Fostex FX 120 Isobaric ?

[ODougbo]

I ended up with a few extra FX120 drivers, and thinking Isobaric may be the way to go. As some may know the FX120 is not idea for full range (wish I had gone with the FE series). I think the biggest issue is the lack of bass - in an enclosure.

However that said I built a set of 4 “tower” boxes (quickie mock up boxes) and the bass is impressive with all 4. Of course the problem here is that is taking up a good deal of space.

I do expect a delivery today for parts for BSC circuit for above. I’ll see how it goes and may build the M. J. King towers, but even he comments “ the bass doesn't blow you away”

So putting this question out there, would an Isobaric/full range be the way to go? Would anyone care to suggest a box size and tuning frequency?

The two speakers are bolted together with 3” bolts, just so I can measure up for a tunnel – I would be going front to back

Thank you for any advise.

Fostex 5” FULL RANGE
KENAF paper/ fiber composite cone
89db sensitivity
Frequency response from 70 Hz to 20kHz
Flange 137 x 123mm HEXAGONAL
Cut-out 103 mm
Depth 54.5 mm
Znom 8 ohm
Re 7.3 ohm
Le@1kHz - mH
fs 70 Hz
Qms 8.4
Qes 0.47
Qts 0.45
Mms 5.3 g
Cms - mm/N
Sd - cm2
BL - N/A
Vas 8.21 ltrs
Xmax 2.0 mm peak
VC Ø - mm
Sensitivity
1W / 1m 89 dB
Nom. Power 30 W
Net weight 1.32 kg

[MJK]

I don't understand any of the statements in your post. The FX120 is a very good full range driver and probably easier to design an enclosure for then the FE-126En.

I have a pair and have used them in an OB system with very good results. I have never designed or built a tower system for the FX120 so I do not know where you found the quote.

An Isobaric design will not increase bass performance, it will only reduce enclosure size. The SPL response will be very similar to a single driver.

For a full range driver like the FX120 in some form of resonant enclosure you cannot expect to get 20 or 30 Hz bass from a driver with an fs of 70 Hz. If you could get bass into the 50 to 60 Hz range that would be an excellent/aggressive design but not one that would shake a room. Getting bass down to fs is probably a more reasonable goal for a simple enclosure.

Martin

[ODougbo]

Here are the plans and quote (near end).

http://diyaudioprojects.com/Speakers/Fostex-FX120-ML-TQWT/]

Attached pic is the towers I built, didn’t spend a lot of time on them and again waiting for the parts for the BSC. The bass is pretty good, with all 4. The plans for the dual chamber boxes was supplied with the woofer.

[MJK]

That is not my design or my write-up, the author's name is at the top of the page. You did not build that design and it sounds like you have not implemented the BSC in whatever you built. The referenced speaker looks like a very good tower speaker design and produces bass to the 50 - 60 Hz range. I am not sure I understand what you are doing so I will stop responding.

Martin

[ODougbo]

Martin, you have my sincere apologies, I had no intention of irritating anyone. Yes more than one project.
BSC for existing speakers.
Isobaric - maybe a test box. [/SIZE]

Originally Posted by MJK

That is not my design or my write-up, the author's name is at the top of the page. You did not build that design and it sounds like you have not implemented the BSC in whatever you built. The referenced speaker looks like a very good tower speaker design and produces bass to the 50 - 60 Hz range. I am not sure I understand what you are doing so I will stop responding.

Martin

[chrisb]

Originally Posted by ODougbo

Martin, you have my sincere apologies, I had no intention of irritating anyone. Yes more than one project.
BSC for existing speakers.
Isobaric - maybe a test box. [/SIZE]

The posted MLTL for a single FX120 is an excellent looking design, including the tested BSC - I wouldn't try to re-invent the wheel.

As I believe others have already suggested, there are probably better ways to utilize these 4 drivers than the complicated build that would be involved in isobaric enclosures.

[ODougbo]

Plans/Pic of dual chamber box:
I did scan, however that file was too large to upload.

[ODougbo]

Chris, thanks, I did like the design, as many other that I’ve found on this site, very inspirational. I have a box full of these drivers, just trying to explore some options.

Originally Posted by chrisb

The posted MLTL for a single FX120 is an excellent looking design, including the tested BSC - I wouldn't try to re-invent the wheel.

As I believe others have already suggested, there are probably better ways to utilize these 4 drivers than the complicated build that would be involved in isobaric enclosures.

[chrisb]

Originally Posted by ODougbo

Plans/Pic of dual chamber box:
I did scan, however that file was too large to upload.

It might bear repeating that the enclosure designs that accompany Fostex drivers haven't been universally heralded as great performers. We've built, endured and burned several ourselves - but that's of course only anecdotal hearsay until you audition a competent design by others. There's a veritable alphabet soup of the initials of designer / DIYers who've posted examples of their work with this particular driver.

Getting back to one of the basic questions on my personal checklist:

what are physical size / placement constraints for the proposed enclosures?

I'd imagine a short list of excellent enclosure designs for this driver would include taller MLTLs and/or bipoles / BLHs, many of which do have "foot-print" requirements that don't work for every situation.

The other alternative of course is to forgo digging for deepest extension and use a much smaller resistively vented (aperiodic) enclosure tuned for smooth roll-off in the 90-120 Hz range, and supplement with powered woofer(s).

[planet10]

An isobarik with FX120 will not improve bass, just allow you to get the same bass from ~1/2 the size box.

It will thou make the driver only usable well below the frequency determined by the distance between drivers (1/2 wavelength round trip causes a peak, and then a ripple train above that)

Since you are not liking FX120 send them all to me and i will dispose of them.

dave