[jwr159]

This is my first post... I could really use some help.

I just wired to France a substantial sum for a pair of Fertin EX20 drivers. There goes my tax refund.

The Fertins 20ex is a field coil driver with many neat features, including a cryo-treated silver wire voice coil, carbon fiber spider, and brass phase plug. According to the specs, the range is 20KHz to  27 Hz. If these are accurate, who knows.

Before I state my issue, I should provide a qualifier. I know next to nothing about speaker design. About a month ago, I heard the Auditorium 23 Solovox speaker, which is a modest sized OB using the PHY driver. I loved it and that is what got me started on this project. Auditorium 23 claims the speaker goes down to the 50-60 range. Check out this site and note the back of the cabinet in the photos. 

http://www.6moons.com/audioreviews/auditorium232/solovox.html

Here is my dilemma. Ideally these drivers work best in a large OB (i.e 5x4 feet or so). The problem is I just don't have the room.  I understand that the driver works well in a TL, although the OB is better.

I have been speaking to Bob Brines about building a QWTL. I have all the confidence in the world that Bob would design the ideal TL for these drivers.

or

Go with a small OB. For those with expertise with OB designs, what kind of base can you get from with this driver using a OB maybe 12" to 15" wide and 36"-40" high. I would include some side wings as well, maybe 6" to 12" inches.

Adding a base driver is an option in the future.

My questions are:

1. what kind of bass could I expect to get from the above OB.

2. How much do the side wings help in lowering the bass? Significant or not much?

3. Would using curved panels like the Solovox help or hurt? Not really sure what effect these would have. 

Any comments or design suggestions would be appreciated.

Thank to all who contribute.

[Bemopti123]

As a owner of a Bob Brines design, the FTA-2000s, I was in the same quandary you have before I plunged into giving Bob a commission to make my speakers.  I was looking into PHY-HP.  When he read the specs, he simply told me that the specs did not allow it to be Mass Transmission Loaded.  Therefore, I decided to purchase the F200 drivers raw then, added the cabinet to it.

I hope that the Fertin would not have similar specs than the PHY-HP, with higher qts.  If that is the case, the TL cabinets you plan to have made by Bob, will be to no avail. 

I have seen the monstrosities that these wide band driver manufacturers ask people to make, I mean planks that run towards 50-60".  That is a little too obtrusive for my tastes, then, even the FTA-2000 transmission lines are rather large, they have presence....So a WAF will definetly will come to play...but my wife did not sat anything, not that they look sexy, but these designs are large, at around 47." 

TL bass is amazing.  Even with a 8" driver it will make your room shake with pounding bass that is extremely rhythmic.  You will not have this type of bass until you have heard a mass loaded TL design.  It is really, really amazing.  This is something that you will NEVER get with OB, unless you begin to add larger 15" in the OB, thus getting it more and more complicated on the way.

Other choices in OB are the JE Labs Open Baffles.  They are not really, really tall, but rather medium in size.  The problem with it is that because the OB is small, the lower frequencies are compromised.  I get some low end, but not the pounding type as in the TL.  You can always add a subwoofer, but even with it, seamlessness is not necessarily easy. 

You have to ask what sort of sound you want...are you a bass head or are you into exquisite midrange?  OB will provide that...hell, the Fertins will provide that in TL, if that can be made to work. 

Fertins have much potential, and the sound in comparison with the PHY-HPs will be different.  The Field Coil drivers are a different beast...you can tweak it to your hearts delight....add more voltage for different flavor.

Ask Bob to see what he says, if that does not work, go OB....like the JE Labs baffle, small, but doable.  I finished my baffles in 4 hours.....Got the exact cuts of plywoods from a home improvement place, cost me around $70.  You cannot lose either way.

Paul K

[jwr159]

Paul:

Thank you for the reply. At this point, I am leaning toward a small OB for a number of reasons.
1. I prefer better midrange than bass performance
2. cost of the OBs will be much less
3. If I don't like the OBs, I can always go with a Bob Brines TL design.

So it all boils down to a design for an OB. For a front baffle that is say 14" wide.

How far back should the side pannels extend?

Should the side panels be angled or go straight back?

Thanks

[Bemopti123]

Check this link....

http://www.audioasylum.com/forums/set/messages/37197.html

The standard OB are narrow and tall...but the design above, eliminates the need to get hinges, also angling etc.... 

It is one panel, easy to make.  I do not like to play with "swinging wings."  I have never seen small baffles, that have swinging wings.  The Auditorium variation has permanent wings, bent  backward.  Not hard, but definetly, more work than the JE version. 

I do not know how much space you have available, but the JE is easier to mate with whatever environments.  Check another link...

http://members.myactv.net/~je2a3/open.htm

These are what I made.  There are infinite number of variations, but the good thing about it is that you can actually build it, without considering and thinking about all aspects of OB design.  Even though the concept is simple, there are tons, I mean, tons of opinions of how to get the sound you are looking for. 

Check my gallery...

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=171&pos=11

Not the most beautiful, but that is what I have playing in my music room now.  Later, I will tinker with a pair of Altec 604-8Ks I got from Audiogon. 

Go out there and build something, you will not regret it.  Fertins, will surely kick your concept of what is good sound a few notches closer to heaven. 

[jwr159]

Paul:

Thanks, those links contain some neat stuff.

It seems like a low and wide, with the driver close to the floor, is better than tall and thin with the driver near ear level.

I really liked the Warfdale picture with the wood panels on either side.

One more question... My guess is if the baffle was mde a bit thinner, say 20" wide, it would result in a loss of bass? Any estimate where the cut off would be based on the drivers specs?

Have you heard the Fertins?

Thanks again,

Jim

[JohninCR]

Jim,

Your driver has adjustable specs, so making it work well can be easy.  If you want small form OB's, or any OB's with full well rounded bass, you're better off accepting the inevitable and planning on bass augmentation.  Then you can get whatever look and size you want, without trying to force a great driver to do what it can't due to the simple physics involved.  For a classy look in a minimal form check out the minimalist thread here in the OB forum.  Put some grill cloth over that woofer, and no wife could complain.  Also, I'll try to post some extreme minimalist examples to the Building a new OB thread tomorrow or Wednesday.

Folding a baffle around a main driver can be made to work, but it's a trial and error process to achieve great results, and in the end the sweet midrange will suffer from trying to dial in sufficient bass.  eg You have to delay the rear wave by a 1 meter distance differential to have your -6db/oct dipole bass rolloff to start at 58hz.  That's a 2m diameter flat baffle, and you'll still end up with an increasing response above 58hz up to almost 200hz.  While this is an extreme example using freespace response, it's a hard dose of reality for OBers because room, placement, baffle and driver can only offset the inevitable dipole bass cancellation to a limited extent.

Please don't let this dissuade you from an open alignment.  You've already heard a hybrid open/resonant alignment that you loved, so you already have a taste of what is possible.  Bass augmentation doesn't necessarily detract from the "single driver sound", and in audible ways I believe it is far superior to manipulating the rear wave and introducing it into your room in a jumbled mess in terms of time and phase.  Resonant enclosures are simply a different kind of bass augmentation via a separate sound source (the terminus)....How can that be considered pure, given the inherent time and phase problems?

[scorpion]

Jim,

With 6 volts on the electromagnet the Fertins will have specs very similar to the Visaton B200 that perform very well in OB:s sized to your prefered dimensions as can be seen in many threads here. The Fertins will be about 5 dB more effecient on the average though. Myself I have driven B200s fullrange in a baffle measuring 40 x 24 " including wings, drivercentre 29 " above floor. Midpanel is 12" and wings 5" and 7" wide. With modest basslift it produced 87 db at 2.5 m distance at 50 Hz in my listening room. The Fertins will probably give some 90 dBs under the same conditions. The limiting factor is cone size and excursion which are about the same for the two units. It will be so cheap to test and the sound will be the best that you can obtain, I'm certain.

/Erling

[nullspace]

Hi Jim --

I have a pair of Fertin 20EX in the JELabs Open Baffle design linked to above. I use a 12v SLA battery to run the field coils, and qts ends up around .5. What bass there is, little <60hz, is of nice quality. I think that low-end response is dictated by amp selection as well -- there is a lengthy discussion of the Fertin on OB over at diyaudio http://www.diyaudio.com/forums/showthread.php?s=&threadid=6060&perpage=15&pagenumber=1. Brian Cherry with his class-A triode PP (low dampening factor) was getting down to 40hz, while I have a crappy 11BM8 PP in Ultralinear (high dampening) for now.

I wouldn't expect that you would get any bass at all out of a baffle just 12"-16" wide unless you had something like a Hawthorne Augie underneath it (which would require separate sub amps).

One thing I've come to appreciate over time is that the Fertins fullrange (and I would suggest ANY fullrange driver of a smallish diameter) do some things very well on an OB -- jazz, girl with a guitar, solo/small ensemble classical etc. But other types of music, even at my modest listening levels of around 75-80db average, sound as though the drivers are a bit overstressed -- my favorite local Philly band Marah, for instance, sounds particularly bad. Nate (nl) over at the High Eff. forum at AudioAsylum has been rolling his Fertins off at 200hz or so, then bringing in biamped woofers underneath and reporting much less congestion. I could see a first-order filter at 120hz being sufficient to keep excursion to a minimum.

Oh, and one last point of housekeeping -- The Fertin 20EX are nowhere near their stated efficiency. At 12v, they're about 94-95db/1w. 

Regards,
John

BTW, Erling posted while I was writing my reponse. I did not like the Fertins at 6v -- marked loss in efficiency and it really lost a lot of the 'field coil magic'.

[scorpion]

I have never heard the Fertins what stroke me was the close similarity between the specs for the Fertin and the B200 at 6 volt. It might pay off to experiment with supply voltage though, judging from Fertins published curves: http://www.jlbcreations.com/fertin/img_hp/courbes20ex.pdf . OB should of course be tested anyway.

/Erling

[mcgsxr]

Having played around with numerous configurations, though not as many as SOME, I can advise this.

1 - subs with separate amp.  Do it, it is the way to go.
2 - experiment - start with cardboard, and play around with shapes you like, and see.  THEN build in wood.

Good luck, it is a fun ride!

[mcgsxr]

Oh, and not meaning to thread poach - but could woofers be mounted beside the main driver in those lowboys, and work OK?

I never thought of doing that - building some low baffles with the 2 drivers mounted in them, isolating the woofer of course...

[JohninCR]

One last idea related to WAF.  Of course you'll want to hear your new drivers right off the bat, so get a sheet of plywood and rip two 1ftx4ft and two 3ftx4ft.  Cut your driver holes in the large ones with a different distance to each side and top.  Use the other 2 as support braces centered behind the driver with a big half circle driver cutout.  This will accomplish 2 things.  1.  Show you what is possible with a big baffle  2.  Break the wife in right off the bat, so she will like whatever you end up doing with them and appreciate the smaller size.  Starting with a very narrow baffle with big pieces of cardboard taped on is another great way to prototype, but don't let her see them in a small form until later.  Big and ugly at first will work to your benefit.

[Bob in St. Louis]

"Big and ugly at first will work to your benefit."

HA HA  Priceless John, that's great!  I love it.

Bob