Please could someone advice me if this will work safely....?

 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 241
Registered: Sep-04
Amp - NAD 3225PE. Not sure of the exact specs (says 150w on the backplate. Possibly rated at 40-50 wpc; maybe it's 70 wpc?. Switchable impedance between 4 and 8 ohms. 1 pair speaker terminals. Accepts both bare wire and bananas.

Speakers - Gale 3030 biwirable design. Reccomended amp power rating: 15-100 watts. Impedance: 4-8 ohms. Response: 49Hz-20Hz. Sensitiviy: 90db.

PLUS....

Speakers - Gale Monitor single-wiring design. Impedance 6 ohms (nominal). Reccomended amp power: 15-100 watts.

The idea is to see if I can get a little more feeling of 'prescence' in the room, by having the monitors used as 'rear' speakers. It's just a sound reinforcment trick, that if sounds nice, I'll keep on and enjoy. If not, then I can just revert back to the original situation.

The question is:
This equipment is precious to me now and I don't want to damage anything.

Will it work safely?

****************************

The only other method I can think of is to use T-bar connections from my CD player, directly to another amp, working independantly, which can drive the smaller monitors. Obviously, this will cost more in having to buy T-bars for all of my sources and the quality may suffer if I can only get cheap ones.

What'd'all think?

Any answers much appreciated,

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 244
Registered: Sep-04
Plus, T-bars would be a waste of money if it sounds crap.
 

Lester
Unregistered guest
It depends on how stable the NAD is. If it has a protection circut, you can try wiring the speakers in parallel with the NAD set to 4ohms. Bring the volume up slowly, and listen at a lower setting for while. Then bring it up some more. If it shuts down, there's your answer. It must have the preotection mode though, or you could do some damage.

You could wire the speakers in series. This would relieve you of damage worries, although I'm not sure if it's the best way to go in terms of sound quality.

Or, you could look into something like this...

http://www.nilesaudio.com/products/speaker_selection_volume.html

You can wire in parallel, protect your amp, and be able to adjust the balance between the two pairs of speakers. They can be had without volume controls too.

Good luck.

L.
 

J. Vigne
Unregistered guest

Varney - I'd give the DynaQuad hook up a shot if your looking for ambience in the rear. Stick "dynaquad" or "dynaquad hook up" in a search engine to find out more.


 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 245
Registered: Sep-04
Ah.... Thankyou! I half expected you to wave me outta town with the crankiness of the idea.

The NAD is a atable amp. That I know about it. I can look to see exactly what's in it in the way of protection by surfing the NAD afficionado, die-hard sites. As far as I know, they all do, including the old 3020 and it's variants.

If I wired in series, that's one, then the other. I remember the science lesson at school. Does one speaker sound better than another or do they both suffer equally?

In parallel, I assume this means with the use of a switching unit, such as you've linked to? having variable volume/balance would be good, because I just would like to hear a hint of something from the rear, rather than a competitive force from the rear.

And I take it, the ommision of a volume control is in order to simplify the path?

Thanks again,

V



 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 246
Registered: Sep-04
One more thing....

When you say 'series', does this mean to take a cable from the input terminal of the front speaker, feeding it to the back one? Or does this mean something else entirely?

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 250
Registered: Sep-04
J.Vigne,

Could this be what you were refering to?

http://home.indy.net/~gregdunn/dynaco/components/QD1/

Now, reading about this is inspiring, and I qoute:

"The Quadaptor does not add anything to the original program, nor does it in any way alter the content or distortion levels of the signals. It is not a synthesizer."

And the price does not look bad, either. Cheers.

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 251
Registered: Sep-04
BTW....
Series? Pah! It works, and I think sometimes I like the extra 'something', but there seems to be a lack of bass control and detail - even from the original front speakers. This, seems to have affected both sets. It's both an upgrade and a downgrade in one easy move.... Can't go wrong with that, can yer....?!

The wife simply says: "It's muddy", which is the best way to describe it.

Yes, Lester, seems you were right in wondering about sound quality.

V
 

J. Vigne
Unregistered guest

What the picture illustrates is the plug in adapter which was sold by Dynaco in the '70's. It was a more complete arrangement of the dynaquad hook up which allowed more control than pervious models. The most basic dynaquad hook up is a simple connection from the + terminal of the right front speaker to the + terminal of the (single) rear speaker; the - terminal of the rear speaker is hooked to the + terminal of the left front speaker. What this gives through the rear speaker is the sum of the two channels. If you look at this closely, you'll see this arrangement was later to become the Dolby Pro Logic system. Dolby made significant inprovements in out of phase crosstalk cancellation, but, basically this is the arangement for a Pro Logic center channel. If you want to run a pair of rear speakers the connection is from FR+ to RR+; FL+ to RL+; and a wire is connected between the - terminals of the rear speakers. Some connections included a volume control to adjust the level of the rear speakers; while others allowed the rear speakers to be switched out completely. What you derive from this arrangement is the sum of the two channels and it may not work well in all applications; some multi track recordings will give a definitely worse sound due to phase problems. Some listeners preferred the connection be made from the two - terminals of the front speakers since this gave the difference signal which is more similar to what Dolby used for the rear channels of Dolby Surround. This isn't a substitute for a matrix system of any kind since the recovery of information is that which is already existent in the information of a stereo recording. It works spectacularly well with some recordings and is bothersome with others. Dig around the web and see what you find. The dynaquad hook up is usually good for a few grins and will be a lesson in hifi if nothing else. If you decide to make the hook up, always raise the volume on your receiver gradually to check for system compatability. I'm unaware of any amplifiers being damaged by this hook up, which is essentially showing the amp a series connection; but, I wouldn't want your's to be the first I learn about that takes a dislike to the arrangement.


 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 252
Registered: Sep-04
Thankyou. I am always cautious, J.

If the injection of the DynaQuad causes the amp to see a series type load, then how is this different to simply taking an extension from the front speaker, which is truly in series? Or does this mean it sees the load as if it were in series, but the system will sound as it would in parallel (which it is)?

At the moment, I am finding that films and certain TV programming benefits from having the rear speakers, but music CDs do not. This may have something to do with how I am used to listening. Live music always comes from the front in reality, whether we hear reflected sound or not- except my room reflects very little, probably. The focus on the front makes the music more intense and interesting. Hearing someone close a door to the left, slightly behind you, makes movies just that little bit more realistic and this is definitely a far cry from any 4 channel surround arrangement.

V

 

Lester
Unregistered guest
"When you say 'series', does this mean to take a cable from the input terminal of the front speaker, feeding it to the back one? Or does this mean something else entirely? "

V

Series wiring:
Amp + to spkr1 +. Spkr1 - to spkr2 +.
spkr2 - to amp -.

Series wiring works best when all the speakers are the same. There is a mismatch of impedance curves and current draw between different speakers, which will not allow the speakers to perform at their best. Perhaps that's the cause of the "muddy" sound, even though they are of the same make.

L.
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 256
Registered: Sep-04
"Series wiring:
Amp + to spkr1 +. Spkr1 - to spkr2 +.
spkr2 - to amp -."

Eh...?

Thanks Lester,

Yes, they are different models and they are different impedance.... The difference between 4 and 6 ohms.

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 257
Registered: Sep-04
Sorry, I don't understand what you've put there, Lester....

I have it wired like this:

LEFT - Amp to front speaker, front speaker to rear speaker.

RIGHT - Same as above.

Is that what you meant?

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 258
Registered: Sep-04
Now I'm confused, because what you've put there means all the +'s and -'s are all mixed up.
 

J. Vigne
Unregistered guest

"If the injection of the DynaQuad causes the amp to see a series type load, then how is this different to simply taking an extension from the front speaker, which is truly in series? Or does this mean it sees the load as if it were in series, but the system will sound as it would in parallel (which it is)?"

The difference in the Hafler arrangement is the rear speakers will only see the difference or the sum between the two front channels. Two + connections at the front will produce sum (common) information. Two - connections at the front will produce difference information. In a simple parallel or series connection the entire information from the front two channels is sent to the rear; creating, in effect, two stereo systems at each end of the room. In the dynaquad hook up, the information arriving at the rear speakers is not an exact duplicate of the front channels.

The amplifier will see a rather benign impedance change since the hook up is neither a true parallel nor series connection.


 

Lester
Unregistered guest
V..

You're wired in parallel. That brings the impedance down, and puts a grater load on the receiver.

Series wiring lessens the load by increasing the impedance.

Here's some linkage...
http://www.usspeaker.com/speaker%20wiring-1.htm
http://www.termpro.com/articles/spkrz.html

L.
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 267
Registered: Sep-04
Ahh - now I think I get it. Thankyou for the links, Lester and thanks, J for the info.

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 268
Registered: Sep-04
Okay, well., I've digested all I can through the posts and your links and thought long and hard about this.

Troubleshooting:
I feel there needs to be more control over the rear speakers - they need to come down a little in volume because of the fact they are now closer to my listening seat than the front ones. This cancels out all the magic that COULD come from the front, but alas, since I was wired up in parallel, in the mistaken thought I was in series, the sound from both front and rear lost a lot of it's sonic definition.

Conclusion:
The best thing I can come up with is similar to another reader, who wanted to know how to power his subs using a second amplifier.
It looks as though the T-Bar connection from source, across the two amps may be the best way forward. Neither amp nor any speaker will (and correct me if I'm wrong here) be saddled with any greater or lesser load, using this method.

Extraneous info:
The 3030s I have at the front are great; the monitors intended for the back are not so great. Used at a lower volume, with a little more bass applied might just tailor the sound stage to deliver extra bass from the back and near the floor. I will be able to switch them on and off at will, too. The use of one splitter (because good ones might be expensive) limits the sources to just DVD, on which I play music CDs, but since my TV decoder and VCR are daisy chained using SCART, I have a spare set of audio outputs on the decoder to send straight to the rear-duty amp. Other sources, such as vinyl and tape can wait.

2 Questions:
Are there any sonic drawbacks to be had from splitting the signal from source between two amps, apart from the quality of the interconnecting RCA splitter?

General concensus I have found here, says that DVD players don't play CDs as well as dedicated CDPs. I wonder why - and does anyone know of a DVD player which is great on sound with music CDs? Many by now will know my preferences are pretty much NAD, NAD and more NAD! Not the only good make, so will consider others in same league. Budget - £200.

Thanks in advance,

V
 

J. Vigne
Unregistered guest

The only consideration in using two amps would be the quality of the amps. But, by splitting the signal with a simple "Y" connector you are still running the signal in parallel. However, with a quality amplifier there should be little difference between no additional speakers and then a series or parallel hook up. If you want to use the "Y" connector hook up, I would suggest you experiment with speaker placement; even turning the rear speakers into the corner or firing them toward the ceiling to get a more diffuse sound field.


 

Bronze Member
Username: Ca_convert

CardiffUK

Post Number: 54
Registered: Jan-05
I have a similar question if I may be so rude as to hijack this thread...

Can I bi-wire a pair of speakers with one set of speaker outputs terminals by connecting in parallel the tweeter and bass driver to the same amplifier terminals (in this case the C352 which only has one set of speaker terminals)
 

J. Vigne
Unregistered guest

Yes, assuming the speaker is biwirable.


 

Bronze Member
Username: Ca_convert

CardiffUK

Post Number: 55
Registered: Jan-05
Thanks Jan, yes the pre-requisite is that the speakers are bi-wirable (in this case possibly B&W 603 S3's which may replace the dm303's i currently use.

Set up in this way, can I expect to hear any sonic improvements?
Also, can you explain how this can benefit the sound? It's surely adding additional cable run into the complete system, and since the crossover is still required, it must still be having the same effect on phase and impedance etc.

I have always believed rightly or wrongly that the point of bi-wiring is to use an additional seperate power amp to drive the tweeter unit. So, would I potentially be wasting my money on a second set of speaker cables?
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 269
Registered: Sep-04
Hijack away - the more information we have the better.

V
 

J. Vigne
Unregistered guest

Biwiring is no more than two separate cables run from one amplifer to the multiple drivers in the speaker. It doesn't matter whether you run from the same pair of binding posts on the amplifier or from A/B connections; the speaker outputs are all tied to the same output devices inside the amp. Biamping requires two ampilifers and (usually) an external X-over in front of the amplifiers to divide the frequencies to each amp. Triamping, of course, just takes this concept to the next level.

The arguments for and against biwiring are as numerous as any where the subjective listener claims an improvement in sound quality against the objectivist who claims wire is wire and biwiring is voodoo created by unscrupulous marketeers. I can't speak to either claim as the results of biwiring seem quite dependent upon the speaker used. Certainly biwiring has become a trend on speakers and there is no guarantee it will benefit each speaker that has additional binding posts.

In the theory of biwiring the back EMF (elelctro-motive force) of the woofer is pushing current back at the amplifier. This is a claim no one should dispute as the voice coil of a woofer is a motor assembly and so it will produce current. This is a well known fact that amplifier manufacturers have tried to overcome for decades. The most typical way to counter this EMF is with substantial current in the amplifier's power supply. Biwiring resulted from an attempt to eliminate this back EMF from interfering with the smaller current being deliverd to the high frequency driver(s). By separating the ground (return) path between the woofer and tweeter, the most direct path for the EMF to enter the high pass side of the X-over is, theoretically, eliminated. Of course, the argument goes that the wires are connected to the same terminal and separating the wires after the output devices of the amp will have absolutely no effect on the EMF path.

My experience has been much depends on the skill of the X-over designer and this will vary from speaker to speaker. I think you'll find most dealers willing to loan a pair of cables to anyone purchasing speakers. This allows the buyer to try it and then decide. That is the best advice I have on the subject.


 

Bronze Member
Username: Ca_convert

CardiffUK

Post Number: 59
Registered: Jan-05
Thanks Jan for explaining technically what I suspected. i undersstand the back EMF effect (quantified as damping factor by the amp manufacturer) but i couldnt see how biwiring reduced this effect since the siganl must pass through the crossovern (unless the bass driver is unfiltered??)
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 270
Registered: Sep-04
Without even begining to get technical, CA_, the simple answer to "are you wasting money on extra cables" is quite simply "No".

At first, I had the cables crammed into the terminals and later twisted the cables together. Now I am using the banana connections to make things easier and neater.

Well, what can I say? You know what amp I'm using here, so it should take little to assure you you'll love yourself for treating your C352 to the upgrade.

On this old thing, the difference is not just audible, minor or sonically noticable - It's HUGE! I simply would never go back to mono-wired speakers again. There is so much revealed when you knock out that x-over, it doesn't matter what amp you're using (within reason).

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 271
Registered: Sep-04
I can only describe the benefits like this:

When there's a huge rush of sound, such as a crescendo - guitars almost drowning the bass etc, the singer howling over all that, too - you can hear the cymbals twitching away - nice and clear, unnafected while the bass relentlessly chuggs away in the distance, solid and unpreturbed in it's focus.

I welcome the music to get messy, so I can keep putting it to the test.... I have yet to be dissapointed.

V
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 272
Registered: Sep-04
"....i couldnt see how biwiring reduced this effect since the siganl must pass through the crossovern (unless the bass driver is unfiltered??)"

"Of course, the argument goes that the wires are connected to the same terminal and separating the wires after the output devices of the amp will have absolutely no effect on the EMF path."

"My experience has been much depends on the skill of the X-over designer and this will vary from speaker to speaker."

The idea behind the biwiring of speakers is to knock out the x-overs completely. Since the x-over is a network designed to filter hi & lo frequencies away from the respective drivers, it follows that the x-over is a both a complicated system which varies from speaker to speaker in order and quality - and a convenient way to minimize on cabling.

When you remove the binding straps which connect the two sets of terminals together at the back of the speaker, you are in effect, disconnecting the x-over from the plan. The two frequencies are then sent to the tweeters and woofers, seperately. This is what I have been led to believe, anyway. So if there is anything else in there before the speaker, and after the terminal post, then please feel free to contradict. My evidence is in the fact that when you connect only one set up, only one set of drivers become active. You either get a 'tweet' or a 'woof' and nothing in between.

The EMF we are trying to eliminate here is that which is generated during the stoppage of one driver, and bleeds back up into the x-over to interfere with the starting of the other. Of course, a very well designed x-over will do the filtering more efficiently, but to knock it out narrows the margin of error down to around zero.

It can only be one step closer to control and purity, can it not?

V


 

J. Vigne
Unregistered guest

What biwiring accomplishes is what I stated; it removes, hopefully, the common path of return for the voltage the drivers produce. The X-over elements are intact in the circuit and do their proper job of high pass/low pass. If this wasn't done, the tweeter would be seeing the massive voltages and current that should only be directed towards the woofer. Asking the tweeter to reproduce low bass will destroy the tweeter within seconds; the excursions necessary for those frequencies are beyond the limits of the small driver. In turn, sending high frequencies to the woofer will result in distortion, beaming and smearing of the high frequencies as the large driver attempts the small excursions needed for those frequencies. All drivers have a natural roll off above and below their frequency limits, but driving them past their limits will do damage. That is the main function of the X-over; other wise, the drivers would run full range. Any driver not designed for that type of response will be damaged by signals outside its bandwidth.

The amplifier still sees the complexity of the X-over; just not the common ground path.


 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 274
Registered: Sep-04
Ahh Crap!

I really should have stuck to art and origami!!!!

V
 

Larry EE
Unregistered guest
I have just read this thread and feel the need to add some comments.

Regarding the "DynaQuad" system. I never knew there was a technical name for this. I first learned about this in the 70's when I opened a "Four Channel Synthisizer" I bought for about $20. It was so light I had to open it up to see what was in side - nothing but a switch and wire.

This is a simple, yet possibly risky, set-up. With tube amps, because they are more robust than Solid State, there should be no problems if the Left and Right amps have a common ground (-). I have used this with Solid State amps but have always been afraid to allow a DC path between the amps. I have put the largest capacitor I have (3900 uF) in series with the speakers and used at least two 8 Ohm speakers to try to keep separation between the channels.

I need to correct Mr. Vigne on his explaination of what this system does. Attaching to the (+) terminals of both amps to the speaker system gives you the difference between the L/R signals. Connecting the (-) in a common ground stereo should of coarse give you nothing.

Think of it this way: Assume you have a single speaker in the rear. Assume you are using a single 1000Hz tone sine wave for simlicity into both amps. Assume both amps maintain proper phasing and the outputs are in phase with each other. The audio voltage signal goes positive out of both (+) terminals at the same time and there is no voltage produced across the speaker to move the voice coil. Now lets just have the tone come out of the Left amp and nothing from the Right. You have the original signal across the speaker. Hence you have the difference.

Now let's get complicated and feed a 1000 Hz tone into the Left channel and 3000 Hz tone into the Right. We now have the speaker acting as a mixer seeing voltage as the signals go in and out of sync resulting in sound of 1000 Hz, 3000 Hz, 4000 Hz (3000+1000) and 2000 Hz (3000-1000). These Beat frequency signals is a distortion of the original signals heard by the ear.

Now lets throw in the front L & R speakers. Let's go back to a single 1000 Hz tone from the Left channel and nothing from the right. The signal comes out of the L(+) terminal and splits some goes thhough the Left speaker to ground (-) and some goes through the Rear speaker to the R(+) terminal where it splits between the Right speaker and the output stage of the right amplifier. Now go back to complex, multifrequency, individual signals from both channels and think of what is happening.

I hope this helps Varney understand why you can't say if the rear speakers are in series or parallel, this a whole different speaker network.

So, while this setup does give a new dimension to 2 channel stereo sound, it also has potential of adding unwanted distortion.

When Dolby used this simple theory of using the L-R (difference) signal for Surround Sound, they did it on the input, line level, signals where they can get the difference signal by using op-amps before the power amps. This maintains the signal seperation betwenn L & R. They also added some time delay to the resulting signal to give the impression of a larger room as well, then feeds rear channel amp(s) to drive the speakers. Of course now days with DSP there are all knds of tricks in their tool box.

Enough for this post.... Hope it helps.
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 275
Registered: Sep-04
It doesn't in fact help Varney very much in understanding anything, but it does encourage me to stay away from this arrangment, as a neanderthal might understand the danger trying to cross a dual carriageway on foot. I'm afraid I am completely thick when it comes to the subject of frequencies, impedance, current and theories of time travel.

V
 

J. Vigne
Unregistered guest

Larry - Thanks for the reply. My information is based on what I read many, many years ago. It has been years since I tried the arrangement since I've owned amplifiers with separate grounds for many years. I don't doubt my description is incorrect. Much of what I remember about the circuit is from Paul Klipsch's description of a center channel speaker derived from the stereo signal fed to a pair of Klipschorns with a Cornwall speaker in the center. The dynaquad hook up is a variation on that derived signal from what I remember. What I seem to remember from the Klipsch papers was a description of the results when the signal was taken from either the + or - post. I have the paper in a drawer somewhere, but my recollection is the paper suggested an audible signal from either hook up. I also remember Klipsch being very certain, in a Paul Klipsch way of being certain, of the results that could be obtained with both hook ups. I further remember the dynaqaud arrangement being a "iffy" quality depending on the signal feed. (That was one of the improvements of the DynaQuad adapter pictured above; the ability to switch the rear speakers out of the circuit when the stereo signal was not appropriate for the hook up.) Of course Klipsch was writing in the early days of stereo when recording techniques were quite simple and the dyna hook up came after the advent of multi mic, over dubbed recordings.

I have two questions for you.

Doesn't the insertion of the large value capacitor affect the frequency response of the rear speaker?

Obviously the difference signals are fed to the rear channels of Dolby Pro Logic. If they are derived from the + signal feed of the two stereo channels; how is the summed signal of the center channel obtained? As you can tell, it has been years since I read the description and I would appreciate a refresher course.


 

Bronze Member
Username: Ca_convert

CardiffUK

Post Number: 63
Registered: Jan-05
Varney - I didnt like to say anything..:-)

I figured the x over must still be in the circuit as explained by Jan. Still doesnt explain why it sounds better (I dont knbow yet that it does since my 303's are not bi-wirable) Is it just another cable company conspiracy theory..?? OOOh hush my mouth.
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 276
Registered: Sep-04
Wouldn't it be interesting if Larry EE turned out to be none other than Larry? :-)
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 277
Registered: Sep-04
Ah, well I can deduce from this it sounds better because the resonances which get sent back up into the x-over from the stoppage of the drivers are cancelled.

Now that's something I read in an article, but I read this after hearing the benefits. I just assumed x-overs were a way to make it possible to have one set of binding terminals, and that bi-wiring was a way of simplifying things, which of course, is wrong.

I don't think it is a cabling conspiracy at all.

V
 

Bronze Member
Username: Ca_convert

CardiffUK

Post Number: 68
Registered: Jan-05
Varney there is an interesting thread in Speakers on cable conspiracy theories. I would go buy a reel of telephone wire....:-)
 

Larry EE
Unregistered guest
"I have two questions for you.

Doesn't the insertion of the large value capacitor affect the frequency response of the rear speaker?

Obviously the difference signals are fed to the rear channels of Dolby Pro Logic. If they are derived from the + signal feed of the two stereo channels; how is the summed signal of the center channel obtained? As you can tell, it has been years since I read the description and I would appreciate a refresher course. "

Yes, the capacitor is a High Pass filter (as is commonly used for a tweeter's crossover "network"). This is why I wanted to use the largest value I could find. But, I would rather sacrifice the sound fidelity than risk the final power amplifier transistors or power supply by making the DC connection through the speakers.

As for the center channel sound, you need to remember that these systems are processed at the line levels. They are not mixing outputs of power amplifiers at speaker level. You must also realize that todays A/V receivers are digital which allows for all kinds of possibilities after the audio siginal is digitized. It's all done with simple, but fast, AND and OR Gates. But in the older analog systems it would still not be a complicated problem to extract the common signals to create a center channel. My first inclination would be to isolate both L & R with buffer amps, invert the L channel, feed into the (-) input of an op amp and feed the R to the (+) input of this same op amp to emhisize the sum of the two signals. I would then take the difference signal I extracted for the Rear and bounce that against this new signal throough another op amp to remove the non-summed signals for a cleaner, more isolated Center.

To do this on a spreaker level, I would say you would feed the L & R (+) to the Center (+) terminal and ground the (-). but this would tie together L & R defeating the purpose of stereo. Paul may have added isolation of the channels through filtering, or even resistor, networks on both sides before the Center speaker (+).

If you think about it, there should be no need for the center channel if we could all sit in the sweet spot for stereo, but alas, we now look for ways to cheat the system. But, things are much easier now with DSP. Remember, the Center channel was designed for movie theaters where the screen is 30 feet wide and you want to focus the dialog back into the center. Previously, with just two channels, people on the right heard voices to the right that should be in the center. The third speaker helped image the sould closer to the center. I wonder sometimes how much this is needed for a 42" TV. Now, we are talking Home Theater here; for Stereo 2 channel music, I beleive two speakers is the way to go.
 

J. Vigne
Unregistered guest

I understand the cap as a blocking device, but how common is it to find DC on the outputs of a modern amplifier? If you get to the point of DC being present at the output terminals, I would assume you've already experienced problems elsewhere.



I wanted to make certain I understood what I had read 25 years ago and, so, pulled out my "Dope from Hope" papers by P. Klipsch. The original discussion of the phantom center channel was printed in the Journal of the Audio Engineering Society in April 1958, volume 6, number 2. It may be possible to find this on line. As I read the article, it appears Klipsch was interested in both the most satisfactory way to derive the 3rd channel and the most cost efficient way to create much the same effect. As this was a period of experimentation in the art of stereophony, there was an assumption that recordings made with 3 microphones might be the most logical way to produce stereo recordings of large venues with aditional channels required for extreme locations. (The Mercury and RCA recordings being made at this time also assumed the use of three channels and have just recently been introduced in SACD format allowing for the first time the original three track recordings to be heard commercially.) Klipsch used both line and speaker level connections to achieve his third center channel. I would say two things are important to remember in his work; first, the amplifiers all used common grounds; and, secondly, the outputs were all tied to auto-transformers which provided a series of taps for impedance matching.

I should state here that I see no connection made strictly between the - posts of either the line level or speaker level connections to make the difference signal. My error from a bad memory. What is interesting is the number of derived channels the experiments could produce. At one point, using a three channel source, the result was an array utilizing three phantom channels and a "curtain of sound" in the depth field.

...................3.................


..1-3 .........................2-3....



.1................1-2.................2..


In the line level connection the phantom center (from a two channel source) is derived by a connection between the L&R +'s with a simple resistive network to pad the level of the center channel. This arrangement provided over 20dB of canellation between channels which always seems to be the largest problem with passive systems.

Eliminating the third amplifer channel and the mixing network for economy became a matter of taking the signals at speaker level. Here the signal used the different voltages available at the various taps on the auto-transformer to accomplish the padding down of the center. L and R front speakers were connected at the + (8/16 Ohm) tap and the common tap. This being the typical connection for a two channel system. The center was derived from the + (4 Ohm) tap of both L and R channels; the right channel + feeding the + of the center and the left channel + feeding the - of the center. This provided, according to Klipsch, a -6dB signal to the center speaker. This assumed matched speakers in all positions and could be substituted with a L-pad for other systems.

I am still confused by the notes at the end of this article in an appendix- June 1960. In this instance "Fig. 7" is the speaker level connection.

"The alternative circuit of Fig. 7 with its 'difference' derived center channel signal may fall short of perfection in some instances, although for most stereophonic material it is indistinguishable from the performance of the a circuit with a 'sum' derived center channel."

He goes on to provide notes on various ways to achieve a center channel derivation which appear in later papers. My confusion is made worse by the example given in the later paper which describes what I see as essentially the same speaker level connection described as a "sum" circuit.


 

J. Vigne
Unregistered guest

While searching for the Klipsch papers I also found my original drawing for the Dyna circuitry. According to my notes Hafler also utilized both an "active" third channel for a front center with a "passive" single rear speaker derived from the +'s of both the L and R front channels. An alternative is provided for a totally passive front center and rear center(single) speaker to be used with two channel sources. In this instance the single rear speaker's + and - posts are hooked only to the +'s of the front L and R speaker outputs at the amplfier. (The derived front center speaker is where I may have got my mistaken information on the "sum"/"difference" connection of my earlier post. In this connection the derived center is taken from the - connection both at the speakers and the amplifier.) At the amp the R + is connected to the R (front) speaker + and the amp's L + is connected to the L (front) speaker +. There is no direct connection between the - of the amp and the - of the front two speakers. Instead the two -'s of the amp are connected to the - of the center speaker. The + of the center speaker is taken from the - post of each of the front L and R speakers. (The - connection of the front speakers is then made through the center speaker.) My notes indicate any pads would be placed in the + side of the center and rear speakers.


 

J. Vigne
Unregistered guest

Finally, I have a shematic of the QD-1 Dyna Qaudapter pictured in Varney's post of 01/23, 12:44 PM. This adapter provided for two rear speakers and no center speaker. Essentially it takes the rear speakers' signal from the + of the L and R front channels running to the + of each rear speaker. The two rear speakers are then tied together at their - posts. The original design of the Quadapter provided a more complex switching arrangement than my schematic where the rear speakers could be removed from the circuit for balance check. The schematic I have shows the switches as individual units which would make the unit buildable without the specific switch used by Hafler though the complexity of the circuit increases slightly. Basically the - connection at the amplifer is fed to the - connection between the two rear speakers by a 20 Ohm resistor in each channel and then to the 25 Ohm L-pad for balance. In my schematic two extra 25 Ohm L-pads are provided for balance between the rear speakers. A simple on/off switch is placed in the connection to the front speakers to provide the ability to switch the front speakers off. I would assume this was to allow the user to hear whether the rear speakers were actually producing sound as the information from the Dyna post is the signal arriving at the rear speakers would be the "difference" signal.


http://home.indy.net/~gregdunn/dynaco/components/QD1/



 

J. Vigne
Unregistered guest


That certainly clears thing up; doesn't it?


 

J. Vigne
Unregistered guest

Larry, your remark about center channels brings up a debate that has been ongoing on another thread. And your comment about two channels for stereo is a matter of disagreement among some. The original Mercury Living Presence and RCA Living Stereo recordings were done with the assumption three channels would become the accepted method for reproducing stereo music in the home. The advent of 1/4" tape recorders brought that assumption to an abrupt end. As you can see in the examples above, three channels were thought to be common in the early days of stereo experimentation.

As to the center in a HT system, it is an easy move from the theater to the home theater for the extra channel. It provids much the same benefit in the home as it does in the commercial theater; giving a wider listening area for the whole family. Also I can vouch for the variability of speaker set ups in the domestic HT. As the TV's have grown larger and the stereo system moved out of the back room to the living room, speakers are often at the mercy of the room's arrangement. I have set up HT systems were the speakers could barely be considered in the same room because the aesthetics of the room had to be considered first and the sound second.

Finally, it is to the ever increasing wealth of Ray Dolby that he took the passive Dyna hook up and turned it into the digital suround system used in every theater and HT in the world. I understand he is looking to sell stock in his company for the first time on the open market at a figure of around $1 billion.





 

J. Vigne
Unregistered guest

I think my last post on this subject will be on the effectiveness of Klipsch's phantom center. Much of his work in this area was tied into replicating what was put on the original tape with as much accuracy as possible. To best understand the output signal, he did quite a few experiments with microphone placement. He claims his derived third channel center was able to accurately reproduce the sound of a locomotive passing using a recording where only two microphones were used. The microphones had been spaced 100' apart. The left and right speakers were spaced 30' apart with a center speaker.



 

Anonymous
 
joeman12
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