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post #241 of 248 Old 01-30-2019, 08:14 AM
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Quote:
Originally Posted by Petr Berka View Post
Maybe stronger drivers have this advantage where restoring force of the spider and surround is very minor compared to the motor force (and compared with other drivers), so it might push little further with fixed distortion number, yet the speaker still won´t run any far ahead from the issue...
Petr,

Maybe I misunderstand your point, but I would say the opposite. The suspension is very strong and finding materials to design these high stiffness suspensions that are also durable is one of the largest challenges in professional transducer design.
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post #242 of 248 Old 01-30-2019, 12:09 PM
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Originally Posted by bennettprescott View Post
Petr,

Maybe I misunderstand your point, but I would say the opposite. The suspension is very strong and finding materials to design these high stiffness suspensions that are also durable is one of the largest challenges in professional transducer design.

Yes, I must suck with describing stuff. I´m sorry for that. You got very good factical point though. I didn´t exactly think about this "situation" you proposed.
What I meant is, that if the motor force is in greater ratio compared to the restoring force in working range, the influence of the spiders and surrounds is lesser. If the ratio gets from 20 to 10 (double the stiffness) in cone excursion compared to resting position, it is very different to ratio getting from 2 to 1 with weak driver....



The devil is in the details though, so we might find that real drivers don´t run much further with this. It is not that simple at all with real drivers, I'm aware. Depends on many things, the most visible is Bl decreasing in cone excursion. Yet, it gets plus points in my book. High Qms, Low Qes, and Qes with Qts being nearly same gives the taste of it. But TS parameters only can be an indicator, as it has no way of knowing how the suspension stiffens up in excursion, or if there is a brick set at 2mm excursion to stop the driver completely. Klippel measurements show this in better light.


The description of the coil situation is perfect. I guess we got caught in the short story description too much.
I knew about different gap size due to the flux density found in the specs. I knew about that it is not that good to simply count with gap height, because there is magnetic field outside of it. I also knew that double the wire doesn´t mean double the coil volume. Yet it all was not sufficient to offset the basic volume math to get the wire into the gap. With split winding coil, we´re now getting into that territory. All makes sense now. Thanks for your patience with us, and all this help.


For the "Essential" part of the response, I hope that it has been established that you, B&C guys, don´t waste your time with bunch of noobs with pocket calculators. (Welp, I might be guilty of often dumbing down complex problems for pocket calculator to get moving fast with educated guess first).
If you have the chance and mood, send my thanks to the B&C staff, technicians and engineers for their work and for their will to provide informations.



We´re getting to the awkward point it might sound like stupid competition wants to start their own business with all that info. :-)

Last edited by Petr Berka; 01-30-2019 at 12:27 PM.
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post #243 of 248 Old 02-24-2019, 02:12 PM
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Hey.


Just popped in to tell about my 8NDL64 adventure in case of anybody was interested.
There is no solution to the excessive wind-noise coming from the motor structure of these beasts. It is an internal noise, and no matter how much I tried (even cutting into the suspect spider), there is no significant help to it. So I´ve basically donated one OK piece and one with altered spider to someone else to play with these. Yet, I need to continue with my project of beasty small and powerfull 2x8" V-slotted tops. Any recommendation for strong, sensitive, hi-fi behaving drivers? B&C at best, other choices not distarted....
Looking at 8MBX51, I wonder if these manage to work in mild horn loading. One can see through the surround and almost through the cone too, on B&C webpage.

Last edited by Petr Berka; 02-24-2019 at 02:31 PM.
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post #244 of 248 Old 10-03-2019, 07:05 AM
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I am restricted to 18 inch cubes (if I want 2 matching subs this is a hard limit) and have been struggling to find the best driver. I want very clean bass between 20 and 120 for movies and normally have set to -15/-10 below reference in a 1500sq3 room. I am thinking of buying a couple of the 15ds115 to use in a sealed alignment and they seem happy with just 45l volume although I am a bit wary as the modelling in winisd with my input throws up some low qts numbers and I cant find any forum builds for anything similar. They would be powered by an inuke6000.
Has anyone built anything along these lines or is it a bad idea with better drivers out there for my use?
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post #245 of 248 Old 10-11-2019, 02:03 AM
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Hello. What space available do you have for your subs? I mean how big? How much volume?
It is cost inefficient to use these speakers for closed enclosures. For closed box, you completely rely on cone displacement volume, and two 15"s will not do much at 20Hz.
For this, you need much more cone area, or other compromises with great impact on either size, price or output. Therefore for smaller rig, I greatly recommend switching to ported, TML or various horn enclosures.
Low qts by itself is not that bad, if you have an amplifier, that can feed the drivers. I´m afraid inuke 6000 is not "it" either", as a rule of thumb.
In a way, there are no better drivers, but you definitely need to look for those higher class hi-fi drivers with much higher available cone excursion, if you insist on your plan.


//I hope I finally put my 21DS115´s in most compact boxes - under 23*23*29 inches. Finishing and measurements ongoing. It seems that is still very usable, and can give most output for my needs in this box size, compared to "any other" driver around (and money).

Last edited by Petr Berka; 10-11-2019 at 02:06 AM. Reason: adding news
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post #246 of 248 Old 10-11-2019, 05:32 PM
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Hi Petr thanks for responding.
Ok a bit of background and i'll try to be brief! Space and placement is limited. If I am going with one suboofer only then I could fit one 20 inch cube in max. If going for two matching then its 17 max each. These are real maximum number with me pushing the size as much as possible.
The room is 1500ft3 so is tiny compared to what most members on here have in the states.
I have got multiple subs and currently running just use one mk v12 which hits 120db at 30 and 110db at 20 at the main listening position due to room gain which kicks in hard about 45. The v12 has one 12 inch driver which think is almost certainly under 15 xmax and driven by 300rms amplifier. The issues happen above 50 where output is between 105db and 90db and there are multiple dips across the 2 seated positions. I want to cross at 120 (if not higher) with my mksound 150 speakers which are brilliant except output doesnt effectively go that low with them being sats. I have had a ultra svs ported sub which gave a huge amount of output but was even worse to eq as the power in the tune just magnifies the 15db hump I have low down.
Sealed I have used a diy fi q15 with about 27 xmax fed by one channel of the inuke (about 1800rms). It has lots of output up to about 70 but isnt the cleanest souding above 80hz.
In all honesty I suspect 2 MK v12 subs would hit my output goals for everyday use but I fancy the project ans seeing how good I can make compared to reatail subs and cost wise I could buy 4 15ds115 drivers for the price of one retail mk v12 sub.
I already have the inuke which I though would be sufficient for most subs with 1800rms/3000 peak into 4 ohm per channel. To get more power than this I suspect i'll need to get a dedicated circuit which I think is overkill for my requirements.
So what I am looking for are 2 subwoofers that will work in 55l enclosures (max) that provide the best balance between very low distortion, transient response and headroom for the frequency range between 17 and 130.
My choices are limited. I could go for daytons HO 15 but they have 13xmax and take about 800rms, they are a little cheaper here than the ds115 but not much. Eminence lab 15 are cheaper still but again are lower xmax and rms handling than the b&c. The Peerless STW 350 is more expensive but I worry about its lower sensitivity affecting the performance above 80hz and driving two of them when rated at 3500/5000. Beyound that most 15 start to want a larger enclosure so we are dropping back to 12 drivers. I would conssider something like the SI HST 15 but the cost imported would be 3 times the cost of a 15ds115 and again I worry about the sensitivity of the long throw drivers to deliever in the 60 to 120 region I am lacking. I like the look of the AE drivers but there 15 probably need a bit more space and only have a 14xmax and again deleivered they are going to be at least double the cost of the 15ds115.
I am open to ported and horns but with my limited knowledge I dont think they would fit with my requirements especially the size.
Any suggestion greatly appreciated.
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post #247 of 248 Old 10-11-2019, 10:49 PM
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Hello.

That brings little more light to the situation.
If you do not have any other choice, then it seems that two15” will have to do that. Two 15”s will overpower one 18” most of the time.Yet, having two 21”s in the same room size, I do not see how two 15”s in 55l boxcould do anything sufficient. I do not have experience with that low tuningsand “theatre setup”. To me it looks like unreachable goal. Hope someone willchime in and correct me on that.
There is no inherent problem with inukes. I was thinking8Ohm drivers, and those high motor strength and low Q drivers need unusuallyhigh voltage. The amplifier has to have that capacity. If you can get 4Ohmmodels, then it should be okayish. Those drivers will have lower Re though,which might strain your amps a little more.
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post #248 of 248 Old 10-27-2019, 06:37 AM
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Thanks again Petr. Unfortunately 2 21 isn't an option for me. Whilst it costs almost the same financially the box sizes are not possible and as a full system its crossing at 100/130 with inwall mains. I am happy with my mains except that they need crossing over a bit higher than a larger speaker would and that is what is making me lean towards pa subs with there higher sensitivity.
Interesting point about the power. My inuke will be on a shared 240v circuit. Whilst not ideal my practical side says anything needing more than that is overkill for my personal needs, which due to a small room and preferred listening level, are far less demanding than your average avsform diy forum member I suspect.
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