The different projects

8/24/12

I have had some Goodman Axiette drivers for years and years with no proper boxes for them. As they only can be mounted from the rear (that came out wrong but you know what I mean).
It is a fullrange driver with high sensitivity and also quite high resonance frequency
Param├Ętres haut-parleur de THIELE et SMALL, sans filtre ni ampli

I have these grand plans for real Onkens for 15” drivers, but I newer seem to get to them, then I read on French site (see above) about tuning of the Axiette in a kind of undertuned bass reflex. So then it stuck me why not make the Axiettes a Onken type of enclosure and try out various ideas in a smaller scale.

So the box is made of 16mm MDF apart from the port walls that are 12mm MDF. Then I have used soft wood for braces and radiusing/ decoration

I could not get a proper tuning and at the same time get a port area equal to the cone area, so I added a 12mm radius bend in the opening of the ports as well as adding a 21 mm radius along the inner part of the ports. The ports are 16mm wide so the total surface area in the begining and end of the ports are about 176 cm2 and with a about 30 cm port lenght and a 45 Liter box the tuning is a bit above 50 Hz. Not the undertuned way of the french site but what the heck
Painting the inside of the ports was stupid as it interferes with the gluing of those small partitions strips. Next time I will use some water based dark wood stain that does not mess with the gluing. I stapled 10mm felt to some of the braces and the sides top and bottom are all lined with 10 felt. Betwen the two braces running down the back I have jammed some fistfuls of BAF.
 The eagle eyed wiever might notice two sets of cables with one set having a set of caps in series. The reason is that the box is prepared for active drive two way systems and then the caps are used to protect the tweeter from any turn on transient.
I also added some felt to the back of the baffle, here you also get a first glimpse of drivers

I used a lot of bolts and captive nuts to bolt the baffle to the rest of the box. The cutout is roughly chamfered to ⅓ ro ½ of the baffle thickness, more work could be done here. I have used Neutric Speakon connector instead of the usual binding posts, I love them and will convert all my amplifers to speakon including my vintage Sansui power amplifer. I do not understand how little we have progressed on speaker connectors in 50 years. The DIN was OK for its time with low powered tube amps, then came the spring loaded terminal with its frayed cable ends and risk of shorts if the “frays” bridged plus and minus. The Binding posts of today and banana plugs of today sure offer golden bling but that is about it.


But back to the Axiette, here how it looks

It does look strange on such small stands but this is what I have.





How does it sound
Right of the bat it sound well balanced, the real bass slam is missing but everything is there in the right proportions.
 Susan Vega: Tom’s diner, sound fantastic
Duffy: Rockferry, still really good
Adele: Rolling in the deep, not to good it does not get the real weight behind it.
Kroumata Percussion Ensamble, BIS CD-232, The BIS record company have a warning label that they do not use compression at all. I have heard this particular percussion ensamble many times and I can testify that as much of the slam and impact is preserved, as far as I can judge it within the limitations of my rooms and speakers. Here it sound good but it still lack the real slam, if this is due to lack of bass or softening of midbass I do not know






Measurements
 The drivers are well matched, the peak at 450 Hz shows some resonance behaviour. The high Q value makes it difficult to avoid a bass hump.  I had trouble when measuring Vas by added mass (a tape roll) reporting that 93 g mass did not lower the resonance by at least 25% as required! Looking at the curves suggested a peak at 20 Hz and an other at 200 Hz and so on.I suspected that the cones are to flimsy and used a smaller diameter roll and got better result. Flimsy cones may also explain the lack of slam.



Vent tuned to about 55 Hz. That 500 Hz peak is not intrinsic to the box as other drivers does not have that peak
 
Frequency response
3 cm response dip closely matches the tuning of the box, quite well balanced response, adding 50 and 100 cm show a slow decline above 2 kHz and a sharp peak at 10 kHz. I have to wait until I can measure time domain response and harmonic distortion before finding out more measurment wise.



I did fiddle around with a peak trap and a Zobel filter, it did tame the peak but took away to much of the tweeter range as well so I will not publish the components used
Concluding remarks
The side walls are vibrating more than I expected, when I build Onken style boxes for 15” I will make sure that they are very well braced. The axiette sound really nice if I avoid to complex music, it it is the cone that is soft and can not “slam” or if the light weight (Mms of 11 gram) cone that is more sensitive to reflections in the rellatively lightly damped cabinet I do not know. I think that the Axiettes sound better than the Lowters I have heard and the Philips 9710 but they are far far behind the magic of the Voxative speakers. So a really respectable driver designed more than 50 years ago, but not a magic blast from the past.