2. speakers
  3. 131276-20253

Why is good, deep bass so difficult? - Myths and their Busters

This is a theme that goes round and round and round on Audiogon. While looking for good sources, I found a consultancy (Acoustic Frontiers) offering a book and links:

http://www.acousticfrontiers.com/guide-to-bass-optimization/?utm_source=CTA

Interestingly: AF is in Fairfax, CA, home to Fritz Speakers. I really have to go visit Fairfax!

And a link to two great articles over at sound and vision:

https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1
https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-2

Every audiophile who is dissatisfied with the bass in their room should read these free resources.

Let me state unequivocally, deep bass is difficult for the average consumer. Most audiophiles are better off with bass limited speakers, or satellite/subwoofer systems. The former limits the danger you can get into. The latter has the most chance of success IF PROPERLY IMPLEMENTED.

The idea that large drivers/subs are slow is a complete and utter myth. Same for bass reflex. The issue is not the speed of the drivers. The issue is usually that the deeper a speaker goes the more it excites room modes, which the audiophile is then loathe to address.

Anyway, please read away. I look forward to reading comments.
erik_squires
enginedr1960
173 posts
 
My system for the three years was using stereo subs and a DSPeaker Antimode 2.0 to do the room correction . I was happy with my bass response until I heard a distributed bass setup at a listening session at another audio files home .Back to the drawing board . I added in two more subs . Installed hi pass caps in my amps used my DSPeakers crossover and stereo sub correction function and good old listening to adjust the levels and now have the best most even bass response in my listening room to date .  Duke is right in this case more subs is less boom in the room .            
erik_squires OP
16,299 posts
 
That a 12/15" woofer is "slow" is a myth, I’m sorry, I’ve proven it over and over again and much smarter physicists than I have explained it. The real issue is that they produce too much deep bass, which integrates poorly in a room without attention. Give me bass traps, EQ and a pair of 15-18" woofers and I’ll scare you right out of the room they are so fast.

As I recall, the large woofers have to move fractions of the small woofer, and have much larger motors, so any issues of mass are more than offset by efficiency (in regards to displacement vs. Hz). Rule of thumb I learned a long time ago, and I may misremember, is that doubling the drivers is the equivalent of using a single driver 2" larger.

So for instance, 2x 8" = 1 x 10" driver. 2 x 10" = 1 x 12" and so forth.

Point is, there is just no substitute for raw surface area if you want deep and low distortion bass. As I noted at the first posting that started this thread, I can really see why this myth is so attractive.

Now, about movement, yeah, you have something, not only the baffle, but the entire speaker can move due to the woofer forces. Cheap fix: Add weights to the top of a speaker. Like 20 lbs at a time. :)

Best,

E
bdp24's avatar
bdp24
9,873 posts
 

To state "a 10" woofer will not keep up with a 6" midrange. Too much mass." is to oversimplify the situation. For one thing, different 10" woofers and 6" midrange drivers have differing amounts of mass; there are some 10" woofers with less moving mass than some 6" midrange drivers. But more importantly, the moving mass of any given driver is only one factor determining it’s "speed"---the size of the driver’s motor (magnet) is a huge factor. A driver with higher moving mass and a bigger motor can outperform a driver with lower moving mass but a smaller motor. By the way, the perceived "speed" of a driver is more a matter of how fast it stops moving when the signal does, and returns to "rest", than it is of how fast it starts moving. The cone of a dynamic driver not stopping when it should is called overshoot. As Newton’s Laws of Motion state, "A body in motion tends to stay in motion"---my own over-simplification!

Likewise, the statement "They must use very stiff suspensions to bring them back to neutral position after every excursion" is not universally true. The stiffness of a suspension is only one factor in the design of any driver, one needing to be balanced against other factors. Some very high performance woofers have stiff suspensions, some don’t. Acoustic Suspension designs (sealed enclosures) require suspensions with far less stiff suspensions than do Bass Reflex, for instance.

Woofers ARE often placed in MDF enclosures, but they don’t have to be, and sometimes aren’t. Baltic Birch plywood is a popular material used by some makers of high-performance subs. That plywood is far stiffer than MDF, it’s resulting resonance at a higher frequency than that of MDF, optimally far above the x/o frequency of the subwoofer.

"Massive objects resonate at frequencies that are hard, very hard to deal with". Sorry, also not necessarily the case. Internal bracing very easily and effectively deals with subwoofer enclosure-wall resonances, the braces pushing those resonances above any frequency the sub will be called upon to reproduce, reducing their audibility to below perceptible levels.

audiokinesis
2,749 posts
 

Soundrealaudio wrote:  "[Woofers] must use very stiff suspensions to bring them back to neutral position after each excursion."

The suspension system is not what brings the woofer's cone back to the neutral position.  IT IS THE AMP!!  As long as the amp is sending signal to the woofer, ITS MOTION IS ALWAYS BEING POWERED BY THE AMP!!  It never has to rely on the suspension system alone.  In more technical terms, Qts is almost always dominated by Qes; Qms typically makes only a minor contribution to Qts. 

Duke

shadorne's avatar
Ag insider logo xs@2x
shadorne
7,477 posts
 
+1 Audiokinesis and Erik

15" and larger woofers are key to good bass. You can’t beat the advantage of a large surface area except with multiple woofers. Multiple woofers are harder to drive so not a good choice. Basically....

One 15" woofer is equivalent to
Two 12" woofers
Three 9" woofers
Six 6" woofers

The amp controls the woofer and the air suspension suppresses the resonance of the woofer if properly designed. A woofer designed to work without a box may have a stiffer suspension but these are an exception rather than the norm.
More to discover