2 x Jack 112 Lite

[Bill Fitzmaurice]

Bill, could you possibly explain WHY this was chosen as a standard please? It seems a bit odd to do it that way.

It's the result you'll get when a speaker is mounted in a wall in an anechoic chamber, the standard that's been used since the 1920s. If you don't happen to have an anechoic chamber handy you have to measure ground plane to get the half-space anechoic result below the baffle step frequency and either elevated or upward firing to get the half-space anechoic result above the baffle step frequency.

[sine143]

Probably to make it easier to test/standardize. It hard to levitate a speaker 50 feet in the air for measurement purposes only

[escapemcp]

Many thanks Bill. It just seemed an odd way to do it and I was wondering why... A lot of things on here seemed 'odd' at first, but I am slowly getting it

[Charles Jenkinson]

OK, I think I got a good result. It's been chucking it down today on and off, so I'm feeling this is gonna be as good as it gets, though I do like the idea of doing it properly. See picture below.

In the picture, the J12 array is 1.25m from the SPL meter (centre right of picture held onto keyboard stand with yellow tape) which is pretty much on axis. I set the DPDT switch up (just in front of the cab on the acoustic foam) to be easily able to switch array on, In Phase (IP) and Out Of Phase (OOP) and off - I like easy repeatability. There are 2 sets of results: First set is where I had initially put some acoustic foam on the bench in front of the cab and some on the 2nd cab just under and to the right of the SPL meter. The second set of results was with more foam spread around - 2x1sqft pieces held against the garage access door with top end of broom handles (brooms just seen in bottom left of picture) where in-plane reflections off the door would be, and some on the shelves to the right, and some stood on the general piles near there leaning against the vertical surfaces, again roughly in-plane with the cab and meter. The cab back was propped in place so no rear reflections. Firstly, I stood against the garage freezer (out of picture to rear left) and got a stable-ish background reading (silence) of 43.4dBC (ish). All subsequent meter readings were done with me standing with back against the freezer.

1st set of results: foam just on bench and on top of spare cab:
main driver alone = 83.4
IP array = 87.4
OOP array = 79.0

2nd set of results: Extra foam on door (to left) and perched on right side shelves
main driver alone = 80.8
IP array = 85.7
OOP array = 76.5

Unless anyone can see any glaring mistakes (other than living on a wet, crowded Island) please let me know, but I think that's it.

[Bill Fitzmaurice]

That's OK to measure the response in that room with the cab in that spot with the mic where it is. To measure just the cab you need to do it outdoors, well away from any buildings. In use you do need to measure the room, typically with the mic placed in the middle of the primary listening area.

[Charles Jenkinson]

...To measure just the cab you need to do it outdoors, well away from any buildings. In use you do need to measure the room, typically with the mic placed in the middle of the primary listening area.

OK, will do. A little learning curve there, but I have the PA+ & RTA mic in hand and will knock on the corner house on the other side of the main street, to borrow electric (school playing field behind), unless another option comes up in the meantime. For this weekend (my boys 5th b'day party), I have a Tapco dual 31 band EQ I bought several years ago, to try to EQ an electric violin (it didn't work for the violin very well - still miles away from an acoustic). Will check the other cab/array tonight with the sine sweep for anomalies/resonances (but not phase - will be the same as other cab). Will then solder the array cables and jacks on cab back - am very low on 18ga cable (2ft) for soldering to the mini DPDT switches - gonna cross between /solder to the slightly bigger stuff on the cab back - talk about spoiling the ship for an apeth of tar. Will then put the following into the EQ on the 6dB gain setting, using top graph between 63Hz and 2kHz and bottom graph above 2kHz (will leave 2k at zero) - I'm going to normalise about 102dB mean, and pull all sliders below 63 down to -6.

I think I may need more bass already as a PA, but things are sort of in hand on that score. Am glad I got the HO's - not far behind OT12's if working solely as tops.

[eq eqgain=6&eqtype=2&dbtarget=102&dbmin=96]J112D3012[/eq]
[eq eqgain=6&eqtype=2&dbtarget=102&dbmin=96]J112D2512M16[/eq]

[Grant Bunter]

Pulling down that big dip from 8 through to 10K by 6dB might be a bit much.
Just try a lighter dip by 3db first and have a listen to some favourite tunes and tweak accordingly.
You might well in fact end up reducing by 6d, but aiming for flat Vs what sounds good can sometimes be quite different...

[Charles Jenkinson]

Am copying/referencing this from Escape’s build thread where I wrote last night: re: piezo array problems.

I was testing the other cab last night with a sine sweep and had some resonance issues in the array. It occurred at 2100Hz (ish) and there were minor effects at some other multiples of that frequency, up to 10k. There was a really odd, what I can only describe as a ‘ghost flutter’, at a much lower frequency (but still in the array) when approaching 10k, and it repeated every time I did the sweep.

Anyway, I taped my SPL meter to a piece of plastic tube and went through the array element by element, pointing the tube in the centre of each piezo. As testing proceeded (also on the good cab as a reference – no probs on that one!) it became apparent that they all read very close to one another except the 5th row (right and left pair) down the array, which were 5 to 8 dB down (and randomly fluctuating) from all the others. The fact the reading was fluctuating makes me ‘believe’ they are not working at all, because the fluctuation seems typical of random wave summations from adjacent tweeters, particularly when the end of the pipe is (I would imagine) to a degree discriminating of what goes down it, based on its angle and attitude to a wave front.

I've checked the offending elements (the good thing about the Jack – you can get the elements off without taking the array out). There appears to be nothing wrong with them in a structural sense, no broken wires or detached piezo discs. They are both the free element type, where most of mine are glued on (round their perimeter) paper cone elements. I'm more than slightly stumped, and would like to think that if I solve these two tweeter elements the ‘resonance’ problem will go away. I’m still not sure in my mind whether a glued piezo cone may or may not perform better than an unglued one – there doesn’t appear to be anything situating the unglued paper cone element in place, so it looks like the whole thing floats around to me – I originally thought the paper cone’s outside diameter was trapped by a plastic spigot/annulus (in the removable back piece) but it doesn’t look big enough on diameter to catch under the annulus, neither does the annulus appear to trap/clamp up against anything else inside the housing. If the whole thing does float (and the cone is not big enough to be ‘held off’ by the annulus) there’s nothing stopping the piezo disc from touching/vibrating against the inside of the plastic housing – that would cause a ‘resonance’, but it wouldn’t really explain the 5 to 8dB down in SPL, for the following reason; by the large quantity of piezo’s out there which are not glued and function perfectly well, the glued/not-glued difference seems moot.

The problem could be cold soldered joints on the tabs, but I thought I had taken care with that, making sure I saw the solder spread/tin out onto the tab beneath the wire. Anyway, it doesn’t appear to affect the musicality of the speakers (at low volume) at the moment even if two elements are not working and/or there is some resonance. I’ll get to the bottom of it ultimately, but I need a break to finish them off (jack & switch wiring) and use them on Sunday.

[Charles Jenkinson]

I had a night off last night, but briefly tried the 2nd cab again, measuring the array with the SPL meter taped onto the tube. The tweeters I thought were not working, actually were working. Very odd, since the 'not working' was repeatable the other night. Also figured out the resonance is most likely rattling tabs, prob due to too much heat when soldering - IIRC I may have run the new temp controlled iron hotter on the second array - oops. I didn't routinely use heat sinking either - double oops. Gonna disconnect main driver, take array out (on service loop) and run a repeating short burst of rising sine sweep 2k - 3k to get repeatable resonance events then go through each tweeter that has a loose tab and hot glue it down.

I read on Micheal Hanson's Boominator website about piezo tweeter burn-in using pink noise - is this a beneficial treatment and noticeable result with the 1016's?

[Charles Jenkinson]

Well, that's about it for this build thread. Just one back left to do the wires to the plugs and switch, but the first one took me 3.5hrs to do (due to DPDT switch and changing between wire gauges), so the second cab I've brought the power wire through the front port to be able to use them tomorrow.

Initial set-up: i got my dual 31 band eq out and plugged everything in. Channel 1 isnt working properly. Bummer. I've sort of mono'd things into channel 2 of the graphic (rca for one Chan and 1/4 jack for the other - they're not the same level!) and set the amp to mono. I quickly dialled the EQ in and hey presto, proper sounding speakers.

[Grant Bunter]

Congratulations Charles

If I was over your way, I'd drag you off to the pub to celebrate...

[Michael Murphy]

Mighty nice build there Charles, those melded arrays look superb. Great info on the IP / OOP testing. I think im gonna get going on some melded arrays myself.

[Charles Jenkinson]

Thanks Grant, pumpsfast and everyone! Am really stoked at how faithful you've all been while i was going through the build. I managed to make a few short videos today - they'll be up real soon in videos section.

[miked]

Glad you got it all sorted out! I also had a few probs with the connection tabs on the tweets de-soldering. I have a temp-controlled iron, but I was finding it difficult to strike a balance b/t leaving the iron pressed on the tab long enough to ensure a good connection b/t the wire and tab, and leaving it on too long and the tab coming loose. The arrays were by far, the biggest PITA of my OTop build. Looking forward to the vids!