If you are going to bi-amp, I would recommend the Eminence Alpha 15A. I believe the Alpha 15A is of better quality construction compared to the Goldwood. You could go OB or H frame.
Since you are biamping the level match to the full range driver is not so important. You coud easily use any of the Fostex or Alpair drivers and even the Jordan driver. The Fostex FF85K is an excellent option, from the stand point of performance and price, if you decide to go that route.
Since you are biamping the level match to the full range driver is not so important. You coud easily use any of the Fostex or Alpair drivers and even the Jordan driver. The Fostex FF85K is an excellent option, from the stand point of performance and price, if you decide to go that route.
Thanks Martin, very good tip and bonus of alpha being cheaper 
Not having heard a ff85k nor the f120a I can only hope the difference is small versus the cost difference in a situation where the bass is not an issue. In the end you get what you pay for typically. so I should not over speculate here.
On another note, I tried to follow your instruction on down loading mathcad so I could purchase your work sheets. I have some pc issue that will not allow me to run it. I am some what computer handicapped
So I will have to stick to your tried and true formula for now.
Cheers
Ed
Not having heard a ff85k nor the f120a I can only hope the difference is small versus the cost difference in a situation where the bass is not an issue. In the end you get what you pay for typically. so I should not over speculate here.
On another note, I tried to follow your instruction on down loading mathcad so I could purchase your work sheets. I have some pc issue that will not allow me to run it. I am some what computer handicapped
So I will have to stick to your tried and true formula for now.
Cheers
Ed
Ed,
My recommednation would be to stay away from the F120A. I have only heard it sound great in one situation (Jim's Metronome with my tube amp), in an OB my pair of F120A drivers sound mediocre at best. If you are going to spend that much money you might consider the Jordan JX92S or maybe the Alpair 10 or 12. The best buy would be the Fostex FF85K in terms of performance/cost. If you start small with the FF85K, you could always change to a bigger driver later if you felt the need and just make the hole bigger.
My recommednation would be to stay away from the F120A. I have only heard it sound great in one situation (Jim's Metronome with my tube amp), in an OB my pair of F120A drivers sound mediocre at best. If you are going to spend that much money you might consider the Jordan JX92S or maybe the Alpair 10 or 12. The best buy would be the Fostex FF85K in terms of performance/cost. If you start small with the FF85K, you could always change to a bigger driver later if you felt the need and just make the hole bigger.
I'm in the process of building this speaker as well. I've ordered the crossover parts
per the original open-baffle design, although I did go with cheaper inductors. A pair of fountek FR88-EX are on the way, as well as a pair of Aurasound NT1-204-8D 3/4" tweeters. I was going to go with the fostex ff85k but it was difficult to find and shipping from the one place I found it was too expensive. I'm hoping the fountek works well.
I'm planning on placing the tweeter close to the fountek and crossing it over very high (at 9khz) just to smooth out the top end. I have no experience building crossovers but the electronics repair guy down the street says he can make a crossover for the tweeter. Any tips about adding the tweeter would be sweet.
For the woofer I'm going to use the hawthorne audio silver iris 15 inch drivers that I already have. The specs look almost identical to the alpha 15a.
per the original open-baffle design, although I did go with cheaper inductors. A pair of fountek FR88-EX are on the way, as well as a pair of Aurasound NT1-204-8D 3/4" tweeters. I was going to go with the fostex ff85k but it was difficult to find and shipping from the one place I found it was too expensive. I'm hoping the fountek works well.
I'm planning on placing the tweeter close to the fountek and crossing it over very high (at 9khz) just to smooth out the top end. I have no experience building crossovers but the electronics repair guy down the street says he can make a crossover for the tweeter. Any tips about adding the tweeter would be sweet.
For the woofer I'm going to use the hawthorne audio silver iris 15 inch drivers that I already have. The specs look almost identical to the alpha 15a.
There are some similar designs on the net that use very efficient full-range or mid-range drivers and I'm wondering how they get those to work. Martins design
says that for this type of design to work the woofer should be efficient and the full-range not so efficient.
Here's a design that seems to fly in the face of what (I think) Martin is saying
Endorphine from Kingston Kitchen
Anyone feel like dropping some knowledge?
ps. Terryo, thanks for the earlier advice on crossover components. I decided not
to take it but only because it was over my head.
says that for this type of design to work the woofer should be efficient and the full-range not so efficient.
Here's a design that seems to fly in the face of what (I think) Martin is saying
Endorphine from Kingston Kitchen
Anyone feel like dropping some knowledge?
ps. Terryo, thanks for the earlier advice on crossover components. I decided not
to take it but only because it was over my head.
He has set the minimum efficiency of the bass driver as 97 dB/W/m. Maximum Qts is listed as 1. The low pass crossover is defined as 2nd order between 300 to 400 Hz. Seems kind of like the designs I have been favoring. Not sure what the efficiency of the mid and tweeter are to get a feel for the combined response.
The problem I have with this site is that he does provide many interesting and creative looking designs but without any initial or final measurements, documentation of the design trade-offs, or any real description of the engineering that he performed to arrive at the design. There is no way to assess if his design is high performance or is just average, if it meets your specific design objectives, or if it is even worth building. A lot of creative thinking but in my opinion not enough hard information to confidently build any of the designs.
Maybe that is just me.
Ed,
When you take away the need to produce bass, there is no contest in mind. I'd pick the FF85 (even ignoring price). You give up some efficiency, but as Martin pointed out early on, that can mean more extended bass (with a passive XO anyway).
Note: my comparisons are based on treated drivers, not stock.
dave
I built these and they do not work.
Now with that statement I have to say the Saba drivers are incredible and can reproduce music with amazing clarity and detail. They can be wonderful run by 1 or 2 watt set amps, But bass integration is difficult because they are so efficient.
The crossover recommendations in that link are off, I dont know what he smokes
I may for kicks try Marin's Hframe and turn down the Saba via active cross over, but I think ultimately to follow Martin's guidelines for fullrange drivers will yield best results.
Thats my 2 cents from living with them for about a year
Ed
You are confirming my speculation David. I see no reason to spend the doe on the 120's, a smarter bet would be to buy your modded drivers.
Ed
Hi,
I have been following the FF85K OB with great interest. I have 8 of these but have not heard them yet.I know some of you are very familiar with these. I have never made an OB, but want to give it a try, I used to make magnetic planers and loved the sound.
I have three main concerns I will put out : 1) A large baffle may give a diffuse/foggy sound stage. 2) The FF85K has little excursion, a small diaphragm, giving limited output. 3) Losing more efficiency with BSC.
My proposal, use three of them in MTM, (Mid-Full-Mid) above an OB sub, rolling off the treble of the outer two to avoid combing and baffle step losses. The narrow baffle should image well. The added output would be welcome as well. I realize there are many considerations here, but any thoughts?
Gary
I have been following the FF85K OB with great interest. I have 8 of these but have not heard them yet.I know some of you are very familiar with these. I have never made an OB, but want to give it a try, I used to make magnetic planers and loved the sound.
I have three main concerns I will put out : 1) A large baffle may give a diffuse/foggy sound stage. 2) The FF85K has little excursion, a small diaphragm, giving limited output. 3) Losing more efficiency with BSC.
My proposal, use three of them in MTM, (Mid-Full-Mid) above an OB sub, rolling off the treble of the outer two to avoid combing and baffle step losses. The narrow baffle should image well. The added output would be welcome as well. I realize there are many considerations here, but any thoughts?
Gary
Gary,
My suggestion is that instead of trying to second guess everything that has been done before, that you just build the baffle and "actually see" if your concerns are warrented.
Many problems that are inhearent with conventional speakers using conventional cabinets are not necessarily applicable to OB.
You've got the drivers, build it to design, then if you think that you can improve it, start cutting down the size of the baffle, adding drivers and elaborating the cross-over until...well, you'll see what you'll see.
BTW: I personally think that MTMs aren't worth the effort, but your "Audiophile" friends will be impressed.
Best Regards,
TerryO
>>>I have three main concerns I will put out : 1) A large baffle may give a diffuse/foggy sound stage. 2) The FF85K has little excursion, a small diaphragm, giving limited output. 3) Losing more efficiency with BSC.
My proposal, use three of them in MTM, (Mid-Full-Mid) above an OB sub, rolling off the treble of the outer two to avoid combing and baffle step losses. The narrow baffle should image well. The added output would be welcome as well. I realize there are many considerations here, but any thoughts?<<<
1) I think the dipole presentation will have a more profound effect on the sound stage than the width of the baffle.
2) The 500 Hz XO largely eliminates the the low Xmax issue.
3) What BSC? None used, none needed, although making a very narrow baffle may create the need--and may lead to other issues as well. And how many Alpha 15a's were you planning to add to correct the imbalance created by upping the efficiency on the high end? Or are you thinking to bi-amp? (which will certainly work, but the idea was a simple, inexpensive OB.)
As TerryO said: give it a try first, then contemplate changes to address whatever short comings you may perceive.
Cheers, Jim
My proposal, use three of them in MTM, (Mid-Full-Mid) above an OB sub, rolling off the treble of the outer two to avoid combing and baffle step losses. The narrow baffle should image well. The added output would be welcome as well. I realize there are many considerations here, but any thoughts?<<<
1) I think the dipole presentation will have a more profound effect on the sound stage than the width of the baffle.
2) The 500 Hz XO largely eliminates the the low Xmax issue.
3) What BSC? None used, none needed, although making a very narrow baffle may create the need--and may lead to other issues as well. And how many Alpha 15a's were you planning to add to correct the imbalance created by upping the efficiency on the high end? Or are you thinking to bi-amp? (which will certainly work, but the idea was a simple, inexpensive OB.)
As TerryO said: give it a try first, then contemplate changes to address whatever short comings you may perceive.
Cheers, Jim
Thanks Jim and Terry thanks for your meaningful responses.;
After some thought on your responses I realize my concerns were prompted by trying to short cut to an end, prompted by the experiences of others. Therefore I will take your advise to first build and then tweak / modify.
Regarding amplification and crossover, I have a FW F5 clone with Peter Daniels boards. It is populated with all premium parts, Caddocks, Riken, Mills, a 500va Plitron xformer and 4 x 22000uf Sikorel caps. It puts out 25w a side, to 2ohms. Can I drive the woofers or just go active, as I had planned from the start?
Gary
After some thought on your responses I realize my concerns were prompted by trying to short cut to an end, prompted by the experiences of others. Therefore I will take your advise to first build and then tweak / modify.
Regarding amplification and crossover, I have a FW F5 clone with Peter Daniels boards. It is populated with all premium parts, Caddocks, Riken, Mills, a 500va Plitron xformer and 4 x 22000uf Sikorel caps. It puts out 25w a side, to 2ohms. Can I drive the woofers or just go active, as I had planned from the start?
Gary
For me, 25 wpc would be plenty of power. But most of my listening is done at an average SPL around 75 (leaving reasonable head room for the transients.)
I can tell you that I use a 2.5 wpc MiniWatt tube amp on my F120a Metronomes (~89 dB sensitivity) and am happy with that. I did try the MiniWatt on the OBs, but the bass was loose and flabby; I take this to indicate that the little tube amp doesn't do well with the passive XO. I don't know how the F5 will work with the XO, but I'm sure it would work a treat with the FF85k!
Cheers, Jim
I can tell you that I use a 2.5 wpc MiniWatt tube amp on my F120a Metronomes (~89 dB sensitivity) and am happy with that. I did try the MiniWatt on the OBs, but the bass was loose and flabby; I take this to indicate that the little tube amp doesn't do well with the passive XO. I don't know how the F5 will work with the XO, but I'm sure it would work a treat with the FF85k!
Cheers, Jim
Thanks Jim and Terry thanks for your meaningful responses.;
After some thought on your responses I realize my concerns were prompted by trying to short cut to an end, prompted by the experiences of others. Therefore I will take your advise to first build and then tweak / modify.
Regarding amplification and crossover, I have a FW F5 clone with Peter Daniels boards. It is populated with all premium parts, Caddocks, Riken, Mills, a 500va Plitron xformer and 4 x 22000uf Sikorel caps. It puts out 25w a side, to 2ohms. Can I drive the woofers or just go active, as I had planned from the start?
Gary
Gary,
I don't know about the F5, but the SETs that I've heard can have problems when the impedance curve of the driver is going up and down and around. I suspect that some of the reputation of tubes in general, and specifically SETs for poor bass performance is more the result of this interaction with the driver than anything specific to the amp. Dave (Planet10) has mentioned that some drivers have a problem with any single-end amp, SS or Tube.
If you had planned on active biamping, I'd go with that, as it's almost always better than most alternatives. For bass duties, relatively inexpensive SS amps are available and don't need to cost a great deal. I'd save that special
F5 for the 300Hz on up portion, you certainly won't run out of headroom and from all that I've heard, they're pretty darn nice sounding amps.
So buy some plywood, cut it to size and install the drivers with crossover or your active solution and you're there! A sheet of A/C ply is cheap and you can try all kinds of things before you arrive at the solution that makes you happy, then build your "good" baffles with the finest kind, throw out your test mule baffles, and it's done.
Good Luck with your project!
Remember, this is a hobby and should be fun, so don't get obsessive.
Best Regards,
TerryO
Don,
It's certainly something that I have to remind myself of, from time to time.
For those that don't know Don, he's so talented (and relaxed) that he makes all this stuff look easy... it just drives me crazy!
Best Regards,
TerryO
I'm not Jim, but a lot of the preferences in listening levels, depend on what type of music you listen to. I like Classical music and therefore would be inclined to listen at a 70-75dB average SPL level, as the dynamic range of classical music can far exceed nearly any other type of music.
At a crossover point of 300Hz, it shouldn't be much of a problem.
Best Regards,
TerryO
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