All Vd may not be equal. If one considers acoustic impedance matching, a larger diaphragm loafing may load a room better (more snap? less delay/overhang?) than a small one flailing to keep up at comparable measured SPL an 18" woofer moving 22mm or a 1" piston with a thirteen foot stroke? My personal subjective experience has left me with the inclination with others in this thread that this may be the case.
I've the good fortune of one of Stereo Integrity's 24" subs sounding thunder in my system and have compared it against other excellent subwoofers including a TC Sounds LMS-Ultra 5400 for several months now. Two drivers I recall you're familiar with and have had a chance to listen to a fair bit and measure if you're the same bossobass as elsewhere. While doing a room walk a while back, switching back and forth between the two (sitting side by side and, later, stacked), I noticed something peculiar: though I was playing a single tone (so no frequency response differences) and level matched with my SPL meter, the 24" was significantly more tactile. The larger driver started shaking my clothes and hair from six to eight feet away while I didn't feel the same until only two feet from the 18" LMS-U going with almost treble the excursion to match SPL.
I'm uncertain how to go about measuring the cause of that when I complete my planned system move, but it was interesting to me that the two drivers would offer such different experiences all other circumstances fairly equal excepting Sd, far as I could tell.
Near field measurement of one of my subs:
Listening position response*:
Slightly larger than average room in an old stick built Craftsman style home. Nothing special and certainly not a car, bunker nor shipping container.
🙄
*Mismatched horizontal scale as these were made for my own edification and not intended to myth bust. Sorry. Check for clearer frequencies in attachments.
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I guess Diogenes didn't notice my comment earlier:
"There are many causes for hearing bass enlargement in a room (as compared to mounting your woofer in your neighbourhood park). The term "room gain" refers only to the effect of playing bass in a SEALED volume, like inside a small, tightly sealed car.
Yes, the physics is real, but the physics will tell you that the effect of "room gain" in your living room is inconsequentlial (unless you live in a tightly sealed shipping container)."
I sure wish all that wishful-thinking about mythical "room gain" (except for small tightly sealed cars) would go away. Do the math.
Diogenes says his woofer shakes his clothes and his "hair." Because it is outside my experience (and my grasp of acoustics*) even with my Klipschorn to have sound waves actually shake the cloth on my clothes and my admittedly sparse hair, I thought Diogenes' comment was unlikely to be veridical until I realized "hair" is probably just a misspelling.
But - come to think of it - there used to be an advertizement of some cassette tape years ago showing a fellow with his hair being blown back cartoon style (by implication by strong sound carried on the manufacturer's brand of cassette tape); funny, I always assumed the photo was made with a strong fan.... but maybe they were using a woofer like Diogenes'?
Ben
*various objects (and windows) in my music room jump-for-joy when I do mic testing with REW. Sure screws up the measurements. And by the way, the dry-wall panels and wood floors also shake which is another good reason you can't expect much "room gain" at home.
"There are many causes for hearing bass enlargement in a room (as compared to mounting your woofer in your neighbourhood park). The term "room gain" refers only to the effect of playing bass in a SEALED volume, like inside a small, tightly sealed car.
Yes, the physics is real, but the physics will tell you that the effect of "room gain" in your living room is inconsequentlial (unless you live in a tightly sealed shipping container)."
I sure wish all that wishful-thinking about mythical "room gain" (except for small tightly sealed cars) would go away. Do the math.
Diogenes says his woofer shakes his clothes and his "hair." Because it is outside my experience (and my grasp of acoustics*) even with my Klipschorn to have sound waves actually shake the cloth on my clothes and my admittedly sparse hair, I thought Diogenes' comment was unlikely to be veridical until I realized "hair" is probably just a misspelling.
But - come to think of it - there used to be an advertizement of some cassette tape years ago showing a fellow with his hair being blown back cartoon style (by implication by strong sound carried on the manufacturer's brand of cassette tape); funny, I always assumed the photo was made with a strong fan.... but maybe they were using a woofer like Diogenes'?
Ben
*various objects (and windows) in my music room jump-for-joy when I do mic testing with REW. Sure screws up the measurements. And by the way, the dry-wall panels and wood floors also shake which is another good reason you can't expect much "room gain" at home.
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Many manufacturers have shown thermal compression when a high voltage is applied to a driver during an extended period of time.
Just ask your self what is the average power dissipated in the voice coil when you listen music at home. I am sure it will be very far from the lowest number you quote, 250 W.
If you detect (or think to detect) thermal compression in your system, it means that your loudspeakers are undersized towards the sound level you require from them.
May be Pano's test.
For long, I tried to achieve some statistics about domestic levels, but it was not a real success.
I neverless can tritely conclude that people liking high SPL at home usually favour high sensitivity loudspeakers for the bass (something like 96 dB SPL / 2.83 V/ 1 m and more for the medium and treble, when they are horns) as those satisfied with reasonable levels usually prefer systems with low or medium sensitivity (84-90 dB SPL / 2.83 V/ 1 m).
So the electrical power dissipated in the bass voice coils of high or low sensitivity systems may be not very different.
If you refer to motional feedback using a bridge à la Voigt, Ian Hegglun* proposed, for the current sensing resistor, to wind a copper wire coil and place it near the voice coil. So both coils share a quite similar temperature which is then somewhat compensated in the feedback process.
(* Ian Hegglun, "Speaker feedback", Electronics World, May 1996, pp 378-383).
I did, but without any facts or measurements included to support your position I mentally filed it away as "inconclusive/to read up on later" with other audio opinions. What is a myth, afterall, but an unsupported belief repeated over and over again as fact? Have you provided support for your position elsewhere? I only occasionally get a chance to catch up on going ons here and may have missed the discussion where you lay out these vague referenced other causes. Hopefully, it was less shrill and insulting than your response here as posting so undermines your position more than mine. I'll chalk that up to a rough morning than a general fault of personality. 🙂
bentoronto said:
Interesting. I'm surprised that someone quick to an argument from authority in acoustics would be ignorant of what anyone who's ever gone to a concert is familiar with and what every other reviewer in the audio rags loves to call "pants flapping bass". Granted, the more tactile aspects involving the shaking of clothing tend happen at frequencies below a Klipschorn's response (I've spent a fair bit of time listening to them in the past and know that they drop off quickly below 50Hz, 35-40Hz at best with the room providing some low end gain. Good for upper and midbass, but not down low.), but any proximity to a drum, piano or upright bass would've exposed you to the experience of feeling it in your chest, pants legs shaking and loose folds of the shirt vibrating in sync with the music.
As for hair, I did indeed write that word; hair as in my shaggy locks and beard. Are you not familiar with what the car audio crowd call a "hair trick"? Granted, most videos of hair standing on end when blasting subs are exaggerations caused by windows effectively acting as ports with the air moving in a similar fashion, but the effect persists with sealed setups. Not the best "music" and certainly an overkill system, but it shows the effect. Find a good, sealed subwoofer, feed it some nice, broad spectrum bass, turn up the levels and stick your head in the cone. You'll discover it right quick.
bentoronto said:
Then you are familiar with how easy it is to separate room rattles from gain in REW with quick, low level sweeps and waterfall plots. Hopefully, you're not being willful in your presentation of room rattles as providing a broad spectrum boost at a fairly consistent per octave slope as is expected with that "mythical" room gain. The rattles are obvious high Q peaks and dips in the graphs I've already provided including that nasty mass damping my floor provides around 8.5Hz (crank it up and I can see the floor boards moving significantly, simultaneously disturbing and awesome); increasing the signal strength or duration of the sweep only makes the peaks and troughs more pronounced, the average remains evenly boosted. Besides, something acoustically real is exciting those rattles down low, something strong enough to be measured at a high level and it isn't leprechauns and unicorns banging on the walls. 😀
My room's characteristics have become quite familiar to me: I'm well aware of the 2.4Hz resonance of the long wall, the 4.8Hz harmonic that makes the large window rattle, the 8.5Hz floor mass damping, the 16Hz short wall resonance, the 31Hz fireplace insert rattle, the 34Hz long dimension node doubling up on it, the 52Hz drywall and clock rattle on the SW wall, the 62 and 67Hz short dimension headaches that forced me to move my listening position, etc and all the rattles an old house gains after decades of use and November winds. They're just narrow spectrum noise on the significant signal of room gain.
Earlier, I found the thumb drive I had stashed my measurements on and combined the above two graphs for a direct comparison leaving the colors the same to avoid confusion.
Nearfield measurement vs. listening position, low level quick sweep to minimize excitation of rattles:
Expanded scale:
Larger versions attached.
The rattles can be seen, comparatively insignificant as they are.
The driver is in a slightly too small cabinet (bit higher Q than I'd prefer), so the steeper than expected roll-off for a sealed alignment helps keep the overall response fairly flat. Though, as is seen in the expanded scale graph, the boost is still at a greater slope meaning that were this my permanent listening room. With a lower Q sub in a smaller room, the low end would be boosted sufficiently above the rest of the bass level to perhaps elicit complaints about "boominess". Too much room gain might even cause issues enough to move someone towards an open baffle sub to minimize it. 😉
Back off this minor hijack, though, I think we may agree in a way about the topic of the thread. I mentioned a fledgling theory I've been toying with about acoustic impedance matching being a cause of tactile differences (hair and all) between small drivers and larger transducers. I've a love-hate relationship with horns and planars, for all their faults, both have that palpable presence with music that small driver speakers don't seem to possess. Why would that be? Perhaps... perhaps it's because planars offer a large surface area, obviously, and what are horns but acoustic impedance matching transformers making a smaller diaphragmed transducer interface with the air as though it has a larger diaphragm?
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If my effort at a little ribbing went overboard, I apologize.
You do get "room gain" when the room is pressurized (sealed tightly including all doors and windows and heating/cooling ducts), all 6 sides are solid (not dry-wall or wood), and starting to build as you drop below the room's fundamental resonance (which may already be below your woofer's range for reasonable size listening rooms). These conditions can be approximated in a small tightly sealed vehicle with no covert ventilation ducts. Even when all the conditions are met, the boost is modest within the practical audible range.
There is a lot of loose chat about room gain on the web (mostly confusing it with a lot of other acoustic matters and speaker placement issues), but a trustworthy treatment can be found at:
roomgain
I don't think room gain relates to any difference between multi-driver subs and single-driver subs. But other acoustic considerations are relevant. For example, you could make a section of a sphere out of multiple drivers and sit it in a corner.
Ben
You do get "room gain" when the room is pressurized (sealed tightly including all doors and windows and heating/cooling ducts), all 6 sides are solid (not dry-wall or wood), and starting to build as you drop below the room's fundamental resonance (which may already be below your woofer's range for reasonable size listening rooms). These conditions can be approximated in a small tightly sealed vehicle with no covert ventilation ducts. Even when all the conditions are met, the boost is modest within the practical audible range.
There is a lot of loose chat about room gain on the web (mostly confusing it with a lot of other acoustic matters and speaker placement issues), but a trustworthy treatment can be found at:
roomgain
I don't think room gain relates to any difference between multi-driver subs and single-driver subs. But other acoustic considerations are relevant. For example, you could make a section of a sphere out of multiple drivers and sit it in a corner.
Ben
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I need to admit that I do not know what you mean by acoustic impedance matching.
My fledgling theory is that not all SPL is created equally. Yes, it may be measured the same at the mic, but our ears are not the only thing that let us "hear". There is a tactile presence to sound. I initially thought that surface area might be the key to how an air space is pressurized. But bass reflex and band pass enclosures seem to rule that out due to the relatively small port area that interacts with the air in the listening space?
A relatively small port area insures that the long low frequency sound waves emitted from it will diffract across the boundary of the baffle, effectively making it a larger "bubble" than the port area. Outside of the near field surrounding the exit which has actual air movement, the extent of pressurization can be measured in SPL.
Sorry, late replies, a burst water heater kept me busy until I fixed it and the damage. Consequences of that old house I mentioned.
No problem now that I know you were just teasing. It's hard to tell on forums especially in my case where I'm not present enough to get a feel for the forum personas of the more active folk.
Vehicles are far from sealed excepting cases of SPL competition rides where they pull out the stops with concrete filled panels, bullet proof glass, etc. Plenty of vents galore in the typical car (heater and A/C, but also typically in the door to keep fresh air flowing in and minimize ears popping when slamming doors), weather seals that are iffy and panels that are almighty flimsy -- panel vibrations will leak energy just as well as a hole. (I've a sub in my pickup [previous owner set it up for one and I had a spare driver, so why not?] and the roof and doors move far more readily than those of my home. An effect more than balanced out when surface area of the panels vs. walls is accounted for, but significant to note.) A well-built, energy efficient modern home is probably better sealed overall for those in the colder climes than the typical vehicle designed to avoid CO poisoning, pained ears from slammed doors and reduce panel weight for fuel efficiency. If my home's doors aren't latched properly, slamming one will cause others to pop open. Something that does not happen with most vehicles thanks to all the intentional leaks.
Oh, just remembered, that truck sub? I had played with it for a while indoors before moving it out to my motive means. While the smaller space did move the frequency that room/cabin gain started (unfortunately into the cheap bass range [50-60Hz] that annoys me), I didn't notice any sudden significant gains down low compared to before. Same sub, same box, listened to in room and in a vehicle -- similar gain profiles, just different frequencies. Wish I had thought to do a more intensive measurement than a few quick sweeps, just because. As I haven't the means to EQ it, I didn't see it worth the bother.
Oh yeah, there was another similar case. Some time back, I spotted a good friend of mine a sub I'd built around a rather hefty 15" to give him some bass while he was building something of his own. Since it was a long drive for me and my truck was already setup for it, I set the cabinet in the passenger seat, wired it up and listened to music the whole way up (maybe getting just a little carried away with the gain control when I was where no one would be bothered). Again, similar gain profile between truck and home when comparing the same subwoofer covering the same range. Though, in this case, I didn't chance to compare with a meter directly, the deep down stuff wasn't significantly boosted against the in room response from what I could tell.
Ultimately, these aren't examples to convince anyone other than myself, but in situations where I should be noticing differences according to your position, I have yet to. Maybe I'll try it again just for the fun of it someday and see what the graphs say if I can get my laptop working right. No rush. Hmm, wonder if I can squeeze that 24" in there somehow. 😀
Thanks for the link, I'll look into it. The designer's speakers have some good aspects I've thought to incorporate into my own if I ever finally get back to work on the project I've been toying with for months. (Time and knowledge, valuable commodities.) But, it will be balanced against the proven math and experience from many, many other sources from decades of professional work that cite room gain as legitimate and significant as well as the many graphs created by fellow enthusiasts using the same software we've both used (REW) that show gains down low that too beautifully follow the math of room gain existing. For, that's the thing, I have the measurements in my hands, meter and graph. Many, many measurements to the point that 20Hz sounded high pitched after so many sweeps to figure out what was going on down low. Afterall, on a corollary, I've seen plenty of theories forwarded about the magic of cables, some with nicely laid out math, but many more measurements and my own hearing pointing towards wire being wire. I'm too cynical, oddly enough, to stop believing what measurements from the tools at hand are showing directly. The brain can come up with many explanations why something must or mustn't be when it is, but our tools don't possess the skill of reasoning out an excuse for self-deception; they just measure and show it as it is.
Well, unless my indubitable awesomeness imparted properties to the subs I've built that has made them perform far in excess of what WinISD modeled and that they really are outputting huge volumes of bass down into the single digits as measured without any room gain. I'd believe that; I am pretty awesome. 😀
Musical sphere section in the corner? Channeling Amar Bose and his 2201, eh? That is the question, isn't it? My thinking that I was bouncing off bossobass was about the importance of Sd in Vd vs. Xmax in the bass loading of a room, that Vd with a higher ratio of Sd seems to impart more tactile impact than one with more Xmax (but large Sd with large Xmax for most Vd being king, obviously. My favorite combination.). Thus far, SPL being equal at similar frequencies and so Vd being equal, I'm noticing more tactile impact with a single large driver than a smaller one of equally high quality moving with greater excursion. So, Sd seems to be taking precedence.
In my sub comparisons this year, at one point I had the SI HS-24 24" sub running up against the LMS-U and two 18" Exodus Audio Maelstrom-Xs (almost comparable to the LMS-U in all but looks, far as I'm concerned), which was mad scientist level entertaining when I fired them all up at the same time (before the amps tripped the 20 amp breaker. Whoops! That was a fun weekend.). The three 18"s have more Sd than the single 24", but though placing them separately around the room smoothed the response, the impact was still lacking in comparison to the skookum woof standing large. It wasn't until I placed the three together that the tactile sensation was back, even after EQing the room modes down some. As I said, I was just having fun and the difference wasn't as pronounced as running the single 18" vs. the 24".
But, cripes, I'm glossing over the fact that these are all seriously badass drivers in the colloquial and not small subs. My perspective is skewed, a 15" looks like a hefty midrange and a 12" looks like a cute little thing (even though a good one in the right situation can raise hell just fine). To get back down to realistic perspectives, biiiig tactile difference between these and more conventional sizes from what I've noticed. However, I haven't done much comparison there (just a single ported 12" [an particularly good one] and a pair of sealed 15"s early on) to see if the trend holds up and even then this is with one system in one room. In a month or two, I might have an idea if multiple small subs may be comparable as I should have a chance to compare against a setup with 16 sealed Flux Audio Bang! 10"s (an unknown that'd almost be a 10" Lab12 in another life). My prediction? All those subs close together will be offer a more tactile response than spread out in four columns about the room although the response will measure better in the latter. But what to measure if SPL is the same (in one location) but one gets my arm hairs moving 😛 and the other not? Sound pressure is covered, but focusing on the other aspects of sound (particle velocity and displacement) are getting a bit out there for me and I'm not running off to buy a Microflown probe. I'd hate to think how much it might make me sound like the PRAT and cable nutters that despoil our hobby so.
Still, it'll be fun giving your a shot and finding out in a very coarse experiential measure what happens.
Me neither. 😛 I felt bad about being jargony, but it was the closest I could come to along the lines of what I was thinking: Impedance Matching
Yeah, I know, that entry is ten shades of vague and embarrassingly uncited, but the better scholarly sources I could find treated it as already-knowns for the readership.
Wish I could explain more about that, but I'm just thinking along these lines, too. Better not to goof and give you the wrong explanation when you're in about the same place I am. Plus, I'd rather not make someone who does know better end up...
We are certainly in agreement with our thinking here. Not all SPL is created equally, but I'd add the conditional..."in the nearfield." SPL meters measure sound pressure levels, which is what's normally discussed here, but...well, let me quote a page from that Microflown outfit I mentioned earlier (just because it's spelled out simply):
Perhaps at the greater wavelengths of bass frequencies, the typical listening room puts us in the nearfield where acoustic particle velocity is a significant component of the sound experience. In that case, a larger diaphragm moving less severely may affect the particle velocity over a broader area more smoothly (one doesn't move a bubble with a pin, but with cupped hands) to create a more tactile experience and potentially arguably a more natural sound though the sound pressure at the mic may measure equally.
No problem now that I know you were just teasing. It's hard to tell on forums especially in my case where I'm not present enough to get a feel for the forum personas of the more active folk.
Vehicles are far from sealed excepting cases of SPL competition rides where they pull out the stops with concrete filled panels, bullet proof glass, etc. Plenty of vents galore in the typical car (heater and A/C, but also typically in the door to keep fresh air flowing in and minimize ears popping when slamming doors), weather seals that are iffy and panels that are almighty flimsy -- panel vibrations will leak energy just as well as a hole. (I've a sub in my pickup [previous owner set it up for one and I had a spare driver, so why not?] and the roof and doors move far more readily than those of my home. An effect more than balanced out when surface area of the panels vs. walls is accounted for, but significant to note.) A well-built, energy efficient modern home is probably better sealed overall for those in the colder climes than the typical vehicle designed to avoid CO poisoning, pained ears from slammed doors and reduce panel weight for fuel efficiency. If my home's doors aren't latched properly, slamming one will cause others to pop open. Something that does not happen with most vehicles thanks to all the intentional leaks.
Oh, just remembered, that truck sub? I had played with it for a while indoors before moving it out to my motive means. While the smaller space did move the frequency that room/cabin gain started (unfortunately into the cheap bass range [50-60Hz] that annoys me), I didn't notice any sudden significant gains down low compared to before. Same sub, same box, listened to in room and in a vehicle -- similar gain profiles, just different frequencies. Wish I had thought to do a more intensive measurement than a few quick sweeps, just because. As I haven't the means to EQ it, I didn't see it worth the bother.
Oh yeah, there was another similar case. Some time back, I spotted a good friend of mine a sub I'd built around a rather hefty 15" to give him some bass while he was building something of his own. Since it was a long drive for me and my truck was already setup for it, I set the cabinet in the passenger seat, wired it up and listened to music the whole way up (maybe getting just a little carried away with the gain control when I was where no one would be bothered). Again, similar gain profile between truck and home when comparing the same subwoofer covering the same range. Though, in this case, I didn't chance to compare with a meter directly, the deep down stuff wasn't significantly boosted against the in room response from what I could tell.
Ultimately, these aren't examples to convince anyone other than myself, but in situations where I should be noticing differences according to your position, I have yet to. Maybe I'll try it again just for the fun of it someday and see what the graphs say if I can get my laptop working right. No rush. Hmm, wonder if I can squeeze that 24" in there somehow. 😀
Thanks for the link, I'll look into it. The designer's speakers have some good aspects I've thought to incorporate into my own if I ever finally get back to work on the project I've been toying with for months. (Time and knowledge, valuable commodities.) But, it will be balanced against the proven math and experience from many, many other sources from decades of professional work that cite room gain as legitimate and significant as well as the many graphs created by fellow enthusiasts using the same software we've both used (REW) that show gains down low that too beautifully follow the math of room gain existing. For, that's the thing, I have the measurements in my hands, meter and graph. Many, many measurements to the point that 20Hz sounded high pitched after so many sweeps to figure out what was going on down low. Afterall, on a corollary, I've seen plenty of theories forwarded about the magic of cables, some with nicely laid out math, but many more measurements and my own hearing pointing towards wire being wire. I'm too cynical, oddly enough, to stop believing what measurements from the tools at hand are showing directly. The brain can come up with many explanations why something must or mustn't be when it is, but our tools don't possess the skill of reasoning out an excuse for self-deception; they just measure and show it as it is.
Well, unless my indubitable awesomeness imparted properties to the subs I've built that has made them perform far in excess of what WinISD modeled and that they really are outputting huge volumes of bass down into the single digits as measured without any room gain. I'd believe that; I am pretty awesome. 😀
Musical sphere section in the corner? Channeling Amar Bose and his 2201, eh? That is the question, isn't it? My thinking that I was bouncing off bossobass was about the importance of Sd in Vd vs. Xmax in the bass loading of a room, that Vd with a higher ratio of Sd seems to impart more tactile impact than one with more Xmax (but large Sd with large Xmax for most Vd being king, obviously. My favorite combination.). Thus far, SPL being equal at similar frequencies and so Vd being equal, I'm noticing more tactile impact with a single large driver than a smaller one of equally high quality moving with greater excursion. So, Sd seems to be taking precedence.
In my sub comparisons this year, at one point I had the SI HS-24 24" sub running up against the LMS-U and two 18" Exodus Audio Maelstrom-Xs (almost comparable to the LMS-U in all but looks, far as I'm concerned), which was mad scientist level entertaining when I fired them all up at the same time (before the amps tripped the 20 amp breaker. Whoops! That was a fun weekend.). The three 18"s have more Sd than the single 24", but though placing them separately around the room smoothed the response, the impact was still lacking in comparison to the skookum woof standing large. It wasn't until I placed the three together that the tactile sensation was back, even after EQing the room modes down some. As I said, I was just having fun and the difference wasn't as pronounced as running the single 18" vs. the 24".
But, cripes, I'm glossing over the fact that these are all seriously badass drivers in the colloquial and not small subs. My perspective is skewed, a 15" looks like a hefty midrange and a 12" looks like a cute little thing (even though a good one in the right situation can raise hell just fine). To get back down to realistic perspectives, biiiig tactile difference between these and more conventional sizes from what I've noticed. However, I haven't done much comparison there (just a single ported 12" [an particularly good one] and a pair of sealed 15"s early on) to see if the trend holds up and even then this is with one system in one room. In a month or two, I might have an idea if multiple small subs may be comparable as I should have a chance to compare against a setup with 16 sealed Flux Audio Bang! 10"s (an unknown that'd almost be a 10" Lab12 in another life). My prediction? All those subs close together will be offer a more tactile response than spread out in four columns about the room although the response will measure better in the latter. But what to measure if SPL is the same (in one location) but one gets my arm hairs moving 😛 and the other not? Sound pressure is covered, but focusing on the other aspects of sound (particle velocity and displacement) are getting a bit out there for me and I'm not running off to buy a Microflown probe. I'd hate to think how much it might make me sound like the PRAT and cable nutters that despoil our hobby so.
Still, it'll be fun giving your a shot and finding out in a very coarse experiential measure what happens.
Me neither. 😛 I felt bad about being jargony, but it was the closest I could come to along the lines of what I was thinking: Impedance Matching
Yeah, I know, that entry is ten shades of vague and embarrassingly uncited, but the better scholarly sources I could find treated it as already-knowns for the readership.
Wish I could explain more about that, but I'm just thinking along these lines, too. Better not to goof and give you the wrong explanation when you're in about the same place I am. Plus, I'd rather not make someone who does know better end up...
We are certainly in agreement with our thinking here. Not all SPL is created equally, but I'd add the conditional..."in the nearfield." SPL meters measure sound pressure levels, which is what's normally discussed here, but...well, let me quote a page from that Microflown outfit I mentioned earlier (just because it's spelled out simply):
Perhaps at the greater wavelengths of bass frequencies, the typical listening room puts us in the nearfield where acoustic particle velocity is a significant component of the sound experience. In that case, a larger diaphragm moving less severely may affect the particle velocity over a broader area more smoothly (one doesn't move a bubble with a pin, but with cupped hands) to create a more tactile experience and potentially arguably a more natural sound though the sound pressure at the mic may measure equally.
^ Thanks for all that. It got some wheels turning.
So, I think there are two possibilities that may be behind the difference between multiples a a single large driver.
1) Vector aspect, acoustic particle velocity. Not sure how this would be different, but it goes along with the notion that not all spl is created equally.
2) Acoustic impedance. Large drivers may have the ability to match the acoustic impedance of the surrounding air better than small drivers at low frequencies (subbass and midbass as discussed here). It couples to the air better.
I wonder if it is the combination? That better acoustic impedance match of the larger driver also relates to acoustic particle velocity. I think this might explain why two drivers of different diameters but same Vd, and same spl capability do not have the same tactile presence.
So, I think there are two possibilities that may be behind the difference between multiples a a single large driver.
1) Vector aspect, acoustic particle velocity. Not sure how this would be different, but it goes along with the notion that not all spl is created equally.
2) Acoustic impedance. Large drivers may have the ability to match the acoustic impedance of the surrounding air better than small drivers at low frequencies (subbass and midbass as discussed here). It couples to the air better.
I wonder if it is the combination? That better acoustic impedance match of the larger driver also relates to acoustic particle velocity. I think this might explain why two drivers of different diameters but same Vd, and same spl capability do not have the same tactile presence.
SOOO, for example 20 hz sine wave at 110 db spl will sound differently coming out of 3x 10.xy inches (same cone area) woofers next to each other (asuming they are not geting benefit of wider placement) as from 1x18 inch woofer? Still not getting WHY, if they are moving same amount of air in same speed - thus creating 20hz at 110db.
That's kinda the point of the thread...still looking for an answer. I think there are other metrics evolved that we don't typically consider. There is more to this than spl and frequency. It is quite possible we don't have the tools to measure these other factors, although we can perceive them.
I think that we need to not only look at SPL, but also harmonic distortion, doppler distortion, IM, etc. While your 10" woofers may be able to create the same SPL, without measuring them, can you claim the same distortion levels? If not, that may be audible, or it may not. Perform the experiment, and let us know.
What I know is that I was totally happy with my 4x12" subs, but decided to run 4x 10" in my new house, due to WAF (they're hidden in the false columns), and I'm totally happy with the results; so is she.
What I know is that I was totally happy with my 4x12" subs, but decided to run 4x 10" in my new house, due to WAF (they're hidden in the false columns), and I'm totally happy with the results; so is she.
I never had propper subwoofer and want one now. I want it to be as "subwoofery" as possible. I was thinking until now that i will build 1 10" in 50l box and add another in time instead of one 12-15" in 100l. How is that "bigger" bass advantage of larger sub compared to better in room bass layout of 2 smaller subs placed by sides? I know i wrote kinda subjective post, basically gathering subjective feelings of guys that have experience with this stuff
I think if you are good with the higher fs that a smaller driver may have, with a sufficiently powerful motor and with enough cone area, a FLH or TH sub with multiple drivers (in one cabinet) can sound excellent with nice dynamics and low distortion.
Fs pretty much determines how low you can go, relative to the type of box suspension used. Only motional feedback can change that.
Apropos some earlier posts, wouldn't it be nice if writers could start their comments with some self-revealing remark like, "Although I have never read a textbook of acoustics, my opinion is...." or "I have a degree in physics from MIT, and based on these studies my opinion is..." or something honest and along those lines. When pigs can fly.
Ben
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Your remark is quite offensive. My comment is indeed from experience and I suppose pigs can fly then - with an actual build based on model and I have measurements. If you are good with an fs of say 50Hz that a 5in driver has, and it has the Qts Bl and Mms combination suited for your alignment then four of these 5in drivers can work well like a 12in driver. Here is the measurement of such a FLH speaker:
This measurment was made for the purpose of demonstrating a passive line level XO (low pass 2nd order) to achieve a low cost filter for a sub in another thread.
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I clearly stated AFTER commenting on your post, "Apropos some earlier posts..."
While your post stated an error of no small proportion, it was not what I was concerned about or what I was directing readers towards. As I stated. And I hope my obviously joking suggestion (that might work as soon as "when pigs can fly") was meant tongue in cheek.
Sorry to have caused you irritation. But the alternative - pointing out specific posts that seemed far-fetched - would be inappropriate. So I used more generic language, hoping that by saying "earlier posts" it would be clear I did not mean you.
BTW, even if you had a dozen drivers with a Fs of 50 Hz, they will never go as low as one driver similarly "suspended" with an Fs lower. If you are relating your experience, then you have an obligation to try to explain why your setting produces results at variance with what I believe is acoustic theory. If you can do so, we'll all appreciate learning some new technique. (I am not saying the lowest note you'll even hear from any driver is Fs... just that boxes are made to coordinate with Fs.)
Ben
While your post stated an error of no small proportion, it was not what I was concerned about or what I was directing readers towards. As I stated. And I hope my obviously joking suggestion (that might work as soon as "when pigs can fly") was meant tongue in cheek.
Sorry to have caused you irritation. But the alternative - pointing out specific posts that seemed far-fetched - would be inappropriate. So I used more generic language, hoping that by saying "earlier posts" it would be clear I did not mean you.
BTW, even if you had a dozen drivers with a Fs of 50 Hz, they will never go as low as one driver similarly "suspended" with an Fs lower. If you are relating your experience, then you have an obligation to try to explain why your setting produces results at variance with what I believe is acoustic theory. If you can do so, we'll all appreciate learning some new technique. (I am not saying the lowest note you'll even hear from any driver is Fs... just that boxes are made to coordinate with Fs.)
Ben
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Ben,
What do you mean by "that"?
You are completely mistaken in your statement "even if you had a dozen drivers with a Fs of 50 Hz, they will never go as low as one driver similarly "suspended" with an Fs lower."
Simply Google Bag End's ELF design, it uses speakers driven below Fs, and goes down to the single digits, although not very loud.Or check out my comments from 4 years ago in post #9 here:
http://forums.prosoundweb.com/index.php?topic=1129.0
As a loudspeaker enclosure designer with over 40 years of experience, and dozens of designs, I can not only assure you that loudspeakers can be effectively utilized well below Fs, and that using them below Fs does not require "motional feedback" to work.
Speaking of which, I'd better get back to it (work), need to set up a pair of subs (with Fb below Fs) in the trailer/float for the Madrid Christmas Parade. The multiple subs (which have more impact than a single large sub the same size as the two), top cabinets, Glen's keyboards and my Theramin and vocals will all be powered from 12v batteries through an inverter. I can guarantee we will be able to drown out the bagpipers if we have to 🙂.
We will be videoing the event, if you want additional proof that "motional feedback" is not required for a sub to produce a lot of SPL below Fs, you can listen to the U Tube posting when it goes on line 😉.
Cheers,
Art
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I'll echo and agree with Weltersys that you can certainly get useful output below Fs. Linkwitz published an article showing exactly how, back in the 1970s.