Wayne Parham Messages: 18678 Registered: January 2001
Illuminati (33rd Degree)
Since the 2123J driver is a 16Ω driver, it will be less voltage sensitive than the 8Ω driver, and will produce less sound pressure at a given drive voltage. So the level of padding required will be reduced as a result.
Midrange padding is accomplished using R4 and R5. You will notice that R4 is 4Ω in series and R5 is 8Ω in parallel. These value provide the right amount of attenuation for the 8Ω driver.
If you wanted the same level of attenuation for a 16Ω driver, you would double the values to 8Ω and 16Ω, respectively. This is the same ratio, and creates the same voltage division, so provides the same attenuation.
But since the 16Ω driver is less sensitive with respect to drive voltage, we actually need to change the ratio. I would probably use 4Ω R4 and 40Ω R5. Try those values and measure to verify. As I said earlier, you may be able to remove the padding altogether.
I finally put together the mid horn and mounted the 290C horn. I used drivers mentioned in my first post.
I would recommend any one without good woodworking skills to buy the mid horn flat pack from Wayne as the mid horn, while very simple from the look, is very hard to make right. The ones I made even though usable are far from being geometrically perfect.
The corner horns I built 10 years ago was a result of Wayne's inspiration. I used his corner conical horn formula and corner horn idea. It provides the same function as the current 7 PI corner horn in this set up.
Right now the crossover is without R4 and R5. I will have to spend more time to get to know the sound before I make changes that Wayne suggested in order to be able to compare later. I'll have to find my sound level meter to do some measurement.
Anyway, here is my first impression: the sound is much sweeter than I expected from such "large" speakers; It can be quite delicate, has a great depth and large background; great ease with tiny and big sound; shows well the personality and skill of the performers of the music. I have some uneasy feeling in regard to tonal balance. It could be due to the crossover without R4 and R5 or it could be just me being used to fullrange single driver speakers which tend to emphasize the upper mid and highs.
I brought up this old thread for reference purpose.
I got a new question.
Using JBL2123J in the mid horn does not give me the large stable "sweet spot" I hoped for even though the sweet spot is larger than my previous stereo had. I have tried to use the crossover with the inductor L2 with value of 2.0 mh or without. I like it without the L2. But these did almost nothing to increase the size of sweet spot. I wonder if you could enlighten me as to where the problem is and what the correct approach is to tackle this problem. I am also inclined to take the easy way out by purchasing a pair of Delta 10A and follow your crossover schematics without any modification. But I like the JBL2123J drivers a lot and really am hopeful that somehow I can keep them in the corner horns.
Wayne Parham Messages: 18678 Registered: January 2001
Illuminati (33rd Degree)
I agree with you on the quality of the JBL drivers, but I also found what you did, that the upper end response was a little subdued. That's why the L2 coil is jumpered on the JBL 2012H. You'll also notice that the 2012H is an 8Ω driver. So when substituting a 16Ω driver like the 2123J, I'd be inclined to remove the attenuation resistors entirely.
This should get you where you want to be. It's wide open, basically a full-ranger, but then again the horn itself creates an acoustic filter. That prevents it from reaching above 2kHz or so.
Also note that the polarity is reversed in some cases. So be sure to check that too. And if memory serves, the 2123 doesn't reach quite as high as the 2012 in the midhorn, so you may want to shift the tweeter crossover down a smidge.
I removed L2 and R4, R5 resistors and jumped where the inductor and resistors left in order to see how this will affect directivity. But this made the class D digital amp that I use to shut itself down. I assume this happens when the speaker impedance is too low for the digital amp. What is the impedance of a "regular" seven PI speaker? What could the speaker impedance be in my current scenario?
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Thank you Wayne for the prompt answer!
