Which head for Acme Low B2?

Discussion in 'Amps, Mics & Pickups [DB]' started by thejumpcat, Feb 9, 2008.

  1. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Your experience makes perfect sense. As you may recall, I identified to Gary Gibilisco, the designer of the iamp, the problem with the infrasonic response. John Dong offered me the same solution which I knew would not work. My iamp200 was modified by Gary to better filter out infrasonics. I now also use fdecks's HPF/Pre (which I helped a bit to design and test).

    You are 100% correct that the HPF cleans up all the clutter while actually improving the sound. The reason is as I just posted above. If you apply John Dong's solution, you end up cutting a band of frequencies centered at 40 Hz (the lowest setting on the frequency slider). By the time you affect the infrasonics enough (and it's not likely you really can), you'll pretty much destroy the tonal balance of your sound.

    To clean up infrasonics and judiciously cut the low end, you really need a HPF with a transfer function as shown here.
     
  2. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    You may be interested in this old post of mine. The Acme B-1 seems to be a fine sounding cabinet. That sound is part and parcel of the design philosophy chosen. One does not simply sit down and make an efficient version of the very same cabinet. There's an old addage in speaker design. You may have only two of the following three:

    1) Small cabinet

    2) Extended low-frequency response

    3) High efficiency

    A designer must trade these things against one another. There is no magic but there are some very clever techniques to get all you can from the physics.

    Yeesh!-- four reply posts in a row. Time to go to work.... :)
     
  3. Jeremy Allen

    Jeremy Allen Supporting Member

    Mar 18, 2002
    Bloomington, IN
    I did; but when I was buying the amp, I read many reports saying "have at least 500watts available," and as I said I found that 400 didn't cut it. Of course, what you're saying is that it wasn't the wattage but something else. I can't go any further than that, alas...

    I thought 3 dB was a doubling in power (i.e., every 3 dB gain means twice as loud)?!

    Salesman: "Oh Mr. Allen, we have a special today at BassCrazy Sound. I can offer you this 650-watt amp for just $200 more than our 500-watt model."

    Jeremy: "You think I just fell off the truck, buddy? Talk to me about currency conversion, damping factor, and headroom, or I'm outta here."
     
  4. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Glad you asked. Yes, 3 dB is a doubling in power. So, going from 400 to 800 watts is an increase in power of 3 dB. So much for the physics. Now the psychophysics. In order to double loudness (which is a subjective attribute), human listeners require an increase of about 10 dB! So, in order to double loudness, you have to increase the power by a factor of 10! A change in power of 3 dB (a doubling) produces only a small change in loudness-- roughly about a factor of 1.2.
     
  5. Jeremy Allen

    Jeremy Allen Supporting Member

    Mar 18, 2002
    Bloomington, IN
    Ah, I see. That electronic music class I took is coming back to haunt me--dB A, dB SPL, dB M, power, intensity, loudness, Fletcher-Munson curves...
    Just give me a GK800RB and a Hartke 4x10!
     
  6. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    This is where I live each and every day. :)