SWR BigBen replacement woofer

#61
Yeah, 6" would be the external diameter of the tube so the net port size is less than that, as you rightfully suggest. I guess using both ports and bringing the air speed down isn't worth it since you don't recommend it as a first solution?
One vent would be 11.9cm long (a bit less than 5"), of course two vents would be a bit less than 13" but they would bring the air speed from 36m/s to 18m/s when sending 600w to the woofer (unlikely, but I want to stay on the safe side).
The problem is, the cabinet is only a bit deeper than that internally, not sure there's room for tubes 13" long... unless I make them stick out for a few inches or use a curved tube.
UPS moved the delivery of the Sigma to tuesday, though. :(
 
#63
ID is the only number that's important.

Something doesn't make any sense.

Just a quick guess, but model with a 6" diameter port and 6" depth. Show the freq. resp. Plot with that data.
 
#64
This is with 500w, 130lt, 40hz tuning, one port (you can see the measurements).
I was talking about "real life measurements" for the port without modifying the cab... it's got two 6" holes on the back, and there are 6" tubes available (external diameter) so the real tube internal diameter is a bit less than that and I guess the internal diameter is what WinISD considers.

500w.jpg
 
#65
Try using Boxsim (Visaton) to simulate the length of the tubes, it takes into account the distance from the inner walls to the tube. The closer the tube gets to the back wall the lower the tuning gets, it sort of virtually lengthens the tube but I wouldn't move it close then 3" (approx 7.5).
 
#66
Good point, Arjank. I'm learning a lot in this topic, as I expected.
This is the cab view from the back, with the 6" (15cm) holes on a 1" panel (2.5cm). They're now on the top side of the cab as I reversed top/bottom of the cab to have enough room for the 6" mid on top. :laugh:

ports.jpg
 
#67
Wait a minute. Earlier you had indicated one 14cm port which is why I questioned this whole thing and said it was to small but in fact there are 2 ports. (Note that there were several versions of this cabinet with different drivers requiring different tuning.

Time to stop and regroup. You have plenty of port area as it is, please post the freq. resp. plot (not the air velocity) to see where we are with the existing duct length. The duct lengths should be the same.
 
#68
Uhm... sorry, I was pretty I reported the ports were two but at this point I guess I didn't... my bad.
The cabinet is 130lt, the ports as I said are 15cm (6") on a 2.5 (1") thick panel. This, according to winisd Beta brings the tuning to 77hz at 1w.
77.jpg
 
#70
With 2" long ports the tuning goes down to 71hz.
71.jpg
Keeping an eye on excursion, if I want to be able to throw 500w at it without going out of xmax, I should tune to 50hz and it would crap out under 40hz anyway.
Man, this is waaaay harder than I initially thought LOL, the improved WinISD makes me face the shortcomings of the speaker in a way the older version didn't, obviously.

Just for my own curiosity I'm modelling the Faital 18FH500 in the same project... well, the extra 3mm of xmax would have been nice to have, the tuning is easier as you don't get out of steam as easily as on the Sigma but the output is more or less the same across the spectrum.
 
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#71
I've put the Sigma 18 specs into AJhorn and below are the results, black curve = 40hz tuning, red curve 50hz (half-space). Tuning lower doesn't make any sense, it won't give much more low end and the "powerdip" gets bigger...
IMO 40hz would be optimal, remember that using these large ports will decrease the internal volume of the cab, so I used 122 liters instead of 130 to do the simulations.

Sigma 18 122ltr 40 vs 50hz.png
 
#72
UPS knocked at my door unexpectedly :)
Spent about an hour wiring everything, the cab is now working, only needs the tubes for the tuning.
Have to say the 6CMBRA sounds better than expected... it's pretty "in your face" but it's not honky as I thought... definitely balanced.
The lows for now are nothing to write books about, due to the fact the woofer needs to break in and of course the high tuning. I'm sending 40hz into it to loosen up (not lower just for safety).
Later today I'll buy the tubes. Yes, for now I plan to tune to 40hz with two 15cm ports (external), 13.2cm long - and them eventually adjust once the woofer suspension is ready to bounce. :roflmao:
For now it sounds like a big 1x15", in flat. Of course if you pump on the lows it gets massive but again, I'm playing safe since the tuning isn't right.
 
#73
Don't worry about breaking in the woofer, the changes are not going to be an issue nor will they have a significant impact on performance. Just another Internet myth with a little bit of truth. Breaking in speakers can lead to speaker damage when you don't understand what you are doing...

You said there were 2 x 6" holes ~ 1" deep. Is that what was there originally?

Looking at your plot, a 4" port depth is going to be about right. Don't worry about the tuning frequency, or the power handling. The real performance of the driver in that volume box is based on the filter shape and coefficients. Everything else is a byproduct.

You need to be more accurate in your descriptions, as you noted it is more difficult that you thought and it gets even more difficult when you leave out important information.
 
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#74
Yes, the cabinet was made like that by SWR: two 6" holes on the back panel, 1" thick. I know it looks a bit odd but I'm 100% sure it's stock, the original owner had a rehearsals room and even told me how a guy fried the original speaker: Marshall 4400 and two cabs, the Ben and the Goliath. Don't know how loud the whole lot was, the room kinda sucked in the lows and the guy killed the speaker. A shame, but gave me the chance to build this cab.

As Arjank says, there was a major difference between WinISD and Bassbox ports dimensions... I'm going to buy the tubes in maybe an hour or so.

You state the performance of the driver isn't affected much by the tuning? Why? Because the box is on the small side?

I hope it gets "warmer" with the tuning and the suspension break-in. Now it's very balanced but a bit "dry" on the lows, as you can guess. I still can't play it with ERBs, all I have access to is a B string on a 5er but the bigger instruments aren't ready to play yet.
 
#75
The performance of the driver itself shifts around but the changes little overall with tuning. It's the shifting around in the direction that benefits the goals of the deigner that is where performance gains are to be had.

You can hope all you want that the driver gets warmer, you can even fo yourself into thinking so, but in double-blund listening tests, and in measurements of TS parameters, the changes from "break-in" aren't seen in this type of driver.
 
#76
Uhm... but I noticed a change in the lows now it's tuned and after a few hours of signal generator... and I'm not the kind of guy who believes in miracles ;)
Who knows. For sure it sounds better with a "traditional" amp than it does with my class D (but more powerful) head. :bassist:
 
#77
Whatever, myths occur because it makes folks feel better about a decision.

I would bet you a fist full of cash that you could not identify the "broken in" driver in a double blind test.

A general comment... when you ask for help, when you don't know squat about the topic you asking about, it's generally not a good form to argue with the folks who do know more than you, and have the experience backing up their knowledge.

I don't understand why you (and others) think otherwise. It's what discourages those who know from contributing on forums into general, it turns into an excercise in frustration.
 
#78
I didn't really want to argue, trust me. I'm not completely ignorant about this but of course, I don't know all the variables... otherwise I wouldn't have asked for help :)
This wasn't my "first rodeo" into cab building/rebuilding but with the older WinISD version, many of your rightful advices didn't make sense at first.

Sorry if somehow my replies sounded harsh, of course they weren't meant that way.
About the woofer break-in, of course I have no proof to back up my theory, no doubt about that ;) probably the difference was only caused by the tuning change (it has to make some difference, otherwise I guess you wouldn't invest time in doing it right). Being a bass builder has put me into the "myth VS reality" spot several times, as you can guess... oh well, thank you for your time, I appreciated it! :thumbsup:
 
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#79
Passinwind, thanks again for posting the link to the new version of WinISD... it definitely takes me into a new era of headaches :roflmao:
And many thanks to Arjank too, for his time and advice. :thumbsup:
 
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#80
Tuning makes (or can make) a difference in the system response. Breaking in a typical woofer used for sub and bass guitar applications generally has no significant difference in the system response, both double-blind listening tests and numerical measurements generally confirm this. That said, in electric guitar speakers, there can be some differences as the ear is MUCH more sensitive to midrange voicing, and the break-up modes of the driver are in part a function of any softening of the otherwise stiff, lightweight paper and suspension. Of course, if breaking in the driver were to cause a large shift in parameters, what mechanism prevents the changes from continuing? Does the driver sound it's "best" at hour number 68? In actuality, the changes are very small.
 
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