Crossing Over Jordan

[dambrus]

Originally posted by Jim Griffin

Also going to a higher crossover point would have made driver spacing problematical as it would have exceeded a wavelength at the crossover frequency.

Can this condition be somewhat relaxed (in this case, and in general) if we're using much steeper crossover slopes, for example digital solution with high order crossover?

For example, if we're using slopes >40dB per octave, can we get away with using crossover point at 4KHz (assuming that off-axis behaviour is still acceptable)?

Regards,
Dutch

[Groundloops]

Hi Jim !

While converting enclosure dimensions given in your whitepaper into metrics I found that the volume of 0.25 cubic foot is only achieved when substracting the reflex tube volume. Even then there is a difference of roughly 0.5 liters. How does this explain ?

Cheers,

Gerd

[Jim Griffin]

On the box size: I have used 0.25 to 0.30 cubic foot volume with success for the specified port tuning so I doubt that you have to worry about a 0.5 liter difference.

On crossing over at 4000 Hz: Sure you can move the crossover higher (3000 to 4000 Hz) but 3000 Hz works quite well in my opinion. Changing the crossover would mean new measurements and a new crossover network. Is it worth the hassle?

[peterpan]

Hello all. I intend to extend the low end of my JX92/RIB. I am thinking of using the seas L21RNX4/P alluminium drivers, I have 2pcs of this. Is 30liter seal O.K with a subamp, or do I have to go passive., if passive, what will be a recomended XOVER @ arround 70hz. regards peterpan

[Groundloops]

So I built it:



I chose the sealed version, lower end will be driven with a pair of active Ripol subwoofers, kinda N-baffle dipole subwoofer with an opening area of 1/3 membrane area or even less.

Here some details of building progress:

Readily shaped baffle front



and back. The JX92S cutout is moulded to avoid any possible air compression.



Enclosure interior - Flanges for speaker mounting made of 20x10 mm beechwood. the cutout area is soaked with epoxy to harden the material. Walls are lined with 10 mm industrial felt.



Crossover made with Mundorf Capacitors and inductors, Mills and Intertechnik resistors.



View of enclosure bottom:



Almost ready ...





Populated enclosure with pure wool stuffing



First listening impression: This little thing has it all. It´s just stunning. Extremely wide soundstage, present voices, silky heights. It´s just a charm to listen. Beats hands down anything I built before, and I built a lot ...

[Emiel]

Nice job!

Did you build it exactly according to Jim's design or did you make some changes?
I'm also thinking of using those drivers, but those are hard to get in The Netherlands. I live pretty close to Germany, so could you tell me where you got those drivers?

Thanks!

[Groundloops]

Hi Emiel,

I bought the JX92S at Boxenbaustelle , the G2Si I ordered along with other parts in Bushland at PartsExpress. There are alternatives to the G2Si, in fact these are the same: Harwood UR2.0 - http://www.hifisound.de/oxid/oxid.ph...0ALU%20RIBBON/ and Fountek JP 3.0 (looks a bit different, but it´s told to be identical) http://www.lautsprechershop.de/hifi/...fi/fountek.htm.

I took Jim´s design nearly 1:1, only the sizes of enclosures are different within a 5 mm range. The walls are made of 22 mm mdf, Jim suggests 1" (25,4 mm) but I think that doesn´t make any audible difference. And as you can see I don´t like rounded edges.

Hpoe this helps ...


Cheers,

Gerd

[giulio]

Jim,

your stated efficiency suggests the tweeter is MUCH less efficient than specced. Can you confirm that?

This is also my experience with the G1. I measure something closer to 93db than the specced 102db. I was puzzled (and initially thought the tweeters were defective) since various people on the net seemed to be using the G1 in high efficiency projects. I have to pad down my Supravox 215 rtf64 quite a bit for the two to match...

Thanks
Giulio

[Jim Griffin]

Giulio,

In this configuration the woofer (the JX92S) has nearly about 4 dB of baffle step compensation. If you start with the spec'ed sensitivity of the JX92S, you are down in the mid 80's dB SPLs very quickly. The G2si ribbon is much more sensitive than this value so it must be attenuated to match.

I haven't seen significant difference between the stated sensitivity of Aurum Cantus ribbon drivers and how they measure. Typically, you'll have to attenuate the ribbon tweeter downward to match with the woofer for most designs.

Jim

[giulio]

Jim
thanks. Sorry got the math wrong on the voltage divider. You do attenuate them around 12db.

My measurements show my G1 are 3-4db less efficient than the supravoxes and I doubt these are 105db efficient

I bought the tweeters directly from Aurum Cantus in China at the time they were still called ESG in the West. They have the same dimensions and look as the G1 (former ESG1). Dunno.

Giulio