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Brian Eno 3 speaker setup, Hafler circuit, etc.

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#1
I just watched a new video from Paul/PS Audio (
) regarding Brian Eno's suggestion to use a 3rd speaker connected to the positive terminals of your amp, placed behind, to play the uncommon audio from both channels, potentially playing audio not heard with a standard 2-speaker setup.

Does anyone have any experience with this? I'm really tempted to try it in my room, but need a bit of time around work and life to give it a shot.

I'm also wondering if there would then be any benefit to hooking up a 2nd speaker to the negative terminals. I'm guessing not in practice, but in theory there would be audio in both phase directions that are uncommon that would be played by having two speakers behind playing the positive and negative side separately.

b6egq8p8sak11.thumb.jpg.f69ae3176a2efcbdcbbf8bf5794a2120.jpg
 

Vini darko

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#2
Seems a good way to break an amplifier. If you do intend to try this put 10W 4-8ohm resistors in line from each posive terminal to avoid the amp seeing it as a short.
I've done somthing similar to create a center channel before.
My main advice is dont try this with an amplifier you care about.
 

mhardy6647

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#3
The Hafler Dynaquad was all the rage at one point, and (more or less) copied in many quad "synthesizer" schemes in the early-mid 1970s, and "influenced" some of the early, matrixed "quad" and "home theatre" formats.

https://audiokarma.org/forums/index...ically-a-hafler-circuit.744384/#post-10093295

Lafayette's morph of the "Quadaptor" was one of the more interesting variants.
https://worldradiohistory.com/Archive-Catalogs/Lafayette-Catalogs/Lafayette-1972.pdf
1610677074741.png



The original, simple "Hafler circuit" was slightly tweaked (with adjustable level for the ambience loudspeakers) in Dynaco's QD-1 box.

https://worldradiohistory.com/UK/Everyday-Electronics/70s/Everyday-Electronics-1975-04.pdf
1610676020832.png

Dynaco QD-1 front
by Mark Hardy, on Flickr
Dynaco QD-1 rear
by Mark Hardy, on Flickr
Dyna_Quadradapter_schematic
by Mark Hardy, on Flickr

EDIT: Indeed, not all amplifiers will see this as a "friendly amendment". :rolleyes:
see also http://techtalk.parts-express.com/forum/tech-talk-forum/58506-simple-halfler-surround-setup
1610676212014.png
 
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#5
I run a trifield setup on my Meridian system, just three main speakers, and it’s really darn good. The algorithm is different than that described here (and digital, so there’s no amplifier shorting issue), but I can vouch for “stereo+” kinda setups sounding great from a two channel source material.
 

Sal1950

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#6
What's old is new again. LOL
 

tmtomh

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#7
When I was in my mid-teens in the mid-'80s, I saw this setup - the variant with two rear speakers rather than one - discussed in a short article in one of my father's hi-fi magazines, probably Stereo Review. I asked him if we could try it on my little system in my bedroom. We bought a couple of cheap 6x9" oval car audio speakers and a cheap Radio Shack potentiometer. He made simple wood or MDF enclosures for the speakers and stuck the potentiometer in one of those plastic project cases, with an on-off switch. We hooked it all up with zip cord, and put the "rear" speakers under my bed on the floor, each one facing outward to the L and R sides of the bed. The main speakers were on bookshelves on the wall opposite the headboard - in other words I would lay on the bed to listen, and the "surround" speakers were situated beneath me.

The effect was remarkably cool and looking back it was shockingly effective given the weird placement of the surround speakers. It definitely worked best when the potentiometer was set low so that the surround speakers were just detectable - it was more whiz-bang when they were turned up but quickly became fatiguing/annoying. Kept at a low volume relative to the front speakers, though, they were really great. Looking back it also seems that the surround speakers didn't need to have great frequency extension - I would guess those car speakers didn't provide much output below 100-150Hz or above maybe 8kHz, but it didn't matter.

I remember my demo track for the effect with friends and relatives was "Leave It" from my then-newly acquired Yes 90125 CD.

For anyone who's not tried it, I'd highly recommend it. My guess is that the majority of folks would not keep the surround speaker/speakers in their setups in the long term, but it's super-fun to play with and you can set it up for peanuts.
 

Duke

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#8
I suggest positioning the secondary speakers FARTHER away form your ears than the main speakers by at least nine inches. The reason is, the ear will localize sounds according to the where they FIRST arrive from. You want that to be the main speakers, with the secondary speakers ONLY adding later-ariving ambience. Nine inches is just barely enough time delay for the precedence effect to kick in and suppress directional cues from the secondary speakers.

Also, use the protective resistor as recommended no matter how sure you are that the left and right channels of your amp have a common ground. And don't ask me how I know about this. I was just a kid.

My recollection is that the net result varied a lot from one recording to the next. But you could do things like disconnect the main speakers and isolate Brian May's backing vocals on a Queen song because of how he was mixed. Eventually I decided it was more trouble than it was worth to optimize the volume of the secondary speakers from one recording to the next.
 
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Blumlein 88

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#9
I used this for a time. Acoustat Twos up front. Maggie MG2s in the rear. Protective resistance included for the rears. Not really that great.

I ran across this thing with early adjustable digital delay and 100 watt mono amp for this purpose. Connected Maggie's in series and the input was the + terminals of the front amp. This could be good. But wasn't good enough often enough to keep.
 
OP
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Thread Starter #11
This could be good. But wasn't good enough often enough to keep.
At the least, probably good enough to try once and waste a weekend with albums known to have cool effects, especially if I just want to sit and have a listen of Ambient 4.
 

Dimifoot

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#12
:facepalm:

Just get a multichannel system, and upmix your music to more speakers
 

Lorenzo74

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#13
I suggest positioning the secondary speakers FARTHER away form your ears than the main speakers by at least nine inches. The reason is, the ear will localize sounds according to the where they FIRST arrive from. You want that to be the main speakers, with the secondary speakers ONLY adding later-ariving ambience. Nine inches is just barely enough time delay for the precedence effect to kick in and suppress directional cues from the secondary speakers.

Also, use the protective resistor as recommended no matter how sure you are that the left and right channels of your amp have a common ground. And don't ask me how I know about this. I was just a kid.

My recollection is that the net result varied a lot from one recording to the next. But you could do things like disconnect the main speakers and isolate Brian May's backing vocals on a Queen song because of how he was mixed. Eventually I decided it was more trouble than it was worth to optimize the volume of the secondary speakers from one recording to the next.
Sorry but Precedence effect states:
“The precedence effect appears if the subsequent wave fronts arrive between 2 ms and about 50 ms later than the first wave front. This range is signal dependent. For speech the precedence effect disappears for delays above 50 ms, but for music the precedence effect can also appear for delays of some 100 ms.[8]” wikipedia.https://en.m.wikipedia.org/wiki/Precedence_effect

i knew first 20ms is important to keep free from reflections, most important if on same axes as direct sound (check Linkwits website).

your 9inches actually turns back into 1.5 ms. too short delta time to allow brain to separate the content from the added ambience.
therefore i would suggest at least 9 feet or 3meters or 9ms far away if you want to keep a reasonable intelligibility and clarity and do not screw up everything.
Make sense?
Best
 

anmpr1

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#15
Back in the day, with Khorns often spaced widely apart (if you had a large room) there was a pretty large center hole. So Paul suggested a center channel Belle (LaScala) to fill in the blank.


In a 1960 paper Paul suggested:

center.jpg

Method of obtaining a sum signal from two power amplifiers by first reversing phase of one of the input signals.

wide-stage-stereo-electronics-world-march-1960-10_small.jpg


This circuit may upset feedback ratio and cannot be used in all amplifiers.

wide-stage-stereo-electronics-world-march-1960-7_small.jpg


Another method proposed by the author to obtain a sum and difference phantom-channel signal with 1:1 transformer.
 

Duke

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#16
Sorry but Precedence effect states:
“The precedence effect appears if the subsequent wave fronts arrive between 2 ms and about 50 ms later than the first wave front. This range is signal dependent. For speech the precedence effect disappears for delays above 50 ms, but for music the precedence effect can also appear for delays of some 100 ms.[8]” wikipedia.https://en.m.wikipedia.org/wiki/Precedence_effect

i would suggest at least 9 feet or 3meters or 9ms far away if you want to keep a reasonable intelligibility and clarity and do not screw up everything.
If 9 feet of path-length-induced delay were needed to suppress directional cues from reflections, we'd virtually never have decent imaging (nor apparently clarity and intelligibility) in home audio. Not saying 9 feet is a bad idea, just imo not necessary.

What I'm looking at is the first onset of the precedence effect. We need enough path length for this to occur. We are looking for when "fusion" - the perception of hearing a single sound from a single direction - FIRST occurs, and that is given as 1 millisecond:

"fusion occurred when the lag between the two sounds was in the range 1 to 5 ms for clicks"

"humans localize sound sources in the direction of the first arriving sound despite the presence of a single reflection from a different direction. A single auditory event is perceived. A reflection arriving later than 1 ms after the direct sound increases the perceived level and spaciousness (more precisely the perceived width of the sound source)."

I'm not sure where 2 milliseconds comes from, except perhaps that by then the precedence effect is very strong, and can suppress the directional cues of reflections which are LOUDER than the first-arrival sound. If you prefer 2 milliseconds, that corresponds to a path length difference of about 27 inches, which is much easier to achieve than 9 feet. Not that 9 feet isn't preferable, but it may not be practical, and is imo unnecessary for trying out the Hafler circuit. My experience (decades ago) was that if the secondary speakers are closer than the main ones, some sounds are localized at the secondary speakers. Adjusting the path lengths so that the sound from the main speakers arrives first fixed that.

Subsequent readings of AES papers (some by James M. Kates as I recall) led to my current understanding that the ear derives directional cues primarily from the first approximately .68 milliseconds of a sound event, and due to lack of precision this was reported by early researchers as 1 millisecond. This approximately .68 millisecond interval is the time it takes for sound to travel around the head from one ear to the other, and corresponds to a path length of about 9 inches. Up to .68 milliseconds, a repetition of the original signal, or reflection, will be interpreted as a (false) azimuth cue . This is why reflections and diffraction on the face of a loudspeaker can be detrimental to imaging precision, and also why narrow-baffle speakers generally have more precise imaging than wide-baffle speakers (the shorter very-early-reflection paths corresponding to smaller azimuth errors). After .68 milliseconds the precedence effect kicks in and starts to suppresses directional cues from reflections.

(The precedence effect does not suppress loudness and spaciousness cues, therefore spaciousness is enhanced by reflections arriving while it is in effect, as demonstrated by the increase in apparent source width [ASW], or image broadening, which can occur in home audio and in concert halls due to sidewall reflections. Timbre is also affected by reflections which occur while the precedence effect is active, as predicted by loudness cues being accepted.)

Of course I could be wrong.
 
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mhardy6647

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#17

tuga

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#19
I suggest positioning the secondary speakers FARTHER away form your ears than the main speakers by at least nine inches. The reason is, the ear will localize sounds according to the where they FIRST arrive from. You want that to be the main speakers, with the secondary speakers ONLY adding later-ariving ambience. Nine inches is just barely enough time delay for the precedence effect to kick in and suppress directional cues from the secondary speakers.

Also, use the protective resistor as recommended no matter how sure you are that the left and right channels of your amp have a common ground. And don't ask me how I know about this. I was just a kid.

My recollection is that the net result varied a lot from one recording to the next. But you could do things like disconnect the main speakers and isolate Brian May's backing vocals on a Queen song because of how he was mixed. Eventually I decided it was more trouble than it was worth to optimize the volume of the secondary speakers from one recording to the next.
What about slightly delaying the signal on the secondary speakers and reducing the level by some 20dB, maybe band passed?
 

Duke

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#20
What about slightly delaying the signal on the secondary speakers and reducing the level by some 20dB, maybe band passed?
Delay would totally work, and is MUCH easier to do today than when the Hafler hookup first came out. Not sure about bandpassing, I'd have to mull that over a bit. Maybe remove some of the low end if things got muddy, but I don't recall that happening.

When I did this in the early 80's, I used a separate integrated amplifier so I could easily fine-tune the relative level with its volume control. Still it was definitely annoying to not get the proper volume dialed in until the song was halfway over, and this was listening to vinyl so immediately restarting the song, while feasible, was not recommeded.

The reason the volume setting varied so much from one track to the next was that the amount and loudness of the content reproduced by the secondary speakers depended on how the recording was mixed, and often changed from song to song, and even within the song. One song I remember in particular was "Fat Bottom Girls" by Queen. The secondary speakers very clearly and fairly loudly reproduced Brian May's isolated harmonizing vocals at the beginning of the song ("Aaaaaaaaaaah you gonna take me home tonight?"). Sometimes I'd turn the main speakers way down for that part just for fun. Brian May has a beautiful voice... but he just happened to be in the same band as Freddy Mercury!

One of the reasons I moved from the Hafler hookup to polydirectional speakers is that, with proper set-up, ime polydirectionals (including dipoles, bipoles, quasi-omnis, and omnis) can do a good job of conveying the venue's spatial cues with no need for fine-tuning from one mix to the next.

(Along the way I also tried the Carver Sonic Hologram Generator and a similiar device called the Omnisonic Imager, as well as with a DIY knock-off of the Polk Stereo Dimensional Array. All had their upsides and downsides.)
 
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