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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Fri Sep 24, 2010 2:41 pm Post subject: |
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Mac, you rule. It was long time ago i rebuilt that crossover, But your explanation made me have a flashback!!
Thats exactly as i remember reading about it now.
I used both solen brand for the cap and inductor and it sounded way better than the stock parts, then i took out the cone tweeter and put that soft dome one in and sparkly top end was heard.
I now plan to find a modest tube amp and pre amp to make a total analog phono listening set up.
Athanasios
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Spanky Ham
Joined: 22 Mar 2006
Posts: 5643
Location: Comedy Central
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| Posted: Fri Sep 24, 2010 2:56 pm Post subject: |
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I am kind of tired, but let me see if I understand. You are adding a supertweeter to your Bose 701s, correct? If so, you want to put a crossover on it for the supertweeter, correct? Are you planning on building the crossover to suppress the low frequencies for the tweeter and to suppress the high frequencies for the Bose drivers? If so, you are going to have issues without measuring the drivers.
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Fri Sep 24, 2010 3:01 pm Post subject: |
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THe formula (it's very easy math, even for the laziest here!!) is:
F = 1 divided by (6.283 x R X C)*
* do the math in the brackets first!
F = crossover frequency
R= resistance of the speaker
C= capacitance (in Farads)
So... C = 1 divided by (6.283 X Frequency X Resistance)
Leave the Bose full range, and put a cap in series with the tweeter.
Note that if you're buying a finished tweeter, as in the old Radio Shack Supertweeters, the cap/crossover is already built in, and it's designed to connect across a full range speaker line.
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whats6x7
Joined: 04 Oct 2006
Posts: 5924
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| Posted: Fri Sep 24, 2010 4:46 pm Post subject: |
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| Curt Palme wrote: | THe formula (it's very easy math, even for the laziest here!!) is:
F = 1 divided by (6.283 x R X C)*
* do the math in the brackets first!
F = crossover frequency
R= resistance of the speaker
C= capacitance (in Farads)
So... C = 1 divided by (6.283 X Frequency X Resistance)
Leave the Bose full range, and put a cap in series with the tweeter.
Note that if you're buying a finished tweeter, as in the old Radio Shack Supertweeters, the cap/crossover is already built in, and it's designed to connect across a full range speaker line. |
You sir are correct. I'm leaving the Bose full range but I'm changing the crossover in the Realistic super tweeters. They are currently crossed at 5K and I want to cross them at 10K. They currently have a 2.7 cap with a .35mh inductor. I ordered 2.0 caps and I'm wondering what will happen if I don't replace the inductor. Will it make that big of a difference?
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Fri Sep 24, 2010 5:27 pm Post subject: |
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| whats6x7 wrote: | | I ordered 2.0 caps and I'm wondering what will happen if I don't replace the inductor. Will it make that big of a difference? |
Your crossover frequency will be around 6khz.
For an 8 ohm speaker and a 12db per octave @ 10khz crossover, the cap needs to be 1.14uf and the inductor needs to be .22mh.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Fri Sep 24, 2010 7:47 pm Post subject: |
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I figured I should also add there are other combination's that will yield the same output.
1.14uf/.22mh as posted above.
1.0uf/.25mh
1.4uf/.18mh
These are just different styles of crossovers.
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Boilermaker
Joined: 21 May 2006
Posts: 527
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| Posted: Fri Sep 24, 2010 7:47 pm Post subject: |
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| Quote: | | You sir are correct. I'm leaving the Bose full range but I'm changing the crossover in the Realistic super tweeters. They are currently crossed at 5K and I want to cross them at 10K. They currently have a 2.7 cap with a .35mh inductor. I ordered 2.0 caps and I'm wondering what will happen if I don't replace the inductor. Will it make that big of a difference? |
If the crossover was sold and intended to be used with the tweeter you have, those values are probaby closer to the proper values, as the stated impedance of speakers are usually nominal and almost always non-linear with respect to frequency unless they are planar magnetic or ribbon style.
Most likely, the reason they chose a 2-pole high pass filter at 5K is that it would have power handling issues below 5K and a 1-pole filter would not reduce the power enough.
If you wish to use a 2-pole (12db/octave) at 10K, I recommend you buy an L-Pad and use the values of C and L that Mac gave you. Use of an L-pad gives you two things: First it represents a closer to 8 ohm resistive load so that your values are correct, and, 2nd it allows you to adjust the volume of the tweeter relative to the main speaker, which you will probably want to do.
If your tweeters are more efficient than your Bose, then the L-pad can adjust them to your content. If your tweeters are less efficient than your Bose, then you are S.O.L.
Also, if you go with the 2-pole filter you should reverse the leads to each tweeter as there is a 180 degree phase shift with a two pole filter.
Bob
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whats6x7
Joined: 04 Oct 2006
Posts: 5924
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| Posted: Fri Sep 24, 2010 9:27 pm Post subject: |
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| Boilermaker wrote: | | If your tweeters are more efficient than your Bose, then the L-pad can adjust them to your content. If your tweeters are less efficient than your Bose, then you are S.O.L. |
Actually, I think that may be the problem and not the crossover. I think the speakers are more efficient than the Bose and are blasting them out. What if I put a volume control on the super tweeters? Any problem with that?
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greg_mitch
Joined: 03 May 2006
Posts: 5320
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| Posted: Fri Sep 24, 2010 10:12 pm Post subject: |
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| whats6x7 wrote: | | Boilermaker wrote: | | If your tweeters are more efficient than your Bose, then the L-pad can adjust them to your content. If your tweeters are less efficient than your Bose, then you are S.O.L. |
Actually, I think that may be the problem and not the crossover. I think the speakers are more efficient than the Bose and are blasting them out. What if I put a volume control on the super tweeters? Any problem with that? |
The L-pad is the volume control.
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whats6x7
Joined: 04 Oct 2006
Posts: 5924
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| Posted: Fri Sep 24, 2010 10:26 pm Post subject: |
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| greg_mitch wrote: | | whats6x7 wrote: | | Boilermaker wrote: | | If your tweeters are more efficient than your Bose, then the L-pad can adjust them to your content. If your tweeters are less efficient than your Bose, then you are S.O.L. |
Actually, I think that may be the problem and not the crossover. I think the speakers are more efficient than the Bose and are blasting them out. What if I put a volume control on the super tweeters? Any problem with that? |
The L-pad is the volume control. |
I understand that but the l pad is a special volume control. I already have a normal stereo speaker volume control. What is wrong with just using that?
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Boilermaker
Joined: 21 May 2006
Posts: 527
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| Posted: Fri Sep 24, 2010 10:40 pm Post subject: |
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| Quote: | | I understand that but the l pad is a special volume control. I already have a normal stereo speaker volume control. What is wrong with just using that? |
Two issues:
1 - Don't you want individual volume controls instead of a stereo unit?
2 - I don't know what type control you have, but an L-pad maintains an 8 ohm input impedance which will mean that only the volume will change - not the cross-over frequency. Most of the newer volume controls are actually multi-tap transformers - Not exactly whatyou want for best sound quality.
Bob
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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dvh99
Joined: 25 Dec 2009
Posts: 2158
Location: nederland
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