Fertin project - calling all open baffle experts

[Variac]

It seems to me you are getting too upset. That is the only way you could make a fool out of yourself here. You certainly wouldn't want to be the sort of person that threatens to take his toys and go home.. something you once accused me of. Perhaps you had this reaction because the Supravox comments were mixed in with Frank's phase comments. In fact, that was what I was trying to ameliorate a bit- I felt your comments to Frank about the Supra recomendation were excessive, about phase more justified. I think your comment was valid, but feel that the truth is that we really don't have enough info on all the Supra products, etc. and should stay open minded to more info, rather than demanding that all agree with you and your friend that they are crap. My Supravox interest was not for field coils at all and I will return to the thread where the lower level models were being discussed. It is these lower level models that I was considering and shouldn't have entered the fray regarding the field coils. In fact I have decided to not discuss speakers at all anymore until I have finished mine. Interestingly they will have Fostex drivers instead of Supravox because I want to buy them soon and I don't have enough info on Supravox-reliability to risk buying them after your warning! Plus the Fostex look really cool!

[planet10]

Originally posted by Variac
Fostex drivers instead of Supravox

I don't think you will be disappointed with the Fostex. They should be a magnificient driver. There is probably as much research in that single driver as has been spent to get Supravox going -- not to say that throwing huge amounts of money at something make them better -- but the Fostexs are well thought out -- now if they would just start making them with alnico or neo or field-coils ... yummmm

dave

[Bob.Obo]

Greets,

I have read with great interest the thread on the Fertins and would be interested in the group purchase.

The only experience I have with FR was a pair of Lowthers in Medallion II cabs but sold those and now use some Unity speakers/TAD2001 and Altec 828/515. The FR concept just seems more elegant.

Keep me posted!
Thanks!
Bob.Obo

[reverendclark]

I guess nothing is going to happen with FC drivers in this context.

Just as well. Unusually, I have the money but no time to start a speaker development project just now and I know I can get Fertins from Black Forest. Still, if anyone comes up with a smokin' deal on FC drivers, contact me privately at phclark@qwest.net. I'm taking this thread off my personal bar.

It's been a slice.

Peter C

[bbaker6212]

Just curious, do y'all think this driver would be good for an open baffle? If not, what type of cabinet do you think? If (big if) I did this, I would be mating it with the LeRibbon tweeter....

MANUFACTURER: ATD

MODEL 17LB
DATE 10/3/2001
Fs 99.7823
Cone Diameter 130.0000
ZMax 36.4923
Re 6.0000
Qms 4.1739
Qes 0.8213
Qts 0.6863
Mms 6.10g
Vas 19.5
dBSPL 92
Power: 100W
L 1kHz 0.7270
L 10kHz 0.1338
Z Min 6.6145
Z AVG 10.2670

http://e-speakers.com/products/atd-wide-range.html
http://e-speakers.com/products/atd-tweeters.html

At 1/3 the cost of a Fertin setup, you think it would sound decent? I'm interested in experimenting/experiencing the open baffle sound but at a lower cost.

[Pan]

Fs of 100 is a little high, you need a bass unit to complement this driver.

Depending on the size of the baffle, I believe there would be a problem with how much air the driver can move = not enough linear travel of the voice coil.

Also there is a 5dB peak at 4kHz that looks ugly and needs a notch filter.

So... view this driver as a midrange in a 3-way!

/Peter

[Phear]

There is the posibility to cover the backside of the driver with cloth, wool or glassfiber. this will increase the power handling in the bassregion, give a little more bass output, & it also makes it less important to treat the wall behind the speakers with absorbing material. This calls for a bit of trial & error, but if it results in a better sounding speaker... I'm going to try it on my (really ugly)open baffles anyway...

/Per

[fdegrove]

Hi,

There is the posibility to cover the backside of the driver with cloth, wool or glassfiber.

IME,it takes away the openness of the OB and you don't get more bass out of it anyway.

Try it if you like though,

[filippo22]

You can try with a Tipole arrangement like my bass section on Tipolo project

ciao
Filippo
www.audiofanatic.it

[bcherry]

Dave at one point suggested an angled cut to hole on the fieldcoil side of the driver. I did that and it opened up the soundstage in every direction. Thanks, Dave.

Now reasonably confident that the drivers have run in I would characterize the strong points of the driver/open baffle as: singing, lilting presentation and oustanding presence/transparency. Bass did eventually fill in and is reasonable enough with careful placement.

During the course of the thread we noted that low powered pp suited these speakers more than SET but no explanation was offered why this is so. Recently, on another board, KYW offered this little nugget:

"> I suppose the conclusion is there will be advantage in
> using field coil drivers in an OB where one can change
> the driver Q to suit.

Up to a point - yes. You really need to start with a Driver having a Qe of 0.5 or more (up to Qe 1.5 or so will be okay) and a sufficiently large baffle. The lower the Driver Qe for a given Fs the larger the baffle has to be (plane baffle, folding back "wings are an idea that is not ideal acoustically IMHO) for the same LF cutoff.

Go below 0.5 Driver Qe and you will NEVER have a large enough baffle to get a reasonably flat response at LF. You can BTW raise the Drivers effective Qe by driving it from a high source Impedance Amplifier.

For example, Brian Cherry uses a PP Amp with 45's that I would estimate to have around 6.5 - 8 Ohm output Impedance without negative feedback used. He comments how this amplifier produces much better bass with his open baffle Fertin's than the Billie Kit, which of course has "only" around 2.5 Ohm output Impedance.

If we do the numbers, using the high output impedance Amplifier will almost double the Qe, so our Qe = 0.45 Fertin de facto turns into Qe = 0.9. On comparison the 300B SE Amplifier will raise the Qe only to around 0.6.

The above should also explain why Brian finds the high output impedance Amplifier a little uncontrolled on Box Speakers where the 300B SE Amp rules."

I include this just to complete the discussion for reference.

Thanks to all for their input.

Brian