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B&C Sub18 Build pics

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Crashpc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Crashpc Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 5:49pm
Of course you can go smaller and worse at once. It is much more difficult to go smaller and better. I am  comparing mediokers or low-end products for the same price. Sometimes the wood work and the wood itself is too expensive for what is inside and what it can do. Some put very poor speakers in big bins, so only what´s left is large box, but not large sound. Those days are (thanks god) slowly but surely go away, to be fully replaced by tactics you mentioned.

You know how I work - I rather put larger powerfull speakers into smaller bins - The bang/buck ratio is not very good, but the power density is very high, distortion is low, and that is my personal goal. Not selling it to anybody. With newer speakers with brutal displacement (both great surface and excursion) you can go smaller than before. But I follow you on the "trick" where marketers really push this to milk and scam people, while I amm talking about rather (many) fractions of decibels  upgrades (up to 3db as extreme) which is not much in real life.


Edited by Crashpc - 11 January 2017 at 5:50pm
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 6:12pm
When you have a chance, try building (Not simulating) enclosures based on the optimum VAS requirements of the loudspeaker. You will find toting multiple boxes to get very low is a waste of time once you move to wards a larger box that can accommodate the VAS requirements of the loudspeaker.

Best Regards,


 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Crashpc Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 7:57pm
Thats how I worked ago, before I found that VAS is not a requirement. We had this talk before, and while I would like to discuss it technically, I am afraid we end up the same. I found that current basic enclosure simulators are VERY reliable, fitting with measured data within 1db/1Hz/ (fraction of ms, or Ohm) etc. Confirmed it again minutes ago on the B&C 18NW100 I had, and on 18NBX100 too. Measurement of the speaker is online at B&C, and the simulation is within 1db/1Hz off from the measurement. How awesome is that...

Now when I see the data fits, I can take for example B&C 18NBX100, and show you what I mean. Maybe you get the sense of my angle of view on things.

Here is Measurement of 18NBX100 from B&C:


That is 90db@30Hz, 95,9db@50Hz.


Here is the simulation of 18NBX100 in WinISD:


See the cursor data down there.
30,1Hz, 89,58db. Fairly close. 50Hz is 94,63. 40Hz is slightly over 1db off too, but we are not comparing the same piece of driver, right? 1db deviation is not abnormal at all. Measured TS parameters are quite off, compared to specifications, so we absolutely know, that they really measured the driver, and it is not simulation based on written parameters, otherwise it would look different.

Now this driver has VAS of 130l (measured). Propably because of the driver was new and stiff while manufacturer did his measurement after some burn-in.
If we put the driver in 130l cab, it would end up very bad, and the simulation shows that too.

Now What if I take smaller box with 21" driver, like B&C 21DS115 and compare...


Oh no, It performs about the same, but in 150l - 1/4 smaller box, but can handle a lot more power, with less excursion (less distortion), and faster GD where it counts (45-100Hz) for a woofer. I.E - it exploits the enclosure it sits in, to a full potential, while 18NBX100 used at its VAS cannot do that, loosing on more powerfull speakers.
Therefore I pick larger stronger speakers. These can make higher power density (db/cubic measure) setup. And when you are space limited, have real car or truck, and only can load it "so much", you take care of it, and look for higher power densities.
Of course, that setup will cost you significantly more, but you dont have to buy another car/truck, so it is even, and the system is small, so you do not have to haul around with it that much.

I have to not forget to point out, that I see and agree with your angle of view. If one needs to exploit the SPEAKER ITSELF to its full potential, it is better to use your strategy, and build the wood around that speaker. I have it opposite - I set the enclosure size and reliability I accept, and then find the driver which will get maximum out of it. Two different approaches, both work for many.




Edited by Crashpc - 11 January 2017 at 9:40pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 9:18pm

If you are content with your sub cabinets falling within -3 dB region within the mid to low 30's, that's all that matters.

 

I would consider that unacceptable for an 18 inch reflex sub more so a 21 inch reflex sub for my requirements. This is why our topology differs.   

 

Best Regards,



Edited by Elliot Thompson - 11 January 2017 at 9:19pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 9:36pm
That depends what you want to achieve. Max spl or lower extension.
Marjan Milosevic
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Crashpc Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 9:38pm
Elliot: Now I see. I put quite some weight on SPL, so there must come some compromise indeed. No free lunch.

Dont let yourself fool into seeing it as unreliable system though - These drivers now have 4,5" to 6" Voice coils, able to handle tremendous amounts of power, and Excursion limits of higher end PA speakers now exceed 30mm peak-peak (Xmax, not Xdam). If you "under tune" this small box with 32Hz Bassreflex, thats the place where excursion of the speaker cone is smallest now. You can add 4-5db of equalization there, and the driver WILL handle. They are crazy! 3000W+ amps for that are not abnormal. So it ends up as a reliable system, having -3db at, or rarely even UNDER 30Hz when tuned. That is fundamental bass, covering all normal musical instruments with ease. Very clever. Of course, I didnt come with it first. I got it from studying white papers, measurements and available presets and setups for commercial products from RCF, EAW, B&C, and more, and I am quite late.

But still, that is PA solution of audio. I see Hi-fi based people buying these beasts too, but using these with very different approach, tuning these at boxes around nominal VAS values so they get usable low 20s or even less for home SPLs (105-115db, depends). And that´s where many speakers struggle, and those with smaller VAS value in even smaller enclosures fail miserably. On that I agree without reservations.

// Marjan M: Depends. When you have enaugh of one, you don´t stick with it that much.
Of course, it´s always design compromise. ALWAYS.



Edited by Crashpc - 11 January 2017 at 9:58pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2017 at 11:46pm

If your top (low midrange) cabinets can play bass on their own, you will not find yourself trying to extract every bit of SPL from your bass bin(s). I've learned that in the mid 1990's.

 

That is why large sound systems (that consist of lots of tops) aim for low frequency extension for their subs. They have more than enough low midrange drivers available to set the HPF to 45 - 40 Hz in their top boxes. This has become even easier as reflex line-array top cabinets are the standard these days and it is rare to see anyone flying fully horn-loaded top boxes.        

 

Small sound systems always lack in the low midrange region. Their top cabinets sound anaemic without their subs. So they require their bass cabinet(s) to play everything from 200 Hz downwards with a lot of SPL.

 

 

Best Regards,

 



Edited by Elliot Thompson - 11 January 2017 at 11:47pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Crashpc Quote  Post ReplyReply Direct Link To This Post Posted: 12 January 2017 at 5:46pm
Yes, I noticed this happens, and I hate it.  I usually tune my tops in 50-70Hz range (depends on size, type of drivers and intention), so crossing with subs at 80Hz is usually a nonissue.
~70Hz is very nice for smaller indoors, as there is usually some room mode/resonance in this range, and you have more drivers working together at this frequency, to mitigate excessive peaks in certain room locations.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 12 January 2017 at 11:00pm

Nothing higher than 40 Hz for my tops. Typically, anywhere from 35 - 30 Hz based on the quantity used.


Best Regards, 

Elliot Thompson
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