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Old 29th August 2008, 11:18 PM   #1
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Default Crossover for open baffle: please need help!

I fell in love with this open baffle project and built these gigantic speakers with vintage Saba greencones plus Eminence Delta 15'' woofers (please see pic.).
The crossover was included in the project so I didn't worry about it. But: midrange speakers crackle, I think they have been little damaged or simply they are too old.
I don't like the tweeters too... The woofers just whisper. Don't know what but of course something's wrong... I tried to listen to greencones only and crossoverless, just with 2uF PIO capacitor in series with the tweeter.
HOW BAD.
Brief, I reverted to my beloved 80's british speakers and just bought -as a replacement- Celestion tweeters (from DL4) and glorious Kef B200 (obviously the Eminence woofers stay).

Now: first of all I hope these drivers could sounds well on open baffle
Then: I'm veryvery scared by making crossover as I definitely haven't necessary skills! (lot of smilies tonight...)
Speakers have different impedance: what this requires?
Maybe someone here will be so kind to help me... And I miss some important specifications too...
Thank you very much in advance for any suggestion.



************************************************** *****

Baffle: 140 cm x 50 cm / thickness 4 cm / bass box w 45 cm, h 80 cm, d 50 cm - the box is open on the back
Tweeter mounting height 100 cm, midwoofer just above, woofer have open box

*Tweeter Celestion: shows 5 ohm resistance

*Midwoofer Kef B200G sp1069: this version (triangular shape) have 16 ohm resistance, 35-3000 Hz . It was used in Kef 304, Ref 105.2 and 105.4.
http://www.kef.com/history/1970/model304.asp
http://www.t-linespeakers.org/drivers/b200.html

*Woofer Eminence Delta 15 PA:


* Impedance: 8 ohms
* Power Rating:
o Music Program: 800 Watts
o Watts: 400 Watts
* Resonance: 40 Hz
* Usable Frequency Range: 48 Hz - 4 kHz
* Average Sensitivity 1W @ 1m: 101 dB
* Magnet Weight: 56 oz
* Magnet Gap Depth: 0.375 inches, 9.53 mm
* Voice Coil Diameter: 2.5 inches, 63.5 mm

Thiele-Small Parameters

* Resonant Frequency: 40.27 Hz
* Impedance (RE): 6.99 ohms
* Coil Inductance (Le): 0.86 mH
* Electromagnetic Q (Qes): 0.537
* Mechanical Q (Qms): 6.56
* Total Q (Qts): 0.49
* Compliance Equivalent Volume (Vas): 293.11 litres, 10.4 cu.ft
* Peak Diaphragm Displacement Volume (Vd): 231.38 cc
* Mechanical Compliance of suspension (Cms): 0.2846 mm/N
* BL Product (BL): 13.59 T-M
* Diaphragm Mass inc. Airload (Mms): 54.89 grams
* Equiv. Resistance of mechanical suspension loss (Rms): 2.1166 N*sec/N
* Efficiency Bandwidth Product (EBP): 76.6
* Voice Coil Overhang (Xmax): 2.7 mm
* Surface Area of Cone (Sd): 856.34 cm2
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Old 29th August 2008, 11:30 PM   #2
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Sounds to me like there is something wrong with the midrange. And you say the woofer just wispers? How much power are you feeding it? Whats the crossover points? I think you will find that the new replacements sound alot better.
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Old 30th August 2008, 12:02 AM   #3
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Oh, how wonderful answer!
I'm really happy you think I choosed good replacements

I'm still regretting the lovely midrange of my old Linn Index Plus (yes they had Kef B200 but another version, I think this SP1069 is little known and rare, found almost no informations on the web).

My amp is an old Nad 3020 series 20 recapped; and this is the crossover as I found it in that ( wonderful ) speakers project:
*tweeter: 4uF series
*midrange: 0,39mh + 80 uF series
*woofer: 4,7mH series + 68uF parallel - this driver is in opposite polarity (please don't ask me why).
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Old 30th August 2008, 12:18 AM   #4
Will is offline Will  Malaysia
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Hi There,
If I were you, I'd invest in 2 more additional power amplifier for 3 separate amps to the 3 drivers (perhaps you can build the gainclone?), get a dcx 2496 and connection cables to interface between RCA and AES/EBU connection; not forgetting a simple preamp. This will get you up several notches and get you going much quicker to audio nirvana instead of harping on passive x-over fillding components one at a time which is slow and without measurement qeuipment you're basically shooting in the dark. With the DCX you can dial in the x-over numbers, play with the relative phase of the drivers and play with the relative sensitivity offset of each drivers to obtain a seamless integration.

cheers.
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regards,
Will
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Old 30th August 2008, 12:24 AM   #5
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I 100% agree with Will on this
It just makes sense. Without the test equipment you are shooting in the dark. And with 3 seperate amps, you can control everything.
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Old 30th August 2008, 12:28 AM   #6
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Will, you open a new world to me. This sounds very interesting, I definitely will investigate this way too.
A digital solution Also if I'm a really analogue man....
Peanut, yes to control everything is my dream!!!
Do you think I could stay with my Nad as a preamp plus 3 Gainclones and the DCX? Or take just 2 more vintage amps (as I have a strange addiction to old devices) plus DCX?
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Old 30th August 2008, 01:05 AM   #7
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To me , its whatever you want to do. You can use the NAD as a preamp if you choose. Thats the great thing about DIY, only you can decide what you truely want.
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Old 30th August 2008, 02:10 PM   #8
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Location: Western Sydney
"necessary skills!" - get them here (before you waste any more money):

Getting started in Crossover Design

The basics (You've got to understand the rules before you can break them :-)
http://sound.westhost.com/lr-passive.htm
choosing xover point:
http://www.speakerbuilder.net/web_fi...xpointmain.htm
Baffle Step Compensation: http://sound.westhost.com/bafflestep.htm

Getting it done:
Jay has a page on designing xovers using manufacturers specs without measuring:
http://www.geocities.com/woove99/Sp...DesigningXO.htm

Calculators:
http://ccs.exl.info/calc_cr.html#second
http://www.sengpielaudio.com/calculator-Lpad.htm

Measurement freeware:
Synrta - http://libinst.com/SynRTA.htm
ARTA http://www.fesb.hr/~mateljan/arta/download.htm
ARTA Jig - http://zobsky.blogspot.com/2008/01/s...t-jig-for.html

Examples from the designs of others can be quite instructive:
http://www.zaphaudio.com/
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://www.rjbaudio.com/projects.html
http://www.humblehomemadehifi.com/
__________________
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 30th August 2008, 10:52 PM   #9
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Wonderful links!
Thank you so much. Drivers will stay silent in their boxes while I'm studing.
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Old 3rd September 2008, 10:09 PM   #10
DanDini is offline DanDini  United Kingdom
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What an excellent thread. This is exactly what I have been looking for expecially the freeware measurement software!

Dan
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