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ML-2C PROJECT COMPLETED: Custom mid-tweeter arrangement

Discussion in 'McIntosh Audio' started by Johnny_Law, Aug 14, 2016.

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  1. c_dk

    c_dk Addicted Member

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    Location:
    West Michigan
    I should note though that I used a replacement dome and super tweeter, removed the crossover parts RR added to the crossover to affect the midome and tweeter response curves. I also moved the 8 inch and dome crossover -3dB down point up 1000 Hz, if I remember correctly.

    By increasing the level of these drivers I could add acoustic absorbing material around the drivers to minimize the effects caused by the cabinet and large grill woodwork.

    The goal was to spend less than a Franklin per pair and improve their high frequency response to a more modern row 10-12 curve instead of their old timey 25 row curve.
     
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  2. Gregory

    Gregory Soundco Kid Subscriber

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    Potomac Falls, Virginia
    What are the two traces again? Yellow trace is a reference or `baseline´? Are they L & R channels? What exactly is the White trace? Did I not read the post well enough?

    I'll compare your swept data to my stepped CW tests and swept (spectrum analyzer) snapshots. These Mc speakers are heavy in the upper bass region, at least my XR6s are.


    -Greg
     
    Last edited: Nov 10, 2018
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  3. Gregory

    Gregory Soundco Kid Subscriber

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    Got around to picking some values off your Spectrum Analyzer plot.

    JL_data_sheet_256.png
    JL_data_sheet_256.png

    What are the descriptions for the Upper and Lower traces? How much power fed to the speaker(s)? How far was mic from the speaker(s)? Can you send test data in ASCII text or CSV file?

    Here's the raw data plotted in Excel:

    JL_SA_FFT_data.png
    JL_SA_FFT_data.png

    Will need more info to scale traces referenced to their rated sensitivity.

    Is that FFT plot displaying voltage? I have it plotted on a speaker SPL (power) scale.


    -Greg
     
    Last edited: Nov 10, 2018
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  4. Gregory

    Gregory Soundco Kid Subscriber

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    The issue above has been bothering me. See bottom of y-axis on FFT plot is dbFS (dBFS).

    Wiki definition: https://en.wikipedia.org/wiki/DBFS

    "dBFS (or dB FS) is a unit of measurement for amplitude levels in digital systems, such as PCM, which have a defined maximum peak level."

    "The level of 0 dBFS is assigned to the maximum possible digital level. For example, a signal that reaches 50% of the maximum level has a level of −6 dBFS, which is 6 dB below full scale."


    Minus 6 dB which is 50% of Max is a voltage ratio, yes / no? How can the data be referenced to SPL at 1 watt and 1 meter?


    -Greg
     
    Last edited: Nov 10, 2018
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  5. Johnny_Law

    Johnny_Law AK Member Subscriber

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    Oh WOW you are awesome for plotting that out! The app I used is Advanced Spectrum Analyzer PRO: https://advanced-spectrum-analyzer-pro.soft112.com/

    I think it simply plots the sound level seen at the microphone vs. frequency. Perhaps the 0 dbFS is in reference to the peak voltage that the microphone in the cell phone can output?

    On the measurements, I took them while sitting in my chair with the intention of discovering any room acoustics, like bass resonance. I wasn't trying to create a 1 watt @ 1 meter response curve. That's why the power supplied was arbitrary, for the specific task of trying to figure out room acoustics in the abstract. I suppose the next step would be an anechoic speaker measurement, and then a comparison of the two plots, whereby the difference would be the effect of the room acoustics?
     

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