Ralph your link is not working! Why not just put a big resistor in series with the speaker? Say 1 or 2 ohms?
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@mijostyn Don't include the parentheses at the end of the link.
A resistor will simply absorb power. The ZEROs transform the impedance so you get more power and less FR error.
@viber6 This statement is incorrect:
Actually, I think that although the SS amp has the capability of providing 2x the power as impedance is halved, the SS amp is still flat in freq response at any given moderate power demand for higher impedance.If the amp is behaving as a voltage source, it will double power as impedance is halved. This also means it will cut power in half as impedance is doubled. The solid state amp will only have flat response if the speaker its driving is intended to be 'Voltage driven'. ESLs are a technology that isn't based on the Voltage Paradigm (see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php for more on that). Under the voltage rules, the impedance curve of the speaker is also effectively a map of its efficiency: peaks in the curve represent resonance, dips represent a loss of efficiency (such as at crossover points). For example if you have a woofer in a box it has a resonance in that box. To control that, the amp has to put out *less* energy (power) into that resonance, which is also seen as a peak in the impedance curve in the bass.
ESLs are not based on a driver in a box. Their impedance curve is essentially based on a capacitance. So with a typical ESL where the impedance varies over about a 10:1 range (the Martin Logans are no exception; 4 ohms in the bass and 0.5 ohms at 20KHz) you can see that to make 92 dB at 50Hz a Voltage Paradigm amplifier (voltage source) will make X amount of power; to do the same thing at 10KHz it will have to also make X amount of power, but in reality is will be about 4X the power because its voltage output is constant with respect to impedance and at 10Khz, the MLs are about 1 ohm. The only thing that prevents this from happening is that these HF impedances are so low that the speaker cable itself has a DCR that becomes significant, and a good number of solid state amps can't double power into such low impedances (IOW they are not perfect voltage sources). IMO Martin Logan is trying to make an ESL that works with solid state rather than tubes but to this end (again IMO) they are only partially successful since brightness is part of the result; inevitable when you mix transistors (Voltage Paradigm) with ESLs (Power Paradigm).
The essence of my post is that although the SS amp has more power capability into low vs high impedances, that doesn't mean the SS amp will have a tonal balance skewed toward the HF when driving an electrostatic speaker. To use our numbers, consider an amp with max capability of 200 watts into 8 ohms, 50 watts into 32 ohms, 800-1600 watts into 1 ohm. Let this amp drive an electrostatic speaker whose impedance is 1 ohm at 20,000 Hz, 8 ohms at 2500 Hz, 32 ohms at 625 Hz. This assumes impedance exactly inversely proportional to freq, although I have ignored capacitive reactance, the true parameter. At 30 watts of output, the amp will put out that same 30 watts into any freq for an even tonal balance. For 200 watts of output, only freq above about 2500 Hz will be undistorted into that speaker, whereas at freq below 2500 Hz the amp cannot put out as much undistorted power, so I agree that under these conditions the amp will sound bright driving the electrostatic speaker.
At 30 watts of output, the amp will put out that same 30 watts into any freq for an even tonal balance.
No, that isn't correct, assuming the amp acts as a voltage source (as almost all solid state amps do, and as some tube amps do to a relatively loose approximation).
In the case of an amp having voltage source characteristics, i.e., very low output impedance, for a given input voltage to the amp it will provide an output **voltage** to the speaker that is essentially the same regardless of frequency, assuming the amp is operated within the limits of its voltage, current, power, and thermal capabilities. And that same voltage will result in more current and consequently more power being delivered into low impedances than into high impedances.
As you are probably aware power delivered into a resistive load equals voltage squared divided by resistance. It's somewhat more complicated than that when capacitive or inductive reactance is involved, but I'm putting that complication aside to try to clarify Ralph's point, which relates to delivery of power (as opposed to voltage) into the speaker. And which relates to frequency response flatness at the output of the speaker, not to frequency response flatness at the output of the amplifier.
Frequency response flatness at the output of the amplifier, on the other hand, is normally defined in terms of how the relation between amplifier output voltage (not power) and amplifier input voltage varies as a function of frequency. That characteristic will indeed be essentially flat in the case of a good quality voltage source amp, as long as the amp is operated within its capabilities. But that is not relevant to the point Ralph was making.
Most speakers are designed to approach a flat voltage response, not power, and amps to be a voltage source. If the source impedance of the amp is rather high (tubes) then there will be an HF roll off. The performance of a solid state amp might sound subjectively brighter but that’s not because it’s tilting up the highs, but because it’s not rolling them off. A speaker designer who designed a speaker with a highly variable impedance AND tuned it for a flat power response would be an idiot.
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