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Old 4th September 2008, 05:14 AM   #11
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Default Re: Crossover for open baffle: please need help!

Quote:
Originally posted by Calamaro
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.
[/I]
Could it be that the connections to the crossover are mixed up?
The midrange crackles, because it is taken to its mechanical limits. Probably connected to the woofer output.
The woofer whispers, because it is connected to the midrange output.
And you don't like the tweeters, because the rest is not working correctly.
You should also check, if both speakers are in phase.
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Old 4th September 2008, 08:02 AM   #12
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Hi Calamaro,

Can I suggest you look into pacificblue's check before you move on. Get something up and running first before you commit something much more expensive.

Start with the mid/widerange driver first, and, on its own.
Then add the other drivers in with any necessary crossover circuitry as you extend the audio bandwidth.

Another document worth scanning -
http://www.pispeakers.com/Speaker_Crossover.doc

I tried to e-mail you but that function is not open via your 'user cp'.

Cheers ....... Graham.
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Old 4th September 2008, 10:00 AM   #13
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Pacificblue and Graham,
thank you for your suggestions.

Drivers are biwired (mid+tweeter / woofer) so mid and woofer are not connected. All drivers was in parallel. I checked the links and all was correct. Woofer was in reverse polarity.
I tried to listen just midrange directly connected to the amplifier+tweeter connected to midrage via 2uF capacitor in series but
-one midrange works well, the other one crackle (that's why I thought it's damaged)
-tweeters sound like dog whistles (ultrasonic????)
Anyway, I think this is the right way, to begin with mid/fullrange and then add the others speakers. I'm reading lot of papers about crossover making, it seems that (also in this field) 'simpler is better', so I'll try to tune a good first order. I'm still trying to understand the following

******************************
from THIEL ws:

"There is a type of crossover system that does not introduce any phase shift or time smear, although it is expensive and difficult to execute. Well known as a technically perfect solution, it was often considered impractical. This is the first order (6 dB/octave) system that THIEL has perfected for practical use and employed in THIEL's Coherent Source systems since 1977.

A first order system achieves its perfect results by keeping the phase shift of each filter to less than 90 so that it can be canceled with a filter that has an identical phase shift of the opposite direction. The phase shift is kept low by using very gradual (6 dB/octave) roll-off slopes which produce a phase lag of 45 for the low frequency driver and a phase lead of 45 for the high frequency driver at the crossover point. Because the phase shift of each driver is much less than 90 and is equal and opposite, their outputs combine to produce a system output with no phase shift and perfect transient response. For any other type of crossover system it is not possible to completely eliminate time smear and phase shift."

http://www.thielaudio.com/THIEL_Site...timephase.html

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

Graham, sorry I didn't know private messages option was disabled.
Thank you for the document.

Cheers
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Old 4th September 2008, 10:32 PM   #14
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The Thiele info is just marketing BS - actually first order crossovers are cheapest to impliment, but have two problems - they don't protect low power rated drivers enough (which I think you've found -as Pacificblue has said), and they need drivers that have a very flat response outside the passband
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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 5th September 2008, 10:03 AM   #15
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Today I've listened to the greencones after a week. Separately, just one for time. With no filters.
Saba 8': one of the drivers is ok, good sound but as pacificblue has said it show difficulty especially on bottom end. The other one crackles so I definitely think it has a problem.
Saba 4': the tweeters are ok. The only problem is (will be) to tune properly filter capacitors.
In the meantime the new drivers are arrived: Kef B200 and Celestion tweeters. I like them. I really do. But I want to end this project keeping vintage speakers so maybe I'll just change midrange speakers with 2 others old ones, something less expensive than Saba (say Graetz, Loewe, or even RFT).
And the problem persists... the crossover!
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Old 6th September 2008, 09:00 AM   #16
DanDini is offline DanDini  United Kingdom
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Quote:
Originally posted by Will
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.
Hi Will,

This pragmatic approach sounds about right for me. The DCX2496 looks nice but is not that cheap. I've seen this auction 280163495024 on ebay and wonder that it might do a similar if less refined/refinable job?

Could you expand on what cabling is required from the AES/EBU to phono adaption? I thought AES/EBU was digital over XLR in which case a simple cable wouldn't do it...

Thanks,

Dan
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Old 10th September 2008, 01:07 PM   #17
DanDini is offline DanDini  United Kingdom
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Quote:
Originally posted by Will
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.
Does anyone know if the DCX2496 offers the kind of complexity that could match something like this:

http://www.linkwitzlab.com/orion_asp.htm

If it can, then it would create a comparitively easy way to set up such a system.

Thanks,

Dan
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