Suggestions for fixing midrange/woofer clash

[prairiemystic]

I made a need some help fixing a 1990's design I made that turned out so-so:
Dynaudio D-28AF 1" dome tweeter
Dynaudio D-76 3" dome midrange
JBL 2235H 15" woofer
vented 6.2 cu. ft/175L cabinet
Xover is a clone of Profil 4

I used up all my energy on the project getting the low end great- making 4 enclosures and dozens of ports to get there as the TS modeling didn't pay off.
But my main complaint is the midrange is poor- image is hard to find, mids are distant, washed out and in the background, more H&V lobes than I'm used to. I think it's the big difference in cone centers (2.3") between the mid/woof on the flat baffle giving poor time alignment but the odd crossover-mid phasing network I thought would help.

I'm open to suggestions here. At the time Audax PR17HR70 midrange was recommended (obsolete now) and I'm thinking the midrange or crossover need to be redone.

[Loren42]

Originally Posted by prairiemystic

I made a need some help fixing a 1990's design I made that turned out so-so:
Dynaudio D-28AF 1" dome tweeter
Dynaudio D-76 3" dome midrange
JBL 2235H 15" woofer
vented 6.2 cu. ft/175L cabinet
Xover is a clone of Profil 4

I used up all my energy on the project getting the low end great- making 4 enclosures and dozens of ports to get there as the TS modeling didn't pay off.
But my main complaint is the midrange is poor- image is hard to find, mids are distant, washed out and in the background, more H&V lobes than I'm used to. I think it's the big difference in cone centers (2.3") between the mid/woof on the flat baffle giving poor time alignment but the odd crossover-mid phasing network I thought would help.

I'm open to suggestions here. At the time Audax PR17HR70 midrange was recommended (obsolete now) and I'm thinking the midrange or crossover need to be redone.

I have used the Audax PR170M with very good success with the 2235H.

I can't really tell, but it looks like the Dynaudio mid may not have enough SPL compared to the 2235H. It may be a few dB short and might explain some of the dullness.

You really need to provide complete details for the total design before anyone can meaningfully provide answers to your questions.

[jerome69]

I think your crossover is not done correctly. Add a 7" is a good idea but not the PR17, 600Hz crossover frequency, too high. It only replace the 3"mid. Go to a 4 way is not a good idea.
I think you just need to redo the crossover, you don't need to do a lot of thing.

Do you have a photo of your baffle ?
If your baffle looks the profil 4, it's OK.

About the crossover, it should be very simple.
Can give us your schema ?

According to the crossover schema of the profil 4
http://img69.imageshack.us/img69/7225/duennaudiokn5.jpg
The transition between the 3" and 1" is easy and very simple, keep it.
The only problem i see is the transition between the 15" and the 3" because the woofer is different, the crossover should be different.
Do you keep the delay line Lp/Cp ? you can remove it because it affects only the mid, a source of problem.
You should only play with L1/C1/R1 ...
I think you could have problem with the polarity of the drivers, wait for your crossover schema...

edit : this a similar project : http://www.parts-express.com/project...roject=AngelF1
I like the fact he have used the same capacitor for mid and tweeter.

[jerome69]

Finally, i looked the profil 4 crossover. I manage to do something like this:

If you have L1 = 3.9mH, C2 becomes 28uF.
I suppressed the delay line and inverted the midrange. Midrange inversion is necessary because acoustic slopes are 12dB.
Crossover frequencies are 700Hz/4kHz. The overall sensitivity will be 93dB/2.83V.
Let us know how the sound changes.

Enjoy

[prairiemystic]

Here is a pic and xover details (old pic missing woofer RC). Solen parts.
Cabinet outside dimensions are 45.5"H x19.5"W x 18"D (3/4" MDF) - Driver centers (from the floor up) measure 22.75", 34.75", 40" (tweeter)
The front baffle is one piece, just two-tone paint.

[jerome69]

Thank for the pictures.
You have to tweak the crossover
-First remove the delay line (0.8mH 24uF), connect the mid inverted and listen. if you want to keep it, you should add the same on the tweeter but i think it is a bad idea.
- The 39uF is too much but you can tune it by ears.
- Perhaps the 47uF is too much but not vital.
You can fine tune the crossover after doing the first tweak.

A comment on the box, you must flush mount tweeter and midrange. It could be better to offset them, see with edge Home of the Edge

Originally Posted by prairiemystic

Here is a pic and xover details (old pic missing woofer RC). Solen parts.
Cabinet outside dimensions are 45.5"H x19.5"W x 18"D (3/4" MDF) - Driver centers (from the floor up) measure 22.75", 34.75", 40" (tweeter)
The front baffle is one piece, just two-tone paint.

[jerome69]

For drivers placement take a look to ATC SCM150
ATC Loudspeakers. ATC Monitors. ATC SCM. ATC Speakers. Manufacturers of speakers, monitors, drive units and amplifiers.

You could have a smoother response.

[picowallspeaker]

Originally Posted by jerome69

- The 39uF is too much but you can tune it by ears.
- Perhaps the 47uF is too much but not vital.
You can fine tune the crossover after doing the first tweak.

A comment on the box, you must flush mount tweeter and midrange. It could be better to offset them, see with edge Home of the Edge

The resistance of 6.8 in series with the 47 µF cap shall be reduced to 1-2 Ohm . And , can the delay line before the dome mid be thinked like a notch filter with wide band ?!
Also ,driver offset can be corrected by tilting the cabinet about 10° .

[jerome69]

Originally Posted by picowallspeaker

The resistance of 6.8 in series with the 47 µF cap shall be reduced to 1-2 Ohm . And , can the delay line before the dome mid be thinked like a notch filter with wide band ?!
Also ,driver offset can be corrected by tilting the cabinet about 10° .

no, no and no.

[wintermute]

Hi picowallspeaker, I really don't think he wants to reduce the 6.8 ohms in series with the 47uF to 1-2 ohms. As far as I can see that is a zobel and doing so will result in an impedance of 1-2 ohms above a certain (I suspect quite low) frequency for the woofer part of the circuit. As the speakers are in parallel, this will result in an impedance of 1 ohm or less above whatever that frequency is presented to the amp.

Prairiemystic I've not seen a network like that before on the midrange with reversed components in the negative and positive legs of the driver. Was the crossover you used designed for the same drivers with the same baffle dimensions?

Your best bet is to do some acoustic measurements of the drivers on the baffle and also impedance measurements of the drivers on the baffle. Then you can put them into something like Jeff Bagbies passive crossover designer or speaker-workshop and tweak away. Also if you do a measurement using the the current crossover as well, you can hopefully see what is going on.

Tony.