Originally Posted by Decadent_Spectre
My opinion is based on personal experience when trying out various drivers in sealed and ported alignments keeping all things equal such as frequency response,room and listening position. I have also altered the sealed box size to alter the box Q but no matter how I sliced it the 21s I was testing were sluggish compared to the 15s. I know and agree that much of the "speed" comes from the higher frequencies yet the 15s still had more control to them when covering the same frequency range as the 21s.
I am obviously not on the same level as someone like Tom so I can not say precisely why this occurs but it does.
I used to believe that size did not make a difference based on the posts here and some of the theory I read until I did my own A/B tests. Theory is good but sometimes it is best to do the tests yourself. Measurements are needed but in the end it is about the sound. Measurements are a means to an end. The end is always subjective sound.
I have used some pro 21" drivers that have good frequency response up high, everything says they should work well with a XO around 120-150Hz but in actual practice and listening the smaller driver sounded much better and "punched" harder but the 21 went louder of course. Josh tested this driver on data bass and also mentioned that it could be used as high as 400Hz but I don't agree. My thoughts are this driver should be used no higher than 80Hz or so.
Originally Posted by Decadent_Spectre
My post had nothing to do with the Wilson sub, merely presenting my thoughts that large drivers tend to be slower sounding so to speak.
My thoughts, as I posted in my follow up post, are a reflection of my own testing of various drivers. I am referring to the 18" LMS Ultra. The Ultra excels in a very specific use and this can be gleaned by looking at the data bass results. It excels at the low bass region below 30Hz in a small box coupled with room gain. At this job I don't believe there is a better driver out there but I was specifically addressing the topic of "slow sounding" drivers. I will emphasize this is my experience with drivers and of course people have different thoughts on the subject.
I would encourage others to use larger and smaller drivers that are both pro style and higher xmax car/home audio type in different cabinets in the same room/setting with the same frequency response and make their own conclusions. I found the exercise to be more informative than any of the theory discussions I have read on AVS or elsewhere. It takes some effort,time and money but for me it was a worthy investment.
My subjective results have been a bit different and I disagree with a few things...
Bass is inherently slow...The only way to change speed in the bass is by modifying the frequency or the level of the signal. That being the case when people talk of speed it is often assumed to mean that there is a sluggish response to the initial rise time of the transient or a lingering of the signal as the cone settles to rest and this is the cause. That there is some smearing and or dragging of the start and stop of the signal. There are some errors in signal tracking with every bass system including in the time domain that is no surprise, but I am dubious at how audible these timing differences are when we are speaking of a few MS difference in the bass range especially with masking content we are much more sensitive to going on at the same time, unless it is truly excessive like due to an overdriven system, or a very bad resonance somewhere in the passband.
Now to point out something else...Bass output is predictable based on swept volume. If you are comparing a 21" woofer to a single 15" and driving both in the same alignment to the same output levels with the same exact FR shape the 15" is working twice as hard because it only has half of the cone area. The 15" needs to be driven 6dB harder to keep up with the 21" which means that it has to move twice as far so it can displace the same amount of air. Since any change in the speed at which the woofer changes direction will alter the frequencies being produced it has to cover twice the total distance in the same amount of time so the 15" actually is moving faster...However that is a bad thing not a good thing, as typically twice as much driver stroke would entail higher power input, less linearity, higher distortion, more mechanical noise etc...If you add a second 15" driver things are at parity with the 21" more or less. Consider that it takes about 5 10" drivers to equal the cone area of one 21". The moral here is that yes most of the time the smaller drivers are moving faster, but it is because they are being driven much harder and they are struggling to produce the signal.
Generalizations by cone size or driver xmax or even mms simply cannot be made IMHO.The control of the motor over the cone assembly in even a weak motored sub driver completely dominates the moving mass and suspension stiffness. A much heavier load for example is the air mass seen by the cone during operartion. A larger SD cone requires a more powerful motor to produce a qts similar to a smaller driver size however it also requires more smaller drivers to make up the sensitivity and output headroom of one larger driver. Let's make a very simple number comprising the information of the drivers motor strength and the area of the cone and call it the "control factor". A CF of 0.185 for a typical 21" driver requires a BL^2/RE of approximately 310. For the reduced area of an 18" it drops to about 224. For a 15" it is now 152 or just about half for approximately half of the cone area as expected. Only 89 for a 12" driver, 61 for a 10" , 42 for an 8" etc. Now that is a static number without a whole lot of context or meaning. Consider that two 15" drivers may have the same BL^2/RE indicating that the motors are equally powerful, but if one only maintains 80% of peak strength over a range of 12mm and the other maintains it over a range of 36mm clearly one is actually far more powerful of a device.
I completely disagree with your subjective comments on the LMS ultra...That has a VERY powerful motor, incredibly low distortion, linearity, well controlled inductance and prodigious headroom, it is also fairly efficient and sensitive in the bass range. It is one of the cleanest most precise bass drivers I have personally encountered from 10-150Hz. That is about as pure as a big powerful subwoofer is going to get IMO. I have listened to almost every alignment imagineable with so many different bass drivers I can't remember them all. I also liked the 21LW1400 and heard nothing slow or sluggish about it until overdriven. YMMV.
Tom's quote explains why there can be some energy storage or delay issues and note that he is making a point that these can be largely affected by filter effects not to mention room acoustics, alignment, etc...only one factor is the driver itself. The driver inductance can create a filter effect which will cause issue however if you consider that this typically occurs most significantly above subwoofer crossover and that in order to meet the same acoustic roll off as a less inductive design will require a less aggressive electronic filter at the end of the day... Inductance also has effects on sensitivity, efficiency and distortion.
I am highly doubtful that anyone would be able to reliably differentiate between 2 different bass drivers running in the same alignment under blind conditions as long as the test is setup correctly. The primary contributers to differences in subjective quality are IMHO due to either: Frequency response differences (Including well outside the filter points), radically different alignments, room acoustics, different placements, sensitivity or level differences, one system being less capable and encountering: Compression, elevated distortion, mechanical noise, cabinet noise, port noise, etc, before the other system and then there is how equal the integration with the rest of the mid and high frequency speaker system is done. There are so many factors to consider. Ideally you would have the systems listened to blindly by multiple people with subjective scoring cards and comments, random order, setup outdoors to remove the room equation, with identical placement, identical equipment other than the drivers, identical alignments (sealed for simplicity) and enclosures as much as possible, FR's within 1dB from at least 10Hz to up past 300Hz, level matched within 1dB, both systems running the same material and both completely within their capabilities let's say a good 12-15dB below any headroom limits. At one time there was some discussion about a GTG to try something like this but it never developed. I would certainly love to see the results of something like this regardless of which way they turned out.
Clearly the raw response of various drivers/systems is vastly different and will sound that way. I'm currently of the opinion that the gap can be narrowed to the point as to be virtually indistinguishable from each other by modifying their performance to match a predetermined response goal or each other, as long as used within both their limits. Anyway this is all my opinion just as you have yours FWIW. There are a lot of people in both camps.Edited by Ricci - 7/26/13 at 9:48am