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  1. #1
    Hostboard Member dominique-tanguy's Avatar
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    Interpretation of measurements

    Good morning to all,

    I am not a sound engineer and I need some help to interpret measurements. I obtain reliable results when I place my microphone close to the loudspeaker (blue curve), but when I place it about 1 meter from the cabinet, in order to measure a full range curve for the 3 speakers, I get a severe dip close to 50 Hz (green curve), which is exactly matching the frequency of the second bump of the impedance measurement.

    Is there any relation, like phase issue ?

    Thank you for your help

    Dominique

    close1m
    impdance
    Last edited by dominique-tanguy; August 6th, 2011 at 02:57 AM.
    Altec 825 (515-8G) Altec 1505B (291-16A) IWATA 600(GPA 802-8G) + Mark Levinson No. 29 - Kenwood KD-8030 - DAC Dangerous Source - J-River

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    Senior Hostboard Member Panomaniac's Avatar
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    Re: Interpretation of measurements

    It is interesting that it comes right at the same place as the higher peak. I don't remember seeing that any any measurement I've done.
    Maybe it's a phase cancellation with the port. What happens if you mask the port or move the mic a little bit?

    BTW, is that your new impedance plot with the current port? I see that the second peak is higher than the first.

  3. #3
    Hostboard Member dominique-tanguy's Avatar
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    Re: Interpretation of measurements

    I am doing some testing with an extended (deeper port). The higher peak to the right is not conventional but the FR measurement and the listening are a bit better. See the incredible low resonance value for a 515-8G... (normally 37 Hz free air).

    Moving the microphone doesn't help and I had the same problem with previous port. I will try tomorrow masking the port.

    We are invited by friends this evening...
    Altec 825 (515-8G) Altec 1505B (291-16A) IWATA 600(GPA 802-8G) + Mark Levinson No. 29 - Kenwood KD-8030 - DAC Dangerous Source - J-River

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    Senior Hostboard Member RonSSS's Avatar
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    Re: Interpretation of measurements

    Room response? Or are you measuring this outdoors?

    Ron
    Enjoying Altec Speakers since 1972

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    Hostboard Member dominique-tanguy's Avatar
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    Re: Interpretation of measurements

    i Ron,

    This is room response, 3 ft in front of the loudspeaker cabinet (VOT) for the green curve and just at the end of the front horn for the blue curve.
    Altec 825 (515-8G) Altec 1505B (291-16A) IWATA 600(GPA 802-8G) + Mark Levinson No. 29 - Kenwood KD-8030 - DAC Dangerous Source - J-River

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    Senior Hostboard Member GM's Avatar
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    Re: Interpretation of measurements

    How tall is your ceiling? It looks higher than average, so could be the floor/ceiling eigenmode that would require significant ceiling modification to decay it away. Most rooms [~ 8 ft high] have this notch around 80 Hz where you have a smaller one, so is the exposed beam ~8 ft up?

    GM
    Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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