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Calibration complete

Discussion in 'Home Cinema Buying & Building' started by karkus30, Aug 13, 2004.

  1. karkus30

    karkus30
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    :thumbsup: Took me the best part of 6 hours though. The BFD was the dogs danglies. Now I have a nice graph starting around 18Hz @ 87db right down to 80Hz @ 76 db couple of bumps at around 60Hz but only a couple of db out.

    The acid test is trying a film. But the graph tells me its definitely going to be an improvement. I can now talk with confidence on the subject of Ultra / BFD calibration.
     
  2. Smurfin

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    umm, what exactly does the graph look like? Your response @ 18hz is +11db over that @ 80hz?:confused:
     
  3. Daneel

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    I know a lot of people recommend a "house curve" (higher output as the frequency drops) but 11 dB sounds a bit much. Still, as long as it sounds good!

    With the Ultra I'm really hoping that between placement, phase control and PEQ I can get by without a BFD. Apart from anything else, there's nowhere to put that damn thing!
     
  4. ShinObiWAN

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    House curves are brilliant for HT in my opinion but less desirable for music.

    To the that effect I have two BFD setting which are geared towards each.

    Regarding the +11dB gradient on the frequency plot, its almost exactly what I use and I find it perfect for really creating some awesomely deep effects on movies.
     
  5. karkus30

    karkus30
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    Just to try and answer all those points !

    The graph is a nice undulating line, dropping smoothly down to the crossover point at 80Hz.

    In my room, the original graph had a peak of around 5db @20Hz, huge peak @ 31.5Hz of around 12db and began to get into serious decline @40Hz by 56Hz it was -20db !

    This was exactly how it sounded during a film. Essentialy, once the Xover frequency was reached the lower mid range collapsed until really low bass effects kicked in at around 40Hz.

    I can really see how I can improve on these results as the graph is fairly flat, it would mean a serious cut throughout the 18Hz to 40Hz level, which would no doubt completely scew up the curve.

    I only use this system for films.

    The acid test is still to come. After 6hrs I was loosing the will to live, so putting a film on , didnt appeal.
     
  6. Smurfin

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    I know what you mean....it's good fun but it gets to the point where you just think.....oh please let me get it right this time :D

    re: the +11db variance, of course if it DOES sound good in your room then that's all that matters, however in my own experience a difference of that much simply results in overblown bass, and movies with seriously low bass just get fatigueing. Having ANY frequency +11db over others is something I'd DEFINATELY be trying to tame. Just imho of course:)
     
  7. karkus30

    karkus30
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    Considering the difference was about 30db originally :rolleyes:

    until around 50Hz its more or less flat (within a 1 or 2db) at 56db there is a slight dip of around 5db. Infact, why dont I just give you the figures and you can plug em into worksheets.

    FREQ RAW SPL
    16 64
    18 78
    20 79
    22 79
    25 78
    28 80
    31.5 82
    36 80
    40 81
    45 82
    50 82
    56 78
    63 80
    71 75
    80 74
    89 56
    100 60
    111 54
    125 58
    142.5 62
    160 60

    Tell me if you think I can improve, bearing in mind I have 9 filters set. 1-6 are cutting freq up to 49Hz by around -4-6db and the rest are boosting between 50Hz and 63Hz by up to +10db.

    Boosting frequencies seems to have a bad effect on the graph.

    Now you know why I did'nt fall over myself applauding the SVS Ultra :rolleyes: Its not the subs fault, but I do think a sub which handled the 100Hz down to 40Hz would have been a better investment. Maybe a second sub that just looked after the below 40Hz signals ! But intergrating that lot would be a nightmare.

    Its one of the reasons I use a different system for music. My Full range floorstanders manage 20Hz(a few db down) and the response is pretty flat from around 25Hz up to 20Khz.
     
  8. Ian J

    Ian J
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    Spreadsheet attached
     

    Attached Files:

  9. karkus30

    karkus30
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    I knew there was a way to do that. I still dont seem to be able to attach thumbnails etc. Comments ?
     
  10. Ian J

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    I assume that your main speakers were disconnected when you took the readings. I wonder if you had them switched on and were crossing over at 80 Hz whether the overall response would be smoother at that sort of level
     
  11. karkus30

    karkus30
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    Im not keen on disconnecting speakers from a working amplifier, so they were just turned down as low as possible and turned speaker face down on the floor.

    I tried the 'escape from earth' scene from Titan AE. The vocals are much clearer and the impacts are more defined, so its definitely better. I have the sw output at -7db and the BFD just clips on the very noisy bits. The sub has the gain set to about the 1/3rd mark. Theres still a bit of intrusive rumble (probably around the 20Hz mark), but thats more a volume thing exciting the room.
     
  12. BAN5HEE

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    Stupid question but where the hell do you go to do all these settings? Is it on your amp or where casue I sure ass hell cant change any of those things apart from on my sub. :rolleyes:
     
  13. karkus30

    karkus30
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    Most is on a thing called a Behringer feedback destroyer, which has a built in 12 channel parametric equaliser. Its kit thats meant for the pro musician, but can double as an equaliser for home cinema.

    You need a bit of kit to measure the sound levels called an SPL meter and a disc full of frequencies which you can download from a website called snapbug. All this get put onto Microsoft worksheets and thats what the graph is.
     
  14. Ettepet

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    I hope you didn't use heavy amplification of certain frequencies, as this is highly discouraged. The sound-quality of these frequencies is terrible in general, which you can easily check. It might even damage your subs Amp at high SPL, during an unfortunate concentrated (sound-effect) burst in that frequency region.

    You should either ignore these (hopefully) insignificant regions, or place the subwoofer in a better location. I use small amplification in certain frequency regions myself, but only by 4 or 5 dB, and with that I do have a completely flat FR between 16-70Hz. B.t.w.: my room is in no way ideal soundwise, in case you wondered. ;)
     
  15. karkus30

    karkus30
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    Ettepet, Im not really sure what your saying ?? I use the amplification I have and the graph shows the db levels. This is the accepted way of setting up a sub woofer. Tried moving the location, but it just wasnt happening. The room that I use at present has terrible acoustics as its square.
     
  16. Nimby

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    Reading this and other threads on testing prompted some thoughts on the subject of tone testing. :rolleyes:

    The experts can look away now. Or hopefully correct any of my mistakes. :boring:

    You should always start a run of sinewave test tones at your highest test frequency and work downwards. This should avoid you blasting your equipment at inaudible frequencies. Which could easily happen if you start very low and then turn the level right up just to hear these strangely inaudible tones! :cool:

    When you hit a room resonance it is the room that amplifies the signal. Not the equipment. Which merely "excites" the room resonance. The equipment is not being put in danger of overload by a true room resonance. Just be sure you haven't got the level too high if it's your first test tone! :eek:

    The test signal should remain at the same level throughout a test run. Which means that you should choose a reasonable level on the SPL meter while still in the clearly audible region. Starting at somewhere around 70-80dBs @ 120Hz seems to work for me. This is impressive enough to be fun without damaging the scenery too much on room resonances.
    There is no correct level. It is a matter of taste. If you start testing at 100dB on the meter then your sub may decide to commit suicide. Rather than play the really deep notes. If the neighbours start banging on the wall then your test level is probably a bit too high. :blush:

    The danger is if you set your test level in the middle of an unknown (but deep) room response trough. If you discover the response is rising fast as you lower the frequency of your tones. Then you should lower the test level and start again from the beginning. Though you may simply be approaching a response peak slightly below your starting frequency. If the level doesn't get out of hand and starts to fall again with lower frequency tones then it was a peak.:lesson:

    Have your SPL meter propped up where your head is at your normal listening position. With the test microphone pointing towards the speakers or sub being tested. The RadioShack SPL meter has a tripod bush underneath if you have a photo or video tripod handy. It is often easier to read the scale if you set the meter on its side. I find it can be read from much further away when you are running back and forth to the computer. To change to the next tone or write down your SPL reading and test frequency.

    Remember to have your meter correction figures handy when you finally plot your column of test figures onto a bit of graph paper or computer spreadsheet.

    If you don't have expensive Windows Excel on your computer then don't panic. Download "Open Office". A free (64MB?) download. Not too painful if you have unlimited broadband. :)

    Don't blame your subwoofer if it is your speakers causing a wobbly bass response. I would always test with the speakers working and normally calibrated first. Long before doing a sub only test. Which is largely of acedemic interest.

    Remember that your speakers are part of the sound reproduction system on all material (music or film). You can't completely ignore the speakers in the bass. Even when they are crossed over as high as 120Hz! Though most are crossed over lower than this.

    If you're running full range, unfiltered floorstanders like me. Then you'd better have your speakers working! Or your test results are completely worthless! :nono:

    All speakers and subwoofers go through a whole series of being in an out of phase with each other. Depending entirely on frequency and your room's physical dimensions. The bigger the room the lower the affected frequencies. But these phase effects are always still there.

    The sub's phase control often seems inneffective. Unless you are cancelling a phase peak between the sub and your speakers. Then you won't notice a thing as you wind the phase control knob back and forth. (Or switch between 0 and 180)

    Adjusting the phase should always be done from the listening position anyway. Not when you're crouched over the sub! :clown:

    Boo! You can all wake up again now!

    Nimby :boring:
     
  17. recruit

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    Nice Post Nimby :)
    Talking from good experience :smashin:

    John
     
  18. Nimby

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    :blush:

    Nimby
     
  19. Smurfin

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    Sinewaves are also known to fry speaker drivers if played back at excessive levels (apparently), so when playing back test tones be VERY careful: it might sound ok to start with, but a big peak that you discover might not be so pleasant...
     
  20. eviljohn2

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    Seems good Nimby. For surround testing I heard that the SPL meter should be vertical (ie. not pointing at any of the speakers really), that should give a more consistent reading all round.

    I can't see how it would make any difference using a freq. sweep from low to high but it probably wouldn't sound as satisfying, nor will the low frequency limit be quite as apparent. (Just noticed that you weren't referring to a sweep but to various test tones in which case you'd be right).

    With respect to the calibration adjustments, if you have the new SPL meter (curvy and very nice as I've just got one from Keene) then I don't think anybody's sure what the adjustments are or even if they're necessary. I'd be very surprised if the same values were used though.

    Smurfin, I'm not sure how sine waves should damage speaker drivers (unless you were putting particularly low frequencies through which the motor can't reproduce without burning out). What would definitely cause problems is if the sine waves weren't pure and contained any DC component. I'm sceptical of the quality of computer generated sine waves such as the mp3's or function generators available. Perhaps someone could advise me? I'd rather not have to go and nick a lab standard function generator from uni!

    Then onto my main question which sort of follows on: Which is the best PEQ? I know lots of people use the BFD successfully but has anyone got any experience with the analogue models that SVS supply for example? I think their cheapest model works out less than a BFD.
     
  21. Nimby

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    A resonance as a result of a room mode will sound louder without the sub or speaker working any harder. I repeat that the sub is in no danger if it is a room peak. It is the room amplifying that particular tone. Not the driver or the sub's amplifier.

    Using downloaded test tones will quickly show if harmonic distortion is present if a tone below 20Hz is clearly audible as a hum. The presense of a higher tone would indicate that distortion is being reproduced. It should ideally be an inaudible "soft & fluffy" air movement. Sensed clearly but not really heard.

    I am satisfied that using high level connections and snapbug's tones in my system that very little distortion is being reproduced. The room can really shake without anything being clearly audible. That's good enough for me. Even if I'm completely wrong about the level of distortion. :blush:

    Square or distorted high frequency waveforms can fry a tweeter rather quickly if at high enough level. Bass/midrange units are usually protected by the crossover. Though some speakers have only a simple capacitance (high pass) filter for the tweeter. Which could expose the bass/mid driver to possible damage I suppose.

    Nimby
     
  22. Daneel

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    What software / tones are you guys using for this and where can I get it please?
     
  23. Ian J

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    Everything that you need to know about using a BFD is on the snapbug site. The test tones are downloadable from here
     
  24. Ettepet

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    What I was saying is that you should NEVER use huge positive gain on your BFD.

    I hope this was clearer. ;)
     
  25. karkus30

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    Had to use +10db @ 63Hz. Apparently you shouldnt use lage increases much below 50Hz due to the sheer power it takes to do that, leaves little headroom. Above 50Hz isnt so bad.
     

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