Though some of you might find this useful.
Rob
Though some of you might find this useful.
Rob
15" driver is 100° nominal at 1 kHz.
That'd be 4430's touted beamwidth match between LF and HF.
[More like 110°, actually, for -6 dB.... ]
If 15" driver is aprox. 100° at 1khz, why do most 3-way speakers cross significantly lower?
For example:
S9800 at 750hz
S9900 at 850hz
TAD 2402 650hz
My opinion:
Because in a cone driver meant to reproduce low bass other factors must be considered, such as cone mass, suspension slackness, woofer response tilt, and range of pistonic behavior. Since the issue when the driver is in effect too small to match the treble beam width is power distribution in the room it only makes sense to obsess about it if the whole room is going to be tested and treated just as carefully. Since home listening rooms almost never are, and studios can be tuned as needed, the speaker designer is free to make good bass and lower the crossover if necessary.
A mismatch of cone and horn beam width is more critical when the cone is too big for the crossover frequency and its beam width is too narrow, because the resulting sound can be very harsh. Note how the horn pattern was narrowed in the Altec Model 19.
Besides that, I think there are still plenty of people who believe on-axis response is the truly crucial matter.
"Audio is filled with dangerous amateurs." --- Tim de Paravicini
@Dave:
Your explanation makes sense, that dispersion match is not the only factor affecting the choice of crossover-frequency...
@Flaesh:
Thanks for that chart.
If i´m reading this correctly, 90° dispersion of a 15" cone would be actually higher, more like 1,3khz. That seems way to high as a crossover for a 15" cone.
A 12" or 10" reaches 90° dispersion even much higher...
So if you are aiming a crossover of ~800hz to a 90° horn, a 12" or 10" would be even much worse than a 15" regarding dispersion-match, correct?
I´m wondering if this chart explains the poor imaging-abilities of the older monitors such as 4343 or 4345.
They had a 10" crossed at 1,2khz to a horn with 80° dispersion.
At 1,2khz the 10" cone has a dispersion of aprox. 150°.
Not matching at all.
A system like the S9900 is said to image a lot better, maybe this is because the 15" cone matches better with the 90° horn...
It's the type of horn and having a reasonably smooth transition where there are no abrupt changes in the DI through the crossover region. So yes you do want a close match at the crossover point. But the horn ultimately controls and contributes the most to the imaging. Check out the 4430 AES paper on this site. It's linked in the post. Virtually all of the modern JBL horn systems are designed using Constant Directivity horns and have their roots in the 4430 design. Take a look at the DI plots for the 9900 also posted here.A system like the S9900 is said to image a lot better, maybe this is because the 15" cone matches better with the 90° horn...
http://www.audioheritage.org/vbullet...peaker-Systems
Rob
"I could be arguing in my spare time"
Hi Dr.dB,
YOu have to read horn dispersion characteristics with greater attention, as most of them have much wider dispersion at lower frequencies, then their nominal specified data. Only very large mouth horns can be specified dispersion on the lower frequencies.
for example (2425 with 2307 and 2308 lenses would have over 140 deg dispersion round 1kHz, I can imagine that 2440/.41/.45/.46/.50 with 2311 and 2308 would behave almost identically round 1kHz or less, if using -6dB level as 'cut-off dispersion level' ):
http://www.jblpro.com/pub/obsolete/Acoustic_Lens_Family1.pdf
while using 2360A horn, the dispersion round 1kHz would be much more controlled relative to the specified data.
regards,
ivica
Hello Ivica
Here is an actual plot from the referenced AES paper. They have the Urei Coax and 511 Altec horn in there as well.
Rob
"I could be arguing in my spare time"
@Ivica:
You are right with these lenses, I can see that in your posted graphs. Thanks.
So I was wrong as the lenses should match the dispersion of a 10" actually quiet well!
So the poor imaging compared to more modern designs must be in the horn itself as Rob mentioned.
@Rob:
I´ve read that paper, thank you.
So the key to good imaging is a Constant-Directivity Horn and a directivity match with the woofer below.
But I would need a equalization e.g. CD-compensation... If you don´t use a M553 crossover, how can this be applied with a usual analog-active-crossover like marchand ?
What about the Yuichi A290 for example?
This is not a CD-horn, right? But do the vanes help control the directiviy-index?
So how does it image?
Does it have 90° horizontal dispersion at ~800hz or is it much wider in realitiy?
You would need to measure the system with the horn mounted to the baffle to see what the response is. Then you would just figure out a voltage drive that is the mirror of the measurement to flatten things out. Canned curves are only aproximations and wont get you the best possible response. The easiest way is just to use a passive network if you are going analog. But that means you need something like LEAP to do the network. If you go digital it's much easier.But I would need a equalization e.g. CD-compensation... If you don´t use a M553 crossover, how can this be applied with a usual analog-active-crossover like marchand ?
Rob
"I could be arguing in my spare time"
The topic of imaging is more than just the horn geometry
In theory above 1000 hertz the transducer should ideally be a point source at a 3 dimensional point in space.
The M2 horn and D2 driver is claimed to approach the ideal
That involves a lot of big ask technical challenges when it comes to implementing with alternative drivers by diy people who are inclined to disagree on what works and what doesn’t work.
For example will a single Be diaphragm compression have sufficient high frequency extension? On paper it looks like it does but subjectively there are opposing views. So some end up adding a uhf horn to extend the highs. But then it’s no longer a 3 D point source. So they grab a dsp crossover and add delays in an attempt to solve that problem. This adds a lot of complexity. Many audiophiles with analogue sources and digital sources argue even the very best out of the box dsp crossovers are not completely transparent and they buy soa outboard ADC and DAC. That requires significant financial resources.
The difficulty for Jbl diy fans these days is taking a concept based on a Jbl engineered design and then implementing it at home with alternative horns and drivers because Jbl no longer supply the drivers and horns directly.
At a more practical level a pure constant CD loudspeaker is claimed to work best when placed in the corners
But depending on your room dimensions and how the room is arranged this might not be appropriate.
Throw horns out of the conversation for a moment and there are numerous multiway direct radiator loudspeakers that are claimed to have outstanding imaging properties. But this comes at a price according to horn loudspeaker aficionados.
However, active loudspeaker technology is starting to gain momentum and the capability gap between conventional direct radiator systems and horn systems is getting smaller.
The point is you can’t look at one loudspeaker performance parameter in isolation. Focussing on one aspect alone could come at a huge penalty overall or involve significant expense. So it’s about getting the balance right with a set of complementary compromises.
In the diy space that will keep you busy.
Thanks a lot, both of you.
How would you judge the A290 Yuichi´s imaging abilities?
Probably the yuichi matches the best with a 15" cone somewhere around +-800hz, right?
Which crossovers would you recommend between a 10" cone (2123h) and the yuichi ?
Btw, how important is a good cone-horn match in reality ?
db,
Try to absorb the significance of the following quote ( regarding imaging ).
The Array horn has a horizontal coverage something like the following pic from POS ( though since the horn is taller, the polar patterns maintain their pattern spreads to a lower frequency ):Originally Posted by GregTimbers
If you want to experience good imaging, one wants to involve one's ears in an audible 6db down-point, that also has nice constant directivity delineation, as seen in the pic ( & is maintained from at least 1K to 10K, with nicely spaced polar lines ).
You'd do well at your young age to discover the paradoxes that lie behind imaging ( which so far have been ignored in this thread ).
Build up something like what RobH shows in his moniker ( any le14 variant will do, as will almost any Altec 811 sized Radial horn turned vertically ).
If you do this, you will eventually forget about the industry wide SR dogma ( of the so-called necessity ) to match polar patterns at crossover.
JBL's best ( horn based ) imaging champ doesn't do that ( it actually beams much like a flashlight > or StarWars "Light-Saber" in the HF ).
Here's the Timbers Array Thread for a bit more background on the subject.
Hi Dr.db,
I have no personal experience with the mentioned A290 Yuichi horn, but almost any owner , here on the AHF Forum said that it is very amusing sound reproducer.
As it has fins in the horn throat, so some kind of internal reflections must have been present, but I have no idea about that influence to the 'imaging'. As known to me almost ANY wide dispersion horn has some kind of internal reflections including M2, DD67/66K, H9800, H9500 , 2370/80......as it is difficult to be 'protected' from the horn beaming for the frequencies over 10kHz. Such internal reflections and diffraction would produce the 'movements' of the sound source depending of the frequencies, as diffraction 'lines' behave as another source, but not for all frequencies, mainly for the higher frequencies.
I believe that You will be satisfied with A290 (with the fins), without fins, I would expect beaming over 10kHz.
regards
ivica
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