A "coneless" speaker as the dummy load for a tube

[zonta]

amp.


Ok. the idea is using a coneless speaker as the dummy load and then wiring a normal speaker to it in serial with a 1M pot in between in order to be able to lower the volume level of the normal speaker.

In this setting, as the output of the tube amp first hits to the coneless speaker we don't need to worry for the load and then with the help of a 1M pot, we can set the volume of the serial connected speaker as we like.

The amps volume would be set to loud enough for the "tube break" yet what we here would be bedroom level.  

Should this work?

Acording to Weber, it does:

http://www.webervst.com/mass.html

The thing that they call "motor" looks like just the magnet part of the speaker without the cone.  Do you think that it is modified somehow?

If not, anyone can do the same with just sacrificing a speaker (since it does not have to be a celestion blueback, aint no big deal...a 20 dollars worth 3rd quality high watt speaker would do fine).

What do you think?

[petemoore]

The dummy load speaker is just that. The speaker coild instead of ceing connected to and driving a cone, is connected to and drives a pad, Something Like a drummers practice pad...it soaks up part of the load, leaving some for the real speaker...[I believe this is the concept of the Marshall Power Brake..
  Fixing the cone to the exact right flexible type 'stuff' [probably some kind of rubbery stuff...that can give alot, but not Give up easily...that speaker coil will pull push and vibrate the tar out of whatever its connected to] would be the trickiest part I think.
 Imitating the resistance of a speaker cone, influenced by the air pressures of a closed cabinet [or open] just getting the coil to not shoot out of the magnet, and still have varied resistance to it's 'throw'....small resistance for small movements and increasingly larger amounts of resistance for larger coil throw or travel.
 The way the coil moves will directly influence the amounts of push the other real speaker gets...and how it responds to transients...Ie if the coil  is held too stiffly...the transients the load it would be absorbing would be altered...[this might be good...some thing to mess with anyway...]...I think the concept is that it reacts just like a speaker that is moving air in front and being restricted by a closed cavity of air [enclosure[ behind.

[Mark Hammer]

There are a few things to keep in mind to bring this off well.

First, you want to NOT hear the "dummy" load.  Essentially, and ideally, all you want from it is what happens as a voice coil moves back and forth in response to output from the amp.  Of course, that voice coil can't simply float in mid-air and has to be suspended somehow, preferably in a manner that mimics the relative resonances and compliance that the "real deal" has.  So, for that, you want to have as much of the overall cone/basket structure in place as you can without necessarily moving air.

We've had extensive discussions about this before on Ampage, and one of the solutions that arises is to simply seal off an intact speaker in a cabinet that damps its audible output enough.  

Another is to deftly remove as much of the cone as you can from the so-called dummy load.  Depending on the nature of the cone material, sometimes it helps to stiffen up the cone by "painting" it with stiffeners like diluted glue or even varnish, that will let you poke a scalpel or utility knife blade through it and neatly cut away only those portions you wish to without tearing anything else.  Bear in mind that the cone is held in place by both the spider (the wiggly part closest to the edge of the coil/dome) and the cone surround (the part closest to the edge ot the speaker basket).  I imagine on fabulous speakers, the spider can manage the task of keeping the voice coil perfectly aligned by itself, but on less ideal drivers the voice coil probably needs both the spider and surround to keep it on the straight and narrow...literally.  All of that means that you probably need to balance out reducing audible air movement by the cone with maintaining structural rigidity of the cone since, whether audible or not, it still has to pull that voice coil perfectly up and down and not permit the sort of lateral wiggle that would translate into distortion or voice-coil burnout by friction.  My gut sense is that reasonable cone-surgery paired with a suitable enclosure would nail the silent dummy load nicely.  That may well be what Weber has in their box.

A separate issue is the degree to which the speaker needs to have the weight/compliance of the cone/coil adjusted in some manner.  Remember than a portion of the fluctuations a true speaker provides (as opposed to a mere power resistor) stems partly from how the cone reacts to sudden impulses in different parts of its frequency range.  Both the compliance of the speaker surround (i.e., how wiggly the edge of the cone is) and the mass of the cone itself partly determine this.  The cone mass is, in turn, determined by overall size, material, thickness, and any intentionally designed properties (e.g., "bell"-like form, ridges, etc.).  Change any of that and you can end up with something where the speaker has a different effect as load than you ntended.  Not having tinkered with it I can't say whether that is something that is easily compensated for with EQ or not.  
In many respects once you are driving the intended/heard speaker at a much lower volume, the tonal response of that speaker changes anyways (MANY speakers sound very different at different SPLs), so all this little nickel and dime crap in the properties of a dummy-load speaker may well be moot by comparison.

[aron]

I have used the prototype mass and I bought another.

It works and I would just buy it from Weber; the price is more than fair.

Does it work? Yes.

[petemoore]

About glueing a section of scavenged cone, to a 'to be used' speaker cone.
 I've repaired speaker cones using speaker cones.
 This CAN be done to great success even if there's a big rip in the speaker...it needn't be labeled 'blown'...this is very low tech, but A/b ing the repaired speaker to the clean one...we couldn't tell which one had repaired.
 You could take a speaker with a good cone/bad coil, and cutout a 'aluminum rim' [I use car rims as an example where material is cut away from a round shape...to make it lighter/strong enough]...into a cloverleaf looking affair...put this over the 'to be a ' dummy speaker...mard the clover leaf on that speaker...cut its cone samely [to cloverleaf] glue the two 'cloverleafed' partial cones together...won't be zackly like a regular speaker but should have good strength, and the weight of the gluem and the doubled thickness partial should come to relatively the 'right' cone weight and you'll have the suspension thing going quite well.
 Now with the big clover holes in the speaker [these will seriously reduce the speakers air moving ability] it should be less loud.
 You could experiment with restricting/resisting the clovercones movement with extra weights, or foam weged tween the frame and cone [etc etc]...this will change the amount of force the real speakers get depending on the movement and position of the dummy load...I don't know the structural CAD's of a power brake, but the more you damp obviously the closer you get to having a dummy cone that's not moving easily...which is the basic intent of the experiment....something I've never read about ppl diddling with, but could be getting that dummy coil suspended interestingly could have interesting results..I think the power brakes coil is suspended by elaborately chosed materials and thicknesses etc.
 You want to leave enough cone structure to withstand the punishments it will be recieving....you don't want the coil to hit bottom but you want some specific degree of movement restriction [closed back cabs restrict harder the farther the coil gets away from its idle position in relation to the magnet.