Question Crossover is affecting brightness of woofers?

Feb 27, 2019
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I am new to configuring hardware. I recently purchased an old JVC AX-R97 165W amp, a pair of Technics SB-TS100 speakers, and a pair of NHT SWS2i subwoofers. The Technics sound great on their own. When I plugged in the subwoofers, it all sounded fine, except for the fact that the subs go up to 500Hz. Because this is my first setup, I figured I would order off-the-shelf two 80Hz low-pass filters (the Lucasfilm THX Technics attenuate well naturally around this point). With the filters on the subs, I encounter two problems. The Technics sound much less bright, with a lot of mids, even when they are playing at my regular listening volume. Also, the subs are now quite overpowering, a minor issue. I am hoping that if I put a pair of 80Hz high-pass filters on the Technics, this will clear up my main issue. Before I spend money, is this true? Furthermore, if I've matched the 8 Ohm subs with 8 Ohm filters, should I match these 4 Ohm speakers with 4 Ohm crossovers or stick to the 8 Ohm? I know this is strange to use speakers of such different impedance, but I have them. Thanks for helping.
 
I seem to remember that the NHT subwoofers were meant to be biamped with an outboard crossover amplifier. That will likely have had an active 18 or 24 db/octave crossover for the subwoofer and main speakers rather than the 6db/oct passive crossover. Having an amp would have allowed the woofer level to be set to match the main speakers. Just adding a crossover to reduced the bass output of the Technics won't let you really match the levels and it's likely that there are peaks and dips caused by the room and speaker placement that you won't be able to fix easily.
Since the Technics were meant as side speakers they would not have had to reproduce bass but were limited by the surround receiver which would have been set to filter bass from them so they could play louder. That means that you can't really assume that they don't go down to maybe 40hz and may not flat in the bass.
If you are connecting the passive crossovers and subs in parallel with the Technics speakers then that can affect them as well.
 
Feb 16, 2019
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Here's the sub manual, in case you don't have it: https://www.nhthifi.com/products/11174-sw2si#specs

JVC specs: https://www.hifiengine.com/manual_library/jvc/ax-r97.shtml

I couldn't find your exact model# for the Technics.

You can use simple passive 6db/oct crossover components, which will consist of a capacitor to filter frequencies below 80hz and an inductor to filter frequencies above 80. I'd suggest maybe 100hz for the speakers, because the summed output at that x-over frequency @ 6db/oct may produce a peak. You'll need 2 each. It pays to choose an inductor with a low DC resistance.

Here's a good chart, showing cap and inductor values for your impedance: https://www.parts-express.com/resources-crossover-component-selection-guide
So choose 8 ohm values for the subs and 4 ohm values for your speakers. You can also see on that page, ways to get exactly the values you need.

This may not be the ideal setup, but sometimes, we must make compromises. The sensitivity of your 8 ohm sub is 89db. I couldn't find that spec for your Technics. Since 4 ohms presents a larger load on your amp (less resistance), the Technics SHOULD play louder than the 8 ohm sub will. Luckily, you may be able to compensate by turning up (or down) the bass.

Here's the kicker: You run the risk of burning up your amp if you drive it too hard. 8 ohm integrated amps don't like running at 4 ohms. You could be asking for trouble. Every octave down in the lower band requires 4X amp power. MAYBE you'll be okay, since the amp will be loaded @ 8 ohms in the low end, but it may run hot. Be sure to keep it well ventilated!
 
Last edited:
Feb 27, 2019
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Thank you Sonic Illusions! It's a lot of help. These Technics are quite old, dual sided speakers built shortly after the conception of the THX standard. I'll reconsider where to set the high-pass cutoff. Thanks for the warning, I've been using the Technics for about a month and the amp never seems warm. Hopefully it's fine, I do not ever turn the knob past half for regular listening.
 
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