Why do you guys pursue a flat frequency response when you buy a subwoofer?

Deep_333 wrote:  "Why do you guys pursue a flat response when you buy a subwoofer?... The minute you put that flat sub in your room and take some measurements, it is anything but flat (it's a rollercoaster with all kinds of peaks/nulls etc, EQ to the rescue)..." 

Deep, I come at this situation from the other side of the fence; I make subwoofers. 

At the risk of overgeneralizing, I see the room as typically doing two things to the response of a subwoofer: 

First, the usually room imparts a gently rising trend to the subwoofer's output as we go down in frequency.  This is because as we go lower and lower in frequency, the room's surfaces become closer and closer to the sub in terms of wavelengths.  So we get progressively more and more approximately in-phase reinforcement from the room surfaces as we go down in frequency.  This trend has been called "room gain" (which may or may not be technically correct), and 3 dB per octave below about 80 Hz is an approximation which has been suggested by a couple of different researchers (Martin Colloms and a woofer designer whose name slips my mind at the moment)... the exact figure of course depending on the room's acoustics as well as the subwoofer and listener locations within the room. 

The second thing that happens is, room interaction imposes that roller-coaster peak-and-dip pattern you mentioned.  The specifics of how the subwoofer's output is altered by the room once again depend on the room's acoustics, as well as the subwoofer and listener locations within the room. 

Imo the first issue can be addressed by designing the subwoofer to have a native frequency response which slopes gently downwards by the approximate inverse of "typical" room gain, or 3 about dB per octave.  I'm not saying this is the only way of addressing this issue, but imo it results in a reasonably good starting point. 

The second issue (rollercoaster in-room response) presents an interesting challenge.  Opinions vary on how to address it. 

I think "flat frequency response" is a reasonable target for a subwoofer system, as long as we're talking about the ACTUAL IN-ROOM response.  I do not think a "flat" frequency response which ignores the room's effects is the ideal starting point. 

Duke

Deep_333 wrote, " Duke, Can you name the popular opinions among sub manufacturers on how they think it should be addressed? Of course, more subs a.k.a an array of 4, 8 or 16 is great for business. But, are there other opinions out there?"

Setting the controls on the subwoofer amp correctly matters a lot. If you’re doing it by ear, first set the level, then the frequency, then the phase. Then cycle back through again a few times. This order is progressing from "makes the most difference" to "makes the least difference."

(Setting the level correctly is particularly time-consuming. Equal loudness curves indicate that a 2 dB difference at 40 Hz is subjectively comparable to a 4 dB difference at 1 kHz, so precision in setting the level really is called for. This also explains why smoothing the bass response pays unexpectedly large subjective dividends, as the ear is arguably doubly sensitive to peaks in the bass region.)

Careful positioning of the subwoofer and/or listening location is beneficial. One particularly effective technique is the "subwoofer crawl". Put your subwoofer in the listening chair and crawl around the room until you find the location where the bass sounds the best. Place your subwoofer there.

Bass trapping or other methods of low-frequency damping improves the bass smoothness everywhere in the room by reducing the magnitude of peaks and dips.

EQ on its own is most suited to smoothing the bass in a small listening area. This is because that roller-coaster pattern you mentioned typically changes significantly for different listening locations around the room. Of course bass trapping and EQ can be combined with other techniques.

A distributed multi-sub system, or distributed bass array, smooths the bass throughout the room by reducing the magnitude of peaks and dips.

A planar bass array consists of a rectangular array of four subwoofers on or in the front wall, with a similar array on or in the rear wall. The symmetrical rectangular configuration minimizes reflections in the horizontal and vertical directions. The subs in the rear wall are delayed such that they cancel the output of the front subs when it arrives at the rear wall, so there is theoretically no reflection in the front-to-back direction. I have no actual experience with this approach.

"Of course, more subs a.k.a an array of 4, 8 or 16 is great for business."

I’d probably make a lot more money selling a single big sub for the same price, as the labor cost to build four small subs is roughly four times the labor cost to build one big sub. I went with four small subs (credit to Earl Geddes) after spending many years trying to develop a single subwoofer "fast enough" to keep up with Maggies and Quads. The solution was to focus on room interaction, because (imo) that’s the biggest problem.

" As far as the manufacturers coming up with a flat response (Rythmiks, HSUs, SVS, etc), Is it just a "statement" that they are competent enough to come up with a flat response? "

I am sure those designers and others have worked just as hard at solving the problems they believe matter most as I have. And they are probably better at hitting their target(s) than I am at hitting mine: You mentioned 4, 8, or 16 subs, and my 4-sub system would be outperformed by 8 or 16 sub systems.

Regarding the "forest of subwoofers" issue, often at audio shows nobody even notices the four small subs sprinkled around the room until they are pointed out. In many cases as the number of subs goes up the size of each sub can correspondingly go down, and in some rooms it is practical to place small subs atop bookcases or on shelves.

Tomic601 wrote: "Duke you really should look at the wave photo I emailed you long ago"

I vaguely recall it, but couldn’t find it when I looked again just now.

Duke

" Duke - I will resend you the hi-rez photo at your AK business email." 

Got it - THANK YOU!  Very interesting pattern of waves on the lake!! 

How were the patterns moving? 

Duke

Millercarbon to tomic601: " So you choose liar. "

Miller, just for the record, I’m not comfortable with what you did there.

In a now-deleted post you called for tomic to do such-and-such or else he was (in your words) a liar, and when he didn’t, you now say he chooses to be a liar. Without overly dissecting it, I’ll just say that seems pretty aggressive to me.

Miller, is there a different way you could have replied to tomic601’s earlier post, one that extended the benefit of the doubt and would therefore likely have resulted in the clearing up any misperceptions?

Duke

Deep_333 wrote: " Now, when subs are being integrated with these speakers, the sub appears to be an afterthought. An end user like myself who’s not a speaker designer or professional audio engineer, is somehow being asked by sub manufacturers to make it all work together somehow."

Given that there is an enormous variation in what kind of main speakers a subwoofer may be paired with, not to mention the enormous variation in room acoustic situations, a one-size-fits-all, plug-n-play solution is not possible. Even if the subwoofer(s) and mains have been designed as a package, low-frequency room acoustics still varies enough that some adjustments may be required during set-up.

You might consider working with the dealer or manufacturer who sold your main speakers, or maybe buy your subs through a dealer who is willing to do the setup.

Deep_333 wrote: "They release a flat curve to make themselves look good and sell a product."

Imo whether or not a flat curve earns a person’s business is their choice. I assume that subwoofer manufacturers who went to the trouble to achieve a flat curve sincerely believe in its merit.

"At the end, its a customer like myself who has to go to enormous lengths and months of tinkering and treatment to make it all work right."

To me, this statement implies that there may be room for improvement over whatever it was you tried.

"I may have very few variables to work with actually... Let’s see, a sub volume control and a crossover if my amp doesn’t have bass management, that’s it. To my knowledge, only Rythmik even offers a phase control that’s more than just a 0-180 flip switch. The rest is...crawl around, throw a bass trap, etc and make it work somehow."

Some subwoofer systems offer more degrees of freedom than others. For the record, Rythmik is not the only one who offers a phase control which is more than just a 0-180 flip switch. (Also just for the record, while I mentioned the crawl and bass traps in a previous post, neither are tools which I rely on.)

"Is my perception right or wrong gentlemen?"

It sounds to me like you are disappointed in your experience with subwoofers, and hold subwoofer manufacturers accountable. Is that correct? If not, can you clarify?

Duke

Deep_333 wrote: "Many hardcore audiophiles i know stick with 2 channel music systems, a.k.a, their high end turntables, DACs, integrated amps/monoblocks, etc with no bass management. These guys try subs and abandon them because they can’t get it to integrate right."

Very interesting. To the best of my knowledge I have yet to have a subwoofer system customer fail to get satisfactory integration with his mains. In most cases they run their mains fullrange and then blend the subs in. Therefore I must give credit to the off-the-shelf Dayton Audio amplifier I use, and to whoever designed it:

https://www.parts-express.com/dayton-audio-sa1000-subwoofer-amplifier-rack-mountable--300-811

Deep: "I sure would not want to add another adc/dac into the chain with a subpar DAC on something like miniDSP for bass management (when i have a Denafrips DAC in my 2 channel setup). Guys i know have waaaay more expensive speakers, DACs, monoblocks, etc on their 2 channel music setups than i do. They are probably not gonna do that either. "

You bring up an excellent point: How do we roll off the bottom end of the mains without any undesirable side effects? Not sure there is a totally transparent solution.

Therefore when I design main speakers with subwoofers in mind, my mains do not need a protective highpass filter unless extremely high SPLs are desired. Their inherent bottom-end rolloffs are intended to blend well with the variable 4th order lowpass filter of that Dayton amp.

Deep: "It may be a loaded market chunk which is out there i.e., if a manufacturer chooses to tap into it and cater to their systems better (monopoly for sure). More DOFs or.... whatever the R&D/solution may be to better integrate them..."

I hadn’t really thought about it in terms of degrees of freedom until this thread. I think there may well be a correlation between (useful) degrees of freedom and good integration with the mains. Lacking the financial resources to develop my own subwoofer amplifier, I count myself lucky Dayton makes an amp with a parametric EQ and a fully adjustable phase control.  My individual passive subs have some adjustability as well.

Duke