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  1. #1
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    Subwoofer crossover taboo

    I have been using the standard 80hz crossover for all of my speakers that i have ever had, large floorstanding speakers to bookshelfs and everything in between. I always thought it sounded really great that way(nothing to compare it too) and that it was also the standard that most followed for optimal sound. Other than the fact that the 80hz setting relieves the stress on the receiver or amp that you are using to drive your main speakers, and it is also allows consumers to use smaller size speakers and not miss out on all the low bass as long as their speakers played low enough to blend with a decent subwoofer. This very reason was the main factor in downsizing my 130lb ea. main speakers that used 5 drivers and had a f3 of 30hz +- 2db, and f10 of 24hz( Mirage M-3si). I also had them biamped with over 400watts of pure power. I had an amp for each channel in my theater, so I had a lot of gear. All that size was going to waste and the speakers crossed over at 80hz made those monoliths sound no different than a bookshelf speaker, although they did play louder. As a point of reference, my subwoofer is a custom build Adire Audio Tempest 15" subwoofer in a 8cf 17hz ported box, driven by a 380w plate amp. I decided to radically downsize my system as I was going to buy bookshelf speakers that didn't really need an amp, a receiver would drive them fine. I sold the speakers off and I bought a pair of bookshelf speakers with a 6.5" woofer and has a f3 of 48hz and f10 of 43hz. I have ran these speakers at 80hz up until now when i got the upgrade bug recently and decided to look for newer speakers with more midbass slam. But I then realized that every speaker that I've had with a 80hz crossover had a similar amount of midbass no matter how big the speaker was.

    This is when i decided to mess with some bass management and different speaker configurations. Before all of this built in bass management in receivers and auto eq features...setting up subwoofers was a real pain. One would have to mess with crossover/phase/gain settings and spl measuring gear to achieve a desired response. And the people that were more focused on the music aspect of their system usually let their speakers play full range and then use the subwoofer as a bass augmentation device to only fill in the "sub bass". Manufacturers such as Rel designed their subwoofers to play ultra low and had crossover points down to 20hz by 1hz increments to cater to the true music lovers that want to run their mains full range.

    Well I'll stop rambling now and get to the point. I decided to use tricks from the old days and combine it with the features of today's receivers(granted mine is 8yrs old, lol). I only run a 2.1 system so this might not be for everyone that runs a full surround system and use LFE filtering. I ran the typical auto eq function of my receiver and let it go through its random tests. The main features i want out of the test is ofcourse the main speaker eq, but equally importantly the auto phase/level adjustment of the subwoofer to the main speakers. After it completed I ran some test tones to my main speakers to see how low they played. I measured strong response down to around 45hz. I then lowered my sub crossover to around that, making sure not to touch the level or phase adjustment knobs. Then I went into the settings of my receiver and I ran my mains as large and put the subwoofer to (mains + sub) setting so the sub plays with the mains running large. The sound is so much fuller and the midbass i've been missing all of these years is finally there. The bass sounds like its coming from the speakers themselves now, especially since my subwoofer is hidden(it was hard for how big it is). These small bookshelf speakers now sound like a full range speaker, and they only cost me $200 US. If any of you guys are curious just try this out, its free and doesn't cost anything, i guarantee you will like the results. The lower your speakers play the better it will sound.

    I also noticed a couple of surprises from this experiment. 1st, is that the bass now sounds better all throughout the room...even and deep. Playing bass from 2 more points in your room follows the idea similar to having multiple subwoofers spread out in your room to even out bass response. I get strong bass throughout the room now as before i would have null spots everywhere when set at 80hz. And these 3 bass sources are eq'd and phased to work together through the auto setup so they don't hinder each other in any way. 2nd, the bass from my 15" subwoofer sounds even deeper, if that is even possible since it plays down to 15hz in room. The lower crossover setting on the sub allows the sub to play lower and cleaner for some reason...I guess because it is working in such a narrow band.

    Most people will tell you to just crossover over your speakers at 80hz and let the sub take care of the bass below that because it was meant to play at those frequencies and it will be cleaner than the mains. Well the way I think of it, is that if the speaker is rated by the manufacturer to play at lower frequencies, then let it . The only caveats I see is that you can't play the speakers as loud before distortion, but that is already at ear bleeding levels...and that it will drive your receiver harder.

    I now have a very simple 2.1 system with just a receiver and it is probably the best sound i've ever had out of any of my systems, including those $3800 retails Mirage speakers I used.

    Anybody ever try something similar and have good results as well?

  2. #2
    Charm Thai™
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    I also have a 2 channel stereo system with a sub. I run the mains full range and cross the sub at 50hz. Very pleased with the results.

  3. #3
    Romanticist Philosopher
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    Smile I use the same idea

    Quote Originally Posted by TheHills44060 View Post
    I also have a 2 channel stereo system with a sub. I run the mains full range and cross the sub at 50hz. Very pleased with the results.
    I set the sub crossover to as close as possible to the capability of the two main speakers and let the main speakers and the sub do double bass so they each do as much as they can for bass production. Double bass just lets all the speakers get all the lowest frequencies. Has really worked well for years and also keeps the subwoofer or subwoofers from doing so much work that they become more distorted or just so distracting. It blends very nicely with my Sony Speakers. I think the one size fits all 80hz setting for THX is not the best for everybody because we all have different setups. My setting happens to be 50hz, too for both subs in my setup.
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  4. #4
    Charm Thai™
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    Quote Originally Posted by Robert-The-Rambler View Post
    ...My setting happens to be 50hz, too for both subs in my setup.
    Sounds like we're on the same page Robert :-)

  5. #5
    Shostakovich fan Feanor's Avatar
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    The subwoofer low-pass depends on one's circumstances and facilities. In my HT setup, my receiver's Audyssey EQ determines the crossover which, to the extend I can understand what it's doing, is 60 Hz.

    In my stereo setup I also use a sub. In this case the mains, Magneplanar 1.6's run full range and the sub's low-pass is set to 50 Hz. This works pretty well since the 1.6's roll-over is about 3rd order with an F3 a little higher than 40 Hz.

    However when I used to run Maggy MMG's I used complementary high- and low-passes at 80 Hz; this made the sub carry all the lows below 80 Hz which compensated for the MMG's dynamic limitations.

  6. #6
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    Interesting enough the only choices for pre-assembled low pass crossovers from Parts Express are 80hz, 100hz and 800hz.

  7. #7
    M.P.S.E /AES/SMPTE member Sir Terrence the Terrible's Avatar
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    I also noticed a couple of surprises from this experiment. 1st, is that the bass now sounds better all throughout the room...even and deep. Playing bass from 2 more points in your room follows the idea similar to having multiple subwoofers spread out in your room to even out bass response. I get strong bass throughout the room now as before i would have null spots everywhere when set at 80hz.
    One question....What did you use to measure your result?


    Secondly, two main speakers sitting out in the room is not the same as distributed subwoofers placed in corners or at midwall positions. Distributed subwoofers placed in a corner get a 9db boost(per sub) from boundary reinforcement, and midwall position will yield at least 3db boost. Mains placed out in the room get ZERO boost from this position, and will suffer cancellation and boost down the middle of the room due to wave interference patterns.

    You really need measuring devices to detect nulls in a frequency response. Out ears cannot detect nulls very well, but can detect a boost. This is especially true when the null is relatively deep, but has a narrow frequency response.

    And these 3 bass sources are eq'd and phased to work together through the auto setup so they don't hinder each other in any way. 2nd, the bass from my 15" subwoofer sounds even deeper, if that is even possible since it plays down to 15hz in room. The lower crossover setting on the sub allows the sub to play lower and cleaner for some reason...I guess because it is working in such a narrow band.
    I don't know which auto setup you use, but none of them are very good at combating wave interference. They do a better job than no eq, but they will not give you anything close to perfection. I know the basic version of Audyssey does not allow you to distribute bass to two subs or two speakers. Only Audyssey Mutli EQ 32XT pro does that.

    A crossover cannot allow a subwoofer to play louder or deeper. That is a perceptual artifact of our ears. A subwoofer who bottom end stops at 15hz with a crossover, will have a bottom end of 15hz without it. A crossover does not add information or boost information. It just splits information between a main speaker and a sub, or a woofer from a midrange and tweeter. By running your speakers full range, you have decreased the dynamic range of that speaker, reduced the dynamic power of the amps, and increased cone movement from the main speakers, which introduces more distortion to the main speaker system.


    Most people will tell you to just crossover over your speakers at 80hz and let the sub take care of the bass below that because it was meant to play at those frequencies and it will be cleaner than the mains. Well the way I think of it, is that if the speaker is rated by the manufacturer to play at lower frequencies, then let it . The only caveats I see is that you can't play the speakers as loud before distortion, but that is already at ear bleeding levels...and that it will drive your receiver harder.
    Speaker manufacturers may give you a frequency response, but rarely does it achieve that response in real rooms. If it does, the manufacturer almost never states a distortion figure for the lowest frequencies the speaker can cover. Why, because distortion rises quickly as cone movement increases, and if there was a distortion limit placed on the driver, it would never reach the manufacturers rated frequency response. If a distortion rating of 10% where placed on the speaker, then the lowest the speaker could play cleanly will rise sharply. Distortion shows up long before ear bleeding levels, especially at bass frequencies. Most receivers amps cannot produce their rated power over all of the channels at 20-20khz. So if you have 7 channels of bass running through it, its power capacity drops very sharply.

    One mid to high end receiver I have owned was rated at 150wpc from 20-20khz in two channels. When you expanded that out to the 7 channels of the receiver, it drops to 80wpc over that same 20-20khz. If you cut that amps low frequency limit to 80hz, then it rises back to 150wpc over all 7 channels. Bass requires much more power than the midrange or high frequencies do, which is why limiting a receiver to 80hz, and sending the lower frequencies to the sub is best.
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  8. #8
    Forum Regular blackraven's Avatar
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    I also run a sub with my Magnepans with the maggies full range and sub set at 45-50Hz.
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  9. #9
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    I had a similar epiphany a few years back which led me to discover single driver "real" full range speakers without evil crossovers driven wide open by one amp while using a second amp to drive full range bass woofers cut off/low passed at 80hz or whatever setting I choose. With this solution I get weighted, musical, fast, transient bass unlike the sound of plodding subs.

  10. #10
    Suspended markw's Avatar
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    Ditto. It only takes over where the mains naturally fall off.

    Quote Originally Posted by blackraven View Post
    I also run a sub with my Magnepans with the maggies full range and sub set at 45-50Hz.
    Main difference is that I found that my velo blended better with my 1.6's when the xover was set about 10 hz higher. Fortunately, maggies are polite enough to not even attempt to try to reproduce what they can't cleanly handle.

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