This is the closest I came to a full range speaker project. I had 4 Fostex FX120 drivers (which are not inexpensive) that needed a home. The plan for the boxes came with the drivers; there’s a small ported box inside, which directs sound into a larger chamber (above speaker in photo).
No complaints about the bass, it’s pretty good, especially with all 4, more than you would expect. The midrange was too predominate, hence the mock up crossover and tweeter.
The question here, what was I doing wrong, even my rudimentary crossover & tweeter sounded much better than the speaker by themselves.
Where did I go wrong? The wrong application?
*For the 12db crossover, I found a site where you plug in the speaker values and hit enter; coils, caps and diagram is shown. I did try/experiment a few times.
No complaints about the bass, it’s pretty good, especially with all 4, more than you would expect. The midrange was too predominate, hence the mock up crossover and tweeter.
The question here, what was I doing wrong, even my rudimentary crossover & tweeter sounded much better than the speaker by themselves.
Where did I go wrong? The wrong application?
*For the 12db crossover, I found a site where you plug in the speaker values and hit enter; coils, caps and diagram is shown. I did try/experiment a few times.
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a few thoughts:
I wouldn't be a bit surprised if the enclosure plans accompanying the drivers did (can) not deliver balanced and extended low frequency performance, thereby "exaggerating" the mid-range, which many folks find a bit forward on all Fostex Full-rangers to start with. You might well be more sensitive than other folks to areas in which the wide metal dome "dust cap" could be at its worst.
Driver break-in - several hundred hours has come to be considered a basic requirement with full-rangers - Fostex in particular - before assessing tonal balance and dynamics.
Listening distance / room modes?
I have heard the FX120 in an enclosure quite different from the (assumed DBR) "factory" design, and while a single per enclosure of most 4.5" drivers can't be expected to lift heavy below 50Hz, they weren't particularly thin or misbalanced.
Currently priced at $125 ea, I wouldn't consider them inexpensive either, and you definitely want to find the right application.
Yes very pricey. The cones are super light and they do seem to react faster then other speakers that I have.
The box is some kind of dual chamber design; the bass is enhanced in the larger chamber. It does work to a degree, all 4 together sounds like an 8” DJ speaker.
I though they may be for an infinite baffle speaker or designed for an information kiosk (and why I bought them in the first place).
I was curious if they would be more balanced a “huge” box?
Maybe a tube amp? (Which I don’t have)
The box is some kind of dual chamber design; the bass is enhanced in the larger chamber. It does work to a degree, all 4 together sounds like an 8” DJ speaker.
I though they may be for an infinite baffle speaker or designed for an information kiosk (and why I bought them in the first place).
I was curious if they would be more balanced a “huge” box?
Maybe a tube amp? (Which I don’t have)
I have a suggestion. Why don't you turn one pair of drivers around to face the back, to simulate a bipole. This just might balance out the sound, but just be sure you have enough space behind the drivers for them to breathe. Secondly, having two full range drivers side by side like that is probably resulting in comb filtering at the high end, prompting the addition of the tweeter. If that's true then you might not need the tweeter at all in this configuration.
edit: you have the speakers against the wall right now, so I understand that bipole is probably not going to be a permanent solution for you. But it should approximate the balance of the sound if you incorporate a BSC filter, or roll off one driver to make a 1.5 way.
edit: you have the speakers against the wall right now, so I understand that bipole is probably not going to be a permanent solution for you. But it should approximate the balance of the sound if you incorporate a BSC filter, or roll off one driver to make a 1.5 way.
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If your listening space permits, I would stack the speakers; driver ends closest to each other. Then listen. There might be favorable cancellation that might tone down the treble. If not, then I would stick a 75mf cap in parallel with the bottom drivers and see how that sounds.
Otherwise, I would turn the speaker into a two-way.
Otherwise, I would turn the speaker into a two-way.
Very nice, thanks! It looks like the front baffle and blue sides – slide out of the outer box ( I guess they can be trimed for tuning.
Looks like somthing I'd like to build.
I thought there may be some type of notch filter for the middle range, just don’t know where to begin.
Looks like somthing I'd like to build.
I thought there may be some type of notch filter for the middle range, just don’t know where to begin.
nope, those colours are just to highlight the different layers of material and delineate the extent of slot ports - dimensions of slots / spacers are calculated for specific driver's T/S parameters - everything is very tightly glued up
Well, as many builders of this design other than myself will attest, these are not a particularly simple build - definitely not as easy as any of the several Fostex factory designs I've completed.
They can sound quite wonderful though.
If you can run the front end of the system on a computer, it should be relatively easy to find a simple EQ plug-in - absent the wherewithal or interest to make detailed in-room measures, you could even tune by ear.
That box doesn’t look too completed, similar to a slot port, but there are two - on the sides.
The cab shown were super quick mock ups with scrap wood, only took 1 ½ - 2 hours (per pair). With some experimenting, I ended up using one thick pieces of square foam; with a large hole, right behind the speaker.
I built the one pair and there wasn’t much to like, with the second pair, at least I was getting some bass. I’m sure they are high performance woofers, but need something to soften the middle, or increse the low end.
The cab shown were super quick mock ups with scrap wood, only took 1 ½ - 2 hours (per pair). With some experimenting, I ended up using one thick pieces of square foam; with a large hole, right behind the speaker.
I built the one pair and there wasn’t much to like, with the second pair, at least I was getting some bass. I’m sure they are high performance woofers, but need something to soften the middle, or increse the low end.
The FR of the FX120 is pretty flat but that measurement is taken with it mounted on an IEC infinite baffle. When the driver is mounted in a box, there will be less bass, resulting in a rising mid response.
A Baffle Step Compensation (BSC) Network is required to even out the FR. Martin King has a good article for this correction. Click for MK BSC
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well, look a little closer - it's actually 3 slots per side - and there's more to this design than a cursory glance might reveal
Are you referring to internal damping scheme on the DBR enclosures in your first photo? That might be contributing to the lackluster bass performance.
Of all its merits, I wouldn't describe the FX120 (or F120A ) as high performance woofers - BSC, bipole configuration, digital EQ etc notwithstanding, there will be an ultimate limitation of bass response.
The article was good, a bit over my understanding. I could assemble the circuit with out problems, have lots of crossover parts here, also good at winding and checking coil values; however, I would need a more basic diagram.
The woofer seems popular; I’m curious if there a previous thread or a circuit board schematic available for a BSC circuit for the FX 120.
The woofer seems popular; I’m curious if there a previous thread or a circuit board schematic available for a BSC circuit for the FX 120.
I was trying to give the little some woofer credit, actually they sound pretty good with selected music, but not so nice with a wider/full selection. So I’m thinking there is potential.
As it is sitting, there is a concealed bottom chamber, very small, almost square, it has a 10mm slot port into the larger section of the box. I only put 1 piece of foam in the smaller chamber.
The tall box does enhance the bass, if you heard all 4, with carefully selected music, they are a wow![/SIZE] [/FONT]
As it is sitting, there is a concealed bottom chamber, very small, almost square, it has a 10mm slot port into the larger section of the box. I only put 1 piece of foam in the smaller chamber.
The tall box does enhance the bass, if you heard all 4, with carefully selected music, they are a wow![/SIZE] [/FONT]
The schema in the article is as basic as it gets. I would consider the Zobel optional and leave it out unless the LR addition ended up affecting the top end as well
dave
I think a BSC circuit is one of the easiest things to design yourself, based upon the width of the baffle. Here are two examples, but keep in mind that these are meant for these particular speakers and not yours:
Fostex FX120 DIY ML-TQWT (Transmission Line) Speaker Project
Fostex FX120 DIY Bass Reflex Bookshelf Speakers
I'm curious: did you take note of my suggestion to turn one pair of boxes around?
These are both well documented projects - being familiar with the Parts Express boxes used in the smaller B, I'd be inclined towards the TL myself - all the math has been done. But I would recommend good quality plywood - $250 worth of drivers per monopole pair deserve better than MDF.
As chaz notes, the calculation of simple BSC is far less complicated than MJK's paper would suggest.
if I had two pairs of FX120 my project of choice would be that MLTL, expanded for two drivers per side, with the bottom driver rolled off at baffle step to make a 1.5 way.
With just one pair, my project of choice would be an OB with a 15" woofer. 😎
BTW here's an online calculator for BSC: http://diyaudioprojects.com/Technical/Baffle-Step-Correction-Circuit-Calculator/
With just one pair, my project of choice would be an OB with a 15" woofer. 😎
BTW here's an online calculator for BSC: http://diyaudioprojects.com/Technical/Baffle-Step-Correction-Circuit-Calculator/
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I was thinking of a micro-tower clone, with one driver facing up, or a standard bipole config.
jeff
1st T-Line project.
Chazdrumzalot, Thanks, exactly what I was looking for (I think….I have FX120’s).
I see now how easy the BSC circuit is, just needed a pic and a simple diagram.
I’m more of a carpenter/cabinetmaker/electrician; and only have limited experience with passive crossovers. That said, I have a drawer full of 14 gauge perfect lay coils, larger then .82, I can unwind them. A electrical engineer friend showed me how to measure them, I did get pretty efficient at that; made up a chart, so no need for a calculator.
The other boxes: I dabbed glue on them, so they are tacked together. I think I could break them apart, but gave up on them in general. But might as well try the BSC circuit on them.
So again (sorry) am I missing something, I have FX 120s?
Thanks again!
Chazdrumzalot, Thanks, exactly what I was looking for (I think….I have FX120’s).
I see now how easy the BSC circuit is, just needed a pic and a simple diagram.
I’m more of a carpenter/cabinetmaker/electrician; and only have limited experience with passive crossovers. That said, I have a drawer full of 14 gauge perfect lay coils, larger then .82, I can unwind them. A electrical engineer friend showed me how to measure them, I did get pretty efficient at that; made up a chart, so no need for a calculator.
The other boxes: I dabbed glue on them, so they are tacked together. I think I could break them apart, but gave up on them in general. But might as well try the BSC circuit on them.
So again (sorry) am I missing something, I have FX 120s?
Thanks again!
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