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Hi,
I put the parameters into the box model. Very interesting. If I use the updated spec. for the FE127 where Fs = 90Hz then my box will produce a little less bass extension than I had calculated it would.
The F120A looks like a nicer driver than the FE127 from the spec. Because the F120A is closer to the spec I actually designed my box for, it works better than the FE127. So with no changes to the Moon_Onken you get a pretty nice response.
There's a small 1dB lift in the bass, but this is likely inaudible and some people actually prefer a small 3dB lift.
Conclusion: the Moon_Onken looks like a great fit for these drivers. Better fit than the FE127's.
Chris/Dave - would love your advice on my thoughts (previous post) for my next speaker project ??
I put the parameters into the box model. Very interesting. If I use the updated spec. for the FE127 where Fs = 90Hz then my box will produce a little less bass extension than I had calculated it would.
The F120A looks like a nicer driver than the FE127 from the spec. Because the F120A is closer to the spec I actually designed my box for, it works better than the FE127. So with no changes to the Moon_Onken you get a pretty nice response.
There's a small 1dB lift in the bass, but this is likely inaudible and some people actually prefer a small 3dB lift.
Conclusion: the Moon_Onken looks like a great fit for these drivers. Better fit than the FE127's.
Chris/Dave - would love your advice on my thoughts (previous post) for my next speaker project ??
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My worry is not about how far the bass goes down, but how big the bump is before it starts falling off.
dave
Gareth, perhaps this has been addressed, but I might add that there may not be accurate modeling for behavior of the resistive ports that are an important feature of the Fonken style of enclosure, so as the saying goes YMMV.
I am famously ambivalent to measurements and modeling, but I can tell you that in playing around with early prototypes of the milliFonken enclosure, that the slot port version sounded much more controlled and smoother around it's roll-off point that the simple round port.
Note the lower sensitivity of the F120A and FX120 - possibly at the threshold of adequate dynamics for lower powered systems.
Based on my extended listening to the F120A Fonkens(teen) last year ( in comparison to several FE127 designs, including Fonken), I'd be inclined to recommend at least 10-15W of P/P triode power for the tube aficionado, and certainly not to compromise the very smooth and delicately textured response of the lowest octaves by undersizing the cabinet.
We had a pair of FX120 sitting on a shelf for many moons, and simply never got around to the boxes for them, but I'd like to think they'd perform closer to the F120A than FE127E. AFAIC, either of the 120 drivers deserve the least compromised enclosure possible if running them near their full bandwidth. No doubt there are other enclosure designs that would work well, but I know for a fact that the approx 22liter Fonkensteen does.
I am famously ambivalent to measurements and modeling, but I can tell you that in playing around with early prototypes of the milliFonken enclosure, that the slot port version sounded much more controlled and smoother around it's roll-off point that the simple round port.
Note the lower sensitivity of the F120A and FX120 - possibly at the threshold of adequate dynamics for lower powered systems.
Based on my extended listening to the F120A Fonkens(teen) last year ( in comparison to several FE127 designs, including Fonken), I'd be inclined to recommend at least 10-15W of P/P triode power for the tube aficionado, and certainly not to compromise the very smooth and delicately textured response of the lowest octaves by undersizing the cabinet.
We had a pair of FX120 sitting on a shelf for many moons, and simply never got around to the boxes for them, but I'd like to think they'd perform closer to the F120A than FE127E. AFAIC, either of the 120 drivers deserve the least compromised enclosure possible if running them near their full bandwidth. No doubt there are other enclosure designs that would work well, but I know for a fact that the approx 22liter Fonkensteen does.
chrisb said:
You can get decent bass performance with big PP triode power, even in a 14L box. Small tube (EL84) PP pentode works too.
Jeff
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You are absolutely right of course. However, my personal view is that the sound of a closed box or BR speaker is not very sensitive to the exact sizing of the box although I will grant that poorly dimensioned ports can create problems.
The calculator is proven to be accurate for regular BR boxes. What I did find that encouraged me, was that when I took the dimensions of the Fonken designs published by planet10 and loaded them into that online calculator, it showed a remarkably good match with what the calculator would have suggested.
What I did was to play around with the design parameters in this calculator and decide for myself how much margin of error could be had in terms of the speaker design. It was quite a lot. In the end, it is the bumps and wriggles in the driver response that has dominated the sound performance of the speakers I built.
As you say, YMMV. I'm certainly not trying to 'sell' anyone on the design I used. One of my goals was to learn something about speaker design along the way so an off-the-shelf design was never an option. I was fortunate in having you guys to 'keep me honest' during the process.
Bigun: You beat me to it. It had occured to me after Dave revealed the true Fs of the FE127, that you may have inadvertently designed the box for the FX120/F120A and not the FE127.
I will knock up a couple of these cabs (off post 2) in the next few weeks and report back.
Thanks for your efforts. I will not hold you responsible if they are not optimum.
I will knock up a couple of these cabs (off post 2) in the next few weeks and report back.
Thanks for your efforts. I will not hold you responsible if they are not optimum.
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I've been blamed for less before 😀
Feel free to email me if you get stuck, my drawings aren't super detailed.
A couple of pointers if I may: applies to any Fonken I suppose.
1) it makes a huge difference if you cut the wood accurately to start with. There are a lot of pieces to be stuck together and lined up if you are going to get nice joints between panels. I know this because I don't have a table-saw and did it with a hand-held circular-saw. I found accuracy to around 1mm was required for me to be satisfied, YMMV. Measure twice, then cut, then measure again. Use a woodworkers Square or equivalent, the pieces must be square with respect to their corners or you'll very quickly become frustrated.
2) build the sides first with their integral ports, then plane/sand/square the top and bottom edges. Careful when you clamp the pieces together that make up these sides that the spacers that create the space for the ports don't slip and slide out of place because they are lubricated by the wood glue
3) do lots of trial fitting of the pieces. In particular cut the holey brace sightly oversize and install it only after the sides front and back are glued into place. this way you can sand it to get a tight fit inside the box before you glue it - otherwise it will not add the required rigidity. Test fit the speaker driver too in order to see that the back of the magnet just kisses the holey brace, or has space to allow for some sitck-on felt pads so that the holey brace is pressing against the magnet of the driver when the driver is screwed into the box. It's easiest to see all of this before you glue the bottom and top of the box. The lid goes on last. Adjust the sizings to suit your drivers, they are different from the FE127's.
4) don't even try to do the 45 degree cuts of the front corners of the box until you are comfortable and confident or a lot of work may potentially get spoiled. Build up some scrap pieces and practice. You do these cuts after the boxes are all glued up. This doesn't happen until you've installed the stuffing but before you fit the driver, terminal cup and wiring. It's a very satisfying moment, when you do that 45deg corner cut, it turns the box into the final shape and exposes neat ends to the ports. Make sure there's enough wood sticking forward of the box when you make the sides so that they clear the front face to ensure that after you cut the angles you have a nice flush finish.
5) I decided to add veneer to the front and sides. It was very difficult to get a satisfying finish. I would think twice about using veneer again. Alternatives are to varnish it and enjoy the visible plywood layers or paint it to suit your taste.
6) don't be shocked if they don't sound great first off. I don't know about the F120's but if they are like the FE127's they will sound awful to start with, a bit harsh and distorted. This will clear up significantly after about 8 hrs of playing music and continue to smooth off for another 100hrs or so. After that you may still find them a bit bright on axis depending what kind of speakers you have been used to listening to all these years. These Fostex drivers are very revealing. Some people will tame the top end by fitting baffle step correction components (not specific to Fostex drivers, applies to any small speaker enclosure). Some people scorn at this. You will be able to make you own decision.
Hope this helps, and hope I haven't been trying to teach an expert something they know how to do better already !
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I look forward to hearing about it - post some photo's when you get the chance.
And - some interesting information on the Fostex drivers here (I hope to do some driver treatment): http://www.diyaudio.com/forums/showthread.php?postid=1870113#post1870113
And - some interesting information on the Fostex drivers here (I hope to do some driver treatment): http://www.diyaudio.com/forums/showthread.php?postid=1870113#post1870113
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UPDATE:
I haven't been using the speakers recently but decided to pull one off the shelf and set it up for an audition.
The clarity is amazing but that 7kHz peak in the cone's frequency response is still too fatiguing. Even with Dave's Trifoil treatment.
It's time to address this.
I did an experiment with Baffle Step Correction. I used a 3.3Ohm resistor in parallel with a 0.33mH air core choke. It helped. It isn't enough yet but a little experimentation and I think this issue will be solved. Even with a 3dB BSC the sound is better without any loss of top end.
I'm also curious as to whether I should try to compensate for the difference between measured and published specs for this driver (see above posts) by modifying the ports ?
I haven't been using the speakers recently but decided to pull one off the shelf and set it up for an audition.
The clarity is amazing but that 7kHz peak in the cone's frequency response is still too fatiguing. Even with Dave's Trifoil treatment.
It's time to address this.
I did an experiment with Baffle Step Correction. I used a 3.3Ohm resistor in parallel with a 0.33mH air core choke. It helped. It isn't enough yet but a little experimentation and I think this issue will be solved. Even with a 3dB BSC the sound is better without any loss of top end.
I'm also curious as to whether I should try to compensate for the difference between measured and published specs for this driver (see above posts) by modifying the ports ?
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OK, now I'm up to 10R with 0.33mH choke, which gives about 6dB of correct at the 7kHz peak of this driver. It may need a bit more but I don't want to kill the sound. Right now it sounds MUCH better than before and yet the hf still has magic.
I sure wish there was a version of the Moon-Onken suitable for the Audio Nirvana Super 8's I have sitting in boxes in my garage. 🙁
Why am I not surprised? 7 kHz is right near the peak of the sibilance BW that makes my teeth hurt if not a bit recessed.
GM
Well, if as you said in post #110 the drivers hadn't been getting exercised a lot lately, they just might need to break in all over again, and the tonal balance might settle down.
The trifoil pattern mitigate some of the upper midrange issued, but the polka dots do a lot to help you hear coherently deeper into the music. Unless overdone with the base or finishing gloss top coats, none of the "HF magic" is lost.
There is, they just won't have any bass.😀
My wife hated them, and we all know what that means..........
Jeff
Some might suggest two possible solutions - but having taste her pastries, the better choice is obviously: try another speaker
Or bigger, but its published specs would be fine for a tiny bookshelf alignment, though of course being so small it wouldn't have any (mid) bass to speak of, so would need some BSC in a larger cab tuned lower.
I guess we could double Qts and use an AS alignment to vent: ~50 L gross tuned to Fs or ~AR3 size IIRC and use BSC if required.
GM
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