Newbie needs Beyma 15K200 help - diyAudio
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Old 3rd October 2008, 10:39 AM   #1
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Default Newbie needs Beyma 15K200 help

My query is rather similar to this one which never got answered fully enough for me. how low can go with beyma 15K200?please help At least some of the plots posted don't work any more and it drifted slightly off topic and I'm just a simple newbie.

Current System
I am currently using a Velodyne SMS1 subwoofer manager/EQ SMS1
this feeds a pair of active Acoustic Energy AE308 subs ran in mono URL=http://www.acoustic-energy.co.uk/About_AE/Product_history/AE308.asp.]AE308[/URL]
An unfiltered signal is sent to biamped Exposure Super XVIII power amps feeding Acoustic Energy AE1 mk2's AE1 (mk2 has better xover and is biwreable).

This set up has response of +/- 1 dB between 22 and 200Hz and sounds great. The EQ on the Velodyne is pushed as far as would really like in order not to damage my subs but not so far as to be asking for trouble yet.

The Plan
I inherited a pair of Beyma 15K200's in high density vented 116 litre cabs (internal dims h64cm, w45cm, d40.5cm). With bracing and magnet spider assembly I figure they have about 108 litres of useable air. They came with front baffles cut for 15'' and 8'' and Beyma CP25 horns. These boxes have just been taking up space for too long.
I thought it would be fun to isobarik the Beymas. I anticipate rolling this sub off somewhere between 35 and 50 Hz in practice to give more of a rumbling presence to the system not to shake the house down though. I don't try to run my system at PA levels. I'll add a pre built sub amp with level and continuous phase (I haven't decided which but I have lots of manufacturer shortcuts already and much forum reading to do). I hope to dial this in with my existing subs to give extra weight and energy when required.

My woodworking skills are poor so I propose to use one of the cabs that the Beymas came in. I will just take a hammer to it and replace the front baffle, retaining the original dimensions. I intend to break up the second cab to provide new front baffle and internal woodwork in new cab. Transmition lines and horns are probably out of the question due to complexity of design and poor woodwork skills.

Will This Work?
I have a WinISD plot for a 95 litre box 4th order bandpass with 12.5 litre front and 82.5 litre rear chambers and port tuned to 43Hz which has a response peaking at -13dB at 20Hz, dropping to -15dB at 50Hz then rising to -14dB at 95Hz and falling off very steeply after 100Hz to -33dB at 300Hz. This plot is unfiltered.

This 95 litre cab plot will hopefully leave me room in my 116 cab for the isobarik chamber.

Avge SPL at 1w1m = 81dB between 20 and 100Hz though

I'll need quite beefy amps to drive this system but the 15K200's are rated at 200w and there are 2 of them to run, the main system runs at 90dB@1w1m.

Any Comments?
If you've bothered to walk with me this far thank you very much. This is where you can tell me my system will not work. Remember this is a first attempt at sub design and I've been at it for 2 days now. I know I have much to learn.
I'd greatly appreciate any comments you may have on my plan.
[
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Old 5th October 2008, 02:21 AM   #2
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Ignore above post.

I've realised an error in how small I thought I could make Isobaric cabinet. Consequently the main cabinet is smaller than anticipated, whole frequency response shifted up and ports don't fit without tuning fs higher too.

I'll keep working at it.
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Old 5th October 2008, 02:46 PM   #3
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Hmm, if your woodworking skills are good enough to mod two cabs to make a new single cab, then you can make a new one from scratch and save yourself a lot of design headaches/compromises. Also, to realize all the performance of using high power it will need a very large/long vent, so a passive radiator (preferably two in a bipolar layout) is required to ensure there's no audible vent harmonics (noise) to comb filter with the mains' output. You could stuff the vent to damp them of course, but then it would heavily roll of its LF output. Another option would be a labyrinth vent, but next to impossible to tune without making a new one.

A way around using PRs is to make a tapped horn, but then it will be >12 ft^3 even using dual drivers in a 'clam shell' isobaric configuration, though it won't take much power to play loud at vanishingly low distortion.

All things considered WRT your app/modest output requirements though, 'clam shell' isobaric in a sealed cab EQ'd flat in-room seems the best solution with these drivers, so now all you have to do is board up one of your cab's horn and vent cutouts. In a corner wired in parallel with at least 300 W (preferably 600 W) on tap you should have no trouble hitting ~DD/DTS reference levels down to around 20 Hz at low distortion, so should 'rumble' pretty good.

BTW, for simming BPs, Hornresp is a much more accurate program overall than WINisd or similar.

GM
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Old 5th October 2008, 11:35 PM   #4
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Yes the isobarik clam looks like a good option.
Simple construction, cleaner bass, less cone displacement etc.
I'm not worried by -3dB output with these sensitive subs given relative inefficiency of tops.

WINisp doesn't indicate closed box for these units but I can't see the problem in a 110 (effectively 220) litre box. Am I missing something in my newbie ignorance?

I'd been modelling some simple ported boxes but at low frequencies they look like they'd flap their cones like baggy trousers on a windy day. Beyma15K200 Xmax=7.5mm.

Horns and transmission lines are probably beyond my build capability. Hornresp isn't working on my PC anyway, though I've not tried too hard to fix it.

I can't use corner loading as side walls are thin plaster into roof apex. They boom horribly when excited by my current subs, let alone 15'' units.



Clamshell it is. Next step is to build and start wooying about amp/filtering/xover.

Cheers for your suggestions.
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Old 6th October 2008, 03:45 AM   #5
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Not really. I mean there's some rules-of-thumb for using T/S specs to get the most bang/buck out of a driver, but the bottom line is any driver will work in a sealed cab and since you're not interested in seeing how loud you can make it and the fact that with isobaric the usable Xmax is doubled you shouldn't have any over excursion problems as long as you don't get carried away with EQ.

They can work quite well in vented if tuned low and due to its relatively powerful motor (low Qts) it won't 'flap around' as long as you don't make the cab so big it's obviously under-damped, though even then you can use stuffing to correct it. Of course all vented alignments 'flap around' below its tuning since it's completely unloaded, so you either tune them low enough that it never gets unloaded or use some form of EQ to protect it just in case.

GM
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