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Speaker Asylum: RE: To set the record straight on this antique JBL stuff... by Thorsten

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RE: To set the record straight on this antique JBL stuff...

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Hi,

> There is way too much incoherent babbling by Thorsten above to
> correct point by point.

It is all entierly coherent and consistent.

> So I will reiterate and re emphasize the main underlying problem
> as it seems Thorsten is intent on spreading his confusion to others.

It is not I who is confused.

> Thorsten doesn't know constant directivity from the tip of his nose.

Really?

> A given loudspeaker's beamwidth or radiation pattern cannot vary all
> over the place as it does with the D130 and 075 JBL and produce a
> constant directivity result.

As I pointed out, if operated correctly the beamwidth/radiation is quite constant in the range above 1KHz. Getting constant directivity below 1KHz requires either large waveguides/horns or dipoles/cardioids.

Neverthess such systems which are strictly speaking only "controlled directivity at higher frequencies are commonly sold as such.

> As the name implies, "constant" directivity means that as frequency
> increases across a loudspeaker's operating spectrum, the portion of
> radiated sound in a given direction remains essentially CONSTANT.

Yip, as I pointed out, if you use the D130 & 075 correctly this dictum is held from around 1Khz to 7KHz with a mild rolloff at higher frequencies.

You suggested earlier that "The Revel Ultima Salon 2 and Klipsch Palladium P-17B are a couple of decent examples of speakers exhibiting constant directivity."

The Salon 2 shows an interesting pattern where up to around 1KHz there is no directivity control whatsoever while above 1KHz it shows a smoothly increasing directivity with frequency.



So you seem to be making things up as you go along, as clearly one of your two statements is untrue....

In fact, I would suggest that the system made up from D130 & 075 hews closer to the textbook definition than the examples you cited, though any of them are not "constant directivity" below around 1KHz.

> A cursory look at the graphs I posted

You seem confused. You posted no graphs. You posted a link to a datasheet for the 2402 (which I agree has the same general radiation pattern as the 075).

You posted nothing for the D130 as nothing exists.

Using conventional acoustics we can however estimate the off axis behaviour of the D130. When you combine this with the data on the 2402 you get a system where above 1.5KHz and up to 7KHz with a constant beamwidth (or constant directivity which is another way of saying the same thing) and a gently narrowing beam angle above and a widening beam angle below.

> demonstrate clearly that the drivers in question are not capable of
> constant directivity - particularly over the frequency bands Thorsten
> was suggesting for them.

First, you have no data on the D130 and you have shown yourself ignorant of basic laws/computations common in acoustics.

I am pointing out that the -6dB Beamwidth of the D130 is appx. 60 degrees from around 1.5KHz to 5KHz and that the 075 has a beamwidth of 60 degrees at 5KHz.

As a result both drivers have matching beamwidth at the crossover point I suggested (we used a 3rd order HPF on the tweeter BTW) and as a system you have pretty constant directivity at frequencies above 1KHz, which in the reality of making speakers is pretty good.

> Thorsen saying the 075 bullet tweeter maintains constant directivity

You need to read again what I wrote, before you claim things I never wrote.

> is a clear indication that he doesn't have a clue what he's talking

Really. Interesting.

> about. Over a +/- 20 degree window, practically every driver in
> existence will appear to have constant directivity. True constant
> directivity implies uniform radiation pattern with frequency over
> a wider angle

If the designed beam-width happens to be 40 Degrees than a +/- 20 Degree window is what you would expect. If you designed for a 60 Degree beam width you would expect a +/- 30 Degrees window.

If you actually understood the meaning of constant directivity you would realise that ANY given beam-width or window can be constant directivity, IF (and this is the key) the off axis response follows the on axis one, but with attenuation.

So a +/- 20 Degree or +/- 30 Degree Beamwidth is perfectly acceptable as "constant directivity", if the other requirements are observed.

In fact, you can buy waveguides/horns with a range of coverage angles, COMMON (but not exclusive) ones are 40/20, 60/40, 90/40, 60/60 and 90/90 (first number horizontal beam width, second number vertical beam width). All of these are offered in "constant directivity".

> a design objective for high fidelity in a near field
> listening environment.

Who is talking near field listening? Stick to the topic.

> Toole, who essentially wrote the book on directivity of loudspeakers,

Correction, directivity in speakers was well documented long before Toole however Floyd E. Toole did some rather interesting work on speaker directivity for domestic listening.

The directivity of the Revel Saloon Speaker you referenced before is based on his work.

> makes it pretty clear in his papers that response off axis to about
> 60 degrees needs to be a carbon copy of the on axis response (excepting
> a minor uniform level of attenuation with each increase in off axis
> angle).

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?

> If the reader of this thread has any doubts, the Revel Ultima Salon 2
> (a product design inspired in part by Toole) I linked to earlier
> possesses a directivity plot that is TEXTBOOK constant directivity.

Actually, this a plain wrong. Plain to everyone to see, the plot from Stereophile was posted above.

It is very easy to see that even above 1KHz (never mind below) the 60 Degrees curve is NOT a carbon copy of the on axis curve but significantly non-flat. And it is actually a good thing that it is so...

Floyd E. Toole main point is that any change in directivity must be smooth and gradual and a situation where first the directivity increases (that is a narrower beam-width) and then decreases (that is beam-width widens) must be avoided.

Now if you cross the D130 & 075 with the original JBL 2.4KHz crossover you will have exactly this problem and you have a rather non-flat frequency response.

Which is why a few of us in the 80's in East Germany re-engineered a fair few Enclosures that uses these items and which had become available quite cheaply into something with a much more linear frequency response AND with a much more even off axis response (if strongly attenuated).

So let's consider. You attribute to Floyd E. Toole statements he never made (to me to), you cannot read basic graphs.

You real problem here is two fold.

First, you have very specific fixed Dogma's according to which the world is supposed to work and a low tolerance to anything that seems to challenge them.

Second, you have enough knowledge to get yourself into trouble, but enough indepth knowledge to understand the subject enough to make sense.

> The response plots of the JBL D130 operated wide band and the 075
> bullet tweeter responses look nothing like this.

How do you know? Again. I have measured such systems, have you?

> Compare the plots of these speakers and you will get a better
> understanding of what constant directivity means and why constant
> beamwidth only suggests constant directivity when it occurs over
> a relatively wide listening angle.

Clearly, you lack understanding what constant directivity is.

A system having a 40 * 20 Degree coverage angle is constant directivity, if it conforms with the basic requirement of an off axis response that equals on axis, but attenuated.

Tou give you an idea of a horn for such a system, look up (for example) the Electro Voice HP4020 Horn .

> Forty degrees listening angle is clearly not in the same ballpark
> as 120 degrees.

Of course not. But 120 Degrees constant beam-width is as much constant directivity as 40 Degrees constant beam-width.

Constant directivity is not defined by a specific angle, but by CONSTANT DIRECTIVITY at a given specified angle...

> It might be in Thorsten's warped, myopic world view

Sorry, but it is that in any decent text on the subject, the tie in to a specific beam-width angle you wish to establish as fact does not exist. In fact, if anything results from a warped, myopic world view it is the incredible bunk you have been spouting...

> Thorsten, given that every successive post of yours on this subject
> has provided further evidence of your ignorance on the subject, it
> might be wise for you to stick with electrical fuse design.

Well, I repeat, someone is clearly ignorant about such things as what constant directivity is in the textbooks and in colloquial use, or how real loudspeakers behave and other such minutiae. So far you have not shown any indication of even the most basic understanding of the Topics you have been so eagerly discussing...

So on the next round you expose less ignorance, perhaps you allow me to suggest a little remedial reading, so we at least understand the terminology...

An excellent overview of different approaches and results for controlling directivity as well as extensive references is given by Siegfried Linkwitz .

Earl Geddes takes a more narrow but well reasoned and supported view of the subject in his paper "Directivity in Loudspeakers" .

Ciao T


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