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.
 
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.
 

Attachments

  • img_0461.jpg
    img_0461.jpg
    47.9 KB · Views: 578
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.

dave
 
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
 
Jim Griffin 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.

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
 
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.
 
nebojsa said:
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.

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
 

otto88

Member
2007-12-05 10:39 am
"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/forums/diy-subwoofers/8190-12-infinity-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?
 
Otto,

Concerning baffle step: Rounding over the edge of the box isn't a baffle step effect. Plus widening the baffle will not totally eliminate the baffle step response. Baffle step is not a diffraction effect. A wider baffle lowers the baffle step corner frequency but doesn't eliminate the spreading effect until you reach the limit of an infinite baffle.

Jim
 
otto88 said:
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 nice thing about the Calhouns is the side driver acts like BSC. The XO is nice as well. Because of the configuration, all that was needed was a little cap and some tweeter padding. The WR's run full so the efficiency is as good as you'll get. It's also adaptable to your room with the boxes being mirror image, you can place the side drivers in or out depending on the distance between them. Makes for interesting imaging.
 
Jim Griffin said:
Baffle step is not a diffraction effect.

Actually it is... but as the frequency of interest becomes "large" in relation to the onject it is diffracting around its manifestation changes. At high frequencies vrs low frequencies the difference in manifestation is large enuff to consider them as different kinds of events. If one looks at the "diffraction" as ones goes from HF to LF you have a continuous transition. This is one of the less discussed issues with using a filter to compensate for BS -- it does not effect the diffraction ripple imposed on top of the step. The ripple signiture is dependent on the baffle shape.

dave
 
Neboja said in an earlier reply on this thread:

"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?"

I suggest that you read this reply and the rest of the thread on the Parts Express forum at:

http://www.pesupport.com/cgi-bin/config.pl?read=387677

There is a photo of the "Smart as a Fence Post" at:

http://www.tgdrums.linaeum.com/lexdiy07/image/projects/Smart_as_a_Fencepost.jpg

The design can be used with only minor changes with most of the Tang Band 3" drivers and can work with just the T-B driver broadband without the crossover and tweeter. You would likely need baffle step comp if you choose to just use the T-B driver full range. I hear that the small Audax tweeter is no longer available at Parts Express but you can perhaps locate one elsewhere.

For the enclosure you can use the Lowe's version (4" x 4" x 42" dimensions) of the composite fence post. The composite fence post makes a quick enclosure with just the addition of end caps.

The TABAQ MLTL design (use the search button) on the DIYaudio forum is similar but uses a custom enclosure.

Jim
 

otto88

Member
2007-12-05 10:39 am
Jim,

Thank you, though I was trying to address two separate things triggered by baffles, edge diffraction and the baffle step.

When I suggested they might be eliminated I was over optimistic . . but would a quarter of a circle (diameter say 12 inch), or possibly a third of a circle, on two sides assist with reducing either "problem"?

The Calhouns seem like a great design. I have a pair of enabled 125s on the slow boat to here, but I'm trying to get by with a single 125 a side, up to about 15 litres.


Dave,

In my situation which design would you suggest?

Do you think the large corner rounds idea has much sonic merit for this or other drivers?

In particular the enabled FF85s that arrived recently. (Modelling the FF85s with their TS that you measured, I find a sweet spot in a BR about 3.4 - 3.7 litres, that I'm pretty set on).

I was about to proceed with a narrow 125 mm wide baffle and a deep box, then I thought the big round overs (as I posted above) would help? Otherwise a scaled fonken, what do you think?

Thank you both
 
otto88 said:
The Calhouns seem like a great design. I have a pair of enabled 125s on the slow boat to here, but I'm trying to get by with a single 125 a side, up to about 15 litres.

Scott has sent me data for some more Calhoun variants, single mouth & single driver


in particular the enabled FF85s that arrived recently. (Modelling the FF85s with their TS that you measured, I find a sweet spot in a BR about 3.4 - 3.7 litres, that I'm pretty set on).

The design brief for µFonken was "as small as possibble". Bigger boxes should be explored. Go for it

dave