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Old 31st January 2008, 06:33 AM   #1
nebojsa is offline nebojsa  United States
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Default css fr125 monopole

Hi Guys, I am pretty new to speakers and design...yup it's trully a healthy addiction. I've been reading it daily for the last 10 months. I have couple of questions rergarding Css Fr125 driver and available designs for this driver. Is there a monople design for this driver, a tower, ofcours? I've seen Jim Griffin bipole, was it actually designed for a single woofer? What would be dimensions for monople tower? The same as Jim Griffin design? Should a tweeter be added or CSS is sufficient? And lastly, what is the difference between FR and WR version? Thank you guys. Love reading all of your posts, very stimulating.
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Old 31st January 2008, 04:17 PM   #2
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Hello from 2 hours north.

There are so many designs for that driver I don't know where to start.

The FR does not need a tweeter for most ears. The WR does. The difference is the FR covers the highs a little better and the WR the lows. I use 2 WR's and a helper tweeter in the Calhoun. Scottmoose and planet10 did the design and drawing, I banged it together. It's just plywood for now, perhaps a finish later. Does the cabinets size matter? I understand those two are doing a half version for a single driver. It's a simple build.
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Old 31st January 2008, 04:17 PM   #3
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Old 31st January 2008, 04:41 PM   #4
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Cal, those look really great! Enjoy them. You can tell your friends how there is an elaborate maze of wood beneath the skin and that it is a difficult to build back horn of Japanese old world design.

Or you can tell them it is a modern BVR that is pretty easy to build.

I love the way those look.

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Old 31st January 2008, 11:01 PM   #5
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They sound pretty good too...

Yes a half version of both a single and a double and a double mouth for a single should come together.

Jim Griffins bipole, is actually the ML-TL GM designed for a single driver, so one could build it as is for a single driver, or half the cross-section, and use a port with half the cross-section. There is also Tim Forman's twin driver ML-TL. Again you'd halve the cross-section and halve the port.

The hard part of doing a box for the FR125 (or WR) is to get the bass under control. I haven't heard Jim's but the version we did of Tim's can get a bit out of control -- an amplifier with low output impedance is absolutly required. Even the miniOnken can loose control and adding foam to the port is more a requirement than an option. This had had us gravitiating towards the smaller boxes, but Cal's Calhouns were a real eye-opener ... these things can rock -- i think even Cal, head banger that he is, was pleasantly surprised once they had a chance to warm up after an extended period of storage.

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Old 1st February 2008, 01:23 AM   #6
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Dave,

You said:

"Jim Griffin's bipole, is actually the ML-TL GM designed for a single driver, so one could build it as is for a single driver, or half the cross-section, and use a port with half the cross-section."

That is not correct. I reran Martin's spreadsheets before releasing the bipole design so the cross-section is appropriate to two drivers in the box.

You can, as you say, half the cross-section area and change the port to convert to a single driver in the box.

-----------------------------------------

Nebojsa,

Frankly, I would not necessarily suggest a monopolar design with just one FR125S unless you can push the box close the wall behind it. That alleviates the 2 pi to 4 pi radiation spreading effect which normally causes you to need baffle step compensation.

For my listening the approximately 86 dB SPL sensitivity rating for just a single driver is adequate only if a baffle step compensation network is used. With a conventional BSC network you would have only an 80 dB SPL sensitivity for the monopolar configuration . 80 dB sensitivity is too low for me.

Other ways to maintain the sensitivity around 86 dB sensitivity is to devising alternatives to reduce or eliminate the baffle step comp is suggested.

The bipolar arrangement acoustically achieves 86 dB sensitivity.

One can also work around the low sensitivity issue by using a 1.5 way configuration (here the two driver box plan will work just fine) and roll the second driver off with an inductor at the baffle step corner frequency. You'll yield essentially a 86 dB SPL acoustical sensitivity.

Another way to address the baffle step concern is to do the BSC at the line level (assumes you have access to the preamp top amp connection in the electronics chain).


Jim
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Old 1st February 2008, 02:09 AM   #7
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Quote:
Originally posted by Jim Griffin
"Jim Griffin's bipole, is actually the ML-TL GM designed for a single driver, so one could build it as is for a single driver, or half the cross-section, and use a port with half the cross-section."

That is not correct. I reran Martin's spreadsheets before releasing the bipole design so the cross-section is appropriate to two drivers in the box.
Jim,

We have been over this before... when you 1st presented this design you said it was based on GMs ML-TL. I checked with him and he had intended it for a single driver. Real-world measurements you provided showed that this was not an issue. IIRC the MJK sim came after the fact.

I have made a similar same mis-step and have it turn out just fine, putting a single FE127 into the bipole diyRef bipole.

That iboth rhese instances worked well shows how tolerent an ML-TL can be.

dave
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Old 1st February 2008, 05:16 AM   #8
nebojsa is offline nebojsa  United States
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Dave, Cal and Jim thank you very much for your responses. Yes Cal we live in the same coridor of perpetual rain and gloom and only music can alleviate that pain.... and yes coffee too, a non prescription drug in Seattle. So, its sounds that is possible to use single driver with same dimensions. I have been looking at all possibilities, different drivers and enclosure shapes. Yes, to my wife's smirk and laughter, I take too long to buy just about anything. The mantra is research, research, research. Furthermore this would be my first project.

Jim, I have noticed that you have shown on a recent DIY exibition a small, thin floorstander, with TB driver and Audax tweeter, do you have more info?

Dave, you mentioned Tim's design which I have taken a peak at. Looks nice. Would you suggest the same tweeter or without it?

Dave, I also like the current post by ecir38 and his fonkens, I tend to like a bit more bass, do fonkens integrate easliy with subwoofers and what diy subwoofer, if any, have you heard it with or would you recomend?

I appriciate your time, thank you again.
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Old 1st February 2008, 05:26 AM   #9
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Quote:
Originally posted by nebojsa
you mentioned Tim's design which I have taken a peak at. Looks nice. Would you suggest the same tweeter or without it?
We used tweeter with WR, no tweeter with FR.

Quote:
I also like the current post by ecir38 and his fonkens, I tend to like a bit more bass, do fonkens integrate easliy with subwoofers and what diy subwoofer, if any, have you heard it with or would you recomend?
The FS Fonken Mk II? We are working on woofer(s) for all the Fonkens. The SDX7 in a 14 litre sealed box with a tad of LF boost seems to work well as a 1st try. We are still working on XO details (the 1st plate amp was a bit of a bust. (Keiga 2.1)

dave
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Old 1st February 2008, 12:32 PM   #10
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"Frankly, I would not necessarily suggest a monopolar design with just one FR125S unless you can push the box close the wall behind it. That alleviates the 2 pi to 4 pi radiation spreading effect which normally causes you to need baffle step compensation.

For my listening the approximately 86 dB SPL sensitivity rating for just a single driver is adequate only if a baffle step compensation network is used. With a conventional BSC network you would have only an 80 dB SPL sensitivity for the monopolar configuration 80 dB sensitivity is too low for me.

Other ways to maintain the sensitivity around 86 dB sensitivity is to devising alternatives to reduce or eliminate the baffle step comp is suggested."



I don't know the formulae, but is this a good idea:
. . a roundover done with a router bit can only be yea big (1.5 inch/ 35 mm radius?), effective at combating baffle edge diffraction, only down to a certain Hz. I can't recall the exact relationship, anyone know it off the top of their head?

Here's a great idea I just saw in a sub. This guy bought pre-curved plywood "rounds" ($$?):
http://www.hometheatershack.com/foru...ity-kappa-vq-\
build-plans.html#post72276 (3 pics)

For a css *r125 box or other box covering the midrange, instead use Sonotube cut into quarters:

Visually, if you're going to paint the boxes it'll be ok, or have a color contrast with timber sides & front.
Sonically, with Sonotube diameter of say 10 or 12 inch, you lower the Hz at which baffle edge diffraction becomes problematic.

Also with sufficient diameter Sonotube quarters, you end up with a much wider speaker (that you'd probably build correspondingly less deep), eliminating or at least reducing the need for BSC and the loss of efficiency

Any value?
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