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Fun with the W5-704D and SB29RDC - MTM and TMM sims

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  • Fun with the W5-704D and SB29RDC - MTM and TMM sims

    I like how this combo is modeling. Jclin4 has a nice MTM project with the W5-704D and XT25 tweeter here: http://techtalk.parts-express.com/blog.php?b=55

    I really wanted to see if a TMM with the XT25 would work, but due to the FS peak in the XT25 and rising low end distortion, I just couldn't get it to fit. So I decided to plug in the new SB29RDC ring tweeter and after a day of pulling my hair out, I finally got it to work with shallow slopes. Then I decided hey why not an MTM, so I did a model for that too. The MTM has LR4 slopes and has a flatter response than the TMM, but of course at the expense of polar response uniformity. The TMM has very flat phase throughout the midrange...will that translate into better sound? Who knows. The TMM has a bit of a peak in the lower treble intentionally, to correct for power response dips as the woofers quickly roll off off-axis. The 5khz peak should disappear within 10-15 degrees, and the 1.7khz bump will be gone by 30 degrees. If a flatter on-axis response is desired, simply change the capacitor in the tweeter network to 8uf.

    Both are 4-ohm designs, and account for 3.5dB of baffle step compensation (floorstander, woofers off ground, placed within 2-3' of walls. Despite the BSC, the design is very sensitive at 93dB nominal. I am a bit skeptical of this and expect a real-world sensitivity of about 91dB. Still, it's a lot more sensitive than most other speakers, improving dynamics and compensating for the somewhat modest 3mm xmax of the midwoofers.

    In terms of cost, both designs will easily come in at under $300 per pair. The driver total comes to $200 per pair, with the TMM XO coming in at about $60 total using all dayton poly caps. The MTM crossover is anywhere from $40 to $85 depending on how much you care about using NPE caps :P

    Here's the TMM:


    And the MTM:
    Last edited by Max_Andrews; 07-17-2009, 06:54 AM.

  • #2
    Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

    Max,

    I would say its a safe bet that either the MTM or TMM would sound very good if someone to were to build it. (You are currently working on a wave-guide with another woofer, correct?) I'm very pleased with the smoothness and lack of harshness of the W5-704D. It still provides much detail.

    I haven't worked with the SB29RDC, but reading from Zaph's comments and measurements, sounds like it might even be smoother than the XT25. To my ears, the XT25 has a tendency to run slightly hot, which I tamed by relatively lower cap values in the high-pass.

    After building the MTM, I much like the sound of multiple mid-woofers over simple MT's. I'm working on a TMM presently. However progress, I am sad to report, is slow. No design or build issues, just a matter of getting my rear-end in gear:

    Tiny TiMMs 2.5-way

    Cheers,
    - John

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    • #3
      Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

      Thanks John,

      Yes the SB29 tweet really is amazing considering the low-end distortion. The one downside is that the large radiating area that gives it great power handling also makes it more directional on the top end. Will this be noticeable in practice? We'll find out... I also really like the high sensitivity of this tweeter - it opens up a bunch of new possibilities with pro woofers that previous tweeters could not keep up with (hence my desire to play with the waveguide).

      Good work so far on the TiMMs, those look fun! I really like the visual appeal of a TMM, and the sonic benefits over an MTM make sense to me. I know what you mean with not getting started and all that - cash is tight for me at the moment so everything I've been doing lately is only on paper :/. But the good news is that if my situation improves I'll have enough speaker designs to keep me busy for the next two years :D

      I find the TMM crossovers very difficult to get to behave the way you want - even more difficult than 3-way crossovers, due to the midrange balance. I think it's easier if you're going for full BSC because then the rolloff of the lower woofer becomes non-trivial, but trying to do 3.5dB BSC with a TMM is really difficult because the .5 woofer is giving you a 6dB boost on the low end when you only want 3.5dB boost :P. This means you've got to get 2dB back into the midrange somehow, I did it by using the SB29 tweeter with a shallow rolloff, which provides some enforcement from 700hz-1.5khz, bringing the mids back into balance. But still there is a little bit of a midbass hump due to the partial BSC issue, so I'm going to guess that these will be on the rich side.

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      • #4
        Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

        Here's a quick rendering of the TMM layout, not a bad looking speaker. It would be even nicer with tapering sides like the PE curved cabs, but I'm afraid I'm not patient enough for that kind of finish :P. One thing I do want to try is lock miter edges, so that the cabinet can be built easily with birch ply and have no need for any further finish besides a quick sand & poly. But of course that means dropping $60 for a new router bit *sigh*:

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        • #5
          Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

          What baffle width you going with here?

          Port size?

          Comment


          • #6
            Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

            Originally posted by Max_Andrews View Post
            Thanks John,

            Yes the SB29 tweet really is amazing considering the low-end distortion. The one downside is that the large radiating area that gives it great power handling also makes it more directional on the top end. Will this be noticeable in practice? We'll find out... I also really like the high sensitivity of this tweeter - it opens up a bunch of new possibilities with pro woofers that previous tweeters could not keep up with (hence my desire to play with the waveguide).

            Good work so far on the TiMMs, those look fun! I really like the visual appeal of a TMM, and the sonic benefits over an MTM make sense to me. I know what you mean with not getting started and all that - cash is tight for me at the moment so everything I've been doing lately is only on paper :/. But the good news is that if my situation improves I'll have enough speaker designs to keep me busy for the next two years :D

            I find the TMM crossovers very difficult to get to behave the way you want - even more difficult than 3-way crossovers, due to the midrange balance. I think it's easier if you're going for full BSC because then the rolloff of the lower woofer becomes non-trivial, but trying to do 3.5dB BSC with a TMM is really difficult because the .5 woofer is giving you a 6dB boost on the low end when you only want 3.5dB boost :P. This means you've got to get 2dB back into the midrange somehow, I did it by using the SB29 tweeter with a shallow rolloff, which provides some enforcement from 700hz-1.5khz, bringing the mids back into balance. But still there is a little bit of a midbass hump due to the partial BSC issue, so I'm going to guess that these will be on the rich side.
            I have a couple of stupid questions ;)

            First, why are TMM's always automatically treated as 2.5 ways, when to me a TMM can just as easily be a simple 2-way, but it never seems to be discussed that way?

            And second, even if it is a 2.5 Way it can be designed to yield any amount of baffle step compensation desired, but it always seems to be referred to as 6dB. Why?

            Jeff
            Click here for Jeff Bagby's Loudspeaker Design Software

            Comment


            • #7
              Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

              Originally posted by dst View Post
              What baffle width you going with here?

              Port size?
              I'm not sure if Max ever built this, but he certainly was having alot of fun with simulations. ;)

              Although he used a different tweeter you can check the Project A link in my signature to give you an idea of internal volumes and port dimensions for 2 W5-704D's in parallel. TMM or MTM should not make much difference, and his baffle width looks visually very close to what I went with.

              Comment


              • #8
                Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

                The XT 25 is best used WITH an impedance compensation network to fully tame the resonance. Much of any "hotness" or fatiguing sound from the XT25 is removed once the impedance peak is dealt with.
                R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                95% of Climate Models Agree: The Observations Must be Wrong
                "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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                • #9
                  Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

                  Have a care if you go with the lock miter. The center spine is fragile in plywood and unusable in mdf. By fragile I mean that it MAY tear out in plywood during a test fit and WILL tear out in mdf. Given these issues, and the setup tedium, I've stopped using the lock miter unless I'm using solid wood.

                  Originally posted by Max_Andrews View Post
                  Here's a quick rendering of the TMM layout, not a bad looking speaker. It would be even nicer with tapering sides like the PE curved cabs, but I'm afraid I'm not patient enough for that kind of finish :P. One thing I do want to try is lock miter edges, so that the cabinet can be built easily with birch ply and have no need for any further finish besides a quick sand & poly. But of course that means dropping $60 for a new router bit *sigh*:

                  I was so much older then, I'm younger than that now.
                  OS MTMs http://techtalk.parts-express.com/sh...d.php?t=220388
                  Swope TM http://techtalk.parts-express.com/sh...d.php?t=221818
                  Econowave and Audio Nirvana AN10 fullrange http://techtalk.parts-express.com/sh...d.php?t=216841
                  Imperial Russian Stouts http://techtalk.parts-express.com/sh...=1#post1840444
                  LECBOS. http://techtalk.parts-express.com/sh...ghlight=lecbos

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                  • #10
                    Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

                    Originally posted by Jeff B. View Post
                    I have a couple of stupid questions ;)

                    First, why are TMM's always automatically treated as 2.5 ways, when to me a TMM can just as easily be a simple 2-way, but it never seems to be discussed that way?

                    And second, even if it is a 2.5 Way it can be designed to yield any amount of baffle step compensation desired, but it always seems to be referred to as 6dB. Why?

                    Jeff
                    What is this a socratic dialogue? ;)

                    Anyway, I'd be interested to hear why you say a TMM can be done as a 2-way. As you probably already know, people assume 2.5-way because they are afraid of lobing problems with the lower woofer. I can understand this concern. Do you not think it's an issue worth worrying about?

                    Also, I agree on the +6 dB. I've found that on designs I've done with a woofer closer to the floor that I've had to dial down the BSC to keep things from sounding tubby.
                    Isn't it about time we started answering rhetorical questions?

                    Paul Carmody's DIY Audio Projects
                    Twitter: @undefinition1

                    Comment


                    • #11
                      Re: Fun with the W5-704D and SB29RDC - MTM and TMM sims

                      Originally posted by Paul Carmody View Post
                      What is this a socratic dialogue? ;)
                      A philo major, and I missed Jeff's use of the socratic method. The internet makes me read (and maybe think) less carefully these days...at least that excuse I'm going with. :o

                      Good catch!

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