I'm with you.
I've found subwoofers and full range speakers to sound better in most rooms, when the [anechoic] response is not extended flat to 20 Hz, but starts rolling off at least an octave higher, and drops at 6 dB/octave or so. The cool thing about vented boxes is that by manipulating box size and tuning frequency, you can get almost any slope you want (above Fb). Sealed boxes are stuck at roughly 10-14 dB/octave depending on Qtc, although that's usually a pretty good match to room gain, also.
Of course, sometimes it's cool to hear what that flat anechoic response to 20 Hz or lower is like, but I find it can be boomy in many average sized rooms. You can get more bass quantity by turning up the volume on your subwoofer output, which to me is much less offensive than a big peak in the frequency response.
Aaron Gilbert
I've found subwoofers and full range speakers to sound better in most rooms, when the [anechoic] response is not extended flat to 20 Hz, but starts rolling off at least an octave higher, and drops at 6 dB/octave or so. The cool thing about vented boxes is that by manipulating box size and tuning frequency, you can get almost any slope you want (above Fb). Sealed boxes are stuck at roughly 10-14 dB/octave depending on Qtc, although that's usually a pretty good match to room gain, also.
Of course, sometimes it's cool to hear what that flat anechoic response to 20 Hz or lower is like, but I find it can be boomy in many average sized rooms. You can get more bass quantity by turning up the volume on your subwoofer output, which to me is much less offensive than a big peak in the frequency response.
Aaron Gilbert
- Commercial products are trying to show "good numbers" which typically means shooting for an F3 of 20hz.
- Not all rooms are created equal; commercial subs would have a hard time trying to design for a "standard" room gain.
- DiY subs make sense to include tailoring for a particular space... only if you know you will never move the sub.
- Many people actually like a "house curve" or rise in response above flat in the lower octave. A flatish anechoic sub and average room gain may well suit more people than a flat in-room sub.
- If the sub is flat anechoically, you can add a fairly simple filter to tailor the response exactly to your room after you have taken a measure of the in-room response. If the sub starts non-flat and is placed into a non-flat room, and the result is still non-flat (because your tailored design isn't perfect), deriving the necessary filter to adjust might be non-trivial (or, perhaps, you just use a BFD with lots of filters).
Personally, I think it makes sense to design the sub flat and have a 6dB or 12dB/oct filter you can activate if desired. It also makes sense to design a sub specifically to be flat in a particular room. Both approaches are valid and have their ups and downs.
- Not all rooms are created equal; commercial subs would have a hard time trying to design for a "standard" room gain.
- DiY subs make sense to include tailoring for a particular space... only if you know you will never move the sub.
- Many people actually like a "house curve" or rise in response above flat in the lower octave. A flatish anechoic sub and average room gain may well suit more people than a flat in-room sub.
- If the sub is flat anechoically, you can add a fairly simple filter to tailor the response exactly to your room after you have taken a measure of the in-room response. If the sub starts non-flat and is placed into a non-flat room, and the result is still non-flat (because your tailored design isn't perfect), deriving the necessary filter to adjust might be non-trivial (or, perhaps, you just use a BFD with lots of filters).
Personally, I think it makes sense to design the sub flat and have a 6dB or 12dB/oct filter you can activate if desired. It also makes sense to design a sub specifically to be flat in a particular room. Both approaches are valid and have their ups and downs.
Here's my understanding.
bluebeard,
To my knowledge, servo sensing and control is done to reduce distortion, and is not inherently related to the frequency response curve. A servo subwoofer could have any kind of response curve you want, just like a non-servo subwoofer. In fact, since the accelerometer/sensor is on the woofer itself, not at your listening position (hey who's going to come up with that idea first?), it doesn't know what affect your room has on the response curve or output levels. All the sensor cares about is measuring the woofer's output so that it can be compared to the input signal, in order for the control circuitry to make adjustments that keep them as close as possible. Wouldn't that be wild though... a wire going from your subwoofer to your listening position so the output at the listening position can be servo controlled. Better yet, go wireless and put the sensor on your head. 'Hey Joe, when did you get a hearing aid'? 'Oh, that's just the accelerometer for my subwoofer'.
Aaron Gilbert
bluebeard,
To my knowledge, servo sensing and control is done to reduce distortion, and is not inherently related to the frequency response curve. A servo subwoofer could have any kind of response curve you want, just like a non-servo subwoofer. In fact, since the accelerometer/sensor is on the woofer itself, not at your listening position (hey who's going to come up with that idea first?), it doesn't know what affect your room has on the response curve or output levels. All the sensor cares about is measuring the woofer's output so that it can be compared to the input signal, in order for the control circuitry to make adjustments that keep them as close as possible. Wouldn't that be wild though... a wire going from your subwoofer to your listening position so the output at the listening position can be servo controlled. Better yet, go wireless and put the sensor on your head. 'Hey Joe, when did you get a hearing aid'? 'Oh, that's just the accelerometer for my subwoofer'.
Aaron Gilbert
Well Aaron, the problem with that lies in the time delay between the sub playing the sound and it arriving at your ear. You can stick an accelerometer on your head, but it will only show how your head is accelerating. You'd need a microphone and it would do absolutely nothing to prevent distortion. You could achieve flat frequency response, but the distortion feedback must be realtime and not delayed by the few milliseconds it takes for sound to travel to your chair. The servo works to ensure that the imput matches the output. On comercial subs (such as the velodyneHGSII subs) the accelerometer's feedback signal is measured thousands of times a second, then compared with the original signal to give the discrepency whether it be that the cone has moved too far in or out or not enough in or out, the correction circuitry will adjust the driving signal to either incrase or decrease current flow to get the sub from where it is to where it's supposed to be. These servos can be used to give flat response, but it becomes much more difficult to implement in a vented box. For this reason sealed enclosures are typically used in servo feedback subs.
bluebeard said:
The BFD is useful when you cannot work out a good subwoofer placement. Parametric EQ is not a cure-all. If they are so powerful, they can turn a Radio shack speaker into a Wilson Puppy. Parametric EQ works best in removing the room modes. They don't change the Q value of the system response. Some people like IB because of their low Q response. If low Q is what one wants, then buy a BFD and turn any high Q sub into a low Q one. It does not work quite that way. In another words, the subtly between low Q and high Q is beyond the resolution of parametric EQ. I have customers going extra length to design bass traps to deal with room modes. I also have customers using BFDs. Both get good results. If a sub has a good sound, it will show even without a BFD at 90% of the time.
Do we really need 14hz extension? It depends on the music materials. Some recordings place the mics at the middle of a music hall. The reverberance is already overwhelming. In this case, one does not need 14hz extension. Also in this case, there is clearly a reference for the frequency response. So the goal is reproduce what one hears in music hall at our rooms. So a flat in room response is good. However, recordings done in this way lack definition. So the majority recordings use a combination of close mics and far mics. In this case, the mathematical relation between what the mic hears relative to what you hear in normal seating position in the music hall is not known. So a flat in-room response may not be best. My personal experience is that with lower bass extension, I can hear the soundstage becomes wider, deeper, and taller, because it reinforces the reverberance information. And finally, the flexible extension setting in our subs is complement to parametric EQ. That is, there are areas that a simple extension filter does best and other areas that parametric EQ does best.
Brian Ding
Rythmik Audio
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