Shiva Driver implementation. (1 Viewer)

[Peter Johnson]

If I build my sub with a set of those dual binding posts, with the metal bar connecting the two sets, is it possible to wire each VC to 1 of the sets of posts?
So with the bar in place, it is a normal 4 ohm load, as the VC's are in parallel, but if I remove the bars, driving as an 8 ohm load and a single VC, then I can simply attach a potentiometer to the other set of posts, and alter the Q of the system?
Seems very flexible to me, but is this correct?

 

[Patrick Sun]

Yes.
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PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; Link Removed

 

[Peter Johnson]

So why dont people do it more often?
I would have thought this flexibility would have been popular...?

 

[Jack Gilvey]

While the flexibility of "resistively damped operation" is nice to have, it's not without a certain cost. Sensitivity is reduced by 6db with only 1 VC, and power handling is cut in half.
I think, in practice, most people don't really need it, designing to a preferred Qtc and leaving it at that. Also, RDO can never lower the Qtc past that of the driver installed "normally" in the box (it can only go higher), so a very low Qtc would still require a fairly large box.
The only application I'm aware of where someone is using this option is in an infinite baffle, where Qts = Qtc. This might prove to be overdamped with a Shiva ot Tempest, so leaving one VC open raises the Qtc to .8 or so. Two drivers are used to counteract the loss of efficiency.
I'm sure there are others, though.
The nice thing about your proposed idea is that you're not committed to anything once installed, so it's easy to try.

 

[Peter Johnson]

Thanks Jack.
I figure it is at least worth a shot. The only expense is dual binding posts and a potentiometer ($5 extra).
Fiddling in LSP cad, it seems that I could get a peak in the 30-40Hz region, which could come in handy for some electronic music I listen too....

 

[Jack Gilvey]

Sounds like fun. What Qtc do you propose to start with, Peter? I'd go with a pretty large box, for a reasonable low Q, maybe 0.577. That way, you can have a "transient perfect" mode for classical music, etc, and bump it up to .7 or so for rock, maybe even higher for movies.
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[Shade Watson]

Peter,
It seems to me that you should use the dual binding posts anyway. That way you have great flexability in amplification.
For instance:
1) Drive both coils with one amp with a 4Ohm load.
2) Drive one coil with one amp with a 8Ohm load. This option will be good if you are using the amp from a low priced receiver that can't handle a 4Ohm load.
3) Drive each coil separatly from the L/R outputs of a sterio amp or receiver with 8Ohm load. Having the ability to use both channels of a stereo amp is a very attractive option.
I am currently building two boxed Shiva subs. I will wire them each with dual binding posts. I will then use my old Sony 110 watt receiver to drive each sub from one of it's L/R channels. This will put a 4Ohm load on the Sony's amps. If this overheats the Sony, I will then wire the Sony to only one coil per sub. This way the Sony will see an 8Ohm load and probably do fine.
If neither of these options works, I will save up for the Samson S700 or S1000. Either of these will probably kick some a$$.

 

[Peter Johnson]

Yeah the dual BP's just give that extra bit of flexibility.
Jack, I had a 127L box in mind. A 127L box in LSPcad is under 0.577, but not too sure about calculating Q in a sealed box.
Does the Q just depend on cab size for a normai wiring?

 

[Jack Gilvey]

Does the Q just depend on cab size for a normai wiring?

That's about it, although the stuffing will have an effect.
The Shiva sealed application notes specify a 101.5 liter cabinet for a Q = 0.577. I think I'd start with that.
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[Peter Johnson]

Thanks.
I get a lower F3 with a 127L box, and 127L box is not too big, although I really dont want to go any bigger than that...
WRT stuffing, I thought that stuffing a vented enclosure was asking for trouble? Wouldn't the stuffing interfere with the port air flow?

 

[Patrick Sun]

Just keep the stuffing away from the port opening.
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[Jack Gilvey]

Peter,
I'm referring exclusively to sealed boxes wrt to RDO, box sizes, and Qtc. I would not use RDO in a vented box, changing parameters in that fashion will probably severely "misalign" your box.
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[Peter Johnson]

Thanks everyone.
One question however...
The SealShiva notes that Jack linked to above state that the shiva will do an F3 of 30Hz or so in a reasonalby sized sealed box. When I plot it in LSPCAD, I get 40Hz?
Seems like a rather large difference in extension...
The RDO will let me extend it to under 30Hz, flat, but this still doesn't explain the contradiction...

 

[Jack Gilvey]

Peter,
I think the difference is that Adire models them with a 12db/oct low-pass crossover with an 80Hz corner frequency, representative of the average receiver, I guess.
If this is not done, the driver can peak above 100Hz, and give a misleadingly high F3 (assuming, of course, you intend to use such a low-pass filter). It's possible to model this in LSPCad using the crossover "wizard". Give that a shot and see what you get.

The RDO will let me extend it to under 30Hz,

Just remember that this increase in extension will be at the expense of transient response, so be judicious with the trade-offs. That's why the pot is better than applying a fixed resistor across the unwired coil.

 

[Peter Johnson]

Yep, thats exactly what it is.
I suppose one of the advantages of doing something in this way is that no change can not be easily undone...