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Multi-Way Conventional loudspeakers with crossovers

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Old 5th September 2007, 11:37 PM   #1871
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Quote:
Originally posted by Brett
but I can see WAF issues for some with this design.
You think
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Old 5th September 2007, 11:41 PM   #1872
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Magnificent! Looks like a victorian factory.


Cilla
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Old 6th September 2007, 12:10 AM   #1873
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I'd like to draw everyone's attention to a comment made by Dr. Geddes in the "Geddes on Waveguides" thread.

Quote:
Originally posted by gedlee


Your last paragraph is right on the money. Turns out the ear masks very well in the frequency domain, but not in the time domain. So if the nonlinear distortion is not time delayed it is highly masked by the signal. BUT, if there is a time delay in the distortion (not necessarily nonlinear) - like HOM or diffraction - then this effect is only weakly masked and quite audible. The important thing is that the masking in the time domain is SPL dependent just like the masking in the frequency domain - except that in the time domain the masking is less at higher levels (the opposite of masking in the frequency domain).

By the HOM, the PERCEPTION of the HOM is level dependent. The generation of the HOM is not.
This is worthy of some thought, along with the previous comment in the thread about the success of using foam in the throat region of a horn to smooth out the transition from the compression driver exit angle to the start of the throat of the horn. (Unless the CD and horn/WG are designed to be used to together, these angles frequently doesn't quite match, thus generating strong HOM's right at the beginning of the expansion.)

Although I don't expact strong HOM's on the flat plane of the baffle, they won't be zero, either. Thus the suggestions to cover all of the rear baffle surface with 3/8" of wool felt, and use full or partial bullnose round-overs on the front surface. Anywhere there's a sharp transition to the expanding wavefront, diffraction will be generated and re-emitted at the boundary edge.

Picking up the previous comments I made above, the topology I've been discussing all along (not the horn version) does have issues with drivers working close to the edge of their ranges. The intuitive answer to gaining more HF extension (by using a smaller driver) runs into the serious drawback of hitting a brick wall at a given SPL level.

Cones are constant-acceleration devices (the acceleration is the same regardless of frequency), and beyond a certain G level, the cone starts to break up - badly. Exotic materials have a somewhat higher ultimate breakup level, but the almost inevitable trade-off is much more severe and chaotic break-up when it occurs - the "brick wall" is much harder and the audibility of break-up is more of a shriek than the gradual onset of mush (with softer materials like paper). Not only that, the choice of different cone materials only affects the onset of breakup by a few dB (keeping the cone size constant) - don't expect a 10 or 15 dB improvement from a "miracle" cone material.

By comparison, large cones don't need to accelerate as much as smaller cones, simply because the emissive area is larger. This means more headroom without resorting to exotic cone materials. The tradeoff is what size is "too large" for the voice coil and spider to control - certainly, we shouldn't be expecting much midrange from a 18" cone. But the cone sizes of 8 inches to 15 inches are wide open - the smaller cone will excel in the small-signal condition, and the bigger one will excel when substantial peak SPL's are required. This is the sense of "headroom" that horns are known for - another name would be "Dynamic Fidelity", something you get from studio monitors but almost never from audiophile speakers.

This, by the way, is why I keep dragging the design back to 12 and 15-inch drivers and large-area ribbon tweeters. I want a reasonable portion of the Dynamic Fidelity of horns without all the endless design hassles - mostly centered around good time-domain performance, the area where horns are weakest. The graph below shows the time performance of the Ariel - compare it to any horn or waveguide system and see which has the quickest return-to-zero decay performance.

The Ariel wasn't even optimized for time performance, since it has a 360-degree phase rotation at the crossover frequency of 3.8 kHz, and the tweeter is acoustically ahead of the Vifa midbass drivers. Even so, it's pretty much returned to zero in 700 microseconds - if the echo at 500 microseconds was chased out, it would return to zero even faster.

The goal for the new system - with the widerange driver, delta-trio bass array, and double-high ribbon tweeter - is time performance as good or better than the Ariel, 10~15 dB more headroom, and oh yes, it would be nice if it sounded good too. For the first go-round, I'll be using MLSSA, and for long-term optimization, teaching myself how to use more modern software (like SoundEasy) on the new PC with the M-Audio 192/24 soundcard.
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Old 6th September 2007, 04:02 AM   #1874
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The goal for the new system - with the widerange driver, delta-trio bass array, and double-high ribbon tweeter - is time performance as good or better than the Ariel, 10~15 dB more headroom, and oh yes, it would be nice if it sounded good too.
Lynn,

Your goal is achievable This impulse response is of my current 3-way system - an active, tri-amplified system. I have chosen a 15" Lambda (93 dB), a 6.5" PHL (95 dB) and a 3/4" Hiquophon (89 dB). As you can see, the time domain performance is comparable to the Ariel's with substantially more headroom. In spite of the size of the drivers (against conventional HiFi wisdom) they are essentially silent in 500 microseconds. The system also possesses excellent detail resolution, while sounding incredibly lifelike. It excels with instruments like guitar, harpsichord and piano - all of which are very unforgiving of time-domain short-falls.

But most important of all... They are very easy and incredibly enjoyable to listen to.

Edward

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Old 6th September 2007, 04:47 AM   #1875
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Nice. Which one is your PHL? I use 1220. Do you listen at moderate levels? Then the 3/4 TW can certainly cope. Because when the Lambda and PHL start to party....
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Old 6th September 2007, 05:39 AM   #1876
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Originally posted by salas
Nice. Which one is your PHL? I use 1220. Do you listen at moderate levels? Then the 3/4 TW can certainly cope. Because when the Lambda and PHL start to party....
I use the PHL 1120 - a true midrange, playing from 350 to 3500 Hz.

I often play the system pretty loud, but I sit about 2.5 meters from the speakers, so the sustained SPL requirements are pretty reasonable. Often I listen at an average level of 85 - 90 dB, but there have been a few sessions where the sustained level were near 100 dB. For a system which is capable of this level of output and is flat from 20Hz to 20KHz, music becomes very hypnotic to me. I have been developing this system for about two-years, and as it gets better and better I find I listen to more music and work on it less.

Edward
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Old 6th September 2007, 06:52 AM   #1877
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PHL is good. I have chosen the 1220 slower brother of yours, bcs I needed a slow cut under 200Hz, and its lower Fs helped. I did a trick with the impedance under 100Hz you see. 3 drivers blending there. Aperiodic mid-woofer 1220 and double 6X9s shielded. But no usual peaks.
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Old 6th September 2007, 07:15 AM   #1878
Salas is offline Salas  Greece
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P.S. Can you post picture here?
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Old 6th September 2007, 08:16 AM   #1879
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Quote:
Originally posted by EdwardWest

Your goal is achievable This impulse response is of my current 3-way system - an active, tri-amplified system. I have chosen a 15" Lambda (93 dB), a 6.5" PHL (95 dB) and a 3/4" Hiquophon (89 dB). As you can see, the time domain performance is comparable to the Ariel's with substantially more headroom. In spite of the size of the drivers (against conventional HiFi wisdom) they are essentially silent in 500 microseconds. The system also possesses excellent detail resolution, while sounding incredibly lifelike. It excels with instruments like guitar, harpsichord and piano - all of which are very unforgiving of time-domain short-falls.

But most important of all... They are very easy and incredibly enjoyable to listen to.

Edward


Click the image to open in full size.

Nice time response - again, I doubt very much any horn or waveguide could match that, at least from the data I've seen published. This takes us to electrostatic territory with much better dynamics thrown in. Curious about the crossover points you've chosen - I imagine the 3/4" HF driver is crossed fairly high, to take advantage of the PHL's extension.

Curious about the pre-ringing over the first 300 microseconds - it's not easy for a tweeter to do that, it looks more like a sound card artifact due the built-in anti-alias lowpass filter - set to 20 or 40 kHz, maybe? Although my MLSSA card is ancient, dating back to 1991, I run it at 120 kHz to avoid lowpass filter artifacts and see what the tweeter is really doing. If the pre-ringing is what I think it is, your speaker is actually better than what's shown above.

I find the rapid decay in the time response corresponds to depth portrayal, or spatial fidelity - not imaging or reverb per se, but an accurate impression of the actual size of the performing venue. Weirdly enough, you can actually sense this before any music starts to play, or likewise with applause, which is extremely revealing of transient distortion and midrange/HF coloration.


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Old 6th September 2007, 09:15 AM   #1880
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Quote:
Originally posted by Lynn Olson



Nice time response - again, I doubt very much any horn or waveguide could match that, at least from the data I've seen published.

Lynn

Then you did not see the impulse responses that I published for my system. But additionally, mine has the same impulse response off axis. No piston sources can do that.
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