Speaker ohm load question

Does anyone know for certain or have first hand experience and can speak to if the GM or other TM amps have the ability to adapt to ohm load changes in real time or does it require a shut down and reboot for lack of better term for the amps to recognize the ohms with the single speaker output 4-16 ohm jack? For example if I'm running my 2 TM112 cabs in parallel for a total load of 8 ohm and want to unplug one from the chain which would swing the load to 16 ohm is that safe to do with amp running?

First be careful. I'm sure it was just a typo but the GM/TM series only supports 8-16ohm speakers, 4ohm is out of bounds! Other than that, yes it's fine to swap on the fly providing you are careful in one respect. The amp doesn't actually do anything to adapt to different impedances at all. It is just made sturdy enough to be able to cope with the mismatch in either direction. In fact most output stages will cope with a mismatch of about 2:1 in either direction, the matching is pretty rough and ready anyway, just have a look at the curve of a speaker's impedance, it's as bent as a dog's hind leg! I would guess that they are actually made to match around 11ohms accurately so they have a pretty equal mismatch down to 8 or up to 16. The important thing is to make sure you don't lose impedance totally and run them without any load in there at all, that is at an infinite impedance into an open circuit. Having them suddenly see infinite impedance is the worst case as it can cause huge flyback spikes at the anodes of the output valves via the output transformer.

I actually have my 4x12 set up with a wood divider inside down the centre line splitting it into two halves so I am running rather like your pair of cabs. In one side I have a pair of 16ohm G12M Greenbacks in parallel and in the other a pair of my original 1960s 16ohm G12Hs, with each pair obviously 8ohms. They are noticeably different in sound and I like to sometimes play one and sometimes the other pair. I installed a modern handle in one side of the cab which was slotted to take two large slide switches. Each of those switches controls one pair of the speakers. I can switch in either pair for 8ohms with a single switch up, both pairs in parallel for 4ohms with both switches up, or both pairs in series for 16ohms with both switches down. These options all suit my JVM205 though it has to be switched off and the plug reinserted in the correct output jack. With the GM36 I can happily switch between the 8ohm pairs on the fly as long as I make sure to never have a no load condition on the amp output at any time even for a split second. That means, as the switches are break before make, making sure to add in the second pair before switching out the first pair. The amp can cope with the 4ohm impedance as I go through the switching process. Switching out a single pair first and going over to the 16ohm series selection even temporarily would put it in a state for a split second with neither switch connecting its pair at all which would be nasty.

Cool thanks I thought it was ok but just wanted to double check. Myself and and another friend are just wrapping up a year long speaker shootout testing a large variety of Celestion speakers and a few WGS models using my 3 HK amps and his collection of modern Orange amps. We got onto this from a discussion one night on why both companies are sticking V30 speakers in most of their offerings and how dumb that seemed considering how disliked the v30 is in many circles. The results surprised us both because we were convinced both companies were doing themselves a disservice pairing their amps with those speakers. We gonna try a put together a little something in the future with sound clips to show our findings

That sounds a great project Iroc. For my money the V30 is a good workhorse speaker but it has a few pairings in which it just plain doesn't work. As you know I don't really rate them with H&K's TM/GM range so far as I have played them, they're too bright which turns to brittle at the top end. One thing that I have wondered but have no way of proving is if it is perhaps an easy speaker for Celestion to use as a base to tune. H&K uses them but they say they are specially voiced for them by Celestion and maybe that is a hint as to their popularity with installers. Just as some cars are open to easy tweaking and tuning while others are just what they are no matter what, maybe the V30 is in its own way a good base for tweaking for individual makers.

Do you prefer the Pulsonic cones in your 60's speakers or the RIC cone best? We'll be waiting forever for my buddy to piece together sound and video clips into anything worthwhile so I'll probably do a very long write up on what speakers we think pair the best with the HK amps and how we tried to approach it scientifically. So stay tuned.

You know what my thoughts are on issues like this Roc, I'm not into navel gazing and trying to find a way of seeing and describing differences in things which are basically the same. I can't hear any difference at all which I could put down to the cones. I'm sure there are measurable (not necessarily audible) differences but how do you know which may be down to that aspect? The magnets may be different material mixes and strengths (no, stronger is not better and a compromise has to be made), the magnetic coil gap may be a different size and geometry, the coil structure and materials will certainly be different, their ages vary by about 30years, every aspect may be tweaked in a slightly different way. And in all of that, the only real difference I hear is that the older G12Hs break up earlier than the modern G12Ms and are just a tad lighter at the bottom, but it is only the slightest bit. For my money, though I like using the classic type, there isn't that much difference if any when live at a gig.

Ok thanks for the reminder. I'll probably bag it and hold off sharing my speaker findings if it's going to be met with the same old naysayers and demands of proof with graphs and charts. You guys have fun it's just not fun to try to participate in a forum dominated by one closed minded individual

I'm very sorry you feel that way iRoc but I have the same feeling about your own side of this issue.

To have people putting forward different ways of viewing what we are playing with is a great thing for all of us, me and those like me included, as it poses new questions for us to think about and answer which expand our understanding of the problems.  That really should be "[all of our] understanding of the problems" if you catch my drift.  During that process of answering those questions there is one overriding aim.  To find the truth and prove it to be that whether it matches our own view or not, not to decide on what we want to be the truth and refuse to test it or even to deny any results which show it to be incorrect.  The quest for the truth is not served by just making any claim you feel like and maintaining it has a right to be right!

You are fighting for the right to have your own claims and your view of things unquestioned, left uncompared against established scientific/engineering fact.  Your ears are more accurate than over a century of scientific development.  This is becoming a common trait in modern life in every area.  The blessed internet gives us all an equal voice in argument despite our lack of knowledge in the particular field.  And that means the process of verification, proving to be true or untrue, is tossed out of the window.  You deny our right to test your view in practical ways and apply scientific (leading us to engineering) standards to it.  You even said yourself "and how we tried to approach it scientifically" so you at least understand the principle, you just don't appear to like it being applied against your own claims.  My claim is that anything I maintain to be true SHOULD be questioned and tested and I welcome your doing that.  I would be extremely interested and grateful in someone being able to point out where I am wrong in any technical argument.  It has happened many times and I embraced it.  That way I learn, I correct my position according to the points they have shown me, and I am wiser and more accurate afterwards.  I am afraid that process of moving forward in understanding doesn't hold any sway with people who think like you.  Which of us does this show to be open minded?

I do not deny your suggestion that the cones can make a difference, I just maintain what I have found myself, that I cannot hear any difference between my two models which could clearly be down to their different cones.  I even stated "I'm sure there are measurable (not necessarily audible) differences but how do you know which may be down to that aspect?"  What I have said is that there must be clear engineering proof of something that someone maintains they can hear.  It is inconceivable with today's engineering capabilities that you can hear something yet not detect any difference with good quality test equipment and procedures.  So let's hold off on maintaining that something is "the truth" until we have that proof, which I understood you were working towards and I was looking forward to reading.  Consider this.  Many musicians wax lyrical about the incredible differences in tone between the older 60s cones which I have and their modern equivalent which I also have.   Celestion, with millions of pounds invested in their testing facilities, maintain that the cone they sell as a replacement for my original is just that, a direct replacement and equivalent.  I even have a personal communication from their own Dr Decibel which states so when I contacted them about it some while back.  You prefer to believe the musical scuttlebutt.  It's "undeniably obvious".

I'm not a "naysayer", and I take exception to being called that.  I am a high standards engineer who loves making music and who understands how claims are proven to be true and has done his homework in our field for many years to the point where I can now bring to mind real life testing and its results in many areas which lead me to my views.  I am always happy to share that proof so others can use it to question what I say and the things they themselves find.  I am always happy to have those views scrutinised (peer reviewed) in order to test their accuracy, that is a necessary part of the "scientific method" which we engineers follow.  I am proud to demand charts and graphs in amongst other forms of proof as to whether something is right or not.  You have no idea how many of those are used in the design of your precious musical equipment in the first place.  Nothing could be made of any value without them as the current plethora of overpriced poorly designed and universally same sounding pedals sold by amateur modders shows.  Decent reliable repeatable electronic equipment including our own audio equipment is not something that can ever be put together by ear and guesswork.

"You guys have fun it's just not fun to try to participate in a forum dominated by one closed minded individual".  What you mean by that is that it isn't fun to appear to be someone who is not automatically amongst the "experts" when you make a claim which is then doubted on factual grounds.  You want this site to descend to the level of almost every other musical forum out there where any old ridiculous claim is made and, when it is pointed out that that can't be true, the doubt is shouted down by a mob of angry know nothings who believe in the ultimate right of the claimant to say what he thinks and be believed.  Everything must be "opinion" and everyone's is equal.  Well everything is most certainly not opinion.  Facts are facts and they are so because they can be proven not just claimed.  Yes it's "fun" to go onto those sites and make claims which make you look like a "mojo guru", a term I regularly use for the platinum eared flat Earthers amongst our musical community.  It's fun but it doesn't make you wiser and better informed and it sure as Hell doesn't take your use of your equipment forwards in any way which is to the benefit of your guitar playing.  It's fun but it distracts and misleads others who are just coming into this field looking to learn, and it passes on the same old tired myths and legends which can so easily be shown to be untrue but never are as the claimants simply deny the process. It's not clever to be ignorant, especially in amongst so much factual information you could drown in it!

Do you believe that the sound of a guitar is different if it uses left handed screws for its bridge and tailpiece?  Do you believe the amp sound would change subtly if you reversed the direction of fitting of some of the significant resistors in it?  If someone came here and claimed that to be true what would you say?

Sorry to lose you and by that I mean by your own choice to leave as I would genuinely welcome your input here.  However, just like mine, it just can't be bowed down to and simply acknowledged to be true when there are factual reasons why it might not be.

To illustrate my point to anyone who is still awake and listening...

PROOF that different makes of 12AX7 valves sound different

Have a look at that site which applies engineering standards to prove that there ARE significant differences between the different makes of 12AX7 around today and to suggest how these valves might sound in comparison with each other.  It sets up a well thought out practical test bed to ensure that all of the valves in the test are run under the same conditions as is absolutely necessary.  It runs through the tests plotting the results and superimposing them all onto one graph for comparison.  Then it becomes laughable.

Remember, the object is to prove that valves sound different.  If they do then their plots should show significant differences.  Skip through the bulk of it if you are not technically inclined, to the last graph at the bottom where those curves are plotted.  Hmmm!  Do my eyes deceive me?  Those curves look remarkably the same to me.  No not exactly but the difference at various points across the frequency axis is ridiculously consistent.  What we are seeing is actually the same curve  with a slight (<2.4dB) difference in overall gain.  Just imagine sliding the bottom curve up to lie over the top one, or any other one for that matter.  There is no difference between these curves which has any bearing in the real audible world.

So what do they do?  They invent a process of "normalisation" where they measure the difference between the curves at various points and set that difference on an expanded scale of 0-10 rather than 0-2.4.  That effectively masks the fact that even the maximum quoted difference of 10 is only 2.4dB in real life but it gives the results more emphasis as "different".  Look at the results plotted valve for valve with their red, grey and yellow bars showing low, mid and high response.  No valve shows a difference in any of its three measurements of over 2 on their scale, the equivalent of <0.5dB.  So how significant is that? (And why did they show the expanded valve comparisons so significantly above the miniaturised graph of the real results? )

A drop in sound level of a music signal of 1dB is only just audible to some of us if played instantaneously against the original.  With audible memory, if the comparison is longer than a few seconds all accurate perception of any difference vanishes.  Look here where some hifi guys discuss and test this? Sound clips of 0dB, -1dB, -2dB, -10dB for comparison  Go to post #11 and listen to the short soundclips there.  You will find that the -1dB clip is only just audibly different if played instantly after the reference, and even the -10dB is not massively lower.  0.5dB is inaudible to the ear, especially in a real life situation.

But this is touted as "proof" that valves do sound different when their own evidence clearly shows that they do not!  This is the stuff that gets my back up.  This is what we should all be fighting against and questioning as musicians as it is the basis for people like these justifying themselves putting their hands in our wallets and ripping us off for stuff we don't need through lies and half truths.  This is why we must bust these myths and the processes which give rise to them.

Speaking of speaker ohm loads: I have the TM212 cab. It is supposedly 16ohm.  I still have the stock speakers in it, the V30s. These are sold as an 8 or 16 ohm version though I can't see the difference marked on them online.

My question:
If I wanted to swap out one speaker inside the 212 cabinet for something more mellow, would I need to buy an 8 ohm or a 16ohm version as a replacement? (for instance, like the V30s, the Celestion Cream 90 speaker comes in an 8 ohm version or 16 ohm)  Thanks!

EDIT: does anyone know if the V30s in the TM212 are 8 or 16 in their own right, as I read elsewhere you should be matching the impedence anyhow

so do I need an 8+8 or 16+16?

Need to research series vs parallel wiring and gain access to the cabinet and determine how it is wired. Also, I always check my ohms by using a meter on the cable that plugs into that amp. That way you know exactly what load you're placing on the amp. Hope this helps.

I heard back from H&K directly who said "two 8-ohm speakers in series is what's inside the TM212"

Hi, sorry to be so slow in replying, just back from Greece after a couple of weeks in the sun drinking ouzo.  What was it the Stranglers said about beaches and peaches?  That's Heaven alright!

Yep, 2 x 8ohm in series inside the 212 giving a total of 16ohms.  Ideally you should replace each of them with another 8ohm.

Now being pedantic and looking at all of the weird possibilities it is possible to replace one of them with a 4ohm for a total of 12ohms as that is within the 8-16ohm range the H&Ks can cope with.  You would get uneven power distribution at about 1:4 across the speakers however so it's not really worth it.  You could also get away with replacing both of them with 4ohm drivers for a total of 8ohms or even put a pair of 16ohms in parallel for 8ohms total.  That's about the best you can do there.

As for measuring speaker resistance with a meter, remember you are not going to get the correct impedance shown in the specs and that's not a problem.  The impedance includes a hefty reactive part, that's inductance and capacitance, which varies with frequency so the impedance of the speaker wanders about wildly over its frequency range anyway.  The resistive part which is all that the meter can show is only relevant at DC which is pretty much irrelevant to us when making music!  As a guide a 16ohm speaker will usually meter out around 12ohms and an 8ohm one at around 6ohms.  Correct amp/speaker matching is important to aim for but not really critical in most cases.  Most robust valve amps will cope with up to a 2:1 mismatch without complaint as H&K have shown in their spec.