Bi-amplification of Loudspeakers

Many audio enthusiasts see bi-amping as an intelligent upgrade for their hi-fi systems. Bi-amping is, simply, the process of "doubling up" on amplifiers in a system and hence doubling available power. This article seeks to point out some important considerations to bear in mind when bi-amping speakers.

Don't Mix & Match
It is crucial when bi-amping speakers that you not mix and match amplifiers. One current trend among audiophiles is to use a solid state amplifier for the bass frequencies, and a tube amplifier for the mids and highs. While this may initially seem logical, there are several reasons why this is a bad idea. Let's take a look at each one independently...

Rise Time
For one thing, two different amplifier designs will inevitably have different rise time specifications (sometimes referred to as event time). For the purposes of this discussion, we will define rise time as the time required for a signal to travel through an amplifier. Depending upon the amplifier circuit, the rise time will vary. Even a small mismatch in rise time will significantly degrade the sound of a bi-amped system.





Consider that in a bi-amped system, there are two possible configurations. The first, pictured above left, is more common. In this scenario, one stereo amplifier is dedicated to the high frequencies, and one amplifier to the low frequencies. The other scenario, pictured above right, is referred to as vertical bi-amping. In this scenario, one stereo amplifier is used to run both the high and low frequencies on one loudspeaker. (Note: In each of these scenarios, obviously two monoblocks could be used in place of one stereo amplifier).

In the case of "standard" bi-amping, any discrepancy in rise times would result in timing mismatches between the low and high frequencies. This sort of mismatch between frequency ranges will degrade the sound substantially because the precision in timing is important to maintain the integrity of harmonics. When a hammer strikes a string on a piano, it is not one frequency which is reproduced, but several - the fundamental and each of its harmonics. In a loudspeaker, it is likely that the fundamental will be reproduced by one driver, and the harmonics by at least one other driver. Hence any timing errors will result in a degradation of tonal balance, and a smearing of the soundstage.

In the case of "vertical" bi-amping, discrepancies in rise times will result in mismatches between the left and right channels. The results will obviously effect imaging, especially soundstage depth. A simple analogy clarifies the scenario: using amps with the same rise time is important when vertically bi-amping for the same reason using cables of the same length is important.

Gain
Another critical consideration is the gain of each amplifier used in a bi-amped system. The greater the gain of an amplifier, the more quickly the amplifier's output will increase as the preamplifier's volume control is augmented. Conversely, as the preamplifier's volume is attenuated, the amplifier's output will decrease at a rate directly proportional to its gain. One simple way to think of the net effect of an amplifier's gain is to associate high gain with bigger "steps" in volume and lower gain with "smaller" steps in volume.

What this means in the case of "standard" bi-amping, is that if the gain of the amplifiers is not matched, the volume of the highs and lows will be changing at a different rate as the volume on the preamplifier is adjusted. In the case of vertical bi-amping, the volume of the left and right speakers will change at a different rate. The effects of these volume discrepancies should be fairly obvious: in the first scenario tonal balance is altered, and in the second scenario the stereo channel balance is altered.

Concluding Remarks
Bi-amping provides many benefits, especially when using lower powered tube amplifiers where the system's overall power output can be doubled easily by simply bi-amping the loudspeakers. Many of our customers at Symphony Sound bi-amp with SET tube amps (2A3's, 300B's, etc.) and enjoy wonderful sound as a result. However, it is important to bear in mind that if certain guidelines are not followed, bi-amping can actually do more harm than good. If careful attention is paid to gain and rise time, it is possible to mix and match amplifiers, but only is unusual circumstances do we feel this is a sensible and prudent approach.

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Rhodium Properties

ON RHODIUM

Rhodium is an element with atomic number 45 and the chemical sign Rh. The name comes from the Greek "Rhodon" which means rose.

Rhodium, which is a platinum metal, is the rarest metal on earth (apart from the radioactive metals) and is only a few (less than 10) tons a year are produced. The metal is silvery white and has a higher melting point and lower density than platinum. Rhodium has low electrical resistance, low and stable contact resistance and high resistance against corrosion.

Rhodium is mainly used in alloys with platinum and palladium. Rhodium can only be plated on nickel, silver, gold or platinum. Plated rhodium is extremely hard wearing. Rhodium is sometimes used in spark plugs for aircraft engines, the tip of fountain pens, telephone relays and in the reflectors of headlamps, mirrors and optical instruments. Rhodium is also used in jewellery, as decorations and as a catalyst.

Because of its low and stable contact resistance and its high resistance against corrosion and wear (for example contact surfaces grinding against each other) it is eminently suitable as material in different kinds of connectors. A surface plated with gold, which is a very soft metal, is worn off much faster than a surface plated with a hard metal like Rhodium.

Summing up: Gold is beautiful, but if you want the best (in sound as well) use Rhodium.

MORE:
Atomic number: 45
Atomic symbol: Rh
Atomic weight: 102,9055
Electron config: [Kr]5s14d8
Atomic radius: 134,5 pm
Melting point: 1964 °C
Boiling point: 3695 °C
Oxidation states: 3

SOURCES
Rhodium occurs natively with other platinum metals in river sands of the Urals and in North and South America. It is also found with other platinum metals in the copper-nickel sulfide area of the Sudbury, Ontario (Canada) region. Although the quantity occurring there is very small, the large tonnages of nickel processed make the recovery commercially feasible. The annual world production of rhodium is only 7 or 8 tons.

PROPERTIES
The metal is silvery white and at red heat slowly changes in air to the resquioxide. At higher temperatures it converts back to the element. Rhodium has a higher melting point and lower density than platinum. It is highly reflective, hard and durable.

USES
Rhodium's primary use is as an alloying agent to harden platinum and palladium. Such alloys are used for furnace windings, thermocouple elements, bushings for glass fiber production, electrodes for aircraft spark plugs, and laboratory crucibles. It is useful as an electrical contact material as it has a low electrica resistance, a low and stable contact resistance, and is highly resistant to corrosion. Plated rhodium, produced by electroplating or evaporation, is exceptionally hard and is used for optical instruments. Rhodium is also used for jewelry, for decoration, and as a catalyst.

HANDLING
Exposure to rhodium (metal fume and dust, as Rh) should not exceed 1 mg/m3 (8-hour time-weighted average, 40-hour week).

COST
Rhodium costs about $ 1.000/troy oz.

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1/4" Stereo, Balanced or Insert?



There's a lot of confusion surrounding 1/4" connectors, especially the kind with 3 contacts.

An example of a 3 contact 1/4" plug, Switchcraft part number 297, is shown above. This part is also called a 1/4" TRS connector, where TRS stands for tip, ring, and sleeve, referring to each of the 3 contact surfaces on the connector. While this type of connector is often called a "stereo" connector it is important to understand that the stereo configuration is not the only way the 1/4" TRS connector is used.

Following are the 3 most common signal configurations for this connector:

• The first is as a stereo connection, most often used with headphones. In this application the tip connection is used for the left *unbalanced positive signal. The ring is used for the right signal. The sleeve is the ground connection for both the right and left. This type of connection is commonly found on high end consumer audio equipment and on professional mixing consoles and recording equipment.
• The second common use for the 1/4" TRS connector is as a *balanced audio connector. In this case the tip connection is used for the "hot" connection, the ring is the "cold" connection, and the sleeve is connected to the cable shield. The balanced 1/4" connection is often used as a line level output on professional audio equipment.
• The third use is as an insert connection, often found on mixing consoles. In this application the tip is used as the send, or output signal from the mixer channel. The ring is used as the return, or input signal to the mixer. On some mixer models the tip and ring are reversed. The sleeve is used as the ground connection for both signals. In this application the signal path in the mixer is broken when the 1/4" plug is connected to the insert jack causing the signal path to flow through the equipment attached to the insert cable. An insert cable would normally have the 1/4" TRS connector on one end and split out to two seperate connectors to attach to the input and output of the outboard equipment.

So, what is the important lesson here?

Don't assume that just because the cable fits the interconnection will work. It is in many cases possible to connect one of the types listed above to one of the other types with an adapter cable. Look closely at equipment manuals to find out exactly how the inputs and outputs are wired. If the two pieces of equipment don't have the same connection type you may need an adapter cable or additional equipment to make your connection.

*Balanced vs. Unbalanced signals - The complete explanation of balanced audio wiring is too big a topic for this post, so I will be doing a complete post on this subject in the near future. Suffice it to say that balanced wiring is a way of reducing external interference in an audio line that requires 2 signal wires twisted together, and in the case of most audio installations surrounded by a braided or foil shield. For a balanced cable to be effective both the signal source equipment and receiving equipment must have balanced connections.
An unbalanced line relies solely on the shield for protection from interference and only requires 1 signal line plus the shield conductor which also acts as the signal ground.

Subwoofer Cables, Fact or Fiction?



A common myth/misconception propagated by the hi-fi audio cable industry is that a special, usually larger and heavier, audio cable is required to connect a powered subwoofer to an audio system. In truth, any good quality audio cable that can be used for interconnecting audio components will be excellent for use as a powered sub cable.

The input of the powered sub is a high impedance type which means only a tiny amount of power is transferred through the cable, the power amplification occurs inside the subwoofer at its internal power amp. Because there is so little power transferred through the cable, its conductor size is insignificant. Typically 22, 24, or even 26 gage conductors are appropriate, and will not have noticeable signal loss even at lengths well over 100 ft.

The signal most commonly used by a powered subwoofer is a limited bandwidth line level audio signal. In this case limited bandwidth means that high frequency information is removed from the signal either at the a/v receiver - preamp/processor, the subwoofers input circuitry, or in some cases both. Capacitance is the primary factor in high frequency loss in audio cables. Since high frequencies are not used by the subwoofer the capacitance of the subwoofer cable is not as important a specification as it would be for interconnecting full range components.

So, don't be fooled by high priced "subwoofer" cables, use a normal audio interconnect and your sub will sound just as good.

Can you make a component video to RGB cable?



On an almost daily basis we receive requests for a cable to convert component video to RGB or the opposite. I'd love to be able to build one of these, and would probably sell quite a few of them. However, there are a few technical issues in the way.

Before I get into the details of what we can and can't do I think it would be helpful to define some of the relevant video standards and terms:
• Component Video - Also known as Y/Pb/Pr, Y/Cb/Cr, YUV, and EIA/CEA-770.

The component video standard calls for three parallel channels on 75 ohm impedance coaxial cables. Component video cables are typically terminated with RCA connectors for consumer applications or BNC connectors for professional applications. The three channels are known as Y (luminance) essentially a black and white representation of the image, Pb (blue color difference) , and Pr (red color difference). All three of these signals are derived from different combinations of the red, green, and blue primary colors present in the image.

The component standard describes several different signal formats which differ in resolution and scanning method (interlaced or progressive). The standard explicity defines the formats as 480i and 480p in both 4:3 and 16:9 aspect ratios - called standard definition, and 720p and 1080i - called high definition. The number indicates the visible horizontal lines of resolution in the image, the letter indicates progressive or interlaced scan. Additional formats are also present on some equipment.

• RGB Video
RGB uses 3, 4, or 5 parallel channels to seperately carry the red, green, and blue primary color signals and timing information. The 4th and 5th channels are used for different implementations of the timing (sync) signal. The 3 channel version has sync combined with the green signal and is also know as sync on green. The 4 channel version has the horizontal and vertical sync pulses combined on a seperate line, this version is known as RGBS or RGB composite sync. The 5 channel version has the horizontal and vertical sync pulses on two seperate lines, this version is called RGBHV or RGB with seperate sync. RGB cables are made with 75 ohm coaxial cables and usually have BNC connectors though RCA connector are occasionally used.

• VGA
VGA and its relatives SVGA, XGA, and UXGA are very similar to RGBHV. This standard is used in computer displays and some projection systems. In addition to the seperate Red, Green, Blue, Hsync, and Vsync signals present in RGBHV the VGA family also have some additional lines for digital data communications between the display and computer. VGA cables have 5 coax lines and a varying number of twisted pairs and single conductors for digital data. The standard VGA connector is a 15 pin high density d sub (hd15).

So, how do you convert from RGB to Component or Component to RGB?
Simple enough, all you have to do is combine the RGB signals according to a specific formula to derive each of the component video signals. For example Y = .299R + .587G + .114B. The Pr and Pb signals are derived with similar equations. The reverse conversion is also accomplished with a similar set of equations starting with the Y,Pb, and Pr values. Also, the horizontal and vertical timing signals (sync) have to be processed and combined with the appropriate channel.

While it looks simple on paper it is too complex to be achieved with a simple cable, fortunately there is a type of device called a transcoder designed to do this sort of conversion. Transcoders vary in price from approximately $250 to $1500 depending on signal quality and features. Many scalers combine transcoding with more advanced switching and format/resolution conversion.

How about RGBHV to VGA?

Good news, this can usually be done with a simple adapter cable with 5 BNC or RCA connectors on one end and a HD15 connector on the other. For this to work the devices on both ends must be set up for the same resolution and format. This cable is just adapting, not converting.

How about Component to VGA?

Many video projectors and plasma displays accept a component signal on an HD15 connector, in this case you can use a simple 3 RCA to HD15 cable to make the connection. It's critical to make sure the display is specifically equipped to accept component on this input since the cable isn't converting component to VGA, it is just adapting the connection for the HD15 input.

Conclusion-

The wide variety of signal formats and standards can make integrating a system challenging. Fortunately it is possible to make the necessary conversions with minimal or no loss of signal quality using the appropriate adapters, cables, and transcoders.

Till next time....