6v6 Posted January 4, 2015 Share Posted January 4, 2015 Hi all, So a while back I made a [url="http://basschat.co.uk/topic/200152-1x12-diy-cab-build"]DIY 1x12 cab[/url], using the Beyma SM212 12" woofer, following [url="http://basschat.co.uk/topic/199000-which-ceramic-12-driver"]some discussion[/url] and considerable help from generous folks on this forum. The cab has worked out great, I've done numerous gigs with it, and it holds it's own in most pub-gig scenarios absolutely fine with just one cab. That said, I'm considering a second cab to stack on top, so I've got a modular rig which will work for both bigger and smaller gig/rehearsal situations. Obviously, I could just build another identical cab (I know this may be the technically best solution), but ideally I'd like to pair it with another smaller (more portable) cab. I'm considering building a cab with a 10" (or even possibly 8") driver to stack on top, but how can I do so in a way which won't cause undesirable phase issues? I've read about designing stacks of dissimlar driver sizes for "similar phase response for optimal coupling", but how do you do this in practice? (I'm somewhat familiar with WinISD, do you just compare phase graphs in there? If so what aspects of the enclosure design infuences that response?) Also thoughts on a suitable driver appreciated - I'm considering a celestion BN10-300x as the sensitivity is comparable with the SM212, it's light, and the price is good for a neo driver (not modelled it yet though..) Thanks in advance for any thoughts Quote Link to comment Share on other sites More sharing options...
taunton-hobbit Posted January 4, 2015 Share Posted January 4, 2015 Thinking out loud here, but Barefaced seem to find no issues with what you're proposing - why not have a glance at the tech stuff on their site, some of it might be helpful - if you're feeling really cheeky, you could pm Alex & ask - he might advise........ Quote Link to comment Share on other sites More sharing options...
HowieBass Posted January 4, 2015 Share Posted January 4, 2015 ... or ask Bill Fitzmaurice on here! Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted January 4, 2015 Share Posted January 4, 2015 (edited) I haven't done this, but I'd want to look at the impedance graphs too. The power distribution between the two cabs at a given frequency could be uneven if they have peaks in different places, working one driver harder than the other. Edited January 4, 2015 by Beer of the Bass Quote Link to comment Share on other sites More sharing options...
Dan Dare Posted January 4, 2015 Share Posted January 4, 2015 Good point from BotB. May be safest to use an additional power amp for the extra cab. Used PA power amps can be had cheaply enough - just drive it from the line out. One extra 8 or 10 won't add a lot, though. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted January 4, 2015 Share Posted January 4, 2015 Mixing cabs can work well, and it can be horrid. The problem is that it's difficult for even an expert to predict it in advance. With identical cabs you know what you're going to get. Quote Link to comment Share on other sites More sharing options...
6v6 Posted January 6, 2015 Author Share Posted January 6, 2015 Ok, thanks all, trial and error I can do just wasn't sure if there was a more scientific method I could be applying. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted January 6, 2015 Share Posted January 6, 2015 [quote name='6v6' timestamp='1420584883' post='2651086'] Ok, thanks all, trial and error I can do just wasn't sure if there was a more scientific method I could be applying. [/quote]There is, but it's way beyond an amateurs skill set. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted January 6, 2015 Share Posted January 6, 2015 Bill's spot on. If you look at the frequency plot on the SM212 spec sheet you'll see lots of minor lumps and bumps as well as the generally flattish overall shape. A different speaker will have its own lumps and bumps and they won't line up. Where they do you'll get the extra output you'd expect, where they don't one speaker will fill in for the falling output of the other. If the manufacturers charts were completely accurate and also made under exactly the same test conditions then you could theoretically line up the response charts and work out the combined response. In practice there are so many little resonances, and incomplete data, so the process isn't practicable. Even if you could do this it wouldn't really tell you subjectively what the speaker will sound like, the only way is to try it really. You don't really need to worry about amplifier load against frequency, most amps aren't going to struggle with two 8ohm speakers and it is the impedance chart and not the frequency response chart you should be looking at to determine load. Phase problems won't differ because you use different brands, that's really just about the distance between the radiating parts of the speaker, additional speakers will lose the top end response off axis more quickly because of this but it would be much the same for any two speakers of this size. I recognise the bug though, you want to try something different this time because you can. You'll end up with a perfectly useable 1x10 and the two speakers might work OK with each other they'll certainly make a louder noise. Sensibly another identical speaker would preserve your sound and give you a lot of headroom. I've gigged that set up and it is impressive, but if it were me curiosity would probably trump common sense. The best value mid price 10 seems to be the Beyma SM110, give it a look at least. Quote Link to comment Share on other sites More sharing options...
6v6 Posted January 8, 2015 Author Share Posted January 8, 2015 [quote name='Phil Starr' timestamp='1420588174' post='2651147'] Phase problems won't differ because you use different brands, that's really just about the distance between the radiating parts of the speaker, additional speakers will lose the top end response off axis more quickly because of this but it would be much the same for any two speakers of this size. [/quote] I guess this was the crux of my question really, e.g is there a way to model the dispersion and/or is there a way to calculate the optimum spacing of the two drivers, assuming they are vertically aligned on the same axis? I'm sure all that may well be "way beyond an amateurs skill set", but as a professional engineer whose not scared of a bit of maths, I can't help wondering about these things [quote name='Phil Starr' timestamp='1420588174' post='2651147'] I recognise the bug though, you want to try something different this time because you can. You'll end up with a perfectly useable 1x10 and the two speakers might work OK with each other they'll certainly make a louder noise. Sensibly another identical speaker would preserve your sound and give you a lot of headroom. I've gigged that set up and it is impressive, but if it were me curiosity would probably trump common sense. The best value mid price 10 seems to be the Beyma SM110, give it a look at least. [/quote] Haha, yeah - guilty as charged - I know building another 12 is the logical choice, I may end up doing that anyway given the reasonable cost of another SM212, I just can't help the serial-experimenter's urge to try out something different too Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted January 8, 2015 Share Posted January 8, 2015 It's probably easier to think of these as comb filtering problems. If you have two points radiating the same coherent wave energy then you get potential interference off axis due to the time delay between the two waves. Basically if the sound (or light or any other wave) has to travel further from one point than the other then it is going to arrive at a different part of the wave. If the difference is half a wavelength then the sound wave from one part of the speaker which is moving forwards arrives at the same time as the wave from the other side moving backwards, resulting in no sound at that frequency.There's loads of stuff on this if you google it but it soon gets into the maths http://en.wikipedia.org/wiki/Comb_filter http://en.wikipedia.org/wiki/Interference_%28wave_propagation%29 The phase problems we normally think of are just down to the distance separating the furthest points that are radiating the sound if they are less than a wavelength apart then no problem at that frequency. Above that you get cancellation off axis and eventually lobing. if the speakers are lined up vertically then the additional fall in off axis response will occur only in the vertical plane. So get the speakers as close as possible and put one on top of the other. There are loads of other comb filtering issues due to reflections from nearby hard surfaces reflecting sounds and even by diffraction from the cabinet edges. Quote Link to comment Share on other sites More sharing options...
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