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zebo-the-fat
2004-Dec-02, 04:28 PM
Does using "Oxygen Free" cable to wire Hi-Fi speakers realy make any difference?
I just use heavy plain copper cable and it sounds fine to me. Is the OFC cable just a marketing gimmick or am I missing something? :o

papageno
2004-Dec-02, 04:37 PM
Does using "Oxygen Free" cable to wire Hi-Fi speakers realy make any difference?
I just use heavy plain copper cable and it sounds fine to me. Is the OFC cable just a marketing gimmick or am I missing something? :o

:-k
As far as I understand, OXF copper is used when we need copper not susceptible to magnetic fields.
But I have seen it used when the magnetic fields are very strong.

My impression is that it is more a marketing gimmick (other factors are more important in speakers).

Anyway, I found this link (http://www.audioholics.com/techtips/audioprinciples/interconnects/cableconstruction.php).

EDIT to add: after having a look at Wolverine's link, maybe the reason OXF copper is used when dealing with strong magnetic fields, is because it is also free of iron impurities.

Wolverine
2004-Dec-02, 04:38 PM
Marketing (http://www.roger-russell.com/wire/wire.htm#oxygenfree), IMHO. Some claim to be able to hear a difference in quality using solid platinum interconnect cables also, but in my experience, the electrons simply aren't picky enough to justify the exorbitant difference in price. Skepticism is definitely warranted where audiophiles' claims are concerned.

Sammy
2004-Dec-02, 04:39 PM
Total scam!

You don't need heavy cable, either. Unless you have VERY long runs from your amp to your speakers, ordinary lamp cord (Zip cord) will do just fine for only pennies. The thick cables promoted some audio outlets are just a way of enhancing profits.

The JREF page has had a series of articles on scams re audio quality and cable size. (www.randi.org/)

Maksutov
2004-Dec-02, 04:49 PM
Does using "Oxygen Free" cable to wire Hi-Fi speakers realy make any difference?
I just use heavy plain copper cable and it sounds fine to me. Is the OFC cable just a marketing gimmick or am I missing something? :o
Here are some opinions:

Link One (http://www.kevinboone.com/hifimainscables.html)
Link Two (http://www.audioholics.com/techtips/audioprinciples/interconnects/cableconstruction.php)
Link Three (humor) (http://www.geocities.com/CapeCanaveral/Hall/8701/Audio_**.htm) Caution: adult language!

I like this quote.


The fact of the matter is that OFHC copper and pure unalloyed copper, both oxidize at around the same rates. Some cable manufacturers use the OFHC as an advertisement that it will not oxidize, or it will oxidize less than other copper conductor materials, but there is no truth to these claims.
Just more devious ways to separate the consumer from lots of his money.

I've been amused by high-end audiophiles since the 1950s. The people with the "golden ears" that don't change with the person's health or age, and can hear something in the sound created by that $200 a foot cable that you can't. Right.

Now to find which type of magic marker it was that improved the sound of CDs when the ink was applied to the disc edge. :D


[edit/add note]

frogesque
2004-Dec-02, 04:51 PM
Total scam!

You don't need heavy cable, either. Unless you have VERY long runs from your amp to your speakers, ordinary lamp cord (Zip cord) will do just fine for only pennies. The thick cables promoted some audio outlets are just a way of enhancing profits.

The JREF page has had a series of articles on scams re audio quality and cable size. (www.randi.org/)

Agree, I've spliced unscreened twin bell cable to extend speaker cables without any drop in sound quality. Put your £/$ into decent speakers and amp.

I know silver plated heavy copper is used in some RF applications but for audio it's a nonsense.

zebo-the-fat
2004-Dec-02, 04:56 PM
Thanks for the links, I knew I would be right about something eventualy!! =D>

Demigrog
2004-Dec-02, 05:38 PM
Nothing beats the EMF shielded optical cables for scamminess. That scam has been less common lately; now the overpriced optical cables claim to have a higher speed of light, and thus less "skew". As if a femtosecond difference matters to a digital signal measured in kilohertz-- not to mention that the drift in the crystal oscillator frequencies of the digital audio circuits would totally swamp the optical cable's effects. :roll:

Just more proof that my morals are keeping me poor: I could be getting rich selling quakery! :(

Nicolas
2004-Dec-02, 05:51 PM
My experience with cables: make sure the electrical contct and guidance is good (so a nicely attached copper cable which isn't rediculously thin), and if it's quite think isolated it gives less hum.

Only step away from this approach if:

*You play really loud and you really need a thicker cable because thinner ones melt through
*You are annoyed with the almost inaudible electrical hum (I only hear it when playing nothing at very loud volumes...) and want better isolated cables.

These very expensive cables may sound a very little bit better, but IMO it is totally not worth the expense. For 5 dollars a cable a normal person has all the quality he will ever need. For 1 dollar probably too, but these can have bad contacts, the cable itself usually is fine.

If you want good sound quality, put your money in 5dollar cables and more expensive speakers, amp and sources. Bi-amping clearlygives a difference. The opinions onsimple biwiring are biased. My personal experience is that, given your speakers are honest double cabled speakers (no internally linked marketing stunt I mean) and an ordinary amp, running 4 cables (4 threads, 2 cables if you want, you know what I mean) to each speaker gives a slightly better sound. The bass is more independent from the high notes and vice versa (eg a continuous high tone doesn't drop away on a bass).

Anyway if you're spending the money anyway, spend it on the gear and not the cables. (or on music, that's where it's all about right?)

zebo-the-fat
2004-Dec-02, 06:45 PM
Bi-amping clearlygives a difference.

My speakers have two sets of terminals for bi-amping (currently linked together and fed by one set of cables per channel) Would it be better to use both terminals by just connecting in parallel with the existing cables, or connect the second terminals to be "B" channel of the amp? (the amp has A & B speaker connections) ?

Wolverine
2004-Dec-02, 06:59 PM
What models of amplifier & speakers are you using?

zebo-the-fat
2004-Dec-02, 07:05 PM
Denon tuner/amp, Monitor bookshelf speakers. (very small speakers, but they sound a lot better than my old and much larger Heybrook HB1's)

Wolverine
2004-Dec-02, 07:06 PM
Could I bug you for specific model numbers? :D

There's a method to my madness...

zebo-the-fat
2004-Dec-02, 07:13 PM
Dennon DRA-455 amp, Monitor Audio Bronze B1 speakers (how do they make such a good low frequency response in such a small box?)

Nicolas
2004-Dec-02, 07:27 PM
I'll start with the possibilities:

*1 cable from amp A to each speaker, speaker bridged (as it is now)
*2 cables from amp A to each speaker (would be plain bi-wiring)
*2 cables, one from amp A and one from amp B to each speaker. Whether this is bi-wiring or bi-amping depends on your amp: if it just internally links amp A and amp B, you are bi-wiring but with a more elegant connection than when ramming all cables into the amp A plugs. Makes no difference for the sound wrt biwiring through A only. If amp A and B are truly separated (which they most probably are with a Denon) then you are Bi-amping. Now the most ideal situation would be when you could adjust amp A and B separately, then you could really use all the pros of bi-amping (you actually colour the sound for each CONE instead of speaker box then, but for this purpose you actually need 2 stereo amps in most cases, or even better 4 mono amps...).

My advice: cables from amp A and B to each speaker, that probably gives you a bi-amped system. You can't colour each cable signal separately, but you have gotten rid of all the problems one cable can give (the bass speaker generating a current on its return and this way killing the high tone). There is a chance you haven't got a proper filter in your speaker or amp, but my guess is that you have (unless your speakers are from a supermarket and your amp is on closer inspection a "tenon" or something maybe..."

I found that bi-wiring already works with cables from 1 meter. Even in the unlikely case that your system wouldn't filter its channels, you'd still have a biwired system.

One more thing: a bi-amped system (I'm jealous, having just a Biwired one)) sounds "different". If you don't like the sound, make it single-wired again. It's your taste, not what "should" be best!

At the moment I have a preamp going to an integrated amp, which has only amp A outputs, which are biwired to my speakers (speakers NEED 4 connectors each to biwire or biamp btw). My aim is to find 2 mono endamps, which I will biwire per speaker. That would still give me a bi-wired system, but with fully separated l/r channels and in full original class A (drool). My preamp has output A and B, so with 4 mono endamps I could make a Class A biamped separated system (anyone has 4 good old mono endamps he doesn't want anymore?). But even with 4 mono endamps I would only be able to change settings per channel, volume and colour would be the same per whole speaker. I would be very happy to ever find only 2 endamps I can afford, thinking realistically.

Wolverine
2004-Dec-02, 07:34 PM
Denon DRA-455 amp

This is why I was asking. :)

Without needing to examine the speakers' capabilities, your receiver isn't designed to run a bi-amped configuration -- it's intended to run one or two pairs of speakers full-range stereo. A/B doesn't imply that there are two separate power output sections that can be dedicated to running high & low ranges separately (and there's no means of adjusting crossover frequencies, etc).

zebo-the-fat
2004-Dec-02, 07:35 PM
Thanks for the advice, I will play this weekend if I get a chance. :D

Nicolas
2004-Dec-02, 07:35 PM
OH so it does not have a crossover?
Well that would give you an elegantly connected biwired system.

Sorry my fault, I thought all Denon would have a crossover

Wolverine
2004-Dec-02, 07:38 PM
My advice: cables from amp A and B to each speaker, that probably gives you a bi-amped system.

Not according to the specs in this case.

tlbs101
2004-Dec-02, 07:39 PM
It's a total scam.

My engineering roomates and I researched this, while in college. We could find no valid reason why the chemical composition of the copper would make any measureable difference (much less audible difference) in the audio quality.

We even went on to actually do some A-B comparisons (using borrowed 'expensive' cables from a local dealer), just to say we did it. I couldn't hear any difference between the 'expensive' cables and 18-ga "zip" cord -- neither could any of my roomates.

We reported back to the dealer, who was not too happy, but he kept right on selling the expensive cable.

Wolverine
2004-Dec-02, 07:39 PM
OH so it does not have a crossover?
Well that would give you an elegantly connected biwired system.

Sorry my fault, I thought all Denon would have a crossover

No worries, it's really necessary these days to examine capabilities on a model-specific basis, since manufacturers have a propensity for doing counterintuitive things.

zebo: I'd recommend just running your speakers full-range as intended. ;)

Nicolas
2004-Dec-02, 07:41 PM
Is there a difference in terminology between a biwired system like mine (cables directly connected with each other) or with a 4 speaker (2* stereo) amplifier, where the contact between the cones has to go through the amps? Without crossover, this officially isn't bi-amping, as there is no frequency difference between the cables (no crossover).

Also there are external crossovers. Where do you need to plug them into your system?

As it appears my Marantz Esotec Sc-6 preamp has no crossover, so I would need an external crossover to ever allow for real bi-amping.

Nicolas
2004-Dec-02, 07:43 PM
Looking at some electronics schemes, it appears that you connect the crossover between the pre-amp and the endamps. So you've got 2 channels (L+R) running from you preamp to your crossover, which has 4 outputs: treble L/R and bass L/R.

This setup means the necessity for 4 endamps when you want to amplify L and R separately too $$$ I think I'll stick to separated biwiring as my future plans...

ktesibios
2004-Dec-02, 08:05 PM
Bi-amping clearlygives a difference.

My speakers have two sets of terminals for bi-amping (currently linked together and fed by one set of cables per channel) Would it be better to use both terminals by just connecting in parallel with the existing cables, or connect the second terminals to be "B" channel of the amp? (the amp has A & B speaker connections) ?

Don't do that. The speaker switching on some home stereo amplifiers is set up so that when speaker A and speaker B are both selected, the speakers are connected in series. The purpose of doing this is so that if you happen to have two sets of 4 ohm speakers and select them both simultaneously, the amp won't see an excessively low load impedance (most hi-fi amps are rated for a 4 ohm minimum load and most hi-fi owners don't know what the total impedance of two speakers connected in parallel is).

If your amp is one of the ones that do this, you would wind up with the woofer and its crossover network in series with the tweeter and its crossover. It's very unlikely that this would injure anything, but it's guaranteed to sound extremely weird.

Unless you can determine whether your amp connects multiple speakers in series or parallel, it's better to do your bi-wiring by connecting both cables to the same output terminals on the amp.

The issue with speaker cable gauge isn't the ampacity of the wires. This becomes a concern only in really high-power installations like sound reinforcement systems. The issue is the resistance of the wires.

The source impedance seen by the speaker is the series combination of the amp's source impedance (for most modern solid-state amps this is very low- a small handful of milliohms in series with a few microhenries) and the resistance of the wires. This forms a voltage divider with the input impedance of the speaker.

The impedance seen looking into the terminals of even a single driver is a complex (in the mathematical sense) function of frequency. Both the magnitude and the phase angle of the input impedance will vary, often considerably, with frequency.

The result of this is that if the wiring resistance is non-negligible compared to the speaker's input impedance, the amplitude-versus-frequency response measured at the speaker terminals will become lumpy even though the frequency response measured at the output terminals of the amp is flat. I've seen this happen. In one case an excessively small wire run from an amp room to the nearfield monitors in a studio control room (about 30 feet of 22 gauge shielded cable) produced amplitude-vs.-frequency variations of nearly 2 dB at the speaker terminals. This was not only measurable, it was clearly audible.

For the run lengths in a typical home entertainment system, 16 gauge wire should be adequate, although there's no harm at all in going bigger. Don't waste your money on anything exotic- lamp cord or SJ from the hardware or electrical supply store will perform just as well as anything the tweak-os will try to sell you.

While I'm on the subject of interconnections, I ought to mention that dirty and oxidized low-level connectors can produce considerable distortion. Oxidized metal to metal connections are nonlinear- in fact, metal-metal oxide junctions have been used to produce rectifiers for AC voltmeters (the ANSI standard for VU meters specifies a copper-oxide rectifier). This nonlinearity generates harmonic and IM distortion products.

Again, an example. In the same control room that had the bad near-field monitor wiring, I found that if I measured the THD+N of the 1/2" mix machine in input monitor mode with my distortion analyzer plugged directly into the machine, it was 0.004%. If I connected the analyzer to the machine via the console patchbay, it measured around 0.25%. The cause turned out to be that the punchblock connections in the cable run from the console to the machine had deteriorated in the years since the installation was done. Reworking them eliminated the excessive distortion.

It's a good idea to unplug and re-seat all the RCA plugs in the back of your amp, preamp etc. every few months to help break up any oxides on the contact surfaces and get a better connection.

BTW, when I take over the world, the use of RCA connectors for anything will be a hanging offense, and snake-oil cable manufacturers who make claims about things like velocity of propagation which would be easily testable and yet hand you a load of anecdotes without any hard data in support of the claims will be burnt at the stake. :evil:

Wolverine
2004-Dec-02, 08:13 PM
Nicolas: It all depends on the gear you're dealing with, as different product lines will be accompanied by different compatibilities and options... this makes it difficult and largely inaccurate to speak on the subject in general (I'd like to avoid confusion here, for the safety of the gear previously described). Bi-wired systems still require a crossover and IMHO are generally geared for higher-end products -- multi-purpose tuner/amplifier combinations like the one mentioned above really aren't intended to be configured in a manner other than full-range stereo.

A bi-amped system of any reasonable quality will invariably be somewhat pricy, and if you're wanting to design a system along those lines it's best to do so in advance of any purchase rather than attempt retrofit products with more limited capabilities not designed specifically for other purposes.

Wolverine
2004-Dec-02, 08:19 PM
Don't do that.

My thoughts exactly! :D

I was too lazy to type a reply with the eloquence of yours. 8-[

Nicolas
2004-Dec-02, 08:27 PM
I'm not planning in modding my equipment or anything, but Marantz has made sperate crossover units, with normal RCA and speaker wire plugs to attach them to.

But with all the differences in construction (and opinion) finding your way is rather difficult in audio land. Some people think that everything will blow your system, some think nothing will...

Anyway my system is not blowing up in it's current config, it sounds better since I have biwired it (I tested it with pieces of music that really make the rather subtle difference clear), and as my system is completely designed to carry mono amps I'll certainly stay on the lookout for those. If I ever find the suiting crossover unit I'll see what I do with it. I'm not familiar with the Denon system mentioned, so asking the manufacturer might be an idea.

enginelessjohn
2004-Dec-03, 10:09 AM
BTW, when I take over the world, the use of RCA connectors for anything will be a hanging offense, and snake-oil cable manufacturers who make claims about things like velocity of propagation which would be easily testable and yet hand you a load of anecdotes without any hard data in support of the claims will be burnt at the stake. :evil:

Can I be Grand Inquisitor please!!!!! :D :D

I've had similar stories in HiFi shops too. My father bought about £1200 worth of Arcam kit from a shop once and the salesman was working on selling the £100 cable to him too. Convienietly that was the point I wandered into the shop, and informed the salesman that it was no better than any other cable. My father was given the cable, (that had apparently been assembled by virgins under the light of the full moon :D) to try, and we took it home. Our comparison, was with telephone cable, and some domestic lighting cable both of which my father had lying about.

Needless to say there was practically no difference between the £100 cable and the lighting cable. And the telephone wire actually sounded slightly better........

There are times when I have needed to use low loss cable, mostly in high power HF work. But it is worth remembering that this was a professional requirement, that gave a measurable improvement.

Also ktesibios, spot on about the corrosion on interconnects causing distortion. And can we include those TV UHF connectors in your purge? :D

Cheers
John

Avatar28
2004-Dec-03, 09:20 PM
BTW, when I take over the world, the use of RCA connectors for anything will be a hanging offense, and snake-oil cable manufacturers who make claims about things like velocity of propagation which would be easily testable and yet hand you a load of anecdotes without any hard data in support of the claims will be burnt at the stake. :evil:

And what, pray tell, would you propose in their place?

Anyways, unless you're just itching to spend more money than you have to, something like this (http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-114) should be fine for your purposes.

If you want OFC, they've got that (http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-144) pretty cheap too (this wire SHOULD also be slightly more flexible if it helps). They've got 100' of 14 gauge for $10 more and 100 ft of 12 gauge for $3 more still. I linked to 100' spools. They've got longer and shorter ones available too.

Fortis
2004-Dec-04, 12:03 AM
Back in the late '80s, when I started getting into hi-fi, there was a fad for wacky products from a guy called Peter Belt. H-fi buffs can be a gullible lot. ;)


Mr. Belt believes that his products work because they alter the morphic resonance energy field surrounding the treated object. Changing the energy field of the object changes our perception of the object. Thus, Mr. Beltís products change our perception of the sound coming from our audio system. The sound is not changed in any wayóit is our brainís interpretation of the sound that is changed. This is not the sort of concept that receives great acceptance in the mainstream audio pressóyou know, the people who say there is no difference between zip cord and Nordost cables. Even in the alternative audio press, Mr. Beltís ideas have received little attention. The only articles that have appeared in the last few years are Greg Weaverís 1999 reviews of Beltís Rainbow Electret Foil (now known as Silver Rainbow Foil) and Cream Electret in SoundStage. (See www.soundstage/belt1, www.soundstage/belt2, and www.soundstage/belt3). Carol Clark discussed Beltís procedure for freezing CDs in your home refrigerator (www.positive-feedback/belt). She also reviewed his P.W.B Red "X" Coordinate Pen (www.positive-feedback/beltpen). Not much press for tweaks that, according to the reviewers, appear to work.

After having read everything on the Belt website, I sent for the free sample of Silver Rainbow Foil being offered at the time. Upon receipt of the foil, I applied the small strips to a number of CDs and then froze the discs, twice, in my refrigerator per Mr. Beltís instructions. The foiled and frozen CDs sounded better than they had prior to the treatment. Intrigued, I ordered more of the Silver Rainbow Foil, along with some Cream Electret and Sol-Electret.
.
.
.

http://www.positive-feedback.com/Issue8/belt.htm

ktesibios
2004-Dec-04, 02:40 AM
BTW, when I take over the world, the use of RCA connectors for anything will be a hanging offense, and snake-oil cable manufacturers who make claims about things like velocity of propagation which would be easily testable and yet hand you a load of anecdotes without any hard data in support of the claims will be burnt at the stake. :evil:

And what, pray tell, would you propose in their place?



XLRs wired to IEC 268-12 would be a good place to start. I'd also make it mandatory that all line-level outputs be transformer isolated, AKA "symmetrical", because they are virtually idiot-proof- you can interface them to balanced inputs of either kind (transformer and diferential) or to an unbalanced input without trouble- even if you don't know anything at all about audio electronics.

I've spent too much time sorting out "why do I hear SMPTE on the lead vocal?" situations caused by someone using a TT-to-1/4" mono or RCA cable to connect a piece of consumer gear to a console patchbay to look kindly upon the little @#$%^&*s. RCAs are particularly egregious because the "hot" signal pin connects before the common does when you plug them in and because most of the ones I've encountered are fragile and have extremely poor cable strain relief.

Just the $.02 of someone who has spent nearly twenty years earning a living in professional audio. :wink:

Nicolas
2004-Dec-06, 09:53 PM
If there's a crossover in your speaker, do you still need one at your amps? (for bi-amping)

Donnie B.
2004-Dec-06, 10:05 PM
If there's a crossover in your speaker, do you still need one at your amps? (for bi-amping)
Yes, that's the idea of biamping -- you do the crossover at the preamp stage, where presumably its audible effects are less and where you have better overall control. Then you amplify each driver (woofer, tweeter, and possibly midrange) independently.

I don't really buy this idea, though. If the speaker system's designer did his job right, the crossover makes a smooth transition from woofer to tweeter, and takes into account the impedance charateristics and rolloff of the driver itself (including its enclosure, in the case of a woofer). The biamp crossover can't do this, so you have to tweak it, essentially doing the loudspeaker designer's job yourself without the benefit of calibrated mics and test equipment. In other words, you adjust it so it sounds good to you, not so that it's flat and accurate.

Nicolas
2004-Dec-06, 10:10 PM
OK, that way. So if your speakers are good, the only advantage bi-amping (using 2 amps) has over bi-wiring would be that each amp can dedicate its power to one speaker (if you're using physical separate amps).

Donnie B.
2004-Dec-06, 10:24 PM
OK, that way. So if your speakers are good, the only advantage bi-amping (using 2 amps) has over bi-wiring would be that each amp can dedicate its power to one speaker (if you're using physical separate amps).
Correct.

Biamping is one of the less-wacky audiophile fads -- after all, you're replacing clean, analog, passive crossovers with nasty, evil active electronics, so the total woowoos probably don't like it.

I think my favorite audio nut was the "golden ear" who swore that listening in the dark improved the sound quality of her system... but only if she shined a flashlight on her speaker cables. I was never sure whether she was just pulling the collective legs of the audiophile crowd. I mean, nobody could really think that... could they? 8-[

Nicolas
2004-Dec-06, 10:28 PM
I was agreeing until the flashlight part, because of the possibillity that you listen more concentrated in an environment with no visual distractions. But I never knew the musical qualities of photons on speaker cable insulation... :D [-X

ktesibios
2004-Dec-07, 03:05 AM
Biamping makes better use of your amplifier headroom, that is, its maximum output voltage swing. To illustrate this, let's consider a two-tone signal, consisting of the sum of a 100 Hz tone at 1 V RMS and a 2 kHz tone at 1 V RMS. We'll assume that the 100 Hz tone is within the passband of the woofer, the 2 kHz tone within the passband of the tweeter, that both drivers present 8 ohm resistive loads and that the power amp has a voltage gain of 20 V/V (26 dB; a fairly typical figure).

The output of the power amp will consist of a 20V 100 Hz tone summed with a 20V 2 Khz tone. The effective (i.e., RMS) value of the sum will be sqrt(20^2 + 20^2) or 28.28 VRMS. If we connect a single 8 ohm load to the output, the power delivered to the load will be (28.28^2)/8, or 100 W.

If our passive crossover splits this so that the 100 Hz component is sent to the woofer and the 2 kHz component is sent to the tweeter, then the power to each will be

Woofer power= 20^2/8 or 50W
Tweeter power=20^2/8 or 50W

Total power to the two-way speaker = 100W. So far the sums come out OK.

But- at some point in time a positive-going peak of the 100 Hz component will coincide with a positive-going peak of the 2 kHz component. The peak value of each component will be 20*sqrt(2), or 28.28V, so the sum will have a peak value of 56.56V. The same thing will happen, in the opposite direction, when the negative-going peaks coincide.

In order to pass the composite signal without clipping, the amp must be capable of delivering a voltage swing of + & - 56V. Translated into effective sine-wave power, that's 40V RMS or 200W into 8 ohms.

So, now we need a 200W/8 ohms amp to deliver a total of 100W to our speaker.

If we divide the signal into LF and HF components and feed each to a separate amp, we can accomplish the same thing with two 50W/8ohms amps.

I used to run a large-club PA which I designed to deliver 100 dB SPL with 10 dB of headroom at 10 meters in a free field. This required an electrical power input (for each of two speaker systems) of 750W for lows, 450W for mids and 300W for the highs. Taking into account the differing impedances of the speakers (4 ohm lows, 8 ohm mids and 16 ohm highs), to manage this with a passively crossed-over system would have required an amplifier output swing of + & - 260V. This is equivalent to nearly 8500W into 4 ohms. By tri-amping the system, each stack could run from one Carver PM1.5 (one channel for the lows and one for the mids) and a Crown DC300 in bridge mono for the highs.

The advantage should be obvious. Of course, I did have access to the measuring equipment necessary to set up the crossover and system EQ correctly, and the know-how to do so.

In home entertainment systems, the headroom advantage might not be so great, but it still exists. In addition, dividing the audio spectrum before the power amps reduces the intermodulation distortion produced by amp nonlinearity.

Finally, low-level active crossovers can implement higher-order filter functions much more easily than passive filters with the low and complex impedances presented by speaker drivers. Designing, say, a 4th-order Linkwitz-Riley passive speaker-level crossover is no easy task, but with opamps it's almost trivial. It's also a lot easier to make sure that whatever filter transfer functions you've selected are

BTW, if you do run a bi-amped system it's neither necessary or desirable to leave the passive crossovers in the speakers in-circuit. If you do this, the transfer function of each section of the system will be the product of the transfer functions of the filter in the active crossover and that in the passive crossover. That's pretty much guaranteed to mess up the system frequency response around the crossover points.

On sort-of exception- in sound reinforcement systems it's routine to connect a capacitor in series with the voice coils of any mid or high-frequency compression drivers. The purpose is to protect the driver in case an amp goes south and starts pumping DC out of its outputs. The series cap will produce a 6 dB/octave high-pass filter with the voice coil impedance; in this case the rule of thumb is to select a capacitor value which will produce a -3 dB corner frequency at least one octave below the crossover frequency.

mid
2004-Dec-07, 11:13 AM
I was agreeing until the flashlight part, because of the possibillity that you listen more concentrated in an environment with no visual distractions.

Well, that and the fact that the flouorescent tube in our kitchen makes a nasty buzzing noise...

Nicolas
2004-Dec-07, 12:32 PM
I can't play records with my TL desk light on, it buzzes loudly through the music. However, if he's got golden ears and no spearate electrical circuit for his audio installation, he will hear the electrical feed of his equipment buzzing through the speakers.

mid
2004-Dec-07, 01:51 PM
The thing is, I wonder where all these people with 'Golden Ears' live. I thought I could hear a nasty intermittent interference noise on a record I was listening to at the weekend. I tried all sorts of things to stop it, thinking it was a loose connection, or something making the preamp play up. After about 10 minutes, I spotted the problem:

Someone three doors down was cutting patio slabs in their back garden.

How much do these hi-fi buffs spend on stopping any outside noises being audible?

Kaptain K
2004-Dec-07, 04:07 PM
BTW, when I take over the world, the use of RCA connectors for anything will be a hanging offense...
While you're at it, add 1/4" phone plugs for pro audio! XLRs for mic and line level. Speakons and bananas for speaker level.

ktesibios
2004-Dec-07, 10:21 PM
BTW, when I take over the world, the use of RCA connectors for anything will be a hanging offense...
While you're at it, add 1/4" phone plugs for pro audio! XLRs for mic and line level. Speakons and bananas for speaker level.

I can say one thing for 1/4" phone plugs- at least for 1/4" TRS connectors used for balanced lines- there has never been any controversy about how to wire them.

A formal (IEC, also adopted by ANSI and the BSI and, belatedly, by the AES) industrial standard for XLR connectors has exixted since the mid-'70s. It specifies that pin 1 is ground, pin 2 is signal + and pin 3 is signal -. This standard has been universal for microphone connectors since long before the IEC tackled it, but whether a line input or output is wired pin 2 hot or pin 3 hot depends on who manufactured the piece of equipment in question.

It's taken nearly thirty @#$%^ years for the majority of pro audio equipment manufacturers to conform to this standard! I still have to sort out the consequences of pin 2- pin3 mismatches on a nearly daily basis.

Since nowadays the vast majority of recording engineers and assistants have no technical knowledge at all, this is a pitfall that most sessions can't climb out of without having to roust out the poor tech guy, trivial though figuring it out is.

Oh well, manufacturer @#$%-ups and other peoples' ignorance are why I have a job, I suppose... :wink:

Avatar28
2004-Dec-08, 11:06 PM
Here's a question for a couple of you guys. I'm been having some problem with my HT receiver lately. Actually for quite a long time. A year or more at least. Specifically I've got a nasty hum creeping in somewhere in the preamp stage. It's been getting gradually worse. Also the OSD is all wavy, especially when it first comes on or isn't full screen. And the quality when it's not wavy is still worse.

I've tried completely isolating the receiver, having it the only thing plugged in to the outlet and d/c all RCAs and all but one speaker. That hasn't helped. I've moved homes completely and it still hasn't helped. It happens on all inputs and it has no phono input. All I can figure is that it's either something in the preamp stage or something in the power supply section. Oh, the hum DOES get louder if I turn the volume up, though it doesn't seem to to quite the same degree as the audio and I THINK it's still somewhat perceptable even if the volume is turned way down (I COULD be wrong on this, though).

So, anyone got some suggestions on where to look? I'm fairly comfortable working inside electronics and have a basic multimeter to poke around with.

ktesibios
2004-Dec-09, 10:01 PM
Here's a question for a couple of you guys. I'm been having some problem with my HT receiver lately. Actually for quite a long time. A year or more at least. Specifically I've got a nasty hum creeping in somewhere in the preamp stage. It's been getting gradually worse. Also the OSD is all wavy, especially when it first comes on or isn't full screen. And the quality when it's not wavy is still worse.

I've tried completely isolating the receiver, having it the only thing plugged in to the outlet and d/c all RCAs and all but one speaker. That hasn't helped. I've moved homes completely and it still hasn't helped. It happens on all inputs and it has no phono input. All I can figure is that it's either something in the preamp stage or something in the power supply section. Oh, the hum DOES get louder if I turn the volume up, though it doesn't seem to to quite the same degree as the audio and I THINK it's still somewhat perceptable even if the volume is turned way down (I COULD be wrong on this, though).

So, anyone got some suggestions on where to look? I'm fairly comfortable working inside electronics and have a basic multimeter to poke around with.

If you have the hum when the receiver has no connections to other equipment (and this includes any RF and video connections as well) save the speaker and the AC line cord, you've pretty well eliminated a ground loop or faulty signal ground connection as the culprit.

If you've definitely established that the source of the hum is internal to the receiver, I would start by scrutinizing the power supply. The first step is to use an oscilloscope to look at what's on the DC rails in the preamp section. If you don't have a schematic, a simple way to locate the low voltage rails is to look for a familiar analog IC (especially commonly used opamps e.g. a 4558, 5524, 5532, TL07x etc.) and scope its power pins. The supply rails at the point of utilization should be nice clean DC, with no visible ripple and very little noise. Set the scope input to AC coupling and crank up the input sensitivity for a good look.

If you find ripple on a DC rail, you need to work backwards to the raw DC supply. What you're most likely to encounter in a piece of solid-state home entertainment equipment is that the low voltage DC rails come from three-terminal voltage regulator ICs. If so, you can look at the raw and regulated supplies by scoping the chip's input and output pins. A small amount of ripple is normal on the raw supply, but if there's more than perhaps one volt p-p or if the ripple waveform is anything but a smooth sawtooth, you've got a problem on the raw supply, most likely a bad filter capacitor. (A cracked solder joint on a filter cap can produce the same effect; if the power supply section is built on a PC board it's worthwhile to eyeball the solder side for bad joints.)

If you find a high-frequency oscillation, either steady or in bursts, on a regulated supply rail and the raw supply doesn't show signs of a failed filter cap, the most common cause is a funky 3-terminal regulator chip. There are usually low-value (10 uF or so) capacitors connected as bypasses at the input and output terminals; if these go bad regulator stability problems can result, but if I see oscillation on a regulator output I usually change the regulator chip first.

If you find a bad electrolytic capacitor in the power supply, the simplest thing to do is to re-cap the whole schmear while you've got it open. Electrolytic caps are cheap and replacing the lot of them resets the lifetime clock for those components. When replacing electrolytics, I recommend using 105C rated components; these tend to give a longer service life than their 85C counterparts.

If the low voltage supply rails are good, take a look at the high voltage rails for the power amp section. These are usually not regulated; the AC from the power transformer is simply rectified and filtered. At full output, several volts of ripple is normal, but under no-signal conditions it should be negligible compared to the DC value. Again, excessive ripple or funny-looking ripple waveforms are an indication of a probable bad filter cap.

If all the supply rails are good, about all I can suggest is to use the scope to signal-trace, working backwards from the output until you locate the stage where the hum is being introduced, and then hunt for something wrong in that stage.

It's a pity I can't hear it. Ground loop, missing ground and power supply hums have distinctive sounds; listening to the hum will often point an experienced audio techie to the area that most needs investigating.

I hope this is helpful. Good luck with it. :wink:

Avatar28
2004-Dec-09, 11:31 PM
Thanks. Actually, for the heck of it, I called the manufacturer. They told me there is actually a service bulletin on this receiver for this exact issue. Even better, even though the receiver is well out of warranty, they've agreed to go ahead and fix it for me. Yippee! Apparently the problem is with a bad capacitor somewhere (he didn't know exactly where).

Unfortunately, the repair shop said that it could take up to a couple of weeks as they're really swamped in audio right now. Apparently another major audio repair shop recently closed down. It also doesn't help that they're the manufacturer certified service center in this area for a LOT of brands. But the guy was hopeful that if they don't need to do any t/s on it, just do the bulletin that it might not take long at all. Lord, I'd hope not. *I* could replace the freaking cap in about 20 minutes (counting warm up time for the soldering iron).