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Audio Calibration Disc?

Discussion in 'Hi Fi Systems & Separates' started by Crocodile, Mar 26, 2009.

  1. Crocodile

    Crocodile Well-Known Member

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    My head hurts.

    I have a pair of Mission M34i driven by a Rotel RA-1062 with a Squeezebox (FLAC) source. I bought the M34i after my old JPW P1 fell victim to "disintegrating foam-rubber cone suspension" syndrome. I didn't have the opportunity to audition but bought on the strength of the M71i I had on a little Denon UD-M30.

    Unfortunately, at exactly the same time as I bought the M34i, & before I had chance to listen to them, BOTH my amp & CD player expired. I dug out an old Yamaha AV amp & Philips CD player but wasn't really happy with the sound. I put this down to the old amp & shortly after bought another, again a Yamaha AV. This was an improvement but not hugely so.

    Which brings me to the thread title - are there any test/calibration disks around that will help me properly assess exactly what the speakers are doing?
    Last edited: May 6, 2009
  2. karkus30

    karkus30 Well-Known Member

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    It's unlikely to be the xovers. However its not entirely unknown for drive units to be wired out of phase within the speaker cabinet (I'm hoping that you have checked to make sure you have actually wired them in phase from the amp to the speaker terminals?).

    The other thing is damaged drive units and bad termination. It's suprising how little sound is put out by the tweeter and it's unusual to find a faulty unit that has done anything else but blown, so it's pretty easy to check that it is working. The bass units are more difficult, but essentially, if you turn everything off and move the cones gently forward and back by hand, then sometimes you can feel a rough patch. If it does feel rough anywhere within the travel it is faulty.

    These are the typical problems, although there is nothing to say that the Xover does not have a fault. Check these areas first.

    After that you have to start looking at the other components.
  3. BlueWizard

    BlueWizard Well-Known Member

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    How old are the speakers? Unless they are ancient, it is unlikely there is a problem with the crossovers unless it is inherent in the design. Crossovers are nothing but coils and capacitors. There isn't much that can go wrong with a coil of wire. Electrolytic capacitors can deteriorate with age, but no one uses electrolytic capacitors any more. Again, for a poly or mylar capactor to go out of tolerance under normal conditions, it would have to be very old.

    Next, exactly how loud is loud? If you are at ridiculously loud volume, then of course your speakers sound like crappola, any speaker would.

    If you want to burn some CD of audio test tones, check out this thread -

    http://www.avforums.com/forums/speakers/925527-audio-test-tones-several-sources.html

    But I'm inclined to think that, until you clearly define loud, we really can't speculate on the problem.

    Steve/bluewizard
  4. Crocodile

    Crocodile Well-Known Member

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    Thanks for the input guys.

    Speakers are definitely correctly wired, at least externally.

    "Loud" isn't really loud at all. It all goes wrong at around 9 o'clock on the amp & the apparent imbalance starts to kick in much earlier.

    I finally did what I should have done before & hauled my tired, aching back into the loft to retrieve the M71i & hooked them up. They sound very, very similar so that rules out any speaker fault.

    As I said in the OP, I've now had these M34i connected to three different amps, a couple of different ICs & different speaker cable. A/B comparison of CD vs Squeezebox rules out a source problem as they sound virtually identical.

    I'm beginning to think it's actually my aged ears that have become intolerant to anything much above background level, at least as far as heavy rock is concerned. :(

    I'll have a play with the test tones tomorrow so thanks for the links.
  5. navier_stokes

    navier_stokes Member

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    How are you outputting from the squeezebox and at what "volume" level?
  6. Crocodile

    Crocodile Well-Known Member

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    Analogue & I've tried cutting the SB volume by as much as half & cranking the amp instead. Makes little difference.
  7. BlueWizard

    BlueWizard Well-Known Member

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    Any chance you have a Volt/Ohm meter around? If not you can get a basic model from any hardware store for under £10.

    Check the resistance at the speaker cabinet terminals, it should be slightly less than the rating of the speaker. For example, an 8 ohm speaker will read about 6 ohms, a 4 ohms speaker will read about 3 ohms, and a 6 ohm speaker will read about 4.5 ohms. Notice, that is about the suggested reading.

    What you are looking for is not precise values, but gross deviations. For example, an 8 ohms that read 3 ohms.

    Keep in mind that you are not actually measuring the individual speakers, you are measuring the system including the crossover, that complicates things. It is, none the less, a good first indicator. If you can remove the speakers individually, and VERY CAREFULLY, you can disconnect the wire an test each speaker. As already pointed out, you need to make sure you put the wires back on exactly the way they came off to make sure everything stays in the proper phase.

    Also keep in mind, that sometimes a midrange or tweeters will INTENTIONALLY be wired backwards. So, it is not enough to just connect (+) to (+), it has to be they way it was originally wired.

    I'm leaning toward the possibility of a damage speaker. It is possible the original person ran them too loud and for too long, and overheated the voice coils of one or more speakers or possibly even the crossovers, though less likely.

    As someone suggested, on the woofers, have you gently pressed the cones in to see if you could hear the voice coil scraping?

    See if you can get some random speakers, they don't have to be as good as the Missions, and connect them to the amp as a way of determining if the problem is with the amp or the speakers. Also, though not easy, if you can get another amp on your speakers, that might help clear things up.

    Next, you do need to carefully manage you levels. If your source has its own volume control, it is possible you have the source turned up way to high and that is causing distortion on the inputs to the amp.

    1/4 (9 o'clock) or 1/3 (10 o'clock) should be a slightly loud but very comfortable sound level. You should be able to compare it to sources that have a fix output level and determine if your variable source is turned up too high.

    I would suggest you play some sound on your source, but with the volume level turned down, then set the amp volume control to 1/4 or 1/3, then bring up the source level until it is consistent with what you should hear from an amp at 1/4 to 1/3, which is a modest level.

    Again, don't turn the source up to a loud working level using the source volume. In a sense you are calibrating it. 1/4 to 1/3 should be modest casual listening levels and when you bring the source level it, it MUST reflect that.

    Once the source is calibrated, leave it along, and only change the listening volume using the amp level control.

    Finally, though this is an extremely limited test, check out these YouTube videos of other people playing Mission M34i's. Make HUGE allowances for the crappola quality of youtube video, and consider that most of the distortion you are hearing is from the video camera microphone and not the speakers. Also, without exception, anyone showing off their speakers on YouTube is playing them WAY too loud.

    YouTube - Home Hifi

    YouTube - SDC10029

    Is what your hearing here consistent with what you are hearing at home?

    Steve/bluewizard
    Last edited: Mar 26, 2009

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