or Connect
AVS › AVS Forum › Audio › DIY Speakers and Subs › Ricci's dual B&C 21SW152 build thread.
New Posts  All Forums:Forum Nav:

Ricci's dual B&C 21SW152 build thread. - Page 17

post #481 of 518
Thread Starter 
Didn't make it to the man cave today. Life had other plans...You know how it is.
post #482 of 518
in the past, i have always given my superstar employees about a week or two before i'd start asking questions, so one day...haha...trivial...just hav'n some fun. ;-)
post #483 of 518
Thread Starter 
Finally fired these up tonight. Initial impressions are summed up here. haven't dropped the hammer on them yet, but they have a nice sound similar to in the sealed cab but obviously with more extension.

I did fail miserably to hit my desired tuning though. . Impedance and acoustic measurement both say that the tune is close to 24.5hz. The design was for 28.5. I will probably lose some sensitivity there. I've always hit my tuning really well with previous ported cabs, so I'm not sure what happened. Perhaps the port mouth is too close to the back wall of the cab, but I figured that about 9" should be enough. I'll have to go back and look at the cab measurements.

Too bad I can't get avs working on my home laptop because I also took before and after measurements of the cabs with and without the pillows used for damping. I could post all of this up when my connection starts working again.
post #484 of 518
"I did fail miserably to hit my desired tuning though."

crazy comment. your concern was hitting too high of tuning, so you hit a little low. no biggie. "fail miserably" doesn't apply to your build. give up maybe a db at 30hz for a db at 25hz...insignificant differences.
post #485 of 518
Quote:
Originally Posted by Ricci View Post

I did fail miserably to hit my desired tuning though. . Impedance and acoustic measurement both say that the tune is close to 24.5hz. The design was for 28.5. I will probably lose some sensitivity there. I've always hit my tuning really well with previous ported cabs, so I'm not sure what happened. Perhaps the port mouth is too close to the back wall of the cab, but I figured that about 9" should be enough. I'll have to go back and look at the cab measurements.

well, 24 hz is obviously not the best tune for a PA Sub but on the other hand it is just about perfect for a home music sub. so if you feel so bad about it you can always send them to me. i'll take good care of them

how is that single round straight port performing ? now that you tried it - do you still think it was the best design option ?

as for the tuning - more than anything IMO having a large port flange should have the effect of lowering the frequency. i'm not sure what your exact design is there.
post #486 of 518
Thread Starter 
35 would be better than 25 for sure. I can't exactly cut the ports down with the way these are built. Oh well. I'll see how they do in testing.

I like the big port. I've always been a fan of the big, straight, round port. Its not always easy to fit it in the cab though. Haven't used or pushed them enough to get really any air flow out of the ports yet. Next week.
post #487 of 518
Thread Starter 
Cavalcade of measurements...

Unfortunately I forgot to take a WT2 impedance measurement of the cabs without the 3 pillows in them as damping. I'll get that this week. Both cabs are pretty close. All of the main frequency response features are the same. 1/24th octave smoothing is all that is used on these so they are basically raw.


Cabinet impedance with pillow damping.




At the driver with damping.




At the driver with no damping




At the port with damping





At the port with no damping




Equidistant between driver frame and port edge close with damping.




Equidistant between driver frame and port edge close with no damping.




At the driver compared, damping vs no damping (Green trace).




At the port compared, damping vs no damping (Green trace).




Equidistant between driver frame and port edge close compared, damping vs no damping. (Green trace).




Equidistant between driver frame and port edge waterfall. Damped.





Equidistant between driver frame and port edge waterfall. Un-damped.







I could not get a far field 2 or 3m measurement that would allow the port and driver output to mix correctly without major room influence. I believe that the port contribution is a little overstated in my close mic equidistant measurements. We'll see about that later. The big spike near 270hz should be the ports 1st resonance. The junk near 150-180hz should be cabinets side to side 1/4 wave resonance, which would have the most area and be least broken up. About 22.75" wide internally. I've seen this same issue in each cabinet build involving an internal width of about 22-23". It appears that adding the 3 pillows robs about 1 to 2 db of sensitivity from much of the range under 150hz. Near tuning there appears to be a loss of some 3-4db and the tune shifts another 2hz downward. I'd consider this significant. On the other hand the nasty peaks and valleys in response due to standing waves and resonances in the enclosure and port are greatly smoothed out by adding the pillows and there is an addition of a little bit of extra extension. Since this is primarily intended for subwoofer duties below 120hz and it is intended to be driven hard for long periods of time, I'll be going sans damping on these so as to retain the higher tune and extra output sensitivity. If I planned to use these up higher than 100-120hz and in a less strenuous high output manner I'd rather have the smoothed out response with some damping in there. I believe these drivers could successfully be used up to 450 or 500hz in the right application. That'd be one capable midbass system.
post #488 of 518
Thread Starter 
Stupid connection issues! It's finally working somewhat better again but still not stable.
post #489 of 518
awesome stuff j.r., just frick'n awesome.

just as a heads up...no connection issues here.
post #490 of 518
I agree, looking at those graphs, they will provide a killer mid-bass system up to 500hz.
post #491 of 518
The corner frequency is that of Genelec studio product, not JBL PA product. basically with massive processing this can be a studio subwoofer with moderate output flat down to very low. or if you want to use it for PA you simply don't use any processing and let the deep bass roll off naturally and realize the full SPL capability. now since this will be a part-time studio subwoofer i think it should have a decent amount of damping inside.

also your equidistant measurement is crap. it should be equidistant from centers of port and driver, not edges.

nice subwoofer overall.
post #492 of 518
Thread Starter 
The internal dimensions are 22.75x26.5x33.75. That is 11.8 cu ft gross. I figured on 9.5-9.8 ft after displacements. The driver, handles and bracing I roughly estimated at 1 cu ft. The port is another 1 cu ft. The absolute most that the enclosure could be is maybe 10.4 cu ft effective. The port is 10" diameter x 21" long including the 2, 0.75" flares. Calculation says that with a 10.4 cu ft airspace the port would have to be 26.5" long to hit a 24.5hz tune. If the cab is closer to 9.5cu ft then the port would need to be 29.5". Basically the port is loading against the back wall and this is adding an extra 5 to 9" of port length effectively. SVS and Epik have been known to do this in their subs to squeeze a lower tuning in a smaller box. I had always heard to leave one port diameter space in every direction for the port. Apparently this is true if you want the port length to tune to the right range. I had thought that 6" to either side wall and 8.25" to the back wall would be enough to avoid a big shift. I was wrong. Although undesirable in this case... It seems to be a very effective technique if you are really cramped for space and desire a low tune. I wonder if Akabak can model this?




Vas,
I'll try to take some measurements with the mic equidistant from the center of each radiator. Brain fart on my end. I was in a hurry.
post #493 of 518
Quote:
Originally Posted by Ricci View Post

I had thought that 6" to either side wall and 8.25" to the back wall would be enough to avoid a big shift. I was wrong. Although undesirable in this case... It seems to be a very effective technique if you are really cramped for space and desire a low tune.

you have modified my original design. your design increased the width of the flange at the internal end of the port. your design essentially terminates the round port not into an airspace but into a network of rather narrow rectangular ports formed by the bracing.

if you stuck closer to my sketch you would still get significant loading at the port end and thus significant reduction of tuning frequency but it would at the same time be smaller. i sort of assumed that you wanted that kind of loading given that you were considering the use of that polk style port that you used on the XXX sub.

your analysis in the above post however is slightly wrong. it is not the proximity to any one boundary that has the major effect here, but rather the fact that you have several boundaries enclosing the port exit on on basically all sides. my sketch had that too - but to a lesser extent. the point is however that if you were to take out all of the bracing ( especially the flange ) the tuning would increase with the same port length in the same box.

as far as effectiveness of this technique i would say that using a large flange should be an excellent way to increase port performance because it lowers tuning ( very slightly ) without obstructing the straight-line airflow path and in fact REDUCING turbulence by switching a 180 degree edge for a 90 degree ( so less pronounced ) edge.

placing the port exit up agains a wall is in itself probably a BAD idea because it will result in more turbulence than tuning frequency reduction.

however the real tuning reduction is to be had from using both simultaneously - that is sandwiching the port exit between the back wall and an enormous flange effectively loading the round port into another slot port. which incidentally is what happened with your subwoofer.

the mistake here was in not properly calculating the magnitude of this effect. not that it would have been easy, but we should have put more effort into it. guess one of the reasons we didn't do it is because we couldn't agree on the optimum tuning frequency to begin with.
post #494 of 518
JR, that's lookin pretty good there buddy.

I'm thinkin that your implementations should land you a nice job in this line of work - designing subs.
post #495 of 518
can't you just plug up a little bit of the internal area if you want to raise the tuning frequency? maybe experiment with some simple closed cell foam blocks or something?
post #496 of 518
Quote:
Originally Posted by LTD02 View Post

can't you just plug up a little bit of the internal area if you want to raise the tuning frequency? maybe experiment with some simple closed cell foam blocks or something?

You could, but that would decrease the efficiency a few dB around the tuning on top of the loss already there.

EDIT: Yeah... this only happens in small enclosures. I forgot how big this one was.
post #497 of 518
really? winisd shows efficiency goes up with a smaller enclosure and same dimension port.
post #498 of 518
Sorry, brain fart there. That could only happen in a small enclosure. It doesn't really apply here. I don't know why I was thinking of this as a small enclosure.

I normally use subs larger than this, I guess that's why.
post #499 of 518
Thread Starter 
To be honest. I'll probably just leave these alone. I misjudged how bad the shift in tuning would be due to the port layout, but on the other hand I can now use that to my advantage in future builds. At least something was learned. I had a chance to listen to some music on them and then crank it up with the kick drum and some bass guitar run through. I like what I heard. No signs of distress and a natural clean sound is how I'd characterize it. Plenty of chest slam. Im only running them stereo at a rated 1400w per side too. Haven't seen the clip lights yet. I'm planning to give each driver a full bridged amp in the end. Should be fun.
post #500 of 518
Quote:
Originally Posted by Ricci View Post

At least something was learned.

mistakes are what it takes to learn most of the time. in the grand scheme of things everybody makes mistakes but not everybody learns from them.

as hard as it may be to believe i make mistakes multiple times a day. and every time i do i think about what happened until i feel that i have extracted most of the lessons from it. on any given day i end up spending probably on average about 2 hours thinking about my mistakes.

in this particular case i think the two important lessons are:

1 - the cards are stacked against DIY.

2 - no design can be thought out too well, only not well enough.

the port loading lesson is an obvious one. when you make a mistake you should never stop with learning just the obvious lesson - there are almost always more lessons to be learned if you think about it some more.

Quote:
Originally Posted by Ricci View Post

I like what I heard.

cool
post #501 of 518
if there is a 'black belt' in avs-diy, ricci should be wearing one.
post #502 of 518
Quote:
Originally Posted by LTD02 View Post

if there is a 'black belt' in avs-diy, ricci should be wearing one.

Ricci is Luke Skywalker, i am Darth Vader and you are R2D2
post #503 of 518
So your Ricci's father. You learn something new everyday.
post #504 of 518
Thread Starter 
Who is the emperor?

Btw I got the second set of wt2 measurements after yanking the damping out. Also got a better close mic response measurement with the mic equidistant between the radiator centers this time. I'll post them up later.
post #505 of 518
Thread Starter 
Equidistant close mic FR.


IMP with damping


IMP with no damping
post #506 of 518
Quote:
Originally Posted by Ricci View Post

Equidistant close mic FR.

looks like a good multi-purpose music sub.
post #507 of 518
what is the "damping" that you are using?

it is interesting to see that the damping seems to increase the minimum impedance. it looks like you are up around 5 ohms in the damped run. is that going to affect power/spl?
post #508 of 518
Thread Starter 
Damping was just 3 strategically placed pillows as shown a couple of pages back in photos. They drop the peak impedance below tuning a lot from about 50 ohms down to below 24ohms and the one above from about 72ohms down to 57ohms. That's efficiency getting cut. Interestingly it does also raise the minimum impedance a hair too. What they improved was the resonances in the system above 150hz and this can be seen in the impedance roughness up top on the undamped version.
post #509 of 518
sorry...somehow i missed that post.
post #510 of 518
"Ricci is Luke Skywalker, i am Darth Vader and you are R2D2"

lol. ok.
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: DIY Speakers and Subs
AVS › AVS Forum › Audio › DIY Speakers and Subs › Ricci's dual B&C 21SW152 build thread.