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Old 9th September 2007, 04:05 PM   #1921
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Quote:
Originally posted by Lynn Olson



I surmise not all readers of this thread are aware that frequency measurements contain less information than impulse response - you can create frequency response, phase response, ETC decay, CSD waterfalls, and lots of other things from the impulse response, but the reverse is not true, since phase or time data is not present in a FR response plot.

I would not surmise that at all. I would expect that most people who frequent this or other DIY groups are more than aware that FR means both amplitude and phase. FR should be express as a phasor,
M(f) exp(jPhi(f)). I don't think there are many people who are thinking only amplitude when they think FR. As you know, there is a one to one correspondence between the time domain and the phasor frequency domain for a linear system. (Nonlinear effects THD, etc, in a loudspeaker measured at moderate level will have very minor effects on the FR obtained from the impulse, or the impulse obtained from the FR. ) Given the proper specification of the FR or impulse you can pretty much go any where you like in terms of post processing, except to extract nonlinear effects. Most DIY'ers that I know understand this.
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One simple example are square and triangle waves, which have identical spectra in the frequency domain, with a diminishing series of 3rd, 5th, 7th and the rest of the odd harmonics. Although the magnitudes of the harmonics are precisely the same, the phases are different, making for a very different waveform.

I believe you are in error here Lynn. The square wave has amplitude that goes 1/n, where n indicates the harmonic, n odd. The triangle has amplitude that goes (1/n)^2

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Allpass functions are invisible in the frequency domain as well -
Again, I guess you are only considering amplitude response.
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Old 9th September 2007, 10:43 PM   #1922
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Quote:
Originally posted by john k...

I would not surmise that at all. I would expect that most people who frequent this or other DIY groups are more than aware that FR means both amplitude and phase. FR should be express as a phasor, M(f) exp(jPhi(f)).

I don't think there are many people who are thinking only amplitude when they think FR. As you know, there is a one to one correspondence between the time domain and the phasor frequency domain for a linear system. Given the proper specification of the FR or impulse you can pretty much go any where you like in terms of post processing, except to extract nonlinear effects. Most DIY'ers that I know understand this.

Yes, a complete FR - including phase - allows computation of other terms, including impulse response. But how often is the complete data set published?

When I look at FR curves going back the Fifties, where's the phase? No way can you extract phase from an old-school swept-oscillator spectrum analyzer (like the Tektronix 7L5), a swept-sinewave graph made on B&K equipment, or a Seventies-vintage 1/3 octave realtime analyzer measurement. The time information was never collected, and cannot be extrapolated from a magnitude-only graph. This was the point I was trying to make.

Going further, it's now 2007, but when you look at specs for most prosound equipment - horns especially - where's the phase or time information? Not there, sorry. The majority of published information is even worse - not only no time data, but the FR response (magnitude only) is smoothed as well, making visualization of resonances very difficult.

All I'm asking for is better, and more useful, published specs. I've been pestering driver manufacturers for any kind of time information for more than 30 years now, and most of the time, all I get is a runaround and lot of hand-waving and excuses why it's "not possible". I usually have to surreptitiously find out who the engineer is and wheedle the data out of him. Surely, after all this time, driver and speaker manufacturers should be publishing FR and impulse data, instead of excuses. Is that too much to ask?

P. S. Actually, I'm a little envious of the higher-class crowd that JohnK gets. The people I meet think they're pretty sharp if they can operate and understand a 1/3 octave RTA, and any discussion of impulse response gets lost in the swamps of "boy, that Altec A7 sure has good transient response". If you ask about the measurements, you get shown a picture of glowing RTA lights or a faded photocopy of a B&K pen graph made in 1952. Kind of hard to calculate the impulse response from that, isn't it? And Altec A4's and A7's ain't exactly portable.
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Old 9th September 2007, 10:47 PM   #1923
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Here's the latest thoughts about the open baffle - will construct the baffle, and measure and audition drivers after the RMAF. Curious to hear what the various EnABL'ed drivers (including Lowther) can do, and also curious if the elusive Fertin widerange field-coil driver will make an appearance.
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Old 10th September 2007, 12:44 AM   #1924
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Default Other drivers worth considering?

Hi Lynn, have you considered Triangle drivers? Bit low on efficiency, but otherwise...

Triangle drivers

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Mike
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Old 10th September 2007, 01:18 AM   #1925
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Quote:
Originally posted by Lynn Olson


Yes, a complete FR - including phase - allows computation of other terms, including impulse response. But how often is the complete data set published?



True, but who builds speakers based on published specks today? Yes, it is 2007. We are way past the 50's. But published specs are missing a lot more than phase, like baffle and box (if used) effects. Isn't that why all these DIY CAD tools generally have at least some kind of rudimentary measurement tool packaged with them? At best published specs are useful only for identifying the general characteristics of the driver; smoothness through the operating band, breakup behavior, etc. What good would the most detailed specs in the world be if they arenít for your configuration?

As for extracting phase form amplitude data, at least of a single driver, minimum phase reconstruction work very well if you have good amplitude data. Maybe pro sound driver manufactures don't supply sufficiently accurate amplitude data, most reprtable hifi driver manufactures do (SEAS, Vifa Peerless, ScanSpeak, etc). While I haven't looked at large panel (like Martin Logan ELS) of horns, I have yet to measure a conventional driver, cone, dome or small ribbon, that doesn't reduce to minimum phase on axis over its useful operating range. So what that leaves is what is the driver offset, a problem which is still of concern using impulse response techniques. Of course, I wouldn't consider 1/3 octave RTA a legitimate measurement of a driver's anechoic response.

I can't comment on the crowd you hang with but most of the guys I know are just average Joes building speakers as a hobby.

Altec A4's and A7's may not be very portable, but a lap top with mic, running any number of cheap (or free) software packages, certainly is.

I can certainly understand that you (or I) don't want to buy and test every driver you may contemplate using in a system, but doesn't it really have to come down to that? No matter how detailed the specs are, they won't tell you how a driver sounds.
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Old 10th September 2007, 08:24 AM   #1926
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Default Re: Other drivers worth considering?

Quote:
Originally posted by mikey_audiogeek
have you considered Triangle drivers? Bit low on efficiency, but otherwise...
Strange.... I thought they were not selling raw drivers these days. Looks like they are.

The 1st speakers I ever built used the very first Triangle driver. I liked them a lot. The neighbors always asked me "who were the musicians you had over yesterday?" or "hey, you're getting really good on that sax." Yeah, just like Paul Desmond.

Certainly worth a look/listen. My 2 cents.
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Old 10th September 2007, 10:49 AM   #1927
Rudolf is offline Rudolf  Germany
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Lynn,
looking at your OB proposal:
How are you going to deal with the energy response step at the crossover between WR driver and tweeter? Up to 1.6 kHz the WR driver will radiate with (hopefully) almost equal power to the front and rear, while the tweeter will only radiate to the front. So you will need some controlled rear wave attenuation over the passband of the WR driver or a second tweeter IMHO.
A "felt tent" behind the driver sounds too "lightweight" for the upcoming task.

In my own applications I never got that right, and I always wondered how the Orion could do without a second tweeter or a rear wave treatment of the midrange.
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Old 10th September 2007, 06:50 PM   #1928
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There was a discussion about impulse responses. I've collected three probably interesting responses: Summa ESP15, Manger 109 measured at Gelsenkirchen HiFi exhibition on axis and from 3m, and my Jordan JXR6 (0.15-30kHz) in steel enclosure with a lot of damping (0,5l free air and 1,5l wool) and at 0deg, 30cm. Manger is meant to be perfectly aperiodic, Jordan - well controlled modes for aluminium diaphragm.
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Old 10th September 2007, 06:51 PM   #1929
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...
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Old 11th September 2007, 07:58 AM   #1930
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Quote:
Originally posted by Rudolf
Lynn,
looking at your OB proposal:

How are you going to deal with the energy response step at the crossover between WR driver and tweeter? Up to 1.6 kHz the WR driver will radiate with (hopefully) almost equal power to the front and rear, while the tweeter will only radiate to the front. So you will need some controlled rear wave attenuation over the passband of the WR driver or a second tweeter IMHO.

A "felt tent" behind the driver sounds too "lightweight" for the upcoming task.

In my own applications I never got that right, and I always wondered how the Orion could do without a second tweeter or a rear wave treatment of the midrange.
Plan to try both approaches, maybe at the same time. At 1.6 kHz, wool felt (and other damping materials) are starting work pretty well. Gary Pimm is using Bonded Logic "Ultratouch" fiber to fill his open-backed dipole woofers with great success - this recycled cotton fiber has high absorptive properties, and Pimm's system has the best, most crisp, and tonally realistic bass I've heard so far.

I'll be using the Ultratouch fiber for the open-backed Bass chamber, and possibly be trying it in small, custom-made pillows behind the other drivers - white pillows would look more than a little silly, but it's easy enough to dye them black before filling them with the Ultratouch fiber.

The whole trick with damping is keeping the fibers several inches away from the cone - this is important - and using organic-origin fibers as opposed to synthetics. I tried lots of different fillings for the Ariel, and was not at all happy with the sound of foam, fiberglass, or polyfill. Wool and cotton sounded the best.

If anything, I expect a dipole is going to be even less tolerant of odd-sounding damping materials - these can have rather weird dynamic-related colorations. If you select a damping material with suboptimum properties, you will hear a noticeable muffled or dynamically constrained quality to the sound - always compare against no damping when evaluating the sonics of damping materials. Compare speaker A against speaker B for quick comparisons - it won't so much be a tonal coloration, but more of a flattened, murky, "closed-in" sound you want to listen for. This is NOT accuracy, it's an unwanted coloration.

It's entirely possible I won't find any damping material acceptable in the midrange - that's a real possibility that affects the rest of the design.

The vertical directivity of the ribbon tweeter will bear on the decision for or against a rear tweeter - as you might expect, it's about subjective decisions of spaciousness and smooth integration with the large-area midbass driver. I also plan to have a wooden disk to fit in the 12" hole that has an 8" cutout for the 8" drivers that look interesting (Lowther, Fertin, et al).

I feel modern designs have gone astray in focussing on dispersion vs frequency compared to the basic sound of the drivers themselves. Considering how grossly colored I find contemporary "audiophile" drivers - I keep being surprised how people are able to ignore such basic colorations while looking at all those pretty-looking polar graphs. I have to be direct here, folks - I really dislike the sound and philosophy of modern high-end audio, sorry. Please look elsewhere if you find the sound of modern high-end even a little bit palatable.

I should warn readers, like I did for the Ariels, that my designs do not follow contemporary trends in speaker design. I optimize for natural sound on solo voice and choirs, followed by naturalistic qualities on other instruments (symphonic), followed by natural spatial qualities (not imaging per se) and realistic dynamics - in about that order. I make no claims for the "best" or "ultimate", but choose to address problems I see ignored in other approaches.

Everything I do is off the beaten path - look at how I design amplifiers. If all of this is just too weird for you, please, look in another direction! There are lots of talented folks here in diyAudio - you have many choices.
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