Bass management with stand alone preamps

The problem that you often run into that makes people think they need bass management is something called a 'standing wave'. This is a bass note that is of such a frequency that when it bounced off of the wall behind the listener, the result is that there is a bass cancellation at the listening chair.
This makes the listener want to turn up the bass, which might come in the form of 'room management' or 'bass management'. If you have a high performance system, both will degrade the sound.


Another issue is when the standing wave is in phase with the incoming bass, creating something called 'super position'; IOW a massive bass output at a certain frequency. Both can occur at the same listening chair.

If you have this problem, room correction might be able to correct the super position but not the null created by the standing wave. No amount of power corrects that and room treatment doesn't work either.

The solution is called a 'Distributed Bass Array'; the best example being the Swarm subwoofer made by Audiokinesis. The idea is that two subs go near your front speakers, the other two are placed asymmetrically in the room boundaries to the left and right of the listening chair (placement is not critical). This breaks up the standing wave and gives you even bass distribution throughout the room.


Problem solved: no need for 'bass management'. Just a second output to drive the subwoofer amp.

esthlos13, yes Trinnov does 8, 16 and 32 channel units using the same system. The Amethyst is the only two channel unit they make. They make a stand alone room control unit but the Amethyst adds a lot of important features like digital bass management, a great DAC and even a phono stage which frankly I would not use. I need two phono inputs and I'm a dyed in the wool ARC guy when it comes to phono stages. But, if the turntable is a minor part of your system and room is limited it is probably fine. Lyngdorf is an out growth of TACT Audio. For some reason Lyngdorf does not offer a stand alone 2 channel processor/preamp which is a shame. The TACT 2.2X was at the Apex of TACT's development and it is an amazing processor/preamp. Built like a battleship it has very high resolution room control, unlimited target curve management and the best bass management I have ever seen. You can change cross over points and filters on the fly and choices are unlimited. High pass and low pass filters are set independently. You want a high pass filter of 97Hz @ 80 db/oct? Just dial it in and hit the go button. It has Dynamic Loudness Control. A series of target curves simulate the Fletcher Munson curves at various volumes and it drifts from one curve to the next as you change volume. You set the curves to be flat at the loudest volume you listen too then as you drop the volume the compensation increases. So, as you drop the volume the frequency balance of the music does not change down to -48 db. None of us ever liked loudness compensation because it only worked at one volume. It was off everywhere else. This system is  great. The music just sounds the same no matter where you set the volume control otherwise it is totally invisible. So, why did this unit not succeed? As you might have guessed I have one. TACT (Boz) decided to market his units directly. He did not use dealers. He was doing this to try and keep prices down. In his genius mind he did not realize that every one was not as educated in DSP as he was or just not as smart. The 2.2X is anything but user friendly. If you put the microphone close to any object funny things would go wrong with the measurements. You had to know when it was screwing up or you got really sick sounding compensation filters. The user manual sucked and the learning curve was steep. He had no dealer support so he got buried in phone calls and problems. His units got a bad reputation and finally Boz just disappeared. If you are techish and computer savvy and see one of these on the market for anything less than 4 grand buy it! You will have a blast. 

Atmasphere, I think you are confusing room correction with bass management. Bass management supplies cross over points, slopes and outputs for sub woofers. Room control without careful woofer set up and acoustic management in the room just shifts the comb filtering around at the cost of a lot of power. I do not like the term room control. I like speaker control better. It is to fix response abnormalities of the speakers or woofers in the position they occupy in the room. If you move a speaker from one point in a room to another its frequency response will change. The most important function of room control is not to make everything Flat. Flat actually sounds awful at volume. Way too bright. It is to make the response of the speakers exactly equal at all frequencies. The result of this is razor imaging. If frequencies vary in volume one side to another you smear the image. Then if you have a good unit that allows you can create target curves and tailor the frequency response to your liking. You can also create target curves for specific purposes. I have a curve with a 3 db notch filter at 3 kHz which I use for violins and female voices that are too harsh. Once you are in the digital domain you can do anything you want. Those that think "room control" is only for bass are sadly mistaken. Audiophiles that hear this in action on a good set of ESLs are dumbfounded. The improvement is such that I do the unspeakable of digitizing the output of my phono preamp and input it to the TACT. 

@mijostyn You are correct in what you say, but if you use a distributed bass array you don't have such profound problems with the bass changing as you move the speakers; much of that is due to standing waves. So this makes getting the bass right a **lot** easier!

I can do better Atmasphere. It is not far off the distributed array idea but is a more powerful. I have mentioned it before on this site. I have linear arrays which project power differently than point source speakers. Their power drops off at the square of the distance. Point sources drop off at the cube of the distance, much faster. The distributed array idea is using 4 rather small point sources. I use 4 woofers set up as a linear array using the walls as boundaries. The two end woofers must be in the corners and none of the woofers can be further apart than 1/2 the wavelength of the highest frequency they are expected to reproduce. All woofers are right up against the front wall. The two inner woofers are facing each other so that their drivers are right up against the front wall. What you get is 4 woofers acting as a single driver. Since they are using three walls as boundaries the only primary reflection is the rear wall which is delayed and down in volume. I built this house and purposely designed it so that there is essentially no rear wall. The end result is very powerful base that matches the output of my ESLs without any standing waves. You can walk through the room and the base response does not change until you get right up against a lateral wall. This is with room control disabled. The ESLs have their signals delayed by less than a millisecond so that the woofers are exactly in phase with the ESLs. I cross over at 125 Hz 48 and 24 db/oct. You can not hear the cross over. It is entirely seamless. Is is much harder to match sub woofers with speakers at lower cross over points because of the longer wavelengths. 100 Hz is around 10 feet. 20 Hz is 32 feet. You try and cross over at 60 or 80 hz and you have to move your speakers 1/2 way across the room unless you have room control that measures the delays and accounts for them. Most don't yet people are trying to cross at 80 Hz and do not understand why things don't sound quite right. Properly set up you should not be able to tell at all  that there are sub woofers in the system. You should be presented with one powerful whole. I have yet to see an analog system do this. They can come close but not quite there. Digital bass management and phase or time management seem to be crucial to make this work correctly. I am sure you have heard SoundLabs speakers. They project a large as life sound stage. With woofers set up like this the bass sounds just as big and powerful as the SoundLabs except the SoundLabs become cleaner and are capable of another 10 db or so if you care to crack all your windows.