1. Full Range Driver Speakers

Mid-January 2007DIY Loudspeaker ProjectFeasting on the Feastrex full range driverand Augie woofer.Review By Dick OlsherI f you have read my recent review of the VISATON NoBox kit, then you already know about my passion for open baffle designs.One key point is baffle size. It's easy to get the impression that bigger isbetter, but that is not necessarily so. An extreme baffle introduces asignificant reflecting surface into the listening environment. It can interferewith the distribution of reflected energy (especially rear-wall reflections) inthe room and may adversely impact the soundfield at the listening seat. A largebaffle is also more likely to flex and resonate due to the action of the woofer.And there is always the domestic spouse acceptance factor.

The largest bafflesize one could imagine is an infinite open baffle, which can be approximated bymounting a woofer into a listening room wall so that it vents into another roomor the great outdoors. The downside, of course, is that the backwave is totallylost from the listening room. Much of a dipole's rich ambiance in fact comesfrom rear-wall reflections, which means that an infinite baffle's in-roombehavior would resemble that of a large closed box. Clearly, too small a baffleis counter productive, unnecessarily giving up bass extension due to front-backcancellation. In my view, the VISATON NoBox baffle meets the Goldilockscriterion: its' not too large nor too small. Approximating in extent thecritical 100Hz half-wavelength, it's just right! Since it makes for an ideal OBlaunching pad, the decision was made to embrace it as a platform for evaluatingvarious woofers and wide/full range drivers for OB applications.Cast of CharactersThe Hawthorne Audio Silver Iris Augie WooferThere is more to Kentucky worth writing home about than merely Bourbon andhorse racing.

I am thinking specifically of Eminence loudspeakers, headquarteredin Eminence Kentucky. And that is where Darrel Hawthorne, the progenitor ofHawthorne Audio, turned to for the design and manufacturing of his driver line.The Silver Iris line consists of a 15-inch coaxial and the Augie – a 15-inchwoofer intended for OB applications. The Coaxial driver came first. Darrel tellsme that following on its success, he wanted to offer a bass augmentation driverthat could extend frequency response low enough in an open baffle contextto fully enjoy almost any genre of music with minimal compromise. And so hewent back to the engineers at Eminence with a wish list in hand to develop theAugie.The Augie is a well-built woofer incorporating Pro features such as a castbasket, a Kevlar reinforced paper cone, a long-excursion poly/cotton clothsurround, a vented 2.5-inch voice coil, and a copper shorting ring. Powerhandling is said to be 225 watts RMS.

Three parameters are essential for idealperformance in an open baffle: a high driver total Q (Q t), a lowfree-air resonance frequency, and a generous excursion capability. The Augiedelivers on all three counts. Maximum cone excursion is a very decent 7 mm.Free-air resonance is 27Hz, and the Q t is 0.92. The latter parametergives the dipole woofer 'wiggle room' to compensate for the baffle step decreaseof 6 dB per octave down to its resonance frequency. The ideal Q t forOB applications is somewhat debatable, with some designers favoring a valuearound 1.0.

Bob Carver's 'Amazing' loudspeaker comes to mind as an extremeexample. The speaker, when it was under review in Stereophile's listeningroom, featured a line array of inexpensive dipole woofers whose chief claim toinfamy was a Q t of about 1.2.While bass extension was commendable, the quality of the bass was lessdesirable. Carver himself characterized the bass quality as 'rolling' andclaimed that he preferred it that way.

To my ears, the bass was simplyill-defined, the opposite of tight; the wrong compromise in my book – quantityover quality. Dipole bass confers certain advantages such as freedom from boxyresonances, but attention to proper damping is still an issue as it is withconventional box woofers.There is, unfortunately, no free lunch. Increasing a woofer's Q t isaccomplished by scaling back the size of the magnet, which reduces sensitivity.The only way to maintain both a high sensitivity and a high Q t is toincrease the woofer's resonance frequency.

Thus, a woofer with a high Q tand a low resonance frequency offers at best only medium sensitivity. Itis not surprising therefore that the Augie's sensitivity is only about 89dB.Measured in the VISATON baffle, the Augie produced impressive low-frequencyextension. The following Figure shows its near-field response which is extendedclear down to the resonance frequency of 27Hz. Very impressive extension indeed!I suspect that the ideal open baffle Q t may well be in the rangeof 0.6 to 0.7, as I found it necessary to slightly damp the bass range byshunting the woofer with a 25 Ohm resistor. Tuning the bass damping may well bea function of the room and personal preference, but I can report that whentweaked as described above and driven with the EAR 834T integrated amplifier,both bass impact and pitch definition were superb. It seems to me that manylisteners confuse bass weight with bass extension and opt for a subwoofer whenbass weight is lacking.

The problem typically lies in the upper bass, the octavefrom 120Hz to 240Hz where much of an orchestra's foundation and acoustic powerresides. This is the octave that box woofers have a hard time coping with,basically managing to sound boxy through this range. In contrast, the Augiemanaged to shine here, elucidating instrumental fundamentals with consummateclarity and 3D realism.The Augie's performance was so open-baffle friendly that I decided to use itas a foundation for several full range drivers. The OB2 finds the Augie matedwith the fantastic Feastrex D5nf. Future projects will feature the Lowther DX55and C55, as well as the new Jordan JXr 6HD module.The Feastrex D5nf 'Naturflux' Full RangeThis innovative Japanese full range represents a collaborative design effortbetween Mr.

Akiyama, the president, and Mr. Teramoto, the builder. While severalother models are under development, including field coil versions, the D5nf(permanent AlNiCo magnet) is said to be their most perfect transducer and coreproduct for some time to come.

I had seen a version of this driver at the 2006CES, and it has, in the interim, undergone a slow maturation process. The designwas finalized during the summer of 2006; the most notable production changebeing the addition of a phase plug – ala the Lowther full range.While from the front this driver may look like an ordinary variation on thetwin-cone full range, the view is radically different from the backside. Thelarge domed iron yoke is the crux of the Naturflux magnetic circuit.Conventional speaker yoke designs produce sharp bends in the flux distributionand fail to optimize the flux in the voice coil gap. Whereas the Naturfluxcircuit is said to focus magnetic flux more efficiently within the pole pieceand voice coil gap, reaching a gap flux density of 16,000 Gauss in the case ofthe D5nf.

Sensitivity is specified as 95dB to 97dB.The cone material is custom paper from one of Japan's premier paper makers,manufactured to exact specifications under controlled conditions. Total mass ofthe moving assembly is an astonishingly low 2.5 gram per unit, and drivers areassembled in pairs with precisely matched cone assembly masses.The low moving mass and large gap flux density results in an explosiveacceleration factor.

Transient speed is superb and the overall presentation isboth dynamic and detailed. The D5nf can unravel complex musical passages withcrystalline clarity, which is no doubt a function of its controlled transientdecay.

It is capable of erecting a titanic soundstage with palpably focusedimage outlines, at least when mounted on the VISATON open baffle. And to top itall of, this is the smoothest sounding twin-cone I have heard to date. No EQnetworks needed here. Cone break up resonances are well controlled.

There is nofly in the ointment in the form of a prominent presence region shout or harshlower treble. The phase plug definitely does its job - the upper treble beingextended to 20kHz, at least on axis. Of course, the extreme treble beams, so beprepared to toe in this driver toward the listening seat. Though, at the otherfrequency extreme, I would not want to push it below 100Hz, at least on an openbaffle. And, as many of you know, I am not a fan of rear-loaded horns. It wouldbe a crime in my book to imprison a driver with the musical integrity of theD5nf in a box!Unlike some of the Fostex twin cones I have worked with in the past, whichfuzz over detail, the Feastrex delights in revealing detail.

Though you hadbetter be prepared to drive the D5nf with a high-quality matching amplifier andfront end. And, for the record, I am still living happily ever after with theAltmann Micro Machines Attraction DAC. The OB2 was quite magical when drivenwith the EAR 834T integrated amplifier, as microdynamic nuances were given fullscope of expression. If you have a weak heart, I suggest you bypass the OB2 infavor of a lower resolution device. In summary, I am inclined to agree withFeastrex' claim of supremacy to the extent that the D5nf is presently the bestsounding 5-inch fixed magnet full range money can buy.Driver IntegrationThe task of blending these two fine drivers was guided by the KISS principle– Keep It Simple, Stupid – at least as simple as was possible taking thedrivers' needs into account. My goal was to maintain a full-bodied balancethrough the upper bass transition region without impacting bass or midrangeresolution, and as it turned out, that necessitated the use of second ordercrossover networks. That may disappoint some purists, but I did try the firstorder approach and was not satisfied with the results.

Full Range Driver Speakers

The final network (shownbelow) makes me very happy and I believe coaxes the best sound possible out ofthe driver complement in the context of the VISATON OB.Parts quality is a major factor in a speaker of this caliber. The capsselected for this project were the auricap metalized polypropylene type byAudience. For starters, this cap is extremely well built, and most importantly,my listening tests showed a clear preference for the auricap over the SolenFastcap. In general, the auricap appears to introduce less fuzz into the signalchain relative to the average metalized poly cap. Its sound could be bestcharacterized as smooth, yet detailed, with excellent transient clarity. Thecritical 48 μF cap in series with the D5nf was built up from three lowervalue caps: 30 + 15 +3.

For the last measure of high-frequency purity, Ibypassed these caps with a 0.01 μF Teflon film cap by Relcap.Some of you may have noticed by now the discrepancy in sensitivity betweenthe Augie woofer and the D5nf (89dB versus about 97dB) and must be wondering howis it possible to match these drivers without padding down the Feastrex fullrange? The answer lies partly in the subtlety inherent in the definition ofsensitivity, which is not referenced to an actual watt at 1 meter, but rather to2.83 V across the terminals of the loudspeaker. For an 8-Ohm load, thattranslates into 1 watt of power sunk into the load. However, in the OB2's drivertransition region, the Augie's impedance is about 6 Ohms while that of the D5nfis 16 Ohms. For 2.83 V across the OB2's input terminals, the Augie isdissipating 1.33 watts to the D5nf's 0.5 watts. The power ratio amounts to about8.5dB and means that the Augie is working that much harder to keep up with theD5nf. Add 8.5dB to the Augie's nominal sensitivity and you end up with 97.5dB.The proof is in the measured frequency response, which is shown below.

These arein-room measurements (with the EAR 834T amplifier) at 1 meter for both the rightand left channels.The impedance curve for the complete OB2 speaker is shown below.AddendumIn view of the need to provide end user support, Feastrex conducts international business solely through established dealers. Feastrex has informed me that they have not established a fixed MSRP for various international markets and interested parties should inquire regarding local dealerships. Feastrex has recently appointed theas its US distributor. Please contact them regarding US retail pricing.Company InformationHawthorne Audio Silver Iris 'Augie' 15-inch wooferWebsite: Cost: $165 ea. (introductory offer)Feastrex Naturfluxtm D5nf full rangeWebsite: Cost: See above addendumMadisound Speaker Components: source for coilsWebsite:auricap by AudienceWebsite.

– well the twodrivers are similar but the most important figures as far as thisarticle is concerned are the QTS and the X-max as these define some ofthe characteristics of both drivers. Lowthers, the 206 and the AN havevery, very low QTS's – 0.18 - 0.24, in the case of the AN it is at thelow end of this range – 0.19. X-max is how far the driver moves and inthis case the AN is more extreme than the 206, and well in Lowtherterritory with an X-max of +/-1mm.So what does a very low QTS and a very small X-max mean? The latter is simpleenough, it means that an 8' driver isn't going to shift much air if itcan only move forward 1 mm at most.

So low bass is a no-no. But thenput it in a ported box? Nope because according to our old friendsThiele-Small, a low QTS driver should not work properly in a portedbox, you'll end up with a bass hump at port resonance, then a big dipfollowed by a nasty rising output through the upper midrange -modelling confirmed this. With the BFB the 206 has an X-max of +/-1.5mm and a QTS of.18, and that design came with a health warning aboutit's PA nature and the need to toe-in to roll off the rising treble –the AN will increase the problem.The advantages of this low X-max is that the coil is underhung and willalways operate linearly in that short range – i.e. Very low distortion,and a lightweight cone that is powered over such a tiny distance bysuch a big motor is going to be both incredibly fast and detailed, butalso hugely efficient – AN claim 96 dbl and for once I think the claimif anything understated. For some people this sort of design is as goodas dynamic drivers get.So what doyou do with a driver with such an extreme QTS and a low X-max? TheLowther is the granddaddy of such designs and was specifically made towork in horn systems, either front or back loaded – never in a portedbox.So everything about the AN driver screams 'horn!'

And as such will be thecheapest, 8', quality driver available for such an application, thoughit's not an ideal cabinet for a beginner.Boxing clever?So what do AN supplywith their driver? A set of plans for a ported box, and a lot ofarguments about how used in this box, the driver will be far betterthan in a horn – ditto Lowthers. So in one foul swoop AN throw out 70years of accepted wisdom – ho hum.But whocares about excepted wisdom – especially as a simple rectangular portedbox is exactly the ticket when it comes to getting DIY virgins on thefirst rung of the ladder – so I chose to follow David's instructionsfor his AN 2.8 speakers, a medium sized (2.8 cubic foot) floorstanderwith a big hole 6' across acting as a port. Every bit as simple as theBFB and of course the plans supplied made it even easier.Designed (in my case) to work with a $30 amplifier I wanted to make this speakeras cheaply as possible – money every object if you like, just to seehow small a budget I could build them for – even I was surprised.BuildingFor most people thiswill involve choosing a panel material, MDF, Chipboard or best of allplywood, all in 18 mm thickness. Then go to your local timber supplierand you'll find that they will almost always have a massive, wallmounted frame saw.Take the plans, stand over the guy doing it, and gethim (or her) to cut all the panels out for you. These saws will cutexact 90 degrees and to an accuracy of under a mm. So once cut, yourDIY project is a simple case of cutting an 8' and a 6' hole and gluingthe thing together.

Now I know loads of people out there are saying“nope I need to buy off-the-shelf', but you should be ashamed ofyourself. Done this way this is easier than screwing an IKEA shelftogether so GET A GRIP! To this you need to add a bit of fibreglassstuffing and of course buy banana socket and solder the wires up –again don't wimp out on me here.But as I said before Iwanted to be cheap. A trip to a local DIY store found a load of pineshelving on 'special offer'. Not ideal I know, but it was good quality,would just need a coat of varnish to finish and when all's said anddone it's a lot stiffer than chipboard even if it is a littleinconsistent.

This, the wood for my speakers, cost 15 euro. Add a eurofor the varnish, glue and a few screws and I had some cabinets. At thesame DIY store they had some sound insulation panels that had beendamaged, 2 euro, and I lined the box with them. I had some long fibrewool lying about (I hate fibreglass) so that went in too. Obviously Icouldn't afford binding posts so I just drilled a hole in the back ofthe speakers and ran CAT5 (cost 10 Euro for 10 metres) cable from thedrivers, through the holes and to the amp – coloured wires for +ve,white for –ve. A dab of hot melt glue to fill the hole and voila!

Acable solution better than ANY binding post (i.e.