Deep Green A dual driver FR speaker using the D3L2QD loading concept by Joost M Riphagen The Whawt/Guppy project never made it to full mode because first of all I had severe trouble finding big enough tubes to make the dual TL subwoofers, and secondly because it all got a bit too much, the setup needs to be biamped and actively filtered adding yet another two boxes to the set (which has three amp (under construction) boxes already preamp/poweramp + separate PSU, add this to the CDP the MDP and TT and G36 enfin you get the pic). This speaker is based on the Magnificat speaker (also in the DIY section) so I refer to that piece and the excellent theoretical article on Mr Loesch's website. The predicted response using the compound driver method I got using the Xlbox spreadsheet by Thorsten including room gain made me take the plunge and try this concept out myself with very different drivers. It looks rather good, does it not? 100 db average, -3dB @50hz and it still has reasonable output at 35 hz (at -8dB). The purple line is a FE 208S in a 15 liter cab tuned to 110hz. Drivers: My take on the concept uses a Fostex 208 Sigma and a Beyma 12AG100 ("The worst driver I paid money for" according to Frater P more on that later). And a modified Motorola piezo tweeter xo'd at 15 kHz or so. My very unscientific observation is that the big 12' driver uses the smaller driver not unlike a passive radiator this effect is very noticeable when the top driver is not connected, sort of a power assist function thus. The beyma is NOT a good choice for building a Afterburner or something like it. Out of the box it sounds almost like a guitar speaker but more congested (even compared it to a Celestion 12G100 I have around). This driver needs a lot of work to get it to sound anywhere decent, it needs to be loosened up, the rock hard suspension is more than partly responsible for the crappy sound one gets at first. It is a PA driver so treat it as such when running it in. I did not need the top-end extension so I removed the whizzer right away, much to my surprise it does not contribute much at all to the treble regions. I tried damping with dammar, at first subtle (but that does not work at all in this case) but in the end I opted for the jackhammer approach and removed the dustcaps altogether and applied a coat of diluted Elmers glue to the cone which I partly sanded off again, to reduce resonances I put some wool in the cavity above the pole piece. I did do some experiment with mass loading but it did not do much good for the transient response ( about the only thing the driver is really good at from the start.. After all this you end up with a reasonably balanced driver that does approximate the sound described with a 'rolled off top end" vaguely. Nothing I would want to use for single driver duties, but… when paired with the Fe208 things started to look much better. (Thorsten suggested a Eminence Delta 12 LF but I found the price to be rather high over here and it would take a 200km trip to pick them up. I can get Beyma around the corner and it costs 50% less so I opted for that one, but if you can get a Delta 12 I would go for that one.) I experimented with a load of RCL filters but in the end ditched the whole lot (as the 12' driver was better run in the sound got better and better) currently I just use one coil in front of the 12' too keep it out of the midrange of the FE 208.The Fostex driver is well known, I used the TS parameters as measured by the German magazine Klang&Ton which differ quite a lot from the ones on the Fostex datasheet. The cabinet: My cabinet is made with a 44mm baffle and full 12mm Matrix style bracing all other panels are 22mm. Even with the amount of bracing I used it is hard to get a cabinet this big really dead. I used ceramic tiles and lead sheet to damp some parts of the sides. Needless to say it is not a thing you want to move often at around 70kg. Tuning (43 Hz) is by two small (47mm flared both sides 22mm deep) holes at the back about 25 cm above the bottom to give a EBS alignment. Finish will be in the 'house' colour popularly referred to as British Racing Green* hence the name Deep Green. All edges are radiused (including all edges of the bracing cutouts). Dimensions are 95H/34W/46D that is about 108 liter — 4 liter for the Beyma and 3 liter for the Fostex. I estimate that the cab is about 95 liters total (net) when the bracing and damping are considered. In retrospect using solid wood would have been a more sensible option as it needs far less bracing and damping. I used MDF, it cheap and machines well (providing that you only use routers/tools with good vacuum dust extraction. If you don't get the dust out is gets mulched around (think Flymo lawnmower) which is bad for the router bits and bad for precision. Dust is bad for you, wear dust protection at all times. Some hardwoods rank along nicely with asbestos… get the picture!? MDF dust is no picnic either (I know at least one person who ended up in hospital briefly as a result), ergo, make a point of it never to buy a power tool without dustsucker interface. If you need an audio excuse: those big industrial vacuum cleaners work well with the motorless version of a Nitty Gritty too! The sound: After a truly weird start , which did reveal ultra deep bass in a big room (not mine) but sounded strangely thin some of the time, I have since added a second hole resulting in a bit higher tuning trading in some deep bass for upper bass. The speakers are really starting to show their true nature at last after a very long run in period. Voices are great, bass is taut and pacy and the overall balance is just much better than the FE 208 on it's own while not diluting things the driver is good at. With percussive sounds you can hear the "tone" better not just the attack. Sensitivity is really high and even with 2 undernourished tube watts (1963 SE EL 95) it is pretty loud. I'm pretty convinced that the EBS tuning will mate well with the lower damping factor of the SET amp that is still under construction. with the big SS amp bass is deep but rather lean. For now it shows that my SS pre-amp is noisy as hell, also my first speaker that makes cable AB testing a very short process. As remarked by someone on the forum this speaker is very sensitive to vertical positioning. I recently put (wrestled is more like it) them on risers placing the lower edge of the top driver at ear height, this resulted in a hugely improved soundstage height and width, tonal balance and a sudden disappearance. Downside is that they are even bigger in the room now… well you can't win them all. Cons: Does little in the way of flattering bad recordings and has very little tolerance for bad upstream stuff. Needs a towtruck to move around. As the Germans would put it : Wie wohnzimmerfreundlich wie zwei hochkant gestellte Fiat Panda's.** * which is not really an exact colour green, it stems from the times when racing cars were colour-coded by country. The colour assigned to the Brits was green — meaning any green. As the target was racing, not looking fancy most cars where often just painted with a brush. So if your AMC Gremlin is a seasick shade of green you have every right of calling it British racing green ** Editor's note: a rough translation is "As living room friendly as two upright placed Fiats Panda's" Top