I'm trying to design something like mini JBL K2, 2x12" + compression horn type of speaker. I'm wondering which speaker placement is better, WTW or WWT for this type of speaker. Crossover Frequency will be around 1k.
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It will be best if your woofer to woofer center-to-center distance is a wavelength or less at crossover (about 13" for 1kHz) for MTM. MTMs can certainly work with greater spacing, but the vertical dispersion lobe can get very narrow at crossover. Here's a nifty calculator so you can play around and see the effects yourself:
Tolvan Data
One way to alleviate the vertical dispersion problem is to use 3rd order Butterworth filters. The 90 degree relationship between the woofers and the tweeter helps the situation. The calculator will let you try that out, too.
Tolvan Data
One way to alleviate the vertical dispersion problem is to use 3rd order Butterworth filters. The 90 degree relationship between the woofers and the tweeter helps the situation. The calculator will let you try that out, too.
Some Altec crossovers were 18dB/oct on the horn, and 12dB/oct on the woofer to achieve phase alignment in a particular application. The question of crossover audibility vs. order is a rather contentious subject in general. Opinions vary, all the way from those who insist on first-order networks, to people like Siegfried Linkwitz who have done testing that suggests that a 4th order Linkwitz-Riley crossover is inaudible. So, YMMV, and all that. For myself, I've had good experience with an LR4 (24dB/oct) crossover between a woofer and horn. I suspect the real "secret" of good crossover design is a lack of frequency response ripples in the crossover region and phase coherency between drivers.
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fpitas, thank you again. I was researching the filter design today myself, and I realized that the speaker design is way more complicated than I initially thought. I think I really have to keep learning. Yes, it seems like the crossover design is one of the most controversial subject in audio society.
Yes; and successfully integrating a horn with a woofer is one of the more complicated tasks, because of the driver offset (among other things). A DSP crossover can make the job easier because the necessary delay can be dialed in, instead of using the relative phase of the low and high pass networks to achieve phase alignment.
There has been several iterations of the K2, which one do you mean?
The minimum horn size makes it difficult to smoothly cross over from a double woofer to a horn.
A WHW has the woofers too far apart and HWW has a directivity anomaly too.
The old DMS-1 monitors used WHW layout and problems are visible in the DI curves.
They have dropped the idea in the new, presumably improved, M2 monitor.
Horn above side by side woofers will need a low cross over frequency and bulky horn.
JBL themselves seem to have found 2 woofers problematic and dropped them for the latter version K2, the s9900.
You would be better with one woofer and a true sub-woofer if you can fit it.
Best wishes
David
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Yes, this is a better way to do a double woofer. But to match the horizontal directivity of the double wide woofers means the cross-over frequency needs to be lower and the horn becomes wider and bulkier too.
Ok for an "ultimate" $42,000 system like the Everest but a smaller system I think it is not the best way to allocate the limited space, or the money.
I really wrestled with these possibilities in my own JBL system before I went one woofer + subwoof and still feel it is the optimum choice.
Best wishes
David
Yes, had a memory about that but didn't check because I don't think it alters my point much.
I believe the latest Everest has bass response just a little rolled off to work in typical rooms in mainly Japanese market.
Probably why it has a second 15" rather than a true subwoofer.
Still pretty nice however!
Best wishes
David.
Hi David,
I had posted a reply to your post earlier today, but it seems like I forgot to press "POST QUICK REPLY' button to finalize it...
Anyway, I was always wondering why JBL dropped WTW (S9500) style, but your explanation is pretty reasonable, I think. Thank you. Their earlier studio monitor 4435 also had 2x15" (one rolled off), which is actually the same as your recommendation, W+SW.
I happened to read a JBL tech paper recently which explains some of the technical background of 4430 and DMS-1 monitors. JBL is (was) very proud of the DI performance of DMS-1 in this paper, but you say it's not really ideal. Do you mean the DI curve of DMS-1 is nothing special for today's standard? or do I misunderstand something?
http://www2.jblpro.com/products/recording&broadcast/LSR6300/JBL.tn_v3n01.pdf
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I didn't know that. It's interesting. I'm a bit skeptical about current JBL monitors' super tweeters with very high crossover point, though...
You are well to be a bit sceptical.
A super tweeter is not used in the professional JBL monitor, the M2.
The super tweeter is used in the consumer systems primarily for "specification" market appeal.
I read that the senior JBL speaker expert just disconnects it for his own use!
Best wishes
David
No disrespect to the DMS-1, lovely drivers, the horizontal pattern is excellent and the horns themselves are fine, I even have a couple.
But if you look at the beam width curve there is a fairly bad kink in the vertical directivity at 600Hz to 1kHz.
This is due to the separation of the 2 woofers plus horn that makes it too directional just below crossover, then the horn is too vertically small to maintain directivity at crossover and just above..
This is the problem with the WHW layout and it is more or less inherent.
Any attempt to increase the horn size to control the pattern just spreads the woofers further apart so it doesn't help.
Their discussion of directivity is excellent but they just skip this bit.
I am a little surprised they choose this layout when they were obviously aware of the problem. Hence the layout of the new, improved M2.
Best wishes
David
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The second woofer is essentially baffle-step compensation. As for the tweeter, in the upper range the large format driver diaphragm starts breaking up, and the large horn directivity starts to collapse a bit, so the tweeter was added. Whether you (or anyone) can hear the 50kHz upper range of the tweeter is another subject
Just had a look at the 4430/4435 brochure that combines the specifications of both speakers in one document.
They show the improved distortion behaviour of the double woofer 4435 compared to the one woofer 4430.
But they only show the directivity of the 4430
A bit sneaky that.Seems to me that if you plan to roll off one woofer anyway then you should optimise for the job and use a true sub-woofer.
Best wishes
David
Just had a look at the 4430/4435 brochure that combines the specifications of both speakers in one document.
They show the improved distortion behaviour of the double woofer 4435 compared to the one woofer 4430.
But they only show the directivity of the 4430
I don't think we were being deceiving, although there would probably be some slight lower mid asymmetry in the horizontal polars of the 4435. Polar curves at that time were measured on a flush turntable of Don Keele's design. The were done in an outdoor ground plane pad with the system standing on its head and the horn on the centerline. It would have been difficult to get a 4435 to balance that way.
David S
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