JXR6 design analysis for near field setup

[deandob]

This might explain why I get excellent imaging and soundstage from my current setup with TangBands, the drivers are flush on the baffle and also flush with the monitor, which acts like the drivers are flush mounted in the wall.

Good point about being off-centre, if you have the drivers in the centre of a too wide baffle for nearfield listening the toe in would need to be more accentuated to still be listening on axis.

Another speaker "wisdom" is to have the drivers at different distances to the edge of the baffle. Is this still relevant with Jordan drivers?

I wonder if anyone has tried the opposite to the Jordan wide baffle, stop any side refraction by placing felt or absorbing material completely around the driver, absorbing everything except the directly radiating outward wave. I'll try this on my Tang Bands to see what difference this makes.

Regards,
Dean

[Dumbass]

Originally posted by deandob
Another speaker "wisdom" is to have the drivers at different distances to the edge of the baffle. Is this still relevant with Jordan drivers?

The one reference book I own is Weems/Koonce Great Sound Stereo Speaker Manual. They recommend off-center mounting, all of their projects use it. I'm not convinced of the importance, unless in some extreme case of a circular baffle or what. In a normal rectangular situation, the distance from driver to edge of baffle is not uniform over the 360 degrees, there is no sharp baffle step dropoff, it occurs over a range of frequencies.

Originally posted by deandob
I wonder if anyone has tried the opposite to the Jordan wide baffle, stop any side refraction by placing felt or absorbing material completely around the driver, absorbing everything except the directly radiating outward wave. I'll try this on my Tang Bands to see what difference this makes.

Weems/Koonce recommend fiberglass on front baffle. This is the whole idea behind narrow baffles, too. Some speaker manufacturers go to extremes, with no real front baffle at all. But you still can't get around the diameter of the driver, eh.

In theory, there is no reflection of directly-radiated sound off the front baffle. Any sound waves that would be "reflected" by the baffle are propagating parallel to that surface.

One place where I can see this stuff being important would be in using a wide-dispersion tweeter (like dome). I know that there are real issues in, for example, whether you flush mount or surface mount, because of the very short wavelengths. So I can imagine surrounding such a tweeter with some absorptive material, and indeed some manufacturers do this.

With cone driver, however, this fails to be important because of beaming. That is, any very high frequencies propagating to the side are already squashed by destructive interference. AFAIK this is true with a driver even as small as 2". (You can calc the freq at which beaming effects come into play, I think compare a wavelength to width of cone but don't take my word for it.)

I know there are complicating factors because of cone flexing (in fact Jordan drivers are designed to optimize cone flex).

Flush mounting simply looks better, in any event.

[deandob]

Dumbass,

For a test, I tried wrapping damp towels around the circumference of the tang band drivers (3"), which would stop any sideways reflection.

For this near field setup I have a tall & skinny front baffle, toed in so that the cones are pointing about 6 inches behind my head, and inbetween the speakers is a flat LCD monitor slightly recessed from the line of the drivers, with about a 2 inch gap between each speaker and the monitor. Normally this setup with a class D amp has a very wide soundstage and sounds similar to wearing headphones due to the closeness of the drivers to my ears.

It did not seem to make much of a difference, if anything the sound became a little more focused but the soundstage did not sound as wide or as encompassing. Maybe the effect of side propogation/reflection is less of an issue when listening near field.

I assume the jordans will react a little differently to the tang bands due to their design.

Regards,
Dean

[Colin]

Off-centre mounting on the baffle will also mean (I presume) that the drivers will be off-centre with regard to the internal shape of the box, which will help spread the resonances a little.

In theory, the Jordan drivers should be less prone to edge defraction as they are designed to beam at higher frequencies. However Ted once told me that he put felt around the drivers of a commercial design of his and it cleaned things up down into the mid-range.

When I mentioned anything between the speakers messing up the image, yes I meant something like a table or surface with hard edges. It sounds like Deanbob's monitor makes a continuous curve from speaker to speaker, which should be ok. Only one way to find out ...

Enough of theory - I've now got my 2.4 litre boxes up and running. The JXR6 is a definite step forward from the JX53 in terms of fullrange use. It has a lot more body in the lower-mid and upper bass. According to my diy/noddycalc spreadsheet, the box should be tuned to a Qts of 0.74 with -3dB at around 128Hz. Sounds about right. There's good output to 100Hz, dropping to 75Hz and not much at all below that. (These are just computer test tones and my ears, so not a scientific measurement.) They sound a little lightweight on first hearing but I'm used to a system which goes to below 40Hz. Once I got used to that, they sound excellent and I'd be happy to use them on their own in smaller rooms. I'm using them near a side wall, six feet or so from the back wall and corners. I haven't experimented with positioning nor have I fiddled with the box stuffing - I just shoved in some BAF wadding, uncompressed, and screwed in the drivers. And I will try the comp components from the JX53 to see what that does to the sound.

They're more sensitive than the JX53, on a par with the JX92, which suggests some intriguing possibilities. The next stage is to wire them to my MLTLs with the 92s rolled off around 100Hz and see what happens.

Ref the 92 sound, the 6s are cleaner in the HF, more natural sounding and civilised. Those looking for such a thing may have their 92 'tweeter' at last (one which runs to 100Hz...).

At the moment, they don't image quite as well as the JX92 or the linear array when you are off-centre (the JX92's rising response is supposed to mimic the linear array effect) BUT I have them in ceramic enclosures with the drivers recessed slightly ref the edges, the intention being to fit felt around them, which will be hidden by a grille. (I don't particularly like seeing drivers and I'm even less keen on damaging these very lightweight foil cones.) I'll fit the felt later today and see what that does to the imaging.

That said - they do image very well when on centre line and I tried moving up between them, similar to how Deanbob will be using them, and, like he said, it was like wearing a pair of high quality headphones. Moving even farther, so the speaker line was just behind the listening position, the image was still locked in front, which felt very strange.

I like these little beasties.

[deandob]

Thanks for the review Colin.

Let us know what you think of the use of felt for absorbing sideways propogation, and if your speakers need a compensation network.

Do you think the drivers will match with a good music subwoofer for below 100Hz?

Regards,
Dean

[Colin]

Hi Deanbob

Now I've spent 48 hours listening to these, they've either broken in or I've grown used to them but I don't think they need any comp at all.

I've also matched them up to my JX92 MLTLs, letting the JXR6s roll off naturally and rolling off the 92s with a 9mH inductor (at around 112Hz according to the Jordan site). The drivers are about 16 inches apart (I simply put the ceramic boxes on top of the MLTLs). These work rather well - if anything the JXR6 might be slightly more sensitive than the 92 so if you can match the bass with an active crossover, you're onto a winner. The sound is very clear, the imaging comes from the JXR6s and the 92s add a welcome touch of bass (although on a singer/acoustic band piece, my partner didn't spot when I disconnected the bass enclosures).

I suspect mine do need felt around the drivers - both driver and cabinet edge are proud of the baffle (the cabinet forms a frame round the recessed baffle) and simply placing a piece of card anywhere near the driver is noticable. However if you recess the driver flush and round the edges, it may not be a problem, especially on wider baffles (my enclosure is 6 inches across). I'll experiment when I find some felt or similar material thick enough to do the job. Everyone round here seems to stock thin, dress-making felt.

Anyway, overall the new Jordans seem an excellent way to get high quality sound out of tiny enclosures - and if the bass enclosures can be hidden away it opens up all sorts of possibilties.

I'll post pics in a day or so.

Colin

[deandob]

Colin, my current 3" setup has the drivers close to the edge, flush with the baffle and have the edges sloped at 45 degrees. I can only notice a small change in imaging / soundstage with sound absorbing material placed around the driver.

For felt or similar sound absorbing material, try an auto sound deadening blanket used to line the insides of car doors.

Regards,
Dean

[Colin]

Good tip, thanks.

(O joy, another local shop which starts to look at me oddly when I explain what I want stuff for ...)

[Puggie]

Nah, find a quality car audio suppliers, they are run by nutcases, they will think its perfectly reasonable. someone like James at Audioscape (Ipswich) would possibly be a good start.

I'm following this as I'm doing something similar with Bandor 50s. Do you flush mount the driver then cover the face with felt, or could I sink the driver into the baffle say 5mm and cut the felt (5mm thick) to be flush with the baffle at the edge. would I still get edge reflections from the wave moving through the felt?

Piano tuner/repairer may be worth a try too, they use a lot of different grades of felt for piano repairs.

[soongsc]

Originally posted by Colin


.. (O joy, another local shop which starts to look at me oddly when I explain what I want stuff for ...)

Sounds familiar.