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| Re: Definimax 4012HO - End of Life [message #91816 is a reply to message #91806] |
Sun, 03 May 2020 23:21   |
Symphonimind
Messages: 33
Registered: May 2018
Location: Singapore
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Baron |
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Wayne Parham wrote on Fri, 01 May 2020 11:10We have several driver options for the π loudspeaker, and a couple of them are in the same quality/price range as the Beyma 12BR70. The Delta Pro driver would be a good choice for that price point, for example.
When this thread was started, it was prompted by the announced obsolescence of the Eminence Definimax 4012HO. For many years, that was the top-of-the-line upgrade option for the three π loudspeaker. It had a cast frame, well damped cone and flux stabilization. So I was looking for a part that had those advanced features to replace it. I settled on the B&C 12PLB100 for that role.
Hi Wayne,
I have just tested the new 3Pi with both 12PLB100 and Delta Pro 12a. As the owner of original 3Pi with 4012 (with DE250), the 12PLB100 is superior in every aspect. Bass is much tighter, the sound is much more clear and focused, THD is really low. I like it very much.
I tried it in a smaller cabinet tuned around 40Hz, the in-room response is well extended into 30Hz region. The sound is phenomenal. However, my stuffing technique is not very good so I got mid leakage peaked around 400Hz and 800Hz, and it ruined the frequency response. Can you share some of your experience on your stuffing technique to get rid of those mid leakage?
The Delta Pro 12A lives up to the reviews. Its bass is tight, the sound is good (but not comparable to B&C in any way). THD is also in the low side. But due to the 4dB higher sensitivity compared to B&C, I have to EQ the system a bit.
Overall, I think that the ending of 4012HO is great. It gives us the chance to upgrade the system to the whole new level and also to have a better option against Delta 12LF.
Thank you very much.
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| Re: Definimax 4012HO - End of Life [message #91818 is a reply to message #91816] |
Mon, 04 May 2020 12:47 |
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Wayne Parham
Messages: 18787
Registered: January 2001
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Illuminati (33rd Degree) |
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I agree with you, 100%. Those B&C midwoofers are really nice. It's a wonderful top-notch in the upgrade path for the three π model loudspeaker. I think this 2020 version is the best that the three π loudspeaker has ever been.
I also agree with you on the Delta Pro. It's a good driver, and worth the small additional cost over the entry-level midwoofer option. It is also higher in sensitivity, so the R1/R2 values need to be populated specifically for that driver compliment. This makes the overall sensitivity as high as the four π model, when the Delta Pro driver is used. The bass response doesn't run as deep with that option, but when used with flanking subs, the extension isn't needed.
Standing wave modes on larger full-range speakers are always a potential problem, as you've seen in your modded box. My cabinet design efforts were more extensive and difficult as a result. This was the case for the four π, three π and two π tower models.
Smaller cabinets and subwoofers are much easier to design, because standing waves don't line-up in the lower midrange. In smaller boxes, the standing waves shift up into the overtone region where insulation on the walls does a good job damping them. In subs, midrange isn't presented so they can't develop standing waves. But large full-range boxes need a little more tender loving care in the design phase, because they are prone to developing standing waves in the lower midrange where they are difficult to deal with.
What I've done is to model the modal behavior within the loudspeaker cabinets, much like modeling room modes. Several years ago, I purchased license to Martin King's spreadsheets to help analyze internal standing waves. I used them to design my larger model full-range loudspeakers, adjusting the size and shape of the box and setting the position of the midwoofer and the port for minimum standing wave anomalies.
As an aside, I didn't have to adjust size/shape of the three π or four π cabinets, but I did manipulate where I put the driver and port in the box. Sometimes just moving the midwoofer or port an inch or two made a big difference. The tower two π speaker - being tall and thin - benefited from adjustment of both cabinet dimensions and driver and port positions.
I am not sure if Martin King is still selling his spreadsheets or not. But you might be able to use the same kinds of tools used to model room modes. The potential problems I see with that approach is the size of the loudspeaker cabinet is small compared to the size of a room, so the tool may not allow the right size chamber to be created. Also, room modes are below 200Hz or so, and we need to analyze the chamber modes over an octave above that.
So if I were going to try to find modal analysis tools to help me look at the cabinet, I would try to find ones that could model chambers down to 2ft3 with each dimension only being a foot to a few feet long. I would also look for tools that could analyze frequencies up to 500Hz. I wouldn't care whether it could go above that, because damping material placed on the walls of the cabinet is able to absorb the sound pretty well at higher frequencies.
What you want to look for is where the "hot spots" are, especially in the 100-500Hz range. We can't have any in this range in the same location as the midwoofer or the port. If a mode exhibits a pressure maxima where the driver or the port are, it will result in a peak at that frequency.
And finally, you'll find that fiberglass insulation that spans the cross-section does wonders for damping midrange frequencies too low to be damped by insulation attached to the inside walls of the cabinet. That's the trick for damping lower frequencies - Space the insulation away from the walls where it can damp pressure nodes better at those frequencies.
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| Re: Definimax 4012HO - End of Life [message #91830 is a reply to message #91818] |
Tue, 05 May 2020 22:58 |
Symphonimind
Messages: 33
Registered: May 2018
Location: Singapore
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Baron |
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Hi mr. Wayne,
I also purchased MJK's MathCAD sheets. I will try to model the cab to find the way to optimize mid leakage.
In my customed cabinet for 3Pi, I totally forgot to implement the stuffing at the mid height of the cab.
After trying 12PLB100 on 3Pi, I cant wait to see a new Woofer option from B&C with 4Pi beside JBL. For B&C, I can quite easily find in my area at the moment. However, JBL driver and especially 2226H is really hard to source locally. And I am not fond of Omega drivers from Eminence. I think that driver line is not really good. For 15inch midbass, Kappalite 3015 is better as a lower priced option, IMO.
The Delta Pro 12A is also great mid priced option. But as our measurement, the crossover needs small modification to match SPL between Delta and CD. In the test box with Delta Pro 12A, I used PSd2013 which has similar sensitivity to BC DE250.
Yesterday, we tested Celestion CDX 1745. It is truely a poorman's DE250. The power compression from 90-98dB/1m is non-existence. THD is really low for 98dB SPL/1m. I did a quick test with LF shelf and 1.2K XO LR4, it came out really good.
The unit to unit variation is really low, at B&C level.
I share with you some of our data so you can consider it. 
CDX 1745 + H290c/QSC152
Frequency response with H290C and QSC152, unit to unit variation
THD - I forgot that which SPL I measured in this graph, but I am sure that It is around 90-95dB / 1m.
Power Compression test + Test crossover
CDX 1745 THD with XO 1.2K LR4
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