SME

Each SP2-12000 *channel* uses two amps in a bridged configuration, so they can't be bridged again. The bridging capability of any amp depends on its design characteristics which should be specified by the manufacturer. Some amps perform better or more reliably *with* bridging. Others may be damaged if you try to do it.

Well, I think most of those subjective terms actually depend strongly on *linear* aspects of response, which is to say those that are relevant when the sub is playing well below its max output. This implies that impulse response *is* very important. However, the problem with *visually* comparing impulse responses is that the differences that are perceptually most important not readily visible in IR plots. IR "speed"/ringing and FR extension/shape are essentially two different ways of analyzing the same characteristics of a *linear* system. This is precisely true for minimum phase (MP) systems, and most subs (measured anechoically) and other physical producers of sound have MP behavior. Audio systems with multiple crossovers are not necessarily MP, but they may be close enough for all intents and purposes. I'm also not aware of evidence that slight excess group delay is especially audible, as long as there is no substantial pre-ringing. So when talking about MP or near MP response, both IR and FR magnitude are just different ways of analyzing at the same fundamental characteristics. A flat FR implies a "perfect" IR, and vice versa. A sealed sub with a 2nd order roll-off in the FR will exhibit an elongation of the IR with possible ringing around the transition frequency (depending on how high the Q is). A vented sub with a 4th order roll-off (plus whatever electronic HPF is applied) will typically exhibit more elongation and/or ringing in the IR than a sealed sub with 2nd order roll-off. Now one can ask, is it the "frequency response shape" or the "time domain ringing" that's audible? The answer is that they are different realizations of the same phenomenon, and perceptually speaking this phenomenon can cause both emphasis of continuous notes around the cut-off frequency and ringing and/or overhang in that region on transients. And again, things get a lot more interesting and potentially hard to predict once you throw in room resonances and whatever spectral shaping was applied to the content. What's clear to me is that certain roll-off shapes have a lot more or less audible impact than others, and I haven't really worked out the details. Any overhang or ringing I hear in music is rarely offensive to me. Movies are another story, and I think the problem there is that soundtracks tend to have an extreme ramp in balance towards the bottom which dramatically amplifies the resonance at the cut-off frequency of the filter they use. This happens in part because cinemas and dub-stages get calibrated with pitiful bass levels. Of course if you use a sub that rolls off at or above the cut-off frequency in the track, you'll probably get even more exaggeration of the sub's roll-off characteristic. Part of the trick with music may be that impulse sounds in real life aren't really pure. Real life kick drums have many natural resonances, and so the emphasis, overhang, or ringing from an HPF on, e.g. a kick drum in a track is likely to just sound like it's a natural part of the kick drum sound. Often this is heavily stylized, and so becomes an essential part of the sound rather than a "flaw". Note also that almost all digital content is distorted on purpose to add higher harmonics / "spectral replicas" of the original lower frequency information. This tends to "tighten" and "brighten" the sound overall, increasing loudness and improving perceived quality. Such processing is likely to be downstream of any HPF, so the HPF resonance on the kick drum also gets "replicated" at higher harmonic frequencies, which makes it sound more like it's part of the sound of the drum when it's played back.

In the design you posted here, you said the you would use ports that were 28" long including the flared ends. For a 32" deep sub, that puts the port end 3.25" from the back wall. I think that'll probably work just fine.

I personally would suggest thicker foam --- 2" or 4" for more out of the way places. I do concur about avoiding foam in the path between the driver and the vent. I honestly don't know how much output will be lost going from 1" to 2 or 4", but I don't think it'll be much if it's not placed too close to the vent (where air may be moving a lot more) or in the path between the driver and vent. In my view, the primary reason to install foam or other acoustic absorption is not to alter the frequency response in the operating range but rather to remove unwanted sound inside the cabinet that's above the sub's operating range, to keep it from leaking out through the vent or interfering with the driver. This unwanted sound is caused by distortion and noise produced by the driver. The distortion can drive standing waves and other resonances inside the enclosure, which can amplify them and cause unevenness in the sound, particularly when the sub is being pushed harder. A thicker 2" foam will absorb much better below 1000 Hz than a 1" thick foam. The standing wave resonances inside that cabinet will start at around 250 Hz, and even 2" thick material doesn't do much there, but it's a big upgrade from 1".

Not exactly. If you cascade two BW2 filters (if your DSP allows you to), you get an LR4 filter, but this is not the same thing as a BW4 filter. The LR4 and BW4 both have the same 24 dB/octave slope below the transition regions, but the transition regions are shaped quite different and have different phase characteristics also.

I would say that if it sounds better, then stick with it. But don't expect this result to always generalize between different rooms/placements or with different sets of speakers.

I'm trying to address both the physical and subjective aspects, but perhaps my posts have not been clear enough. In theory, the wider bandwidth system will be faster. In practice, the results depend a lot on details like what the speaker+ sub system is doing, what the room is doing, and how perception resolves all of that. Without being more specific, I can only conclude that this blind comparison could go either way. I'm assuming that headroom within the nominal passband is unlimited in order to simplify the discussion. Obviously *in practice* a vented sub will probably reproduce the signal better than a sealed sub if things are being pushed. That's a whole other discussion and an important one, but I don't think it the one the OP is focused on. It's not what I focus on, given my 4x21" system which is operating well below its limits 99.99% of the time. So sticking to just the linear / low-level operation stuff, it's not necessarily the physical ringing per se that's making the vented sub sound distinct from the sealed sub. The physical ringing is (assuming small physical distance between driver and vent) one and the same with the physical impulse/frequency response of the sub. Assuming no major playback chain EQ, that response interacts with the room to yield a composite response, and that composite response is perceived somewhat consistently throughout the room, despite dramatic variation in literal measured FR/IR. There are *a lot* of details here that affect what is ultimately perceived. Though the differences in response shape between vented and sealed are likely to still play a big part in this, just as the spectral balance of a soundtrack has a big affect on how it sounds when played back. I'm not sure what you mean by gently, but I'll assume you mean using a filter that has minimal perceptual consequence around the transition area. That being the case and on an ideal system, I expect the main thing that would change is apparent *weight*, which is actually not related to apparent speed. However when you take into account speaker/sub resonances (including at the bandwidth limit of the combination) and room-induced resonances, then a broadly increased emphasis of LFs is likely to amplify the audibility of those problems, which can definitely increase apparent thickness, overhang, and apparent slowness of the perceived sound. Try not to get confused by the fact that lower frequencies oscillate more slowly. The "speed" is not determined by how fast the lowest frequencies oscillate. The "speed" is determined by the composite sound. If you start with a unit impulse, you have a sound with equal balance across the spectrum. If you apply a high pass filter in order to reduce the low-frequency part of the spectrum, then you actually elongate the impulse substantially, and this manifests as ringing around the cut frequency. The lower you cut, the less the amplitude of the ringing is relative to the initial impulse. To pick a real life example. If you hear a large helicopter overhead with blades that have a strong 8 Hz fundamental, is the bass you are hearing and feeling "slow"? Not really, unless it's really far away so that all you can hear is the rumble. In reality the sound is more of a chopping sound, rich in higher harmonics that make it quite fast even though it repeats at 8 Hz. I can play e.g. "Ready: Player One" with and without Bass EQ. The movie is steeply filtered at 20 Hz, and without Bass EQ all the sounds have a notable overhang, especially the big hits. If I add Bass EQ, the overhang is gone and the sound becomes more realistic. The air has a kind of palatability, as though you're really present. It's apparent throughout the track because the movie uses SH synth very well. The big hits don't ring, they just pummel you. If you've heard a real-life car crash, you know what I mean. Likewise with big fireworks. There's an *oomph* that the sound has, in addition to the *slam* factor. It still happens *fast*, but has a ton of weight too.

I would say that higher Q resonances tend to be more *obvious* even though the lower Q resonances may be more *audible*. The subtle distinction here is important. It is also my experience that both low Q and high Q flaws can cause annoyance. The high Q flaws are much easier to identify though. I agree that there's almost never a good reason to use a narrow-band boost when producing a soundtrack. However, any high-pass or shelf filter which abruptly cuts the bass below some frequency tends to have a similar effect. And these are actually quite common with real-life content. Most music has significant filtering at 30 or 40 Hz, and tracks with hotter bass often ring a fair bit down there. Most of the time though, it sounds OK for the actual track, like it was done that way on purpose. That is, the overhang often compliments the rhythm. OTOH there are movies that really ramp up the bass and then cut off steeply, which causes an annoying and repetitive one-note rumble to follow every sound. These are unfortunately quite common.

Great progress, and I agree the work quality looks nice from the pictures. You got this done a lot faster than I did.

Awesome question! This is not correct. The fastest sounding bass is the *widest bandwidth bass*. Technically, bass gets faster with more extension in either direction. The audible overhang is caused by ringing from one or more interacting resonances. In an outdoor setting, the major resonance will be for the sub itself at the bottom of its bandwidth. The sound and audibility of this resonance will depend on it's shape and bandwidth and how this resonance interacts with the content itself. It's complicated, and I'm not confident that I can give a straight answer as to what bandwidth/Qtc is optimal or whatever. It's something I plan to study in the future. Throw the sub into a small room, and now you shaping effects from the room plus room resonances that may also interact with everything else. So here things get even more complicated. If you run a typical "Room EQ" systems to try to "fix" the room, you're adding even more variables, and not necessarily improving the characteristics that matter that most. When I speak of resonance interaction, I'm talking about the consequences for perception, which can be very complicated and non-linear. A common misconception is that narrow bandwidth (or high Q) resonances are more audible because they ring for longer. It is true that high Q resonance ring longer; however, perception seems to be much more sensitive to medium-wide (or medium-low Q) resonances. The lowish Q resonances can dramatically amplify or suppress the audibility of coincident high Q resonances as well, and are probably of primary importance to perceived transient response. Sorry I can't say much more than this, despite having worked for years on developing my own methods for optimizing bass response. I am very satisfied with the results I'm getting, but I'm a long way away from being able to state a set of "rules" for what matters to perception. I am currently running a system with 5 Hz extension and a very generous "house curve". As optimized, the room contributions are nearly inaudible, especially in the seating area. It's as good or better than any outdoor system I've heard, and it's rather stunning that such is possible inside a small listening room. Extra extension in the soundtrack makes it even better. Most movie soundtracks are processed throughout with subharmonic synthesizers which can restore ULF bass content that had been stripped by filters earlier in the recording chain. Sadly, most such movies get filtered again after the SH synth, but if the downstream filter is mild or can be reversed with BEQ, it makes a *big* difference to the bass for me. Even if it's filtered at say 20 Hz instead of 40 Hz, a SH synth augmented kick drum just slams so much better. I hear and feel the SH synth contribution literally everywhere, even in normal dialog (!), and it improves realism if it's not overdone.

I think you meant "cut in the opposite direction where it pulls into the work" here. It's much easier to control the router when the tendency is for it to be pushed towards you rather than pulled away from you. While it's OK and often a good idea to do shallower cuts, you don't want to move the router to slowly. The spinning router bit rubs against the cut edge of the workpiece and generates a lot of heat. This can overheat the bit, causing premature dulling and breakage, and/or burn the workpiece. Moving the router slowly allows more heat to build up, and furthermore, while the bit is actually cutting, the material that's removed absorbs a lot of heat. The higher the RPM, the higher the feed-rate should be. Though you may need to make even shallower passes to avoid stressing the bit. Contrary to @peniku8 suggestion, I recommend dropping the RPM a bit from the highest speed (if your router allows this) so you don't have to rush the cuts as much. At a medium RPM, a feed rate of 2-3 inches per second is likely in the ballpark you want. Try to avoid making "dust" and make small "chips" instead. When cutting a 15" diameter circle, that means that making the full circle around should take ~20 seconds to do. No worry about the braces looking ugly. Mine often do too. Edit: Also note the sound and feel the of router. Both should be relatively smooth. A lot of vibration or screeching means something is likely wrong. (I'm not sure if you get much screech when cutting MDF anyway, but it's something to pay attention for.)

Thanks for helping to clarify things. Though thinking about it now, when cutting circles I think you still want to cutter to enter "from behind" on the outside edge where there's slightly more material to be removed. Another important detail when cutting circles is that the inside piece that's to be removed must be separately anchored, and directly clamping it is not usually possible. Instead before making the cut, it should be anchored to a larger underlying sacrificial piece using a couple finishing nails, and the sacrificial piece should be well clamped. As an advanced technique, there are very exceptional cases to the rule of avoiding climb routing: specifically when exiting at the edges of BB plywood where climb cut of *just the last tiny bit* avoids unsightly blow-out. Doing this safely requires appropriate technique to ensure control of the router is maintained. CNC is a totally different thing because the router and/or table are mechanically controlled, so climb cutting is usually preferred for CNC to avoid blow-out.

Hey! You need a jig to cut circles if you don't have one. Parts Express sells one, or you might be able to buy one from a woodwork store near you too. Definitely learn as much as you can before you start trying to route. It's important to clamp the work tight. Also always route in the direction that makes the spinning cutter bite the wood from behind. When the spinning blade hits the wood, it deflects the router in the opposite direction, and it's always safer and more stable to be pushing against the deflection rather than trying to "ease it forward while keeping it from flying out of your hands". Keep us posted.

My counter would be that the bandwidth is too large and too smooth to be a TH. The EQ might help with smoothing response, but what about overall bandwidth?

Occasionally when watching movies with heavy ULF during the day time (often for critical evaluation), I notice motion in the corner of my eye coming from the flexing of the large, nearly floor-to-ceiling living room windows on my left wall. Yeah, the Hi Def Digest graph looks like it's probably "wrong", at least in terms of level normalization. Just comparing the peak levels between the two at 30 Hz, they are too far apart for lack of dialnorm compensation to be the only fault.

Is that a sealed alignment or something else? It sure does drop like a rock below 20 Hz.

The short answer is that different windows were likely used for each piece before averaging. There is no universal PvA. Different windows types and sizes change the emphasis of certain aspects of response.

The design looks OK. The ports definitely exit close to the cabinet wall, but I think that will be OK as long as you don't go any closer. The wall will help lower the tune a bit more than the flared pipe alone would. However if that's your cut-sheet list, you are missing something very important: bracing. Bracing helps stiffen up the cabinet walls so that they don't flex as much which causes some bass to be lost and causes the enclosure to resonate at somewhat higher frequencies, coloring the sound. The bracing design is a little tricky being that you have to clear the driver as well as the vents while trying to avoid letting any panels have more than a 6-8" span unbraced. You might also want to build in some extra support for the vents, near the rear, being that they are quite long and presumably only attached at the front baffle. (You might also want to put foam or cloth between the tube and brace to avoid buzzing sounds if they vibrate against one another.) Ensuring no more than 6-8" of panel is unbraced is a good rough target, but often some compromise is necessary. Either way, some bracing is much better than none. You will also want to add a light amount pf absorptive material (polyfill / pillow stuffing is popular as are denim scraps) around the inside panels to try to reduce resonances in the air cavity, which can also transmit through the panels. After accounting for bracing, the cabinet volume will probably be a tad smaller, maybe 6.5 cuft (?) depending on design. That should still tune at around 20 Hz.

Sorry I can't help there, but ... I love the playa pyro pachyderm! I did a couple burns, last time in '06. That year it felt like it was just a huge event, especially on Friday and Saturday nights when there were so many people everywhere who were so frelled up that I could have convinced myself I was in a raver zombie apocalypse. Also, I've been to places like Washington DC National Mall, NYC, and (gasp) Boston, and no other place has a greater proportion and variety of law enforcement agents than Burning Man. The event is a kind of a psychedelic fun house in the middle of an alien, post-apocalyptic police state planet. I understand the event is now roughly *twice as big* as it was then. It's amazing to me that it still functions, which is kind of a marvel of its own. Have fun with that car! Is there going to be a bar on top?

I had the problem of spinning the bit too fast with *hand-held* routing in my speaker builds. I broke a couple 6 mm bits that way before I learned about RPMs and feed rates from the CNC forums. So I dropped my speed setting to "2" out of "6" (about 10k RPM I think) and sped up my manual feed rate. That helped a lot, but I still needed to make very shallow passes (like 3 mm or less) to avoid problems. That's what I did with my subs. Unfortunately the compression bit I used caused nasty tear-out because the tip of the bit is designed to be on the *other side* of the work-piece where it pushes chips up and towards the piece instead of away from it. So I think for my next project I will use a down-cut bit with very shallow passes and hopefully be able to keep it sharp long enough to use on more than one project. BB plywood just seems to be the worst enemy of cutters. Maybe the material I'm getting is just particularly nasty? It builds some damn good speakers and subs though.

I'd say it's 95% likely the cinema.

There's likely a lot more than just rumble in there. :) That mid-bass looks impressive too.

Hi @maxmercy, I'd like to request that you post the BEQs you did. You can post them in the private forum instead if you want. My wife has requested that we screen these films over her Xmas break, and I figure this would be a great time to evaluate your candidate BEQs. I can give honest feedback including sharing any tweaks I make myself.

I'm sure that rings like crazy! And it's got only "3 Stars" dynamics to boot. I haven't seen that movie yet though. I think a lot of people have floor or wall resonances around 25 Hz, and so a track like that is likely to shake things like crazy, especially on vented subs with a similar tune. I've been mostly slacking a bit on movie watching lately, but I did watch "MI4:Ghost Protocol" tonight (for the first time) and thought the bass and overall sound design was very solid. I wish more movies had bass like that.

My SP2-12000 is still on 120V, on the same 20A circuit as all the rest of my gear including: a 55" LCD TV, 2 Emotiva XPA-5 gen2s, a Motu 16A, a Denon 3313CI AVR, two (fairly low power) PCs, a BD player or PS3, and a couple routers. Loud movie bass passages with ULF lasting several seconds can be tickling the clip lights, but I've still never tripped the breaker or even heard any sign of distortion suggesting voltage sag. The mains run from the panel is only about 15 feet, which might make a difference. Also, my subs are crazy efficient at 30 Hz and up, so the amp doesn't have to pull much current unless there's a lot of ULF.