H&K GrandMeister 40 with two cabinets?

I am dummy when it comes to impedance and ohms.
So I have the GrandMeister 40 Deluxe. The speaker output has 8 and 16 ohms on it. I have been using the Marshall MX212R (160 watt) horizontal cabinet - it has two 12 inch speakers and has 8 ohms listed on it.
I am considering buying the Hughes & Kettner TM212 - it has two 12 inch speakers as well, it has 120 watts, 16 ohms, and an IN and an OUT on the back with the word parallel in between.
Can I plug both of these cabinets into the GrandMeister at the same time with no damage to the amp?
If so, would it be speaker cable out from the GrandMeister to the IN on the H&K cabinet, then speaker cable out of the H&K cabinet OUT to the IN on the Marshall cabinet?

I had much the same questions when I first got my GMD40. Basically, the output of the amp can handle between 8Ω and 16Ω of load. Anything higher or lower than that impedance and you risk damage to the amp. From the way you describe how you want to connect your amp to your speaker cabinets, it sounds to me like you're wanting to hook them up in series. The Marshal cabinet has an impedance rating of 8Ω load all by itself. This is fine if you want to run it alone. However, if the H&K cabinet has a combined load of 16Ω and you want to run it in series with the Marshal cabinet, that will be too much load for the amp as they will add to each other, e.g. 8Ω + 16Ω = 24Ω, which is too high.

If you were, for example, to run both cabinets in parallel using something like a cab combiner to do so, instead of in series, you'd need a formula to calculate the load since both cabinets are of different impedance. Unfortunately, when calculated together, running both cabinets in parallel would equal out to a total load of 5.333Ω load, which is too low.

It looks like you have two choices: You either find another cabinet that's rated at 8Ω that you can run in series, e.g. that has an input and an output like the H&K cab you want, or you can buy the H&K cab and rewire it so that its impedance equals out to a total load of 8Ω and then run it in series with the Marshal cab. That will give you a total of 16Ω total load, which is within the safe operating envelope of the amp.

Much appreciated Jereth! My original intent was to have one cabinet at home and one at my band’s rehearsal space, figured why not find out if you can run them both together. I’m getting too old to lug around stacks anymore, plus the GrandMeister is plenty loud enough for the metal music we play. It’s a pretty versatile amp and I use it in my solo music which is any kind of genre. For me, it seems the best option is to find a cabinet that is rated 8 ohms that has the input and output and run it in series. Thanks again for the help!

Glad to help. As you can see from my profile picture it is possible. It's just a matter of understanding how impedance is calculated and hooking things up in the correct way.

Personally, I have a bit of a weird setup. The B52 4x12 on top is mono and is rated at an 8Ω load, like your Marshal. The problem is the Jackson cab on the bottom. You see, that cab can be run either mono or stereo, but each of those ends up having a different load rating. If I run the cab in mono, it's a 16Ω load just like the the H&K cabinet you want to get. The B52 has an input and an output just like your Marshal cab and, just like in your case, if I run them in series in that way the load will be way out of spec. However, if I run the Jackson cab in stereo, each input is rated at 8Ω. Since they represent a symmetrical load I can run both sides of that cab together in parallel to give a combined total load of 4Ω. I achieved this parallel wiring by using what's called a cab-combiner. Alone it would be too low to run with the amp. But, when I then ran the B52 cab (8Ω) in series with this cab-combiner (4Ω), they summed for a total combined load of 12Ω, right in the sweet spot.

The only other way would be far more expensive, e.g. buying 2 of the H&K 2x12 (16Ω) and running them in parallel with a cab-combiner, and then in series with your Marshal cab. If money is no object, then this would achieve all your goals. However, if you're like the rest of us mortals, I think you would be better served just finding another cab with the correct rating. It'll save your amp, several headaches, and your pocketbook in the long run.

Hey guys,

Just a really quick comment: I think the H&K 2x12 sites provide a parallel out, not a series out. This doesn't change your situation, but may be useful if you get it and try a different cab with it.

A couple more options: I am assuming the speakers in the H&K are each 8 ohm, wired in series. You could wire the parallel jack to only connect one speaker. Then, you could use the two cans together as a 3x12 (you'd need a parallel splitter from the amp, since you replaced the parallel jack on the H&K (or add another jack that is only connected to one speaker).

Or, something like this: https://www.tedweber.com/z-matcher

I am NOT recommending this, but many people run slight mismatches all the time. Some amp manufacturers (Mesa being very vocal about it!) recommend experimenting with slight mismatches for tonal variations. Pretty much all of these recommend NOT exceeding half or double the rating. So, a 5.3 ohm load on the 8 ohm tap would b OK. Or, a 24 ohm on a 16 ohm tap would be OK. A 2 ohm load on an 8 ohm tap or a 32 ohm load on a 16 ohm tap would be BAD!

All that said, I do not know how H&K feels about mismatches. It could be that they took all this into account when labeling the speaker out at 8-16 ohm. YMMV, and caveat emptor! This is the interwebs, so take everything with a grain of salt.

Pretty much said already but just to confirm and add a bit of context...

Both the amp and the cab definitely have parallel connected sockets inside each of them.

There are two problems with matching cabs to amps.  Firstly there is impedance matching.  The impedance of the speaker load slung on the output is passed back, ("reflected" is the correct term), to the output valves as their anode load by the transformer which multiplies up the value according to its own windings.  This multiplying factor is a constant for any particular winding of the transformer so the valve anode load impedance must change according to how the speaker impedance does.  The valve output stage is designed and optimised for a particular impedance in their anode circuitry and the transformer primary reflecting the speaker load does this job.  If you connect too low or too high an impedance the valves see the wrong load and that can cause effects which can be catastrophic to them and to the transformer.  Believe it or not it's more risky to run with too high an impedance than with too low, particularly with no load at all which is an infinite impedance and should always be a real no-no with normal valve amps.  The H&K amps with their resistive power soak and Silent option help with this problem.

Speaker impedance is not anything like precise and it is correct that most amps will tolerate a degree of variation, usually around 2x either way.  An 8ohm speaker generally has a resistance (not the same thing as impedance as it means basically at DC so no inductance or capacitance effects to worry about) of around 6-6.5ohms and a 16ohms is generally around 12-13ohms.  This is usually quoted in teh speaker specs and you can measure this with a bog standard DC resistance meter.

Different makes of speaker will all vary from each other slightly even though they are quoted as the same impedance as they all have a non-resistive part to their impedance which is frequency dependent, (and temperature dependent and voltage level dependent and so on).  Their impedance actually has a sharp peak around their resonant frequency which dips to around their DC level in the lower mid frequency range then climbs again as frequency increases.  As the H&K amps are already set to work within a range of 8-16ohms there has already been a bit of the usual latitude taken into account.  I wouldn't push them too much further by going outside of that if you are playing at volume.

In the case of the amp outputs this means that you can't work with two paralleled cabinets of normal impedances other than 16ohms.  Anything lower than that and you will end up below the recommended 8ohms.  16ohms//16ohms is exactly 8ohms so if one of those drops below 16ohms then the overall impedance must drop to below 8ohms.  Paralleling impedances always results in a value less than either of them individually.  Likewise with 8ohms and 8ohms in series giving 16ohms you can't increase either of those any higher without increasing the overall impedance to above 16ohms.  Two impedances in series always give an impedance higher than either of them individually.  (These are rules of thumb for use in the case of speaker impedances.  There are complex cases where those two rules may not apply but these are for much more complex circuitry than ours.)

Now to the often forgotten bit!  The other factor you must take into account is the power dissipation in each speaker.  Consider this example.  We have 3x 8ohm speakers.  We put two in parallel to make 4ohm then the other one in series with these to give 12ohms overall.  We are in the zone and it sounds like a result!  However, you must consider that the two speakers in parallel are each taking only half the current of the third one and they also have only half the voltage of the third one across them too.  Let's say we are able to pump 30W through that 12 ohms total load.  The power is split between them as 5W to each of the parallel pair and 20W to the third series one.  That is a serious imbalance and could even be enough to burn out that series speaker if you are unaware of it.  Suppose you were using 3x 40W speakers and a 100W amp.  Sounds fine with 120W of speaker and only 100W of amp.  However, the split would then be 16.7W for each paralleled and 66.7W for the third!  Not good by anyone's standards.

Great info, as usual. We didn't even mention speaker sensitivity and the balance of the actual sound coming from the separate cabs!