Sitting Room Build: Jack 12 Lite

[Grant Bunter]

Thanks Jools.

I'm wondering about both running-in the speakers and doing the air-tight testing. What shape wave does the tone need to be? And how does the voltage Bill suggests in the instructions relate to amp output - or how do I measure it? And is the volume difference when establishing polarities for the woofer and melded array obvious? I guess if it isn't - as Bill says - it doesn't matter, but I want to get that right,

Use a sine wave to run the drivers in, at the voltage described in the plans. You need to get a DMM or digital multi meter to do this, a cheaper one should be fine, it just needs to have a 200 volt AC setting. Ask us more when you get one. Run them in before installing in cab.

especially as the next step is building a set of T39's, so that in that rig, the Jack 12's are going to be putting out a lot more HF.

You're thinking isn't quite right here.
The benefit in running subs is that your Jacks don't have to work as hard reproducing LF, because the subs are now doing that.
Taking away the LF from full range cabs like the Jack does seem to tend to free them up quite a bit, and my own experiences with using full range cabs as tops for the first time somewhat surprised me.
The T39's are more efficient at producing LF, and, unlike the Jacks on poles (which decreases LF output) stay on the ground.
BUT the Jacks can only put out as much HF as they can. Running T39's with them doesn't mean they can put out more, or that they can be pushed harder to do so.

It's not the wrong decision to go that way though for bigger gigs. However, if you find the Jacks aren't keeping up to the T39's output wise for mids and HF, the only answer is to build more Jacks...

[HugoMack]

Thanks Grant.

On their own, the way I'll use them, on their own the J12Lites will limited by their LF capability.

With subs, that limit goes us up quite remarkably - at least that's how it goes with my current rig (Eon 15's, and JBL 18" subs). The effect of that is that the Eons produce more mids (above cross-over) and HF, so the any polarity probs would be more obvious. But OTH as the piezos are clearly marked + and - , maybe I'll get the polarity right?

[Grant Bunter]

It should be in the plans to swap the wiring with the HF array and use whatever sounds loudest.
Ears are great for checking polarity lol...

[HugoMack]

It is - hence my question. Are iphone sound meters good enough for this?

[HugoMack]

Hi Grant - I've found my DMM (Microdonta 22-169 DC/AC max 400 volts).

SO how do we proceed?

[Grant Bunter]

Hi Grant - I've found my DMM (Microdonta 22-169 DC/AC max 400 volts).

SO how do we proceed?

Read your manual lol, I hope you got one.
Really, that would be just to understand the hold button. All the rest is automatic.

So, set up a X value sine wave on your puter, or however you plan to play that.
Plug it into your amp, via a mixer so you get a nice line level.
Turn the amp on, with volume knob/attenuator on full.
Place the red probe on the +ve output and the black probe on the negative
(if your amp only has speakon outputs, plug a speakon socket in without it's protective cover, and put red in +1 and black in -1).
Turn on the DMM to DC/AC setting. Adjust the attenuator until you get the required voltage.
Turn off the amp, hook up your speakers for run in, amp back on, start your timer...

[HugoMack]

Thanks Grant. To preserve the amp, should I connect up the speaker as a load, then tap the speaker terminals with the DMM? Also, presumably I can break them both in at the same time - in series?

[Tom Smit]

There is no need to put a speaker on to test the voltage because the load will be still be there (infinity....which is more than a speaker). The only time where it would be a concern if the amp is of lower quality and can't deliver the current at the required voltage, and thus pulling the voltage down. Besides, with a speaker hooked up, it may intolerable to listen to.

[HugoMack]

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[Tom Smit]

Good-lookin' cabs!

[HugoMack]

Thanks Tom. It's the Tuff Cab paint!!

I'll do some better ones once I've got the hardware fitted and the Tuff Cab has properly cured.

[HugoMack]

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Getting technical!!

Here's the speakers being broken in as prescribed by Drs Bunter and Jools. I was a bit daunted by it, but 9 volts 30Hz sine wave is a pretty distinctive level of cone movement - much more and the table top starts jumping, so that's obviously too much. Will kepp this setup for when I've installed the speakers, to test for cab leakages.

Thanks again guys!

[Grant Bunter]

Yay!
Looks perfect!

Just be wary if your driver has a rear vent hole that you're not blocking that with the pillow, making the voice coil not being allowed to cool.

There's no reason not to break in both at the same time either.
Just wire + to + and - to minus on the 2 speakers.

If that's to noisy, swap the + and - wires on the second speaker and they will be out of phase, and almost silent...

[HugoMack]

Will check the venting/cooling asap. The second speaker is actually in the chair in the rear, below the level of the table top -wired in parallel.

[HugoMack]

Would you also break in guitar speakers using 30hz sine wave @ 8-10 volts. I'm thinking EVM12's which benefit from breaking in (me not having graduated to this level of tech until now...)