Any experience using 8 ohm taps for 16 ohm speakers?
Anyone have 16 ohm speakers? Whatcha got? Mine are Electrovoice drivers from 1956. I moved them from a Fisher President II console to new Enclosures I had built. 15" woofer, 37 lps, monster magnet, 15W (brother of 15B used in the big Klipshhorn). Re-coned the woofers twice over the years. Luckily cone with cloth surround is still available. Electrovoice Horn Midrange and Horn Tweeter, Electrovoice Crossover, Presence and Brilliance controls. These are what I might try on 8 ohm taps. Having Presence and Brilliance controls designed for the crossover/drivers may help that be successful. |
I guess it was 1958. http://www.fisherconsoles.com/President%20II.html I inherited it from my uncle. I have all the components, use the console for firewood. Originally the woofers shot out the bottom, unit was on 8" bronze legs. TT and tape deck in the 2 drawers. |
The original Quad ESL is a nominal 16 ohm load, but it’s impedance varies from 2 ohms (at 15kHz) to over 30 (at 80Hz)! That's why Peter Walker designed the Quad II tube amp with relatively low output impedance (it's damping factor is about 20), and most solid state amps aren't a good match for the speaker. But then most tube amps, with their high output impedances, aren't either. One that is, is the Futterman OTL's, a favorite amongst Quad enthusiasts. Very low output impedance for a tube amp. |
bdp24 , that is interesting, thanks. general info suggests a slight boost in mids if using 8 ohm tap for 16 ohm speakers. found this informative. https://music.stackexchange.com/questions/25434/using-an-8-ohm-amplifier-output-with-a-16-ohm-cabinet A tube power amplifier (like the final stage in your Mark V) has to have an output transformer to lower the output impedance (the "Ohms") to a level appropriate to drive a speaker. What does that mean? Well if you know what voltage and current and power are, then one way to look at impedance is how much of the power you are putting out is in voltage and how much is in current? That ratio is one interpretation of impedance. The ratio of voltage to current coming out of power tubes is relatively high. But you need lots of current to make a speaker move, so you have to trade some of that voltage in for more current. That's what a transformer does. How much do you trade in? The answer to that question is chosen by the amp designer and is your amp's rated output impedance. That means your amp is designed to put out its rated power with a specific ratio of voltage to current. The amp will pretty much put out how much voltage it's putting out in any situation, and it's designed to put out a certain amount of current along with that. Designed meaning that if it is not allowed to put out all the current it can, then you won't get the full rated power, meaning your sound will be quieter and maybe less clear. However, if your amp is allowed to put out more current than it is supposed to, then bad things can happen. Current creates heat, more current is more heat, and too much heat can melt things. Like your output transformer. If your transformer isn't the first to go, then there are plenty of components in the amp that can be melted or just destroyed in other ways by passing too much current. So you have to hold your amp back from running crazy with current. This is what a speaker's nominal load impedance number is meant to indicate. It's not a precise number, but it's good enough for making sure you're not letting your amp run away with itself and overheat. Here's the short short version: If your speaker cabinet's nominal load impedance is equal to or greater than your amp's rated output impedance, you will be safe. Safe at least in terms of not overheating your amp. If the speaker's impedance is higher, as stated before you won't get the rated output power and there may be some tonal changes. There are lots of interesting interactions between a speaker cabinet and an amplifier, so how the sound will change isn't so easy to predict, but if the speaker impedance is higher, you can safely experiment and found out how it sounds. One more thing to check is that the rated power dissipation of the speaker cabinet is greater than the rated output power of the amp. That way all the current coming out of the amp won't melt the speaker. If you ever get into live sound PAs, just know that it's a different world because those amps are not tube amps. You still need to pay attention to power levels for sure, impedance not so much, and the rules of thumb will be different. But that's not relevant to your question. I just didn't want you to think back to this years later and think you can set up your PA the same way as your Mark V. shareimprove this answeranswered Mar 27 '15 at 1:33Todd Wilcox42k44 gold badges7979 silver badges143 |
another tidbit found " I had this conversation with Robin Trower about 5 years ago in the Marshall Theater. He told me he likes to run his amps on 8 ohms into a 16 ohm cab. He then played some while I switched the selector on the back of the amp between 16 and 8 (not while he was playing of course!). He then declared, "there's not much in it really". In reality it can depend on the acoustics of the room/stage on the night etc. etc. whether it sounds better or not. |
http://blog.hughes-and-kettner.com/ohm-cooking-101-understanding-amps-speakers-and-impedance/
Case 1: running a 16 ohm speaker with an 8 ohm amp output With this combination, the voltage at the speaker output will rise, while the current will almost halve. The power will drop, although you probably won’t notice it too much, as this combination will likely increase the mids in your tone. So long as you don’t overdo it – make it a rule of thumb not to connect a speaker with more than double the output impedance of that of the amp – this method can be quite useful, as you can effectively boost the mids in a cab that might otherwise be lacking in this department. |
found an old thread, 2017, from this site https://forum.audiogon.com/discussions/is-it-ok-to-use-an-8-ohm-tubed-amp-to-power-16-ohm-speakers |
