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potential hotrod project - JAMO S 805

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  • potential hotrod project - JAMO S 805

    It's been a while but I figured it would be an attention getter to post my intention and see if anyone has tried measuring the response of the budget Jamo S805 towers. I think the tweeter looks familiar and the woofer may be weak but probably easy enough to make these driver work with an upgraded filter design. I intend to run the usual tests on the drivers in the cabinet without the crossover and then figure out what I have to work with. If the drivers look good but the factory x/o does not then I'll design an new filter network and post my results. For $160/pair my cost NIB how bad can these be?

    Has anyone measured these or the other bookshelf version that uses the same drivers? Just curious and wondering if anyone knows the source info on the factory drivers?

  • #2
    Well, a good crossover is a pearl beyond price, it's true. However, cheap woofers often have small magnets, no shorting rings, and a tiny Xmax. None of that is reworkable. At very low volumes that may not matter. I suppose a high-order crossover on the woofers may keep the IMD down to some extent.

    The cabinet probably needs extensive bracing too, but that's doable.
    Last edited by fpitas; 05-02-2022, 09:21 AM.
    Francis

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    • fpitas
      fpitas commented
      Editing a comment
      The cabinet probably needs extensive bracing too, but that's doable. I suppose a high order crossover on the woofer may keep IMD down to some extent.

  • #3
    Finally got the factory crossover out and was able to get some FR measurements of the raw drivers in-cabinet:

    JAMO FR IN CABINET RAW.docx

    First question - what did I do wrong to show a 150+ dB scale? Assuming that is just an ARTA setting what about the response? It looks like that 5" woofer is actually good up to 3kHz without any nasty breakup. The tweeter shows a steep roll off above 5kHz which was not expected considering how this system sounds as-is. Maybe my old *** ears finally cannot "see" above 10kHz now?

    I did take some LIMP measurements and forgot to copy/paste so I'll have to re-do those to post but what I saw was typical for the TWT plus a WFR in a ported cabinet. FYI - the TWT minimum Z after the resonance peak was about 3kHz so I am considering an 18db high-pass filter. The woofer had a typical rising Z beyond its 80 Hz tuning peak so I may add a Zobel or not.

    The cabinet is typical darker color MDF about 5/8" with a single internal brace with about one square foot of poly damping attached to one side panel and the back.

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    • #4
      What you do is gut it and turn it into a set of Amigas

      But seriously, if those cabinets look at least halfway decent, they might be a decent alternative to building your own cabinets.
      Isn't it about time we started answering rhetorical questions?

      Paul Carmody's DIY Audio Projects
      Twitter: @undefinition1

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      • #5
        OK Paul - thank you for the reply but that is not the point. I am just trying to do something different to prove it is possible to upgrade an existing product. I think you get that. The cabinets are actually really good so I need to decide if it is better to upgrade the crossovers - OR - do an active design with a 4-ch KABD amplifier board and DSP it as best as possible.

        I am kind of disappointed in the lack of response positive or negative on this forum. And personally I expected a little bit more from you Paul because obviously you are a well respected contributor.

        At the risk of getting Canceled I will ask one more time for some constructive feedback or this will be my last post to this Cool Kids Club...

        BTW: no one has bothered to answer any of my tech questions regarding how to use ARTA/LIMP and I think that kind of sucks!

        Comment


        • Steve Lee
          Steve Lee commented
          Editing a comment
          Dude, I feel your pain.
          The issue here is that no-one here is on your time-clock/cycle nor inside your head/sphere of thought right now.
          There was a recent XO design competition and gathering and those very capable people have their own designs and successes and accolades to absorb and enjoy right now - the season for you is not now.
          As Buggers (below) stated - you need to be patient but don't just go away in a huff/anger - keep trying things until someone here has the time and focus to be inspired by your issue.
          It takes decades to get good at this hobby and years to perfect a single design.
          Act like a cat and have thick skin and just keep coming back at it while reading as much as you can and experimenting until you start to understand it all.
          This is one of the most complex yet solvable conundrum hobbies known to man outside of understanding/living with women going through menopause that can be had for mankind.
          Both require time, effort, patience, TOLERANCE and a dedication to just giving up on your desires and settling for what can be achieved without driving into a bridge abutment at 100 MPH.
          Be of good cheer and KNOW that you are not alone, now or ever in this endeavor.

          Best wishes!


      • #6
        For someone asking for FREE advice, being rude and disrespectful is not going to help your cause...Perhaps some patience is advisable.

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        • #7
          Not sure what ARTA/LIMP ? you asked, but (as you most likely know) the 150dB level (you measured) is irrelevant. Relative SPL is all that matters for an XO design. I'm sure there's SOME setting (of TOO MANY to guess at) where you could lower your SPL plot to some reasonable level (like 85-90dB?)

          IIRC (I DID look at your .doc file) your time window was probably set too long (unless your mic-floor/ceiling/walls distance exceeded 8' in all directions). Not that THAT matters much when designing an XO up around 4-5kHz.

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          • #8
            Tip 1: You'll get much better response if you post the pictures directly rather than embedding in a Word attachment. That slows down folks ability to actually see what you're talking about and you'll get better engagement.

            ARTA questions:
            • You didn't include any information on what you're using to measure (mic / interface). There's a good amount of additional background to determine what is going on. My setup dumps FRD files in the -100dB range because the levels are not calibrated. The response calibration is good though, so the relative response curves are fine and I just adjust the dB range up to a useable level in programs and ignore the absolute dB level. I can make a perfectly fine crossover that way, just have no idea what the actual sensitivity is.
            • Did you gate the measurements? Looks like you may have with the mark on the graph at about 150Hz, fairly short gate.
            • You've applied 1/3 octave smoothing, way to heavy handed to see what is going on.
            • That rolloff above 5k is super suspicious, I'm not sure I trust your measurement setup.
            LIMP - you didn't actually post any detail or have any discernable questions on that. I use DATS V2, those with home setup LIMP rigs are pretty rare to help.

            I go through a lot of detail on measurement and crossover design starting with ARTA in this project if that helps.
            Electronics engineer, woofer enthusiast, and musician.
            Wogg Music
            Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

            Comment


            • #9
              Originally posted by VT_Audio View Post
              OK Paul - thank you for the reply but that is not the point. I am just trying to do something different to prove it is possible to upgrade an existing product. I think you get that. The cabinets are actually really good so I need to decide if it is better to upgrade the crossovers - OR - do an active design with a 4-ch KABD amplifier board and DSP it as best as possible.

              I am kind of disappointed in the lack of response positive or negative on this forum. And personally I expected a little bit more from you Paul because obviously you are a well respected contributor.

              At the risk of getting Canceled I will ask one more time for some constructive feedback or this will be my last post to this Cool Kids Club...

              BTW: no one has bothered to answer any of my tech questions regarding how to use ARTA/LIMP and I think that kind of sucks!
              No one is "Canceling" you.

              I will say that a lot of us got our start in DIY Audio by "upgrading" crossovers.

              To me here's your next step:

              Take raw measurements of woofer and tweeter (without crossover components) of FRD and ZMA files. Input these files into some sort of Crossover design software. Then plug in the values of the crossover the speakers came with. From there, start tweaking values until you can come up with something better. Then, buy the crossover parts and take a listen.

              Alternately, you can go full active and use a DSP setup and just play with curves until you get something you like. Although you probably will still want accurate FRD and ZMA data.

              Sorry I don't have any help with ARTA or LIMS. I don't use that software. I hate fighting with measurement software; so pretty much once I got a system that worked for me, I'll keep it going until Windows refuses to run it anymore.
              Isn't it about time we started answering rhetorical questions?

              Paul Carmody's DIY Audio Projects
              Twitter: @undefinition1

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