B&C 21DS115 23hz 800L TH build - Page 3 - AVS Forum | Home Theater Discussions And Reviews
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post #61 of 75 Old 08-10-2017, 04:25 PM
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Originally Posted by cattskinner View Post
...
I am a novice about this stuff, admittedly. But, any thoughts/observations welcome. If the modeling is at all accurate -- within a reasonable tolerance anyway -- it is a fairly solid endorsement for the TH if the size is not prohibitive. Yeah, this horn looks like a coffin for Sasquatch ...

the relationship between extension (lower tune) and less output capability just above the tuning point (excursion limited droop) is accurate.


this is one reason why despite the prevalence of edm/dubstep and other that have significant content in the 25-35hz ball park, you'll still see a lot (perhaps most?) ported p.a. cabs tuned in the 35-40hz ballpark. with the lower tune, you get more extension, but would need to haul around twice the cabs, at least in some sense.

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post #62 of 75 Old 08-10-2017, 04:45 PM
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Originally Posted by cattskinner View Post
I have been goofing around a little comparing modeled results on Hornresp, seeing what a difference in tune does to the driver's capacity. I trust HR a little more than some of the other modeling programs, as it more closely predicts the actual measured results on several of the systems documented on DataBass. A couple I checked against were the Othorn, G-horn, and the JBL 4645C. All were quite close, and not just around the roll-off and tune.
Modeling the 21DS in a 180L cabinet optimized for music reproduction (I'm assuming A0/27.5 hz is the lowest encountered, but that is just allowing for conventional instruments. Low B on a 5 string bass is right around 30.5hz, etc).
I set up a 180L cabinet tuned to about 32hz (in gray on the first thumbnail), and compared the results with the same displacement but the tune dropped to about 23hz (which is what my horn modeled at; actual tune turned out to be 22.2hz). 2000watts, Xvar on excursion. Pretty dramatic difference; there appears to be a rather substantial penalty 30- 60hz going with the lower tune.
Next thumbnail is my TH modeled against that result. Interesting, and I wish I could know how it stacks up in real world.

I am a novice about this stuff, admittedly. But, any thoughts/observations welcome. If the modeling is at all accurate -- within a reasonable tolerance anyway -- it is a fairly solid endorsement for the TH if the size is not prohibitive. Yeah, this horn looks like a coffin for Sasquatch ...
Are you using the Lossy Le feature in Hornresp? If not you should be. If not then the sims won't match the measurements well at all.

Comparing the sim vs measurement overlaid that was posted awhile back it looks like you are not using the Lossy Le feature - if you indeed are not and you turn it on you will find the sim matches the measurement a lot better.
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post #63 of 75 Old 08-10-2017, 05:09 PM - Thread Starter
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Hmmm, I am not using the lossy Le feature, and am not familiar with it. How does one employ it (or find it, for that matter).
Thank you for the input.
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post #64 of 75 Old 08-10-2017, 08:05 PM
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Double click the Le label in the input screen. When the Le label is clicked it will turn red and you will know it's on, then all your sims will show the estimated effects of lossy Le.

The DS has much higher inductance than any of the other B&C drivers and lossy Le will play a significant role. Once you utilize the feature in Hornresp your sim will match you measurement much better. It would be best if you could measure outside with no nearby boundary reflections with a mic distance of at least 2 meters but you can't always have everything so just do what you can.
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post #65 of 75 Old 08-10-2017, 11:45 PM
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Quote:
Originally Posted by diy speaker guy View Post
Double click the Le label in the input screen. When the Le label is clicked it will turn red and you will know it's on, then all your sims will show the estimated effects of lossy Le.

The DS has much higher inductance than any of the other B&C drivers and lossy Le will play a significant role. Once you utilize the feature in Hornresp your sim will match you measurement much better. It would be best if you could measure outside with no nearby boundary reflections with a mic distance of at least 2 meters but you can't always have everything so just do what you can.
Since you brought it up I am curious how much different the DS is compared to the 152.
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post #66 of 75 Old 08-11-2017, 05:46 AM
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Mark Seaton measured them both, I think it was in the B&C audiophile thread. There's a pretty clear difference in the measurements even though they sim almost exactly the same if you don't use the lossy Le tool. If you do use the lossy Le tool they don't sim the same and the sim will match the measurement better.
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post #67 of 75 Old 08-11-2017, 05:58 AM
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Quote:
Originally Posted by diy speaker guy View Post
Mark Seaton measured them both, I think it was in the B&C audiophile thread. There's a pretty clear difference in the measurements even though they sim almost exactly the same if you don't use the lossy Le tool. If you do use the lossy Le tool they don't sim the same and the sim will match the measurement better.
Big thanks again for the reminder. I looked at the Skhorn and the 21DS115 does not look very good at all compared to the SW152 and big coil selected.
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post #68 of 75 Old 08-12-2017, 08:57 AM
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Yeah, the SW is simply a better driver (in more ways than one), that's why it costs more. Don't trust simple sims with drivers with high normalized inductance, you won't get what you expect. It's the same issue as putting a UXL in a Gjallerhorn - sure it will work but it won't be pretty, not nearly the same response as the original driver.
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post #69 of 75 Old 08-12-2017, 11:13 AM - Thread Starter
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Interesting angle on the lossy Le feature. Enough so that I applied it to some of the lower inductance drivers (with a favorable Le/Re) in well established, thoroughly real-world tested designs ...

...and I'm not quite ready to buy into it. Take a look a "with" and "without" comparisons for the Othorn (21SW152-4), the G-horn (TC 5400, a very low inductance driver), and the Lilwrecker with the CVX. Attached are the thumbnails.

Just stirring the pot a little, I really don't have any skin to lose over it -- I am happy with my horn whatever the sim's say, and would happily do it over the same way . Admittedly I am casting doubt on a modeling feature that someone about a billion times smarter on the subject designed, but I am not quite ready to write off of the DS. I am interested in "The Truth," insofar as any simulations can elucidate since I just might build a duplicate "Sue," or I have given some consideration to a slightly modified 2-part Skhorn going with a 22hz tune. SO, I would at this point just buy another DS and have at 'er.

So the comparisons I've attached kind of raised my eyebrows a bit.
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Last edited by cattskinner; 08-12-2017 at 11:20 AM. Reason: My lousy spelling ;^)
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post #70 of 75 Old 08-12-2017, 12:29 PM
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it isn't stirring the pot. the 21ds115 can model really nice in a ported horn. it just doesn't model the same as some other drivers. the 21sw152 gets its strength the hard way--more magnet. the 21ds115 cheats a little with more windings. all other things equal, lower inductance is better. but things are never equal. :-)

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post #71 of 75 Old 08-12-2017, 01:15 PM
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I'm not asking you to buy into anything, just to keep an open mind and do some sim vs measurements comparisons and a bit of research. I'll go at this in three different ways.

1. This should be the least convincing since there's no hard evidence in these quotes but it will probably actually sway more people a lot more than the actual data. Do you trust Ricci and Mark Seaton? Here's a couple quotes about lossy Le from them.

Quote:
Originally Posted by Ricci View Post
What I like to do is model with both regular and lossy LE engaged and get to where both are compromised to look most acceptable. End result will be somewhere in between but closer to the lossy LE model.
critique my HE15 tapped horn design

Quote:
Originally Posted by Josh Ricci View Post
I believe this tweak is useful for all drivers. If it is tried on tweeters or small midranges you'll often find that the changes are miniscule. The changes are largest on big subwoofer drivers with a high normalized inductance. Drivers without shorting rings, very long coil winds, many layer coils, big motors with a lot of steel in and around the gap, high moving mass and /or low motor force, so it is more useful in those cases. However it seems to be closer to matching measurements for all drivers with it applied.
http://www.diyaudio.com/forums/subwo...ml#post5070906

Quote:
Originally Posted by Mark Seaton View Post
The HE15 is a driver with a big coil in a rather tall gap. You should absolutely be modeling the lossy Le to get a representative model...
critique my HE15 tapped horn design

2. Look up and read Leach's paper on lossy inductance. He's quantified the issue mathematically and derived complex inductance parameters that can be measured and used in simulations. Unfortunately none of the popular simulators except Unibox will accept complex inductance parameters.

Also look into the paper I wrote. It's an easy 15 minute read and if you like you can just skip the text altogether and look at the pictures at the end. I took 22 different drivers in a total of 30 enclosures (all measured by Ricci except one) and simulated the enclosures they were measured in with the measured t/s parameters with and without the lossy Le tool. In EVERY SINGLE CASE the lossy Le tool provided a sim that matched the measurement much closer than a simple sim ignoring lossy Le. These included a whole bunch of sealed boxes, a few sims of the Othorn and even a front loaded horn. You can download the paper here - https://sites.google.com/site/amateu...and-adjustment

3. Do your own comparison sims vs measurements - you can reproduce my results with any driver of this type that data-bass has measured and you can sim the SW and DS that Mark Seaton measured. You can also sim your own horn that you measured with and without lossy Le engaged. I guarantee you that the results will be more accurate with the lossy Le tool than without. Every time.



Lossy Le is a known phenomenon, it's been thoroughly quantified mathematically by Leach and also by Wright. Unfortunately the complex t/s parameters aren't accepted in any of my favorite simulators so I created my own method with help from LTD02, David McBean (author of Hornresp) and Ricci's measurements. This tool has been proven to work much better than a simple sim 100 percent of the time for all types of enclosures. It's not perfect since this method is quite simple and does not use complex inductance parameters but it's a lot better than ignoring the issue.

If you have questions about this I'd be happy to answer but do a few comparison sims vs professional measurements and a bit of research first.
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post #72 of 75 Old 08-12-2017, 02:15 PM - Thread Starter
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Great, thanks for the info. Appears to be very well supported by some folks who design, build, and measure. Much appreciation for your links to the reading, I'll give it a look.

Too bad I can't measure outside. I do have nearfield measurements, with the horn mouth dragged into the middle of what is a very lossy room (which also opens unimpeded into the rest of a 4200 square foot house), and the measurement looks pretty fair ... a little better than expected. One thing I would wish for with anechoic sweeps would be the system sensitivity. I do recall Riccci writing that often TH's turn out with a slightly lower corner and slightly less sensitive than modeled. Low corner on the in-room sweep is 20hz, and the tune came in at 22.2hz vs a modeled 23.6 ... minuscule diff really. As far as moderate peaks and dips, wth, it's in a room, and that is what eq is for.

I've yet to do more sweeps at my MLP and elsewhere in the room to get a better idea of what my room response is doing.

Couple more thumbnails, actual in-room response, my horn with & without the Loss activated, and a comparison to the Othorn w/SW152 for kicks & giggles. Yeah, it would appear I might be giving up a few dB on max SPL compared to modelling without allowing for inductance, not enough to sell the farm over IMHO.

Again thanks for the info. Still quite new to this.
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post #73 of 75 Old 08-12-2017, 02:59 PM
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Originally Posted by cattskinner View Post
Great, thanks for the info. Appears to be very well supported by some folks who design, build, and measure.
Just to be clear, I'm not sure Mark Seaton was endorsing the Hornresp lossy Le tool, maybe he was, maybe not. I'm not even sure if he uses Hornresp or is aware of Hornresp's lossy Le tool. But he clearly favors considering lossy Le issues at least.

Quote:
Yeah, it would appear I might be giving up a few dB on max SPL compared to modelling without allowing for inductance, not enough to sell the farm over IMHO.
It's not just the different frequency response to consider with lossy Le issues. The response becomes more damped due to the lossy Le losses. This indicates that perhaps a bigger box would be more suitable. When you consider that power compression will also make the response even more damped (if you run it hot enough to get into power compression territory) the response can end up REALLY bad.

If you want to simulate some power compression on top of the lossy Le losses, just add some extra Re. Very heavy power compression can result in a doubling of Re. So double your Re and see what happens to the response. It's not likely that you will run into heavy power compression with a horn like that in a residential setting, but it's something to consider for future designs, if you are interested in taking this hobby further.

(Simply adding Re is not a perfectly perfect method of predicting power compression response either, but at least it's a pretty good educated guess about what's going to happen).

If you look at some of Danley's stuff, his designs are usually very underdamped since they are meant to be used at very high power levels which will in turn lead to heavy power compression. In his underdamped designs the response will actually get flatter as it gets into power compression. When you get into heavy power compression the frequency response kind of "melts" away, leaving peaks where the impedance peaks are. The more Re you add to simulate power compression, the more the frequency response will start to look like the impedance curve. 2x Re is a practical limit though, at and beyond that limit you are into extremely heavy power compression and the voice coil is likely to be hot enough to melt.

Personally I like to design at least a bit underdamped even if I don't plan on getting into heavy power compression. It just seems the right thing to do. This was my thinking even before I became aware of lossy inductance and the issues it presents, mainly influenced by reverse engineering Danley designs.

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post #74 of 75 Old 10-20-2017, 04:40 AM
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So, this has made it to the short list of things I'm considering building.

I've gone back and forth a few times, first I was planning on building othorns, so I ordered the 21sw152 for them...that morphed into skhorn, and probably half a dozen other possibilities, and then I saw this one on facebook. Size is almost completely irrelevant. Being lazier than I care to admit, slicing a few sheets of wood longways and folding it up seems very appealing. The driver seems to model well with and without lossy LE, and it's playing right up there in the ballpark with some of the more popular designs.
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post #75 of 75 Old 10-20-2017, 06:25 AM
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Using the SW152 has proven to be a very well designed motor and doesnt really need the Lossy Le selection selected when modelling. The DS115 does though.
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