Tweeter to match JX92S

[AntM]

I'm looking into building a MLTL design using the Jordan JX92S

http://documents.jordan-usa.com/Encl...31-MLTL-MD.pdf

The JX92S is an excellent driver when used in a fullrange, but as is typical with many full-range drivers, has a poor off-axis response. I'm planning on adding a tweeter which can be optionally enabled with a simple (ideally first-order ) crossover. I will then be able to listen to them either full-range for superior imaging when listening directly in the sweet-spot, or as a 2-way.

Because of WAF, I don't want to increase the height of the enclosure too much. I'm also keen on mounting the tweeter as close as possible to the fullrange, as I would probably keep the crossover frequency high (maybe 6kHz) and I want to avoid lobing effects as much as possible.

Another factor is that the Jordan has a rising on-axis response, which means that it is better used off-axis. This means that the partnering tweeter should have a very good off axis response.

The question, as always, is which tweeter to use. I've shortlisted several models including
Vifa's XT25SC90-04, NE19-VTS-04, XT19TD00-04 and SB Acoustic's SB29RDNC.

Has anyone had experience of using any of these units?
My requirements are:
- small faceplate to allow close mounting
- good off-axis response
- excellent THD
- Good subjective performance.

I may also consider cutting the tweeter faceplate with a router to allow close mounting.

Any opinions gratefully received.

Ant

[jerome69]

Why don't you make a true 2 ways with a true crossover ?

For 180$, the price of one JX92S you have a pair of drivers for a 2 ways. And they sound better.
Exemples :
Parts Express DIY Project
Others
Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter
Zaph|Audio - 4" Bargain Mini
Peerless HDS PPB 830860
Vifa PL14WJ-
SEAS 5INCH
Fostex FE126E +

[GDO]

Originally Posted by jerome69

Why don't you make a true 2 ways with a true crossover ?

For 180$, the price of one JX92S you have a pair of drivers for a 2 ways. And they sound better.

Is this your personal experience, or are you just quoting Zaph ?

Have you built all the other models you mention, or are you still quoting?

[GDO]

Btw,i don't think it's a good idea to stick a supertweeter on top of a jx92s. In my experience this doesn't work. Much better to make a real xover at a suitable freq, dictated by directivity concerns, that is 3khz for jx92s.

A very good match to jx92 in this setup is an AC ribbon as proposed by Jim Griffin, excellent imho:

Jim Griffin Jordan/Aurum Cantus in a PE Box

[GM]

Agreed, its rising response makes for a problematic blending if not using a super tweeter array.

+1, I've auditioned his monitors and they are two ways done right enough for most folks.

GM

[jerome69]

Originally Posted by GDO

Is this your personal experience, or are you just quoting Zaph ?

Have you built all the other models you mention, or are you still quoting?

Personal experience with loudspeakers in particular with fullrange. Never built the models given as choice example . I didn't only quote Zaph .

A fullrange covering 30Hz-20kHz : diameter 5"
Designs

These new designs are smaller than the first generation designs yet provide output to, or below, 30Hz thereby restoring the bottom octave.

Yesssssssssssssssssss !
I don't need to listen this to predict it will never work.

[AntM]

Thanks for your comments. Actually the design is somewhat inspired by the Aurousal VS.

Aurousal VS VirtualSource? Floorstander*

This uses two JX92S drivers operating without a crossover in a MLTL cabinet (except for baffle-step compensation). There is an additional tweeter which just helps with the top-end. The crossover frequency and order is unspecified but I suspect it has a high crossover frequency to just help in the top octave where the Jordan driver's dispersion characteristics are lacking. The design has had some outstanding reviews, so I am convinced there is merit in the idea:
Aurousal VS review from TechRadar UK's expert reviews of Hi-fi and AV speakers
Aurousal VS review from the experts at whathifi.com
Aurousal VS loudspeaker - Review [English]

I have designed a few 2-way speakers with varying success, then recently I built a sealed box design built around the JX92S. I must say I was astonished by the performance that could be achieved by a single drive unit in a simple enclosure. I put his down to several well-known disadvantages in two-way designs:
- loudspeaker impedance varies with temperature, therefore crossover characteristics will also vary, both long-term and instantaneously
- the dispersion characteristics of a 2-way will change suddenly around the crossover frequency from narrow to wide, This will alter the frequency response in a way that is dependent on room characterisitcs. This has inspired designs that attempt to match the dispersion characteristics of the two drivers around the crossover frequency (using waveguide-loaded designs such as The DXT® Tweeter - a waveguide lens for dome tweeters
- The harmonic content of natural instruments is difficult to re-create correctly in a 2-way design due to magnitude and phase variations.
- Vertical lobing (i.e. spatial comb-filtering) can occur due to interference around the crossover frequency.
- Real difficulty in making a good design built around the necessary engineering compromises, particularly for an audio DIYer without having good test equipment and modelling tools.

Of course full-range designs are far from perfect and I'm intrigued by the idea of providing a little extra help at the top-end.
the Aurousal loudspeaker uses a polymer/silk dome Neodymium unit, possibly quite cheap. It also occurs to me that if the crossover is above 10kHz, 2nd-harmonics and above are out of the hearing range (and likewise above 6.6kHz crossover, 3rd harmonics are unimportant), so maybe THD is not that important as long as IMD is OK. ). Also the ear should be pretty insensitive to frequency response variation in the top octave.

I've considered the JX92S/ribbon design but then it starts to looks like a conventional 2-way with the above issues.
Any thoughts/comments?
Ant

[jerome69]

The Aurousal VS VirtualSource™ Floorstander is a 2.5 ways speaker.
The tweeter looks to the Dayton nd20fa
Dayton Audio - ND20FA-6 Specialty-Drivers
Put a tweeter without a serious crossover is for me very laughable : take "advantage" of fullrange but with a tweeter to help . In fact without doing the job correctly (good phase tracking).
I think it is possible to make a clone of this loudspeaker.

Jim Griffin design seems to me a good design. Look the 15° measurement, no problem of directivity near the crossover frequency.
http://documents.jordan-usa.com/JX92SG2siDesignPak.pdf
The G2Si could be replace by the Fountek JP3.

Hope this helps.

[AntM]

Thanks for your input. I'm concluding that using a super-tweeter with the JX92S will not suffer the usual vertical lobing issue too severely as the off-axis response of the JX92S is so poor. This means that the interference patterns/(spacial aliasing if you relate this to beamforming) will be less of an issue even if the tweeter-woofer distance is more than the half the crossover wavelength. I should model this in Matlab if I get the time. This is all assuming that the speaker is used off-axis. The on-axis response will be somewhat problematic, still. I'm accept some of your points, Jerome, that this is an uncoventional approach, but, hey, that's what DIYing is all about. Otherwise I can just buy the next off-the shelf 2-way that appears in my local hi-fi shop whilst a small part of me (and my wallet) dies.

So, in conclusion, I've ordered the Vifa XT19, which has an excellent off-axis response, a smooth distortion profile, with third and higher-order harmonics below -70dB if I crossover above 3kHz

http://www.zaphaudio.com/temp/Vifa-XT19-HD.gif

My gut feeling is that this tweeter will sound great, and give me the option of using it either as a supertweeter or with a conventional crossover.

I've just had some birch plywood cut, ready to pick up this afternoon. I may post the project if anyone is interested.

Ant