How much improvement in sound in (bookshelf) speakers by running high pass to them?

Ilusndweller

Junior Member
Ive drawn a conclusion based on 2 experiments and am looking for comments. My conclusion is that a noticeable improvement in sound can be had by using a high pass filter, especially the closer the high pass filter matches the natural rolloff of the speaker on the low end. Though I could see bringing the filter up 5 Hz or so, but not too much. I dont doubt that everyone who has been actively biamping/or biamping via DSP has already known this and am looking for comments, especially on bookshelf speakers and from people who can control things more precisely than I have the ability to. Where do you like your high pass frequency set with respect to the speaker low end spec?

My two experiments both involved B&W CDM-1SE speakers which are rated down to 58 Hz. The first high pass filter is a feature of my B&K AVP-1030 5.1 pre, 80 Hz I believe@12 dB/octave (has opposite low pass to subs). This took out too much bass from the speakers when played alone but when used with the sub (or two) can sound quite nice. Though think I still like running the speakers full range, even when used w subs. It has been a while since Ive had it set up, but I will shortly. The second high pass Ive tried is a NHT SA-2 sub amp which offers line out high pass @50, 75, 100@12 dB/octave as well as a fixed high/speaker level high pass at 100Hz/6dB/oct. The 50 Hz@12 dB works/sounds fantastic with these speakers. Cleans/tightens them up. I know some of you can control things even more precisely than me (variable high pass frequencies/steepness/types of filters/etc) and have experimted a lot more than me and I would love to hear comments. I figure I will get the bookshelves sounding their best (which I believe is close to where they were designed to play on the low end) then blend in the subs. Basically Im contemplating adding another black box (the SA-2) to my soon to be setup 2.2 system over running the bookshelves full range. The subs will be getting 80Hz and below from the B&K. It seems odd, bc the high and low pass of the B&K were meant to work in conjuction with each other but my ears say the NHT is a better match.
 
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JohnVF

Administrator
Staff member
While not specifically dealing with your question, it has always been my experience with subs that everything sounds a lot better when the left and right speakers are cut off where the subs come in so there's no doubling of those low frequencies. Now if there's a steep drop off in the speakers without the help of a high pass/cutoff I would assume this is less critical and you just bring the sub in lower. But depending on the particular sub, and the particular speaker, sometimes I wanted to bring the sub in higher than the natural rolloff of the speakers. In fact, most of the times I did, with small speakers.

BUT...its been a long time since I ran a sub with anything.
 

Ilusndweller

Junior Member
Thanks! 80 Hz-58 Hz= 22 Hz overlap of subs and bookshelf speakers is slightly unsettling but unfortunately I can not experiment further. Too bad the SA-2 doesnt have a variable low pass line out that I could run to the subs. Im happy with the sound though, or was about 5 years ago when I tried this briefly in the basement. I will probably use the amp just for its high pass filter. I couldnt find a frequency response chart for the CDM-1SE (58 Hz low end) but did find one for the CDM1. This speaker (prior model of mine) looks identical to mine but it is only rated to 64 Hz. A high pass @50 Hz, 12 dB/octave from the NHT SA-2 would seem to match up with my CDM-1SE quite well, imagining what the graph would look like for my speakers. The graph is for the CDM-1, not my CDM-1SE. I also tested the 75 Hz (and 100 Hz) high pass filters of the NHT and for these speakers and to these ears, they were too high for best overall sound when mated with a sub or two.
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TubeHiFiNut

Administrator
Been a long time since I've run bi-amped subs, or subs at all.

When I did, I used simple plug-in filters on the input of the power amp as the high pass filter. Those filters are specific to the input impedance of that power amp.

I would then use an active crossover as the low pass filter.

YMMV.....
 

Ilusndweller

Junior Member
I was thinking of something yesterday that I feel is very relevant and helped me form my opinion on the importance of this. When I was recording (granted this was often at bassy/boomy venues), I would sometimes run a 6 dB/octave high pass filter @50 Hz (to mics in avatar). I probably did this about 1/3 the time and feel it was significant in improving the sound. The reasons as to why a high pass filter can be used to improve the sound on both the recording and playback side of things may be different, but in a more general sense it just comes down to removing unwanted/uneeded energy to improve sound. I believe after a while I upped settings to 12 dB/octave @50 Hz or 6 dB@75 Hz at the Ventura Theater.
 
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RichPA

Junior Member
I've run a number of bookshelf/sub setups, and I've always preferred to run the main speakers full range. But these have all had substantial low-frequency extension (ACI Sapphire III, Paradigm S2, Salk Silks) down to 45 Hz or lower.
 
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