New Guy with a B&C 21SW115-8 build going - diyAudio
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Old 19th January 2013, 02:43 AM   #1
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Join Date: Jan 2013
Location: Pocatello, Idaho
Default New Guy with a B&C 21SW115-8 build going

Greetings, all. Just signed up today. I'm just trying out a build I just completed, B&C 21SW115-8 in a 256L bass reflex. Currently I am running Sub out >>20Hz FMOD hi-pass >> Behringer electronic crossover >>
  • 20-80Hz >> Behringer EP4000, bridge mode >> B&C 21"
  • 80-200Hz >> QSC USA850 bridged >> JBL 2035H 15" 92L bass-reflex centered beneath TV screen
6 satellites, custom 2-way sealed .5ft^3 w/JBL 2123H and JBL 2404 compression drivers, 3k passive crossovers driven by the AV receiver's internal power.

I've been muddling around semi-informed and thought this would be a good place to learn a few things. I used the DIY Spreadsheet to arrive at my port calculations for both the sub and mid-bass, but really don't know what to make of the "Comparisons" page, or how to interpret the "Power Response" graphs. I could use some help with that.
Mostly I am interested in music play-back, but like movies to have some authority too. My design goal was a solid SPL and reasonably good low end extension.
First impressions; Powerful and very solid. I'm liking the slap I am getting, not boomy, and it rattles my lungs pretty well. I replayed through the scene in "Independence Day" where the aliens nuke the first skyscraper several times, watching the cone excursion...very moderate even when things began falling off shelves. So far, so good, liking the system pretty well.

Of course, it's not DONE ... what kind of lame hobby would this be if it were done?


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Old 19th January 2013, 05:23 PM   #2
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So what is the bass reflex cabinet tuned to?

Don't want to see you ruining that expensive b&c driver from over excursion with only a 20hz high pass.
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Old 19th January 2013, 06:50 PM   #3
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Quote:
Originally Posted by m R g S r View Post
So what is the bass reflex cabinet tuned to?

Don't want to see you ruining that expensive b&c driver from over excursion with only a 20hz high pass.
Good point. I tuned the cabinet to a theoretical 30Hz. The hi-pass has been a matter of interest to me for the same reasons, and where I could use some help with the DIY Excel spreadsheet, which I was goofing around with last night.
This driver has a pretty hi SD, moderate XMax & XVar. When I model the "Comparisons" using an active 12dB/octave 20Hz hi-pass and 80Hz low-pass, room gain at 30Hz, and 750 watts, the Large Signal response gives pretty strong response down at 20Hz. ??? If I input a lower SD that goes away. When I model a 30Hz Hi-pass, it also goes away. Am I correct that the Large Signal Response/Power Response is intended to (roughly) model the actual "heard" volume in something other than an anechoic listening environment? Since I'm not playing it in free-field, but rather a 13' x 15' room, that's more what I'm interested in ...
That said, anything over 750 watts w/20Hz hi-pass shows excursion beyond Xvar (using that 750 watt value because that is what my amp will drive per channel into 8 ohms). With a 30Hz hi-pass, it will model acceptable excursion with up to 2500 watts, and the (room response?) shows a gain of several dB from 30-60Hz, but no gain at all @ 20Hz ... still falling off at the same rate.
My question; I'm not shooting for subterranean response like a genuine LLT but wouldn't mind reasonable response at 20Hz. So am I inputting data correctly on the "Comparisons" page? If so, I've got a nice balance of depth and volume.
UPDATE: I disconnected the QSC, and am running the B&C on one channel, 20-80Hz, the JBL 2035H 15"on the other channel 80-200. Listening to a some Yellowjackets with some very low electronic passages and watching the excursion, that beast was making my head feel funny. A JBL tech-rep I'd spoken with told me that the air in an adult's lungs resonates at around 60Hz, and that might account for the slight feeling of nausea I was experiencing. Through all of this, the B&C just seemed to yawn with indifference. The combination is doing a whole lot with a combined 1,500 watts.
Forgive my rambling enthusiasm, but I'm really liking this B&C driver. It's on-paper performance, other than power handling, is not hugely different from the JBL 2245H it is replacing. My ears are telling me a very different story.


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Old 19th January 2013, 09:09 PM   #4
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Quote:
Originally Posted by cattskinner View Post
Good point. I tuned the cabinet to a theoretical 30Hz. The hi-pass has been a matter of interest to me for the same reasons, and where I could use some help with the DIY Excel spreadsheet, which I was goofing around with last night.
This driver has a pretty hi SD, moderate XMax & XVar. When I model the "Comparisons" using an active 12dB/octave 20Hz hi-pass and 80Hz low-pass, room gain at 30Hz, and 750 watts, the Large Signal response gives pretty strong response down at 20Hz. ??? If I input a lower SD that goes away. When I model a 30Hz Hi-pass, it also goes away.

That said, anything over 750 watts w/20Hz hi-pass shows excursion beyond Xvar.
My question; I'm not shooting for subterranean response like a genuine LLT but wouldn't mind reasonable response at 20Hz.
Listening to a some Yellowjackets with some very low electronic passages and watching the excursion, that beast was making my head feel funny. A JBL tech-rep I'd spoken with told me that the air in an adult's lungs resonates at around 60Hz, and that might account for the slight feeling of nausea I was experiencing. Through all of this, the B&C just seemed to yawn with indifference. The combination is doing a whole lot with a combined 1,500 watts.
Forgive my rambling enthusiasm, but I'm really liking this B&C driver. It's on-paper performance, other than power handling, is not hugely different from the JBL 2245H it is replacing. My ears are telling me a very different story.
Cattskinner,

Moderate Xvar? A JBL 2245H has an Xmax of 9.65mm, the 21SW115 has 16mm (that's 1.25 inches peak to peak) before it is non linear, and almost twice that before Xlim (damage). That is about 5 dB more output potential (with enough power), which at 20 Hz sounds twice as loud to your ears.

SD (cone area) is fixed, why would you lower it in a sim?

If you want real 20 Hz output from a BR, you need to tune it to 20-22 Hz, but output above will take a serious hit.
Checking actual tuning is important too, your "theoretical" 30 Hz tuning might be 25, a 1/3 octave difference, or 35, a 1/6 octave difference.
Don't expect very much usable response below tuning.
Tuning can be easily verified using sine wave tones, watching a small dot painted on the cone, excursion will be at minimum at FB.
You can also watch the dot and see if you actually exceed Xmax with program material or pink noise.
And use a 24 dB BW HP a few Hz below actual tuning, not a 12 dB filter, no reason to turn unusable output in to heat.

I doubt the sims are very accurate as far as excursion below Fb, the suspension of the 21SW115 is pretty stiff. With 750 watts available, unless you are in to gross clipping I doubt the amp could get anywhere close to Xlim with your speaker.

Even open air your speaker has enough LF output to make one feel nauseous, when running in a pair of 18SW115 with a 20 Hz sine wave near Xmax sitting on the floor after listening for only a few minutes I felt sick for 15.
The chest resonance around 60 Hz is not what makes most feel nauseous, it is LF below 30 Hz, with 20 Hz or below definitely giving a feel of uneasiness well before nausea.

Have you seen the cone move 1.25" peak to peak yet?
If not, you have hardly tickled it.

Have fun!

Art

Last edited by weltersys; 19th January 2013 at 09:22 PM.
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Old 19th January 2013, 10:30 PM   #5
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Thanks much for the input, Art!

Yeah, I had no idea how to check the actual tuning, and that is useful info.
I'll look into the 24/octave Hi-pass. As far as playing with the SD, I was playing with it wondering how cone area affected the sim, trying to wrap my head around the audible difference between large and smaller drivers that have similar on-paper sensitivity, power input, and frequency response; Why do large drivers just sound "bigger" in comparable alignments? I played live music in nightclubs for quite a few years and could never account for that. My technical knowledge is "entry level," to be generous.

Heh, and no, I have not seen it move quite that much. BUT, I couldn't stand starving it for power, so I bridged the EP4000 back into it; it moved pretty well when I watched The Fellowship of The Ring during the fight with the troll. And you're right about the fun part!
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Old 19th January 2013, 11:12 PM   #6
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Quote:
Originally Posted by cattskinner View Post
Why do large drivers just sound "bigger" in comparable alignments?

Heh, and no, I have not seen it move quite that much. BUT, I couldn't stand starving it for power, so I bridged the EP4000 back into it; it moved pretty well when I watched The Fellowship of The Ring during the fight with the troll.
Large drivers sounds "bigger" in a comparable alignment because they are louder, more cone area in a bigger box.

What was the most peak to peak movement you have noticed during the troll fight?
Any guesses to what frequency the P to P was at it's greatest?
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Old 3rd February 2014, 05:08 PM   #7
badman is offline badman  United States
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Quote:
Originally Posted by weltersys View Post
Even open air your speaker has enough LF output to make one feel nauseous, when running in a pair of 18SW115 with a 20 Hz sine wave near Xmax sitting on the floor after listening for only a few minutes I felt sick for 15.
On the upside, no more kidneystones and you released a lot of arterial plaque- and possibly some dental)
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I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!
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Old 4th February 2014, 03:22 AM   #8
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Heh, yes to all the above! I'm currently putting the B&C up for sale (nothing at all the matter with it, just time to move on to another project). I'm looking for a bit more extension, and have become interested in tapped horns. I have an Fi Q15D2 on the way, and we'll see what happens :^)
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Old 4th February 2014, 08:00 AM   #9
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Make sure to have a DATS or get your woofers tested for actual parameters. Then designing a TH will be easier for your 15's.
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Old 6th February 2014, 06:53 AM   #10
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Can you post some pictures of the sub?
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