Weber MASS 200 Attenuator

A lesson in Sound Pressure Level



08/31/2026
Today we are looking at the MASS 200 amplifier power attenuator from Weber Speakers, Inc. These days there are all sorts of attenuators and load boxes out there with all sorts of features like speaker emulators, computer interfaces, IR loaders, etc. Why am I looking at a straightforward attenuator? Well, the main reason is that I want an attenuator to simply... um, attenuate. I just want to lower the volume of my tube amps to allow me to use the power amp distortion they offer without irradiating me. I'll still put a mic in front of my amps to record. While shopping I did want a unit without too much coloration as I attenuate so I pursued an active attenuator for that. All right, now we are getting into terminology. Let's talk about "active".

Attenuators work by converting all or part of the current being fed from your amplifier into heat before it reaches the speakers. They come in two basic forms:
Passive: A bunch of resistors are stacked between the amp and the speaker with a switch to choose the amount of resistors and thus resistance you want to apply, and thus how quietly you want the speaker to output you sound. An example is the Scholz Power Soak from the 1980s.
Active: A "speaker motor", basically the permanent magnet, voice coil, and pole piece from a speaker, is placed in the incoming signal to dynamically react like a speaker does. Then some form of variable resistor is placed in line to choose how much more signal you want to reduce to heat. This combination preserves much of the dynamic response of the amp-speaker combination better than a passive attenuator does.

Of the two, I wanted the response of the speaker motor and the ability to smoothly adjust the loudness offered by a wirewound resistor. I also wanted a high-end makeup control in case the business of attenuation soaked up some of the high end. And now we add another factor: fitting the unit to my amps. Now, I did want the attenuator to handle both my American amps that output at either four- or eight-ohms impedance and my British amps that output at sixteen-ohms impedance. And then there is the issue of power capacity. I read all around and no-one really explained how to match the unit to the power capacity and gain level of the amp except Weber Speakers. Weber's formula goes like this: for '60s, '70s, and early '80s gain levels, choose an attenuator that offers twice the capacity of your amplifier. Got a 50-watt amp? Get at least a 100-watt attenuator. Once you get into heavier gain amounts like '90s and later high-gain amps, you'll need more than that. I've got amps rated up to 65 watts and only one of those is a higher gain amp. Weber's 100-watt and 200-watt attenuators cost nearly the same. According to them, you pay no tone penalty for using an attenuator rated above your amp's needs.

And finally, that impedance thing. I have a few amps. Several attenuator companies make multiple models, each designed to be used with a single impedance. It makes no sense to me to own three attenuators when there are attenuators that offer either switchable impedance or "impedance swamping". The meaning of that last term is that the attenuator is built so that it can handle any of those impedances without even throwing a switch. From my study, that is accomplished by placing a non-inductive wirewound resistor in the circuit.

So now, dear friends, you know the criteria that led me to my choice. From that point I did what anyone else does: I got on the Internet and started my research. It only took five or six years and the purchase of a non-master control amp for me to get off the dime and settle on the one I wanted. The attenuator I chose was the Weber MASS 200 because is active, it is impedance swamped, it will handle the output wattage of my amps, and it has a treble make-up control. Schmart. I ordered one, noting that they advise that the attenuators are built to order and their build time may be seven to ten days. Weber asks that you real their attenuator FAQ before ordering and it is quite helpful. Mine went out the very next day after the order was placed. Now, it was held up on the way by a tornado that hit one of the route cities of the delivery company, Fed Ex. Fair enough.


Courtesy Weber

The Physical Facts
The MASS 200 arrives well-packed from the factory. The unit itself lives in a rather large-ish sheet metal box, 7 13/16" wide, 5 9/16" high, 7 7/8" deep. It is reasonably solid and heavy at 7.4lbs. There are cooling slots in the top over the wirewound resistor that serves as the main speaker volume control. A big old screw is screwed through the bottom of the box, presumably to secure the speaker motor. Rubber feet protect the screw. The color scheme is black with white lettering. On my "no options" unit there are an Input From Amp, two Speaker Outputs, and a Line Output on the back panel, all served by 1/4" jacks. On the front there are the Speaker Volume, Treble Compensation, and Line Out Volume, as well as a Bypass toggle switch. There you go: pretty straightforward. There are two additional options available, neither of which I purchased: a headphone output with its own volume control and a footswitch jack for the Bypass that uses a relay, and thus requires a power supply to operate.


Courtesy Weber


So, how does this thing work?
I applied a bit of brain power and decided to crank the unit's main volume all the way up and the treble compensation all the way down as a starting point. We don't have to compensate if we don't attenuate, right?   ***Ear plugs in***   I connected up the amp and speakers with speaker cables, set the bypass switched to "up" to bypass the attenuator, and powered up the amp. Everything sounded normal. Flip the Bypass switch down to insert the attenuator and there wasn't much difference because we've got it cranked all the way up with little-to-no attenuation. We are playing a very loud twenty-watt Marshall SV20H amp today at about eleven o'clock on the volume controls, so it is pretty ear-splitting loud at full volume on the attenuator. We are talking about 110db in twenty-watt mode and 100db in five-watt mode when measured with the Decibel X iPhone app at two feet in front of the amp. Thank you, ear plugs.

Now we start turning counter-clockwise on the attenuator's "Speaker Volume" to lower the sound pressure level. As Weber advises, the movement of the main volume control feels gritchy because you are working a wirewound resistor, not a potentiometer. It's all normal. I've been there before because I did electronic experiments as a kid. Thanks, Dad. By about ten o'clock on the attenuator we are at a level that I think won't damage my ears in small doses. We've knocked down both of those unattenuated numbers above by ten db. That makes the amp's five-watt mode a little closer to bedroom level. By the numbers, with the amp volume controls around eleven o'clock, we are talking about 100db in twenty-watt mode and 90db in five-watt mode after attenuation. I think OSHA will allow you around four hours at 90db. So, we go with five-watt mode on the amp.   ***Ear plugs out***   So far, I am not hearing too much tonal change other than what I would expect from a lowered volume on any audio device, ie., the effects on the ear of lowering volume that occur due to the Fletcher-Munson Equal Loudness Curves. That is pretty darned amazing, given all the negative attenuator talk on the Internet. Now the amp sounds decidedly smaller, but everything does when you lower the volume. That is why stereo amps used to have a "Loudness" control - to restore the low and high-end that is lost in lowering the volume. I wonder if most of the hoo-hah on the Internet about losing frequency response with attenuators is from people who don't understand that your ears hear differently at lower loudness levels? Or, is this just an excellent attenuator? Hmmm... Whatever. You can raise the sparkle a bit with the treble compensation if you positively feel bereft. After twenty minutes of continuous playing there is a little heat coming out of the vent slots over the volume control but it really is quite minimal.

So this box makes a marked improvement on the minimum sound pressure levels available from a very loud amp, meaning that it brings down the amp's lowest usable level to a survivable point where you aren't dooming yourself to ear damage. Bravo!!! It is well built, straightforward to operate, and well worth the admission fee.





WEBER MASS 200




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