In-line capacitors

Huxley

Novice Member
Hi, I'm new. I've just joined and hope to get some advice about my situation.

I don't have a lot of money to spend on HiFi, and quality stuff is very expensive where I live, but I've been able to knock a system together that is sounding pretty damn good to these ears.
I'm using a 200w Douk/Nobsound mini-amp and a pair of Yamaha NS F150 floor-standing speakers. These speakers are 6 ohm with a frequency response of 37Hz to 30KHz. Really I could just leave it at that and I'd be quite happy.
However, I recently got made an offer I couldn't refuse on a couple of Monoprice 8 inch powered subwoofers. I've wired them both up to my amp using the speaker-level connections. What I've found is that I can barely turn them up because the bass response of the Yamaha speakers already goes down pretty low. I currently have the subwoofers set on the minimum volume setting and turned to their minimum low-pass frequency which is 50Hz. Everything sounds great, but there's a lot of power that the subwoofers could be adding to the system that would seem to be going to waste.
I just bought a couple of 400 uF capacitors rated at 100v. I have heard that if I put these in-line with my speaker connections it will cut the low frequencies < 100Hz of my Yamaha speakers therefore allowing me to turn up the subwoofers and perhaps get more clarity in the midrange from the Yamaha speakers at the same time. I am a complete novice at this sort of thing, any advice about this and whether it will work or is even worth doing would be very much appreciated. I wanted to check before I try wiring those capacitors. Thanks!
 

Ugg10

Distinguished Member
Theoretically this should work. The capacitor will act as a first order (6dB/octave) high pass filter. Using a couple of online calculators 400uF will start to roll the Yamaha’s off at around 200hz, very gently at first and has a -3dB point at around 60hz. This assumes that the impedance at that point is 6ohms. However, the speaker impedance curve will change quite a lot and have a peak of maybe 20-30ohms at the resonant frequency of the woofers (assumed to be around 35hz ish). Without an impedance plot this is about as good as you will get.

100v rating should be ok as the amp output is likely to be below 50v even at full volume, 250v versions would have given a bit more headroom.

If you put the capacitor in series on the +ve line of the speakers, I would download a free frequency analyser app for your phone, play pink noise (assuming you have Spotify or similar or there are online resources) and take a before and after measurement to see the difference.

If you go for it do let us know how you get on.
 

Huxley

Novice Member
Theoretically this should work. The capacitor will act as a first order (6dB/octave) high pass filter. Using a couple of online calculators 400uF will start to roll the Yamaha’s off at around 200hz, very gently at first and has a -3dB point at around 60hz. This assumes that the impedance at that point is 6ohms. However, the speaker impedance curve will change quite a lot and have a peak of maybe 20-30ohms at the resonant frequency of the woofers (assumed to be around 35hz ish). Without an impedance plot this is about as good as you will get.

100v rating should be ok as the amp output is likely to be below 50v even at full volume, 250v versions would have given a bit more headroom.

If you put the capacitor in series on the +ve line of the speakers, I would download a free frequency analyser app for your phone, play pink noise (assuming you have Spotify or similar or there are online resources) and take a before and after measurement to see the difference.

If you go for it do let us know how you get on.
Thanks a lot Ugg10 for your reply. I tried it, and it did pretty much what I had hoped it would do. It cut frequencies lower than a bass guitar and gave a noticeable vocal boost. I was able to turn the subwoofers up to full volume without any boominess, giving a nicely defined and punchy low end.
However, after listening to lots of music over the last few days I came to the conclusion that it didn't sound as natural as before. There seemed to be missing frequencies in the low-midrange or others that seemed unnaturally loud. I guess this is only to be expected, really. So I put things back as they were and I'm happy with it. It was worth a try though!
 

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