whines wrote:That happened with me with my first t39, the casters were too close to the corners. :/ Quick work with a dremel to cut away the plastic that overlapped worked fine, and it's really unnoticable.
Array screwed on. The service loop wire pair to the array is caught up by a tie wrap looped round one of the tweeter bosses. To loose the loop, just snip the tie wrap, its easy to get at since it is round the boss/body one of the tweeters, but hard to see unless you're looking for it.
The soldered wires of the array tweeters are not too obtrusive. Besides, I know what they do, so that takes the edge off.
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Last edited by Charles Jenkinson on Sat Jul 27, 2013 4:33 pm, edited 1 time in total.
2xJ12L (3012HO) switchable/melded
2xT30
Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.
And put some foam on those bare wood bits and pieces!
I know money often seals the deal, but seriously, quality is an investment, not an expense... Grant Bunter
Accept the fact that airtight and well-braced are more important than pretty on the inside. Bill Fitzmaurice
I'm back on phase testing now, though this time it's the main driver to the tweeter array, at 2kHz cross over frequency. A bit of a tricky one, again. How far does the SPL meter need to be away from the speaker? And what about reflections? I find if I move around the garage even though the meter doesn't move relative to the cab, the meter reading is going up and down all over the place. If I stand still it calms down. What dB difference should I see between 'in phase' (IP) and 'out of phase' (OOP) - a bit of an awkward question because it might not be 180 degrees OOP even if it is OOP. Until I get the environmental aspects a bit more controlled it's difficult to say what the meter readings are, but my initial reckoning is that if 2kHz has a wavelength of 6.75" to be in phase the tweeter needs to be 6.75" from the driver or thereabouts, and to be out of phase it needs to be 3.4" + 6.75" or any multiple of 6.75" added onto half the wave length. The actual distance looks like neither 6.75" nor 10.2" but somewhere between. Anyone any ideas for a J12L?
Time to go to bed now - don't want to be keeping all the neighbourhood dogs awake, howling!
Cheers,
Charles
P.S. I thought I'd run the wire forward through the port and hold the back on as a rudimentary first pass on bass response. It was bouncing all over the place at 30Hz and 10v and took some effort to press on (though I appreciate there isn't any 'response' till 60Hz-ish, just moving air). Nice.
2xJ12L (3012HO) switchable/melded
2xT30
Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.
Those bare spots will cause internal reflection of the mid and higher frequencies, with possible mixed in-phase and out of phase response. But, you must measure outside, away from any obstructions or objects, within 17 meters. Also, you don't want to hold the measurement mic as handling noise will skew your results.
As far as whether the array is in-phase or not, just listen with your ears. If it is louder one way, leave it. If there is no difference, so be it. You are in the home stretch!
I know money often seals the deal, but seriously, quality is an investment, not an expense... Grant Bunter
Accept the fact that airtight and well-braced are more important than pretty on the inside. Bill Fitzmaurice
I didn't have the back on the cab whilst initially attempting to set up the phase test, as discussed in that last post - having said that, that may be one of the problems, with reflections from the back of the cab coming round to the front, via the internal walls of the single-width brick-wall garage, with lots of (probably not very absorbent) crap in. However though, I take your point about mid-range reflections and will damp the small areas of the baffle remaining before finally screwing the back on.
As to listening for if it's louder or not with my ears, I got myself an SPL meter when phase checking the tweeters because I couldn't hear the difference between in phase and out of phase with white noise, ...and my hearing is not bad. It's probably untrained, but not bad. This is a similar scenario: the sine tone is so pure and the reflections are probably so multiplied in a garage, that it is a very confusing process for ears. Just moving my head from side to side in the space I was in, the volume (yes I use that word without reservation) went up and down. My head has two ears, one on either side - they are slightly larger than the average ear.
Has anyone else had any enlightenment about this tweeter to driver phase setting, or is it just a process of finding bigger, emptier spaces with less reflections until things stabilise? I suppose the other question is is their a standard tweeter phase setting for the J12-melded with the cross-overs made from the standard Erse parts, i.e. does + go to + or to -?
My next attempt, weather permitting, will be in the back garden, with the mic dead on axial centre about 5 ft from the front of the cab, everything elevated off the floor, and possibly with a few screws holding the cab back on (to eliminate reflections from the back bouncing off the shrubbery) and of course the extra bits of foam on the baffle. Hopefully i won't have to explain the need for the 'high pitched ringing noise' to anyone.
Do I need to damp the stiffening flanges on the back panel aswell (in photos on page 12)....?
2xJ12L (3012HO) switchable/melded
2xT30
Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.
DJPhatman wrote:Those bare spots will cause internal reflection of the mid and higher frequencies
Only if the bare spots are at least three inches in dimension. As for taking measurements, the mic should be at least 2 meters from the front of the cab, with the cab at least 2 meters off the ground to minimize floor bounce response dips. The low end won't be as strong as it would be measured half-space, as it is in the SPL charts, which requires the cab be measured ground-plane below 300Hz and free-space above 300Hz, the two results then summed.
DJPhatman wrote:Those bare spots will cause internal reflection of the mid and higher frequencies
Only if the bare spots are at least three inches in dimension. As for taking measurements, the mic should be at least 2 meters from the front of the cab, with the cab at least 2 meters off the ground to minimize floor bounce response dips. The low end won't be as strong as it would be measured half-space, as it is in the SPL charts, which requires the cab be measured ground-plane below 300Hz and free-space above 300Hz, the two results then summed.
Surely this is cheating a little by fattening up the sub 300Hz response?? Or is this the way all manufacturers do it?? It seems that it would not be truly representative of how the cab would sound either on stands or half space. Can you possibly explain why it is done like this, as I am sure there is a good reason. Thanks
escapemcp wrote:
Surely this is cheating a little by fattening up the sub 300Hz response?? Or is this the way all manufacturers do it?? It seems that it would not be truly representative of how the cab would sound either on stands or half space. Can you possibly explain why it is done like this, as I am sure there is a good reason.
It is the AES/IEC standard. It exists so that when you're comparing different speakers it's always an apples to apples situation.
What are the aspects of electrical (crossover) influenced phase and acoustic (positional) influenced phasing on main drivers and melded tweeter arrays that might differ from one persons J12 to another?
2xJ12L (3012HO) switchable/melded
2xT30
Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.
Charles Jenkinson wrote:What are the aspects of electrical (crossover) influenced phase and acoustic (positional) influenced phasing on main drivers and melded tweeter arrays that might differ from one persons J12 to another?
None, using identical components. But I don't assume that's going to be the case, so that's why the test procedure to make sure of correct polarity is in the plans.
escapemcp wrote:
Surely this is cheating a little by fattening up the sub 300Hz response?? Or is this the way all manufacturers do it?? It seems that it would not be truly representative of how the cab would sound either on stands or half space. Can you possibly explain why it is done like this, as I am sure there is a good reason.
It is the AES/IEC standard. It exists so that when you're comparing different speakers it's always an apples to apples situation.
Bill, could you possibly explain WHY this was chosen as a standard please? It seems a bit odd to do it that way. I am sure there is a good reason, but I'm racking my brains trying to work out what it is!!
Thank you
