Subwoofer myth or misunderstanding?

[mikesiskav]

I see quite a few people posting all the time that there is no such thing as fast or tight bass. They say that if a subwoofer sounds slow, then it's just because of the room set up. While I certainly believe that room set up, frequency response, and harmonic distortion are important factors in subwoofer performance, I also believe there is more to it than just that. For example, how fast can the movement of the woofer start and stop? What about ported vs sealed? What are your thoughts on this subject?

[curtis]

I think when people say "fast" they just don't know the proper terms for what they are hearing.

Excellent impulse response, excellent transient response, and fast decay...all make up a "fast" subwoofer.

[mikesiskav]

I totally agree Curtis. Unfortunately, it seems that most people these days have over simplified subwoofer sound quality. They think maximum output = sound quality. I like output capability too, but it's only part of equation.

[davef]

I see quite a few people posting all the time that there is no such thing as fast or tight bass. They say that if a subwoofer sounds slow, then it's just because of the room set up. While I certainly believe that room set up, frequency response, and harmonic distortion are important factors in subwoofer performance, I also believe there is more to it than just that. For example, how fast can the movement of the woofer start and stop? What about ported vs sealed? What are your thoughts on this subject?


I think when people say "fast" they just don't know the proper terms for what they are hearing.

Excellent impulse response, excellent transient response, and fast decay...all make up a "fast" subwoofer.


I totally agree Curtis. Unfortunately, it seems that most people these days have over simplified subwoofer sound quality. They think maximum output = sound quality. I like output capability too, but it's only part of equation.

In my professional opinion, when it comes to subwoofer sound quality - as long as frequency response is reasonable, transient accuracy is the most important factor. This is the characteristic that people unknowingly refer to when they use the term "fast". It's not the speed of the woofer itself, any woofer producing 20Hz moves at the exact same speed - it is how quickly that woofer stops and starts, and there is tremendous variation in this.

These days, with Audyssey and various other room EQ processing, frequency response and phase is easily corrected for (to some degree) - while transient accuracy of the subwoofer can not be corrected.

[sludgeogre]

In my professional opinion, when it comes to subwoofer sound quality - as long as frequency response is reasonable, transient accuracy is the most important factor. This is the characteristic that people unknowingly refer to when they use the term "fast". It's not the speed of the woofer itself, any woofer producing 20Hz moves at the exact same speed - it is how quickly that woofer stops and starts, and there is tremendous variation in this.

These days, with Audyssey and various other room EQ processing, frequency response and phase is easily corrected for (to some degree) - while transient accuracy of the subwoofer can not be corrected.

Totally agreed. This is where the LCD-2 headphone gets things right as well. There are a lot of headphones that can get down to 20 Hz and below, but people see the 5 Hz rating on the LCD-2 and go "OH WOW SUCH BASS!" Then they buy it and they think Audeze lied because they aren't basshead headphones. Well, duh, it just means it can produce deep bass, it doesn't mean it throws it in your face all day, only when it's actually called for by the music, and even then, it's tight and accurate, not like a dance club in your head, which is what people are thinking they are getting.

[billy p]

Different strokes for different folks I guess...purdy sure some of the folks who crave massive spl into the low teens or single digits are willing to forfeit some accuracy thou not much to reach their inevitable goals....you guys must experience first before you rule it out.... IMO.

[mikesiskav]

I don't know about anybody else but it's not my intention to say that people who want extreme output or extension don't care about quality, or that you can't have extreme output and quality. My point is that it seems quite common these days to see people who judge subwoofer performance solely on output levels and they deny the existence of other performance metrics such as bass detail and articulation. And I've definitely heard some high output systems. In fact I installed a complete JTR system with 2 Captivator subs for a client of mine. It was a very impressive system, at least for movies. Didn't really spend much time listening to music with it.

[astr0b0y]

@davef How is driver transient response measured? Is it a near field measurement of SPL vs time?

[billy p]

I don't know about anybody else but it's not my intention to say that people who want extreme output or extension don't care about quality, or that you can't have extreme output and quality. My point is that it seems quite common these days to see people who judge subwoofer performance solely on output levels and they deny the existence of other performance metrics such as bass detail and articulation. And I've definitely heard some high output systems. In fact I installed a complete JTR system with 2 Captivator subs for a client of mine. It was a very impressive system, at least for movies. Didn't really spend much time listening to music with it.

I agree folks often resort to buzz words in discreptive terms relating to subwoofers. Honestly.. I'm not immune from doing so.... on the rare occasion but I am fully aware and understand how transient response reproduction has a significant roll to play in a subs design and/or SQ.

My old dual opposed unit sound great for movies but lacked some definition found within certain musical passages used during my demo sequences, much to my chagrin. I must preface this by adding I was also comparing it to my SB13U at the time. Easy fix really by a simple upgraded to the "SE" version drivers....instant improvement...less overhang ... better suited IMO for quickened pace or tempo changes....often required with musical pieces...I suspect and likely where transient response is often lost.

Curious though to your final comment regarding the Caps.... I would suspect they'd be equally up to the task with music and movies going by their pedigree. Unless.. of course these were the massive units like Cap 4000 ULF or OS LFU designed specifically for HT SPL race purposes.

[N Boros]

I see quite a few people posting all the time that there is no such thing as fast or tight bass. They say that if a subwoofer sounds slow, then it's just because of the room set up. While I certainly believe that room set up, frequency response, and harmonic distortion are important factors in subwoofer performance, I also believe there is more to it than just that. For example, how fast can the movement of the woofer start and stop? What about ported vs sealed? What are your thoughts on this subject?

I think what Dave is saying is absolutely true that some subwoofers just have better transient response and will just sound better than most others. However, say that we take a subwoofer with exceptional transient response and just randomly place it in some room. It is possible for the bass to sound bloated and slow, just due to poor placement. Typically people only have 2 or 3 places to actually place a subwoofer in a room due to aesthetics. Are those choices necessarily going to be the best place to locate the subwoofer for even frequency response and the least amount of peaks and dips. Probably not. Then there are many in the audiophile crowd that don't like to use room eq. So it becomes impossibly difficult to get the subwoofer to "sound" accurate in your room. Fortunately, if one has a room that is nearly rectangluar and sealed it is possible to know exactly where to place multiple subwoofers to fix a lot of the issues related to the room. But, in a room that deviates from sealed and rectangular you are back to trial and error and now with multiple subwoofers.

I have spent a lot of time over the past several years learning to understand what some of the detailed measurements of subwoofers (like on audioholics.com and data-bass.com) mean in terms of the performance of the subwoofer. I can understand why people just look at raw output numbers when picking the subwoofer. Because it is difficult to learn what the other measurements are telling you. Even understanding everything about what the measurements on data-bass.com for a specific subwoofer is telling you there is still plenty that is lacking when you are listening to the subwoofer.

Talking about loudspeakers instead for a minute, a few years ago I decided to sell my Axiom M22 speakers and upgrade to the Ascend Sierra 2 speakers. The Axiom speakers were just fatiguing to my ears. After watching a blu ray movie for about 2 hours, with the volume set at -30 dB my ears would be ringing. Switching to the Sierra 2s this mostly went away to where I can listen louder and longer and not get this hardly at all. You would think that something like to this would show up in detailed measurements and be something significant and easy to spot. Maybe the off axis performance, or distortion or something was just plain bad in one of the measurements on the Axiom M22s. Unfortunately, that is not the case. The following link gives good detailed measurement for both the Axiom M22s and the Sierra 1s (I don't have distortion measurements for the Sierra 2, but I would think that they would be at least as good as that of the Seirra 1s at the same output level): http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=16&Itemid=140 I was baffled that while the Ascend speakers do measure a bit better in some areas, it isn't like the Axiom speakers are measuring wildly inaccurate, where something definitely points to why they are fatiguing to my ears and many others as well.

So I guess that I am at the point where while I will look at measurements very carefully to weed out speakers that are not accurate. For example many of the esoteric speakers measured on Stereophile accompanying the review, have terrible measurements and are quite inaccurate. I just completely disregard such speakers from my pool of speakers I might be interested in listening to. But, from there things seem to get a little tricky. While you can look as some different measurements, it doesn't always correlate to a big or audible difference in what we hear from the speaker. At least not for a layman like me and this might be true even if I had more experience because we need access to more measurements to be able to get a clearer picture of what the speaker is going to sound like.

[mikesiskav]

I agree folks often resort to buzz words in discreptive terms relating to subwoofers. Honestly.. I'm not immune from doing so.... on the rare occasion but I am fully aware and understand how transient response reproduction has a significant roll to play in a subs design and/or SQ.

My old dual opposed unit sound great for movies but lacked some definition found within certain musical passages used during my demo sequences, much to my chagrin. I must preface this by adding I was also comparing it to my SB13U at the time. Easy fix really by a simple upgraded to the "SE" version drivers....instant improvement...less overhang ... better suited IMO for quickened pace or tempo changes....often required with musical pieces...I suspect and likely where transient response is often lost.

Curious though to your final comment regarding the Caps.... I would suspect they'd be equally up to the task with music and movies going by their pedigree. Unless.. of course these were the massive units like Cap 4000 ULF or OS LFU designed specifically for HT SPL race purposes.

Hey Billy, I didn't mean to imply that the Caps were not impressive with music. What I meant was that we didn't listen to much music on the system, so I can't really give an opinion on them for music.

[davef]

@davef How is driver transient response measured? Is it a near field measurement of SPL vs time?

Microphone placement and SPL are irrelevant. To measure transient response (impulse response) - one must work or use testing gear designed to function in the time domain rather than frequency domain. A unique series of frequency impulses (maximum length sequence) is sent to the unit being tested. The microphone then picks up this sequence and a series of calculations is performed determining the deviations in the original sequence compared to the return sequence. Once the impulse response is calculated, nearly every other loudspeaker measurement can be determined from this data, including frequency response, by applying an FFT to the impulse response data.

https://en.wikipedia.org/wiki/Maximum_length_sequence

It is not something the typical hobbyist will be able to measure, which is likely why it is so rarely discussed regarding subwoofer performance. Additionally, it does take the right equipment and user knowledge to perform correctly. Besides Rythmik, I am not even sure if any of the other ID sub manufactures have access to this critical performance data, or even care about it. It is something we take very seriously (#1 priority in the design of many of our loudspeakers) and it is vital to Rythmik as well - transient accuracy is greatly enhanced by Direct Servo.

[davef]

Different strokes for different folks I guess...purdy sure some of the folks who crave massive spl into the low teens or single digits are willing to forfeit some accuracy thou not much to reach their inevitable goals....you guys must experience first before you rule it out.... IMO.

Not quite sure what you are referring to when you mentioned "rule it out". I have evaluated every type of subwoofer out there - from models designed to fill large theaters and concert halls - to those designed for ruler flat response and as good as possible transient accuracy. Like speakers, different subs for different purposes - no point in comparing apples to oranges.

[billy p]

Not quite sure what you are referring to when you mentioned "rule it out". I have evaluated every type of subwoofer out there - from models designed to fill large theaters and concert halls - to those designed for ruler flat response and as good as possible transient accuracy. Like speakers, different subs for different purposes - no point in comparing apples to oranges.

That remark was not directed at you or others members within this thread... if I dropped the "you" perhaps it would not sounded as a challenge...like you said it's about trade offs and I know unequivocally that all subs do not sound the same and fwiw....I use a different house curve for music vs. home theater for that reason....albeit with the same sub.

[astr0b0y]

Thanks Dave, really well explained. The link to maximum length sequence was perfect to get me reading more on this.
Do you design a driver with an impulse response as a target or is it a result of the rest of the design process the determines this?

[davef]

Do you design a driver with an impulse response as a target or is it a result of the rest of the design process the determines this?

There are many factors in driver design that influence its impulse response, optimize one characteristic and you end up changing other parameters. It is all a compromise.

While I won't get into any of our design secrets, one simple aspect to improve impulse response (all other things being equal) is to decrease moving mass. However, in a woofer, decreasing moving mass also increases efficiency and decreases bass extension.

I always try to achieve what I feel is the right balance of all driver characteristics to match the particular design. For example, in designing the final version of the Sierra-2 woofer, we sacrificed bass extension in order to go with a very low mass cone to improve impulse response to better match the near perfect impulse response of our Sierra-2 ribbon tweeter. We were lucky because we were able to go with a larger diameter cone in the same space which helped us get back some of the lost extension due to the higher efficiency of the larger cone. Many other optimizations to this woofer were implemented to improve impulse response - even in the crossover design, but I won't reveal this info.

It is for these reasons why I spend so much time on driver design instead of simply using off-the-shelf components. I'm not saying off-the-shelf is bad (it would certainly make things easier and less costly for us) - but this is how we do things as I am obsessed with total performance, not just good performance in one or two characteristics.

[MusicHead]

Dave, please do continue to be obsessed! We like the results :D

[theophile]

I always try to achieve what I feel is the right balance of all driver characteristics to match the particular design...but this is how we do things as I am obsessed with total performance, not just good performance in one or two characteristics.

I applaud your commitment, dedication and obsession with music reproduction, Dave! All AA owners greatly benefit from your passion and excellence to achieve accurate fidelity performance in a well made and beautiful product! :cool:

Ted