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Load Boxes, Attenuators, Impedance Matching

Discussion in 'Ampage Area' started by Hammerhands, Apr 10, 2018.

  1. wabash slim

    wabash slim Friend of Fred

    Age:
    68
    Feb 10, 2010
    lafayette in
    A silent speaker and isolation box is the same thing. Essentially, it's a speaker in a double box, one in front and one in back, heavily damped. They should have a mike inside to feed a mixer. I'd avoid the other ideas. Putting both sides of a speaker to ground would let the smoke out of the amp.
     
  2. MTurner

    MTurner Friend of Fred

    Age:
    62
    Aug 17, 2010
    Clayton, North Carolina, USA
    That, too.
     
  3. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    Not on the amp!

    Say you have a speaker, just a speaker, and you connect both ends of the voice coil to earth ground. Now you make noise, the speaker works as a generator. I think at the furthest point from ground in the speaker coil, there will be a pretty high voltage and the voice coil will heat up. But I’m not really 100% sure. Why can’t you just dump energy?
     
  4. wabash slim

    wabash slim Friend of Fred

    Age:
    68
    Feb 10, 2010
    lafayette in
    The speaker's connected directly to the amp, ergo, the amp'll will release it's smoke. You must dissipate energy; use it up somehow, usually as heat. You could use a load resistor, or an attenuator box. Problem is that a load resistor is a resistive load, not a reactive load (which a speaker is) and not a perfect solution.

    A speaker can be used to produce energy from sound---sometimes they're able to be used as microphones as seen in some old school intercoms. Actually a dynamic microphone IS a speaker in reverse---sound pressure is converted to electrical energy to drive a circuit in an amp or recording device.
     
  5. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    Thinking back to my favourite grade 6 science demonatration, the more lightbulbs you put in parallel, the harder it is to crank the generator. Putting both sides of the coil [of an otherwise unconnected speaker] to ground would be like putting an infinite number of lightbulbs in parallel with the generator.

    I think that means you are increasing the reactance and the magnet would probably heat up, not the coil. But the speaker cone would probably tear apart first.

    Part of that demonstration was getting one or more kids to agree to hold onto both poles of the generator. That would get you so fired now. The advantages of 6th grade education.
     
  6. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    It’s a bit late now, but here is what I understand so far on the subject of the title of this thread.

    Load Boxes and IRs.
    One of the latest trends to try to get the sound of a cranked amp at no or low volume is to use a real amp crank it up, plug it into an active load box instead of a speaker and send the signal, the same kind of signal you get from a DI box, through some kind of processor to make it sound like a mic’d cabinet.

    A load box can be just a resistor, sometimes known as a resistive load box or maybe a dummy load box, but the signal you get from that doesn’t sound a lot like what you get from a DI box connected to a real speaker cabinet.

    A reactive load box tries to act more like a speaker. When an amplifier sends power to a speaker, the speaker coil moves in some direction, some power get stored in springy part of the cone. Then when the speaker moves back to neutral, it creates a signal that gets reflected back to the amplifier. The signal is altered, and there are other effects because the speaker has inductive and capactive properties.

    I’ve also seen a few inductive load boxes, which I suspose are different than reactive load boxes in that they use more inductors and less capacitors to try to mimic what a speaker does.

    [Have to keep these posts short]
     
    Last edited: Apr 14, 2018
  7. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    IRs are Impulse Responses. The impulse is a sweep of sound going from a very low frequency to a very high frequency. You record the response that you get after playing the impulse.

    IRs are commonly used in two ways:

    If you play the impulse [the impulse in this instance is just a short click instead of a sweep] in a room, then you record the sound until all the echoes fade, you can use that, really by simple multiplication, to make a very good similation of the sound of the room.

    The other way is to send the sweep sound through a speaker. The respose compared to the impulse tells you how the speaker and mic have changed the signal’s frequency. When they show a graphic representation of it, it looks exactly like a speaker’s frequency response graph. If you apply that like a graphic EQ to the signal you get from a DI box, you get a quite realistic sounding simulation of the speaker cabinet and mic.
     
    Last edited: Apr 14, 2018
  8. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    The difference between an attenuator and a load box is that an attenuator is designed to lower the volume you get from a speaker cabinet where a load box is intended to replace the speaker cabinet.

    Some attenuators can be used as a load box. The DI signal from most attenuators used in such a manner do not sound very much like the signal you get when the DI is attached to a real speaker. The signal tends to be spikey or hairy. This can sound very good! The more you attenuate, the more spikey it gets.
     
  9. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    Impedance matching

    Most of the popular reactive load boxes come with a fixed impedance for the input. One popular model comes only in 8 ohms. So if you want to use that load box with an amplifier that only has 2 ohm output, you need to use an impedance matching device, which is almost always a transformer, or risk damaging your amplifier.

    These transformers were pretty common at one time, but now I think the only options are the Peavey Automatch and the Weber Z-match. I’ve read Mcintosh uses them, but I have yet to find a McIntosh one. There’s one called a Zero but the price is for audiofiles. I’ve also seen a super high-end audiofile one using what look like old Hammond autotransformers on eBay for about a grand. And Turner of Australia seems to make one.

    I think you may be able to improvise something with a 70V line transformer [which seems to be exactly what the Peavey Automatch is] or an amplifier’s output transformer.

    Because of the cost of shipping the Weber, I’m either going to have to wait until I’m ordering from the U.S. or figure out something else.

    I started looking at winding an autotransformer, but the number of turns I calculated was too much for something I’ve never done.
     
  10. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    Isolation Cabs, Silent Speakers, Isolation Boxes.

    So, instead of a load box, why not DI a real speaker. It looks like not many people are trying this. The common use for an isolation cab is to put a microphone in the cabinet and use that output. This sounds pretty good, but some complain it is boxy.

    The louder the speaker gets, the less it sounds like a real cabinet.

    These seem to range in price from about $400 to $1400. Some sound very good, some do not. I haven’t seen too many videos where they use it with IRs. Let me blow the evening looking at that.

    An isolation cabinet is a speaker and a microphone in an insulated box.

    A silent speaker is another name for an isolation cabinet but is also the name of an inductive load box someone named Kolbe was selling.

    An isolation box is where you put a speaker cabinet and a microphone in a huge sealed box.
     
    Last edited: Apr 15, 2018
  11. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    There are a couple of youtube video by Pete Thorn that get pointed out as pretty good introductions to IRs.



     
    Last edited: Apr 15, 2018
  12. Garruchal

    Garruchal Electromatic

    33
    Oct 21, 2013
    Seattle
    My take on this: I'm a classical pianist turned guitarist. I was raised on chamber music, Debussy, Chopin and Mendelssohn. I married another pianist and started playing guitar all the time because I was sick of being a classical musician.
    I found that I just couldn't take the high volume of typical guitar amps and wanted a cranked amp sound at lower levels. I tried a few amp simulators, digital amps, etc., until I settled on Princton Reverbs as my preferred sound. Still too loud when cranked, except when I am playing with my band in a performance, at which time I put it on a stand to get it up closer to my ears. I bought my amp a Night Light Jr. It works great, and gives me mostly what I need. It sounds exactly the way I want my guitar to sound on a recording.
    The point of this post:
    The other guitarists that I play with are hard core traditionalists. Guitar into [really old] amp is the only way they know how to get the sound they want. So, when I built a studio in my garage, I made it possible for everyone to get the sound they wanted: the drummer is in an isolation booth, and I built little isolation booths for the guitar amps as well. They can crank their amps but still stand in the room with me and the singers and bassist going through a DI.
    They hated it. They thought their amps sounded like cardboard. It is the same exact sound which will be on the recording, but they were listening through headphones while they played and hated the sound. They were only happy when standing in the same room as their cranked amp while listening to the other players on their headphones.

    The attenuator is not the problem: it does not change the tone of the amp very much. It is the volume in the ears which changes the tone. If you are a high-volume guitarist, having a good amp next to you is the only way you can get the sound you want.
     
    Hammerhands likes this.
  13. Ricochet

    Ricochet Gretschified

    Nov 13, 2009
    Monkey Island
    Brian Neunaber brings up an interesting point in the manual's introduction of the Neunaber Iconoclast speaker/cab emulator.

    "Loudspeakers used for guitar amplification do more than simply make the signal louder. They dramatically shape the signal—significantly attenuating very low and very high frequencies, while less dramatically affecting other frequencies. Furthermore, the loudspeaker can interact with the amplifier that drives it, resulting in a dynamic response.

    Unfortunately, guitar loudspeakers can be highly directional and dependent on positioning. Where the listener stands (or places a mic) in front of a guitar cabinet can drastically affect the sound. Placing the cabinet too close to a wall, tilting or raising it off the floor will also have a dramatic effect.

    The loudspeakers themselves—especially those used for guitar amplification—can have serious deficiencies in their response. These speakers are chosen primarily for their ability to shape the sound at the extents of the response curve, as well as for high sound output (sensitivity). Response smoothness is sacrificed, which is generally required for high-fidelity sound.

    IRs (impulse responses) of guitar speakers are digital samples of the loudspeaker’s response and are therefore susceptible to these same deficiencies. To make matters worse, they are usually sampled at specific point-positions rather than averaged over an area or volume, which results in an inaccurate representation of the apparent response.

    To mitigate these issues, recording engineers may mic guitar cabinets at multiple locations, use multiple mics, or even multiple cabinets and mics. Likewise, IRs are often combined (averaged) together for the same reason. Iconoclast avoids all this complexity by directly producing a smooth response.

    Iconoclast decouples the tone-shaping aspect of the guitar speaker from the process of amplification, allowing you to independently sculpt your tone while avoiding the deficiencies of guitar speakers and IRs. Placed after your pedals and/or preamp, Iconoclast completes your signal chain and provides a direct output to headphones, a recording interface, mixer or powered speakers.

    Even in cases where amplification is required, combining an Iconoclast with a compact, high-fidelity powered speaker has several advantages over a traditional guitar amp and speaker:
    • Higher sound output per unit weight
    • More consistent sound over a wider angle (lower directivity)
    • Less dependence on positioning
    • Generally more rugged and easier to transport
    • Easier to run stereo
    Given these factors, we firmly believe that running direct with Iconoclast yields a superior experience to that of a dedicated guitar amp."
     
  14. Lizardkinged

    Lizardkinged Friend of Fred

    Age:
    31
    Oct 5, 2009
    Michigan
    I've begun to wonder why people like Ted Weber hasn't started designing speakers to go after the attenuators for studio or home-rocker types who want to move the cones more than a loud-speaker should really be run at home or in confined spaces.

    Could build them to sound like his current popular models, you still generally have the reactive load from the speaker motor inside his attenuators...
     
    Hammerhands likes this.
  15. Hammerhands

    Hammerhands Country Gent

    Aug 26, 2011
    Winnipeg
    They do everything to maximize SPLs.

    They have those speakers where you can turn them down. I’m not sure if they sound the same.

    But, Ted Weber is dead, don’t blame him.
     
  16. TV the Wired Turtle

    TV the Wired Turtle Gretschified

    Jul 25, 2009
    so cal
    Is there a better demo video than the kid w a crappy strat and dirty tones for the Iconoclast. I viewed it w a JBL surround unit from my mac mini.
     
  17. Lizardkinged

    Lizardkinged Friend of Fred

    Age:
    31
    Oct 5, 2009
    Michigan
    I understand why LOUDSPEAKERS are made to maximize SPLs, I'm talking about speakers specifically to be run with attenuators. For people who aren't leaving home.

    The Eminence speakers with built in attenuators are great. i have 2 of them (both models). They're actually mechanically attenuated. The motor/coil is shunted mechanically or moved away from the magnet, which is similar to being starved of wattage. So you have to attenuate with your EQ.
     
  18. Ricochet

    Ricochet Gretschified

    Nov 13, 2009
    Monkey Island
    Judging from the comments on the Neunaber site they've sold quite a few, but oddly I haven't seen a single decent demo yet, including the ones from Neunaber. o_O
     
  19. TV the Wired Turtle

    TV the Wired Turtle Gretschified

    Jul 25, 2009
    so cal
    I was surprised to not see an XLR out on em
     
  20. Ricochet

    Ricochet Gretschified

    Nov 13, 2009
    Monkey Island
    It has impedance-balanced outputs for driving long (balanced) cable runs, if that is your concern?