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Strange response from Dayton AMT Mini-8

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  • tomzarbo
    replied
    Here is the in-box measurement from my Bantams micro speaker which uses the AMT Pod-4 automotive tweeter pair.

    Click image for larger version

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    Somewhat similar dip in a similar place. I used it as a natural low end roll-off on my speakers which used the Dayton ND-91 woofer.
    High cross, but it works fine in the real world.
    The final result was a very flat frequency response.

    TomZ

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  • fpitas
    replied
    Looks like it's a real power dip, not just an off-axis excursion; so you could potentially fill it in with EQ.

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  • Wolf
    replied
    It's a -5dB swing no matter how you look at it.
    Wolf

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  • zx82net
    replied
    Originally posted by Chris Roemer View Post
    Oooh, I'd say there's nothing wrong w/your measurements.
    If you overlay the mfr. curve, they look pretty darn close.
    The mfr. curve shows a -7dB dip @ 6.5k, rolling off below 5.5.
    Yours have a -10dB dip @ 6kHz, w/the rolloff near 4.5k.

    Your shoulder and dip are about 10-15% LOWer than advertised.
    You've nearly got an extra 1k of pass-band, but that's not uncommon.
    It's equivalent to a dome w/a 1k advertised Fs that measures in closer to 850-900.
    I'd say that's often typical.
    Hmm, ok I guess that matches. Their datasheet graph is a little more favorable, there is a 5dB dip, but it looks more like a ripple there. It seems like their 3.5kHz to 40kHz spec is way off the mark. Fortunately the full range I have as a mid doesn't start becoming too directional until a little above 7kHz. I guess datasheets are datasheets, but I kind see this messing up a few designs.
    Attached Files

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  • Chris Roemer
    replied
    Oooh, I'd say there's nothing wrong w/your measurements.
    If you overlay the mfr. curve, they look pretty darn close.
    The mfr. curve shows a -7dB dip @ 6.5k, rolling off below 5.5.
    Yours have a -10dB dip @ 6kHz, w/the rolloff near 4.5k.

    Your shoulder and dip are about 10-15% LOWer than advertised.
    You've nearly got an extra 1k of pass-band, but that's not uncommon.
    It's equivalent to a dome w/a 1k advertised Fs that measures in closer to 850-900.
    I'd say that's often typical.

    Click image for larger version

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    Leave a comment:


  • danmarx
    replied
    Hard to dispute that kind of data, that's definitely these tweeter's response characteristic. It doesn't match the datasheet very well, but then performance can vary in production I suppose. This might be a bit too far off to be acceptable though. At least for a drop-in for an existing design that was presumably based on some other performance characteristic of that tweeter. If you're up for a redesign of the crossover, you could make them work. I think I would just shelve this AMT in this case and find another tweeter. If you're set on the AMT, maybe try the bigger brother, the AMT2-4. Slightly larger face, but plays lower based on specs. Not sure about the AMTs though, never done a build myself with them, done a couple ribbons/planars, they definitely like a higher crossover point compared to domes. Generally speaking. Cool little speaker too, hopefully you can figure something out.

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  • DeZZar
    replied
    Agree, continue that 7K roll off or try a different tweeter.

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  • Billet
    replied
    I know you may be trying to clone an existing design, but can you simply cross the tweeter over at 8k or so. I'm pretty sure that 3" Tang Band will play as high as you need.

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  • zx82net
    replied
    No smoothing:
    Attached Files

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  • zx82net
    replied
    More images:
    Attached Files

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  • zx82net
    replied
    OK, I've now run the tweeter in for about 8 hours and done a load of measurements:
    • with and without crossover
    • horizontal axis scan
    • vertical axis scan
    • distance scan
    • baffle modification
    • gating on/off
    All of these are attached.

    Note: only the tweeter was driven during these tests

    Anything else to try? I'm beginning to think this is a manufacturing problem.
    Attached Files

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  • danmarx
    replied
    Is the measurement dead on-axis with the tweeter? I've seen something similar but only when the mic is directly in the front of the tweeter. Trying moving off axis left or right 10° or so and then up or down and see what you get. Also try moving the mic further away. This looks maybe specific to mic placement. And while it's likely real for that exact location, not necessarily indicative of how the tweeter behaves or sounds as a whole. Also agree with the no crossover measurement, get that out of the loop to make sure it's not interacting in a weird way. Also, you can set the start frequency of your sweep in REW to ~2 kHz.

    Leave a comment:


  • Wolf
    replied
    Is this measured with or without mid in play? Mid could have a breakup peak causing the cancellation. If not connected, then it's an artifact of the tweeter, which last i knew, was not good below 7kHz anyway.
    Wolf

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  • zx82net
    replied
    Originally posted by DeZZar View Post
    What distance have these measurements been taken at and what gating has been applied?
    ~30cm, no gating.

    I was slightly nervous about connecting the AMT to the amp without any crossover, but I can rustle up a capacitor from somewhere.

    Agreed those crossovers are far from optimal, but I'm not actually using the crossover as a crossover, it is just a signal splitter between HF and LF channels in an active 3 way system. The roll-off for the driver is actually controlled by the DSP. There's a diagram here:

    https://techtalk.parts-express.com/f...linkwitz-3-way

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  • DeZZar
    replied
    What distance have these measurements been taken at and what gating has been applied?

    Leave a comment:

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