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Old 28th September 2013, 03:12 PM   #1
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Default Crossover for different impedance drivers

I want to make a set of Totem Mites. I have the information about the size of the enclosure and the port width and length and also the drivers used.

The Tonsil GDN 13/40/2 (the woofer in the Mite) comes as 8 ohm or 4 ohm. After doing a few online calculations, it appears that they must use the 4 ohm driver, as all the calculations I did give a box size of about 5.6l, which is exactly the same as the Mite's volume. If I insert the 8 ohm driver's specs into the online calculators, the box size comes out as 10.7 litre.

The Totem website says the Mit's impedance is 8ohm!

What is the best way to go about designing the crossover for different impedance drivers? Is it just a case of using an L-Pad resistor network to get the SPL of the tweeter to match the woofer and then use a series resistor in line with the woofer to make the impedance 8 ohms, then carry out the usual crossover calculations?

Thanks in advance
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Old 28th September 2013, 11:43 PM   #2
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I'm sure others will correct me if I'm wrong, but I see no connection between driver impedance and box size?

The functional cabinet size is related to Vas, and the frequency you want the box to resonate at. Which in this case is about 53hz.

Next, it is next to unheard of to put a resistor in series with the bass driver. I wouldn't say never, but it is rare. Just build the crossover to match the drivers.

http://totemacoustic.com/en/hi-fi/co...pecifications/

Just a thought, which other can correct as needed.

Steve/bluewizard
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Old 29th September 2013, 03:17 AM   #3
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In fact both versions are very different. Only thing in common is that they share the same Fs (53Hz).

Tonsil GDN 13/40/2 8 ohm - GDN 13/40/2 :: Tonsil - Sklep internetowy e-tonsil
Tonsil GDN 13/40/2 4 ohm - GDN 13/40/2 4 ohm :: Tonsil - Sklep internetowy e-tonsil

T/S parameters like impedance, Vas, Qts and Xmax (gap is the same/height of coil is different) are all different in this case. This will inevitably give a different enclosure as a result.

OP, you can design a crossover for different impedances, just use the right one for each of the stages.
Example: For a 8ohm woofer start with a 8ohm crossover for low pass, for a 4ohm tweeter start with a 4ohm crossover high pass. This is the usual, if the opposite reverse impedances, for 4ohm woofer start with a 4ohm crossover for low pass, for a 8ohm tweeter start with a 8ohm crossover high pass. For 6ohm impedance procede in the same way. You should then simulate (SPICE software or spreadsheets) and test with drivers and components (models) for YOUR final work and MODIFICATIONS before auditioning.
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Old 29th September 2013, 07:19 AM   #4
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Thanks for the replies. I don't understand why Tonsil would make 2 drivers of different impedance with completely different characteristics.

Totem's website says the Mite is 8ohm impedance. Surely with a 4ohm woofer and 8ohm tweeter, it should be 6ohm. Anyway, if I work out an L-Pad resistor network for the tweeter and then work out the crossover for each I should be OK, right?
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Old 29th September 2013, 07:52 AM   #5
AllenB is offline AllenB  Australia
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Consider each driver as what it is electrically (the impedance) when using components to cross them, but look at their response when deciding what to do to them.
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Old 29th September 2013, 10:03 AM   #6
Dissi is offline Dissi  Switzerland
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Some links:

Diy Totem Mite
Totem Sttaf DiY
http://www.speakerlab.gr/papers/totem_REB.pdf
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Old 29th September 2013, 11:11 AM   #7
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Thanks for the replys. I use a mac, so would UniBox be a good spreadsheet to use?
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Old 29th September 2013, 12:05 PM   #8
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The Mite uses the lower Qts version of the Tonsil woofers... (I know because I've designed them ), the GDN 13/40/2 4-ohm. You should not worry about impedance differences too much, because of the higher sensitivity of the tweeter, it has a series resistor before the high-pass section , so even if you use the 4 ohm woofer, the impedance will be roughly equal for the tweeter part. Anyway, if you check the impedance curves of most speakers, they show a quite wide fluctuation in their impedance, from the minimum of the woofer imp. (3-4 ohm), up to the 20-40 ohm region, specially if they are not compensatad for impedance. (The Mite is not.....) It uses a simple 5 part 2-nd order X-over (2 coils, 2 caps, one resistor).
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File Type: gif Mite x-over.gif (13.6 KB, 129 views)

Last edited by dragonweed; 29th September 2013 at 12:14 PM.
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Old 29th September 2013, 12:13 PM   #9
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Well, as you see, it is actually NOT the Mite's x-over, but it is very similar to that one on the picture
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Old 29th September 2013, 12:50 PM   #10
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Thanks Dragonweed. The image you showed says the drivers are GDN 15/40/5 and the XT25. These aren't what the Mite uses. What is the crossoveer frequency shown.
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