Hi Kofi,
I've been pluggin' away in Mathcad with Martin Kings' totally awesome worksheets. Using numbers derived from the plans I posted earlier, I found that one of them actually works pretty good (BS-25). It does need a ~3-8 ohm series resistor to flatten out the midbass (I used 4 ohms in the simulation).
Here are some dimensions for you:
(inside dimensions)
18.5" tall
10.6"d x 10.6"w
driver centered on the front
port: 4" dia 7.5-8" long
stuff to taste - it should work fine without stuffing
Here are some screencaps of the worksheets (ported.mcd). I also used the 'excelsub.xls' excel spreadsheet as a sanity-check to make sure everything was working correctly.
http://furtive.us/images/speaker/ff225k_freq.gif
http://furtive.us/images/speaker/ff225k_imp.gif
http://furtive.us/images/speaker/setup.gif
http://furtive.us/images/speaker/excelsub_freq.gif
I also did some simulations of the BIB pipes; the response looks terrible as expected, so they'll probably sound great! BTW, I have built the BIB pipes loaded with some RS-1354 drivers. They do work suprisingly well!
To Scottmoose: The 'stock' size pipes seem to sim better than the larger ones you suggested. I didn't run a whole lot of variables, though, as the only windows machine I have is a Pentium 166 circa '96!
-Hans
I've been pluggin' away in Mathcad with Martin Kings' totally awesome worksheets. Using numbers derived from the plans I posted earlier, I found that one of them actually works pretty good (BS-25). It does need a ~3-8 ohm series resistor to flatten out the midbass (I used 4 ohms in the simulation).
Here are some dimensions for you:
(inside dimensions)
18.5" tall
10.6"d x 10.6"w
driver centered on the front
port: 4" dia 7.5-8" long
stuff to taste - it should work fine without stuffing
Here are some screencaps of the worksheets (ported.mcd). I also used the 'excelsub.xls' excel spreadsheet as a sanity-check to make sure everything was working correctly.
http://furtive.us/images/speaker/ff225k_freq.gif
http://furtive.us/images/speaker/ff225k_imp.gif
http://furtive.us/images/speaker/setup.gif
http://furtive.us/images/speaker/excelsub_freq.gif
I also did some simulations of the BIB pipes; the response looks terrible as expected, so they'll probably sound great! BTW, I have built the BIB pipes loaded with some RS-1354 drivers. They do work suprisingly well!
To Scottmoose: The 'stock' size pipes seem to sim better than the larger ones you suggested. I didn't run a whole lot of variables, though, as the only windows machine I have is a Pentium 166 circa '96!
-Hans
Yes, I know about that! The problem faced is quite unique in my experience -namely a QW design that is cannot be accurately modelled in the currently available versions of Martin's MathCad sheets (and that's coming from me -a fairly rabid supporter of Martin and his work) for reasons noted on the other thread. Basically, the current sheets don't factor the room into the equation, its interaction with the cabinet, and the position of the mouth. And with this cab, all of those, as you yourself know as a fellow builder, are critical. So we have the bizzare situation where you make a change that should be an improvement in practice (like using a larger mouth, which should allow for better bass propogation into the room), but seems to screw up the simulated response even further!
As an aside, I discovered last night, much to my (pleasent) surprise, that a version of this pipe for the Sigma built by Terry used almost identical dimensions to those I suggested, so it seems I'm not alone.
Cheers
Scott
As an aside, I discovered last night, much to my (pleasent) surprise, that a version of this pipe for the Sigma built by Terry used almost identical dimensions to those I suggested, so it seems I'm not alone.
Cheers
Scott
Woo! Alright!
Sorry for the delayed reponse, but I was sick and then I got an unexpected visitor in the form of a Category 4 hemorrhoid that I like to call Hemorrhoid Adam , being that its the first one of my life. My GP took a good, long look and said, "Wow, that's a nice one." I informed her that we were now on a first-name basis. Got some prescription creams with just about the funniest looking applicators you ever saw.
But enough about Adam...
OK-- I'll work on trying to draw an appropriate enclosure for this. Never done this before, so I'll post and you can rip it apart, noting my ignorance.
Hot dog! I'll try to draw out both your MLTL suggestion and Scottmoose's BIB concept and post for your perusal. Looks like me and Adam got some work to do.
Kofi
Kofi Annan said:
I thought the UN Secretary General would have better taste than to drink Irish whisky. Talisker is where it's at.
Give me a fine late bottled vintage port any day... with cognac of course.
Probably safer to stick with the smaller version of the scaled up BIB box initially, as that low Xmax of the 225 might not be thrilled by a hefty load. If you wanted to throw caution to the wind, just scale the original cabinets up by 20% Never having tried it, I don't know if it'll work; what I can say is that this cabinet geometry works well with the FF165K, and so far as I can see, looks like it should be ok with their bigger brother too. If not, a pair of FE206Es will be quite at home, as I gather from a few people who've built these boxes scaled up for 8" drivers. I'm waiting on the FE206ES-R myself... devilr:
Happy drawing (and drinking?)
Scott:
Probably safer to stick with the smaller version of the scaled up BIB box initially, as that low Xmax of the 225 might not be thrilled by a hefty load. If you wanted to throw caution to the wind, just scale the original cabinets up by 20% Never having tried it, I don't know if it'll work; what I can say is that this cabinet geometry works well with the FF165K, and so far as I can see, looks like it should be ok with their bigger brother too. If not, a pair of FE206Es will be quite at home, as I gather from a few people who've built these boxes scaled up for 8" drivers. I'm waiting on the FE206ES-R myself... devilr:
Happy drawing (and drinking?)
Scott:
Then Talisker is what I shall have! Love scotch, so I'm headed to my local packy this weekend to git me some.
Also, not to belabor the point, but there's some wonderfully humorous subtlety to the very first visual representation of a Category 1 'roid. Note that there's a line pointing to the lower section of the artist's rendering with a caption that simply states "Anus".
You know. In case you wondered.
Umm... what do you consider the "smaller version"?
Kofi
Kofi Annan said:
A simple cap XO is the common way to do it. You either want to pad it a bit or just move the XO up an extra 1/2 octave or so to effectively give you 3 dB of attenuation at the XO point. So somthing like a 1.3 or 1.4 uF cap.
dave
PS: The radio shack pod tweeters have a very close relative to these inside them....
8 1/2" W x 14" D x 89" tall. OK, not small, I admit -we're talking relative here! Fingers crossed it's got sufficient Xmax to work well in these enclosures -if it has, this could be interesting! Who knows?
OK-- so is there an easy way to calculate the correct value for the crossover cap to accommodate variable crossover points? Anyone care to provide me with an "in the ball park" formula to use so I can buy a variety of caps to test multiple crossover points?
Also, due to the size of the BIBs, I don't think I'll be able to place the tweeter on top of the cabinet, so I'll need to mount it inside. So, what does common wisdom dictate? Directly above the driver or offset a bit?
Remember-- you think, Kofi do.
Dave-- are the RS pod tweeters available for purchase still or is this one of these discontinued items like the 1197?
I'll be sure to remind my wife that this is the smaller version.
Kofi
Oh yeah--
And where should the port be? I know we've talked a lot about ports in this post, but I gotta know.
Kofi
And where should the port be? I know we've talked a lot about ports in this post, but I gotta know.
Kofi
Kofi Annan said:
there is a simple calulator here: http://www.mhsoft.nl/spk_calc.asp
just plug in the frequency you want into the first order calculator. You can also calulate l-pads there as well.
Joe
Kofi -If you tried the enlarged BIB box, I'd strongly advise roughing up a pair first out of some scrap or very cheap material like chipboard to see if it would be worth pursuing properly (total time: 2 hours tops, plus a bit for the glue to dry). That way it would save tears and frustration if it didn't work out. The original 7"x14"x70" cabinet, designed for the infamous RS 40-1354 5 1/4" driver works well with various drivers up to about 6 1/2", including the FF165K, especially when run off high resistance wire (I'm using 24AWG magnet wire with the 165; the 225 will probably need 30AWG or some series resistance), and the 165 has the same 0.3mm Xmax as the 225. So logic suggests its bigger brother should work in a scaled up version. That said, we all know about logic and reality, hense my suggesting that you build a rough, cheap pair first to test it out first. Unfortunately, these pipes don't sim properly in Martin's wonderful MathCad sheets, as they are very room and position dependant, which the current versions of the sheets do not account for. So unfortunately it's rather a case of there's only one way to find out if it'll work or not, and that's to try it and see.
If you're wondering where the dimensions come from, they were the quick and dirty approach. The total line length of these boxes, which are a Voigt type horn / TQWT terminating in free space, should be set to 1/2 the wavelength of the driver fs.
Not having the theory to hand (I believe it's in the Fostex Craft Handbooks, which are next to impossible to get hold of) I'd suggest initially simply scaling the width up by 20% to allow the drivers to fit. The depth probably needs an equivalent increase too (Bigger Is Better? I believe Wavebox over on Audioholics did just that to good effect for the FE206E, though that has a much larger Xmax) but I perhaps foolishly work on a policy of one thing at a time when I can't simulate things accurately. These won't be optimum, especially with the original 14" depth, but should give an idea about whether it'd be worth pursuing peroperly. TC himself, GM or MJK will be able to offer much better suggestions regarding the dimensions I'm sure -any thoughts guys?
Ah yes, nearly forgot. This cabinet MUST be either pushed against a rear wall, or better, shoved into corners to work properly. But as there's always some room dues to toe-in, you could perhaps try a rearward firing tweeter, like TC does with his Super Abby using the FF165K.
Cheers
Scott
If you're wondering where the dimensions come from, they were the quick and dirty approach. The total line length of these boxes, which are a Voigt type horn / TQWT terminating in free space, should be set to 1/2 the wavelength of the driver fs.
Not having the theory to hand (I believe it's in the Fostex Craft Handbooks, which are next to impossible to get hold of) I'd suggest initially simply scaling the width up by 20% to allow the drivers to fit. The depth probably needs an equivalent increase too (Bigger Is Better? I believe Wavebox over on Audioholics did just that to good effect for the FE206E, though that has a much larger Xmax) but I perhaps foolishly work on a policy of one thing at a time when I can't simulate things accurately. These won't be optimum, especially with the original 14" depth, but should give an idea about whether it'd be worth pursuing peroperly. TC himself, GM or MJK will be able to offer much better suggestions regarding the dimensions I'm sure -any thoughts guys?
Ah yes, nearly forgot. This cabinet MUST be either pushed against a rear wall, or better, shoved into corners to work properly. But as there's always some room dues to toe-in, you could perhaps try a rearward firing tweeter, like TC does with his Super Abby using the FF165K.
Cheers
Scott
Kofi Annan said:
Kofi, you can use a switch to insert a smaller cap in parallel with the main cap.
This is for small steps, of course, otherwise you would switch from one cap to the other.
But even 100nf makes difference on a 1st order crossover on a tweeter.
Kofi Annan said:
When figuring out the value i start with a value i know is too small (say 1 uF maybe a bit less) and then listen, add a bit (say 0.1 uF -- clip leads are your friend), listen, a bit more, continuing until i start to notice the tweeter is getting a bit much and then back off. This process can take days or even weeks so make sure that the caps are accessible.
Here is the idea:
dave
Will do. I think I can get by with some MDF for the first blush, but Lowes will need to do some cutting for me.
I'd still like to know about the port, however. How big is the port in the BIB and is it in front or back?
Also, are there any objections to using the FT17H Fostex tweeter? I think this would cross over well, but whaddoiknow? Also, where should I mount the tweeter in the BIBs?
Going to make an attempt at drawing these out. Stay tuned.
Got it! Thanks!
Kofi
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