Turning normal speakers into SDA’s

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Comments

  • delkaldelkal Posts: 568
    mlistens03 wrote: »
    delkal wrote: »
    mlistens03 wrote: »
    Delkal,
    Great to hear that it worked! I’m gonna give it a go tomorrow after school. We have yet to make it to the HobbyTown to pick up resistors. We were literally sitting in the parking lot, when we got invited to lunch and we left. :confused: I don’t know why I couldn’t have just run in, but parents sometimes have reasons for things beyond my reach. Oh well.

    Check the DC resistance of your speakers first so you can get an idea what resistors to use. The Polk M10 bookshelf speakers I used are rated as 8 ohms but the DC resistance was closer to 4.5ohms. I know this is normal but when I wired them with the interconnect the DC resistance dropped below 3 and I started to worry. I would guess two 8 ohm speakers wired with the interconnect is the equivalent of a 4 ohm load. My amp needs a 6 ohm minimum so I added a one ohm 10 watt resistor on each input to make up for this.

    I played the system for a while at moderate to loud volumes and the amp and the resistors stayed cool. But when you wire two speakers in parallel you get lower impedance and that might be a concern. Just be aware.

    I will certainly be careful.
    I’m going to use a set of Boston Acoustics CR-75 speaker’s, which IIRC don’t drop below 6 ohms at any point in their frequency response. I don’t think 3 ohms will be an issue for most amplifiers, especially at the levels I listen at (usually less than 90 DB, so under a watt.)

    Maybe but adding a one ohm resistor at each speaker input will buy you some insurance. Yes you will lose a little power but a resistor won't effect the sound. And you can always turn your amp up a few decibels to compensate.

    And you are going to use a cheap spare amplifier.....aren't you? Most cheap receivers don't like 3 ohm loads. Start off being cautious.

    I didn't get much listening time in yet but I did notice a difference from where I placed the "SDA" speakers. I started with them positioned on the inside of the main speakers but thought I heard a difference when they were place outside. I want to put them further out but for now I don't have an interconnect wire long enough.

    And let us know your opinions when listening,
  • mhardy6647mhardy6647 Posts: 22,951
    mlistens03 wrote: »
    What is up with the top and bottom drivers on the left side in that pic Doc? They seem different from the rest of them all... is that normal?

    No idea -- I know very little about the SDA models; I was busy with graduate school & starting a family in those days. :)

    BTW this is the source document to which I should've provided a link earlier:
    https://us.v-cdn.net/5021930/uploads/attachments/5/2/2/8/4/34018.pdf

  • mlistens03mlistens03 Posts: 2,632
    delkal wrote: »
    mlistens03 wrote: »
    delkal wrote: »
    mlistens03 wrote: »
    Delkal,
    Great to hear that it worked! I’m gonna give it a go tomorrow after school. We have yet to make it to the HobbyTown to pick up resistors. We were literally sitting in the parking lot, when we got invited to lunch and we left. :confused: I don’t know why I couldn’t have just run in, but parents sometimes have reasons for things beyond my reach. Oh well.

    Check the DC resistance of your speakers first so you can get an idea what resistors to use. The Polk M10 bookshelf speakers I used are rated as 8 ohms but the DC resistance was closer to 4.5ohms. I know this is normal but when I wired them with the interconnect the DC resistance dropped below 3 and I started to worry. I would guess two 8 ohm speakers wired with the interconnect is the equivalent of a 4 ohm load. My amp needs a 6 ohm minimum so I added a one ohm 10 watt resistor on each input to make up for this.

    I played the system for a while at moderate to loud volumes and the amp and the resistors stayed cool. But when you wire two speakers in parallel you get lower impedance and that might be a concern. Just be aware.

    I will certainly be careful.
    I’m going to use a set of Boston Acoustics CR-75 speaker’s, which IIRC don’t drop below 6 ohms at any point in their frequency response. I don’t think 3 ohms will be an issue for most amplifiers, especially at the levels I listen at (usually less than 90 DB, so under a watt.)

    Maybe but adding a one ohm resistor at each speaker input will buy you some insurance. Yes you will lose a little power but a resistor won't effect the sound. And you can always turn your amp up a few decibels to compensate.

    And you are going to use a cheap spare amplifier.....aren't you? Most cheap receivers don't like 3 ohm loads. Start off being cautious.

    I didn't get much listening time in yet but I did notice a difference from where I placed the "SDA" speakers. I started with them positioned on the inside of the main speakers but thought I heard a difference when they were place outside. I want to put them further out but for now I don't have an interconnect wire long enough.

    And let us know your opinions when listening,

    I was going to use my Technics SU-v75. Its not a super cheap receiver, but it has devalued a lot. I still don’t trust it though, I’m gonna add some resistors, but I imagine it can’t hurt for a brief test, cause I don’t know when we’ll make it to HobbyTown,
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • mhardy6647mhardy6647 Posts: 22,951
    Here (again FWIW, I am obsessing again...) is the Ur-review of the Ur-SDA loudspeaker, from High Fidelity January 1983.

    https://www.americanradiohistory.com/Archive-High-Fidelity/80s/High-Fidelity-1983-01.pdf
    Starts on page 41

    qs4oeld757by.png
  • FestYboyFestYboy Posts: 3,698
    mlistens03 wrote: »
    What is up with the top and bottom drivers on the left side in that pic Doc? They seem different from the rest of them all... is that normal?

    They are mass plugs for tuning the Fs(?) Of those drivers.
  • delkaldelkal Posts: 568
    mlistens03 wrote: »
    delkal wrote: »
    mlistens03 wrote: »
    delkal wrote: »
    mlistens03 wrote: »
    Delkal,
    Great to hear that it worked! I’m gonna give it a go tomorrow after school. We have yet to make it to the HobbyTown to pick up resistors. We were literally sitting in the parking lot, when we got invited to lunch and we left. :confused: I don’t know why I couldn’t have just run in, but parents sometimes have reasons for things beyond my reach. Oh well.

    Check the DC resistance of your speakers first so you can get an idea what resistors to use. The Polk M10 bookshelf speakers I used are rated as 8 ohms but the DC resistance was closer to 4.5ohms. I know this is normal but when I wired them with the interconnect the DC resistance dropped below 3 and I started to worry. I would guess two 8 ohm speakers wired with the interconnect is the equivalent of a 4 ohm load. My amp needs a 6 ohm minimum so I added a one ohm 10 watt resistor on each input to make up for this.

    I played the system for a while at moderate to loud volumes and the amp and the resistors stayed cool. But when you wire two speakers in parallel you get lower impedance and that might be a concern. Just be aware.

    I will certainly be careful.
    I’m going to use a set of Boston Acoustics CR-75 speaker’s, which IIRC don’t drop below 6 ohms at any point in their frequency response. I don’t think 3 ohms will be an issue for most amplifiers, especially at the levels I listen at (usually less than 90 DB, so under a watt.)

    Maybe but adding a one ohm resistor at each speaker input will buy you some insurance. Yes you will lose a little power but a resistor won't effect the sound. And you can always turn your amp up a few decibels to compensate.

    And you are going to use a cheap spare amplifier.....aren't you? Most cheap receivers don't like 3 ohm loads. Start off being cautious.

    I didn't get much listening time in yet but I did notice a difference from where I placed the "SDA" speakers. I started with them positioned on the inside of the main speakers but thought I heard a difference when they were place outside. I want to put them further out but for now I don't have an interconnect wire long enough.

    And let us know your opinions when listening,

    I was going to use my Technics SU-v75. Its not a super cheap receiver, but it has devalued a lot. I still don’t trust it though, I’m gonna add some resistors, but I imagine it can’t hurt for a brief test, cause I don’t know when we’ll make it to HobbyTown,

    I understand..........But just so you know my brief test stated getting louder and louder! :)

    Do you have speaker stands that puts the SDA drivers at close to the same level as your main speaker drivers? I didn't experiment yet but I am pretty sure you need it that way. Putting something on the floor probably won't work.

    There is a good chance your setup will sound even better than my garage sale / spare parts rig.
  • mlistens03mlistens03 Posts: 2,632
    delkal wrote: »
    mlistens03 wrote: »
    delkal wrote: »
    mlistens03 wrote: »
    delkal wrote: »
    mlistens03 wrote: »
    Delkal,
    Great to hear that it worked! I’m gonna give it a go tomorrow after school. We have yet to make it to the HobbyTown to pick up resistors. We were literally sitting in the parking lot, when we got invited to lunch and we left. :confused: I don’t know why I couldn’t have just run in, but parents sometimes have reasons for things beyond my reach. Oh well.

    Check the DC resistance of your speakers first so you can get an idea what resistors to use. The Polk M10 bookshelf speakers I used are rated as 8 ohms but the DC resistance was closer to 4.5ohms. I know this is normal but when I wired them with the interconnect the DC resistance dropped below 3 and I started to worry. I would guess two 8 ohm speakers wired with the interconnect is the equivalent of a 4 ohm load. My amp needs a 6 ohm minimum so I added a one ohm 10 watt resistor on each input to make up for this.

    I played the system for a while at moderate to loud volumes and the amp and the resistors stayed cool. But when you wire two speakers in parallel you get lower impedance and that might be a concern. Just be aware.

    I will certainly be careful.
    I’m going to use a set of Boston Acoustics CR-75 speaker’s, which IIRC don’t drop below 6 ohms at any point in their frequency response. I don’t think 3 ohms will be an issue for most amplifiers, especially at the levels I listen at (usually less than 90 DB, so under a watt.)

    Maybe but adding a one ohm resistor at each speaker input will buy you some insurance. Yes you will lose a little power but a resistor won't effect the sound. And you can always turn your amp up a few decibels to compensate.

    And you are going to use a cheap spare amplifier.....aren't you? Most cheap receivers don't like 3 ohm loads. Start off being cautious.

    I didn't get much listening time in yet but I did notice a difference from where I placed the "SDA" speakers. I started with them positioned on the inside of the main speakers but thought I heard a difference when they were place outside. I want to put them further out but for now I don't have an interconnect wire long enough.

    And let us know your opinions when listening,

    I was going to use my Technics SU-v75. Its not a super cheap receiver, but it has devalued a lot. I still don’t trust it though, I’m gonna add some resistors, but I imagine it can’t hurt for a brief test, cause I don’t know when we’ll make it to HobbyTown,

    I understand..........But just so you know my brief test stated getting louder and louder! :)

    Do you have speaker stands that puts the SDA drivers at close to the same level as your main speaker drivers? I didn't experiment yet but I am pretty sure you need it that way. Putting something on the floor probably won't work.

    There is a good chance your setup will sound even better than my garage sale / spare parts rig.

    I’ll most likely use my Mission speakers as stands, as the top of their cabinet almost perfectly reaches the top of the wood veneer on my LSi’s.
    I’m getting excited for this!! If the results are as good as you are saying yours were, it may never be taken apart again... :wink:
    Also, a quick question. Could I use a Y-connector on the RCA pre-outs on my Yamaha, and then run that to my power amplifier and the receiver for the SDA effect? Then I wouldn’t have to worry about converting the signal to line level, etc.
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • mhardy6647mhardy6647 Posts: 22,951
    Probably, but you might want to read this before you do, whether you end up goin' for it or not :|

    https://www.rane.com/note109.html

    OK for splitting signals per Rane, kinda less than ideal for mixing outputs (e.g, the time honored sum to mono). :p
  • Viking64Viking64 Posts: 4,232
    FestYboy wrote: »

    plugs

    I never cared for that look.

    xgkqiin51ebz.jpg
  • mlistens03mlistens03 Posts: 2,632
    mhardy6647 wrote: »
    Probably, but you might want to read this before you do, whether you end up goin' for it or not :|

    https://www.rane.com/note109.html

    OK for splitting signals per Rane, kinda less than ideal for mixing outputs (e.g, the time honored sum to mono). :p

    Thanks for sharing that!
    It seems like the way that I would do it is supposedly OK. splitting each main preout signal into two. I have a few of these kicking around, so I’ll try and give that a go tomorrow as well.
    Thanks again, to everyone!
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • delkaldelkal Posts: 568
    mlistens03 wrote: »
    Also, a quick question. Could I use a Y-connector on the RCA pre-outs on my Yamaha, and then run that to my power amplifier and the receiver for the SDA effect? Then I wouldn’t have to worry about converting the signal to line level, etc.

    I don't immediately see anything wrong with it but I don't know. If that works it would be a big advantage to the way I have my system set up. I have dual outs on my CD player. These are fed into two totally different integrated amplifiers / speakers combos. The volume of the main speakers and the SDA speakers is totally independent. I can listen to one or the other (or both) but I have to turn a knob for each. This works for experimenting (and it is cool to listen to just the SDA speakers).

    In your case (if it works) you could set the amount of SDA effect with the SDA integrated amp and it should track the volume changes from your preamp.

    The system I described is different from the signal to line level setup Ken described. I do not get the signal for the SDA side from the main amp's speaker output. I get both signals direct from the CD player.
  • mlistens03mlistens03 Posts: 2,632
    edited September 2018


    Sorry, I wasn’t clear, what I mean is, can I use 2 Y-connector’s to split the left channel into two and split the right channel into two, and then use those two channels for the two amps?
    Thanks!
    Post edited by KennethSwauger on
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • mhardy6647mhardy6647 Posts: 22,951
    Not sure if anyone's interested, but here's what the Hafler (Dynaco) QD-1 Quadaptor looks like.

    44548732302_99072271df_b.jpgDynaco QD-1 front by Mark Hardy, on Flickr

    43689162665_e620445778_b.jpgDynaco QD-1 rear by Mark Hardy, on Flickr
  • It would be relatively easy to create a "Rube Goldberg" SDA. An example would be a pair of RTA15tls (or similar), and a pair of Monitor 4s. Place the Monitor 4s on stands, on the outside of each RTA15. Disconnect the tweeters on the 4s, then connect and invert the signal from the opposite channel. You could even put a 2nd order high pass filter inline, at around 150 Hz to mitigate bass cancellation. A poor mans 3.1tl.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
    Cables: Speaker: Furez 10/2 with GLS Locking Banana Plugs
    Interconnect: Furez 10/2 with SpeakONs
    ICs: Custom Furez by Douglas Connections
    Den:
    Bose 901 Series II Continentals Restored, Re-Built Equalizer with Elna Silmic IIs, Sonicaps, and Silver Mica Caps
    Carver CT-3 Pre, Carver C-500

    dhsspeakerservice.com/
    Exclusive Distributor of Gimpod's Custom SDA Circuit Boards

    "And keep her under 70, would you, huh? Betty likes a slow ride"
  • xschopxschop Posts: 1,074
    2 sets of 5jr's with outer tweets disconnected and inner MWs swapped to 6510s sound great as well with CRS+ crossovers.
    When I first started experimenting I was curious what the sub bass drive inductor would do when the MWs were in separate enclosures.
  • mlistens03mlistens03 Posts: 2,632
    edited September 2018

    Thanks for telling me!
    Could I do what I was talking about, and then connect the bookshelf speakers to the positive and positive terminals on the amp? Would that create the difference signal?
    Sorry if I’m being difficult.
    I did pick up resistors, although HobbyTown didn’t have any 1 ohm resistors that weren’t ceramic, and I don’t know where I could put a very hot resistor. I’m gonna dig around in a broken amplifier that I have here, and see what I can find.
    Thanks again!
    Micah
    Post edited by KennethSwauger on
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • pkquatpkquat Posts: 664
    I'm late to the thread, but I say go for it. It's much easier to do with two separate amps, but much harder to synchronize the volume that way. I've thought of @westmassguy 's example before as an experiment, and even compared the crossovers, although I was mostly looking at the difference in the high pass since people find issue with the tweeter crossover on the RTA15. In theory though you could use a 3.1TL crossover with an RTA15 + M4 combo, but the bass might not be in perfect sync.

    Here's an @mhardy6647 project. Use two identical full range speakers. Split the source. Run one source directly to the inner stereo pair. Run the other source through an equalizer lowered to roughly half volume, and then to the amp wired out of phase. Play with the equalizer to see what cancellation frequency range and volume has the best affect. Play with the spacing and see how the sound stage changes. A side project of this would be to see how different recording styles change the affect.

    Going slightly off topic and relating to the stereo difference signal thread, there are are a variety of recording techniques and microphone types that are supposed to accurately reproduce the sound stage in scale and make use of the the cross talk and natural cancellations. Essentially the microphones are picking up the cross talk and cancellations, and when the speakers are set up just right, the reproduction will be very accurate because they are reproducing the cross talk and cancellations in perfect timing when they reach our ears.

    Further off topic, the 3.1TL has always been a mystery to me. As I understand it for the rest of the range, the dimensional speakers are about 1/2 output of the stereo speakers, either in volume or number of speakers. Based on this, the dimensional speaker on the 3.1 would in theory need to be twice the volume of a single stereo speaker, and likely over driven, so I must be missing something.
  • mlistens03mlistens03 Posts: 2,632
    edited September 2018

    Thanks!
    pkquat wrote: »
    I'm late to the thread, but I say go for it. It's much easier to do with two separate amps, but much harder to synchronize the volume that way. I've thought of @westmassguy 's example before as an experiment, and even compared the crossovers, although I was mostly looking at the difference in the high pass since people find issue with the tweeter crossover on the RTA15. In theory though you could use a 3.1TL crossover with an RTA15 + M4 combo, but the bass might not be in perfect sync.

    Here's an @mhardy6647 project. Use two identical full range speakers. Split the source. Run one source directly to the inner stereo pair. Run the other source through an equalizer lowered to roughly half volume, and then to the amp wired out of phase. Play with the equalizer to see what cancellation frequency range and volume has the best affect. Play with the spacing and see how the sound stage changes. A side project of this would be to see how different recording styles change the affect.

    Going slightly off topic and relating to the stereo difference signal thread, there are are a variety of recording techniques and microphone types that are supposed to accurately reproduce the sound stage in scale and make use of the the cross talk and natural cancellations. Essentially the microphones are picking up the cross talk and cancellations, and when the speakers are set up just right, the reproduction will be very accurate because they are reproducing the cross talk and cancellations in perfect timing when they reach our ears.

    Further off topic, the 3.1TL has always been a mystery to me. As I understand it for the rest of the range, the dimensional speakers are about 1/2 output of the stereo speakers, either in volume or number of speakers. Based on this, the dimensional speaker on the 3.1 would in theory need to be twice the volume of a single stereo speaker, and likely over driven, so I must be missing something.
    Unfortunately, I don’t have the funds for new speakers just for this project. :confused: I do like the ideas though, both Westmassguy and pkquat.
    Post edited by KennethSwauger on
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • Just try and use what you have laying around. No need to invest in crossovers or anything like that. Just for shites and giggles, use any two pair. Only concern, is the load on the receiver/integrated. Two pairs of 8 ohm speakers in parallel is 4 ohms or less.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
    Cables: Speaker: Furez 10/2 with GLS Locking Banana Plugs
    Interconnect: Furez 10/2 with SpeakONs
    ICs: Custom Furez by Douglas Connections
    Den:
    Bose 901 Series II Continentals Restored, Re-Built Equalizer with Elna Silmic IIs, Sonicaps, and Silver Mica Caps
    Carver CT-3 Pre, Carver C-500

    dhsspeakerservice.com/
    Exclusive Distributor of Gimpod's Custom SDA Circuit Boards

    "And keep her under 70, would you, huh? Betty likes a slow ride"
  • mlistens03mlistens03 Posts: 2,632
    That’s something I’m worried about. My speakers for the SDA effect (Boston Acoustics CR-75’s) don’t have any info online about their impedance, other than 8 ohms nominal. I don’t know how to measure the impedance, so my plan is to play it safe and run them on the Crown, which has protection built in, and then use the Technics and the Missions for the mains, because I know that they can run on the Technics just fine.
    I wanted to get some 1 or 2 ohm resistors to wire in series with the speakers, and I still will most likely, but all they had at HobbyTown was ceramic resistors in those resistances, and I don’t know how that’ll work out with how much heat they produce.
    Thanks again!
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • mlistens03 wrote: »
    That’s something I’m worried about. My speakers for the SDA effect (Boston Acoustics CR-75’s) don’t have any info online about their impedance, other than 8 ohms nominal. I don’t know how to measure the impedance, so my plan is to play it safe and run them on the Crown, which has protection built in, and then use the Technics and the Missions for the mains, because I know that they can run on the Technics just fine.
    I wanted to get some 1 or 2 ohm resistors to wire in series with the speakers, and I still will most likely, but all they had at HobbyTown was ceramic resistors in those resistances, and I don’t know how that’ll work out with how much heat they produce.
    Thanks again!
    You can get 100 watt L-Pads for not a lot of coin too, instead of the resistors.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
    Cables: Speaker: Furez 10/2 with GLS Locking Banana Plugs
    Interconnect: Furez 10/2 with SpeakONs
    ICs: Custom Furez by Douglas Connections
    Den:
    Bose 901 Series II Continentals Restored, Re-Built Equalizer with Elna Silmic IIs, Sonicaps, and Silver Mica Caps
    Carver CT-3 Pre, Carver C-500

    dhsspeakerservice.com/
    Exclusive Distributor of Gimpod's Custom SDA Circuit Boards

    "And keep her under 70, would you, huh? Betty likes a slow ride"
  • mhardy6647mhardy6647 Posts: 22,951
    mlistens03 wrote: »
    That’s something I’m worried about. My speakers for the SDA effect (Boston Acoustics CR-75’s) don’t have any info online about their impedance, other than 8 ohms nominal. I don’t know how to measure the impedance, so my plan is to play it safe and run them on the Crown, which has protection built in, and then use the Technics and the Missions for the mains, because I know that they can run on the Technics just fine.
    I wanted to get some 1 or 2 ohm resistors to wire in series with the speakers, and I still will most likely, but all they had at HobbyTown was ceramic resistors in those resistances, and I don’t know how that’ll work out with how much heat they produce.
    Thanks again!
    You can get 100 watt L-Pads for not a lot of coin too, instead of the resistors.

    This is a very good idea!

    As to measuring impedance, it's actually not all that hard to do, at least for a driver sans crossover. I do not know how accurate the results would be when applied to a multi-"way" loudspeaker with an onboard crossover, though. I've never really thought about it.

    http://sound.whsites.net/tsp.htm

    Heck, today one can use a phone instead of a generator to get the needed signals! :p
  • mhardy6647mhardy6647 Posts: 22,951
    pkquat wrote: »
    I'm late to the thread, but I say go for it. It's much easier to do with two separate amps, but much harder to synchronize the volume that way. I've thought of @westmassguy 's example before as an experiment, and even compared the crossovers, although I was mostly looking at the difference in the high pass since people find issue with the tweeter crossover on the RTA15. In theory though you could use a 3.1TL crossover with an RTA15 + M4 combo, but the bass might not be in perfect sync.

    Here's an @mhardy6647 project. Use two identical full range speakers. Split the source. Run one source directly to the inner stereo pair. Run the other source through an equalizer lowered to roughly half volume, and then to the amp wired out of phase. Play with the equalizer to see what cancellation frequency range and volume has the best affect. Play with the spacing and see how the sound stage changes. A side project of this would be to see how different recording styles change the affect.

    Going slightly off topic and relating to the stereo difference signal thread, there are are a variety of recording techniques and microphone types that are supposed to accurately reproduce the sound stage in scale and make use of the the cross talk and natural cancellations. Essentially the microphones are picking up the cross talk and cancellations, and when the speakers are set up just right, the reproduction will be very accurate because they are reproducing the cross talk and cancellations in perfect timing when they reach our ears.

    Further off topic, the 3.1TL has always been a mystery to me. As I understand it for the rest of the range, the dimensional speakers are about 1/2 output of the stereo speakers, either in volume or number of speakers. Based on this, the dimensional speaker on the 3.1 would in theory need to be twice the volume of a single stereo speaker, and likely over driven, so I must be missing something.

    Heh... this will be added to the long list of gotta get a round tuit projects.
  • mlistens03mlistens03 Posts: 2,632
    mhardy6647 wrote: »
    mlistens03 wrote: »
    That’s something I’m worried about. My speakers for the SDA effect (Boston Acoustics CR-75’s) don’t have any info online about their impedance, other than 8 ohms nominal. I don’t know how to measure the impedance, so my plan is to play it safe and run them on the Crown, which has protection built in, and then use the Technics and the Missions for the mains, because I know that they can run on the Technics just fine.
    I wanted to get some 1 or 2 ohm resistors to wire in series with the speakers, and I still will most likely, but all they had at HobbyTown was ceramic resistors in those resistances, and I don’t know how that’ll work out with how much heat they produce.
    Thanks again!
    You can get 100 watt L-Pads for not a lot of coin too, instead of the resistors.

    This is a very good idea!

    As to measuring impedance, it's actually not all that hard to do, at least for a driver sans crossover. I do not know how accurate the results would be when applied to a multi-"way" loudspeaker with an onboard crossover, though. I've never really thought about it.

    http://sound.whsites.net/tsp.htm

    Heck, today one can use a phone instead of a generator to get the needed signals! :p

    Thanks!
    Not Tom or Trey or Jim just Micah
    KEF Q150s, NAD 1155 preamp and 4155 tuner courtesy of DaddyJT, NAD C352 playing power amp, BJC Belden cables, Technics SL3200, Marantz CD6004 courtesy of Clipdat, Salamander Archetype rack, Millenium Falcon :)
    I've always thought the goal of high-end audio was not to have your neighbors bang on the wall and say, 'Turn that darn music down' but to have your neighbors bang on the wall and say, 'Tell your friends to go home and you can practice later this week'.

    Resident Child of Club Polk
  • You may want to look into some digital crosstalk cancellation options. As my screen name suggests, I have used ambiophonics in a small setup which gives similar results to SDA speakers but without the extra drivers and with more options for adjusting parameters. I use the miniambio box which appears to no longer be available but you can purchase a similar item called MiniDSP 2x4 which can run an ambiophonics crosstalk cancellation plugin.
    2 Channel - Polk SDA-2BTL full upgrades, Carver TFM-35, Peachtree iDAC, Chromecast Audio (optical), Bugle II phono pre, Technics SL-1500 w/ M97XE
  • mhardy6647mhardy6647 Posts: 22,951
    FWIW, besides the popular MiniDSP product(s), good ol' PartsExpress just introduced a similar product that is meant to be easier to use out of the box than the MiniDSP gizmos. No hands-on experience, YMMV, etc., etc. -- but seemed worthy of mentioning in the context of this thread, even before the post above. :)

    https://www.parts-express.com/dayton-audio-dsp-408-4x8-dsp-digital-signal-processor-for-home-and-car-audio--230-500
  • mhardy6647mhardy6647 Posts: 22,951
    Apropos of nothing: Happened to be perusing an old, old issue of High Fidelity (courtesy of www.americanradiohistory.com) looking for Something Else Entirely... and happened upon this Rodrigues cartoon. It seemed strangly apt for this thread, so I figured I'd share it here. :)

    5e1zh75k8usr.png
    source https://www.americanradiohistory.com/Archive-HiFI-Stereo/60s/HiFi-Stereo-Review-1967-12.pdf

    The late Charles Rodrigues was the hifi cartoonist (as well as a contributor to Playboy, National Lampoon, and others). :)

    frsobngufchb.png

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