Subwoofer speed is in the room, not the box

@gdaddy1 

Dali Epicon 6   Exceptional!! 

They are rated to 32.5hz with VERY high tech woofers. You cut them @70hz?

Thanks. I love the speakers. I know some don't like the voicing (bump up at ~4 kHz), but I'm mostly a relatively low-volume listener. I have a very odd shaped room with many non-parallel walls; not bothering to post because I'm moving to Europe soon and will have a more normal-shaped room. Current room has a few modes (left sub has a deep cut at 68 Hz and a very slight boost at 130 Hz, right sub filter cuts a bunch at 55 Hz and a tiny bit at 350 Hz).  But with the subs where they are, I get "glorious bass" in and near my listening position.

I agree the Epicon's bass response is nice. But it still requires a just a little at the bottom end; to me, that little bit contributes to the soundstage. There is no way I could move the DALIs enough to fix their bass interactions with the room without destroying my soundstage. By crossing at 70 Hz I solve two issues: (1) decoupling mains placement from subs placement; and (2) ensuring that both the mains and subs are in a fairly linear portion of their response curves and away from their limits, meaning my active crossover really is pretty symmetrical around the crossover point (something @erik_squires points out as "a cardinal point" in a different response). That still leaves the DALI's "very high tech woofers" to handle 70 Hz - 2250 Hz.

Every room is different, so it is possible that, when I get to my new home, I may be in a position to place the subs more symmetrically with respect to speakers and cross them lower than 70 Hz. As Erik points out, that might allow crossing at a lower frequency. But every room is different, so I'll measure, experiment with various configurations, and listen carefully in the new location. And just in case, I am building an audio conduit to a location that allows flexibility in sub placement, and that location is part of the dedicated audio circuit to help minimize the chance of a ground loop.

@erik_squires 

This is of course a cardinal point. I would never do with a built-in DSP/filter of a sub, instead using a Xilica DSP for both the mains and subs, actively, with elaborate filter settings and finely scaled adjustments. 

Hadn't hear of Xilica before. Looks very interesting. Which model(s) do you have? 

Sure bass horn loading is a different case…. i’m flat to 20 in a regular room without resorting to cutting down every tree in the mythical forest… Enjoy the music ;-) 

@sfgak wrote:

Hadn't hear of Xilica before. Looks very interesting. Which model(s) do you have? 

The XP-3060. It's controlled wirelessly via my laptop, which makes setting filter values for every driver section on the fly from the listening position a very straight forward approach. Neat. 

@tomic601 wrote:

Sure bass horn loading is a different case…. i’m flat to 20 in a regular room without resorting to cutting down every tree in the mythical forest… Enjoy the music ;-) 

I was going to say reaching 20Hz is the easy part, but making that last audible octave and a half matter (say, down to 15-ish Hz) is no small feat. For it to really matter you need prodigious cone/air displacement area, ample power and/or high efficiency, proper flooring and overall room construction, etc. Numbers are easy; how they're real-world applied and experienced is quite another thing. 

Not saying what you've achieved with your subs setup is this, that or the other (obviously, I don't know), but all things being more or less equal (and that's the tricky part) the larger and more efficient subs setup will reproduce the lower octaves more effortlessly, relaxed and viscerally. Whether 20, 30 or more Hz at play here is at first secondary vs. how these frequencies are reproduced.

That horn sub variants need to be indeed very large just to reach 20Hz is another matter, not least with non-truncated Front Loaded Horns (I mean, for all practical intents and purposes in anything other than houses: forget it), but here I've found tapped horns to be the best option and overall compromise. For what they do at their size (20 cubic feet per cab with a 23Hz tune) with low distortion, high SPL output there's really no equal to my mind. 

@clio09 Then I will say it. John Hunter is wrong. He is interested in selling as many subwoofers as he can and not in designing the best possible subwoofer.

@tomic601 ​​@erik_squires @phusis This is not all that complicated. Most of you are right, you just need to be able to explain it better.

The speed a woofer cone travels is a sinewave function. The average speed to produce a note at a given loudness is a function of size. The smaller woofer has to travel farther to displace the amount of air required to produce the note at that volume so it has to travel faster. The speed is not an issue but "farther" certainly is. Dynamic speaker suspensions are linear only for a very short distance. At some point, depending on the suspension's design, the suspension becomes progressively stiffer until it can not move any farther without ripping it apart. Because of this non linearity distortion increases logarithmically with excursion distance. This is why larger drivers or multiples of smaller drivers have lower distortion levels. They do not have to move as far so they do not have to travel as fast. Bigger is always better, not worse!

Boominess has two causes, the subwoofer running into the midrange and a resonant, shaky enclosure. To keep the sub out of the midrange people historically lowered the crossover point. This is a problem for a number of reasons. Much of the impact or dynamic factor comes at higher frequencies in the 80 to 100 Hz range. You want the sub running certainly up to 80 Hz and I will go no lower than 100 Hz. The solution to this problem is running steeper filters, not lowering the crossover point. The problem here is analog filters are terrible at this. You have to have a digital crossover then 8th order and higher is no problem. Running that high a high pass filter for the mains is mandatory or you will have a hot mess. This is advantageous anyway from a distortion and headroom perspective. 

Making an enclosure that does not shake or resonate is a very hard problem to solve. The easiest part is using a balanced force design. You put a driver in opposite ends of the enclosure running in phase. The Newtonian forces then cancel out. Making an enclosure that does not resonate is much tougher and very expensive, more expensive than most commercial manufacturers will tolerate because they have to remain competitive. This is the reason I make my own. You can see a picture of the final versions before finishing. I plan on doing a full pictorial of their construction  so others can copy them if they are inclined. These will be high gloss black. The walls are 1 7/16" thick. Plywood was used instead of MDF because it is stiffer. The individual sections are only 4" wide. The subs sit on the floor horizontally on two spikes right up against the wall. They lean on a special pad. Because they do not vibrate at all nothing will get transferred directly to the wall. Small sealed enclosures are always best with subwoofers but you have to have a lot of power and high resolution digital EQ. Then you can make any sub run flat as a carpenters dream. 

The last problem is time alignment and this is best done with a digital crossover and room control which is really speaker control. 

With subs running up to 100 Hz and cut off at 48 dB/oct or higher, if you want more impact just turn the sub volume up a little and you can have it without affecting the midrange or treble. I run mine hot by about 6 dB which gives the music a "live" feel at less than ear shattering levels. A great subwoofer system is more felt than heard. In reality, the faster a subwoofer cone has to move the worse will be it's performance.