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-   -   help with adding a subwoofer to a pair a 2-way speakers (http://www.diyaudio.com/forums/multi-way/211916-help-adding-subwoofer-pair-2-way-speakers.html)

pepsi 2nd May 2012 12:42 AM

help with adding a subwoofer to a pair a 2-way speakers
 
hi,

I've got a pair of 2-way speakers with crossovers inside and a passive sub with a low pass filter at 120hz. I want to wire the sub in parallel with the speakers. can i add a capacitor in series with each of the speakers to make a high pass filter so that they cross over with the sub nicely?

also, can i somehow feed my sub a mix of both left and right outputs of my amp?

many thanks,
matt

RockLeeEV 2nd May 2012 02:59 AM

Quote:

Originally Posted by pepsi (Post 3008352)
I've got one stereo amp, a pair of 2-way speakers with crossovers inside and a passive sub with a low pass filter at 120hz. i want to wire the sub in parallel with the speakers.

can i add a capacitor in series with each of the speakers to make a high pass filter so that they cross over with the sub nicely?

I would not recommend it passively, especially at that frequency. You'd be better off just plugging the vent and running the main full range. But in parallel you might have insufficient current to drive this pseudo 3-way.

Why not get a cheap active crossover - like miniDSP. This is one of those cases where bi-amping is very justified.

Inductor 2nd May 2012 04:30 AM

1 Attachment(s)
Look here for this example of the Visaton Tabula.
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories
12 db Crossover Table
picture credits for Visaton

pepsi 2nd May 2012 10:29 AM

Hi,

Thanks for your replies!

Quote:

Originally Posted by RockLeeEV (Post 3008448)
I would not recommend it passively, especially at that frequency. You'd be better off just plugging the vent and running the main full range. But in parallel you might have insufficient current to drive this pseudo 3-way.

what problems would be caused by my amp not being able to supply the current? i would have thought that it would only limit SPLs when my amp is reaching its limits? also the speakers don't have a port so i would need some other way of rolling off the bass. i appreciate the idea about going active and would love to do it but i want to keep the costs down. i've another system I'm currently setting up which will have an active crossover.

thanks for the crossover diagram, inductor. it looks ideal. i assume it will sum each channel to the subwoofer while also providing a low pass filter?

will it be ok to add the high pass filters in front of the 2-way crossovers that i've already got?

also would you or anyone be willing to help me with the maths in order to determine the values of the components?

AllenB 2nd May 2012 10:47 AM

Adding a passive crossover to high-pass a woofer at a low frequency is not simple. It can make things worse, so is better when designed from measurements.

Fortunately it is not always the best thing to do in this situation. It can be better to leave the mains running full range when adding the subs. Subs also require careful placement into your room.

If your main speakers and each sub are rated at 8 ohms and your amp rated to handle 4 ohms (all of which are common) then you should be OK. Although it may be possible to go beyond such limits with care, at the least you risk blowing fuses which should indicate that this is not advisable.

ZLyzen 2nd May 2012 12:24 PM

I plan on driving the sub on my 2.1 system with it's own dedicated amplifier, actually a l4780 in bridged mode since the sub is 8Ω. Now my question is, there will be an active filter to cut off the sub's high frequencies, would I be more satisfied with also cutting the satellite's low frequencies or is this not necessary, and if I do such should I flip the polarity of the sub?

Cal Weldon 2nd May 2012 02:39 PM

-Zack,

Perhaps you should start your own thread rather than hijack pepsi's.

Thanks.

Inductor 2nd May 2012 02:40 PM

Quote:

Originally Posted by pepsi (Post 3008688)
will it be ok to add the high pass filters in front of the 2-way crossovers that i've already got?

No, because it will change/interact with the passive crossover. Good that you know it's not advisable.
Quote:

Originally Posted by pepsi (Post 3008688)
also would you or anyone be willing to help me with the maths in order to determine the values of the components?

Better I make another suggestion, choose one.
1. Using a 2.1 amp system.
2. Using two woofers or lower sub drivers (instead of one) one for each channel with a passive crossover.
3. Using two full range speakers for stereo.:cool:

pepsi 2nd May 2012 02:52 PM

Hi Allen,

Thanks for the reply. I measured the DC resistance of the sub driver and it's exactly 4ohms. The DC resistance of each 2-way speaker is 4.6ohms including the crossover. What other measurements would I need to make in order to design a workable passive crossover like Inductor suggested.

I don't want to run the 2-way speakers full range because I want the sub to take some of the work away from what will become the mid-range woofers amd hopefully they will play the mid-range better.

pepsi 2nd May 2012 03:06 PM

Can I put the high pass filter before the passive 2-way crossover that I'm already using?

Quote:

Originally Posted by Inductor (Post 3008913)
No, because it will change/interact with the passive crossover. Good that you know it's not advisable.

Will the bad interaction between the HPF and my 2-way crossover sound worse than the benefits I'll get from having a sub take care of the low end?


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