My amp has 4, 8, and 16 taps. If my speakers are 4, what strain, if any, on any of my amp tubes will that have?If you put the speaker on the 4 ohm tap, none, but the output transformer will likely be losing some performance- they can often lose as much as an octave of bandwidth in the bass, and they will run warmer. That warmth is also causing the amp to make slightly less power, as the heat is coming from the power tube output.
And yet, the guy who designs some of the most fantastically successful speakers made anywhere in the world today says nevermind 16 ohms, even 8 ohms is obsolete.As far as solid state is concerned, this may well be true from a marketing perspective. But this is high end audio, where minimizing colorations is important, and distortion causes most of the colorations we hear- for example the brightness/harshness of solid state. The 3dB more power thing is a really weak argument- put another way, if you want to get the **best sound quality**, your amplifier investment dollar is best served by a higher impedance speaker. OTOH, if **sound pressure** is your goal, then you have a 3dB argument for 4 ohms (as opposed to 8) **if** you have a solid state amp that doubles power into 4 ohms. But you really pay a price doing 4 ohms- not only do you have more distortion, but most amps will run warmer (even class D) and the speaker cable becomes critical. On that basis it would be a stretch to claim state of the art performance when the amplifier is thus compromised.
His demo is about loudness, saying 4 ohm will produce 3db more VOLUME than 8 ohm. IOW, it helps him with efficiency.To be completely correct, it helps with **sensitivity** which is not the same as efficiency. Efficiency is unaffected. What the higher sensitivity number is saying is that the amp is now being asked to make twice as much power! That's completely different from a speaker that is 3dB more efficient- the latter would mean that an amp with half the power would play just as loud!
Like everything electronic, math is involved. Efficiency is stated as a certain sound pressure with 1 watt. Sensitivity is stated as a certain sound pressure with 2.83 volts. Into an 8 ohm load 2.83 volts is 1 watt; into 4 ohms its 2 watts. This is a 3dB difference. Since tube amps don't double power as impedance is halved, efficiency is the more useful specification, but since the industry went solid state, the sensitivity spec has taken over. You can make any speaker seem more "efficient" by reducing its impedance though parallel drivers but what is happening is the sensitivity is being increased while the efficiency is unaffected. You do have to pay attention to this nuance when selecting a speaker to work with an amplifier!
1. how importance is bias to sound? (I don't care about heat or tube life).Bias can be pretty important. Usually it is used to place the output device (tube or transistor) in the most linear portion of its operating curve. So it can have a noticeable and measurable effect on the sound.
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2. speaker cable inductance ..... gauge ____ awg
mijostyn said
" the wire you are using probably has high inductance. You should use 18 gauge wire that is a jacketed twisted pair like this".
Guage: Cat 5 8 strands is 15 awg. Two Cat 5's, 16 strands, is 12 awg.
https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html
I don't really understand inductance. If speakers are high efficiency (mine are), and I/you have more than enough power from the amp, speaker
3. equiv 15 awg, is inductance an issue?
Inductance (Back EMF) might increase amount of current needed, but
4. enough power: does it have any effect on the music's frequencies?
The inductance of the speaker cable plays a role, but so does capacitance and DC resistance. I would not place too much importance on any one characteristic. In theory, the cable has what is called 'Characteristic Impedance' which is the character where the cable is properly terminated by the impedance specified. Put another way, if the cable has a characteristic impedance of 8 ohms, if an 8 ohm load terminated the cable, there will be no reflections from the load back to the source. In this case from the speaker back to the amplifier. But in practice, no speaker is a perfect resistive load, and the back emf from the speaker dominates the minor reflections, so what becomes more important is that the speaker cable simply be kept as short as possible so that its errors are minimized. This FWIW is why I developed a balanced line preamp, so the amps could be placed as close to the speaker as practical. When doing this you hear an immediate improvement in bass impact and resolution. In a nutshell- keep your speaker cables short and used cable with plenty of conductor to do the job.
The amount of power you have might affect how much bandwidth the amplifier has. This is particularly true of SET amplifiers, where power past about 7-8 watts falls short of the definition of 'hifi' (the smaller the SET, generally the wider bandwidth it is; this is why the type 45 power tube, which is only good for 0.75 watt, is the 'best' sounding). With push-pull tube amps this limit is more like 60-120 watts, but in both of these examples its assumed that there is an output transformer on the tube amp (some tube amps don't have output transformers so are not bandwidth limited at any power level). Some solid state designs don't scale well as power is increased, but most of those I've encountered are older designs employing coupling capacitors at the output of the amp.
