Dual Impedance Question

[Mustang Marvin]

Maybe this is a little off topic, but I know there are some on this forum who can give me an answer.
I have 2 Altec speaker systems. One is 8 ohm the othere is 16 ohm. I was curious as the the effect of using both the 8 and 16 ohm taps on my Mc Intosh MC 240 to drive both sets either individually or Both at the same time. They both have the same bass drivers, 416's, but different compression drivers, 806 vs 399.

What are the effects or hazzards of attempting this?

[techmecca]

Maybe this is a little off topic, but I know there are some on this forum who can give me an answer.
I have 2 Altec speaker systems. One is 8 ohm the othere is 16 ohm. I was curious as the the effect of using both the 8 and 16 ohm taps on my Mc Intosh MC 240 to drive both sets either individually or Both at the same time. They both have the same bass drivers, 416's, but different compression drivers, 806 vs 399.

What are the effects or hazzards of attempting this?

don't do both systems at the same time - you'll double load the outputs and make the amplifier unhappy

you can make a switch box that connects the 16 ohm output taps to the 16 ohm system OR the 8 ohm output taps to the 8 ohm system but don't let that OR become an AND... driving both systems you'd be loading down the output transformer and the tubes driving it. The transformer could heat up and fail or the tubes will fail... nothing good will happen - and those transformers are really expensive to fix or replace.

I would not risk it

[Mustang Marvin]

Thanks John for your comment. I will not use them together. BTW, which do you prefer. 8 ohm or 16 ohm and why?
Thanks again,
MM

[techmecca]

Thanks John for your comment. I will not use them together. BTW, which do you prefer. 8 ohm or 16 ohm and why?
MM

It depends on the amplifier ... actually it's about matching an amplifier to a speaker system. I have to say that there is really no clear cut universal answer to your question... so... long answer

I work primarily in recording studios and these days that covers a wide spectrum from big studios with huge speaker systems, to mastering studios where the room, speakers and power are all tuned toward maximum fidelity at reasonable listening levels, to in-home studios where most of the time people are listening with headphones and then mixing on small self powered speakers.

At one extreme there is a crowd that seems to want to develop multiple acoustical Watts in a control room, for mixing. The loudest control room I was ever in was one where I spent a full day with another tech friend replacing drivers... a LOT of drivers. The total amplifier power on hand was just a little over 10KW... all Crown Studio Reference 1's and 2's. It was a small control room. Jack and I got everything buttoned up and brought on line. We checked the crossovers and so on and ran the system up to around 132dB_SPL (this after installing ear plugs AND donning our shooting range muffs) and the system, after tweaking, was deemed acceptable... sounded "clean" through the protection... measured well considering the complexity of the system... okay lets call the client in. He came in... put on some of his recent mixes, and cranked it up beyond 132, to "all the way"... I quickly clocked the room at over 140dB_SPL somewhere near the mix position and then fled because I couldn't breathe and my heart was getting confused.

For that system it was 8 ohm drivers all directly connected to amplifiers capable of welding... and maybe 4 ohm drivers could have worked "better"... though I really can't think of why "better" would, in any way, be a system capable of breaking over 20 dBW at the listing position, but in this system it was all about big fat cables and providing large amounts of of current flow through low impedance voice coils... and the heat sinks on the drivers that had them got warm.

so... anyway that is one type of system where the goal is to produce as much noise as possible from every driver all at once and the lower impedance allows one to transfer more power because for any given voltage at the amplifier's output terminals you can push double the current through a voice coil with half the impedance and thus double the power in the driver... assuming the amplifier can do the current.


Tube amplifiers... like a MC-240... driving partial or fully horn-loaded speaker systems are a whole other thing.

In your case you have a push-pull pair of 6L6GC or = output tubes coupling through a center-tapped transformer with a primary impedance of somewhere around 6000 ohms and having secondary taps of 16, 8 and 4 ohms. Your speaker systems have passive crossovers. Those were designed around a particular set of drivers each with some specified nominal impedance and efficiency... all mounted in an enclosure, with it's own efficiencies for coupling those drivers to an acoustical space.

With tube amplifiers it's about power matching and power transfer so efficiency is key... you don't want losses. So you have to have everything nominal... speakers have to work in enclosure, crossovers have to be optimized to the drivers, the amplifier has to couple as efficiently as possible through the crossover to the drivers and so on... it's a system

I have noticed that some crossovers really care a lot about what source impedance is feeding them... others less so. I have a number of 604 based systems and for those the power amplifier matters. I can set up the voltage gain of the amplifier and make everything as equal as possible from one amplifier to the next and I get a range of results both in efficiency and simply in how the system sounds. This seems to be on the crossover... different crossovers with the same speaker and cabinet can be more or less sensitive to what drives them.

My general rule of thumb is that if a system was designed to operate powered from tube amplifier with impedance matching taps on the outputs then I want to drive that speaker system from a tube amp like your MC240 or an MC275 or a couple MC75's or Radio Craftsmen 500C's or DuKane whatever... or a MC2120 which is a transistor amplifier with an auto transformered output with various output matching taps. I just find that these speaker systems and their crossovers seem to work better in that context.

I've noticed that series connected networks seem to be more picky about the amplifiers source impedance than parallel connected networks.

If your two speakers systems are all complete and nominal - meaning the drivers and crossovers etc all match up to the original design - and let's say for argument's sake they are are identical except for the system impedances I would say that they should sound and work the same assuming you are properly coupling your amplifier to them - selecting the appropriate tap on your output transformer. There should be no inherent advantage based on impedance IF you major concern is that they sound good and you are listing at sane levels. The main thing would be to couple them correctly to the amplifier. With your amplifier there is no advantage re headroom because the 8 ohm tap will also be lower voltage and you must use the tap that matches the load to keep the amp happy.

so to draw this to a close - what I am saying is that you can't really pull out one parameter like system impedance and ascribe to it an advantage one way or another that is universal... especially in interactive systems like transducer systems... getting electrical turned into acoustical or acoustical into electrical is not a straight and simple path. You are actually going from electrical to magnetic to mechanical(acoustical) or from acoustical to electrostatic to electrical... mics and mic preamps are another fun area to play in...

the real answer is ... which of your systems is closest to nominal given the condition of the drivers, crossovers, enclosures and parts available... which system was better designed for the purpose to which you are applying it... and so on... and then, you have a good amp for this so make sure it's happy and use the tap that matches the system

which sounds better to you?

there is your advantage

look up damping ratio - I have only one essay in me per day

[Mustang Marvin]

Thanks John.
Whew, although thoroughly confused I believe you have answered my question.
One other question while we are on the subject. I have heard different opinions on which speaker (mine are altec Valencias) perform with different impedances. Mine are 8 ohm. I also have a pair of DIY speakers with similar construction and size at 16 ohm. I have heard the 16 ohm speakers perform better at with a tube amp and pre amp (MC240 and MX110).
I have not heard the DIY system as of yet. They are still under construction. The DIY speakers use Altec 416's with 399 comp drivers and 805 horns crossed at 800 Hz. I don't play them too loud, but I like a realistic volumn. I listen to mostly instrumental music. The Valencias sound great with 8 ohm. I was just curious as the 16 ohm recommendation.
Your comments are most welcome.
Marvin