players in larger spaces often experience very loud notes which resonate

due to a tube amp having an open PA microphone or a guitar amplifier that feeds into a hanging microphone, the design must

consider not only the natural advantage of non-ringing and non-resonating circuits of the amplifier, but also the environment and

the speaker characteristics themselves, a problem that most consumer paired and matched bass amplifications systems do not

claim to address or support solutions for.  This is just another advantage in buying from a firm started by a real life audio designer.

The resonance of any room can be found by taking the speed of sound divided by 2 and dividing that quantitiy by length.

Every square room has 3 frequencies: a 40 foot by 30 by 10 room is resonating at 14(40') ,18.6 and 56 Hz. for instance.

We believe that bulky and oversized speaker cabinets are mostly a technology of the near past, or we would like to help make it so.

How To Address Bass Cabinet Size Concerns.

Any signal which comes into the preamp must be filtered in real time in order for an instrument player to hear themselves playing.

This makes real time equipment much different from most studio electronic designs. A signal from a stringed instrument also begins

its life at somewhat higher amplitude and better tonal characteristics as compared to the same string vibration seconds later.

Oscillators and filters are employed to slightly change this signal, but they must work fast enough to act in real time, almost instantly.

The current digital standard is DVD, which is lower noise and faster than CD at 24 bit 96 kHz AD/DAC versus 16 bit and 41 kHz.

A multiple oscillator preamp would be called a synthesizer, because the sting vibrations trigger and excite other oscillators which

in turn produce their own sound and add to the original signal. Filters are for mixing the signals, such as equalization controls and

bass and treble controls. Reverb and chorus, the two most important ‘effects’ are oscillators. Most amplifiers also have circuits

that act as limiters and noise gates which cut out unwanted sounds. But remember that all these do take time to process a signal.

Below is graphic output of a signal that begins as noise and is resolved into a tonal component that now has its average as a root tone.

As time is squeezed, the higher harmonics are lost, as with a series chain of pedals that lose all the high harmonics or the loss of

the first 3 harmonics in 20 to 100hz bass sound.

In the near past, the time delay, although small, also caused the dropout of lower frequencies and bone shaker dynamics which

in turn prompted musical equipment designers to try to compensate by building larger speaker enclosures that approximated a resonating

oscillator in themselves. These by the physics involved were always limited to one target frequency, usually 16 to 32 cycles per second.

This big box baffle technique then added back lost signals by resonating or ‘boosting’ that spectrum of the amplifier’s output

that fell into this range and had the advantage of needing no additional current or voltage at all in order to drive it. For even more

bass boost, subwoofer systems added power to the speaker enclosure, or ‘bi-amped’ cabinets. This eliminated any interference

from line level harmonic filters, often called crossovers, and added control of the initial punch at early time domains.

The car amplifiers you see at 1000 watts are actually over rated. Their power source of this theoretical gain is mainly the battery.

At 12 volts this requires 89 amperes from the alternator, which is possible on heavy duty alternators but leaves little to recharge on.

Most use an inverter to convert to 30 volts DC, so with 25 percent efficiency and diversion losses, this requires an alternator of high cost.

The largest alternators run about 180 amperes when the engine is turning higher RPM's. The sound is not good due to lack of supply power.

Devices draw current at steady voltage. Amperes needed varies with volume. These car amp's will only work for a minute at full volume.

The Kennedy 500 is rated for continuous output at 500 watts into 8 ohm loads. This type of rating has very little in common with watts

drawn or maximum volume for short durations.

The Key to understandnig amp's is that 'clean' sound results from processing a signal quickly without the side effect of time delays which

begin a cycle of more power required to control and filter them. Resonating enclosures take time to begin resonance and to quiet down.

When an amp has more speakers and their additive wattage begins to equal the amp continuous wattage rating, there is more power

transfer while the efficiency is lower. When combined with special effects and filters it all means the amp must deliver it's current

at a fast enough rate and with enough cooling to sound 'good' and not damage itself or speakers; most importantly at bass frequencies.

Thus an amplifier for car audio rated at 1000 watts of music program sound material is not even close to a bass amp rated at 1000 watts.

Every multiple of power used by a speaker equals the cone excursion's square root of that factor. The acoustic power resulting (db or

SPL watts) multiple=power multiple. Only about one percent of the total power is converted into sound by the speaker, however.

Thus a speaker can produce more sound at higher frequencies, time domains being equal. For every 10 hz increase in frequency, the multiplier

of the original power doubles. A speaker with twice the excursion requires sixteen times the power at 60 Hz ( to reach the same excursion)

as that speaker at 20 Hz if the cone excursion were half as long. Incremental watts Power =ref. Xmax ^n where n is the number of 10 Hz above 20 Hz.

The high transfer of power at high cone excursion drives efficiency down and makes that 99 percent exotherm of heat inside the speaker.

Every doubling of cone excustion results in quadrupling the sound pressure power from the speaker which then requires four times the

(voltage*amperage)=wattage from the amp, but the power supply needs to supply the square of required current for a short duration of time.

Because of the small 1% incremental effect on hearing, a stereo amp has to be ten times more powerful to sound twice as loud and a mono amp must

put out 5.3 times the power. If, however all the change in power came from voltage increased to the speakers, then a monaural amp would

only need to have 2.5 times the output power rating to increase its decibel pressures enough to sound twice as loud. A big difference is in

how energy is delivered/used by 'a' or 'the' speakers. Vintage speakers have 1/4 inch cone excusions on subwoofers. Now they are 1/2 inch.

The double cone excursions seen today in stereo speakers is following the standard 30 watt to 200 watt per channel power increases available now.

Using more than one subwoofer per channel would very likely ruin any modern stereo, unlike the high voltage Kennedy instrument amplifier.

see voltage calculator online

These days a set of 5 10 inch bass guitar speakers fit into a 4 inch space, or 4-3/8" with backing cover board; or 5-1/2 overall with grills.

The series/parallel wiring diagram results in 8 ohms by using 5 16 ohm speakers for extra damping factor. The Kennedy amp can power 4.

The width is between 26 and 26-1/2" which is the same as the wood custom case accessory in width, making a good looking combination.

The speakers are less expensive because the wattages do not have to be so high - they add up. 2000/20=100 watts per speaker at 2 ohms.

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