JX92S now in full voice

[RAndyB]

From a somewhat mediocre, frustrating performance to fulfilling the promise of the designs in one easy step - drive them with a decent amplifier. In my case a pair of ESP P101s.

So far I have built 5 different cabinets.

The first is the "obvious" MLTQWP from M J King's excellent calculations. It is rather "shouty" - too many sharp peaks in the response, and made from 18mm MDF.

[RAndyB]

The next is from MJK's calculations again - this time an extreme version of the MLTQWP format. The bass is big and low, not too badly controlled, but the top end is not well served by the large front face. Triangular is a very good baffle shape. Smooth "step" transition because of the huge number of different distances to an edge.

[RAndyB]

Third came the standard transmission line straight from the Jordan web site. I should revisit this with the new amplifier, but on first hearing it gave nothing more than the previous two, slightly less top end clarity if anything. So it was never tidied up.

[RAndyB]

The KEF egg surround speakers were favourably commented on by my dear-lady-wife, so an egg design was produced.

One of the problems of the previous cabinets was that there was too much bass for the room (nominally 15' x 12' x 9'). The slight lift just before roll-off was hitting a room resonance and.... BOOMING.

This design is in a cabinet of about 8 litres as recommended. The port is a piece of plastic waste with internal diameter of 50mm, and length 250mm. This size is calculated as correct by various web-site offerings (I am very grateful to all of them).

The cabinet is made from 18mm chipboard. I became frustrated and bored with trying to get a perfect shape and perfect finish, so did a reasonable job and put on a few coats of paint.

How it sounds is more important. No microphone/sound card yet, so SigJenny (http://www.natch.co.uk/) and a pair of ears must suffice.

Meaningful sound output level starts at note 1 C (32Hz). At 7 D (2500Hz) there is an unpleasant peak. this coincides with the peak predicted by The Edge (http://www.tolvan.com/edge), but to my ears is more pronounced than that. Continuing up the scale produces a series of small peaks until something (my ears or the soundcard) fail at about 13kHz.


With BSD correction optimised it sounds good. Top end very detailed - as you would expect from this driver, bass moderately well controlled, goes well down to give a good impression of the fundamental at a believable level. It can shake the floor.

[RAndyB]

The success of the first Egg made the next decision easier - it was the candidate to be cloned. In the spirit of DIY experiment, it is made of MDF. It also has an integral stand, and looks a bit silly. It has a 38mm diameter port, 150mm long.

It too starts at 34Hz. After reading a Port Tuning thread (Overporting: definition & effects?), I explored the subject. This narrow port is blowing plenty of air around - I can feel the draft on my face 250mm away. Similar peak at about 2500Hz.

Despite the differences, these two perform much the same; even so stereo imaging is not completely secure.

[hm]

Hello RAndyB,

you forgot the TUBA
http://www.ejjordan.co.uk/links.html

http://www.hm-moreart.de/3.htm

http://www.hm-moreart.de/76.htm
http://www.hm-moreart.de/37.htm

for such a test i give the plan for nothing.

[RAndyB]

Horst,

not forgotten; my dear-lady-wife is not enthusiastic about something quite so large.

I have wanted to build a horn for a long time, the Tuba tempted me at one time, but ...

The graphs look good, and the transient response is excellent, so maybe I shall build them if I move to a house where they would look better.

Regards,

Andy

[Colin]

Or try the triangular MLTL. Nice, lounge-friendly shape and it gets rid of parallel surfaces, so no shout. The choice of 31 or 48" designs might give you the chance of avoiding the in room resonance, depending which version avoids it.

[RAndyB]

Colin,

I recall your triangular MLTL design. Did you post a picture of them finished?

The sudden emergence of plenty of energy from the speakers at 34Hz is due to a standing wave in the room, it is very obvious when moving around, as are several more at higher frequencies. Any design must take account of this and give an acceptable balance.

I wanted to do ported just to hear for myself whether it was as evil as some say. It isn't, in fact it may have advantages ignored by its detractors, even over sealed box.

Having built the second egg, I realised that the stand should be the port, with an arrangement of feet to allow air from the port not to hit the floor.

Particularly annoying is the fact that the MDF (integral stand) version has an Aural Aura about it. I had hoped that the nasty high pitched MDF whine would go away when used like this, but it does not, it continues to colour the sound.

When I can get back to speaker building and when I buy some JXR6s and put them in cabinets, then the JX92Ss will be hung on a wall in the other room. A fresh set of cabinets will be necessary (won't they?). So another set of experiments can begin!

Regards,

Andy

[Colin]

Originally posted by RAndyB
Colin,

I recall your triangular MLTL design. Did you post a picture of them finished?

Ha ha, still gloriously unfinished in appearance. Partly because I can't bring myself to dismantle and finish. I also think I made a couple of compromises with them so am waiting for the fine weather again to work up a second pair.

Come on, global warming, hurry up.