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Multi-Way Conventional loudspeakers with crossovers

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Old 20th September 2007, 07:48 PM   #2111
DDF is offline DDF  Canada
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Quote:
Originally posted by ucla88


Hi Dave,

The mechanism postulated is that a whizzer cone effectively acts as two different drivers. While each may be min phase, the system might be slightly nonmin phase.

I suppose it's a reasonalbe hypothesis. I've never tested any whizzer cones (not really high on my list) so I don't have any experimental data one way or the other.

Hi Mark,
I was thinking along these lines: "is it possible that lower delay somewhere in the system could still result in the same frequency response, for a driver using a whizzer"? This after all defines min phase, in practical terms.

I can't see any physical way of achieving the same response with lower delay, but I guess just because I can't envision one, doesn't mean that one may not exist.
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Old 20th September 2007, 08:21 PM   #2112
gedlee is offline gedlee  United States
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Quote:
Originally posted by DDF


There’s also a thread in these boards, where an author is taking the same somewhat secretive approach with his HOM based loudspeaker system. So why be surprised when I feel less than inclined to give away all the cookies myself, without full discosure?

Without my oferring more detail, maybe there's not much else to discuss on this topic.


Your first point is incorrect in that there is nothing that I have not or will not discuss in regard to my work.

Your second point is quite correct.
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Old 20th September 2007, 08:29 PM   #2113
DDF is offline DDF  Canada
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Quote:
Originally posted by gedlee




Your first point is incorrect in that there is nothing that I have not or will not discuss in regard to my work.

Your second point is quite correct.
Untrue in that you are rightly protecting your commercial rights and income in that thread, with-holding info.

I won't continue to tolerate this level of disrespect, so I'm out.

I also appologize to Lynn that I was part of his thread turning in a less than constructive direction.
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Old 20th September 2007, 09:04 PM   #2114
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Quote:
Originally posted by soongsc

The one who shows it in a product will be leading the technology.
As described somewhere in the SE manual, the Cepstral functionality is a work in progress.

I think you have already addressed the key issues. Each time one changes measurement envoronment, it's best to redo a room signature capture. Once the method of room signature capture is derived, the other parts are pretty common to most software out there. The question really would be what signal is best to extract room signature?
This is what I was saying before. Tell me how you would "derive" the room signature, not how easy this would be once it has be derived.

I started on a paper about inmpulse editing when Bohdan and I were working on the cepstral editing back in May. If I have time I'll post the analysis of what I did on my web site. Part of the "work in progress" referred to in the SE manual.
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Old 20th September 2007, 10:42 PM   #2115
BudP is offline BudP  United States
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Lynn,
Quote:
The subjective goal is to have all three cone drivers sound like one driver, at any listening distance, including no more than few inches away from the front panel. My speakers have always done this, and the new system must do this as well. Nearly every other subjective goal is secondary.
Just make sure you send the woofers for EnABL also. Your concerns will be minimized and likely completely eliminated and the "merge" distance will be within 2 inches of the baffle plate and will not alter as you move about.

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Old 20th September 2007, 10:49 PM   #2116
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Default Re: Re: Re: Raven

Quote:
Originally posted by Lynn Olson




The problem with the ICTA is [snip] .....
I understand you concern, but the ICTA is a little difference. Criticism of the ICTA approach not with standing let me return to the original question about offsets required for alignment of first arrival which you did not address. If you are only going to align the wide range and tweeter that is fine.


Now with the ICTA, as I said, things are a little different. Aside from the fact that you don't like the WMTMW format and the large inter-driver phase difference, let me say a few things about coherence. First, we discussed the MTM part and the difference between a dipole MTM and a conventional MTM system previously with regard to the ballooning of the (power) response around the dipole peak and the M-M cancellation as compensation. Second, in the ICTA we are talking about a 150 Hz crossover so the drivers are all acting like omnidirectional sources at that point. (I don’t intend on using this type of crossover for the MTM section.) Third, at 150 Hz the driver separation is such that the pair of mids and pair of woofers basically act as a single source centered on the baffle. What this means is that the amplitude and phase response of each pair is basically independent of position for fairly wide of axis angles, both vertically and horizontally. Sure if you get excessively close to the speaker this will not hold. It won't hold for any speaker. But at 1 M and beyond the proposed ICTA layout acts like two coincident point sources at the crossover frequency and the inter-driver phase difference, while exceeding 90 degrees, remains nearly constant over very wide vertical and horizontal angles. While I accept your comments on inter-driver phase differences, I believe that the issue is not so much about how big they are, but how they vary with position. The variation of the inter-driver phase difference will be a function only of driver separation and the position of the observation point (be it distance or vertical/horizontal displacement). That is, it's geometric and the same for all crossovers. The caveat is that some types of crossovers are more sensitive to variations in inter-driver phase variations. The LR type are the least as the response can never exceed 1.0, Butterworths are more sensitive and the response and reach +3dB when the inter-driver phase goes from 90 degrees to zero. With an inter driver phase difference of 120 there is a possibility of a +6db peak as the inter-drive phase goes to 0. And remember, were talking about dipoles here. So, in effect, between the front and rear sources we already have an “inter-driver phase difference” that varies for 0 to 180 degrees with frequency on axis.

In other words, (in my experience) inter-driver phase difference isn't the issue. Variation of inter-driver phase difference with position is.

We are obviously of different schools here, but like you I believe that the final judgement is in the listening. I suspect that both your system and mine will be speakers to reckon with. Of course, I don't antisapate driving mine with a SET amp. Tubes are fine, but I want to see a minimum of 100 watts. Like Patrick Henry said, "Give me muscle or give me deaf!"
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Old 21st September 2007, 12:53 AM   #2117
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by john k...


This is what I was saying before. Tell me how you would "derive" the room signature, not how easy this would be once it has be derived.

I started on a paper about inmpulse editing when Bohdan and I were working on the cepstral editing back in May. If I have time I'll post the analysis of what I did on my web site. Part of the "work in progress" referred to in the SE manual.
Well, if I had the math skills, I could probably derive it. But I could explain the physical aspects and ideas step by step if someone is willing to see if it's mathematically possible.
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Old 21st September 2007, 02:03 AM   #2118
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Sorry for a couple stupid questions from and amateur, but, Lynn could you clarify a couple things for me?

1) Precisely which did you find objectionable, phase difference between drivers, or phase *angle* difference between drivers?

2) Do you find this more objectionable than combing between large, widely spaced drivers with low XO slopes?

Thanks.
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Old 21st September 2007, 06:13 AM   #2119
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Default The Low

Lynn ... How low do you anticipate your system will go, and what would be realistic goals? Somewhere a loss of good hi fi quality must occur. I realize there are a lot of variables. I have a buddy trying to get into the 20's and still maintain hi fi. I barely get that low with my LLT (shelved, 300 L 18" monster) and it certainly is not stereo quality, only HT good. He claims that if you build to 20hz it will cover the whole bass spectrum well. I need a better/more realistic plan to present to him.

Recordings, either wax or those little 5" plastic things must run out of quality around a -3dB of 40hz if I guess right, excluding the newer rock which is not music, IMO. Most recording guys that I have talked to have said that, also.
Zene
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Old 21st September 2007, 08:53 AM   #2120
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JohnK, thanks for your patience with the occasional cranky tone of my postings - mood swings as I chase out the last of health hassles, I guess.

For augerpro: there's no good standard terminology, partly because it's awkward to measure, too. The fullest description is inter-driver phase angle.

I find this meaningful because phase only exists in relation to other things - in usual audio terms, it is referred to the original electrical signal, and thus becomes the relation between the electrical and acoustical output. This isn't the only way phase can be used, though: it can describe the relationship between a pair of drivers, instead of between an electrical signal (the input) and the acoustical result sensed at the listening position (the output, with compensation made for transit time).

The standard polar diagrams depict the interference pattern between idealized single-point drivers at a single frequency. This can be steered by the phase angle between the two idealized sources - with the worst case, 180 degrees of phase rotation (not the same as reverse polarity) - resulting in a null aimed directly at the listener. This is obviously undesirable. It also has the practical result that nulls close to the listening position make the speaker very difficult to measure, with small changes in microphone position resulting in large changes in frequency response - leading to questions of which one is real. The answer is - none of them, and all of them. If a speaker has multiple personalities in a space only a few degrees apart, it has serious design problems.

This describes what goes on when drivers are fairly widely spaced acoustically - one or more wavelengths apart. Sound travels at 344 meters/sec, or looked at differently, 13,760 inches/sec. You can work out for yourself (in wavelengths) how far apart drivers are at the crossover frequency (as measured from the centerlines of the drivers).

JonhK and I are describing something rather different - what happens when drivers are quite close together acoustically (a fraction of a wavelength). I am asserting, based not on academic studies but personal experience, that even though large inter-driver phase angles do not appear on polar diagrams (due to proximity of drivers to each other), that it is audible nonetheless. However, all I am describing is my own subjective experiences, not what anyone else is hearing. I would guess audibility - or rather, tolerance - of inter-driver phase (with drivers that are acoustically close) may depend on the auditioner.

My experience with this is a legacy of working on the Shadow Vector SQ quadraphonic decoder - a system based on phase-shifting all-pass networks - and information gleaned from personally meeting Laurie Fincham (KEF) and the staff of the BBC Research Labs in the mid-Seventies. As a result, I've been careful to design loudspeakers that have relatively small and well-controlled inter-driver phase relationships.

My own personal criteria for a successful crossover is to turn the speaker on its side (on a sawhorse), drive it with pink-noise, and audition the drivers as I walk towards it, ending with my face a few inches away from the front baffle. If the crossover is successful, it always sounds like one phantom driver located between the two (or more) physical drivers, at any listening distance. If a crossover is only partly successful, it breaks apart into two (or more) sources at some critical distance (typically a metre or so). If it is a failure, the illusion of a single driver never happens at any distance, including listening distance.

What Laurie Fincham taught me was that the small deviations in frequency response near the crossover frequency also cause significant deviations in inter-driver phase, thus steering the polar pattern up and down at mid/high frequencies, and causing disagreeable "phasiness" at lower frequencies. Since drivers are mostly minimum-phase, correcting the frequency deviations near the crossover also conveniently corrects the inter-driver phase deviations as well. The result is an acoustical crossover that actually follows textbook behaviour, which is why KEF named it "Target Filter Function" design.

If this fine-grained compensation is not done, the chances of an acoustical crossover following textbook behaviour is close to zero - about as likely as standing under the window of a bank and hoping money will fall out. You can wait a long time before that happens.

This is NOT, repeat not, the same as "linear-phase" response. That is completely different, and refers to the relationship between the electrical input signal and time-compensated phase at the listening position. The awkward thing about "linear-phase" is the electrical signal is inaudible - that's why we have a loudspeaker in the first place! The question for linear-phase systems - assuming that is a valid goal - is sensitivity of the ear to phase distortion. The audio-engineering community is not in agreement on this one, although linear-phase proponents have claimed otherwise.

For Zene Gillette: It's an open question how effective the Gary Pimm filling technique will be - I think of it as being somewhere between a really short transmission line and a loudspeaker version of a cardioid microphone. It does go lower than a pure dipole, but the impossibility of assuring exactly 6 dB of rear-wave attenuation tells us it is really a quasi-cardioid, with a small rear (inverted-polarity) lobe at some frequencies, and a small (noninverted-polarity) lobe at others.

At a really wild guess, Pimm's method delivers somewhere between an octave and a half-octave more bass than a standard free-air dipole, with a somewhat different (less exuberant) spatial presentation. My WAG is somewhere between 50~80 Hz.
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