FR88Ex based micro-Onken ?

[barbarous]

I had a similar question as the OP. I wondered if I could make a microFonken with a pair of Fostex FE87E I own. On the datasheet the Qts is 0.92, the Qms 3.77, the Vas 1.03L, and the Fs 140 Hz. Would I need to change the box for this driver, or is it roughly equivalent?

I also wondered, as far as the eNABL process goes, if a speedball pen is necessary. I have experience doing detailed small scale painting, but no experience with a pen.

 

[planet10]

Dave - your data shows quite a spread, suggests that box designs should be tolerant to this kind of thing.

Exactly. Particularily because -- if my current views on T/S hold -- "parameters" will change depending on where the volume is set, and with the dynamics of the music.

Interestingly, the box they came in includes a printed statement that this is a matched pair, which I wonder out loud as it doesn't seem very economical for the manufacturer to do this unless the matching is simply within their 'factory spec' for all drivers.

They'd have to have a pretty streamlined process (cheap labour helps). And a simple matching algorithm that assumes more drivers coming off the line all the time, I wonder how tight they are?

dave

 

[planet10]

I had a similar question as the OP. I wondered if I could make a microFonken with a pair of Fostex FE87E I own. On the datasheet the Qts is 0.92, the Qms 3.77, the Vas 1.03L, and the Fs 140 Hz. Would I need to change the box for this driver, or is it roughly equivalent?

Not really. An optimum box for it would be closer to a milli. That said with a set of flat-paks at hand, i'm going to try a set of ~40 year old FE83A in a set.

I also wondered, as far as the eNABL process goes, if a speedball pen is necessary. I have experience doing detailed small scale painting, but no experience with a pen.

I found the Speedball Pens a PITA (and very expensive). I switched to #56 & #99 caligraphy tips (#56 now included in Ed's kit). People have successfully used paint brushes, but skill would be required.

dave

 

[Bigun]

And do we know if the FR88EX would benefit from the 'dots n dashes' ?

 

[Uncle Meat]

Interestingly, the box they came in includes a printed statement that this is a matched pair, which I wonder out loud as it doesn't seem very economical for the manufacturer to do this unless the matching is simply within their 'factory spec' for all drivers.

Mine didn´t include such statement. However, Qts differed by 0.01 and Fres by 1 Hz only... Amazing

Dots n dashes? Hmm, I guess in this case the effect will not be worth the effort. There is already a 5mm wide rubber rim on the cone...

 

[Bigun]

I'm going to try and persuade my kids to build this thing. We'll see.

First off, they don't want a slot port on the front, for no other reason than how it looks. I'm now thinking if I can move it so that it vents underneath, lifting the box off the desk surface with some spiked feet. Is there a guideline for the height off the desk surface - I was thinking of at least equal to the diameter (narrow part of the slot) ?

 

[planet10]

I'm going to try and persuade my kids to build this thing. We'll see.

First off, they don't want a slot port on the front, for no other reason than how it looks. I'm now thinking if I can move it so that it vents underneath, lifting the box off the desk surface with some spiked feet. Is there a guideline for the height off the desk surface - I was thinking of at least equal to the diameter (narrow part of the slot) ?

Slot out the bottom (at the back) works. I have one of the classic GR Mar-Ken7 variations drawn this way. you can play with loading height... i'd lift it higher than one vent height (maybe tipped back somewhat too)

dave

 

[planet10]

Dots n dashes? Hmm, I guess in this case the effect will not be worth the effort. There is already a 5mm wide rubber rim on the cone...

I have yet to find a driver that doesn't benefit. Rubber surround is immaterial. I do wish it was inverted thou, that it bumps up is a deficit.

dave

 

[Uncle Meat]

Seems OK. But I think such small boxes with feet doesn´t look good.
If they shall reside on a desk, I would let the baffle extend at the bottom, so they stand slightly tilted backwards.

 

[Bigun]

On the contrary, slender spiked feet look great, they are like 'high heels' for speakers

 

[barbarous]

Not really. An optimum box for it would be closer to a milli. That said with a set of flat-paks at hand, i'm going to try a set of ~40 year old FE83A in a set.

I found the Speedball Pens a PITA (and very expensive). I switched to #56 & #99 caligraphy tips (#56 now included in Ed's kit). People have successfully used paint brushes, but skill would be required.

dave

Thanks for the answers. So the milli 4.5 liter would work-- should I shrink it a bit, or is that right on? I find speaker volume math a bit bewildering, but I can shrink dimensions easily enough.

Ed's kit looks way cheaper than buying the items separately. If I painted them though I'd just need the paint, which I think I can get locally. (I assume color doesn't matter, though Ed's kit specifies it.) I'm curious as to how it sounds but I also like the way it looks, so I figured I'd give it a shot.

 

[GM]

-- "parameters" will change depending on where the volume is set, and with the dynamics of the music.

They'd have to have a pretty streamlined process (cheap labour helps). And a simple matching algorithm that assumes more drivers coming off the line all the time, I wonder how tight they are?

Absolutely, cab size will increase and Fb decrease for a given response 'flatness' with increasing power due to VC heating, so ~aperiodic with its variable cooling effect on the driver's heat rise is the best compromise cab design and no doubt a major reason why it was used rather than sealed in the early cinema/PA bass horns when power handling was low and efficiency needed to be uniformly high.

I imagine that with today's automated assembly that the sum of its individual parts tolerance is the low/high range of acceptance and since statistical analysis is normally used to determine how many parts in an assembly batch are to be checked, a so-called matched set could mean anything within this low/high range unless the unit is offered with a manual matching service.

Manually assembled drivers OTOH can be quite close. Altec specs were typically very tight (< 2% variance), and if you requested 'X' specs to match some existing drivers they would get them pretty much spot on at no additional charge if it fell within that particular model's parts variance. Of course the trade-off was high cost, I was paying $hundreds$ (inflation adjusted) for a single 15" woofer, so if a driver is being sold today as 'matched' for some piddly sum, I couldn't reasonably expect anywhere near this sort of accuracy.

GM

 

[planet10]

Thanks for the answers. So the milli 4.5 liter would work-- should I shrink it a bit, or is that right on? I find speaker volume math a bit bewildering, but I can shrink dimensions easily enough.

I never did do a complete alignment/design. Just some initial work that determined that the FE83/87 were going to need a box close to the same size as i could already squeeze an FE127eN into. I then moved on to the FF85.

The colour for EnABL does not matter (as long as it is flat paint -- the metallics do not work). Personally i much prefer a contrasting colour, the feedback it gives makes application easier and usually a cleaner pattern. I am contemplating an upcharge for stealth applications.

dave

 

[Bigun]

Well I have the wood today and a new router

I'll probably refine the design ideas a bit but I hope to have a home for my new Fountek's sometime over the next couple of weeks.

I couldn't find the binding posts I had ordered with the drivers though. I checked with Solen to confirm they weren't on back order and they confirmed they had been shipped in the same box. But I couldn't find them. I have to credit Solen with some excellent customer service - they have put some replacement posts in the mail for me - kudos Solen

 

[planet10]

http://www.diyaudio.com/forums/full-range/210106-fountek-five-fr88ex.html

includes 'Ken-Lite

dave