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Old 29th May 2009, 04:19 PM   #1
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Default Possible Summer Project

Well, I would love to build a set of bookshelf speakers just for fun. I think I have the tweeter picked out, looks interesting and Zaph really liked it. It is the SB-Acoustics SB29RDC-C000-4 Ring Dome tweeter. It is a new take on the ring radiator from SB. The woofer is going to be the SB Acoustics SB17NRXC35-8. I am targeting a crossover frequency ~2100Hz and 24dB slopes. Anything more than that I need help with, which is why I am coming here. Anyway, any help or advice is appreciated.
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Old 29th May 2009, 04:52 PM   #2
Thawach is offline Thawach  Thailand
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Free air resonance Fs 600 Hz of Tweeter is very low. crossover frequency ~2100Hz will be ok. the woofer has a good freq respond. i think only xo order 2 for the woofer,u will get transient and dynamic better than order 4.
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Old 29th May 2009, 04:56 PM   #3
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Based on Zaph's testing that woofer has a fairly ragged breakup around 2.5-3K so I am not sure I want to use only a 2nd order on the woofer.
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Old 29th May 2009, 05:20 PM   #4
Thawach is offline Thawach  Thailand
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i just seeing now, can 't use order 2th . ok with 4th will be better
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Old 29th May 2009, 05:27 PM   #5
DcibeL is offline DcibeL  Canada
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A crossover around 1800-2000Hz will work well. I wouldn't want to go too low with that tweeter to make sure that the 2nd harmonic will not be a problem, although a highish 2nd harmonic with low 3rd, 4th, and 5th should not be very offensive.

I would aim for 4th order acoustic slopes. This may require a little extra work with the woofer due to the cone breakup mode, but looking at the distortion graphs, breakup distortion isn't a problem until about 4kHz, and is dominated by 2nd harmonic, so the hurdle will be achieving the right slope for a flat response.

Good luck with your project, this driver combo should make for an interesting and very good sounding speaker if done correctly.
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Old 29th May 2009, 05:32 PM   #6
DcibeL is offline DcibeL  Canada
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http://www.rjbaudio.com/Audiofiles/FRDtools.html

http://www.geocities.com/woove99/Spk...esigningXO.htm
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Old 29th May 2009, 06:41 PM   #7
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Quote:
Originally posted by DcibeL
A crossover around 1800-2000Hz will work well. I wouldn't want to go too low with that tweeter to make sure that the 2nd harmonic will not be a problem, although a highish 2nd harmonic with low 3rd, 4th, and 5th should not be very offensive.

I would aim for 4th order acoustic slopes. This may require a little extra work with the woofer due to the cone breakup mode, but looking at the distortion graphs, breakup distortion isn't a problem until about 4kHz, and is dominated by 2nd harmonic, so the hurdle will be achieving the right slope for a flat response.

Good luck with your project, this driver combo should make for an interesting and very good sounding speaker if done correctly.

How about 4th order slopes on the high and low pass at 2k. I wish Zaph had the impedance plots so I could see what the impedances are around the crossover frequency to help with calculation. Also, do you think any filters will be needed for the design? Lastly, one of the members on htguid who has used the SB drivers extensively has said the phase of the tweeter will be ~10 degrees off of that of the woofer. How would I compensate for this?
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Old 29th May 2009, 07:42 PM   #8
DcibeL is offline DcibeL  Canada
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Zaph includes impedance on the frequency response graphs, however the resolution is really not very good to use for calculations. You can either trace the impedance from the datasheet, or wait until you have the drivers in your hands and measure it yourself.

It is clear to me that perhaps you have not embarked in crossover design previous to this project. I would advise reading through the above links I posted, as well as looking through the documentation for the spreadsheet applications mentioned in those documents. Most of the FRD tools, although somewhat unintuitive, have fairly well written documentation explaining each function of the application.
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Old 29th May 2009, 07:49 PM   #9
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Yes, never done it before, that's why I am here I really would like to get these working and see how they compare to my B$W DM603 S3.
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