Switchable 4 ohm, 8 ohm Cabinet

There is no such thing as a cabinet that can switch from 4 Ohms to 8 Ohms. The reason Accugroove stopped selling cabinets with that switch is because it was all a ploy.

Do a search for Accuswitch on here.

The new Epifani D.I.S.T. cabs can do it, and they seem to be the real deal.

Why even bother? The difference would barely even be noticeable.

With a little know-how, a couple of high powered resistors and a switch, you can make any cab switchable.
You would need a couple of these -
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As to which ones, how many and how to wire them (parallel or series) is all dependent on the cab you're looking to make switchable and how much power you plan to put through it.

Important to note however that just because it could work doesn't mean it wouldn't suck. The power lost as heat would make the whole ostensible benefit of switching load values worthless.

bongomania said:

Important to note however that just because it could work doesn't mean it wouldn't suck. The power lost as heat would make the whole ostensible benefit of switching load values worthless.

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That power has to go somewhere. You forgot to mention that it would have an effect on the overall Q of the cab as well.
I would definitely be concerned about heat building up in the cab doing something like this, but it's totally "doable".

The only other option (without dissipating / wasting the extra amp power to heat) would be to custom make a cab with dual voice coil drivers where the second coil on each driver can be switched into, and taken out of, the circuit to provide the necessary impedance.

Zagnut, your dual voice coil idea is very creative thinking, but unfortunately it wouldn't work.

The electrical Q of the dual-voice-coil configuration would be doubled when the single-voice-coil configuration was used, because now your electrical motor would only have half as many turns in the magnetic gap and so would be only half as strong. The bass response would fatten up drastically, and efficiency would drop by 3 dB.

One possible way to do a switchable cabinet would be to start out with six 6-ohm drivers. With two parallel sets of three-in-series, you'd get 9 ohms (whic is pretty close to 8). With three parallel sets of two-in-series, you'd get 4 ohms. Offhand I can't visualize how to make the reconfiguration with the flip of a single switch, but maybe someone smarter than me can figure it out.

DukeLeJeune said:

Zagnut, your dual voice coil idea is very creative thinking, but unfortunately it wouldn't work.

The electrical Q of the dual-voice-coil configuration would be doubled when the single-voice-coil configuration was used, because now your electrical motor would only have half as many turns in the magnetic gap and so would be only half as strong. The bass response would fatten up drastically, and efficiency would drop by 3 dB.

One possible way to do a switchable cabinet would be to start out with six 6-ohm drivers. With two parallel pairs of three-in-series, you'd get 9 ohms (whic is pretty close to 8). With three paralleled pairs of two-in-series, you'd get 4 ohms. Offhand I can't visualize how to make the reconfiguration with the flip of a single switch.

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I agree. Varying the overall impedance either way would effect the system Q throwing the balance of sound all out of whack. My idea is just that, an idea. It would achieve what the OP is asking for, but not necessarily sound great (or even good).
You're idea, utilizing 6 ohm drivers, sounds interesting. I gave 6 ohms a quick thought, being many car subwoofers are dual coil, 6 ohms per coil. When each is wired parallel with itself (12 ohms each), then paralleled with each other, the overall impedance is 4 ohms.
Of course there's 1 problem with both of these. I don't recall seeing any 6 ohm guitar/bass/PA drivers recently and car subwoofers don't make ideal bass cabs.

Even though the idea of using dummy load resistors sounds plausible, I still don't know how to keep the impedance change from affecting the system Q of the cab.
If brand x amp makes 400 watts rms at 4 ohms and 200 at 8 ohms, the loss is only about 3db. Not audibly noticeable to 97% of people. So the problem with half the amp power going up in heat really isn't going to affect output level at all. But the Q, well, that's a bigger issue.

Blah114 said:

I e-mailed Accugroove.. they no longer make the cabinets, the El Whappos, etc.. that can be switched to either 4 or 8 oms.. I am needing, perhaps, a giant cabinet that can be paired with the Genz Benz 6.0 Shuttle 12T.. either by itself, or WITH the 12T.. in other words, it would be nice to draw the 600 watts entirely from the 6.0 @ 4 ohms.. but during other times, draw 8 ohms x2.. using the 12T cabinet + whatever I may end up buying.

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I should have mentioned this earlier. You're amp is rated at 375W/8 ohms; 600W/4 ohms, correct?
When amplifier power is doubled, rule of thumb is you will only see an increase of approximately 3db (decibel). That's not even a whisper. Of course, having the extra power available is nice in case it's needed, but the level of output is hardly noticeable. To achieve something twice as loud, you need approximately 10x the amplifier power.
What I'm basically suggesting is, get another 8 ohm cab. That way you can run both together to get the full potential of the amp and you can run just 1 cab if you choose. The 3 decibel difference will be unnoticeable to your average person.

Blah114 said:

are you saying Accugroove's "Accuswitch" was BS? Was it a gimmick? If so, that turns me off.. but I am not ready to judge until I research it...

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Yes it was BS, and that is what your research will turn up. Sorry.

zagnut said:

When amplifier power is doubled, rule of thumb is you will only see an increase of approximately 3db (decibel). That's not even a whisper. Of course, having the extra power available is nice in case it's needed, but the level of output is hardly noticeable. To achieve something twice as loud, you need approximately 10x the amplifier power.
What I'm basically suggesting is, get another 8 ohm cab. That way you can run both together to get the full potential of the amp and you can run just 1 cab if you choose. The 3 decibel difference will be unnoticeable to your average person.

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This is correct!

They didn't. However the word on the street corner is that AG had been sold a fake technology by someone else, so AG was acting in good faith and did not realize he/they had been duped. At least that's one version of the story.

ZAGNUT:When amplifier power is doubled, rule of thumb is you will only see an increase of approximately 3db (decibel)

What about when you add another 8 ohm cabinet of the same speaker efficiency (size x Number of speakers) Say you have a 2x12 and add another 2x12. You double the power : (2) 8 ohm cabinets make 4 ohms total. Also twice as much air moved.
What is the ultimate benefit?

Things like this work:
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You could give the specs to Plitron and they could wip up a high quality autoformer for your needs.

Or you can just forget about trying to squeeze out every watt. It doesn't matter that much. Sound Pressure Levels matter. Add more cabs or buy high efficiency designs like http://www.billfitzmaurice.com/.

The impedance of the system arising from different driver hookup configurations does not affect system Q. Unfortunately many years ago JBL published at least one set of instructions advising against series connection of woofers, stating that this would negate the amplifier's damping factor because the second voice coil's resistance would be in series with the first's, and vice versa. The myth has been perpetuated ever since.

My counter-argument is that a separate, series-connected voice coil does not behave as a resistor, any more than the first half of a voice coil acts as a resistor in series with the second half.

I happened to have some of test equipment out, so before posting this I ran the T/S parameters on two woofers in series vs the same two in parallel. The variation in Qes, Qms, and Qts came to about 1%, which is within the margin of error for my test equipment. This data refutes the JBL paper. I knew it would, because I manufacture two loudspeaker systems that use series-wired drivers and I'm familiar with their measurements.

Now, adding a resistor in series with a voice coil will definitely raise the system Q, and in my opinion is almost never a good idea. But series connection of identical woofers will not. And I have the data to prove it:

Parallel connection (8-ohm woofers): Qes = .551; Qms = 2.87; Qts = .471
Series connection (8-ohm woofers): Qes = .547; Qms = 2.81; Qts = .468

While we're at it, just for fun:

Single 8-ohm woofer: Qes = .543; Qms = 2.83; Qts = .455
Single woofer w/8-ohm series resistor: Qes = 1.30; Qms = 2.87; Qts = .893

Bluedyna, assuming your amplifier delivers double the wattage into the 4-ohm load resulting from adding a second identical 8-ohm cab, you'd get a net increase of 6 dB in output. This breaks down as follows: 3 dB from the doubling of power, and 3 dB from the doubling of air displacement (from having twice the cone area). To be precise, this applies to frequencies where the two drivers are less than 1/4 wavelength apart; as we go up in frequency from this point, there will be progressively more and more destructive interference between the drivers and as a result up there they'll sum to less than the theoretical 6 dB increase.

I await a test of the D.I.S.T. cabs from Epifani. Apparently, as stated above they do it for real-with dual voice coils. The Accugroove thingy was BS.

Blah114 said:

I e-mailed Accugroove.. they no longer make the cabinets, the El Whappos, etc.. that can be switched to either 4 or 8 oms.. I am needing, perhaps, a giant cabinet that can be paired with the Genz Benz 6.0 Shuttle 12T.. either by itself, or WITH the 12T.. in other words, it would be nice to draw the 600 watts entirely from the 6.0 @ 4 ohms.. but during other times, draw 8 ohms x2.. using the 12T cabinet + whatever I may end up buying.

I have an 8 ohms Bergantino that I like a lot.. however, I have been offered money for it.. such that I would make a bit of a profit selling it.. I won't miss it much if I can buy a similar 12 or 15" cabinet.. ideally, the el Whappo, or similar.. 800 watts or less would be ideal.. but then I discovered Accugroove no longer makes the switchable 4 ohms vs 8 ohms cabinets.. perhaps I can find a used one..

Can you all kindly educate me with your opinions.. I want the flexibility of a 4 ohm cabinet for some shows.. practices.. and then an 8 ohm for other situations.. the Genz Benz with two 8 ohm cabinets is nuts.. I love it, but I am tired of lugging the gear around too.. for shows, just the 12T cannot cut it.. I was thinking if I grabbed an El Whappo-type cabinet.. that would solve my problems.. Acme and others do NOT make a selectably resistant cabinet.. suggestions appreciated!

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Yes, the Accurgroove thing was a hoax (or at best, a mistake). No one is sure if it was from dishonesty or incompetence, since the manufacturer never has said a word about it (other than taking it off the market). Do a search or just find the old Bass Player review.

Epifani is eventually coming out with dual impedance cabs using what I understand is the only method that will work (dual voice coils). Given Epifani's track record on time to introduce from announcement at NAMM, I wouldn't hold your breath!

I find the whole thing sort of a moot point at this time. There are many heads capable of running at 2.67 ohms (or below), which functionally gets you to the same place. And, if you like the Genz stuff and want to keep it lightweight, just get the Shuttle 12 Max, which has two power amps that can run virtually any combination of cabs you could thing of.

Also, the idea of using a very small 8ohm cab like the 12T, combined with a large 8ohm cab doesn't make much sense anyway, since the 12T would draw the same power as the larger cab. It makes much more sense to get an amp that can run at 2ohms (or a dual amp model like the Shuttle 12 Max), and a large 4ohm 212 cab. That way, each driver is seeing the same amount of power.

Or... what makes even more sense is to just get another 12T cab. That would still be a nice small rig, but would significantly increase the volume and low end of your rig in a balanced way (i.e., two 8ohm cabs of the same design). You would notice a BIG difference.