The different projects

12/21/12

Klinger Horn part 3.

 The Eminence driver ME150-08 Thiele Small parameters


In red the Eminence driver and the Philpips in brown and Gamma in black.
I have changed the curve layout and added will use the Eminence as a reference as it very close to the current Gamma 12A Surprisingly the Philips and the Eminence is close to identical, with the Gamma weaker in the bass.
 

 Then it was time for the Fane Cresendo 80W


Very similar Fane Cresendo 80W and the Eminence in the klinger horn

Then it was the classic vintage horn driver Isophon 30/37A
The driver has a large plastic cup covering the magnet, the purpose of this I do not know.
Also in this case very similar to the Eminence.

The finaly the Beyma G320, For some reason way out of spec with Fr in the 70-80 Hz  range. With twise the weight of any of the other drivers they are monsters.
Here the 60 Hz peak is reduced  4dB, the 70 Hz peak by 2 dB the 95 Hz peak has shifted down to 85 Hz. If one could cut 3 dB or so of the 85 Hz peak the horn would be 35-130 Hz +/- 3dB. If damping material, corner reflectors or internal Helmholz resonator would do the trick is a matter of some experimental work to find out.








Next up is vintage  Philips bass driver

If I measure the drivers myself using Woofer Tester 3 I get very similar (and good) results.
When measured mounted in the horn:
Omnimic Near field and in horn mouth


Quite similar result to the other closed box driver the Gamma LA1231, In the Philips data sheet there is peak at 1.5 kHz and then a rollof above 2 kHz, in my nearfield measurement I do not pick up that peak but the roll off is more or less as specified..

The horn output in the 35-45 Hz range is 5 dB down compared to the two peaks at 60 and 90 Hz. That is a 5 dB improvement as compared to the Gamma driver, not bad.

Now I am out of closed box drivers and I will try out some PA drivers. First out will be an Eminence ME12-1508 driver, according to Eminence the driver is a version ordered by their european distributor and it is the same as the  Delta 12A of their standard set of drivers. Thiel Small paramterers are the same except for inductance that is higher but that is a tricky parameter to define as voice coils do not behave as text book coils.

12/20/12

New horn project. A classic about 50 years old. A backloaded horn for 12" drivers. It is acually built in soft board and then has a shell of chipboad around it.


 I had some initial trouble as the horn is made for rearmounting the drivers and the lid is to small to fit many of my drivers. So I made a external baffle that could take drivers either way. The baffle was screwed and sealed to the front.



The first driver that I tested in this horn using Omnimic and Woofer Tester 3 was the Bulgarian Gamma LA1232, that worked surprisingly well in the Kuben horn. Low Fr of about 30 Hz huge Vas of 300 liter and moderate Q of 0.4 hardly a classical horn driver



This is how the near field response is mid center about 5 cm in front of the dust cap



Mouth opening in the middle (all measurements on the same spot.



Falls  rapidly below 50 Hz and has some  4 dB peaks at 55 and 90 Hz. The sound is surprisingly good with those soft board panels I expeced no bass and all buzzing vibrations but it does not sound that way. The Klinger is about 300 l and the Kuben about 200 l so I had higher expectations than that on the Klinger, perhaps an other driver...

11/21/12

I have been thinking about building lighter horns of La Scala size, and one critical feature would be having the walls of the bass chamber in bent hardboard only 6mm thick. To accomplish this I have to fasten the board to bent wood. I tried this with some scrap material. Every other cm I allmost cut through the wood using a japanese pull saw,

I discovered that the wood splinters very easy so everything has to be predrilled, I also have to test how wide the wood strip has to be to fit screws and perhaps a sealing strip. Time to scramble up some prototype...

9/16/12

Horns in the home "Kuben" (Klipsch LaScala bass bin)

I got these very  solidly built speakers build according to the article below. Very skilled carpenter but less experienced as a loudspeaker the builder was. The 12" bass driver was mounted flush on the backwall of the chamber (as per the drawings). For this particular driver it meant that the driver or surround would hit the MDF at the slightest cone motion. This was sorted out by adding a subbaffle with a cicular cutout of 270mm now the cone can move 12mm. I also added some crossbraces for the sidewalls of the horn opening that vibrated quite a bit. I also added corner reflectors in the corners and in front of the driver.

As I have a selection of 12" drivers at home I decided to try them all out. First out was Beyma G320 a 10 kg monster of pro driver.  Built for midbass hit has very low Qes and quite high Fr.
The beyma has quite drooping bass but very good midrange exension, this blue trace is shown in all the other graphs as reference. Measurements were made using XTZ Room Analyzer II, microphone at 80 cm distance on axis and with the horn propped up on a 50 cm high table (to reduce early reflections)

Next up is the Fane Crescendo 80W, an other pro element but with a higher Qes.  Notise the incease in bass output
 This is a vintage bulgarian Gamma LA-1231, low Fr mid Qes and very large Vas. Much lower sensitivity than the pro drivers. More extended bass but also a hump at cutoff.  Midrange output is way beyond what you expect  with a calculated mass roll off  below 200 Hz
 Isophon 30/37A a vintage alnico driver and a classical horn driver shows a very flat response from below 250 Hz to 1250 Hz
 MGR30P40 a new budget driver does surprisingly well with good output from below 63 Hz to 500 Hz or so. Calculated mass roll off is 156 Hz, usable range is much higher.
 Finaly the old Seas 30FA, this is a 15 Ohm driver so the sensitivity is really 3dB higher. It is very similar to the Fane driver

I have 10" bass drivers with what I thought was good slam, but horns are something else.  Now I am thinking about building a pair. With some twist and turns of course. Just the basshorn is 40 kg adding top and driver the Klipsch La Scala is 78 kg, this is way to much in my taste. Replacing the MDF with 12mm plywood would cut the weight in half but it would also be to flimsy, a lighter structure either require a very different layout or fancy material that is both light and stiff.

I am sure that the midrange output can be affected a lot but changes in throat geometry, subbaffle thickness and so on. But I think some general conclusions can be made.  For maximum over all output PA drivers are what you need. However, in a domestic setting were the demand for output is far less HiFi drivers might be better. The PA drivers tend to fall of in the low range.

The low pass frequency is way higher than the mass roll off that LP=2 x Fr/Qes. This does not mean that it will sound good to 1 kHz just beacuse it has output to that range. Other have found that simulation of drivers with modest BL work really well in this horn http://www.linnaraudio.com/simuleringar/kuben/index.htm

One way to tame a horn driver with to low Qes for the particular application is to add some series resistance.
Adding 0.7 Ohm as in an average crossover does not change much

 Adding 2.2 Ohm as in a really budget crossover, will supress the 100-500 Hz range a bit, in effect bringing up the bass peak a little bit
 3.3 Ohm more of the same
 4.7 Ohm still more of the same
 8.0  Ohm now it looks more like the Gamma driver.  I would prefer to use equilizing to lift an overdamped prodriver, but connecting a series resistor and try it out is easy.

These Thiele-Small parameters suggest a closed box in the 60-100 range, marginal for bass reflex and absolutly not a classical horn driver.


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.