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Arts dual lab 12. |
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Hemisphere 
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Joined: 21 April 2008 Status: Offline Points: 2244 |
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 Posted: 26 August 2017 at 5:36am |
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You won't have any real issues with over-excursion as the lab has a huge capacity to go past it's xmax before damage, it just won't sound quite so great.
Apparently acceptable (or even detectable) distortion in peaks at 35Hz for most people is like 25-30% THD+N anyway. Certainly the lower the frequencies, the harder we find it to detect distortion. My comment about use outdoors was based on my first ideas about their output, but if you're not able to supply enough amp power it may still be an issue. It'll be interesting to hear how they do.
Edited by Hemisphere - 26 August 2017 at 7:29am |
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Hemisphere
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Posted: 26 August 2017 at 6:50am |
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Thinking a bit more about that BMS 4x12 idea. After adding the volume of ports, drivers, grille area in front of baffle, cabinet walls and so on. 230 litres is viable but 280 is optimal. With 280 internal it comes to around 385 litres external. 105x56x65.5. It needs to be 105x56 at the front just to fit the 4 drivers on the baffle. 80kg or so with reasonably well braced 18mm/paint/hardware.
Ports are large and long enough to keep vent velocity down to 40m/s even at 6000w input. You can get it down to 30 but you've then got so much port you'd need to add another 25 litres of volume, and virtually the entire baffle would be drivers and ports, but it is possible (and would allow for theoretical extension of the bass with EQ up to 10000w input with 40m/s vent velocity) So it's about the size and weight of a single horn loaded enclosure. Very power hungry (only 96dB/watt despite 4 drivers!) but an iNuke NU6000 for 369 Euros can give it all it needs to reach 134dB at 40Hz, 132dB at 34Hz (it goes 3.4mm over xmax at 48.5Hz, and 3.4 again at 31Hz with that input level). Given the extents people go to get that sort of level of output in the low 30's with stacks of horns I'd say it's a fairly economical and straightforwards option. It's the same size as the X1 bandpass subwoofer with a similar frequency response, but output is greater and obviously a lot more hifi. The drivers are categorised as 'bass midrange' so it's a one box solution. You could run it to 250Hz even. All in you'd be looking at something like 1200 Euros a built, loaded and powered box, or you could build it in very compact halves for ~600 each. (Assuming you already have an LMS - limiter not optional! A bit extra for DSP in the amp.) Which on the market gets you something like this https://www.andertons.co.uk/p/TS218/subwoofers/alto-ts218-active-18-sub -10dB at 35Hz  At the higher end of PA 218 subs though you've got stuff like this for ~3500 Euros. http://www.fbt.it/en/products/mitus/mitus-218sa I can't understand how on Earth they arrive at their 145dB half space claim though. Amp power is listed as 2000w RMS 4000w peak. Even if the true peak is 8000w and the system is 102dB/watt, that's 'only' 141dB calculated. From the spec sheet: http://www.fbt.it/documents/31106/394149/Mitus+218SA/cfa2476b-670b-4ca0-863b-cb2c13c03885 The amp can actually only provide 2000w for 2ms bursts.. it lists a 'max peak' rating of 4000w, but that must be somewhere in the microseconds so it's totally worthless. Published response chart has a peak of 103dB sensitivity, but at 35Hz it's only 95dB/watt. So actually 136dB peak SPL, 128dB at 35Hz, vs 135dB peak SPL, 132.5dB at 35Hz with the 4x12 So it's a very close match, for three times the price, with a 15% bigger box, 12% more weight, and considerably less low frequency extension. Edited by Hemisphere - 26 August 2017 at 8:35am |
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Shortrope
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Joined: 08 July 2013 Location: Ireland Status: Offline Points: 1232 |
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Posted: 26 August 2017 at 9:22am |
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Very interesting...tempted to try this out!
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My Tinnitus is coming along nicely!!
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doller
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Joined: 19 July 2014 Location: japan Status: Offline Points: 538 |
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Posted: 27 August 2017 at 5:40am |
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The Verdict.
My set up.  The racks I took only used the PX 10's  The main Pa Peavey.  His racks and a very dodgy distro.All bridged I think I don't know what amps were powering what.  I was there for the DJ's. It was monitor duty and the main PA was a different firm. I took it as a chance to have a test and a informal booth party. My set up was about as bad as it could be. Plonked on a beach no walls or corners. For testing I thought it was a good senario I could hear just what the boxes can give by themselves. So, the 218 thing. Output. the 218 is I would say has a wee bit more. So I was wrong. Throw the 218 wins too. No surprise there. Lowness the 212 was best quite a bit lower. You would need 8 outside. Biggest problem I had was that the PX clipped for the first time in near 300hrs use. Didn't happen in the workshop. Reading the Amp Log it said that the impedence was dropping too low. Now, a bit confused was it below 4r or 2r. Need to work that out. I was pushing hard intentionaly. I would say that you need a good 2r amp to make these work. I will dust off some old iron this week and test. The speakers still had a far bit more in them I would say. The excursion wasn't at danger levels. All this said and someting that links nicely to Hemisphere's post was sound quality. I would still take them over a 218 or 118 because they sound stunning. They sound like a horn without the throw. The bass is deep , punchy and really nice to stand infront of. Makes you want to dance bass. After 15min of standing in front of the peavey it was so nice to get back in the booth. I did have it in the sweet spot (but I would say that). These are an indoor bin totaly. So much more output inside. Next week they are off to a club night. Looking forward to it. |
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Hemisphere
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Posted: 27 August 2017 at 9:04am |
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I think the reason the 218 wins for 'throw' is probably down to the falling response of the Lab12. It peaks at 40Hz in this enclosure and it's down about 5dB by 100Hz, so by the time it gets to the 'bite' of the bass, the bit we hear more than feel, it's going to be lacking unless you've EQ'd that area up (and to be fair it will be receptive to lots of EQ boost in that region if you have the amp power). The upper bass always throws less far than lower bass to begin with, so that effect would be accentuated.
Impedance is the other thing - it's a 6ohm nominal driver. Did you possibly wire it as if it was 8ohms? If you can get it, the BMS 12s305 wins hands down in this enclosure, even as a simple drop-in replacement with no redesign of the box (as Art Welter confirms). It solves the issue of falling response, has a standard 8ohm rating, weighs 2kg less, extends further, more efficient, etc. Not many clear downsides. In the UK the Lab 12 is very expensive also. 218 pounds vs 149 for the BMS. (actually to match the response of the original box as closely as possible the ports should be tuned a little higher to 37.3Hhz, then the lower bass plots overlap almost exactly for the same watt input, so efficiency is actually the same except when you get to the upper bass (then it's up 3dB at 110Hz).
Edited by Hemisphere - 27 August 2017 at 9:57am |
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bob4
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Posted: 27 August 2017 at 10:12am |
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I dont think it was a fair comparison. The 218 is close to a corner, that 1 m high solid wall is going to help quite a lot by reflecticting the bass back. Although the cab is on a scaffold raised a bit and not right up to that cornwr, i would argue its close enough to make a significant difference. I'm sure your cabs would give more oomph as well if you positioned them in a similar way.
Nice work, love the bins! |
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doller
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Joined: 19 July 2014 Location: japan Status: Offline Points: 538 |
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Posted: 27 August 2017 at 10:29am |
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You are a man who knows his stuff Hemisphere. I would say you are spot on with your predictions. I would love to try the bms, just to inport 8x would be pointless. I can get the labs here for aroud 125 quid. It is one speaker that is cheaper. I am crossing these to kicks at 70hz. I am aware of the graph. I have plenty of kick on this system needed lower that was one of the points.
They are wired as a 3ohm box. With new amps I wasn't too worried. The PX specs are confusing. The sales bumf says 1000w 2r the A3 peice of paper you get as a manual says 4r only. Go figgure. The amps do a good job of keeping everything under control. Quite impressive for a cheapo. Problems only arise when I push hard. Under normal conditions not a problem. The amp psu and prosseser never get danger hot. Reading the device info. Even after 8 hrs pounding. I think the main problem with these outside is that you could kill the drivers without any sign of it coming. They are so clean up to max. Few beers and a heavey bass tune. Off to the recone shop. |
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Hemisphere
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Posted: 27 August 2017 at 10:52am |
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Cheers - to be honest my knowledge is patchy theory poorly backed up with practice, full of assumptions and often fundamentally wrong but I've been making an effort to be more thorough recently - less assumptions, more research and application of theory through simulations.
Talking of which I was looking at the impedance plots for the Lab 12 vs the BMS, and it seems like the impedance in the passband you're playing through them may be lower than the rated 6ohms. Your amp almost certainly shouldn't run 2ohms, it's probably a case of 'technically can but probably should't, especially not on sub frequencies' - the engineering department and the marketing department are often in disagreement on ohm ratings! So if you wired them at 3ohms, but it was actually presenting something between 2-2.5 ohms in subs played right at the limits of the amp, that would do it. So for example, in your passband, the BMS rated 8ohms has impedances of: 66.5 ohms (peak) at 58Hz 23.5 at 70Hz 8.1 (trough) at 36Hz 21.5 ohms at 28Hz. vs the Lab 29 ohms (peak) at 46.5Hz 6.1 ohms at 70Hz 5.6 ohms (trough) at 33.5Hz 7 ohms at 28Hz So by these points at least, if the BMS is 8ohms then the Lab is more like 4ohms, and in many areas (28Hz and 70Hz ie) the impedance for the Lab is incredibly low - considerably less than half of the BMS. Edit: Those drivers will take a LOT of excursion. The most likely cause of death would be amp power over their rating. Peaks will be less of a problem than sustained RMS tones, so with high power you'd absolutely need an RMS limiter. I think excursion is something like 25-30mm each way, 50-60mm peak to peak on the Labs, before damage. If you forget to high pass, that might do it but you'd still need to get very unlucky with some unusual music that decides to blast some 20-25Hz tones at maximum amplitude. Even with 1500w input to the box, the excursion of the Lab at 25Hz is 25mm.
Edited by Hemisphere - 27 August 2017 at 11:04am |
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bob4
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Posted: 27 August 2017 at 11:37am |
Careless needledrop could do that as well..... I bought an ecler nuo2, that doesnt seem to have a low pass filter or at least not a very steep one. Needledrops make my cones jump literally. Didnt have that problem with my previous mixers |
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doller
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Posted: 28 August 2017 at 8:15am |
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I Know what you are saying bob about the sea wall. I was still happy to test them this way. Inside they are a very different animal. The main thing that I came away with was sound quality. No honkey bass really pure.
I was trying to work out what kind of impedence the amps would be seeing. You did the work for me thanks Hemisphere. When I do a DJ event I always put a Allenand Heath z14 inbetween the djm and lms. Maybe a bad thing but works very well for me. I almost never hit the limiters. Only after I have had a few beers. At the moment I don't have the amp power to really destroy them. Eyeing up K3's. I have switched them over to an old QSC 3800 If they weren't 40 years old they should give me 900 into 2r. I can't honestly here much difference in output. They will sit on 2r all day long. Doubling would give 3 db I know. I might test them on a pl4 to see if I can get the over xmax. They really don't seem close yet. I have the grill sitting 15mm off the basket so I hope it would hit that first. Then I would know. I think they are sitting just over the 2r. so the amp was telling me 4r. |
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doller
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Posted: 28 August 2017 at 1:31pm |
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May as well post the few build pics I have. Hope to paint them this week.
handles routed out  Baffel template  First cut 32mm baffel  second cut  bracing  Used the off cut fronm the baffel to locate the port board   inside without the top panel.  Hard wood runners so they don't soak up spilled beer. MDF has a habit of doing that.  Loading. 
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Hemisphere
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Joined: 21 April 2008 Status: Offline Points: 2244 |
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Posted: 28 August 2017 at 1:52pm |
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Great build - good call on the runners. Just looking at that row off drivers you get a feeling of the sort of sound these must be putting out - The magnet to cone ratio is just phenomenal!
Edited by Hemisphere - 28 August 2017 at 1:54pm |
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Hemisphere wrote: