Cheap driver/box combination to get low and loud |
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1649 |
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There is an argument that a tall box can be easier to load
into some vehicles, as you may be able to tip it backwards into the vehicle
over the lip of the load bed from an upright position, or lift one end in at a
time from horizontal. I haven’t tried either of those as I've always been on
crews of 2+ people and/or had vehicles with ramps any time that shape box has
been used, so can’t vouch for this directly though.
If you want to split your project into singles, just halve
the net volume from the original calculation, or check out any of the existing
plans for singles – Fane, B&C, 18Sound and probably several more all have
plans for that size box freely available on their websites. I wouldn't recommend trying to utilise a vent that is only
baffle thickness in length, as that will restrict you to either very high
tuning frequencies (for a sub) or very small vent areas, which will result in
unacceptably high amounts of port noise as airspeed will be really high. To calculate your actual box size, start with the modelled
Vb, add in the things you definitely know about (eg the size of the port), add
in a reasonable estimate for things you don’t (Eminence for example quote a
volume occupied by all their drivers, so find one about the same size & weight
as your driver and use the value from that) and things like bracing and
handles, then just do the arithmetic. For example, say you had Vb = 250l, driver ≈ 7l, port ≈ 1.9l,
a couple of bar handles ≈ 2l, bracing ≈ 5l then you have a total of approx. 266l
to accommodate. Divide that by 6.3 (your width, in decimetres now) and you get
42.2, so your depth and height can be any values (in decimetres again) which multiply
together to get that eg 6x7.03, or 600mm high by 703mm deep internally. Add up
the height of your port, with the timber used to create it, and the diameter of
the driver itself and a couple cm extra for clearance to give yourself a
reality check that you can still fit everything in. Then put as many strips of material in as bracing as you can
fit in whatever allowance you originally gave yourself for that – again there
are plenty plans out there to give you an idea of how much and how it is best
laid out. I’d have a think about that width, for a couple of reasons:
depending on where you’ll store and transport it, that may end up a little
wider than you really want to carry – 63cm internal makes 66.6 external, plus
the width of your arms if you’re carrying it may make getting through some
doors a little awkward. You may also want to think about the size and shape of
any vehicle you’d use to transport it – make sure at least one and preferably
two of your external dimensions fit in integer multiples across the width of
the vehicle so you can pack it neatly and securely. Last suggestion: If one accepts the extended definition of
Xmax (ie (Hc-Hg)/2+Hg/4)) as valid then even a cheap P.Audio like the IMF-HP18B
will achieve about the same output as your dual 18 box described at the top of page
3, per
driver, as long as you don’t want to push it too low. 130litres, tuned to 36.3Hz, 100Hz Butterworth 24dB
crossover, 39Hz Butterworth 12dB High pass overlapped with a 7dB boost at
34.6Hz (Q of 3), net power (where the boost is in effect) 1200W (ie what you’d
use to get headroom anyway): |
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app
Old Croc Joined: 26 December 2013 Location: Finland Status: Offline Points: 2435 |
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^Pure niceness from you sir! Much thanks!
I might need to rethink the "plan",again :D |
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app
Old Croc Joined: 26 December 2013 Location: Finland Status: Offline Points: 2435 |
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Okay.I decided not to go with the cheapest drivers :D
I have a few options Im thinking that might be usable but still on the "cheap" side.What would you use in reflex box and what of the following would be the ONE! And the options are: PD.188 http://www.precision-devices.com/Product-Details/PD188 costing 239 euros. Fane sovereign pro 18-800P http://ljudia.fi/Archive/ProductFiles/939813/Pro18800P%20-%20Specification.pdf 219,50 euros Eminence sigma pro 18 http://ljudia.fi/Archive/ProductFiles/934244/Sigma%20Pro%2018%20-%20Specifications.pdf 217 euros. P.Audio E18-600s http://ljudia.fi/Archive/ProductFiles/938569/E18-600S%20-%20specifications.pdf With a cost of 150,05 euros Which one of these drivers would you use to make a loud/deep and efficient 18" sub or 2? Its a different ball game to use 2x150euros drivers than 2x239euros drivers...300euros vs 500euros.Of course if the sound is twice as good its ok to get the 5ooeuros costing drivers :D But if not... Any comments and experience on the drivers listed above appreciated.Please feel free to add a driver in the same price range If you feel like it. Thanks! edit.Not being a super power hungry driver but still playin low/loud is also considered a good thing. Edited by app - 11 November 2014 at 1:24pm |
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mini-mad
Old Croc Joined: 13 July 2012 Location: london Status: Offline Points: 6903 |
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Or the P.Audio 18elf..... €160 driver...
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If it sounds like a gorilla is trying to escape, turn it down.
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app
Old Croc Joined: 26 December 2013 Location: Finland Status: Offline Points: 2435 |
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Thanks!Too bad theres not certain p.audio drivers available easily ordered from finland or sweden. Would I benefit from using 4ohm drivers? for example these http://www.eminence.com/pdf/Delta_Pro_18C.pdf they are on sale for 124 euros. That would be roughly 250 for a pair which is "in budget". |
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app
Old Croc Joined: 26 December 2013 Location: Finland Status: Offline Points: 2435 |
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^The Idea is to get this http://www.thomann.de/fi/behringer_inuke_nu3000dsp_amplifier.htm or http://www.thomann.de/fi/behringer_inuke_nu6000dsp.htm this amp.which are class d so it wont suffer from heat problems (I suppose) .
I think there is more downsides than good things about using 4ohm speakers... |
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1649 |
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The PD and Eminence both have relatively low Xmax values, and in the case of the Eminence they don't publish enough info to make even a slightly informed guess about whether or not you can push them any further than that.
The Sovereign Pro, using the extended calculation I used for the P.Audio IMF, comes out a little lower, so as a first approximation you wouldn't be able to push it quite as loud/deep, assuming that calculation is valid. The E18-600S specs seem a little off - they quote Mms as lower than Mmd, when it should be the other way round. If we assume Mmd is right and scale up for Mms accordingly, then we actually end up with parameters that are consistent with the remaining ones given. (I think the 117.4g Mms is simply a typo for 171.4g, which fits the scaling from Mmd too) The higher Qes and Fs compared with the IMF do mean it would rely much more on EQ's to stay reasonably close to flat below 40Hz in a small box, which also means that the effective power required goes up, because of the extra boost. In the same size box as the IMF, it would end up needing too much power to fully utilise its excursion, so you'd need to increase box size to about 155l to get flatter without relying on excessive boost. That's still quite a lot more compact than the 250l you suggested a few posts back, so may well be worth it for you. Even with the increased box size compared with the IMF, this does require more processing, including an extra out of band parametric EQ to keep the upper bass/lower mids flat and a higher High Pass Filter frequency for excursion control. These do mean that Group Delay is a little higher than for the IMF, so the very lowest notes may sound a little "slower". One thing to be aware of is a phenomenon known as Hoffman's Iron Law. This basically states that box size, LF extension and Efficiency are unavoidably liked in a 3 way compromise, so if you want high efficiency and good LF extension, then box size has to increase to allow that. If you want a compact box, then either efficiency or extension will suffer. It would be well worth having a really good think about how big a set of boxes you can manage therefore, as that may influence what drivers to go for - eg if a large box would be perfectly OK then some less efficient drivers may become more viable. However, the total amount of air a driver can compress (Vd on the spec sheets, calculated as Sd*Xmax), will still determine how loud it can get at low frequencies, so if you're checking out other drivers always look for (or calculate) that as an early part of your evaluation. Regards, David.
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Mark James
Old Croc Joined: 15 January 2006 Location: rig side Status: Offline Points: 5309 |
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+1^^^
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me so horny me love you long throw
horn loaded for her pleasure |
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bitSmasher
Old Croc Joined: 23 June 2012 Location: Melbourne Status: Offline Points: 2295 |
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On this box posted above, 130L / 36hz
How big a vent would you recommend? I ask as I'm almost finished my own design, first one from scratch, and it's very similar... I'm caught up at vent size now How high an air velocity can we tolerate? I see 30m/s posted regularly - can we accept higher velocity at the lowest frequencies? ie 40-45m/s at 35hz, when at xmax, which I wouldn't expect to occur very often |
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1649 |
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To be completely honest, I've yet to turn any of my models into actual boxes, so I can't say for sure. Tony Wilkes, who's opinions on vented boxes I had a lot of time for, mentioned he aims for
20-25ms-1, so that's probably ok. Untill such time as I get round to building and measuring anything myself, I wouldn't recommend anyone else risks anything with a higher airspeed than that. There is a Paper written by some JBL design guys for the AES that summarised a lot of research on port behaviour; while some of it is a bit over my head technically speaking the general conclusion was that it's definitely worth using the biggest possible port you can accommodate as some artifacts start showing up earlier than the classic "chuffing" type noise.
One version of it is here: http://koti.kapsi.fi/jahonen/Audio/Papers/AES_PortPaper.pdf Cheers,
David |
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app
Old Croc Joined: 26 December 2013 Location: Finland Status: Offline Points: 2435 |
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Man this designing is hard work. I just cant seem to get things like I want to.Winisd is coming out of ears at the moment
I bet theres many nice, budget sub plans out which people are sitting on. Please share if you have some good ones or know where to find some. |
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bass*en*mass
Old Croc Joined: 03 September 2009 Location: "unknown" Status: Offline Points: 4009 |
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might be worth saving a little more on drivers and go for a tried and tested design that works well with your type of music?!
you wont regret it ;) sorry if i didnt read properly but have you stated yet what sort of venues you have access to and whats the masteplan with your new toys? would make it easier to recommend a design suitable for your needs :) |
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