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In Reply to: RE: Bohlender Graebner available again posted by Roger Gustavsson on April 17, 2016 at 11:13:04
My favorite drivers are back.
Ding PoisonM Your friend can build a Neo8 line array and use the MG20.7 bass driver and tweeter with a new separate frame for the Neo8 and tweeter. The Neo8 array has serious power handling ability and is far more sensitive. The array (with sufficient baffle) can play to 200 hz quite loudly without bottoming out or burning.
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Soooo, I'm thinking I should take advantage of this, before they go away again! :-))
Satie, if I used 2x parallel connections of 3 in series ... I end up with a 6ohm mid driver ... which is about 1200mm (4') long.
Re. XO configuration, based on your experiences with these drivers:
Q1: Do you still recommend only a 6dB HP filter for these Neo8 mids? So they roll off naturally at the top end - which would result in something like:
- bass LP 18dB @ 300Hz
- mid HP 6dB @ 500Hz
- ribbon HP 6dB @ 4KHz?
Q2: Or should I continue with a mid LP (like on my T-IVa mids) when crossing over to the ribbon? Which would result in something like:
- bass LP 18dB @ 300Hz
- mid HP 6dB @ 500Hz
- mid LP 6dB @ 3800Hz
- ribbon HP 6dB @ 4KHz?
Thanks,
Andy
OK
Two things. First is how much baffle are you going to provide them, as you can see in the spec/info sheet (I didn't look to see if they put them back online) baffle loading changes the FR in the sub 1khz range.
Second is how loud you play, the louder you play - the drivers will bottom out at a higher freq. At 126db it bottomed out at 800hz or so with the lower mid going from weak to MIA..At 100 db you are flat to below 300 db and bottom out about 250 hz. Playing to 110 db you will have a slightly weak lower mids but I don't have a solid -3db point for you - I would guestimate that an array of 6 with ample baffle on one side will go to 500hz at 110 db (if you care)
.
The more drivers in the array the lower the freq at which they are usefully additive and the smaller is the gap resonance peak at 11-12 khz. There are still traces of it at 6 per side, none at 9 per side. I should point out that though on axis the FR will roll off at 14 khz with the regular Neo8, the off axis FR of the array will drop off earlier - 3db @ 11-12khz at less that 30 deg off axis. .The PDR version will get to > 14khz off axis (well at a reasonable angle) and will ony droop on axis to -3 to 5 db at 20 khz
My solution is to cut off at 150 hz 6db and stretch the bass LP up to 250 hz LR4 or 200 hz B3. That way there is hardly any phase on the driver and I can plug in the ribbon tweeter at the 18khz 1st order (still shares the 150hz HP so is not really exposed to very low freq)
I starte out with B3 symmetrical and equidistant drivers at 300 ant 6khz. I didn't have a head in a vice problem but having measured the off axis FR I wanted to stay out of trouble on the dispersion side. So I pretty much did the same with symmetrical LR4.
I then experimented with letting the driver array play full range (hence my knowledge of when it bottoms out) and just added in the tweeter and bass with B3 and LR4 at various freq between 6 and 12 khz. Never got it to mesh perfectly.
The compromise solution was to go linear phase for the entire speaker, so 1st order symmetrical at 250 hz and appx 8 khz avoided the head in a vice most of the time and had the most perfect imaging I ever heard. Of course with an equidistant arrangement of all the drivers. I think that would be the place to start. You would then only bottom out the mid array at 300hz when playing 110 db peaks (since you are sitting closer - I measured at 3m) It is not bothersome since the bass panels are only 1st order in this setup and fill out the missing bits 250-500 hz perfectly adequately on 110 db peaks.
I experimented with myriad other XOs for different placements. Ask and I will answer if you have anything in particular in mind.
In your version Q1 you have no mid LP - If your drivers are equidistant then you can LP at the same freq as the tweeter. 4 khz is still marginally too low for the ribbon to operate with a 6 db HP, so I would take it up till you have the beginning of dispersion problems - likely 6-8khz. Otherwise the ribbon will show you its displeasure at being driven hard with a metallic sheen to everything. You can try doing the Bass LP at 1st order instead of 3rd and experiment with lowering the LP to 150hz if it is not interfering with .clarity. If the bass' intrusion into the 300 hz bothers you then do cut it off at B3 at 300hz - or even lower. Just that you will no longer be able to have time alignment and you will need to get it in phase carefully according to how your drivers are offset from equidistant.
In Q2 I am guessing that you are offsetting the XO from symmetrical -3db freq to compensate for offsets from equidistant driver placement. If that is not the case the mid-tweeter should XO symmetrically, and up to an octave higher, And the bass LP freq should be matched to get you in phase and compensate for offset.
Go by ear if you have a variable XO and then measure.
If your listening levels are more civilized then you can crossover the tweeter lower and take it to as low as 4khz so long as it has another HP before it in the 100-500 hz range. If you can set it up to share the mid HP then that will simplify it somewhat,
Lots of options
Thanks very much for the detailed response, Satie.
I have a lot to think about but I thought I would post a pic of my L channel 2 panels - and give you baffle measurements.
I'll respond to your other comments, later.
The flash kind-of 'sees through' my sock material - but at least you can see the drivers clearly.
Re. the baffle arrangements for the Neo8s - they will replace my T-IVa mid panels. The mid/ribbon frame is 10" wide - so there's:
* about 5" of baffle on the outside of the mid panel, and
* at least 17" of baffle on the inside - given the mid/ribbon frame is butted up against the bass frame.
Which I would've thought is more than adequate?
Regards,
Andy
Looks like plenty of baffle to me, Andy.
I think you are going to love the results if you go with the NEO8 arrays.
There are so many viable configurations with these drivers. I ended up with symmetric XOs at 260Hz and 3KHz, 48db/oct throiugh the DEQX and a 40Hz LR4 hand-off to a sub. That way no driver is close to breaking a sweat no matter the volume level.
Please keep us in the loop as you do this project.
Awesome frames, BTW.
The single sided baffle should be sufficient.
Guitar slim, Though I never used 48db filters, I did use LR4 and the tweeter was definitely stressed at my play levels at 4 khz, not to speak of 3khz. The compromise was 5 khz LR4 or B3. The tweeter does not have that much of an advantage over the Neo8 mids at 5khz and below. The Neo's dispersion is still pretty good at 5khz and detail retrieval is pretty much on par at these freq. Cohesion wise I liked keeping the low treble with the mids on the same driver.
Hi Satie! Thanks for your thoughts.
I never noticed any limitations of the ribbon with the steep slope at 3KHz, but then it's possible I don't listen as loud as you.
Maybe next time I'm playing with the DEQX I'll try raising the mid/tweeter crossover frequency.
Some time ago I had to replace a ribbon and went a month or so running the NEO8 arrays as mid/tweeters and was surprised how dramatic the difference with not having the ribbon "sparkle". Maybe not surprising.
Anyway I expect 5KHz is a good choice.
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