SME

I don't know how big your events are, but I imagine you are running with quite a bit of headroom there? I mean, those Danleys get pretty loud, and you say they match well with the 6 Skrams in your usage? I hope some day I get to meet you, to see/hear your setup, and maybe even get to try out my "alien technology" in your signal chain.

What is your measurement apparatus like? Is the woofer measured down-firing or side-firing? And is it mounted on a well-anchored, large open baffle? Or is it free air? These things might make a significant difference, which may be more pronounced with some drivers than others. I've only ever measured my drivers the "wrong way"--- facing up on a table top, and my BL measurements almost always come in a bit below spec. Except once, when I tipped and carefully held a driver in a horizontal orientation for an impedance sweep so I could compare. I did read a higher BL that way, but not as high as spec. I suspect a properly anchored measurement jig would close the rest of the gap. Either way, my final product(s) have tended to perform closer to manufacturer's specs, so I just accept that my measurement methods tend to low-ball BL.

I wonder if "Klippel Verified" 18 mm Xmax includes Le linearity? I didn't see any mention of shorting rings. I wonder what HF extension looks like.

Thanks for the compliment and for the clarification. That looks like an amazing setup!

That's a major understatement with those numbers. I'd imagine your system gets exercised a bit more with movie content? Just for clarification, are both sets of numbers measured in "slow" mode? Or "fast" mode? Or are they peaks? Is it the same for both? Your words "I'll run" along with "and hit" make me curious. I've found 79 dBA to be about right for a "reference level" for most music, and from there, C-weighted levels vary quite a bit depending on how much bass the system and the program have. The program alone can be a huge variable. I can easily go much higher while staying clean and comfortable, but not for very long if I want to avoid hearing threshold shifts. And I do this with a fraction of the raw output capability that you have. So yeah, you've got headroom.

I'll just add that subwoofer responses are mostly minimum phase (MP). What this is implies is that the magnitude frequency response (FR) essentially *determines*, the phase and group delay response. They are mathematically interchangeable. If you have a MP system and you have perfectly flat FR, then the group delay (GD) will be perfect *by definition*. Real subs always have at least a low-end roll-off somewhere, and you will usually see group delay rise and peak in the area of the roll-off transition. The most notable exceptions to "mostly minimum phase", where subs alone are concerned, is when you have multiple radiators (like a driver and its vent) that are physically far apart. Other potential causes are design / build quality problems like resonating panels, badly designed vent systems, etc. Now, once you cross over (XO) to speakers, the resulting response is likely not MP anymore, at least for frequencies in the XO region, because of the physical separation involved as well as some excess GD from the summing in the XO itself. Likewise, the room itself has a substantial effect on the measured responses, and the contributions may or may not be MP, depending on the configuration, frequencies considered, measurement location chosen, etc. Note that in general, in-room FR from a sub varies *a lot* vs. location as a consequence of the acoustics. With all that said, what makes bass sound "fast" or "tight" is mostly a question of *neutrality* across the low frequency spectrum, and that depends at least as much on the room as the sub. If the sound has audible resonance at some mid-bass or sub frequency, then it will tend to overhang or "boom" there. Small listening rooms in particular often have strong standing wave resonances that can contribute a lot of slop and boom to the sound. These resonances can quelled or eliminated with skillful application of EQ (which is typically MP, by the way), but results vary a lot depending on the particular approach. The best sounding systems are almost always tuned by hand beyond some point. You can also try using an auto EQ product like Dirac, Trinnov, Audyssey, etc. I won't endorse or recommend any of these, but they are popular and offer rudimentary hand-tuning functionality. I'm working on my own auto EQ technology that I believe to be capable of achieving outstanding low frequency neutrality in a variety of listening rooms, but it's not ready for public release yet. Sorry I can't offer more specific tips, but bass quality in small listening rooms is fundamentally tricky, and the particular sub choice is probably not as important as other factors. The main thing with choosing subs is ensuring you have enough headroom for the SPL you want for the frequency range you want, and ensuring the FR (outdoors) is reasonably clean to a high enough frequency, something like 1/2-to-1 octave above where you intend to cross it over. If you are looking at 24" and 30" subs, enough headroom is not likely to be a problem unless you want it *really really* loud. Less compression and lower distortion at medium output levels are also a plus. Don't ignore or skimp on the speakers either. Bass doesn't stop at 100 Hz, and bass up to 200 Hz and beyond can be very tactile if the sound is neutral enough to perceive it. Too many systems with big subs are woefully inadequate in the crucial upper bass region because the are too small to keep up with the subs. This is all the more important for a "tight" sound.

How did the testing go?

I see. Does he work with impedance data and measurements for the particular drivers? That's necessary to get a high quality result, and then said crossover won't deliver equivalent results with different drivers. I have no idea, sorry. See my last post: "The problem with the CH201 apart from the steep drop above 10 kHz is the horn termination being too short, which messes up frequency response between 3-6 kHz." I personally wouldn't choose it for any of my designs, but I may have different priorities than you.

Peaks at 30 and 60 Hz are harmonically related, which means they likely potentiate each other perceptually. And I wouldn't be surprised if those movie scenes happened to have peakiness at those same frequencies. I suspect this is a trick used on some live sound stages---EQ boost at the kick drum fundamental and a few of its harmonics, tweaking the relative levels by ear as needed---to get a very powerful slam effect, albeit at the cost of lost clarity of content elsewhere in the spectrum. This may be the "easy" way to get slam, but the result is very much conditioned upon the content, which is easy to control in a live setup. The "hard" way, which delivers excellent (and might I add *detailed*) tactile sensation and slam for a variety of content, is to target total neutrality. I don't believe this is possible to achieve in a "normal" listening room using conventional methods including near-field listening and treatments. Those things can certainly help, but even tiny residual issues can profoundly alter perceived response, including tactile aspects. This is the primary reason it's taking me so long to debut my tech. My own listening room is not stable enough to give consistent sound from day-to-day, and much of my time has been spent figuring out precisely which variable acoustic features in my room are most responsible for changes. This is much harder than it sounds because of how erratic perception behaves under these circumstances, and that's also something I've had to discover and learn about as I go. Ultimately this whole experience has profoundly altered my understanding of how auditory perception works. All these seemingly non-intuitive things make way more sense under an alternate paradigm, one which I hope will be able to offer a rational explanation for a lot of other confusing and mysterious things about audio. We'll see.

Good to see you back on the forum! See my above post. I would have agreed with all of this like three years ago. Now I'm a heretic. I believe this kind of analysis is seriously flawed. Equal Loudness Contour data is interesting, and I think it describes real trends in apparent loudness vs. frequency. However, it is a big mistake to generalize about complex music signals from data obtained using pure tone sine waves. I'd argue this is *especially important* when trying to reason about audibility thresholds. Pure tone sine waves are very unusual in nature, and our brain's reaction to them may not be a reliable indicator of how it reacts to complex signals. For example, I believe most people hear to 20 kHz and beyond, but not sine waves. The same is likely true at the bottom of the range. If auditory perception is an inferential process as I argue, then the simultaneous presentation of associated harmonics (or sub harmonics) increases the listener's ability to accurately hear at the extremes. That's because those associated harmonics are almost always present to a degree or other, so it makes the information about frequency extremes more "trustworthy". It's a kind of redundancy of information that increases confidence. On the flip-side, we're highly dependent upon harmonic structure to make sense of anything that we hear, so it's very hard to pin down the perceptual consequences of different kinds of distortion. I wish I could remember who it was, but I saw a lecture from (IIRC) an old Bell Labs perceptual coding research engineer who would play two audio samples at his seminars, one with like "10% THD" and one with like "0.1% THD". The latter one sounded far worse than the former being that he cherry picked the examples to illustrate his point. The one thing I *know* about distortion is that real life content comes loaded with it and "how that distortion sounds" on a playback system is highly dependent on how neutral the playback system's linear response is. Ironically, the harshness that listeners often associate with "distortion" (not an unreasonable association, given that harshness does audibly increase if the amount of added distortion increases) is likely not the fault of the distortion per se but of the linear (i.e. "non-distorting") aspects of the playback system which make a mess of the harmonic structure. I hope to be able to demonstrate this for interested audiences some day soon. A key seems to be in the low frequencies because the lows are the foundation of the harmonic structure, to which everything else is perceptually compared. The lows are also the primary source for distortion harmonics because that's where most of the energy is. So if the lows are out of whack, as they almost always are in small listening rooms, then the mids and highs will be out of whack too. I'd bet audiophile listeners often blame the "mids" and "highs" for many sins committed that are actually committed in the bass. I've naively done it.

No, but not because of the different impedances. The biggest issue is that the high frequency section is a lot more efficient than the low frequency section and needs attenuation to play at the right level. Another issue is that you really need a high low pass filter for the mid or else it will make a mess of your upper mid response. And you probably want to cross closer to 1500 Hz. More generally to get good sound quality you really need a crossover that's custom designed for the combination of drivers, which for your case is actually 3 different drivers. In your first post, you said you'd designed custom crossovers, so I figured you had some experience with crossover design. Your later responses indicate that the subject is quite new to you. I'm not sure how interested or inclined you are to learn about crossover design. It won't be easy unless you have a fair amount of skill with math and electric circuits as well as some basic acoustics knowledge. If not, then you'll want to plan on investing a lot of time learning. You'll also need to invest in a measurement system and learn how to use it. Crossovers are even tougher for passive 3-way systems like you're planning and any situation in which the drivers are far off in level. If you go this route, you'll have a much easier time if you have active DSP available so that you can experiment with different configurations without having to buy and swap out parts, but this means buying more amps and possible an external DSP unit if your amps don't have DSP functionality built-in. Perhaps a better idea is to look for an existing design to build. I'm sorry I can't offer much in the way of recommendation, especially given your limited budget and the fact that you've already committed to woofers. I think you'll want to look at some other forums, like diyaudio.com (more music oriented) or the DIY section on avsforum.com (more home theater oriented). Maybe you can find a design that incorporates the woofers you bought. If not, you might look at 2-way designs and consider doing an active crossover to the woofers. Alas, this also means buying more amps and possibly an external DSP. A third option is to not worry about sound quality and just build something, trying to learn as much as you can along the way. The design you suggested (assuming the crossovers adequately protect the drivers) should certainly make soun, and quite a lot of it. It probably won't sound good in the upper mids or treble. A speaker with a single GRS planar radiator may sound a bit better but not great and probably won't play as loud either. It might sound better than the Ciare CH201 you're looking at. The problem with the CH201 apart from the steep drop above 10 kHz is the horn termination being too short, which messes up frequency response between 3-6 kHz. Good luck, whatever you decide to do.

I've always regarded MDF to be heavier than BB plywood, so I decided to try looking it up: https://www.inchcalculator com/how-much-does-plywood-weigh/ Different products will vary a bit, but the chart there suggests BB is only about 70% as heavy as MDF. I do agree that BB plywood is stronger and more durable than MDF. There are other pros and cons. MDF is more messy and toxic to work with (dust) but also a but more forgiving. MDF has more adhesives which may improve its damping properties. Many speaker makers argue that the damping properties of MDF make it superior to BB despite the lower stiffness-to-mass ratio. My thought is that MDF is OK for things that don't get moved/transported a lot and where weight is not important. For big subs that get moved around a lot, MDF is not a good idea. If BB plywood is exceedingly expensive in AU/NZ perhaps look for another high quality hardwood plywood product. As I noted above, BB tends to have thinner plies than other types. Another benefit of BB plywood over other stuff is that it tends to be void free. (Tends to---alas the last stock I bought still has a few small gaps )

I think you need to clarify, to us as well as maybe yourself, what your design priorities are here. Do you care about sound quality at all? Or are you trying to go as loud as possible as cheap as possible? Or are you willing to give up some output for better sound quality? Or save up more money for better components? You also haven't said anything about the intended application except "monitors". Usually accuracy and sound quality are prized in monitor design, and often the monitors are used at pretty short distances and so don't necessarily need a lot of output. How close will you be sitting? What are the room dimensions? How loud do you intend to listen? I think they may have a couple 6" coaxial designs, some might be 4 ohm and/or under $200. You can look around at PE or whatever. But I have to ask, why the interest in 6" now? You do realize you won't get nearly as much output from a 6" as from a 10"? And lower cost drivers will typically have smaller magnets which usually means less output as well. I think it's only adequate if you don't care about sound quality. The peaks are caused by cone break-up which involves an non-pistonic resonant motion of the cone, which also causes the directional dispersion of sound to change abruptly near those frequencies. Put another way, those peaks look quite different depending on what angle you take measurements from. You can suppress the peaks with a notch filter, but you cannot fix the dispersion abnormality which will occur on top of the usual dispersion problems of having a large driver handling high frequencies. The driver also may behave chaotically around those resonances, particularly the higher frequency ones, which could cause unpredictable interaction with your notches. Realize that break-up is a problem that affects all drivers at higher frequencies, but smaller drivers can go higher. This along with the overall narrowing of high frequency dispersion from large radiating areas is why tweeters are almost always small. The best, and often expensive high frequency drivers use an exceptionally stiff and light material like beryllium to push the break-up frequency as high as possible. Hence, any kind of "full-range" or "mid" driver will usually give poor treble quality. It's just physics really. Also, have you designed a crossover before? Three separate notch filters in addition to the rest of the filtering will make for a fairly complicated crossover and possibly a fair amount of expense for those parts. Even a simple crossover can be tricky to get the best sound from. That's a little better than stacking them on the front, and is probably better than either the 4 x 4" configuration or a single 5". Still, it's own specs indicate it tops out at 8 kHz, which isn't going to sound so good on top of the other issues. I'd bet a lot of people who buy those use a super tweeter and accept an imperfect crossover as one can't really cross to that thing cleanly at so high a frequency. What appears to be its most attractive feature is that it's open backed, and so a single unit can be mounted in a thin panel to make a dipole. If you intend to mount one or two onto a cabinet you'll likely need to give them their own airspace separate from the woofers, and it's nt clear how such a mounting will affect their performance.

Stiffness is most important, and Baltic Birch plywood tends to be stiffer than most other varieties, not just because birch is a hardwood but because the boards are assembled from a greater number of thinner plies compared to most plywoods. Higher mass also helps with blocking sound transmission, more for high than low frequencies, but it also lowers the fundamental resonant frequency of the panels at which disproportionately more sound is able to pass through. Hence, most speaker and sub construction tends to favor higher stiffness and lower mass.

Welcome @RCAguy ! Frequency response specs for a sub, even if done "honestly", often don't tell you much about its real capabilities. A DSP (including the one built-in to most powered subs) can re-shape the frequency response, and a lot of commercial subs rely on DSP bass boost to achieve their specs. Of course EQ can't compensate for the physical limitations of the driver and available amp power, but in practice it is often very beneficial to design a sub whose innate response starts rolling off much higher than its intended bandwidth and then compensate for this as needed using DSP/EQ. Since you're new here, let me recommend you check out the main site at https://data-bass.com/ where you'll find measurements of various subs taken to their limits at frequencies across the spectrum. Not only is DSP bass boost very common in commercial integrated designs but it's also becoming very popular among DIY sub builders as often the better drivers have natural roll-off that can be easily compensated for. What really matters for bass performance is high displacement and sufficient amp power. And doing it "cleanly". Distortion is an extremely complex subject, one that can't be understood by simply considering THD% at different frequencies. The relative distribution and structure of harmonics is also important as is the particular content and its characteristics. There's no simple answer to how much THD is acceptable, and I don't think there ever will be because the notion represents a misunderstanding of how perception works. In my opinion, *linear* response of the installed system is the most important attribute for sound quality. For low frequencies in small rooms, this is a major problem with no easy solution as yet. Strategic acoustic treatments can help but are only a partial remedy. Linear response directly impacts the structure of both naturally occurring harmonics and harmonics produced by distortion (often on purpose during production---to improve sound quality). Objectionable linear response flaws likely introduce irregularities in the presentation of harmonic structure, which interferes with the brains means of isolating sounds from one another in the acoustic scene. This causes listener confusion, hearing of spurious auditory content (i.e. "hearing treble" or "hearing bass" that's disconnected from the rest of the sound), and harsh or uncomfortable sensations felt in the ears or even other body parts. If music at 75 dB "hurts your ears", it's probably your brain telling you it's hearing something unnatural that it doesn't know how to process. The "harsh treble" you think you're hearing might actually be caused by problems in the bass. Anyway, this this stuff interests me a lot, and I'm working on new methods to improve linear response for low frequencies (and high frequencies too). I have a DSP technique that sounds *very promising*; it seems capable of almost entirely neutralizing the acoustic signature of the listening room in addition to the speakers themselves. It is in this kind of situation that I think low THD for subs in particular may be important. Linear DSP can be used to alter the linear response to whatever I like, but this processing cannot touch any distortion produced the amp or subs. For a speaker, that's not too big of a deal, especially if the driver response is fairly clean without EQ. Most of the distortion produced is likely to be quite regular, so even if it becomes audible it's likely to sound natural and pleasing. However, for bass and especially the sub range, the room interactions make the distortion much more irregular and therefore much more likely to sound objectionable, and there's no way to fix this with linear processing. I have no idea how important this is in practice. My system uses subs with very low distortion as far as subs go and has enormous headroom. It might be a bigger problem for small speakers pushing their bass limits all the time. Or pro speakers under similar circumstances. Servo control might be a key solution. Please forgive my ramblings.

Hmm, I can't seem to edit my post above. Anyway, I see that that coax is probably out of your price range. Another caveat is that the crossover design between mid and top might be tricky. Still, you'll be hard-pressed to find a better performing combo for 400 Hz+ in a 10" circular format. Another option would to be to install a couple small mids (like those 4") together with a small WG or even a dome tweeter, crossed at like 1500 Hz. Though obviously you're going to have to give up some mid output for that. I'm wondering though, why do you think you need 12 mm Xmax from a mid driver that only goes to 400 Hz? You do realize that you need 4X displacement to get the same SPL every time you drop an octave (until the PRs start to do their thing)? If your 8" mid is doing 12 mm at 400 Hz with any realistic music, then those woofers will be turned into confetti by the content at 50 Hz. So I guess a lot depends on what your budget allows and how much you want to compromise quality for output. If you just want something LOUD, then your original design will get the job done, but if you care about upper-mid / high quality, you options are pretty limited from here.

Why two? Are you trying to get super loud treble? Realize that FR measurements for drivers are usually done on a very large baffle. A driver with good looking measurements on a large baffle likely won't look or sound as good on a smaller baffle and no waveguide, especially with three other adjacent drivers to interfere with it. Panels radiating through the same rough area won't be much better in this regard. How committed are you to your design? Can you make it taller and/or go 3-way? It's very hard to find a good driver to cover 400 Hz+ unless you're going to use a coaxial of some sort (effectively making the speaker 3-way). If you're already committed to the cabinet dimensions and woofer choice, this might be a good option: https://www.parts-express.com/B-C-10CXN64-8-10-Professional-Neodymium-Coaxial-Speaker-80-x-80-Degree-8-Ohm-294-5962

That depends on the impedance at that frequencies of interest, which depends on the cabinet design. Also, long-term is a very loaded word. How long is long-term One second? One minute? One hour? One full day? Those are all likely to have different answers, and the longer durations will also depend on the cabinet ventilation and ambient air characteristics. To echo @peniku8, pure voltage limiting is not ideal. The driver can probably take 3-4X as much or more voltage (meaning at least 9-16X power!) in the very short term than it can take in the very long-term. A "fool-proof" voltage limit setting will completely waste your amp's potential. Anything higher and you can certainly fry the driver if you try hard or screw up bad. So ideally, you want a limiter that's based on actual power output over time and that responds relatively slowly so that it doesn't get in the way with normal music. I have no idea what limiter options you have available to you, but it's also helpful to consider what kind of content you're going to play, including the crest factor, which is the ratio (in dB) between peak and average signals. There's a huge difference between signal that peaks hot for kick drum every 60 bpm and EDM bass drones that might blast the sub at its port tune frequency with square-wave like signals for an entire track.

I'm not using any Hypex amps. I'm just reporting on others' experiences. If the inputs can be modified to accommodate the Motu 16A and related products, that's good news for those willing to go through the trouble. I'm not aware of other amps that had this problem with the 16A thus far.

Perhaps those are Aussie dollars which are 1 : 0.76 USD (currently). Even still! @h3idrun: Tthat driver should do pretty well. Dayton also has a new 21" with similar motor and price, albeit 8 ohm vs. 4 ohm impedance. I don't see it listed at your store, but you might contact them and ask if they are planning to stock it soon: https://www.parts-express.com/Dayton-Audio-PSS555-8-21-Pro-Subwoofer-with-4.5-Voice-Coil-8-Ohm-295-050

What @Ricci said, but also how is the oak floor constructed? Is it suspended over another floor or above the slab? Or is it right on the slab? The difference in that regard isn't huge, but it's there. Much more important is the room geometry (including adjoining spaces that are normally open to the main space) and specific placements within the room.

Or a floor resonance. And for that matter, I believe that audibility thresholds for content at the frequency extremes within typical audio program can be much lower than audibility thresholds for pure sine waves. Pure sine waves are actually extremely unnatural sounds and may be one of the worst possible "test signals" for assessing human hearing. Real sounds almost always have lots of THD, and audio programs almost always have additional THD---because it sounds better (in moderation). The tricky thing is that the audibility of ULF is probably very dependent on the quality of the rest of the bass response. And as we know, rooms small enough for ULF reproduction to be practical tend to have major problems higher up in the spectrum. In hindsight, @Bossobass Dave may have found a decent formula for good ULF: small footprint floor-to-ceiling stacks of subs placed in at least two corners and Linkwitz Transform via very broad stroke EQ. I'm told his room had an impressive 5 Hz floor resonance, but another factor may have been the quality of the response of his systems above the ULF. I have no idea where the actual thresholds may be for systems with "ideal" responses. My frequency response optimization is probably a bit too coarse in frequency resolution below 20 Hz. I have plans to enhance the DSP capability so I can process with high res all the way down to single digits. That improvement could be transformative. I do have a very mild floor resonance at 5.5 Hz, and curiously I don't always notice it, even with the same content! It also depends on what the rest of the frequency response is doing. I'm finding the same is true for other "felt" bass. So audio can facilitate or mask tactile sensation and visa-versa. Amazing!

Room dimensions and rough floor plan would also be helpful information.

Thanks! Hopefully the "burn-in" phenomenon is normal and is something that's usually done at the factory.

I can't recall where, but I have read that many brand new electronic components (capacitors among some things) do have a break-in process, but it is very rapid, essentially done after the component has been charged for a few seconds. Distortion of 0.1% isn't exactly high---*it* might be slightly audible in an amp depending on the particular nature of it---but if the problem vanishes after pushing it briefly, it doesn't seem like anything of much practical concern. However, this does suggest that Hypex is not testing the finished components at their specifications before shipping them. I'm rather surprised, as this doesn't seem like a difficult or expensive thing to do. Unrelated to this, I know that Hypex amps will not accept a signal from the Motu 16A audio interface (or others in the same family) that I use together with a PC for many channels DSP. Something about how the 16A analog outputs are driven just doesn't jive with the Hypex amps. I don't really understand it, but it was reported on in detail here among other places. Lastly, IIRC someone I know managed to get a Hypex amp (one with builtin DSP, I believe) to go unstable (i.e. noise at full blast) by feeding it high-level ultra-low frequency signals. I believe he first implemented the ULF boost via the built-in DSP and later used an external DSP, and both caused the unit to go bananas. I'll see if he wants to come onto the forum and share his experience, so you can hear about it first hand.