Fostex FF125K 4.5" speaker - diyAudio
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Old 19th April 2005, 04:53 AM   #1
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Question Fostex FF125K 4.5" speaker

I am going to be building some transmission line stereo cabinets soon and I am looking for advice on some mid range speakers. The crossover points will be 160 HZ and 3,000 HZ. I have a budget that I am working with and do not want to spend more than about $40 to $45 for each mid range unit. I have seen in the Madisound catalog that there is a nice Fostex speaker, model
number FF125K. It is a 4.5" unit that is 8 ohms, has a 92 db spl,
and is rated at 50 watts (peak, I think). It has a free air resonance of 72 HZ. The freq graph looks pretty flat from 150 HZ
to 3,500 HZ. This is a full range speaker, but it fits into my price range and I like the freq graph for the crossover points that I will be using.

Does anybody have any suggestions for other mid range units that I could use that are within my design and price limits ?

Thanks ! !
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Old 19th April 2005, 08:42 AM   #2
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The best midrange is often a FR... the FE103 was what 1st came to my mind, the FF125K gets less exposure, but what i have seen has all been positive.

What are the other drivers?

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Old 19th April 2005, 05:42 PM   #3
Greg B is offline Greg B  United States
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I had a pair of the older made in japan FF125. They make very good high resolution midranges in a 3 way, and are one of the best bangs for bucks in the fostex line IMO. I think i like the mids a bit more in the FE108EZ, but the freq extremes might actually be a bit better with the cheaper FF. Both are sweet and musical. It'd sound harsh with SS probably.

HOWEVER, this is a horn driver, and as such it has rising response that you will need to deal with. My lowpass ended up looking more like 3rd order with a damping resistor on the shunt. It's not going to be 92db all the way down to 150hz unless horn loaded. I would actually cross it higher and use a clean midbass/woofer for maximum efficiency. I ended up using a 3500 crossover point, but for best integration I glued a felt disk over the metal dustcap. It was also very good run stock, with a piezo supertweeter crossed in very high. Makes a good full range too, with a cheap highish DCR small gauge aircore choke to flatten the response.

GB
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Old 20th April 2005, 06:28 AM   #4
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Thank you for your thoughts and ideas. I have a pair of titanium tweeters that I bought at MCM Electronics, part number 53-530.
I will also consider the Dayton planar tweeter that costs about
$29 in the Parts Express catalog. I will cross the tweeters over at 3 or 3.5 K using a 12 or 18 db unit. I will build a separate box for the mid range, tweeter and crossover, so that I can experiment a bit.

The woofer is a 10" unit. I am lacking on the thiel parameters for the unit. About all that I know is, it is 8 ohms, has a free air res
of about 35 or 40 HZ, has a 2" voice coil, big magnet, and is rated to handle 370 watts peak power. It has a treated accordian cloth suspension, and the cone is ribbed. The spyder is a large diameter type. It has a cast aluminum basket. The unit is made in Guangzhou, China, by the Ming Hua Mfg. Co. I bought it in 2003 during a visit to Shenzhen.

After more thought, research and advice, I will build a pair of transmission line cabinets for the woofers. The quarter wave line length of a 38 -40 HZ wave should be about 7.5 feet. The classical design is what I am leaning toward, with a tapered line and a slot at the end. I may experiment using a block of wood to seal the slot, and also place a bass reflex tube in the block of wood, to try and fine tune the enclosure. I will only let the woofer go up to about 150 or 160 HZ, and then cross it over to the Fostex FF125 K unit. I am hoping that the TL line will go down to 30 HZ accurately and cleanly, perhaps lower.

Back in 1980 I actually built two pair of TL cabinets for my stereo system. The first pair used 10" woofers with a slot at the end. The second pair used 12" woofers and passive radiators at the end of the line. Both were pretty good considering the era back then. And considering that I had not the slightest idea what I was doing. However, I am pretty good at working with wood, as I have built many cabinets in the past for my electric guitar and various stereo setups.

Another question is this: Is MDF really sonically better than 3/4 inch marine plywood ? Almost all of the cabinets that I have built in the past have been with high grade plywood. Perhaps the TL cabinets should be MDF ? Your thoughts and ideas please.

Any thoughts and ideas regarding the classic TL would be appreciated, thanks.
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Old 20th April 2005, 07:46 AM   #5
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Quote:
Originally posted by barth2102 Another question is this: Is MDF really sonically better than 3/4 inch marine plywood ?
MDF is only cheaper... not better. Usually you hear the question the other way.... is plywood better than MDF? The answer to that is, usually it is.

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Old 20th April 2005, 07:50 AM   #6
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Quote:
Originally posted by barth2102
Any thoughts and ideas regarding the classic TL would be appreciated
Classic lines are more often than not, less than optimal... measuring the T/S of your bass drivers would give you a real edge on getting the most out of them. If you do just wing it, start the line at, say, 3 Sd, and offset the driver (the ratio in the MJK tables would be what i'd choose)

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Old 20th April 2005, 05:56 PM   #7
Greg B is offline Greg B  United States
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That's for sure. There is no point in torturing yourself anymore with ROT cut and try methods for TL design IMO. See Martin King's website and read everything would be my advice. If you must, a moderate Qts driver will typically work OK in a classic TL, though it's better to have a bit higher Qms than is normal for sealed box type drivers. Just a warning - I cut up lots of failed TLs in the bad old days.

Those drivers may be OK, but I wouldn't hesitate to use the fostex can hold it's own with much more expensive types. It may be better sounding without a tweeter. The TL's I built using the FF125 as a mid used a focal 10W something for the woofer. I crossed the mid at about 650 and 3600hz first order (acoustically).

Between the crossover and winging it on the TL, this project may be a bit of a challenge.

GB
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Old 21st April 2005, 05:00 AM   #8
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I want to thank you all for your thoughts and ideas. Okay, so I need to measure the woofer to get the thiel parameters. I have no test equipment and no knowledge of how to do this. Please recommend a good starting point for this, such as reading material and perhaps test equipment. I am within a few hours drive of Seattle. Is there any place that I can go in Seattle to have this test done ?

I think that the 10" woofer that I may use is a pro sound unit, not really intended for hi-fi use. But if it has decent spl and will go to 30 HZ cleanly, I would like to use it. I also have some aluminum cone 10" woofers from MCM. They have a fs of 34 HZ, and I do have all the thiel parameter specs on them. If both pair of units are at all close in the specs, I would like to experiment with them
to see which pair sound best.

If a classic TL is not optimum, can anyone suggest a more efficient TL design ?

In my next reply, I will try to attach a picture of the 10" pro driver from China. I have a bunch of other drivers from China, with aluminum magnesium cones like the hi-vi units, but I have no thiel
specs on these units either .

thanks again everyone !
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Old 21st April 2005, 05:30 AM   #9
Greg B is offline Greg B  United States
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It's actually a lot easier to test T/S parameters than you might think. I know there's an online tutorial or two somewhere. Perhaps someone will chime in. All you really need is a multimeter and a couple resistors. You can use your computer for a signal generator.

Which MCM drivers do you have? The cheap MI drivers they sell are fairly well suited to 'classic' TLs.

GB
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Old 21st April 2005, 06:49 AM   #10
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Here is the technique i use (but hopefully not for long -- FuzzMeasure should have T/S generation really soon now).

http://www.diysubwoofers.org/measure.htm

dave
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