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Old 21st August 2011, 11:23 AM   #11
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Quote:
Originally Posted by prairiemystic View Post
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
I'd ditch the D76 and get a B&C 6MD38. You'll need to re-do the xover though.
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Old 21st August 2011, 12:01 PM   #12
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Click the image to open in full size.

I analyse this schema, crossover frequency 500Hz and 4kHz. 39uF & 47uF are finally OK for me. You just need to remove the delay network (0.8mH/24uF) and connect the midrange inverted.

This schema is very classical and work very well but with a delay network it is a disaster. The difference of offset between the 15" woofer and the 3" mid is at least 4", 10cm, it's very hard to compensate physically.
You should have some diffraction problems, could be resolve by flush-mounted the mid-tweeter and offset them on the panel. It could be a second step of improvement.
Note a measurement can tell what's happen but it is an investment.
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Old 21st August 2011, 12:26 PM   #13
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I heard this speaker in the late 80s. Very nice sound, but lacking a bit in midbass dynamics and very "polite" sounding.

3 major issues I see -:

1 - 500Hz is too low to cross to the D76AF, especially first order. Domes don't have the Xmax and dynamics below 500Hz.
2 - You have no resonance compensation network on the D76, effectively making the crossover freq more like 300Hz which is WAY too low for any dome.
3 - The ladder network may have been fine to merge with the Dynaudio 30W54 woofer, but it's unlikely to be suitable for your JBL.

Options -:

a) Raise the crossover point to 800Hz and add resonance compensation across the D76.
or
b) Add a 7-8" midbass driver, handling 200-800Hz.
or
c) Replace with D76 with a good 4-5" midrange driver.

Assymetry in drive placement would probably help your imaging situation.

Last edited by David Gatti; 21st August 2011 at 12:47 PM.
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Old 21st August 2011, 12:56 PM   #14
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by David Gatti View Post
I heard this speaker in the late 80s. Very nice sound, but lacking a bit in midbass dynamics and very "polite" sounding.

3 major issues I see -:

1 - 500Hz is too low to cross to the D76AF, especially first order. Domes don't have the Xmax and dynamics below 500Hz.
2 - You have no resonance compensation network on the D76, effectively making the crossover freq more like 300Hz which is WAY too low for any dome.
3 - The ladder network may have been fine to merge with the Dynaudio 30W54 woofer, but it's unlikely to be suitable for your JBL.

Options -:

a) Raise the crossover point to 800Hz and add resonance compensation across the D76.
or
b) Add a 7-8" midbass driver, handling 200-800Hz.
or
c) Replace with D76 with a good 4-5" midrange driver.

Assymetry in drive placement would probably help your imaging situation.
From my experience with the 2235H it will not play well above 500 Hz due to some nastiness with cone breakup. 800 Hz may be pushing it depending on the slope.
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Old 21st August 2011, 01:47 PM   #15
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Quote:
Originally Posted by Loren42 View Post
From my experience with the 2235H it will not play well above 500 Hz due to some nastiness with cone breakup. 800 Hz may be pushing it depending on the slope.
Ouch
To improve the crossover, measurements are needed. A replacement of the 3" dome could be a better solution.

To raise the crossover frequency to 700Hz, just replace 47uF and 39uF by the 24uFs.
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Old 21st August 2011, 04:05 PM   #16
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I think the OP put the cart before the horse. You can't expect an off the shelf crossover to work with any drivers you throw at it. You must first know each drivers output characteristics. Only after that can you design a crossover that makes the drivers work as a complimentary set to reach a desired goal.
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Old 23rd August 2011, 03:39 AM   #17
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Bear with me, I'm a bit overwhelmed digging into this. Three things I tried to do originally, that did not work out:

1. I wanted a low xover freq 300-400Hz since the woofer is large; looks like I should move up to 500-800Hz (with the 6dB/oct xover), otherwise the mid gets pushed too low.
What I have now I measured the woofer 1/2 voltage at 500Hz (without the Zobel). Inductor DCR=0.3R and L=3.9mH; woofer DCR=6.0R and Le=1.2mH and my math is out to lunch fc 198Hz (6.3R+(1.2mH+3.9mH)). Zobel should be ~6R/33uF. Does it cancel Le out? Even then fc=257Hz.

(side note, the JBL 4430 and 4435 were two-way systems using the max. recommended 1kHz xover freq... 4430/35 and http://www.jblpro.com/pub/obsolete/443035.pdf)

2. The 5dB mismatch between the mid and woofer efficiencies. The 2235 is 93db/1W/1m and D76 88db/1W/1m? and the delay network seems to lose a few more dB (measuring voltage on the driver).
I'd have to go to a better matched midrange.

3. The time alignment of the drivers
I thought the delay network would compensate for some of the difference in centers.
Otherwise, angle the front baffle or maybe a satellite enclosure on top with tweeter/mid.

Next I tried jerome69's suggested xover changes - I removed the delay network and went to a 24uF cap. It's a big difference, at least there's an image now and the mid's are upfront. What I really notice is the vertical lobes (dead spots) are gone. I'm gonna try it for a while but this still feels like a mess.
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Old 23rd August 2011, 07:59 AM   #18
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It has took to me a lot of time before understand something in electro-acoustic. You have to deal with electrics and acoustics

I can give you a response for
1. The response is not simple. You can't add L+Le, it is not correct. The Le of the driver limits the treble. The L you put to filter do something but depend on the diffraction of the baffle (baffle step). Here there is no baffle step with the 2235H, the L gives a slope and the R-C does the rest.
You can read this :
epanorama.net/Speaker impedance
http://users.ece.gatech.edu/mleach/papers/vcinduc.pdf

2. No the midrange is already attenuate ! you don't need to change it !
For me the sensitivity of the mid is near 90dB. The contribution of the midrange is lower. Take a look on one of my design with 12dB acoustic slopes : Click the image to open in full size. The sensitivity is 85dB but the mid contribute only 82dB. The tweeter and the woofer are important ! In you design the mid contributes to 90dB but you need to attenuate it because you have a boost from the 6dB high pass.

3. In your case "time alignment" is not necessary, i don't think you will have a better sound. In my schema above, the difference of acoustic center between the mid and the woofer is 10cm at 1m... In your design you should push back the mid and tweeter to 10cm too.
The delay network on the mid isn't a good idea because the tweeter contribute a lot as seen and you don't delay the tweeter !
I think it's better to make a good placement of your mid-tweeter to minimize diffraction and smooth the overall response.

Quote:
...but this still feels like a mess.
I don't understand ? The loudspeaker seems to play better now ?
You just need make fine tuning, making it sounds very realistic. Old design school, old method of works !
If the JBL2235H is a good driver, the sound must be very good !
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Old 24th August 2011, 03:42 AM   #19
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jerome, thanks for your help! It does sound much better The mid does not sound odd, it sounds fine now (without the delay network). Matching theory and design is much harder with loudspeakers and lack of knowledge. Do you recommend any S/W for crossover design?

Eons ago, I had a summer job with a big telecom company in their acoustic lab. There was $10,000's in Brel & Kj equipment, an anechoic chamber, and MLSSA on a PC. With all that space and equipment, it was still hard to make good acoustic measurements. I used it on the woofer/cabinet/port work. Then went back to school and could not use for the mid/tweeter.

I will revamp the crossover and if I am still not happy, try a cone midrange or mid-bass add on.

The JBL 2235H is an dynamite driver. I fell in love with it in the 1980's (when things were big) and reminds me of old Altecs in sound.
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Old 24th August 2011, 04:44 AM   #20
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Quote:
Originally Posted by prairiemystic View Post
jerome, thanks for your help! It does sound much better The mid does not sound odd, it sounds fine now (without the delay network). Matching theory and design is much harder with loudspeakers and lack of knowledge. Do you recommend any S/W for crossover design?
Yes i use S/W a lot, it misses some functionalities but it's free. You have an other simulator with excel sheet : PCD, not use it but have some interesting functionalities.

Quote:
Originally Posted by prairiemystic View Post
Eons ago, I had a summer job with a big telecom company in their acoustic lab. There was $10,000's in Brel & Kj equipment, an anechoic chamber, and MLSSA on a PC. With all that space and equipment, it was still hard to make good acoustic measurements. I used it on the woofer/cabinet/port work. Then went back to school and could not use for the mid/tweeter.
Yes measure bass is very difficult. But we can do now very good gated measurement at home. The validity of this measurement is above 200-300Hz. If you have large space, you can go lower.

Quote:
Originally Posted by prairiemystic View Post
I will revamp the crossover and if I am still not happy, try a cone midrange or mid-bass add on.

The JBL 2235H is an dynamite driver. I fell in love with it in the 1980's (when things were big) and reminds me of old Altecs in sound.
Ok !
I verified with edge your driver placement, i didn't see big problem.
Do extensive listening
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