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Old 4th October 2011, 02:41 PM   #1
ODougbo is offline ODougbo  United States
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Default Great Bass with FX 120

It took an extra pair of cabinets (4), but very happy with the results. The bass is very nice, punchy and very natural sounding. No equipment to measure with here (other than generator), but the bass is impressive down to 30hz – 25hz.

There was way too much mid range overlap without mid/treb reduction for rear pair of speakers, so I connected a huge pair of iron core coils (to the rear pair), the bass was noticeably rubbery; replaced them with a large pair of Air Core (shown). Both set have been lying around for a while and the value (stickers) are worn away. However, with a/b testing with the coil shown: roll off starts at 300hz – 350hz.

I don’t know what’s going on with the BSC, not doing anything as far as I can tell, again simple a/b testing and there is no noticeable difference. The middle is not bad, however I would like to experiment with the BSC. Shown is a .9 coil and .47 resistor, connected to the front facing pair.

Any advice would be helpful?

*The cabinet plans came with the Fostex speakers, the top section has 3 sound damping techniques, light coat of rubber spay (let dry for a week), standard white wool and 1” square foam block.
Attached Images
File Type: jpg FX Front 1.JPG (118.5 KB, 364 views)
File Type: jpg SPK in back 1.JPG (159.1 KB, 350 views)
File Type: jpg BSC and coil.JPG (136.5 KB, 336 views)
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Old 4th October 2011, 09:38 PM   #2
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Up the resistor value: it has to be comparable to the voice coil's impedance to give any significant attenuation.

Actually, if you've already low-passed in the rear drivers, there shouldn't be much need for BSC, as the addition of extra drivers for the lower frequencies will counteract the baffle step problem.
If you disconnect the BSC circuit altogether, how does it sound?

Chris
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Old 4th October 2011, 10:54 PM   #3
ODougbo is offline ODougbo  United States
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Thanks; raise the resistor value, that’s the answer I was looking for. I didn’t remove the BSC, just used clip leads around them it, that should bypass them. I don’t have any complaints about the mid, just wanted to experiment.

The bass is impressive, like an 8” ported subwoofer, there were things vibrating around the room at different low frequencies, quite amazing for such a small driver (right side only, with generator).

The folks that heard them today were impressed; they do have a pleasant tone, natural sound.

Btw, these are prototypes, probably never move them. I’m going to start micro towers tomorrow (pair); I don’t think it will take long to build now that I have a good idea what to do (same plan, just stacked, 55” tall boxes).

Thanks for the link ;-)

microTower-maps

Last edited by ODougbo; 4th October 2011 at 11:13 PM.
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Old 5th October 2011, 02:34 PM   #4
Greg B is offline Greg B  United States
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Cool. I would also suggest that you lose the BSC on the front driver/box. You don't technically need BSC with a rear driver.

Filter only the back. I suggest using both a zobel network and a series coil on the rear driver, if the mids/treble is still tilted up. The coil can't really work properly unless the impedance is flattened by the zobel.

Because it is mounted rear facing, make certain that the connections of the rear driver are reversed: + goes to - and vice versa. If connected otherwise, you have made very complicated open baffle.
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Old 5th October 2011, 02:53 PM   #5
ODougbo is offline ODougbo  United States
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Thanks Greg,
I started the 55.5” tall pair, so far so good, putting both ports in the back; it’s going to have some cool factor. [The front will only have one 4” diver]
Okay, will remove the BSC, didn’t think it was doing much anyway.
I was wondering about the huge coils (probably 4.0mh) I ran in series (for the rear pair) it seemed too easy. Also guessed that with all the coils, somehow it might diminish the treble.
My only “complaint” about the sound is the high end; they just don’t have the open air sound like a 1” dome tweeter. However, that said they do sound bigger than life, way bigger then a pair of 4” drivers.
zobel network….I’m 99% workworker AND good at guessing the rest. lol
* Yes, did end up wiring the back pair in reverse, the speakers move together.
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Old 5th October 2011, 03:01 PM   #6
Greg B is offline Greg B  United States
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Not having any filtering on the front driver may well clear up the treble. Resistor and coil quality can have a big impact on the sound. If there not there, it's not an issue.

Well, yeah, the idea of a BSC coil in series is to roll off the treble (and upper mids). 4.0mH isn't really out of line. As a WAG I'd say 2.0- 2.5mH is big enough. Especially with a zobel

Zobel Calculator
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Old 5th October 2011, 04:23 PM   #7
ODougbo is offline ODougbo  United States
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Thanks, won’t have to guess now…….. I’m assuming the 4.0 coil(s) are right off the amp, then the zoble across the speaker?
I may also bi amp, but would like to keep it simple and use one amp – btw, It doesn’t take much to drive these speakers. FX120(s) are 8ohm, so 4ohm total. The amp has a A/b switch, which is making life easier.
Thanks again.
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Old 6th October 2011, 11:48 AM   #8
ODougbo is offline ODougbo  United States
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Greg, I see now; after the coil, which I'll have to measure.

Here's a pic of the 55" towers underway (Medex board).

The pic (top down) is front baffle, front of box (no baffle) and back view. It looks more complicated than it is, basically two boxes stacked.
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File Type: jpg Micro-4.jpg (17.1 KB, 165 views)
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Old 7th October 2011, 05:41 AM   #9
Greg B is offline Greg B  United States
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Yeah, zobel goes across the driver terminals, think of it as part of the driver. The coil is traditionally in series with the plus, but it could be in series with the ground, it doesn't matter.

You may want to try facing both drivers the same way, just for kicks. It may or may not sound better.

What amplifier did you end up using? I concur with other opinions that a lower power gainclone or tube amplifier is the best bet. The FX120's big brother the FX200 I found rather unforgiving of signal chain quality, and I suspect the 5" version has the same tendencies.
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Old 7th October 2011, 11:53 AM   #10
ODougbo is offline ODougbo  United States
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Experimenting with different amps, been trying a few, I don’t have any good quality -low power - amps, only “black boxes”, that said, I do have a Nakamichi receiver a neighbor passed along when he moved; when I tested it a year ago, it had a nice “soft sound”.

I ended up cutting the front woofer holes 4” and the back 4.5” so I would need an adapter plate to insert the back speakers in “normally”. The idea was to attenuate the treble into the damping material.

I measured the large air coil inductors (shown), they are 5.6mh, also found a pair 6.5mh iron core; the plan is to experiment with a push button switch and listen to the roll off, then order the parts for a zoble.

The cabs are going good, wrapped them in white birch veneer yesterday, ordering red dye for finishing.

Last edited by ODougbo; 7th October 2011 at 12:12 PM.
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