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Low-Midrange/Mid Enclosure Frequency Response

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  • Low-Midrange/Mid Enclosure Frequency Response

    Not sure if I'm interpreting this frequency response graph correctly. It looks like I get the best Midrange response without an enclosure. I won't be using this driver below 200hz so should I drop the enclosure?

  • #2
    Those results are bizarre, so I suspect your measurement protocol isn't kosher.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      Not sure what I'm lookin' at there - YOUR measurements? Gated? At what? Baffle size? Box particulars? (looks nothing like Scans FR, why do you suppose?)

      With a "Q" of 0.25, I think I'd like to box it up to around 0.70 (0.50 at least).

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      • #4
        I'm sure my measurement protocol is bad. It was consistent between the three measurements I took with the different enclosures, but not a good test of the speaker itself. I just barely learned to connect the Dayton Mic with REW. The large swings in the red might be reflections off the flat cap of the PVC. It did the same when I put the PVC on sheet steel. But when I put the PVC on a folded dog blanket it softened the peaks and troughs.

        Let's see. The RED empty baffle was 4.573 liters, a 4" pvc pipe 24 inches long. The BLUE filled baffle was the same dimensions except filled with fish aquarium carbon pellets until I had 11 inches of free space inside the PVC, or the length of cylinder the enclosure software said was optimum for a sealed box of 2.2 liters. I used the 13 inches of carbon pellets in an attempt to suck the life out of the midrange backwave.

        I'm curious about the QTS of .25. Does that matter across all frequency ranges? Enclosure software explanations say it's good to be at 0.70 QTS but it sounds like they're talking about the bass range below 250hz. Except in the case when the enclosure is too small and overdampens causing a peak around 600hz. (https://www.ht-audio.com/pages/SpeakerBasics.html)

        Seigfried Linkwitz used this .29 QTS Seas driver in his 4 way open baffle design LX521 for lower midrange. His upper midrange has a QTS of .67. And his pair of 10 inch woofers has a QTS of .27. So there must be a combination of specs and use cases to determine baffle design.

        http://www.seas.no/index.php?option=...=44&Itemid=461

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        • #5
          You need to look at your impulse response with your measurement and ignore any crap from the first reflection (i.e. gating the response so only the direct driver created impulse is recorded). the shorter the gate, the higher the cutoff frequency (useful measurement). Generally speaking - 5msec is possible in most rooms (which provides for 1.7 metres in flight time). This is good for 200Hz up. Anything below that, the room / reflections will screw your FR. If you want to compare enclosure rolloff AND / OR baffle changes - you need to measure nearfield then use a tool that can apply baffle step / ripple (from a simulation tool - such as The Edge). then it can combine to your gated response to give you a driver only resposne, including baffle step, ripple.

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          • #6
            Can you find any measurement on-line of the driver in particular? I'd recommend measuring to get close to that to confirm your protocol. Even it means constructing an IEC baffle and comparing to manufacturer measurements - also using the nearfield splice method I mentioned above. This ensures you are getting reliable data which will be essential for box AND crossover design.

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            • #7
              My measurement mic bit the dust. I'll have to wait for the replacement before I can test again. In the meantime, this configuration worked surprisingly well. It's the green 6" Charlotte pipe from Lowe's with a 6x4" white PVC coupling and a 4x4.52" black flexible coupling. They're both filled with those WalMart fleece dog blankets. If you see the green pipe at Lowe's grab a screwdriver and knock on it to see how you like the sound.

              Too bad I can't measure these because I think the small aperture and angle of the white coupling really helped knock down the backwave reflections.

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              • #8
                Another useful measurement is impedance. I'd expect to see some anomalies with your above mounting due to lack of "breathing" space behind the basket / cone (even at lower excursion midrange frequencies). This "backpressue" anomaly should show up as jaggies in the impedance measurement at the resonant frequency.

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                • #9
                  That's excellent. I didn't understand the purpose of impedance testing or how it fit in to speaker design.

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                  • #10
                    Impedance is speaker design. Looking at your chart above it's not obvious how you got that result, just as it isn't obvious with this modeled response:



                    Looking at the impedance for that same model it's obviously some sort of pipe, even without seeing the SPL chart.




                    Stuffing the pipe would show up in the impedance chart as well.



                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

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                    • #11
                      Originally posted by bradley.s View Post
                      That's excellent. I didn't understand the purpose of impedance testing or how it fit in to speaker design.
                      I crudely think of anomalies in an otherwise smooth impedance curve as anything that is "resists or unloads" the cone movement - therefore increases or reduces impedance. An example of impedance increase is an overly stuffed enclosure, backwave pressure. An exanple of unloading would be operation below a ported cabinet's tuning frequency.

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                      • #12
                        Originally posted by bradley.s View Post
                        My measurement mic bit the dust. I'll have to wait for the replacement before I can test again. In the meantime, this configuration worked surprisingly well. It's the green 6" Charlotte pipe from Lowe's with a 6x4" white PVC coupling and a 4x4.52" black flexible coupling. They're both filled with those WalMart fleece dog blankets. If you see the green pipe at Lowe's grab a screwdriver and knock on it to see how you like the sound.

                        Too bad I can't measure these because I think the small aperture and angle of the white coupling really helped knock down the backwave reflections.
                        one question,,,,is the backwave of the speaker actually going INTO the pipe or around the rubber clamped parts ??

                        What are the clamps attached to??

                        COuld you do a from below view?

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                        • #13
                          It utilizes a "gravity clamp".

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                          • #14
                            The driver just happened to be the right size. The top edge of the flexible coupling seals against the driver's aluminum faceplate and around the white coupling. The cone diameter of the speaker is the same diameter as the white PVC inner diameter. As long as I keep the axis of the Charlotte pipe perpendicular to the transverse plane of the Earth's core I don't need to tighten the hose clamps.

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                            • #15
                              Received my new mic today. This is what the green tube looks like on REW.

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