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MultiWay Conventional loudspeakers with crossovers 

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7th February 2018, 03:54 PM  #591  
diyAudio Member
Join Date: Jan 2016
Location: Padova

Quote:
I have 2 woofer (8ohm) in parallel with RE = 5,7 ohm Le = 1,06mH So Resistance is (5,7 * 1,25)=7,125 ohm Capacitor is (0,00106 / (7,125*7,125))=20 uF circa Is this correct? So the impedance of the woofers is not important in this step right? Thanks 

7th February 2018, 04:00 PM  #592 
R.I.P.
Join Date: Jul 2004
Location: Scottish Borders

No.
You design the crossover to suit the load it sees. It sees 4ohms because that is what two paralleled 8ohms drivers feels like.
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regards Andrew T. 
7th February 2018, 04:04 PM  #593 
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Location: Padova


8th February 2018, 07:00 AM  #594 
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Join Date: Oct 2008

Yes, I meant per side. If you use two woofers together you can do it a few different ways. Andrew has shown the most common. If you do it that way then just halve all the resistance values compared to using one driver... The driver resistance will be halved, the resistor to use in the crossover should come out at half the value that it would be for just one driver. The capacitor should come out at double the value for one driver.

23rd March 2018, 04:34 PM  #595 
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Join Date: Feb 2017

AllenB...... Thanks for the educative material. Its a fantastic read for beginners like me.
A couple of questions with regard to my build which is a take on Paul Carmody's Sprite with a couple of twists. I am planning on using the ND908 full range drivers as separates using the same filter as the Sprite (0.9mH coil and 20uF resistor in parallel). I have already made a stock Sprite build last year which was quite good in the bass department, but I found the treble to be not very open (BTW, its quite shouty without the filter). So, it got me thinking on making separates with the ND908's which would cross over 1st order to an 89dB AMT8 tweeter around 9000Hz. Each separate will be in a 5W x 8H x 10D box (outer dimensions using 1/2" MDF). I had another set of of the Sprite filter lying with me and planned on using them in the build. My confusion was on where to add the low pass filter on the full range i.e. before or after the BSC. After reading your article, I am considering on going with a 2nd order crossover on the AMT8 and the ND908 and crossover at 7000Hz to take care of the slight rise in response of the ND908 at this region. The components that i'll be using for the crossover will be a 0.25mH coil in series and 2uF cap in parallel on the full range and a 2uF cap in series and 0.25mH coil in parallel on the tweeter. I'll be adding a 9dB LPad on the tweeter after the high pass filter using a 5.1uf resistor in series and a 4.3uF resistor in parallel. Now the issue would be to ensure that the speaker doesn't sound shouty and adding the BSC components. Going by your article, the BSC can be added to the woofer after the crossover i.e by adding the inductor in series and the resistor in parallel. The inductor value shows 0.9mH (570Hz region) if i consider the 8"H or 0.5mH (900Hz region) if I consider the 5"W of the box. As I mentioned earlier, I already have a pair of 0.9mH coils with me. Please let me know if I am on the right path or there is a different way to go about this. My confusion was how to incorporate the BSC in the full range crossover. The BSC point and crossover point are quite far off from one another. 
24th March 2018, 12:17 AM  #596 
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Join Date: Oct 2008

In the original filter for the 8 ohm version, the reactance of the 0m9H inductor gets to 20 ohms around 3k5Hz. This means that by 7kHz you are more or less dealing with just a 20 ohm resistor in series with the driver and you can use this when calculating your values. (Since the driver impedance will be partially inductive, the total will be slightly less than the sum of the driver impedance and the 20 ohms.)
The driver impedance will be rising at this frequency. If you were to use the RC impedance flattening method you will also affect the original filter. In this case I think it is the intention to try to avoid that. (not to say that you couldn't try it or there aren't a number of different ways this could all be done.) However if you use a 2nd order low pass filter you will gain some immunity from the variations. It is unfortunate that inductor values tend to come out large when you are working into a high impedance. 
24th March 2018, 01:30 AM  #597 
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Join Date: Feb 2017

Thanks Allen.....
So, my understanding from your response: 1. If I add the Sprite filter, the amp will see around 2628 ohm past the 5000Hz mark (the 20 ohm resistor in series with the 8 ohm ND908). 2. I need to calculate the 2nd order low pass filter at 7000Hz based on a 2628 ohm impedance for the ND908. The inductor value would be around 1.2mH based for a 2nd order LR. If my above understanding is correct, I needed some more clarifications: 1. By adding the filter, have I changed the total impedance/load which the amp will see per channel. If so, then with the tweeter being 8 ohm and the ND908 now presenting a higher load and the wiring between the two being parallel, will this affect the total load being seen by the amp. Or is the calculations for parallel speaker connection load only applicable for two completely separate speakers on each channel and not for 2 or 3 way crossover networks where multiple drivers are used per channel. 2. Will I need to tweak the LPad on the tweeter in light of the above. I had planned a 9db LPad based on the 89db AMT8 tweeter and the 81.4db ND908. 3. Will the BSC be before the low pass filter i.e. AmpBSCLPFZobel network (if any)Driver. Sorry for asking such basic questions. You are one of the very few pros on this forum who answer questions of newbies without being condescending or admonishing us. Really appreciate your patience and time. Last edited by bsl100; 24th March 2018 at 01:33 AM. 
24th March 2018, 06:05 AM  #598  
diyAudio Member
Join Date: Oct 2008

Quote:
Quote:
Quote:
and you can assume you'll want to do it.. but not because of the difference in impedance. Most amplifiers that you buy have a near zero output impedance and this means they provide the same Voltage regardless of the impedance of the load they are driving even if it is different at different frequencies. Quote:
Here is where it really comes down to choice. If you want to avoid altering the existing sound and also keep it simple, then use AmpLPF(L and C)BSCDriver. If this gives you a reasonable value of components to work with then this should give you a start. The typical way to do this would be the way you have suggested above. If you do this, the BSC will have a greater effect on the filter. This will make it more difficult to predict the result if you aren't measuring. That's the only reason for making this suggestion. 

30th March 2018, 05:56 PM  #599 
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Join Date: Feb 2017

When you say BSC, I assume you are talking about the resistor and inductor in the original plan.
Here is where it really comes down to choice. If you want to avoid altering the existing sound and also keep it simple, then use AmpLPF(L and C)BSCDriver. If this gives you a reasonable value of components to work with then this should give you a start. [/QUOTE] The picture is now becoming more clear. A couple of questions: 1. Would this be valid for a LPF 1st order too? i.e. AmpLPF(L)BSCZobelDriver. 2. Would the Zobel stabilise the impedance to around upto the crossover point i.e will the amp see 8 ohms if I use an 8 ohm Zobel network? 
31st March 2018, 04:41 AM  #600 
diyAudio Member
Join Date: Oct 2008

If you go first order, you will be putting a capacitor in series with the RL circuit. It can go on either side of the RL, it makes no difference because each part has the same current running through it.
Please tell me what the Zobel is for and why you want it. Is it to make the amp see 8 ohms? Is it to make the crossover see 8 ohms? Is it to make the BSC see 8 ohms? 
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