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    Running two ST-70's from same source

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    mazeeff

    Posts : 116
    Join date : 2014-01-06
    Age : 61
    Location : Grand Rapids, Michigan, USA

    Running two ST-70's from same source

    Post by mazeeff on Fri Aug 08, 2014 5:25 pm

    I am currently running a 1967 ST-70 with a Shannon Parks driver board. I am considering a 2nd ST-70 connected to the same source, running a 2nd set of identical speakers. The 2nd ST-70 could have a VTA or stock driver board. Do all driver boards have the same inversion/delay between different models? I am concerned about the two ST-70's being out of phase, or adding delay that results in echo/reverb. Does anyone have any experience in doing this?

    Mike

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Running two ST-70's from same source

    Post by Bob Latino on Fri Aug 08, 2014 6:36 pm

    Mike,

    The VTA driver board maintains absolute phase of the incoming audio signal. I am pretty sure that Parks driver board does also. I do not believe that you will ever notice any delay between the amps with two different boards. The Parks board is very similar to the VTA driver board.

    Note - to all reading this .. To see if your amp maintains absolute phase > Get a 1.5 volt DC battery either AA or AAA and two little jumper cables with alligator clips on both ends. Take the grille cloth off your speaker. Pull out one cable from your preamp and leave the other end connected to your amp. Connect one alligator clip to the center pin of the open end of the interconnect and the other alligator clip to the outer shield of the open end of the interconnect. Get your battery and tape the other end of the alligator clip that went to the outer shield to flat NEGATIVE side of the battery. Now > keep your eyes on the woofer of your speaker and touch the alligator clip that went to the center pin of the interconnect to the dimpled (positive) end of the battery for about 1/2 second and note if the woofer moved OUT (the amp maintains absolute phase) or the woofer moved IN (the amp inverts absolute phase). Some may cringe at sending 1.5 volts DC into an amp but I have done this a number of times and it does work. Just do it long enough to see the woofer move OUT or IN and remove the connection. If you have the VTA stepped attenuator you can reduce the input voltage a little by setting the attenuator at half way or something like that.

    Now sometimes certain PREAMPS will invert polarity and if you do use one that does this, any VTA amp will maintain the inverted polarity to your speaker terminals. If this is the case, all you have to do is reverse the positive and negative wires at the speaker terminals to maintain absolute phase linearity of your system. In general you always want the leading edge of a transient sound to cause the speaker to move OUT rather than IN. On my downstairs sytem I have a BAT VK-30SE preamp which has a polarity switch. For nearly all music the positive polarity seems to sound best. One day, I was fooling around with the switch as a vinyl record was playing and noticed that the record seemed to have a better soundstage with the switch in the INVERTED PHASE position. The only thing that I could figure is that during the recording process onto tape or from the tape to the cutting of the master, someone used an amp, preamp. mixer etc. that reversed polarity. Usually recording engineers are aware of such things but mistakes do happen ..

    Bob


    Last edited by Bob Latino on Sat Aug 09, 2014 5:48 pm; edited 1 time in total

    mazeeff

    Posts : 116
    Join date : 2014-01-06
    Age : 61
    Location : Grand Rapids, Michigan, USA

    Re: Running two ST-70's from same source

    Post by mazeeff on Fri Aug 08, 2014 7:12 pm

    Thanks Bob. This is very helpful info!

    audiobill

    Posts : 271
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Running two ST-70's from same source

    Post by audiobill on Sat Aug 09, 2014 7:00 am

    Of interest, from PS Audio:

    Absolute phase, or more properly ‘polarity’, has long been a hot topic. The concept is simple. In a stereo system a positive going waveform should result in the speaker driver moving forward, pushing and compressing the air in the room, rather than pulling and decompressing it, on the leading edge of the instrument or vocal ‘attack’. This is all good until the actual recording itself was made in the wrong polarity. Many of us hear great differences when reversing the polarity of the recording.

    My friend, George Louis refers to himself as the Polarity Pundit, so dedicated to making people aware of this problem as he is.

    I have often questioned why this occurs. It clearly does, I can hear major changes on a per-recording basis. Others can’t. One of my favorite authors, Soundminded (aka Mark Fisher) has weighed in with perhaps the best explanation I’ve yet read.

    “When studying how these instruments vibrate, they vibrate in complex modes called Bessel functions. One part of a string or drum head is moving in one direction while another part is moving in the opposite direction. If you could see the vibrations they’d look like the surface of the sea, seemingly incoherent. But they are not. This is the string or drum head or triangle breaking up into its fundamental and harmonics. You could look at it as vibrating at each of those frequencies one at a time and then adding them together. When they vibrate at harmonic frequencies the string or drum head break up, different parts moving in opposite directions at any given moment. In these cases the term absolute phase makes no sense because whether the first vibration reaching your ear is a compression or rarefaction depends on where you are listening from. Walk around a violinist while he’s playing and see if you hear any difference.

    For blown through instruments, horns which are brass and woodwind instruments, pipe organs, and the human voice the first arriving sound wave is always a compression. This is because air is always blown out through them, never sucked into them. In controlled tests some people are sensitive to phase reversal and some are not.”

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Running two ST-70's from same source

    Post by zx on Sat Aug 09, 2014 9:08 am

    With Audio most if thay can go back an forth in an out of phase.... are sensitive to phase reversal .....
    I can hear an so can other when the Ac is pluged in one way are the other......in phase theres more deeper base.....an the highs are rolled down a littel....i have found this ezeys to tell on the AC  on my ESL speaker bias......Some say the AC makes NO diff....well it sounds better ione way are the other.....
    I found this when i was in the Audio biz in the 80s-90....SS or tubes.....we like a lot of shops had a speaker switch box....an you could ezely go back an forth froum your seat.. on the same speakers an same amp....all CJ tube preamps are out of phase... this let them uses one less tube..keep the audio path shorter.....speakers wire must be reverset..
    Just one mans finding.....




    thanks for the info an site Bob..........

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Running two ST-70's from same source

    Post by sKiZo on Sat Aug 09, 2014 3:16 pm

    Polarity in regard to speaker building is arbitrary enough with some designs that it's not assigned until after the speakers are built and tested. Here's a couple McIntosh upper mids used in their XR series ... notice the polarity dots ...



    Killer speakers by the way ... I plan on being buried in one of my XR16's ...  rabbit

    PS ... that's just with the 035 upper mid element. The other three drivers don't have this issue. Not aware of any other drivers in the McIntosh stable that do ...

    ~~~

    Playing with phase can be fun though. That's basically what the synth modes of my Sansui quads do. Add to that my own version of "sexophonic" sound, where the rear quad channels drive two sets of speakers via a Dynaco Quadraptor. One set is above and slightly behind the great comfy chair, and the other mid height around 10 feet back. The quadraptor allows me to balance those front to back, in effect giving me one set of speakers with incredible depth of field. The Hafler rephase gives just the right touch of remix to keep things "real".

    And that's not all!

    Both rear speaker sets are Bose ... 201's at the rear, and 161's overhead - and we all know how they like to play with dispersion and delay. All in all, it's a one of a kind system that works surprisingly well ...


    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Running two ST-70's from same source

    Post by zx on Sat Aug 09, 2014 6:48 pm

    i must say for years an years the Dynaco Quadraptor was an may i say still is... one of the best way to get that real sound you speak of......i hear you 100%...thanks for point this out...time just keep moveing on....In my room today i have a pr of ML ESLs that i got sounding like the Quadraptor
    funny i need all my audio setups to sound the same...........with are with out tubes....tube just sound so right when this is the open,Big,full sweet sound we like....
    An how about that Hughse.AK-100....hehe..haha...i got mine out... thay wernt even shiping when i got mine ...being in the Audio Biz had it peks....some of my bud say.... i only got in the Biz was to get Audio at the right price...thay were right.. an i was lucky




    thanks for the site Bob...........

    mazeeff

    Posts : 116
    Join date : 2014-01-06
    Age : 61
    Location : Grand Rapids, Michigan, USA

    Re: Running two ST-70's from same source

    Post by mazeeff on Sat Aug 09, 2014 7:10 pm

    What would be the audio impact, if one speaker in a stereo setup, is wired backward? With the L & R channels out of phase, would I expect a reduction in overall volume?

    Mike

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Running two ST-70's from same source

    Post by zx on Sun Aug 10, 2014 8:52 am

    The sound image will move from the center to the left are right.....an you well lose bass....try it an you well see..... an if bouth speakers are wired backwards.....one way well sound better....again the bass well be better one way are the other....
    have fun an get the best sound....for you.




    Thanks for the site Bob.....

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