A Couple questions about Feedback Destroyer

Discussion in 'Archived Threads 2001-2004' started by GaryP, Jan 4, 2001.

  1. GaryP

    GaryP Second Unit

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    Okay guys,
    What kind of equipment/software are you using to tell if you have humps and dips in your bass response? I'm assuming an SPL and a disc of some kind of LFE sweeps. If this is correct, what software should I look into getting? If I'm not correct, slap me upside the head and point me in the right direction please. [​IMG] I'd like to know if I could use a BFD, but first I want to see what my room response is like, before I go any further. Thank yu in advance for any suggestions.
    Gary
     
  2. Timmy

    Timmy Stunt Coordinator

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    )This wasn't listed in your post, but I used a precision audio generator connected directly to my powered sub. I used it to plot the rooms response from 20 to 100hz with a RS SPL (compensated for the RS meters non-flat response).
    I then connected the audio generator to the BFD input, with the sub to the BFD output and set the filters.
    LFE "sweeps" generally go by too fast to get accurate readings.
    Once I plotted out my room, I dialed the freq-gen to the first peak, activated a BFD filter, adjusted the cut to the desired spl... all while holding the frequency steady at the peak (not sweeping). I then varied the freq slightly above and below the (now flattened) peak to adjust the filters bandwidth.
    There are many ways, mine is just one of them.
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  3. GaryP

    GaryP Second Unit

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    Timmy,
    Where do I get a precision audio generator? And what kind of cost am I looking at?
    Thanks,
    Gary
     
  4. TerryC

    TerryC Stunt Coordinator

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  5. GaryP

    GaryP Second Unit

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    Terry,
    I've got your file downloaded (Thank God for DSL [​IMG] ) and do have a CD-Burner (Converting to a wave file won't affect my outcome will it?). Mostly, I just want to verify that these sweeps wont trash my driver (Velo CT-120)
    Thanks,
    Gary
     
  6. TerryC

    TerryC Stunt Coordinator

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    Gary,
    These are the very same sweeps I use to test all the subs I built. Converting to Wav. doesn't change their response(used SpectraLabs to confirm this). You won't harm you sub unless you just get crazy with the volume and turn it full for more than 5 to 10 seconds on the lowest sweeps(below 25hz or so). As long as you play in the 90db to 110db at the one meter mark with the rat shack meter you are going to be fine.
    Also I think Velo has circuitry that kicks in limiting output if it detects too much distortion or tryingto push it past its limits although this could only be on their higher end subs?
    Terry
     
  7. FrankD

    FrankD Stunt Coordinator

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    If you want to dish out a few more bucks (cost approximately $460.00 US with microphone) look at the Behringer Ultra-Curve 8024. It has a sine tone generator that moves in small increments (approx half Hz) and pink noise as well. It also has an RTA analyzer. However it only has 3 parametric equalizers points and the others equalizer points are fixed (at 20, 25, 31.5 40, 50, 63 and 80 Hz etc all at 1/3 octave bandwidth with only adjustable gain).
    ------------------
     
  8. Timmy

    Timmy Stunt Coordinator

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    I bought a B&K 3100 precision gen for $65 on EBay. If you have a friend that owns an electronic repair shop, one could borrow one as well
    But Terry's (MP3 15-80Hz Sweep, 1Hz increments-5 Seconds each.(Big 7.73MB @ 190kbps File) is ideal as well.... as long as the final output to the sub is linear in response?
    The only reason I ask is that PC based tasks like this are not taken that seriously by those writing the software, and by the CDR/CDRW drive mfgrs. To where a 2db "dip" or "peak" here-n-there is not considered a problem... but may appear in our HT use as a small room peak/dip.
    How does one know (after burning the CD) that when this disk is played in your DVD player for room plotting purposes, that the audio going to the subs input is indeed flat across the 15 to 80hz range (or is this not a concern with current PC hardware)?
     
  9. TerryC

    TerryC Stunt Coordinator

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    "The only reason I ask is that PC based tasks like this are not taken that seriously by those writing the software, and by the CDR/CDRW drive mfgrs. To where a 2db "dip" or "peak" here-n-there is not considered a problem... but may appear in our HT use as a small room peak/dip."
    I don't know how accurate that statement is based on my experiences? I've used Spectralabs to compare a burned CD a little while back and after copying they were EXACT duplicates(I even posted the results here on HTF). I've also converted that MP3 to a wav. file and burned it then compared it to the original it was basically the same as the original. But that just might be my PC?
    "How does one know (after burning the CD) that when this disk is played in your DVD player for room plotting purposes, that the audio going to the subs input is indeed flat across the 15 to 80hz range (or is this not a concern with current PC hardware)?"
    Download a free demo of Spectra plus, install it and run a cable from the output back into the input of your sound card and it will display the results when the file is played. In my system it comes out flat.
    Terry
     
  10. Martin Schmencke

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    "I bought a B&K 3100 precision gen for $65 on EBay"
    And what percentage of the original list price would that be ? [​IMG]
     
  11. Marv

    Marv Stunt Coordinator

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    I thought I read somewhere that testing with sine waves are only good for near field testing? Warble tones should be used for testing responses at the listening position.
    Is this correct?
    -Marv G
     
  12. TerryC

    TerryC Stunt Coordinator

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    Marv you are correct.
    Regular sine waves can cause standing waves which can cause nulls. Pink noise is the norm but impossible to use without an RTA unless its pre filtered into realative frequencies or ocataves. Warble tones are good too but again you need an RTA. There may be some better files out there but its my guess these will work almost as well and easy to do with only a Rat Shack meter.
    Terry
     
  13. Patrick Sun

    Patrick Sun Moderator
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    Ahh....I was wondering why the warble tones were on my Stryke BassZone CD. I'll use those warble tones for the EQing of my room later this weekend if I can squeeze it in between sleep and eating. Before I was using the sine waves for the EQ-ing and getting those funky dips and bumps. Thanks for the info, guys.
    ------------------
    PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; LDs
     
  14. Timmy

    Timmy Stunt Coordinator

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  15. Mike Boniferro

    Mike Boniferro Second Unit

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    Terry, with your file... how do you know for sure (easily, without counting??) what frequency you are hearing. I've heard of people making 99 track cd's with sweeps on the first 15 tracks and then each track after that represents the frequency being heard (16-99). Would this work better/easier? also, does anyone have anything like this in a ZIP file kicking around that they could post somewhere for download?
     
  16. TerryC

    TerryC Stunt Coordinator

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    Patrick,
    Be sure to let us know if you find any differences. Maybe do a before and after test but be sure to re-test the before part. [​IMG]
    Timmy,
    Another inexpensive(free) Tone generator is located here: http://www.nch.com.au/action/index.html
    Just scroll down a bit. I've never used it but the Mark Hayenga does, or at least I think he does as he is the original locator of it.
    Mike,
    I just made a word document and print out. This is what it looks like:
    Sec....HZ
    0-5 =15hz
    5-10 =16
    10-15=17
    15-20=18
    20-25=19......
    That way it's easier to use. Make sure as you get to 60seconds you start using 1:00 instead as that is how your CD player will show the time.
    Terry
     
  17. Mike Boniferro

    Mike Boniferro Second Unit

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    Terry,
    that is what I figured... I was just assuming that the different tracks method would be easier. I used your sweep and it worked absolutely fine. I was just curious if there was anyone out there with a file that included many tracks to represent each frequency [​IMG]
     
  18. Dave Campbell

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    With the NCH generator, the frequency response is dependent on your computer sound card.
    My RS meter usually reads 1-2 dB less than Stryke test CD for frequencies less than 16 Hz relative to 20Hz.
    But I like the fact that you can set exact frequencies so this is what I use.
    ------------------
    Hideaway Shivas
     
  19. Adam B

    Adam B Auditioning

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    I would hesitate using a PC soundcard tone generator for equalization purposes. I know my soundcard's (SoundBlaster 16) output amplitude drops greatly at lower frequencies. It does about .880V until 80 Hz then rolls off to .321V at 20 Hz.
     
  20. Michael_T_Jones

    Michael_T_Jones Auditioning

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    A question about using the file TerryC linked to.
    My DVD player will not play cd-r's. Would there be any problem with burning the disc and then playing it through my cd player instead? It is connected to the same receiver/sub output.
    If I do this and tame the sub with the Behringer Destroyer Pro unit, will I get the results I am after.
    Or should I look for a music cd somewhere that will instead play through my DVD player?
    Thanks,
    Mike
     

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