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Old 25th January 2013, 06:40 AM   #1
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Default Converting a 2-way to a 3-way

Hi all,

I'm about to start my first DIY speaker project (not counting the re-build of my parents' suitcase "hi-fi" when I was 14).

I'm impressed with Madisound's SEAS Idunn speaker kit, at least as it looks on paper. Amazingly flat response and virtually non-existent THD.

The Madisound Speaker Store

But F3 is only about 50 Hz. So I'd like to add a passive subwoofer to the package, possibly the SEAS 10" L26RO4Y. In a ported cabinet its F3 is 28 Hz and F10 19 Hz. This is the woofer used in the Orion 3.5.

http://www.madisound.com/pdf/L26RO4Y-D0004.pdf

My question is: Can I tie the L26RO4Y to the Idunn system using this 4-ohm, 130 Hz crossover from Parts Express?

Subwoofer Crossover 4 Ohm 130 Hz 200W 260-221

The PE xover has a passthough with 6 db/octave bass rolloff to drive the rest of the speakers in the system. It is actually a band-pass filter.

I would build cabinets to house all the drivers, with isolated compartments for each, per their respective specs. Will adding this xover require changes to the existing Idunn xover, or change the behavior of that system, other than feeding it reduced bass?

Here is the schematic for the existing Idunn xover:

http://www.seas.no/images/stories/di...g/idunn_xo.jpg

Thanks!
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Old 25th January 2013, 11:29 AM   #2
Jay is offline Jay  Indonesia
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It's a pity that such a good drivers must have such a bad crossover solution...

There could be efficiency issue with the big woofer. And I pity the Idunn...

But I understand, we all have this problem to choose from difficult options:

(1) Total 3-way passive crossover design is not easy, but probably the best. Find the proven project.

(2) Active sub crossover with extra amplifier for the subwoofer. Usually an opamp in the signal path

(3) Your plan with total passive with cheap crossover. It can be simulated to see the chances, but even so I think doesn't worth a try.

You haven't built the Idunn, so search for 3-way project alternative.
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Old 25th January 2013, 12:35 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

It could be done with a redesign of the Idunn x/o to have less BSC
for level matching and proper design of the bass to mid crossover
sharing the BSC issues with the bass unit via the crossover.

Nice drivers with the wrong crossovers is not good.

rgds, sreten.
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Old 25th January 2013, 01:09 PM   #4
Toaster is offline Toaster  United Kingdom
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If you can find a pair of decent sounding subwoofer plate amps, I would strongly suggest building separate active subs, even if you configure them as stands for the Idunns. I expect a passive design is possible, but it really isn't your best option- IMHO of course! It would be worth considering constructing the Idunns in sealed enclosures (0.2 cu. ft. is suggested for and f3 of 97Hz), preserving the same frontal width so as not to screw up the BSC. The plates amps would only drive the L26s and would not be involved in the signal path to the Idunns. You could always start with one sub and see how that goes! If the boxes were built well the potential is there for a very good sounding- and fairly compact- speaker system at a reasonable price.

Last edited by Toaster; 25th January 2013 at 01:20 PM.
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Old 25th January 2013, 01:24 PM   #5
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by GaryM44 View Post
The PE xover has a passthough with 6 db/octave bass rolloff to drive the rest of the speakers in the system. It is actually a band-pass filter.
that ad-on filter is likely to screw up the whole speaker

the 2way is possibly ok, and affordable
build it, and in the meantime save up some more money for a plateamp

if you use two 8ohm subs you might get away with a single mono plateamp
better to buy one real good subamp, rather than two crap ones

but thinking about it, using a single sub might give you enough spare money to buy a plateamp instead of the second woofer
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Old 25th January 2013, 01:27 PM   #6
Toaster is offline Toaster  United Kingdom
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Heh! parallel posts!
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Old 25th January 2013, 05:59 PM   #7
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Thanks guys. I think you've convinced me to power the subs with plate amps, control the crossover point from those amps, and then pass the signal back to the power amps unaltered to drive the Idunns. This plate amp looks like it would do the job:

http://www.madisound.com/pdf/KG5230-Updated11-2012.pdf

Any other thoughts/suggestions on this setup?
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Old 25th January 2013, 06:30 PM   #8
system7 is offline system7  United Kingdom
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Gary, a good three-way will knock a 2-way into a cocked hat!

Like this: 3-Way Classic

A good three way uses a very special optimised midrange driver. The rest is easy.
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Last edited by system7; 25th January 2013 at 06:35 PM.
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Old 25th January 2013, 08:51 PM   #9
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Quote:
Originally Posted by GaryM44 View Post
Thanks guys. I think you've convinced me to power the subs with plate amps, control the crossover point from those amps, and then pass the signal back to the power amps unaltered to drive the Idunns. This plate amp looks like it would do the job:

http://www.madisound.com/pdf/KG5230-Updated11-2012.pdf

Any other thoughts/suggestions on this setup?
If not use the service they provide to design new crossovers.
Crossover Design: The Madisound Speaker Store
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Old 26th January 2013, 02:13 AM   #10
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system7 ---

I can see that the 4.5 in midrange would have better transient response in its range. That would give me a 4-way system when mated with the subs.

However, the link you gave does not show any THD plots, and the overall FR is not as flat as the Idunns. But there may be other 3-ways that compare in those respects. I'll keep looking.
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