Avalanche 15 hellllllp

Discussion in 'Home Theater Projects' started by AhsanR, Oct 17, 2006.

  1. AhsanR

    AhsanR Stunt Coordinator

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    I am running an ascendant audio Avalanche 15 with a 500 watt bash amplifier in a 6 cu ft enclosure.. The entire speaker is complete, however, I am running into a problem that I have created for myself. The box is tuned to about 20hz, with dual 4 incch precision ports.

    The speaker is a dual voice coil speaker, and I've only wired it through one voice coil (mistakingly). My question is, if I open the box back up (groan) and if I wire it through both voice coils, will it be a significant improvement (I'm a bit underwhelmed)?

    My second problem lies in with my amplifier. I have heard that the bash amplifier has a 5db bass boost that takes away from the under 20 hz material. If this is true, should I mod it to where the bass boost is eliminated?

    Thanks alot guys, alot of blood and sweat have went into this project, I'll have pictures up soon!
     
  2. JimPeitersen

    JimPeitersen Second Unit

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    I believe the AVA's were dual 4 ohm drivers, correct? If so, wiring them in parallel would lead to a 2 ohm final load. I'm not sure that the BASH amps are comfortable with this load. The series connection would lead to an 8 ohm load, with means that you are sending the driver only about 250 watts - which is really underpowering that particular driver. I am fairly sure that the BASH amps have a slight boost and a subsonic filter at around 18hz. You should be fine with your box tuning.
    I would run the speaker in parallel, which should significantly increase your SPL's. That driver in that box should impress all but the crazy "bass-heads."
    JP
     
  3. Robert_J

    Robert_J Lead Actor

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    The Avalanche was dual 2 ohm according to the AA site - link. Wire the coils in series.

    With a 20hz tune, did you lengthen your ports to 26.3" each?

    Finally, where did you hear the info about the BASH amp? I've heard they are pretty much flat down to the SSF at 18hz. If you got it at PE, a quick search of the forum should give you the correct answer. If not, then they have some great phone support as well.

    -Robert
     
  4. Brent_S

    Brent_S Second Unit

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    According to PE's 500 watt BASH spec sheet, you've got roughly a 3db boost between 31-35hz with a rumble filter cutoff at 28hz. You're definitely losing potential output below 20hz.

    If it's dual 2 ohm, then wire the coils in series as Robert says. That amp's not designed for less than 4 ohms (at least for any length of time).

    Google should be able to turn up articles on running only one voice coil of a DVC...think you're losing 3db of efficiency. You've also altered the T/S parameters relative to both coils driven. The enclosure volume/tuning is designed around the T/S parametes so you may not be getting what you expected in frequency response/output since your design was most likely modeled with both coils driven.

    -Brent
     
  5. AhsanR

    AhsanR Stunt Coordinator

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    ADVICE TIME NEEDED:

    Alright guys! I finally wired it right, and let me tell you... it sounds almost like a different speaker.

    But here's a question, since this is my first experience with big bass, what should I expect.

    i played the pod race scene from Star Wars, but I was expecting the whole house to be shaking uncontrollably. Am I missing something here? The elephant stomps in the lion king sound very realistic, but I was wondering if there was any way I can make him stomp HARDER, to where I can not only feel it, but experience it (IE stomp even harder)

    Abover 35hz it sounds just fine. I mean - I wouldn't want anymore. Its that loooow end that I want more.

    My bash amp is set at 500 watts (which is the max).


    Do you guys think if I did the mod on the Bash amp that it would give me that last last last desired oomph that I desire? (since Brent above said that it cuts out anything under 35hz by a -5db)


    OR should I not even bother and get a 1000 watt amp from Parts Express and expect that desired oopmh from there?

    I'm just a little underwhelmed thats all.
     
  6. Robert_J

    Robert_J Lead Actor

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    The cheapest thing to do would be to mod your current amp. Less than a dollar for resistors.

    If you really want some bass, lower your tuning to around 16hz or lower and get a Behringer EP-1500 or a Buttkicker amp. The EP will give you slightly more power but the BK amp is fanless. Also, if you decide to get another Avalanche (the remaining inventory will be on sale soon) then the BK amp can easily drive a pair.

    -Robert
     
  7. Brent_S

    Brent_S Second Unit

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    Actually, I didn't say that, but I do need to correct myself (read on). [​IMG]

    According to the "modifying bass boost" section in the spec sheet, the stock cutoff frequency of the 500 BASH is approximately 31hz. I say approximately b/c the stock resistor combination isn't in the bass boost tables, but why split hairs over 4k ohms. That means it starts rolling off response hard below 31hz...the Q's 1.2 . I imagine that filter could easily cost you 10db or more of output at 20hz, relative to whatever your sub would produce with no filter. The signal is reduced more the further you get below the cutoff frequency (Fc).

    I looked at the boost tables too quickly in my first post. The boost is actually 2db in the 36-40hz range. In simple terms, if your soundtrack called for 100db @ 38hz, the boost will ask the amp/speaker to produce 102db to play that 38hz note. By itself, the boost would probably be unnoticeable since the room can easily add larger peaks/dips to your frequency response.

    The bass boost/rumble filter are really the same circuit so you can't change one without effecting the other. I don't have the Avalanche15 loaded in WinISD, but would imagine your best choice would be swapping resistors to get either the 18.7 or 13.9 cutoff with only 1db of boost. It really depends on how fast you eat up excursion below 20hz.

    The HPSA amps (500 & 1000) have default cutoffs at 18hz. Seems like a mighty expensive solution to changing two resistors. If your alignment can handle 1000 watts without bottoming, it might be worth it to you. In terms of SPL output, 1000 watts will only get you 3db more than 500 watts.

    Just for fun, I tried to model an example in WinISD using a driver I do have. For the boost/cutoff, I used a 2nd order Butterworth HP filter with a Q of 1.2 with Fc of 31hz. I don't know what alignment the HP in the BASH is so the slope could shallower or steeper. Without the filter, this model is good for 108db @ 30hz, 106db @ 20hz. With the filter model engaged, no other changes...105db @ 30hz, 98db @ 20hz. YMMV.

    BTW, for anyone who cares...for some reason, the 300 watt BASH has a different stock setup... 1db boost from 25-30 with Fc=17.7. Go figure.

    This should address your PM to me. Let me know.

    -Brent
     
  8. John Wes

    John Wes Stunt Coordinator

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    I'm curious, at that wattage rating, you should have plenty of bass one would think. Given number one that the sub is placed right to begin with.

    One other thing, how do you know that the amp is set for 500 watts output? Does that mean that it's cranked "all the way to the right"?

    By chance have you also calibrated your source output? Maybe it's just set too low.
     
  9. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    John,
    I think Brent has correctly identified the problem. Its not that the Ava or the amp don't have enough power ... its the high-pass filter in plate amp - set way too high. For this sub I'd move it down to 18-19Hz to regain 1/2 octave of extension.
     

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