Yes that's for sure also, the main one though is the amp, it has to
control the speakers movements, wild and varying loads, high and low
impedances, and not be upset by any back emf from the speaker either.
None of this is a requirement to getting good neutral bass. This is not to say that the relationship between the amp and speaker isn't important, but its a simple fact that no speaker needs a great deal of damping, and many don't need much at all. What's more important is to make sure the amp isn't struggling to drive the speaker!
So why do you think so many manufacturers make low impedance
loudspeakers? 16 ohm speakers are a rarity. With ESLs you don't have
much choice and they all pretty much do the same thing as capacitive
loads. But, dynamic speakers could be designed with higher impedance.
Maybe it is a marketing problem?
I was looking at specs and I noted
the ARC Ref 750 had a slew rate of 20 volts/msec. Your amp is 600
volts/msec. Why is yours so much faster and how does that effect the
sound.
Next silly question. If you were using two 8 ohm drivers in a
subwoofer would you hook them up parallel for 4 ohms or series for 16
ohms and why?
@mijostyn Quite simply the market is dominated by solid state amps. Four ohms is often used to make the speaker seem a little easier to drive (higher 'sensitivity'). But if you do the math you find out very quickly that sensitivity and efficiency are two different things- and with tubes, efficiency is a far more important spec. This is because compared to solid state, tube power is expensive. So you need to make the best use of it that you can. In the old days speaker designers did exactly that- that is why older speakers are often 16 ohms and usually more efficient.
(A side note, more efficient speakers are more expensive to build, in some cases by a factor of 10 (the woofers in my speakers cost about $2000 each on that account) so by going to lower efficiency a speaker manufacture can make more money. I'm of the opinion that chasing the almighty dollar has a lot to do with so many 4 ohm speakers out there. Quite often when changes happen in audio, **its not so much for performance as it is profit.** To give you some examples: when the industry went from field coils to permanent magnets it was fueled by cost savings; from tubes to transistors it was the same (no output transformer, no filament circuit); from high efficiency to low efficiency (if the amp manufacturers were able to make that much more money, why shouldn't the speaker manufacturers), from analog to digital (everything about digital is less expensive than analog from recording to playback)...)
While ESLs are indeed capacitive but unless they are self powered like some of the old Acoustats, they all have a matching transformer which steps up the voltage from the amp to drive the panels themselves. So the designer of the ESL can set the turns ratio and thus the impedance range of the speaker. This is how Martin Logan gets 4 ohms in the bass while a Sound Lab is 30 ohms.
We get the speed in the output section from having no output transformer. As a result, the output section has a lot of bandwidth- it can go up to 30MHz no problem (many years ago when we first noticed how high the bandwidth was, we tried using it with a CB radio to see if it would boost the output of the walkie talkie and the amp was easily able to do it)! So we limit the bandwidth in the voltage amplifier section mostly to prevent damage to tweeters from RFI.
If it were me, I would put two woofers in series rather than parallel (they will act the same way in the box regardless) because I would want the speaker to make the most of the tube amp connected to them that they can. I've heard many people say the amp can't control the woofers as well this way but that's poppycock- what's really happening is solid state amps make less power into 16 ohms (half of what they will do into 8 ohms). Now you can't get away with this if the woofers are dissimilar- they will tend to color each other. But if they are identical woofers this works quite well. I've heard a good number of speakers that are wired this way and they work great.
Now here's an interesting tidbit about that- when you wire the speakers in parallel the sensitivity goes up by 3dB as opposed to a single 8 ohm driver. When you wire them in series the sensitivity goes **down** by 3dB, meaning that the 16 ohm version is 6dB lower sensitivity than the 4 ohm version! But the actual efficiency in either array, or with just a single woofer is **exactly the same.** This is really confusing not just for regular people but also for speaker designers. I've run into many that think the efficiency goes up when a pair of speakers are put in parallel. But what is happening there is that they are confusing 'sensitivity' (2.83 volts at 1 meter) with efficiency (1 watt/1 meter). At 8 ohms the two are the same; into 4 ohms 2.83 volts works out to 2 watts hence the 3 dB increase; into 16 ohms 2.83 volts is 1/2 watt, hence the 3dB decrease. But if you apply 1 watt to the array whether its 4, 8 or 16 ohms if the woofers used are all the same the way it works out into 4 ohms (with 1 watt, not 2.83 volts) is 1/2 watt is dissipated by each driver and the same is true at 16 ohms, or if a single driver is used and 8 ohms it dissipates the entire watt.
There are a lot of designers that don't get this bit! I'd point one or two out to you but I really don't want them mad at me :)
