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Midwest Audio Fest

It’s that time audio enthusiasts!

Registration for the 2019 Speaker Design Competition is now open! Visit midwestaudiofest.com for details and to list your speaker project.
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We hope to see you this summer!

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Midwest Audio Fest

It’s that time audio enthusiasts! Registration for the 2019 Speaker Design Competition is now open! Visit midwestaudiofest.com for details and to list your speaker project. We are excited to see all returning participants, and look forward to meeting some new designers this year, as well! Be sure your plans include a visit to the Parts Express Tent Sale for the lowest prices of the year, and the Audio Swap Meet where you can buy and trade with other audio fans. We hope to see you this summer! Vivian and Jill
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2x 15w4531 in series

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  • 2x 15w4531 in series

    Hello all,
    In a series of, somewhat expensive mistakes, I have an amp and speakers that really don't care to play together.
    The speakers are an WMTMW design, using all Scanspeak drivers.
    The amp is a handbuilt kt88.
    The mismatch is the low impedances presented by the WMTMW design. 2ea. 18w8531/ 15w8530/ 1ea 6640 tweeter.
    I split out the crossover to bi-amp, (18w's driven by SS), but still have a impedance minima (3.1 ohm) with the 15w's/6640 portion.
    I am wondering, would swapping out the 2x 15w8531's (parallel) for 2x 15w4531's (series, with appropriate xover change), be a possible (though a bit spendy) solution?
    I am currently.....driving them all SS, but really like the tube amp, and would like to use it.
    thanks for looking

  • #2
    What amp are you using that can't handle a 3.1 load. You need an amp upgrade.
    craigk

    " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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    • #3
      Originally posted by RIKKITIK View Post
      Hello all,
      In a series of, somewhat expensive mistakes, I have an amp and speakers that really don't care to play together.
      The speakers are an WMTMW design, using all Scanspeak drivers.
      The amp is a handbuilt kt88.
      The mismatch is the low impedances presented by the WMTMW design. 2ea. 18w8531/ 15w8530/ 1ea 6640 tweeter.
      I split out the crossover to bi-amp, (18w's driven by SS), but still have a impedance minima (3.1 ohm) with the 15w's/6640 portion.
      I am wondering, would swapping out the 2x 15w8531's (parallel) for 2x 15w4531's (series, with appropriate xover change), be a possible (though a bit spendy) solution?
      I am currently.....driving them all SS, but really like the tube amp, and would like to use it.
      thanks for looking
      My Opinion: The thing with tube amps is not so much that they cannot drive low impedances, they just don't perform as well with highly reactive loads, they prefer a more resistive load, a flatter impedance profile. Do you have a 4 ohm option on the tube amps output transformers? Series wiring two woofers is just fine, but you lose voltage sensitivity, you get less output, so it would require you to pad the tweeter down to match the level of the woofers.

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      • #4
        Ummmm, I doubt the doubt in my amp....
        Don Sachs Kootenay 120....
        I also have a Rogue Audio ST90 that has a limitation with the impedance as well.
        Both are KT-88, both have 4 ohm taps.

        The 15w8530's (uncoated) are actually slighty more efficient than the 15w8531's (coated) version.

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        • #5
          Passive crossover? Perhaps you could share the crossover schematic, you never know what the experts here might dig up.

          The designer says 3 ohms is fine, according to a quote in this ad.

          Don Sachs Kootenay 120 KT88 Power Amp For Sale - Canuck Audio Mart

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          • #6
            Your tube amp would actually be happiest with the two 8ohmers in series. Your biamp setup makes it easy to accomodate.
            You will lose no max spl.

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            • #7
              "The designer says 3 ohms is fine, according to a quote in this ad. "
              Speaking with Don directly, and owning the actual amp, it is NOT 3 ohm compatible. 3.5 ohm "iffy", 4 or 8 MUCH better. The Rogue kind of backs up that conclusion.

              "Your tube amp would actually be happiest with the two 8ohmers in series. Your biamp setup makes it easy to accomodate.
              You will lose no max spl."
              Thanks, that's what I was thinking.

              i was trying to post the DATS impedance sweep, but it's saved in PDF "view", and I'm not sure how to import it. But basically, there is little phase rotation at the minima, (< 25 degrees), which (I think) suggests it's an "impedance/current" issue.
              Also, Troels Ellam D with 2x 15w8531's shows a roughly similar minima, so I'm not too sure an x-over redesign with that combo will succeed.
              The speakers are Tyler H3's, I couldn't have purchased the drivers alone, for what I paid for the speakers. They desperately needed a notch filter on the tweeter's fs (6640's). Once I added that, and padded them a bit (1.5-2 dB) they sound really nice,,,,with SS anyway.

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              • #8
                Originally posted by davidB View Post
                Your tube amp would actually be happiest with the two 8ohmers in series. Your biamp setup makes it easy to accomodate.
                You will lose no max spl.
                Thanks,
                I originally misread what you answered.
                After I realized what you were saying, I read up a bit more.
                I always thought you lose 3db in series vs parallel. I read that is not necessarily the case. Agree amp would be happier with 16 ohm. Definitely worth investigating with necessary x-over changes.
                A lot easier on the wallet $ too.

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                • #9
                  Well, voltage sensitivity is an issue with a fully passive system but not here.
                  The same diaphragm area and travel means the same max spl.

                  And if you like expensive caps you will save with higher impedance.

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                  • #10
                    Mucking around with $8K speakers because your amp can't push them?

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                    • #11
                      Originally posted by djg View Post
                      Mucking around with $8K speakers because your amp can't push them?
                      Well, yes/no.....
                      It's more of a, "which dog is dead?" scenario.
                      The speakers msrp IS around $8K, I paid < $3K used.
                      Excellent drivers, nice cabinetry, but not if my "preferred" amp isn't happy with driving them.
                      Trying to decide....
                      Do I abandon the amp?......great sounding amp, but vacuum audio does have "strings attached".
                      Do I abandon the speakers?......high quality drivers, and, "as is", they sound VERY good with an excellent SS amp. They sound OUTSTANDING with the vacuum amp, up to the point that it runs out of current.
                      Is it worth pursuing, and pouring more $$ in them...probably not. But, as I said.....which to abandon?
                      But I did feel it WAS worth asking about and, if, in the process I learn something.....all the better.
                      The series vs parallel adaptation/info was the primary interest in the original question.

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                      • #12
                        I guess doing reversible wiring changes to your speakers is a good first step. Do you still get the impedance dip if you don't bi-amp, run the Tylers with just the tube amp?

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                        • #13
                          Yes, actually two impedance dips if run "full range".
                          One dip to 2.9 ohm at 78hz, another of 3.1 ohm which is fairly broad, from about 150hz to 450hz.
                          Bi-amping, splitting out the woofers from the MTM section, the 3.1 ohm dip remains but is more narrow. The LF filter section of the MTM portion raises the impedance below the roll-off frequency, so the dip narrows but remains.

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                          • #14
                            I'm out of my shallow end of the pool on this, but several designs I've seen have an optional impedance flattening network specifically to accommodate tube amps. Possible you could get some help with that.

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