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Old 11th April 2006, 12:14 AM   #1
punk is offline punk  Italy
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Default Fostex FX120 review and ideas for new project

It looks like there are not so many people that ended up buying the Fostex FX120, despite there seems to be a widespread good opinion about this driver. WEll, I guess I will now confirm what I basically wrote a couple of years ago.

PROS:
The FX 120 is defintely a great fullrange driver. Even in a cardboard box, it's in my opinion better than RS 40-1197, FE83 (unfair comparison, I know) and most bookshelf 2-way commercial speakers.
So far I tried only 12lt. BR in two very different enclosures with simialr results. It has a great and full midrange, including the lower end of voice frequencies, which is what most small speakers totally lack. Mids and higher freq. are never harsh tough or unbalanced. You never get that cheap-whizzer-cone feeling. I imagine someone may want a super-tweeter, but...not the readers of this forum section, I guess !

CONS:
that boomy (and slow, somehow) bass you get from a BR is just not good. It does not match the great great job the driver is doing above 100Hz!
Now, I know, I know, it's a 5" fullrange and it not supposed to go down to 20Hz and I was too lazy to try a TQWT, but this speaker needs help in the lowest freq. range.
Another so-to-say disappointing feature is that it took FOREVER to break in. Weeks of listening and then one day the magic happens. Not talking about a small difference either!

THE PROJECT :
I recently bought "by chance" two RS 40-1301A 15" woofers for a few dollars and was thinking about a design like linkwitz's orion. Open baffle FX120 (unfiltered of course) + RS 15" woofer in BR or sealed. The requirement for these woofer is ultimately to fill a little gap, I don't need to get every last Hz out of them. Unfortunately I don't have any datasheet about these RS drivers.

Can anyone help ? What are the critical parts of such a design ?

thanks,

Lorenzo
P.S. attached RS 40-1301a pic
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Old 11th April 2006, 12:53 PM   #2
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Crossover and active EQ!

Could be an interesting project that.
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Old 11th April 2006, 01:40 PM   #3
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Default FX120

Hi,

I have had the FX120 in a sealed 6,5liter volume. It is a grat driver but you need a sub/bass under it. But I would use a 8" bass. A 15" is tooo big. It will not match with the sound of the Fostex.
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Old 11th April 2006, 04:17 PM   #4
punk is offline punk  Italy
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Default Re: FX120

Quote:
Originally posted by Roemhild
Hi,

I have had the FX120 in a sealed 6,5liter volume. It is a grat driver but you need a sub/bass under it. But I would use a 8" bass. A 15" is tooo big. It will not match with the sound of the Fostex.
Yes. I've built other speakers before and would agree 8" can do almost anything you want, but I don't want to buy new drivers if I don't have to. I'm sure I can get the 15" to work in the right way, my concerns would be more on directivity and speed... these thing have a small magnet and a big plastic cone.
I also must say I love the sound of big PAPER cones.

However I found this and may soon change my project:
http://jamo.com/Default.aspx?ID=2250...roductID=17723

and can't get it out of my mind !
what do you think ? are 4 eminence alpha worth a shot ?


L.
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Old 11th April 2006, 05:54 PM   #5
KCHANG is offline KCHANG  United States
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Default OB all the way!

Hi Lorenzo,

The Jamo configuration is very close to how I plan to use my FX120's, although I will use a wider baffle and without a tweeter. I have several cheap 15" subwoofer drivers for that project. I have done several speaker projects using fullrangers or widerangers on OB sitting on BR boxes, and they worked out nicely, but I still like dipolar bass better.

My FX120 drivers are still new in boxes. Nevertheless, I once helped a friend put together a pair of OB speakers, each of which used the FX120 from about 250Hz up, a 12" driver from about 250 to 100Hz, and a Dayton IB 15" woofer for the lower bass. All the drivers were mounted on a simple open baffle. Active crossover and EQ for the dipolar bass was used. Even though the system was quickly slapped together, the sound was very nice and showed a lot of potential. He moved away shortly after that so I do not know how that system sounds now. A two-way system using the FX120 on OB augmented by a woofer for dipolar bass will be simpler to build, and I'm pretty sure that such a system will sound very good. I have pretty high hope for my FX120+Woofers OB system, and would expect that system to sound quite natural and neutral.

Without knowing the parameters of your RS woofers, it is hard to tell whether they will be suitable for the OB application, but it is worth a try, although more likely than not you'll need to EQ the bass. Also, as ScottMoose said, you may want to consider using an active crossover, which will reduce the excursion of the FX120 and may make driver integration easier.

Ciao,

Kurt
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Old 11th April 2006, 09:56 PM   #6
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Default its tough...

I tried the fx 120 in BIB horns (see other forum) and the results were great. the bass speed of the fx120 is not the best though. I tend to prefer the effect of low qts on bass in general. it got quantity, but not that last air of refinement present in the midrange of the driver. so the sound in the end was less coherent than I desired. I am splitting hairs here though. none of my freinds ever knew the difference. all they thought was "geez, all that bass out of a 2.5 inch cone?" my favourite midrange out of the 120 so far was when it was in an open baffle. pretty quick but very even frequency wize

I would use a nice active EQ at 100- 130 or so hz, 9-12db roll off with a cheap 10 inch pro sound (emminence) woofer from parts express. you could run the fx120 full range (better sound) or EQed (more volume). the pro sound woofers (i think it is emminence alpha) are cheap, and the qts of the woofer is suited to OB I think. the speeds should match OK. the sound should be real big.

I saw a project to this effect a little while back on an american website. I forget the name though. shoulda wrote it down.

well, good luck.

Clark
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Old 12th April 2006, 05:33 AM   #7
punk is offline punk  Italy
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Default Re: its tough...

Quote:
Originally posted by KCHANG
Hi Lorenzo,

-cut-

A two-way system using the FX120 on OB augmented by a woofer for dipolar bass will be simpler to build, and I'm pretty sure that such a system will sound very good. I have pretty high hope for my FX120+Woofers OB system, and would expect that system to sound quite natural and neutral.

Without knowing the parameters of your RS woofers, it is hard to tell whether they will be suitable for the OB application, but it is worth a try, although more likely than not you'll need to EQ the bass.
Also, as ScottMoose said, you may want to consider using an active crossover, which will reduce the excursion of the FX120 and may make driver integration easier.

Ciao,

Kurt
Yes, I have to measure the parameters. I don't have all the equipment yet and it looks like it will be hard to get any info from radioshack.
I may sell them on ebay e save for eminence woofers, which have the high qts I need.
What is the difference in an OB between 2 and 4 woofers, in your opinion ? A great improvement?



Quote:
Originally posted by blumenco
I tried the fx 120 in BIB horns (see other forum) and the results were great. the bass speed of the fx120 is not the best though. I tend to prefer the effect of low qts on bass in general. it got quantity, but not that last air of refinement present in the midrange of the driver. so the sound in the end was less coherent than I desired. I am splitting hairs here though. none of my freinds ever knew the difference. all they thought was "geez, all that bass out of a 2.5 inch cone?" my favourite midrange out of the 120 so far was when it was in an open baffle. pretty quick but very even frequency wize

I would use a nice active EQ at 100- 130 or so hz, 9-12db roll off with a cheap 10 inch pro sound (emminence) woofer from parts express. you could run the fx120 full range (better sound) or EQed (more volume). the pro sound woofers (i think it is emminence alpha) are cheap, and the qts of the woofer is suited to OB I think. the speeds should match OK. the sound should be real big.

I saw a project to this effect a little while back on an american website. I forget the name though. shoulda wrote it down.

well, good luck.

Clark
Well, same question for you : 1 or 2 woofers per channel ? They;re not that expensive....


thanks

L.
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Old 12th April 2006, 04:33 PM   #8
KCHANG is offline KCHANG  United States
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Default Go for 8!

Hi L.:

If you have the space on the OB and are willing to spend the money on the drivers, I'd recommend using at least two woofers per side. Using two woofers instead of one would significantly reduce the excursion of each woofer, which is an important consideration for dipolar operation. It may also be an important factor when you use cheaper drivers that normally do not have much excursion capability. Also, the enhanced coupling to air at the longer wavelengths provided by the increased moving surface area may also reduce the bass boost needed.

In my main speaker system, which uses 75" line-source drivers from 180Hz up, I have four 18" woofers on OB on each side for dipolar bass. The 8 woofers together provide a large total moving surface area, and the drivers are barely visibly moving even when playing japanese drum music at a floor-shaking level.

As to the Eminence Alpha drivers, if you are referring to the 15" one, I'd not choose it for OB, mainly because of its highish Fs. This may not be a problem for you, however, if you intend to use a separate subwoofer for the deep bass. Its Xmax is not very impressive, but might be OK if you use two or more drivers. Also, its Qts is quite hight. I don't like high-Q drivers in general, and prefer to use a driver of a lower Qts (but >0.4) and EQ it to get the bass right. You may want to consider the Dayton IB 385-8 15" woofer (PE295-455), which is great for OB, with its Fs of 20.8Hz, Qts of 0.65, and Xmax of 14.3mm, and a price of $110 each when you buy 4. One of this driver will equal 3 or 4 of the Eminence Alpha 15" in terms of excursion and will give almost one octave more bass extension.

Kurt
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Old 12th April 2006, 06:39 PM   #9
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Default geez,

well, kchang, it sounds like you have a very seriously dynamic system... that is awesome. I have a few horn subs with 18s in them. they will rock a partay.

I was only referring to the 10 inch alpha. it is like 40 bucks or so. i guess you could use two per side. i personally would be happy with just one per side though. i guess it depends on room/ preference.

clark
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Old 12th April 2006, 09:12 PM   #10
KCHANG is offline KCHANG  United States
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Default Horn subs!

Hi Clark,

What's the design of your horn subs with18 inchers? How low do they go? I bought four Eminence LAB-12 drivers with the intent to build two LAB horns, but those drivers have been sitting there gathering dust for almost 3 years. Too many projects, too many drivers too try, and too little time!

I've heard Dr. Edgar's Titan system several times, and I think the ability of the eight 18" dipolar woofers to move air is close to that of the Seismic sub. Don't know about the dynamics. To me, if a flute sounds like a flute through the system, I'm happy. How often do people say: "Boy, that flute sounds so dynamic!"?

Kurt
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