Help...I need a crossover for SS 18W/8545 and SS D2905/9300 - diyAudio
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Old 13th November 2002, 11:54 PM   #1
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Default Help...I need a crossover for SS 18W/8545 and SS D2905/9300

I am in great need of a crossover for Scan Speak 18W/8545 and Scan Speak D2905/9300...
I will try to describe my cabinet due my bad English. It is 1010mm high and 237mm wide (25mm radius+5mm flat+177mm woofer+5mm flat+25mm radius). The baffle is angled 6 degrees to obtain a correct mechanical phase. The cabinet walls is made of 2x19mm MDF-board + 4 mm oak glued together with a resonance-damping glue called HQ-box, the baffle is made of 32mm MDF-board +32mm oak. Inside there are a matrix design like in Thiel's speakers, all internal walls have 4mm bitumen plates glued with HQ-box, the side an top walls are slightly angled (the wall gets thinner towards the back of the speaker) just to guide the remaining resonances to the back of the speaker like some of Wilson Audio's concepts. There are no parallel valls inside the speaker. I use pure wool as damping material inside the cabinet, and a piece of 12mm bondex damping material on the back wall behind SS 18W/8545.The free volume inside is 17 litres + 4 litre off free space filled with sea-sand. I use a aerodynamic port made by Sonic Design to vent. the closure. I have bi-amping terminals from WBT. The top of the speaker is decorated with a 8mm thick black glass, glued with HQ-box. I use rubber damping feet instead of spikes. The total weight of a complete single speaker is about 46kg...my weight is 72kg... )

Enough about the cabinet...I have tried several self-designed crossovers and some i found on the web...but I am not happy with the sound I get. My question is...if I ask very nicely can anyone please help me with a "reference" filter for these two units? Or maybe guide me to a place where I can find a competent crossover that you can recommend. I have spent lots of time, money and effort on my cabinet, but haven’t got enough skills to complete a crossover that is good enough. I feel that the above mentioned units have a great potential but it's out of my reach just because of a badly composed crossover. You are my last hope and I would be most grateful if you could help me.

With hope of benevolent treatment.

/J
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Old 14th November 2002, 12:07 AM   #2
halojoy is offline halojoy  Sweden
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Default 8545 builders

here is some recently started projects with 8545

Design for Scan Speak Revelator + 8545k

toster will use 8545+9500
let me introduce myself

maybe you can discuss with them
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Old 14th November 2002, 12:21 AM   #3
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Unfortunatley there is no such thing as a generic 'reference' crossover, applicable for a given set of drivers.

The best XO's are designed using measurements taken with the drivers mounted in the baffle where they will be used. Using the mfg's measurements or anything other than measurements taken from your baffle is a crap shoot
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Old 14th November 2002, 11:32 AM   #4
Mark25 is offline Mark25  United Kingdom
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Hi softman,
this would appear to be a good "starting point" for your x-over.

https://secure.wilmslow-audio.co.uk/...o_Isis_31.html

i know you can also get this driver arrangemant in floorstanding form, so the x-over could be suitutable for different cabinets. HOWEVER, it could be worth speaking to them in case they have to make some changes.

Regards
Mark
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Old 14th November 2002, 02:48 PM   #5
navin is online now navin  India
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let me understand this...

1. your cabinet is 1m tall, and 0.23m wide (approx) i assume you cabinet is about 0.25m deep too (interal dimensions)

2. the baffle is 64mm thick (32+32) and the sides are 42mm thick plus bracing

3. your net internal value is 21 liters of which u have filled 4 liters with sea sand. the rest of the volume i assume is used by bracing.

4. the weight is 46kg.

i am not clear on some details.

1. your gross internal volume (volume before braces, sand etc...) shoud be in the region of 60 liters. of this you have consumed 40 liters in bracing and yet the weight of the cabinet is ONLY 46 kg. it should be more.

2. the 64mm thick front baffle can create an oil can effect for the 8545 i suggest that the hole in the wood which is on the inside be made about 10-15mm larger in diameter

3. thick baffles only store more energy. anyway it seems your baffle is quite solidly built and well braced so i assume you are aware of this.

there is no reference design. if there was this forum would be dead. the 2 biggest advatages we DIYers have is that we can design and build our speaker/amp/whatever depending on our taste and also inculde some compensation for our particular rooms. No speaker manfacturer has this advantage.

as a starting point i wold do the following.

1. listen to the woofer only. do not connect the tweeter. block the tweeter hole for now.

2. use a series inductor try values between 1 to 2.5mh although if you want a narrower range try values around 1.5 to 2.2mh

3. once you have a reasonable sound from this add a few caps in parallel with the woofer. you could try 6.8, 10uf, and even parallel both 16.8uf in parallel. see if you like the changes.

4. install the tweeter and add a 3.3uf cap in series with the tweeter. slowly up this to 4.7uf or 6.8uf. if that is not enough add a 0.7mh inductor in paralle with the tweeter. i would suspect you should be happy with values between 4 and 7uf for teh cap and 0.5mh and 0.8mh for the inductor.

5. try reversing the tweeter terminals. given the low value cap in parallel with the woofer and large value inductor in parallel with the tweeter your slope will in less than 12db / octave but more than 6db/oct.

listen to each change atleast overnight (2 nights). listen to 3-5 albums you know well. listen to other sources (live music, other good speakers) so that you are reminded of other "references".

hope this helps
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Old 15th November 2002, 06:02 AM   #6
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Mr Softman,

You have a schematic in Your inbox.

Best regards\Morello
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Old 15th November 2002, 07:02 AM   #7
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Cool I need the crossover schematic too :P

Can u send me the schematic too???
Tomi
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Old 15th November 2002, 08:05 AM   #8
navin is online now navin  India
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how close are teh schematics to my thumb ruleXO? just for acedamic knowledge
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Old 19th November 2002, 07:11 PM   #9
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Thumbs up Greateful...

Navin, thanks for sharing your knowledge. I have read a lot of your posts on this forum and learned a lot.

/The Swede…Softman
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