Subwoofer crossover taboo

[Benihana]

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.

Anyone that is running a 2.1 system with similar equipment should try this out and see if it works in their setup.

 

[dragonhawke]

Hmm I don't know why Hsu discontinued the MBM-12, sounds like it would fit your needs perfectly.

 

[LeninGHOLA]

The MBM 12 isn't dicontinued, I don't think. They have them for sale new still. Put in nearfield, one could definitely help bump your frequency response where it needs to be without running your mains hard and low.

Otherwise, crossover points will be dependant on what sub/driver/enclosure/crossover order you are using. Not all subs will react as well to such a low crossover point. This also brings up room modes - experiment with sub placement, doing a sub crawl every time you can when setting up a system. The way a room ineracts with a sub can create nulls in certain frequency range areas. Finding the proper place in your room can sometimes remove the nulls, and you can further adjust peaks and nulls with an EQ.

The 80hz crossover from mains to sub suggestion isn't a rule by any means. It is just a good starting place for those without the proper tools or desire to tweak their system optimally. There is no rule on what crossover point to use. Each sub will have its own sweet spot and limitation.

Ideally, if using an EQ, you would be trying to tame peaks, rather than bringing nulls up. That way you aren't driving your sub too hard outside of spec, but still getting a flat response.

 

[Sycraft]

Well there's good and bad to crossing speakers lower, even when they can handle it. The good is that you spread out the bass generation more. That helps deal with eigenmodes in the room. That can yield more flat bass extension at your seat. The downside is that the woofers have to work harder and have more excursion when you play those low frequencies, which increases their distortion at higher frequencies.

The ideal solution is more subwoofers. You don't do it for more volume (you could, but in small rooms that is almost never a problem) you do it to spread out the bass generation which gives better response. You use two, or even more, subs spread around the room.

That is, of course, more expensive. However it is a "best of both worlds" thing in that you get the benefits of crossing higher and lower (you cross them higher) at the same time.

 

[TESLA]

80 Hz isn't so much a recommendation as it is a starting point (as stated earlier in the thread). In fact, I would say that for most speakers, if we are to choose a standard recommendation, 40-60 Hz is a better range.

As for setting the sub enclosure's crossover, if you are going to use a receiver or EQ system, then I would recommend setting it to the max, essentially taking it out of consideration, and using the EQ's crossover settings. Most EQ software will then set levels and crossovers accordingly, at least for HT.

For 2.1, this is usually a very simple operation, but for surround, crossovers are usually set per speaker. (In my current setup, my center channel actually has a lower crossover point than my towers.)

For music, I myself tend to prefer full range with a sub used for augmenting the extremely low frequencies, at least for (relatively) lower volume listening.

Subs have larger drivers, which means that they can move more air with less movement. This translates to lower distortion levels at low frequencies at higher volumes. So for music that I like played loud, I then do usually prefer a crossover point.

Other than that, sub crawls and room treatments are your friend. As always in audio, if you are looking to improve performance you would generally want to look at improving, in order:
1. Your Speakers
2. Your Room
3. Everything Else

In fact you can argue that 1 and 2 in that list can be swapped.