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Now, to be fair, advocates of steep filters are, as a group, rather critical of time coherent designs. They point out that first order speakers can have lower power handling because of extra stress on the tweeters, that there is an increased potential for a malady called ‘lobing’, and that proper power response is more difficult to achieve. (lobing means that there are variations in tonality within the speaker’s soundfield. Power response is a poorly named factor that refers to how well a speaker energizes the room with respect to frequency response.)
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The fact is that these things are a bit more tricky in first order designs, but that with thoughtful engineering and testing, and a slightly more generous driver budget, these concerns are not any more problematic than in steep filtered speakers. In fact, in our designs, tweeter failures are almost unheard of, lobing effects are only noticeable within a few feet of the speaker, and our power response performance is among the very finest in the industry. We believe that those arguments are ‘straw dogs’ intended to distract buyers from the real issue.
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Contents Slanted Baffle Aligns Crossovers, aka Filters, Step Response - Other Troubles
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OK, now let’s take our best shots at TIME INCOHERENT designs. For starters, scrambling the waveform is . If your goal is to come as close as possible to recreating the original musical event, then why in the world would you want to throw out the precious timing information? This is not a trivial question.
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Think about this: if any other part of the stereo chain - the microphone, the recorder, the medium - be it phonograph, tape or CD, the CD player or cartridge, amp or preamp, or any of the cables or interconnects - scrambled the waveform the way a typical speaker does, it would be considered BROKEN ! Even a 39 cent op amp is expected to pass the waveform more or less intact!
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Why should a speaker be exempt? Because you want it cheap ?????
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OTHER TROUBLES WITH COMPLEX FILTERS |
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Steep filters are complex, and present a complex load to the amplifier. The capacitors and inductors used in crossovers are reactive - they are resonant - they store energy and release it later (that's how they work). An amplifier faces a 'difficult load' when the speaker’s crossover has a few dozen of these parts. The mechanical analog of this is a network of springs, each with a different stiffness and size. Each with a different resonant characteristic. An amp can deal with one or two springs, but a whole bag of the damn things is often too much to handle. The amp spends precious power
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trying to control the ‘springiness’ of the load that would be much better used making music. When we say that an amp ‘won’t drive’ a speaker - this the most likely underlying reason. Some customers spend HUGE amounts of money for BIG BRUISER , BIG MONEY, CATEGORY 'A' amplifiers whose principle skill is the ability to control 'difficult' loads. Our simple, first order filters are a breeze for amplifiers to drive...so, far from straining the amplifier, the system sounds dynamic, robust and lifelike!!! |
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(this is an aside: You will hear the term ‘phase correction’ used by the designers of time incoherent designs. This is utter nonsense purveyed by guys who estimate that you really don’t understand this stuff, and that you are not likely to fathom what is actually an obvious fallacy. Here’s the skinny - you cannot correct phase errors! Think about it! The word ‘phase shift’ or ‘phase error’ actually means delay in time. Once a part of the signal is delayed - ‘correcting’ it would require going backwards in time - something even the best loudspeaker designers can't do. Now, because time only goes one way ...timing errors can only be made worse, never better! The very best that we can do is to NOT disturb the time domain in the first place. Once disturbed (delayed) there is just no ‘correcting’ things. Obviously.)
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Note that we said that filters are inherently resonant circuits, (they store energy and release it later) which means that they RING (!!!) Of course, filter ringing is a very bad thing, and also quite audible, so we should know a few things about ringing. Everything in nature rings - a bell rings, you ring, the sun, moon and stars ring. The only two questions about an object’s ringing are: ‘what frequency?’ and ‘what Q?’ Frequency - you already understand. Let's explain Q. Q means "resonance magnification".
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An easy example that will help you understand Q is the ringing of a bell. It is designed to have a specific frequency, and a very, very high Q. That is, it is easy to excite and, once excited, rings on and on... Now imagine stuffing a sock or a sponge into that bell. You will not have changed its resonant frequency by very much, but you will have greatly lowered the Q. Now it just does NOT want to ring. |
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First Order filters are, by nature, "critically damped". That is, they have the lowest possible Q. They do not want to ring, and since they employ but a single reactive element the problem of ringing is absolutely minimized. Steep filters, on the other hand, usually have intentionally highish Qs. They ring like crazy. They often ring very audibly. Imagine that dauntless audiophile - who is concerned with every possible source of resonance in his system, right down to those spongy little feet under his CD player....but his speaker's crossover is ringing like a bell !!! GAK !!!
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