Paul's Posts — 21 September 2011
By Paul McGowan
Do you have a subwoofer or two in your system? You should.
Unless your loudspeakers have a built in powered subwoofer, or you have added a sub, you aren’t getting the full musical experience the artists intended.
I am not familiar with any standalone loudspeaker that is full range in your room – despite the claims of loudspeaker manufacturers who, for some unknown reason, seem to get personally offended when you suggest their products are lacking and need some help in the bass.
I always smile when I read that a particular passive speaker pair is touted as “full range” and flat to 20Hz. Truth is, it may measure flat when you place the measurement microphone 1 meter away from the speaker in an anechoic environment – meaningful only if you sit that close and don’t have a room in the way.
The goal of any high-end setup is to deliver a full range of audio, from 10Hz to 20kHz at the listening position. In almost all cases, it requires a pair of separate subwoofers to accomplish this. There are two reasons for this: most loudspeakers don’t produce flat response down to 10Hz and the perfect placement in the room for a speaker pair is most likely not the perfect place for producing bass.
The separate enclosure of the subwoofer gives you the freedom to place it in the room where it gives flat response at your listening position.
If a well recorded pipe organ doesn’t drop your jaw when you’re listening then your system needs a sub. No doubt about it.
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erich.j.henkel
Hello Paul,
1. thanks for the tipps regardind positioning the loudspeakers; my next free Saturday is booked for it
2. Can you give some advice about integrating a subwoofer as well? Cross Over frequency (my B&W 804 should have .-3dB at 37 Hz, with clossing the flowport B&W recommends a phase shift to 180°, how loud should it play etc.
Looking forward hearing about this
Erich
Paul McGowan
My best advice on subs is to do everything by ear: there aren’t any set formulas I am aware of that work.
The end goal is to have your B and W’s sound like they have low bass – not to all of a sudden have your attention pointed to the subwoofer on low notes. This is called seamless, when it sounds like your main speakers have more extension.
Obviously you want to keep the sub frequency low – but here’s the thing – it has to overlap the main ones to be seamless and that’s ok – it’s not critical.
Positioning the sub and the level on the sub are what you will play with.
Pale Rider
I have to concur. I have 6 excellent speakers in a 5.0 configuration [two together providing the center channel], and they have excellent lower register response and speed in either 2.0 or 5.0 mode. But not flat to 20Hz or lower. They need help for the system to get there. So, I am having two subs built for the system, and I just picked up a calibrated microphone and mini-mixer with phantom power to help me get them set up correctly in my room. While my wife is less than thrilled at the prospect of two more boxes, she appreciates the fact that we will have some flexibility placing them. I emphasize “some,” of course, because the best location for bass may not be her idea of the best location.
RobJK
I think the Vandersteen Models 5 and 7 probably qualify as standalone full range speakers. Their built-in subwoofers not only have an 11-band equalizer to even-out room response variations, but the subwoofers are perfectly matched in phase to the mid-woofers. So unlike many stand alone subwoofers, you don’t have to worry about the audible disconnection of a separate box. I don’t know if they are flat all the way to 10Hz, but they certainly are down to about 16Hz. Additionally, the Q is adjustable, so you can dial in anything from very tight response to a warmer response based on your personal preference. I’ve had separate subwoofers before, and some were very expensive, but none performed as well as the full range Vandersteen Model 5A.
Paul McGowan
The Vandersteens are, indeed, excellent. However, they still have the problem of placement. The best place for the sub to couple with the room and your listening position is almost never where the best place for the imaging of the main speakers. Only a separate sub solves this, even with the EQ available, because turning them up louder at specific frequencies doesn’t fix the problem.
Having written that, if you don’t want the hassle of separates, then the Vandy’s are probably an excellent choice. Richard makes awesome speakers.
RobJK
I agree that subwoofers are essential for recreation of the full musical experience. My point is that the Vandersteen Models 5 and 7 utilize true subwoofers, in a full range design. And, this complete system addresses the placement dilemma. Granted, placing the loudspeaker in the optimal location for best imaging means that the subs are not as efficiently coupled to the room as a corner placement would provide, but high acoustic coupling efficiency isn’t necessary since the rest of the system is adequately powerful. One of the reasons Richard includes the 11-band equalizer is to overcome the problems caused by less than optimal loudspeaker placement for bass. The dealer adjusts the equalizer using a real-time spectrum analyzer to obtain flat response below 20Hz—from the listening chair—not from 1 meter in an anechoic environment. So, the system is actually tuned to the requirements of the room to produce exceptionally flat and extended bass response. Vandersteen accomplished this in the analog domain, long before Audyssey MultiEQ XT32 made it simpler, but accomplishes much the same in the digital domain.
So, the “best practice” of corner placement for maximum room coupling is not required as it would be for a smaller or less robustly built subwoofer. Only if one were to be in an exceptionally large room, would greater coupling efficiency ever be necessary in Vandersteen’s system. I know of no other system which more expertly handles the competing requirements of optimal placement for imaging, while providing optimally flat extended bass. In my fairly large listening room, the Vandys’ provide more bass volume than my ears (and body) can handle. It is a mystery to me why more manufacturers haven’t adopted a similar system. In my opinion, I will gladly trade slightly less coupling efficiency, for the much more important aspect of driver coherence. I have yet to hear any separate subwoofer/satellite system be able to provide the seamless coherence between drivers of which the Vandersteen system is capable. When the fundamental frequency is emitted by the subwoofer, its harmonics must be coherent in time and space in order to accurately reproduce the waveform at the listening location. To build on some of your prior posts; once you train your brain to hear the benefits of driver coherence, it’s hard not to be bothered by the audible problems of separate subwoofers.
Mark Malboeuf
“Granted, placing the loudspeaker in the optimal location for best imaging means that the subs are not as efficiently coupled to the room as a corner placement would provide”
There are those of us in the camp that suggest that the corner is the worst place for a sub, for the same reason that having the sub locked to the speaker position is a problem. These positions tend to create huge peaks and troughs in the low end room response, which then require huge amounts of EQ to smooth out.
The usual approach to speaker placement is to choose a place where it interacts with the room the least, for the best imaging, etc. You wouldn’t place the speaker somewhere that required EQ to correct for room interaction (unless you absolutely had to). This is the idea with separate sub placement – put them where they cause the least problems/sound best to you, and you won’t have to deal with the problems inherent in the use of lots of EQ.
Given the full range configuration of the Vandersteens, it sounds like a good compromise. I personally can’t afford them, so good two-ways (with all of their positive attributes) with a couple of good subs (with their flexibility in placement and adjustment) provide very good bang for the buck. If you were seated in my room with your eyes closed, I think you would have a tough time pointing to the subs’ locations – the bass comes from where you expect it to.
Nyal Mellor
It is difficult to optimally integrate a subwoofer with a pair of stereo speakers without high resolution acoustic measurements. There is simply not enough information in a piece of music to be able to do this effectively IMO. Maybe some golden ears can do it but not me!
The correct procedure should be to as follows:
1) measure the stereo speakers (both playing together) without the sub using a 1/3rd octave smoothing
2) analyze the slope of the rolloff, remembering that the one octave is a doubling of frequency
3) set the crossover on the sub to the slope and frequency that the mains are rolling off at. Typically you’d use the -3dB point as the crossover frequency but it does depend on what slope crossover you are using
4) measure the stereo speakers and sub together, preferably using a real time analyzer
5) adjust phase and polarity so that the frequency response at the crossover frequency is as flat as possible
6) coarsely set level by looking at the RTA and broadly matching the level of the sub and mains. You will need to do this by eye since there will be peaks and dips in the response due to room modes and speaker boundary interference
7) now you can fine tune level by listening to music. This is the only time IMO when you need to use music. Ensure you play a number of different styles of music. Finding the right level shouldn’t take too long
Subwoofer crossover frequency and placement considerations:
- the crossover frequency should be below 50Hz and preferably lower. Whilst THX and others maintain that we are not sensitive to the direction of frequencies below 80Hz I disagree (and so do other acousticians)
- one sub is good, two is better. If you listen to acoustically recorded (not close miked studio productions) then there is significant difference in the information between the left and right channels which adds to the sense of spaciousness and envelopment
- if you place the sub against a wall you do not have to deal with speaker boundary interference effects, plus you get free SPL capability (a good thing)
Equalization:
- there is NO downside to equalization if it is done properly. Unfortunately it is often misapplied. Assuming you do not try to equalize a phase interference related boost or dip then EQ flat out works especially in dealing with peaks in the frequency and ringing in the time domain associated with modal resonances.
I have written about a lot of these things on my blog (linked below)
Nyal
Nyal Mellor
http://blog.acousticfrontiers.com
Mike48
It’s been my experience, too, that subs are a necessity for the last couple of octaves, because of the positioning issues others have raised. The mains I use have good output into the low 20s, but when they are out in the room for good imaging, the lows are not so good. When the speakers are pushed towards the walls, the bass is better but the imaging suffers.Those of us with Tact gear find it useful here. It measures the main and sub responses and provides an electronic crossover with correct levels and timing. It can also smooth out remaining room issues. I still find that some fine-tuning by ear is helpful.