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If you took a guitar speaker


1001gear

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Dummy load = Yes

 

Attenuator = Not necessarily, Its fixed not variable.

 

The dummy speaker would consume wattage while giving nothing back.

 

By itself it would keep an amp safe from damage.

 

If run with another speaker it would consume half the wattage but that doesn't mean the volume would decrease by half. Speakers are not linear when it comes to producing sound. If you had a 50w amp and a speaker and a dummy speaker each would consume 25w. The difference in decibels between 50 and 25w is not that great.

 

The cone itself doesn't matter, you could easily dampen it or stick it in a completely sealed box, but the coil and the magnet do matter. Its the resistance and attraction of the two magnets that cause a phase shift in the signals voltage vs current (ELI the ICE Man) E leads I in an inductive circuit. I leads V in a capacitive circuit.

 

AC Impedance is measured in AC ohms which is totally different then DC ohms. A fixed resistor provides no phase shifting in an AC circuit. A Coil provides inductance which has a variable resistance based on Frequency of the AC signal. Music varies in pitch. A musical signal varies in frequency.

 

A coil stores a charge as a magnetic field. It resists creating that field and its charge is converted back into an electrical charge when the field collapses. That charging and discharging of the magnetic field causes a time delay. The voltage from the amp changes immediately, but the current between the transformer and speaker coil lag behind.

 

The higher the frequency the more the coil resists being charged because the magnetic field takes time to grow. A fixed resistor has no magnetic field so changes in frequency has no additional changes in resistance. An amp and speaker are designed to produce fairly linear volume throughout the sound spectrum of 20 to 20Khz. When there is no speaker inductance the load is no longer variable and its frequency responses and distortion levels will vary in odd ways. You often hear complaints that using an attenuator puts a blanket over the sound. A fixed resistance is part of that.

 

If you used a series of switched dummy speaker loads to consume wattage it would be the best solution for attenuating an amp but it would also be impractical because of the speakers size and the mathematics maintaining a proper impedance.

 

If you had an 8 ohm speaker and an 8 ohm dummy speaker you'd have either 4 or 16 ohms total. You'd have a drop of 50% on the speakers wattage. If you used two 16 ohm dummy loads in parallel with the 8 ohm, you'd still have a 50% drop on the one speaker and the two 16 ohm dummy speakers. (100W amp would drop 50W on the 8 ohm and 25W on each 16 ohm speaker)

 

If you had one 8 ohm speaker, and three 8 ohm dummy loads wired in series/parallel so each speaker saw 25W, then 3/4 of the wattage would be consumed by the three dummy speakers which produce no sound in return. The single speaker would be the only one producing sound.

 

Again 25W vs 100W is not that big a difference when it comes to decibels and the weight and bulk of 4 speakers when three aren't being used is impractical. There are better solutions like simply using low SPL speakers that do a poor job converting wattage to sound or simply buying a lower wattage amp if you need lower sound levels.

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I get what you're saying. This hypothetical fake speaker would act like a speaker in every way except moving air. Nuther thing, is is it possible to take a working speaker and rather than muffle or box it in, baffle it with concentric cone shaped baffles and thereby reduce or eliminate acoustic output?

 

Last thing, they have speaker output modeling, why not just speaker models? IOW you send the outs of your amp to a digital simulation of a speaker. Your amp can't tell the difference.

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Is is it possible to take a working speaker and rather than muffle or box it in, baffle it with concentric cone shaped baffles and thereby reduce or eliminate acoustic output?

 

Not sure I get the idea on what you'd be suggesting here. When you say baffle it with baffles - it baffles me. :D

 

Without damaging it, mounting it flat against a flat board would do a good number on killing sound while still allowing some cone movement, then putting it in a small padded box to prevent back waves from escaping would be my best suggestion. Much of it would depend on the type of speaker. You can get a small, high wattage, Hi Fi speaker with a low SPL and get it mounted in a small box. One of these handle up to 200W and have an SPL of 89/ I have a pair of the 10" and though the sound quality isn't bad the, volume they put out is pathetically weak. https://www.parts-express.com/pyramid-studio-pro-wh8-8-woofer-accordian-surround--290-260

 

If you really want to cut volume just use this speaker in place of the other that's too loud instead of using a dummy load.

 

A dummy load is good when you want to use an amp and silence its output which would be an option. Mount a high wattage small speaker in a sealed box. You could even add a speaker emulated line level out for about $3 in parts and a $10 speaker. No need to add the digital part, but you could.

 

Personally I'm not a fan of attenuators and using a speaker level out for anything but driving a speaker.

Back in the 70's/80's it was common place because many tube amps didn't have line level outs. I used one with my Ampeg V4B bass amp for years so the sound guy didn't have to mic my amp.

 

I even built one into may Bassman amp. All you need is these few components connected to the speaker jack. The speaker of dummy speaker needs to be connected too.

 

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This will get you line level but its really not the best solution any more. Any signal taken from a speaker output is going to have a really high noise floor. its much better to take the signal before the power amp then add speaker emulation.

 

You can plug one of these into an amps effects send or line level out then simply select that cab type you want. You can buy one as low as $25 on ebay. I bought two so I can digitally emulate a stereo signal from just about any source including straight from guitar pedals. Does a hell of a good job too.

 

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When recording with a band I'll mic my amps. Of course my one Marshall head has a speaker emulated line out from the factory and it sounds killer compared to the miced cab so I usually mic one amp and DI the other.

 

For solo stuff I don't even bother powering up amps. The small multi effect units with built in amp and cab emulation have gotten so good now I don't even have to be bothered with an amp. That one Vox Stomplab G1 unit I have has 50 different amp head types and 15 different cabs to choose from. That's a hell of a lot of combination for tones, plus you have the full array of effects. You simply cant match that kind of diversity unless you can afford to buy all 50 amps and cabs.

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Lemme address the baffling for now. These would be conical overlays of some kind that fit right over the speaker. They wouldn't impede the cone just block the radiation. I think if you designed these correctly you could get dramatic reduction of acoustic output.

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My studio has multiple layers of sound absorption, dual layers of sheetrock separated by an air gap, 5" of cellulite insulation, plywood exterior and solid brick exterior. Sound, albeit low still passes through it all.

 

Maybe the best solution would be to simply discharge the permanent magnet. Then the cones electro magnet has nothing to push against or be attracted to. You'd still have the Ferris core so the coils induction should still occur.

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