A Sensitive Speaker

Discussion in 'DIY' started by ultrabike, Mar 1, 2019.

  1. numbercube

    numbercube Acquaintance

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    Do those little wiggles from 200 to 400 Hz in the impedance curve always show in CSD, distortion and / or FR?

    What's also a quality factor when a big woofer is about to be crossed high is the rising impedance in the mids from 200 Hz to 1k. Low slope =usually low distortion...
    This 18" inch woofer from Oberton looks good on paper:
    https://www.oberton.com/en/products/ferrite-loudspeakers/461-18b35.html?showall=&start=0

    fs 32 Hz, Qt 0.32, mms 130 gr, xmax 9 mm, low voice coil inductance.

    https://i.imgur.com/WtuEmZX.jpg
     
  2. Priidik

    Priidik Friend

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    Hard to tell.
    Usually, the heavy coned sub drivers show less distortion in 20..100 Hz range (even with 2.83V),
    perhaps the light-->soft cone produces some 2. harmonic by breakup.
    Haven't seen CSD-s below 100 Hz.
    Most of 2. and 3. order distortion in bass comes from the motor/suspension non-linear characteristics.
    Low inductance in company of high BL indicates the use of heroic means in motor (shorting rings, extended pole piece) which act to reduce distortion in mid/high bass to mids.
     
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  3. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    Resonant modes in drivers usually show up as small peaking in impedance curve. I wouldn’t fret about CSD’s under 100Hz too much as most drivers will operate in pistonic mode and decay will be room dominated.

    Usually the biggest problem with these cheap drivers is a plethora of resonant modes. Especially with those which employ breakup to have more higher frequency extension.
     
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  4. crazychile

    crazychile Eastern Iowa's Spiciest Pepper

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    Great thread. A buddy of mine and I went through a similar mental exercise when he wanted to build an improved Klipsch Cornwall that had the great midrange/top end of the Klipsch LaScala, yet keep the nice slam factor of the Cornwall. This is still a work in progress as he's having some cabinets made professionally.

    I'm not a horn expert by any means but I've noticed that in the Klipsch heritage line the highest efficiency comes from the LaScala, Belle, and Klipschorn models where the bass is horn loaded, but at the expense of losing the deepest bass for efficiency. I don't know if thats always the case with horn loaded bass, or just a Klipsch thing.
     
  5. Armaegis

    Armaegis Friend

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    Sort of a tangential question... In my head I just got this image of a woofer response as an energy distribution chart. So then when you change the loading characteristic of the woofer, does it actually increase/decrease energy or is it simply a redistribution of that total possible energy to different parts of the spectrum?
     
  6. Poleepkwa

    Poleepkwa Friend

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    This had me thinking that my current surrounds are probably too large for it's intended usage.
    Some smart people recommended that the surrounds should be quite a bit smaller than I currently have.
    They act less like pointsource and not " compete" with the fronts as the surrounds are usually quite a bit closer.

    He suggest I put these into a smallish sealed box mounted directly against the wall/roof. http://www.sbacoustics.com/index.php/products/coaxial/6in-sb16pfc25-4-coax/
    These are priced right and the specs seem reasonable.
     
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  7. ultrabike

    ultrabike Measurbator - Admin

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    I dunno about the size of the surrounds, but those SBA coaxials are really nice.
     
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  8. ultrabike

    ultrabike Measurbator - Admin

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    The crossover for the midrange maybe a little too high. Most 6.5" woofers start beam above 2.5 kHz. For this reason and also to remove the need of the notch in the midrange, here is a new proposed design, but take it with a grain of salt. I have not build this (yet).

    For this design I'm not using the 15" low frequency Kappalite. Instead I'm using the Eminence Kappa 15" LFA. Note Eminence makes all kinds of random Kappa woofers. Again this is the LFA variant which is cheaper than the Kappalite, but with a little less xmax (like 5.5 mm which is not bad) and less volume requirements.

    Box (I arranged the midrange and the tweeter side by side to help with driver integration):
    box.PNG

    Ports (4 ports, which ideally should be placed close to the woofer - 4x 4" diameter by 14" depth for 38 Hz F3):
    port.PNG

    Tweeter Xover (2.5 kHz with in the specified range of the tweeter Peerless/Vifa BC25SC08-08 using the 8 ohm variant to ease amplifier load):
    xover_tweeter.PNG

    Midrange Xover (2.5 kHz and 350 Hz - Eminence Alfa 6CBMRA):
    xover_midrange.PNG

    Woofer Xover (350 Hz - Eminence Kappa 15LFA):
    xover_woofer.PNG

    Impedance (5 ohms or above):
    impedance.PNG

    The use of this Kappa 15LFA driver allows for a smaller box: 142 liters. It is still quite large, but not 200 liters.

    If you guys find anything wrong or if I missed something let me know.

    I also did some research about other alternative designs. This falls into the Klipsch Cornwall type speakers with a large 15" woofer. There is the Klipsch RF7 dual 10" woofer alternative. Indeed I found through modeling that such a speaker will go lower and just as loud. But the a tweeter would have to be crossed relatively low since there is no midrange and the 10" woofers start to beam above 1500Hz or even sooner (maybe 1.2 or 1.3 kHz like the RF7). The location of the woofers also starts to act up as there may be some cancellation in the midrange (the two woofers may start to add up oddly close to 1 kHz because of driver offset - which can be handled perhaps by xover of the two woofers). But is a possible and doable design as proven by the RF7 itself. The box would still be about 140 liters, but it would be narrower and deeper... like the RF7.

    I like this one better though. I feel the Forte might fall behind in bass to the RF7 because a single high output 12" woofer may not be able to do what two low Qts 10" woofers can there. But I feel a 15" like this Kappa (or the Cornwall) might do much better. Time will say.
     
    Last edited: Mar 11, 2019
  9. ergopower

    ergopower Friend

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  10. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    I’m skeptical of 12” and 15” woofer integration with compression horns. They will go loud af, but quality wise... I’d be very careful.
     
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  11. ultrabike

    ultrabike Measurbator - Admin

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    Coaxials w compression drivers seem a bit difficult. Mainly because Eminense does not seem to list specifications of the compression driver performance while mounted in their woofers (which acts as a waveguide/horn).

    So, one has to do the characterization.

    I personally would prefer non-coaxial designs that are well specified, if going DIY. Eminence does seem to characterize compression driver performance in a number of their horns.
     
  12. Priidik

    Priidik Friend

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    This could be interesting mated to a 15 or 18 inch woofer + supertweeter: BMS coax
     
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  13. Nano Works

    Nano Works Rando

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  14. murphythecat

    murphythecat Self Imposed Exile

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    why do you put the mid and tweeter next to each other? I understand it improves the bass to mid measurements, but you could just put the tweeter on top of the mid and make the mid-tweeter off center, the woofer in the middle. this should give a even response...
     
    Last edited: Aug 18, 2020
  15. Philimon

    Philimon Friend

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    Speaking of coax, here is an interesting one, compression mid and tweeter.

    What about something like the TitanXL from diysoundgroup? Info here. Not too expensive and seemingly lots of trials/users. They are sold out from diysoundgroup whenever I look for them and are now currently unlisted but that could be because of the site move. Likely could find much info in diy section of avsforums but that site sucks to navigate on mobile.
     
  16. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    BMS also has a bunch as well. They haven't really caught on in PA circles probably due to their high price. For home they'd be a challenge as you'd need pretty huge horn (SEOS 30 minimum) to have horn loading low enough. And then there's the question of sound quality. For the driver you linked to there's a bunch of resonances visible in the impedance graph. You'd need a very complex filter to combat them all and this kind of surgical work with passive high level filters is almost impossible due to part value drift due to age and thermals. It might be doable with convolution based digital filters, but it's hardly elegant.
     
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  17. Nano Works

    Nano Works Rando

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    I realized that I buried my question deep in the reply and it was not easily visible. Direct question for Ultrabike or others here who may easily say Duh! - What software package is generating the outputs shown through most of this thread? It's one I haven't seen before. I used a few, however, this one looks pretty comprehensive with enclosures, baffles, crossovers, etc.
     
  18. ultrabike

    ultrabike Measurbator - Admin

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    For coherence. Sensitive drivers are very large and if I arrange them in the classical way, nulls start to happen depending on sitting position.

    What you are saying could improve performance. But note the proposed arrangement may result in the mid-tweeter being too close to the edge.
     
  19. Priidik

    Priidik Friend

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    Nulls will happen either way, you just turned the problem 90 deg.
    Happy middle way is 45 deg.
     
  20. purr1n

    purr1n Finding his inner redneck

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    Jeff Bagby Crossover Excel is what I use. @ultrabike uses something different. You set alignment for drivers x, y, and z. Then you set listening position / ears. Then you see how much your xovers screw things up as you move listening position. Generally as you move farther away, things stabilize. However important for 1st and 3rd order designs (unless you do strict MTM and blah blah blah) to know which tilt the vertical polar axis goes.

    excel.png
     
    Last edited: Aug 22, 2020

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