Grounding in Loudspeaker Circuits

[clm811]

Having reading a number of recommendations regarding the use of “Star” Grounding in the wiring of loudspeaker crossovers, ostensibly to lower noise in the loudspeaker circuit, it appears to me that the use of grounding in the high-level signal path may be comparable to that used elsewhere in the audio circuit (in application, if not in importance). So fa I have been playing around with using a ground plane in the external (passive) crossover enclosure, although I haven’t been able to draw any conclusions so far.

Today, while reading J.A.’s review in Stereophile of the Esoteric MG20 Loudspeaker, I notice that the design employs 5 binding posts. According to the reviewer: “…one pair each for the tweeter and the woofers, and a fifth that grounds the amplifier’s output to the drive-unit chassis…doing so with conventional amplifiers is said to reduce the noise floor by shielding the voice coils from RFI.”.

I'm intrigued and intend to experiment more with this,wondering if the idea of grounding & shielding can/should be extended to include the use of shielded speaker cables and/or running a seperate ground lead from the amp through the (external, in my case) crossover to the loudspeakers...

Anyone else here experimented with this, or have knowledge to share about this topic?

-Chas

[sreten]

Hi,

It is because that speaker is built by Tannoy and Tannoys have
a five post terminal block to allow this feature. You do not need
an extra post or speaker cable wire to ground the drivers chassis.

Simply connect the drivers to the negative input.

/sreten.

[clm811]

I received the following reply to my post on the Audio Asylum:

We have the safety-earth wire in the AC power system that is commonly called "ground." Some, but not all, audio equipments have the chassis connected to this wire. It is tied to an earth electrode at the circuit breaker panel (in USA and similar schemes), where the neutral wire is also tied. Because of the distance from the audio system outlet to the circuit breaker panel, this safety wire is not a good RF ground. Any claims that it provides a way to reduce RF noise are more or less false depending on how great this distance is.

An audio system has a zero signal reference that is also called "ground." This creates a great deal of confusion among audiophiles. The two grounds are not tied together in any consistent way, so any given audio system with "grounded" equipment has some variety of ground loops. These loops are pathways for electrical noise to be added to the audio signal.

Further, there are two kinds of audio power amps. One kind has the (-) output terminal close to (but not necessarily shorted to) the audio ground potential, while the other kind produces a balanced output, where the (-) terminal signal is equal and opposite the (+) terminal signal referenced to the system audio ground. I'm skipping over the DC bias present on both output terminals of switching amps for the moment.

Most speaker cables are not shielded, but the one system in my experience with the most natural detail uses shielded and damped cables. I believe the shields on the speaker cables of this system are tied to the (-) terminals and not the audio or safety-earth grounds.

Connecting the speaker "ground" (speaker, speaker cable shield, or both) to either the amp chassis or the audio ground could create problems. Speakers are large objects and may make good antennas. Injecting the RF noise they pick up into the audio system ground loops may make things worse instead of better. Furthermore, if switching amps with DC bias on the speaker terminals are used, this bias appears between the voice coils and the magnets. Any shorts could destroy the amps and speakers.

IME, it is important to damp the RF resonances in speaker cables and crossovers. Filters that damp normal-mode RF ringing on speaker cables (such as the Walker Audio High Definition Links) may also be useful. Be careful about grounding speaker cable shields or speaker metal parts. The details of how to do this properly are proprietary, so undo the grounds if the sound gets worse. -Al Sekela

This just about covers it. Thanks Al & Sreten!

-chas

[bzfcocon]

I would tend to agree and extrapolate the post above, grounding seems to be more or less a mess.

Having to connect several different audio equipments together, with/witout grounding can be pretty frustrating - at least in a home environment. Adding "grounding" to loudspeakers scares me a little bit more..

[jtsaudio]

Tannoy use a separate ground terminal on their own "Prestige" series loudspeakers, as well as the Esoteric MG series speakers, which they make for Teac.

"The Prestige line employ a unique fifth speaker terminal in addition to a bi-wire pair...With the driver chassis grounded via the 5th terminal, and by using appropriate speaker cable, this proven technology ...electrically earths the driver chassis to dramatically reduce radio frequency interference circulating in the hi-fi system. Eliminating this RF ‘noise’ brings substantial improvements in mid-range clarity and further enhances the soundstage imaging."

They imply using either shielded cable or a separate ground wire. I'm not sure how well this works, but for a commercial design they do use good parts(hardwired crossovers, Hovland & Clarity Caps, van den Hul wiring, etc.) and build to a very high standard.

-Joe

[clm811]

Thanks, Joe for the confirmation.

Not that I lack originality, but alot of the ideas I get and things I try are inspired by and based upon extrapolation of ideas and techniques I see elsewhere.

I biwire my external crossovers and use star-grounds because these are common practices in high-end designs used by credible designers. The folks at Tannoy have used the 5th terminal to ground the woofer baskets in their top models as well as the Esoteric MG series; Consequently, I'm experimenting with and researching this concept.

In Joseph D'Appolito’s book, "Testing Loudspeakers", he writes:"…in practice, cross-coupling in the crossover networks and the common ground wire introduce low frequencies into the tweeter and high frequencies into the woofers. This makes the case for bi-wiring."

If audio signals can couple(treble into woofer and bass into tweeter)via the "common-ground"(I prefer to view these as "signal+/signal-" leads), then isn't it logical to assume that some RFI can get in as well?

In low-level circuits, we employ star-grounds and shielding to deal with this...

Another trick I'm experimenting with is a shunt RC filter across the speaker binding posts (a'la Walker H.D.Links, Enacom, etc.). Some people simply use 10ohms/.01uF; however, the optimum value of R and C for a particular system depends upon speaker impedance, as well as the characteristic impedance of the speaker cables.

-Chas

[infinia]

Ground "heaven" for speakers is the storage caps at the power amp. Or in practice the negative terminal of the amp. This as another post suggests bi-wire.

Don't use ground planes on passive X-overs, just causes problems. Besides they don't shield magnetic coupling anyway which is more important here.

To reduce cross coupling and feed thru between drivers circuitry, watch the orientation or better yet spacing between inductors is key.

[clm811]

I received a response to my query on Audio Asylum from the renowned Jon Risch, who wrote:

"About cable "ground":
http://www.AudioAsylum.com/audio/cab...sages/503.html

The point here is that you really can't look at a loudspeaker crossover "ground" as something special and separate from the hot leg, and as if it were to be treated separately.

In fact, by trying to 'star ground' a loudspeaker crossover, you might end up separating the two current carrying polarities (the 'ground', and the 'hot' runs) locally, and thus, increase the inductance, which will actually cause MORE/HIGHER error voltages to occur at the drivers, etc.

See:
Cable inductance, and how it is controlled
http://www.audioasylum.com/audio/cab...ssages/17.html
and

Separated speaker cable conductors:
http://www.audioasylum.com/audio/cab...es/127756.html

2nd, unless the 'shield' of a speaker cable is part of the current carrying circuit, it will distort and adversely affect the EM fields present in the rest of the speaker cable, e.g., throwing a shield over a two conductor speaker cable that is only connected at one end or neither, will cause more problems than any it might be helping to solve.

RE inherently shielded speaker cables, see:
http://www.geocities.com/jonrisch/s3.htm

These cables use the shield of a coaxial cable to carry the current, so they do not cause the problems I speak of.

3rd, running a separate ground wire directly from the amp to the crossover would create a second ground return path (assuming you did not sever the original ground lead current path) which would NOT be paired with the hot lead and thus could not help lower the inductance, and it would also be likely to cause sonic problems from the imbalanced EM fields and lack of inductive cancellation that would normally occur with paired send-return wiring. If you disconnected the original ground, then you would have a separated pair of wires, the original hot wire, and the new "out-in-left-field" ground wire, thus raising total inductance quite a bit, and again, raising the error voltages at the loudspeaker crossover and drivers. Jon Risch "

Thanks, Jon!

-chas