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  • 6ohm drivers in a MTM speaker

    Is it a bad idea to use 2 6ohm drivers in parallel for a MTM speaker? Sorry for the question if this has been discussed before. I do not have a specific build yet, just a concept that I was thinking about.

  • #2
    That would give you a 3 ohm load which will be hard on some amplifiers or may cause the amp to go into protect mode or fail altogether.
    Series gives you 12 ohms which is kind of high. 6 ohm drivers are usually meant for two-way type speakers.

    TomZ
    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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    • #3
      I used the RS150s in parallel at 6.3 ohms each in the Udique project with only a minor dip below 4 ohms.
      John H

      Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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      • #4
        Originally posted by billiam

        Thanks. I was thinking that. Probably best to just stay away from the idea.
        Whoa, hold on now. Not sure why you'd give up so quickly. Not every speaker has to be made for a cheap 8ohm receiver. There are plenty of options for amps that will handle 4ohm and therefore 3ohm loads. Any of the bajillion cheap TPA3116 amps should have no problem, for instance. And there are versions that even do 2 ohm. And there are plenty of commercial speakers that drop to 3ohm. I currently have an MTM that dips to 2.5ohm and plays just fine with the excellent TI Class D amp TPA3251.

        Your MTM would likely be over 3 ohms anyway, maybe 4. And that should be doable for any 4ohm rated amp.

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        • #5
          True, I'm speaking in generalities, it's impossible to say what two '6 ohm' speakers will do impedance-wise at what frequency without testing or simming.

          The problem is that '6 ohm speakers' are like 'car subwoofers' in that... it's a title more or less. It's a generalization to assume that wiring two 6 ohm woofers in parallel will cause issues for an amplifier... or even be '3 ohms.' It all depends on the specific specs of that particular driver. A drivers impedance changes with frequency, and the crossover also has an effect on impedance as well...so it's not a static specification.

          My experience has been that even two 8 ohm drivers in parallel yielding a 4 ohm load can cause problems for an amp when driven hard. My "Cello's" speaker for example dipped to below 3 ohms for part of the lower bass region which caused my rather hearty amp to go into protect mode at louder volumes. We had to fiddle with the crossover a bit to get it to where it wouldn't shut the amp down because of the impedance dip. But that was because of the characteristics of that particular pair of woofers. If I had used two 4 ohm drivers in series yielding an 8 ohm load, that would not have been an issue.

          Starting with '3 ohms' with possible dips below that could cause issues for many amplifiers when cranked up a bit, even good ones..... or it may not depending on the driver or amp. I was speaking more in terms of general guidelines without knowing which driver you were thinking of specifically. It may work out fine for you, or it may present challenges for your intended amplifier...

          ....sticking with 8 ohm drivers in parallel, or 4 ohm drivers in series usually eliminates the possibility of this issue, I think that's why the majority of speakers I've seen use that topology, generally speaking -- and why I said what I said /\ up there.

          TomZ
          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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          • #6
            drivers?

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            • #7
              Originally posted by billiam

              ​Can't a woofer be called a driver as well? Did you not know what was meant by the question? You could always just not respond.
              Before you flip out, all he wants to know is what brand and the number of the woofer. You did this before on this forum. If this is how you react to everything in life you must be a really miserable person.
              craigk

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

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              • #8
                what brand and the (part) number of the woofer?

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                • #9
                  Originally posted by Chris Roemer View Post
                  what brand and the (part) number of the woofer?
                  ​First, let me start off with an apology. craigk brought up something, I have to admit, made me do some thinking. Since being diagnosed with Leukemia, going through chemo, and having it in remission, I have noticed a change in how I react to things. Probably for the worst at times, and I am sorry. On a brighter note, making speakers, getting out into the garage doing stuff, helps me to relax.

                  ​My question was an idea of a concept. I was thinking about 6.5 inch drivers from Dynavox sold by Parts Express. Once I saw that I would probably need to take into account amp issues, I just felt that it was best to drop the subject.

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                  • #10
                    I donít think you can say for sure until you model it. Your resulting impedance curve could be just fine for a four ohm stable amp, especially if your impedance phase is reasonable.
                    Projects:

                    transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                    Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                    References: http://techtalk.parts-express.com/sh...-My-References
                    Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

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                    • #11
                      Almost any good amp can handle a 3 ohm load as long as the phase is not horrible, and you are not lisrening at 120 db. I think you would be fine using the Dynavox if that is what you have.
                      craigk

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

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                      • #12
                        I'm gonna play the P.Poooper here.

                        MOST commonly, an 8n(ohm) "nominal" driver has an "Re" pretty close to 6n, and a set in parallel will load an amp (probably around 200-300Hz) to a 3n minima.
                        Most 8n amps (esp. vintage gear - from 20-40 yrs ago) won't like that kind of a load, esp. if you like to crank it.
                        OTOH, most modern 4n amps are made to be happy pushing into a 3n load, 'cause that's close to the Re of a 4n (nominal) woofer.

                        So, along comes DynaVox w/these "6ohm nominal" drivers. They sport an "Re" spec of 5.2-5.4 ohms.
                        A pair in parallel would load and amp to a minima close to 2.6-2.7 ohms. I'd say NO vintage (8n) amp will like that, and since many have little in the way of protection, it's likely that that magic smoke might be liberated.
                        On a newer ("4ohm") amp, they might be OK, but also could cause trouble at higher volumes.

                        If you HAD to make an MTM w/them, I would: use a 4n stable amp that has short-circuit protection, AND . . you would want to use a series inductor in the low-pass filter w/ high DCR (so, no I-cores or LARGE # inductors need apply). You could even go 3rd order and use TWO series coils, like #18 or #20s. This will alter the "Q" in the box model probably. As always, the REAL answer lies in the simulation.

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                        • #13
                          OTOOH, I just looked at the z-plot for their -622 driver.
                          Their curve shows 6n @ 300Hz.
                          Curious, as personally I'd rate this as an 8n "nominal driver". Also, I don't see their claimed Re near 5.2n anywhere on that plot. YMMV.

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                          • #14
                            Originally posted by billiam View Post
                            Is it a bad idea to use 2 6ohm drivers in parallel for a MTM speaker? Sorry for the question if this has been discussed before. I do not have a specific build yet, just a concept that I was thinking about.
                            Take a look at the Shumakubins loudspeakers designed by Pete Schumacher. MTM+MM
                            "Our Nation’s interests are best served by fostering a peaceful global system comprised
                            of interdependent networks of trade, finance, information, law, people and governance."
                            - from the October 2007 U.S. Naval capstone doctrine
                            A Cooperative Strategy for 21st Century Seapower
                            (a lofty notion since removed in the March 2015 revision)

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                            • #15
                              Originally posted by JRT View Post

                              Take a look at the Shumakubins loudspeakers designed by Pete Schumacher. MTM+MM
                              Hi, would you be able to point me in the direction of a write-up of dimensions, parts, and such? I tried a link from an article I found and either my work is blocking it or it is no longer valid. Looks like an interesting idea for a future project. Thanks

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