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In Reply to: RE: To set the record straight on this antique JBL stuff... posted by Thorsten on July 13, 2012 at 07:57:57
Thorsten said regarding Floyd Toole's objective regarding constant directivity of loudspeakers :
"Really, would you care to substantiate this with with a citation from the actual paper (including page/chapter) where he says that this is the ONLY option?
I've read various papers from Toole and distinctly remember him using the words "carbon copy " to describe frequency response measured far off axis in comparison to that measured on axis or close to on axis. I said nothing about "ONLY OPTION" so cut the projection crap. But since you challenged me on this very basic concept - I'll direct your attention to figure 25 on page 14 here:
http://www.harmanaudio.com/all_about_audio/loudspeakers_rooms.pdf
Once again, I'll reiterate for other potential readers here - constant direcitivity in the context of a loudspeaker indicates response lines off axis that are essentially the same as the on axis response only shifted down a few db in sensitivity. One should see what looks like a number of parallel lines that extend out to about 60 degrees. This is a speaker that possesses constant directivity - NOT TO BE CONFUSED WITH CONTROLLED DIRECTIVITY WHICH THORSTEN CLEARLY HAS DONE. The 075 bullet tweeter is a narrow directivity(+/- 20 degree) high output tweeter capable of 110 db at 1 meter and 1 watt. It was never intended to be used in people's living rooms and anyone who suggests it for such an application is totally clueless. The poor, uneven off axis response at frequencies it was intended by JBL to be crossed up to the D130 at are precisely the problems Toole has focused on in his papers - such as the one linked to above.
The internet is a great place to gather and share information. Unfortunately, any idiot can link to someone's website or paper and claim that they know what is being said. In the process, it is not unusual for the idiot to twist or misinterpret what is being said and then disseminate that misinterpretation widely on forums such as this.
Thorsten also said:
"Who is talking near field listening? Stick to the topic."
Most living rooms, based on the wavelengths generated in audio systems, constitute the near field zone. Scan Speak, a prominent loudspeaker manufacturer, has dedicated itself to designing and building some of the best loudspeaker drivers for this environment - the low sensitivity 8530K being a prime example. The two drivers you brought into this discussion were never intended for home use. They were designed to be used in large spaces and in public address applications where far field conditions dominate. None of the virtues you have tried to describe for them have any use in a home listening environment. Their performance is exactly the opposite of what Toole lists in his papers as design objectives for home use. I've been staying on topic. You on the other hand have not. Perhaps you should heed your own advice or better yet, see a psychiatrist for your various neuroses and projection issues.
Follow Ups:
Hi,Okay, lets clear up some more confusion.
There is much woffle that is completely meaningless and empty verbiage which I cut...
> I've read various papers from Toole and distinctly remember
> him using the words "carbon copy " to describe frequency response
> measured far off axis in comparison to that measured on axis or
> close to on axis.Then it should be trivial to supply the reference. BTW, I have ALSO read the papers AND retained copies on my hard drive for reference...
> http://www.harmanaudio.com/all_about_audio/loudspeakers_rooms.pdf
Does not contain "carbon copy"...
> But since you challenged me on this very basic concept -
> I'll direct your attention to figure 25 on page 14 here:This is labelled "design objective for a room friendly loudspeaker"...
It does not show either a constant directivity or a controlled directivity system. It does show what Dr. Toole recommends and many others (if you had cared to peruse some of the references I provided you with) would disagree, though all would generally agree that figure 25 is a better choice than figure 24.
However, many would submit that this here is an even better choice than figure 25:
And even though this speaker (the Geddes "Summa") has a large variation in directivity below 1KHz, it is generally nevertheless considered "constant directivity", both by it's designer and audio professionals in general.
AND if you had paid any attention, you would have noticed that the Speaker system using D130 and 075 crossed over at around 5KHz will actually exhibit a SIMILAR off axis response, though not with as smooth curves.
> Once again, I'll reiterate for other potential readers here - constant
> direcitivity in the context of a loudspeaker indicates response lines
> off axis that are essentially the same as the on axis response only
> shifted down a few db in sensitivity. One should see what looks like
> a number of parallel lines that extend out to about 60 degrees. This
> is a speaker that possesses constant directivity - NOT TO BE CONFUSED
> WITH CONTROLLED DIRECTIVITY WHICH THORSTEN CLEARLY HAS DONE.Nope, what you claim to be a "constant directivity" speaker, namely the typical design following Dr. Toole's recommendation are precisely NOT Constant directivity, becuase they show a rising directivity index with frequency. What is important with designs that follow this principle that rise in directivity is smooth and continous.
Again, had you perused the references I gave you you would know that...
To take something from Siegfried Linkwitz's site about a good example of what Dr. Toole advocates:
This loudspeaker exemplifies Floyd Toole's loudspeaker directivity requirements. They are the result of extensive listening tests where different box loudspeakers were ranked according to preference. The directivity index increases smoothly from 0 dB to 10 dB, without signs of the two crossovers in its frequency response. Moderately wide dispersion horizontally. (SL)
So, if anyone is confused about constant directivity, controlled directivity and what Dr. Toole advocates it appears that this person is you. Further, you ascribe to Dr. Toole claims you cannot back up (and which I doubt he would have made like that) and misrepresent your misunderstanding as his intentions and recommendations, when nothing could be further from the truth.
> The 075 bullet tweeter is a narrow directivity(+/- 20 degree)
> high output tweeter capable of 110 db at 1 meter and 1 watt. It
> was never intended to be used in people's living rooms and anyone
> who suggests it for such an application is totally clueless.Are you SO SURE about that?
So if JBL had domestic styling 2-Way systems using the 075 marketed as HiFi Speakers these where "never intended to be used in people's living rooms" that would make you a boldfaced liar and actually the one who is "totally clueless"...
Now, let's look at the 1957 Catalog JBL issued for home customers (they had different ones for pro audio)...
Wow... I spy with my little eye the 075, so clearly JBL intended it for home use...
Even further, JBL's Systems/Pricing Page from this catalog shows many 2-Way systems using the 075...
Even worse, the 1976 Home Components catalog still has the 2-Way D130 and 075 in the list of recommendations .
Quel Domage, either everyone at JBL from AT LEAST 1957 to 1976 (or later - I still remember seeing this Combo in the 80's) according to you was totally clueless .
> The poor, uneven off axis response at frequencies it was intended
> by JBL to be crossed up to the D130 at are precisely the problems
> Toole has focused on in his papers - such as the one linked to above.Now we come to the crux of the matter. And I agree, the original JBL system with a 2.4KHz 2nd order Crossover network created quite a few problems, not just in directivity but also in the frequency response, as I found out in the mid-80's when such systems came my way (long story how).
As we had a fair few of these available and as they had some interesting characteristics to their sound quality we did a fairly comprehensive job of characterising them and the re-engineering them.
Now this was over two decades ago, so I am not 100% on specific values (and the papers are long lost), however we used two LCR Equaliser on the D130, but no lowpass, to get the frequency response pretty flat, a short "Hornreflex" for the Bass which gave a boost in the 100-500Hz range that was a bit low and a 3rd order highpass somewhere around 5KHz for the Tweeters.
As I commented also before, this system measured pretty flat on axis and had a very CONSTANT DIRECTIVITY Response off axis. As Constant Directivity was one of the big buzzwords of the time and one needed to buy very expensive new horns to get this "Constant Directivity" we where pretty pleased that we achieved the same using very different means.
It may surprise you, but I have been dealing with such things like speaker directivity for the better part of three decades, in practice.
> The internet is a great place to gather and share information.
Yes, it be a good ting if you did that a bit more. You would perhaps come across a little less clueless if you did.
> Unfortunately, any idiot can link to someone's website or paper
> and claim that they know what is being said. In the process, it
> is not unusual for the idiot to twist or misinterpret what is
> being said and then disseminate that misinterpretation widely
> on forums such as this.That sounds like an excellent description of what you have been doing, if I may say so.
> Most living rooms, based on the wavelengths generated in audio systems,
> constitute the near field zone.Really? Now, exactly what is the definition of "near field" in the context of acoustics?
Do you even know? Here a good (but not exclusive) definition...
The near/far field transition is typically defined at a distance of d^2/l, where d is the effective diameter of the driver, and l is the wavelength of sound. Note that means that as you either increase the diameter OR play a higher frequency, the near/far field transition occurs at a further distance.
Taking for example a 4" radiating diameter and 1KHz we get what distance as near/farfield transtition?
Are you really suggesting that anyone lives in a shoecarton?
Honestly, your total lack of understanding acoustics makes it again time for a double-facepalm for you, honestly, I would think your face should smart something fierce by now...
Now, I would really suggest you actually apply yourself to the subject and gain some basic understanding, if you wish to debate the merits or not of my original recommendation, which send you on this thread of perfect and utter tomfoolery. As the old sages used to say, a little knowledge is a dangerous thing.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Edits: 07/14/12
There was no "pro division" and "consumer" or "home" division of JBL in the 50's. Lansing's focus and experience was with large spaces such as theaters and broadcast production facilities. The mix/match brochure which in some instances utilized the bullet tweeter contains speakers that were "functionally designed for professional and 'built - in' use" as well as speakers that appeared to be designed as home furniture. Because Lansing decided to use some of the same drivers in cabinets that could be put in a home does not mean the drivers were originally designed for that purpose. The acoustical interactions between loudspeakers and different spaces were not known at that time anywhere near like they are today. And opportunistic business decisions drove marketing - not always correct science or engineering.
Also, a speaker that exhibits constant directivity doesn't preclude a slight narrowing of response with frequency. The key to constant directivity design is the uniform response lines (or essentially parallel response lines)over successively wider listening anlges at the frequencies where directivity can be controlled - from approximately 1 khz to 10 khz. As noted earlier, the Revel Ultima Salon 2 excels in this capacity as evidenced by the Stereophile test plots I linked to earlier and as suggested by figure 25 on page 14 of Toole's white paper that I linked to. Bringing up the flatness or lack thereof for a directivity index plot is a side distraction that confuses people like you.
Everything I've stated in this thread has been derived from personal experience and from the experience of other's like Toole and Olive. My experience with JBL goes back to the first set of speakers I ever owned - JBL L 19's back in grammar school in the 1970's when I first started building loudspeakers and amplifiers. There's nothing you're going to be able to tell me that I don't already know about Jim Lansing and the company he formed. My understanding and knowledge goes far beyond advertising brochures. And despite all my concerns over your ignorance and misguided assertions, I can at least give you credit for recognizing the inherent value of JBL product quality in general. Where specifics are concerned, however, you still remain completely out to lunch.
And yes, I know the difference between near field and far field and the murkiness of the subject based on the relationship to wavelength - that's why I stuck with an absolute. If the dimension of the lowest produced frequency can exist well within the distance from the source to the listening reference point - it HAS to be considered far field. I expected you'd nitpick this issue too since as evidenced by all of your posts, it's in your nature to use the sharing of information as a competitive exercise rather than a means to benefit oneself by learning from others while occasionally helping others learn from one's own experience.
"I have you here at a disadvantage of course, as I am quite familiar with such systems." - Thorsten earlier in this thread.
ugh
Hi,
> If the dimension of the lowest produced frequency can exist well
> within the distance from the source to the listening reference point
> - it HAS to be considered far field.
Nope, the definition used in common acoustic texts is quite precise. It includes wavelength and radiation area for reasons that should be self explanatory.
Of course you make up definitions that suit you and your agenda on the spot (like so much else in this thread), however that does not make them true.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Thorsten babbles:
"Nope, the definition used in common acoustic texts is quite precise. It includes wavelength and radiation area for reasons that should be self explanatory."
Since there are many wavelengths involved, a definition based upon a specific wavelength is not useful or accurate. This definition is more useful and accurate in the context of a typical loudspeaker listening environment than anything you're likely to come up with that's based on the Fraunhofer definition of far field:
"The near field is the area very close to the machine where the sound pressure level may vary significantly with a small change in position. The area extends to a distance less than the wavelength of the lowest frequency emitted from the machine, or at less than twice the greatest dimension of the machine, whichever distance is the greater. Sound pressure measurements in this region should be avoided."
And it is commonly accepted in the industry and can be found here:
http://www.acousticvibration.com/sound-basis.htm
And it is exactly the same definition I used.
Now who is inventing what?
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