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In Reply to: RE: 6 - 7 octaves if you're into low fi... posted by villastrangiato on July 11, 2012 at 10:35:18
Hi,> Similarly, use of large drivers (12- 15 inch) has serious drawbacks
> when implemented in two ways and crossed over from 1500 hz up.Not really. It has some fundamental design requirements that need to be understood, considered and implemented, as has every engineering project under the sun.
> Wide variations in off axis response when transitioning from an
> oversized driver to a tweeterAre an indication of very poor design.
Let us take an example of a good design, that originally derived in the mid 40's from german designs but moved beyond the original.
In this case we have a driver that is coaxial and uses the cone as waveguide.
(an interesting aside, in the 1980's then new Cepstral analysis and extensive listening confirmed the cone shape originally derived from german designs as one of the absolute best waveguides, over all the the then and even now fashionable "CD" geometries)
This driver has a near constant directivity index between 500Hz and 5KHz, above 5KHz DI increases and below 500Hz (depending on box size and mounting) it decreases.
When mounted and placed correctly the system has a flat on and off axis response from the LF Cutoff to around 5KHz with a falling off axis response above 5KHz.
The driver in question BTW is a 15" 2-way Tannoy coaxial from the same era as the JBLD130.
> (whether a five inch crossed at 3.8khz or a 15 inch crossed at 1.5khz)
> kills imaging performance.Actually, using a driver/system with insufficient DI is what kills imaging, or large changes of DI over a narrow bandwidth.
The problem you suggest can only happen in hamfisted designs turned out by those who fail to understand the first things about speaker performance and design.
BTW, once you understand the action of the D130 Cone system you will understand why it actually offers a 40Hz-6KHz usable bandwidth with a pretty flat power response (that is integrating on and off axis response) and in fact a rather flat response at the listening position, without needing massive room treatment to control the reverb caused by poor speaker directivity.
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: 07/11/12Follow Ups:
Operating a driver at frequencies where the wavelength is smaller than the driver's diameter results in frequency combing or destructive interference off axis. This is acoustics 101. If you wanna argue that fundamental point, go read some basic texts on acoustics or talk to the hand.
Thorsten said:
"The D130 I mentioned is good to well past 6KHz!"
The D130 was a 15 inch driver. The wavelength at 6khz is about 2.25 inches. If one were to cross that driver over to a tweeter anywhere near 6khz, there would be a very narrow dispersion pattern between 1500 hz and the crossover frequency. At the crossover frequency, the dispersion would flare out or as is commonly said in the industry- "bloom". This may be high fidelity to you. To me and the industry professionals I know, it's rubbish. All of the JBL drivers I've ever used were extremely well made, low distortion units. But that doesn't fix a novice's poor design or misuse of a driver.
Hi,> Operating a driver at frequencies where the wavelength is smaller
> than the driver's diameter results in frequency combing or destructive
> interference off axis. This is acoustics 101.Indeed, had you ever progressed to acoustics 102 you could have noticed that your 101 version only applies to rigid pistons, which do not even exist in in Thiel & Patner / Accuton drivers.
So, acoustics 102 is to stop engaging with unrealistic oversimplified theoretical models and to engage with the real devices, something that based on literature I read in my misspend youth was quite common in German acoustics decades before I was born....
> If you wanna argue that fundamental point, go read some basic texts on
> acoustics or talk to the hand.Look who is talking. I read those decades ago and actually spend time observing said rules in practice.
> "The D130 I mentioned is good to well past 6KHz!"
>
> The D130 was a 15 inch driver.Correct. It also used a "NAWI" profile cone and a fairly soft paper for the cone. This has, invariably if we observe acoustics based on evidence, certain results.
> The wavelength at 6khz is about 2.25 inches.
And?
> If one were to cross that driver over to a tweeter anywhere near 6khz,
> there would be a very narrow dispersion pattern between 1500 hz and
> the crossover frequency. At the crossover frequency, the dispersion
> would flare out or as is commonly said in the industry- "bloom".Surely, this would depend on a number of factors.
For example, given the driver does not use a rigid piston, we experience reducing radiation diameters with rising frequency. Of course the cones profile will still provide a waveguide.
So as long as we match the directivity of the 15" Woofer where it hands off to the tweeter we are likely in pretty safe territory. Now the tweeter commonly used by JBL "back in the day" was the 075, basically a 38mm ring radiator with a fitted waveguide that provided 40 Degrees -3dB beam-width from a few KHz to supersonic frequencies.
Unsurprisingly this fits the bass/mid driver very well.
Now you may be considering some Spam Skweek Darkenator or other HF driver designed and employed contra lex naturam as mate, ignoring the hopeless of any SPL match or any attempts of matching directivity, these are quite poor specimens to do HF.
Well, an uninitiated, ignorant novice may try such.
> This may be high fidelity to you. To me and the industry professionals
> I know, it's rubbish.You expose nothing here than your total lack of understanding basic acoustics, or a refusal to put them to work. Come on, we are talking > 60 years ago stuff here.
> All of the JBL drivers I've ever used were extremely well made, low
> distortion units.So they are.
> But that doesn't fix a novice's poor design or misuse of a driver.
This I agree with completely.
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: 07/11/12 07/11/12
"So, acoustics 102 is to stop engaging with unrealistic oversimplified theoretical models and to engage with the real devices, something that based on literature I read in my misspend youth was quite common in German acoustics decades before I was born...."
- Thorsten on the value and benefit of running a 15 inch woofer at tweeter frequencies.
I got your real devices right here, Thorsten:Here's a the current list of top rated loudspeakers from one of the most popular review magazines in the world today:
Aerial 20T - 2 9" woofers crossed over at 300hz
B&W 800 Diamond - 2 10 inch woofers crossed at 350hz
KEF 207/2 - 2 10 inch woofers crossed at 120hz
Revel Ultima Salon II - 3 8 inch woofers crossed at 150hz
Sonus Faber Amati Futura - two 8.75 inch woofers crossed at 80 hz
Sony SS-AR1 - two 8 inch woofers crossed at 400hz
Vandersteen 7 - 12 inch sub woofer crossed at around 90hz
Vivid Giya1 - 2 11 inch woofers crossed at 220hz
Verity Audio Sarastro II- 11 inch woofer crossed at 150 hz
Wilson Maxx 3 - 13 inch and 11 inch woofers crossed at around 150hz
Revel Ultima Studio 2 - 2 8 inch woofers crossed at 230hz
MBL 101E Mk.II - 12 inch woofer crossed at 105hz
See any 12 or 15 inch drivers on this current highest rated speaker list crossed over higher than 500hz, let alone up near 5 or 6khz?
Btw, Einstein - the 15 inch woofer in the Meyers Sound X-10 is crossed over at 950hz - which is about as high as anyone would want to go in order to maintain a reasonably high level of fidelity. JBL has been crossing over its 14 inch woofers in house systems at 750hz and lower for years (my old 250Ti Limiteds cross at 400hz). So nice try on the Meyers - but as usual - WRONG.
Given your apparently high opinion of your understanding and experience, I'm guessing that you think all the folks who built the above speakers didn't pass "acoustics 102" yet. Or perhaps they're all part of a conspiracy to ban 15 inch woofers from the home loudspeaker market, right?
Tell you what Thorsten. RMAF is coming up this fall. The show could always use some added comic relief to draw attention away from borish, snobbish, audiophools constantly badgering one another about who makes the best loudspeaker... Perhaps you could help lighten the mood a little by giving a seminar on why you think the industry has it all wrong - that it should be using 15 inch woofers in controlled break up crossing over to tweeters at several thousand hertz... That should get some laughs if nothing else.http://www.youtube.com/watch?v=BNsrK6P9QvI
Edits: 07/11/12
Hi,
> Double face palm time, yet again...
Yup.
Stereophile review of JBL Synthesis 1400 Array BG loudspeaker which uses a 14" Midbass crossed over at 750Hz.
Stereophile review of Tannoy Dimension TD12 loudspeaker which uses a 12" Midbass crossed over at 1.3KHzHz.
Stereophile review of Tannoy Churchill loudspeaker which uses a 15" Midbass crossed over at 1.1KHz.
Not reviewed but very much worth a good listen is the Meyer Sound X-10 Studio Monitor which uses a 15" Midbass crossed over at 950Hz.
In the history of Studio Monitors many examples of 15"2_ways may be found, be they from Kinoshita, TAD/Pioneer, JBL, Urei, Altec and many others.
The example of the D130 with 075 Tweeter crossed over at around 5KHz is extreme, HOWEVER, as the tweeter has constant directivity at 40 Degrees Dispersion you may find yourself surprised just how well this actually works acoustically.
I have you here at a disadvantage of course, as I am quite familiar with such systems.
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)
Or are you just one complete non stop joke?
Everything you just posted was a repeat of what I've been saying. Crossing a 15 inch woofer above 1.5khz (up to 6khz as you suggested earlier) is something a total novice or fool would do. And then after contradicting yourself by requoting the information I originally posted, you claim:
"I have you here at a disadvantage of course, as I am quite familiar with such systems."
Technically, given everything you've been babbling about in this thread, you wouldn't know your rear end from a hole in the wall. I suspect that given the response of others to your non sense in this thread, I'm not alone with this sentiment.
But you apparently have no shortage of audacity or arrogance. For that, you get high marks.
Hi,> Are you as deranged as your posts suggest?
>
> Or are you just one complete non stop joke?Well someone here clearly is.
I have no particular agenda (e.g. I do not own a warehouse full of NOS D130 and 075 which I am trying to talk up in value - I wish I did though).
I merely use them as an illustration that most "truisms" and generalisations (such as "A 15 Driver must be crossed over below XXXHz" or "A 5" Mid bass is the best in all time") are in fact completely false.
Now I should note that I am not suggesting to generalise from concrete examples (e.g. the D130 & 075 crossed at 5KHz), so for example a Car Audio 15" "Competition" Subwoofer Driver most certainly would not be suitable to a two system crossed over at 5KHz, yet it is possible to make such system GIVEN THE RIGHT DRIVERS AND ENGINEERING.
I notice that you omitted to answer my question if you actually measured such a system (especially DI) as I described (that is very precisely the JBL D130 and the JBL 075 crossoed over at around 5KHz)?
Have you? (I have, BTW).
And if you have not measured it, how can you claim to know what it measures like?
And it would seem you have also omitted to peruse the specifications issued by JBL for these drivers either (which may prove illuminating, FWIW).
> Everything you just posted was a repeat of what I've been saying.
Actually posted a list of speaker references where the highest crossover was 400Hz for 8" Woofers, which did not include a single 15" (FWIW) and with which you suggested that was some general technical consensus or some such that large drivers must be crossed over low (below 400Hz, which you suggest should be the maximum for an 8"Driver in your post).
I pointed out that very successful designs exists that do not follow these rules and in fact cross over very large drivers quite high, compared to your examples.
Now the JBL D130 I have been consistently referencing is a wideband 15" that does operate up to 6KHz quite successfully (the old EV SP-15 and the Goodmans Axiom 401 also did quite well, all said, but their Cone/Whizzer design kind of played havoc with the directivity and frequency response) and I did not suggest that any other drivers where suitable to such a design.
The D130 of course has narrow dispersion at higher frequencies, which is why the competent Engineers at JBL elected to mate it with an equally narrow dispersion tweeter, so the directivity index for the complete system is both very high (in other words it creates very little room reverb) and quite even from the midrange and up.
You may very well debate with me if a high and slow change/constant directivity index is a good thing for music reproduction or not, that I would suggest is a matter of taste. Some people like Bose 901's, some like MBL Omni's, some like very narrow dispersion systems instead.
Let them all eat cake. We baked a very nice Almond cake with German Buttercreme frosting recently (thanX to massive willpower by all of us some is still left, but not by tomorrow Tea time), I suggest something at least as nice, or nicer (Schwarzwälder Kirschtorte?).
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: 07/12/12 07/12/12
I don't remember seeing measurements of a 12" or 15" woofer at 45° looking 'flat' above 1,500 Hz. Flexible cone or not, and whatever its shape is.
Yves
Hi,
> I don't remember seeing measurements of a 12" or 15" woofer at 45°
> looking 'flat' above 1,500 Hz. Flexible cone or not, and whatever
> its shape is.
Why would remotely desire flat response at 45 Degrees? I would desire significant SPL Rolloff, ideally all the way to the bass, but practically to as low as possible, which incidentally mandates a large acoustic structure (Baffle, Horn, Cone).
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)
...he's moreso referencing the beamwidth transition from driver to driver in the crossover region. A radical shift in dispersion in the crossover region is not generally filed under "well blended".
You would think coincident driver arrangements would avoid lobing tilt issues though...
Cheers,
Presto
Hi,
> I think he's moreso referencing the beamwidth transition from driver
> to driver in the crossover region.
Alas, so am I.
Of course we need to match woofer's and tweeter's off axis response. However HF drivers exist with any dispersion pattern under the sun (and absent something suitable simply design a suitable waveguide), so it is up to the designer to match the HF directivity to that of the LF.
Now just because this directivity (Index) is high for the LF it does not follow that there will not be a smooth transtition.
> A radical shift in dispersion in the crossover region is not
> generally filed under "well blended".
Well, what can say? You are preaching to the first apostle perhaps?
> You would think coincident driver arrangements would avoid lobing
> tilt issues though...
They do. I am quite fond of Coaxials, back to the old Schulze/RFT TH315 (developed from the first ever coaxial be Dipl Img Exckmiller) I owned i n the 80's.
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)
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