Home Speaker Asylum

General speaker questions for audio and home theater.

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

Hi,

> For those not familiar with the 075 JBL "bullet" tweeter - it is
> an antique that dates back to 1957!

Yes. And the D130 is an antique that dates back to 1948, as I repeatedly pointed out.

> No doubt, you're probably thinking - "what putz is bringing up a
> 55 year old loudspeaker transducer in the context of THE BEST
> MIDBASS EVER thread?"

As the requirement for time was "EVER" and as the D130 CORRECTLY APPLIED is quite exceptional in terms of low distortion and low compression, surely it qualifies.

BTW, I have been trying to ignore your repeated insults, but they get tiring and moreover reflect more on you than on me.

> If you've never heard a JBL D130 or 075, I can tell you from
> personal experience, they're not for high performance home sound.

I am unsure what you have heard, it would be useful if you where more specific.

> They aren't even considered high fidelity in today's pro market when
> compared to the 2200 series of woofers and 2400 series of compression
> drivers.

In the Pro Market the D130 would be hopelessly underpowered, however that does not make it low fidelity per se.

> The D130 worked fine in venues like the Grateful Dead's "wall of sound".
> In that application, directivity and controlled off axis response were
> not major concerns. Similarly, the 075 tweeter functioned reasonably
> well for the intended purpose.

You may be mistaken. If you look at the WOS you would notice that unless the drivers had very narrow "controlled directivity" the whole system would not work well as there would massive cancellation issues. And the guys who designed the WAS did know what they where doing.

> But everything Thorsten has said in this thread about these drivers
> has been way off the mark. The 075 bullet was intended to be crossed
> down around 2.5khz - no where near the 6khz upper limit of the D130.

Has it been? I did remark that the COMMON crossover for the D130 and later versions was around 2.5KHz however a higher crossover could be used and in fact I have done so, in sound reinforcement applications and quite successfully (hence I also noted the requirement to EQ out the upper midrange boost present in the frequency response of the D130).

> In looking above at some of the rambling stupidity posted by Thorsten, I > noticed a glaring error that could probably confuse some of the less
> experienced people who might come upon this wacky thread. In the
> interest of avoiding widespread misinformation, I'll add another
> correction here.

Before you correct you should perhaps read what others write

> Constant directivity in the context of high performance loudspeakers
> implies that the flat frequency response expected on axis is largely
> duplicated as one steps further and further off axis horizontally
> from the speaker. Textbook constant directivity loudspeakers will
> show a gradual attenuation of response with increasing off axis angle.

Correct.

> So for example, at 30 degrees off axis, the response will be
> essentially flat from the lowest frequency to around 10 or 12khz
> - but it will be consistently down 2 or 3 db from the on axis response.

This you can only find if you employ dipole or cardioid bass systems, with monopole bass or full size (not foreshortened and reduced mouth size) Bass horns you invariably have a directivity index of 0dB at low frequencies as the sound radiated will "bend around" the edges of the enclosure.

This gives to the so-called "baffle step" in the anechoic on axis response, which is actually an indication of changing directivity (not of frequency response changes per se). Above that "baffle step" the the directivity indexwill be around 6dB up to where drivers/horns etc. display a greater DI which then dominate the speakers behaviour independent of any Baffle etc.

So with real "constant directivity" speakers such usually is only possible at higher frequencies. A good example are the Speaker Systems designed by Earl Geddes which are generally accepted as "constant directivity" yet still have 0dB DI at lkow frequencies.

The second issue we need to look is exactly how much the SPL will be attenuated at a given off axis position in the frequency region of the speaker that conforms to constant directivity.

Is that 3dB down at 30 Degrees as you seem to suggest it should be?

Well, realistically it depends on the intended beamwith of the design.

If I for example design a speaker with a 40 Degree horizontal beamwidth than at 30 Degrees off axis I would expect a much greater attenuation, meanwhile if I where designing a speaker with a 120 Degree beamwidth I would be greatly disturmed if I measured a 3dB attenuation.

> As one goes further off axis to 60 degrees, it might approach
> 5 or 6 db of attenuation up to around 10 or 12 khz. The Revel
> Ultima Salon 2 and Klipsch Palladium P-17B are a couple of
> decent examples of speakers exhibiting constant directivity.

They expect a certsain particular directivity behaviour, however they are not as such indicative of the specific performance a constant directivity speaker will have, this (as remarked above) will depend heavily on the designed beamwidth.

> The major departure from parallelism for the Tannoy is only happening
> in a narrow frequency span. If this driver were operated up to 5khz,
> the difference in slopes would be dramatic.

BUT I was not recommending to operate this driver from Tannoy up to 5KHz was I now.

> " the off axis response will be significantly attenuated above a few
> 100Hz, ultimately forming in the midrange and up to ultrasonic
> frequencies a CONSTANT DIRECTIVITY system."

> you'll see a nearly 15 db drop off from 2.5khz to 5khz in response
> at 60 degrees off axis but at 30 degrees off axis, the 2.5khz response
> value is virtually indistinguishable from the 5 khz value. This is a
> text book example of a driver that is NOT exhibiting constant
> directivity.

Actually, as I suggested a 5KHz crossover (for a good reason BTW), let us look what is happening at 5KHz, shall we?

At 30 Degrees we have the -6dB point at 5KHz. For 10KHz the -6dB point is at around 22 degrees.

Now what is -6dB angle at 5KHz for a JBL D130? Well, it is basically that of a 4" Shallow Dome. As anyone who ever took some acoustics will know, this gives at 5KHz around 60 Degrees beamwidth, or in other words a -6dB angle of 30 degrees.

Holy Grass Mud Horse! The "Bass Midrange" driver and the "Tweeter have exactly the SAME beamwidth at 5KHz. Maybe this important? Nah, WTFDIK... Of course, we still have to deal with non-flat on axis (and off axis) response of the D1`30, it cannot be operated just "open", but needs a suitable LCR Equaliser to flatten up the boosted upper midrange.

As to directivity further down in the frequency response, at lower frequencies progressively more of the cone surface of the D130 comes into play (as is usual for wideband drivers that operate in effect in bending wave mode) for a 15" piston the frequency where the beamwidth is 60 degrees is at around 1.5KHz.

Se we have a system that will have a pretty constant beamwidth from around 1.5KHz to beyond 5KHz and has declined only to 45 degrees or so at 10KHz. The 30 degree off axis response will be reasonably flat from 1.5KHz to around 7KHz with a little rolloff at 10KHz and mean level that is 6dB down on the on-axis response.

I tend to consider such a behaviour a good indication of the presence "constant directivity". I measures this stuff BTW back in the 1980's in the anechoic chamber of the RFZ in Berlin, using B&K gear.

So I see you completely validated my 5KHz recommendation with your analysis of what WOULD HAPPEN IF we used the original 2.4KHz crossover... I'd thank you, but I think you are a rude and insulting little so and so, so I will leave it here.

Ciao T

PS, if you do not know the formula to calculate beamwidth vs. piston size look it up in a good beginners text on acoustics and if you doubt my point of the 4" near piston for the D130 at 5KHz look at the datasheet.

If you feel the need to further expose your ignorance, please feel free, I have a big can of "whoop-ass" with your name on it here...

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?


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