At port tuning, cone excursion almost stops, even at very large SPLs.
There must therefore be some huge pressure acting on those cones to keep them from moving.
Would that pressure amount to a significant SPL gain inside the cabinet?
Yes, and the same thing happens outside the cabinet as well. The sims clearly show how resonances affect things outside the box and we know what effect room modes have on in room response so it shouldn't be too hard to extrapolate and imagine what effect resonances have inside the box. There's going to be a boost but not as dramatic as I think you think it will be.
Sticking a mic inside any regular ported box would be misleading since there would be maximum "room gain" due to the small dimensions, the extremely rigid and airtight construction of even a poorly constructed box (as compared to a room with drywall and 2x4 framing), maximum amount of boundary loading due to the small size, and the fact that you can't get the mic 1 meter away from the cone and port unless you happen to have a room sized ported box lying around.
In other words, in this case, IMO the construction is a lot more important than a helmholtz resonance, although a resonance in the right spot certainly would help the cause.
Sticking a mic inside any regular ported box would be misleading since there would be maximum "room gain" due to the small dimensions, the extremely rigid and airtight construction of even a poorly constructed box (as compared to a room with drywall and 2x4 framing), maximum amount of boundary loading due to the small size, and the fact that you can't get the mic 1 meter away from the cone and port unless you happen to have a room sized ported box lying around.
In other words, in this case, IMO the construction is a lot more important than a helmholtz resonance, although a resonance in the right spot certainly would help the cause.
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@ Doggyboy
The reason i, & others, posted with Warnings/Links about the Very real dangers associated with VLF/ULF f's, was prudent i believe.
After your latest post, it's a lot clearer what your position is
The question i posed earler still remains though, how many cinemas/HT systems would actually be capable of reproducing these f's, either at the levels you will mix at, or at all ?
I'm not saying don't try to achieve it, i'm sure you will
It's probably prudent, but i'll admit that many of the posts I make on the internet receive rolling eyes in response and it gets a little old after awhile.
I'm always wanting to push boundaries in anything I do and so people either don't think i'm serious or don't think i'm sane.Hopefully you mean I do have a sane position about it.
How many cinemas? Not many, but then like I said this is multipurpose.
- Todd AO has a system with 22 Bag End subs to master 7hz and 19hz waves into Black Hawk Down. I'd like to do the same on a fraction of their budget just as capable of mastering THX quality for some of the top cinemas on the planet. There are some commercial cinemas i've heard of with like Danley's stuff for down to 10-11hz, I believe the Chicago Pier is one. For any cinema yes... then sure they can't appreciate the best of the best, but does that mean I should master with a lesser system? How do you win awards doing that?
Todd AO has the same overkill but obviously some appreciate it which is what gets them hired. - There is some legitimate reason to have what i'd call beyond THX ability or at the very least to still fully master things flat out requiring an uncommon system - Location Based Entertainment projects. Places like Disney or Six Flags can have audiovisual rides that exceed by far the normal cinemagoing experiences. Wanting to do a project like that has been a dream for a long time - will it actually happen, not necessarily, but i'll have the rig that lets me.
- The aforementioned personal experiments. I'm fully aware that what i'm proposing is probably a system capable of injuring me. The same would go with a boom car though. Hopefully i'll be less stupid than typical youtubers though. Thankfully I know the best safety protocol of all - it's simply rotating that knob counterclockwise.
Having a system that I never have to worry about breaking or exceeding in demand what it can put out is a plus to me.Oh. @_@ Well I haven't planned anything solid yet, I just assumed subs side by side made sense since most car audio 'wall' systems were like that and assumed fitting enough was even part of the problem, but seeing people hitting 150db inside a pickup. It also seemed a good way to have the backsides fire into the small chamber and the fronts fire into the home theater room. I'm not sure of the best way to do it, just not familiar with Infinite Baffle design mostly, but i'll learn up pretty soon. Hell the wall could be concrete if it has to to avoid vibrations, or thick plywood. My main points was that having a particularily small area was not a problem/hopefully greatly easing reaching the goal, and I don't think i'll need much more than 4 subs anytime soon especially with the excursion they seem to have. (especially since at about 500w apiece it hits my 2kw desired limit anyways, unless working in IB manner they should be powered less)
Wasn't planning any stupid Steve Meade type abuses, no, this is for professional use - mastering bass as deep as the Todd AO studios did, and possibly beyond for certain specialized uses. I'd be no more surprising people than people get surprised going to the best cinemas. It's just I can't afford 22 Bag End Infrasound subwoofers to create content. All the 18's aren't so much for playing loud, just DEEP.
The construction is anything it needs to be.
Was more a question of pressurizing a small area. Thats why I said it was an open discussion. Should it be concrete? It will be concrete. Is plywood fine instead if thick enough? Since 150db SUV boxes seem to hold together fine being plywood - i'm basically just sitting inside the back chamber of the box, so whatever the box normally is it's fine for it to be. I assume maybe drywall wont hold up at extreme levels inside the 'mastering room' but the home theater side would have drywall to provide a finish over something alot firmer like concrete block or at least plywood layers. The main thing i'd like to retain is the ability to have as thick as possible of sound deadener which could possibly include up to as thick as strawbales actually as an incredibly effective and low cost one as long as it didn't screw up the infrasound performance. Being inside an echo chamber isn't really the goal and I assume it will only deaden things below maybe half the wavelength of the width of sound absorbant if I understand the physics. Obviously i'm willing to give up maximum db for sound quality, I think i'll have enough of them.As to electronics, i'm not so sure why it should be a problem, the 5hz on the quad 18 system I was blown away by certainly was impressive, using a Crown Reference amp. I'm confused why 4hz is so different for electronics though, signals are signals? Surely full bandwidth recordings at whatever volume of tidal surf and similar have 4hz tones being amplified just mixed along with all the other frequencies. I just assumed most amps were never tested for such things mostly. I understand the difficulties of high frequency amplification more than I would for low frequencies. I'd assume if not flat some equalization would hopefully correct for it. If not, then whatever I can get is whatever I can get - 8hz was the big goal, anything more is gravy and curiosity. If the required hardware is too custom or radical, it would never be available for a commercial project either even probably location based entertainment setups, and though i'm curious about the lowest of the low it has limits too.
Do the advantages of IB make up for the requirement of such a 'large' room? A larger room is alot harder to pressurize I thought. What are the advantages of IB anyways? Now that it's all recommended and I agreed i'm just wondering why i'll build it that way.
Efficiency?Other than size are there downsides to the IB enclosure? I assume the lack of suspension means mechanical damage at low frequencies would be the greatest risk.
Were talking about two separate rooms, the same subs feeding both - the smaller one originally intended to be the size of a van or minivan, in which i've seen 150db quad 18 systems with similar excursion in a small space before. I don't expect that kind of level in the 'home theater' at all. But then it sounds like my small room needs to be alot larger afterall.
3-20hz was the ideal goal of the design, not what I expect to accomplish, the goal was based upon the Thigpen rotary subwoofer which apparently does 115db at 3hz. (and below but there's no audibility below that due to human physics)
If quad 18's will do 150db at higher frequencies in an SUV of a given size then yes I was curious how deep it could play if my goal was deep frequencies instead of max SPL. When i've seen a quad 18 system play 150db at 32hz, I assumed with super deep tuning and small room gain I wondered if I might still get 140db at 16hz, 130db at 8hz, 120 at 4hz? I mean 22mm Xmax is still a huge displacement of air. Or maybe it ramps off quicker than that.
Servo amps it is! If it has to be and if I still honestly try for 4hz. Actually it was something like that I was thinking of but couldn't remember what I was referring to, amplifiers outside normal audio amplifiers used for other purposes. What drivers were you thinking of to reach 4hz, or would those 22mm Xmax 18's linked earlier do the job?
Massive damping in the room is planned.
The only 'trick' i'd like is a big room and a small room fed by the same subs because unless the IB room is ginormous it should let me hit substantially deeper/louder levels in the small room. If that's not really feasible, then the single home theater room might as well be the only such room, possibly designed smaller itself in a compromise.
Otherwise on the two room design, the small room can be as small as possible down to minivan size (but sounds like it has to be larger), the larger room i've guestimated at 3000 cubic feet, about 9ft tall, 14.5ft wide, 24ft deep or so. The latter shouldn't have a problem hitting THX levels in room which is the main goal with multiple 18's, the smaller room/backchamber for the infinite baffle is what i'm assuming I have to make smaller in order to play louder or deeper.
If those linked near the beginning of the thread would work for infinite baffle I see no reason not to use them. Stereo Integrity | HT Subwoofers with 22mm Xmax and around 500-600w power handling mechanical limited not thermal. Unless there was some other value leader for reaching the targets.
PS I still haven't totally ruled out large concrete horns and stuff either like the guy who built a 10hz horn in the floor.
Though will continue exploring the infinite baffle designs to get a better idea of a total system cost to compare vs the cost of some extra concrete construction instead.Technically at this point both sides are right.
I admitted the exploration of a small room/large room approach as one way to reach the db levels desired being easier to pressurize a small place. The walls would be rigid. But I want as much sound absorption stuff on the inside as I can because if it's just an echo chamber that doesn't help mastering alot, it would ruin fidelity. It's possible I can only have one or the other, or it's possible there's some compromise level between the two - i've so far openly acknowledged not knowing which the solution is. I assumed strawbales might not attenuate infrasound much due to the wavelengths, since I was told it wouldn't really block room modes either, obviously far thinner room treatment devices can be used too but it was just a random idea for a cheap sound absorption.I'm sorry I probably should have clarified - this would be a room within a room. Whether plywood with lots of bracing or concrete block or earthbags a very solid outer room would be built. The strawbales were originally planned to be inside of that almost like an anechoic chamber. Obviously less severe sound deadening could be used. The "small" room could be even more solidly constructed if it's hitting high db levels.
I plan to do all of those things having assumed they were necessary, I had things like that planned before I even posted. I mostly asked for help saying "whats needed?" and my response has generally been that I plan to do whats advised. Other than double sequential doors of decent STC I didn't expect any real openings into the room. I know that special HVAC is needed for very demanding home theaters, I hadn't gotten as far as figuring out how to do that other than planning to take it into account in the design whatever solutions others had worked up for places like movie studios. Maybe that's as simple as lacking forced air ducts. So my biggest concerns were size, shape, and subwoofer design as the challenges I hadn't figured out yet.
Are these really massive and unsolvable problems though? :- P Being a presentation room there potentially doesn't even need to be outlets in the room if everything is wired up in an equipment room anyway. I know they make airtight lighting for factories, heck any lighting behind a solid window is airtight. I didn't consider any of these engineering problems to be large enough to really be worth commenting on. Other than I might well try to figure out low buck or unorthodox ways to do many of them.
The rooms construction methods will be whatever they have to unless obscene cost becomes the primary barrier with no other ways to work around the problem. I'd just encouraged people to brainstorm with that as a base assumption so far in a couple different ways. Near the beginning I was mentioning I was aware that the rooms construction would be the first step to maximize what the rest of the system can do. It seemed like until the size and shape were even known many other problems were academic.
I know there's other responses but this is getting really long and it's late so i'm just hitting post. If I need to comment more in a day or two i'll follow up to anyone else I missed.
The "trick" would not be difficult at all, assuming proper location of the small room/large room and a shared infinite baffle multiple driver speaker plenum.- Todd AO has a system with 22 Bag End subs to master 7hz and 19hz waves into Black Hawk Down. I'd like to do the same on a fraction of their budget just as capable of mastering THX quality for some of the top cinemas on the planet. There are some commercial cinemas i've heard of with like Danley's stuff for down to 10-11hz, I believe the Chicago Pier is one. For any cinema yes... then sure they can't appreciate the best of the best, but does that mean I should master with a lesser system? How do you win awards doing that?
Places like Disney or Six Flags can have audiovisual rides that exceed by far the normal cinemagoing experiences.
The only 'trick' i'd like is a big room and a small room fed by the same subs because unless the IB room is ginormous it should let me hit substantially deeper/louder levels in the small room.
I question the use of the small room, as there are no large rooms or open air facilities that your LF mixes made in a small room will relate well to.
In an acoustically large room (most theaters) the level from the sub will drop off with distance.
A small room allows even pressure throughout at an SPL that would only be achievable for the front row in a theater, or at "ground zero" in a ride.
If you want to make "award winning" mixes, I'd suggest a mix facility that approximates the intended listening environment.
You can't "scale down" a 113 foot long 10Hz wave, and how it sounds in a theater will be far different than the experience in a small concrete bunker, both in terms of achievable SPL and acoustical response.
That does not mean it won't be fun for you to listen to low bass in a "pressure chamber", just don't expect it to be a reason you might win awards for mixing.
Art
There's a BIG difference between 32 hz in a car stereo and 5 hz in a home setting. First let's examine raw 2 pi spl in a ported box. With a 30 hz tuning you can get about 140 db from the same four 18 inch drivers within xmax. (Let's ignore the fact that they can't handle enough power to get them to that level and the effects of power compression if they could - there are other drivers that can handle that much power but these particular ones weren't made for that.) Take those same four drivers and tune the box to 5 hz and you get 104 db. That's a difference of 36 db. Next let's examine the strength and rigidity of a car body to that of drywall. There's not much to say about that.
Anyway, you seem to talk about car audio a lot. Try not to take too much inspiration from the car audio guys unless you know a bit about the designer. Some of them know what they are doing but the majority of them are 18 year old kids that haven't got a clue.
Let me try this a different way. Instead of thinking what would be enough to keep 5 hz soundwaves in, think about what's enough to keep a high speed military tank out. It's not exactly the same thing but if you can reach those standards it will be a good room for containing infrabass.
The wavelength of 5 hz is 226 feet, the half wave would be 113 feet. How many straw bales do you have? Do you have room for a 113 foot thick wall all the way around the perimeter of your room?
There is absolutely no need to cater to the 4 hz crowd since you can probably count on your fingers the amount of people in the world that have a system capable of producing 4 hz at realistic levels.
Think of it this way. There's a massive crowd of audiophiles that demand recordings with no dynamic compression. Does anyone care? There's a couple of little studios that cater but in the big picture, no - no one cares. Is it possible to make electronics flat to DC? Yup, and it's not that hard but good luck finding that equipment. And at some point it NEEDS to be protected against DC if anything goes wrong so your speakers don't fry. You can probably even modify your own electronics to remove any high pass filters and cap protections but I wouldn't do that.
IB is just another word for large sealed box. Download WinISD or similar simulator to get all your answers to this and other enclosure efficiency related questions.
I already showed you graphs that show the difference in room size vs pressurization. The conclusion was that size is not nearly as important as air tight, stong, rigid construction, especially below 10 hz.
I'm assuming that's 115db in room, but I'm not really sure about that. Do you know? If not I'd suggest trying to find out before trying to match it's specs. Regardless, 115db at 3 hz is just about useless, you won't really be able to perceive it. I've seen pics of modest sized rooms with 3 rotary fan subs and there's probably people that have more than that in a single room. As Don mentioned, I think you will need a lot more than 115db at 3 hz to make this worthwhile.
I don't really understand this. It would cost 10's of thousands of dollars to construct a large concrete under floor horn but your budget for the IB setup is for only four cheap 18's and a bit of wood to make a baffle (or manifold) - well under $1000. ???
No, the airtight construction is far from unsolvable IF you are aware of the issue and plan ahead. But from your previous posts I had no indication that were aware of the issue OR that you wanted the type of construction that would afford these benefits.
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It is not necessary to try to damp a 5 Hz resonance in a small room as envisaged by the OP, because there is no such resonance. As I said in an earlier post, room resonances will start much higher.
I know that, Don. The original mention of straw bales had to do with sound isolation outside the room. See the quote below from page 1.
Regardless, if used as bass traps the straw bales would need to be INSIDE the room and I'm pretty sure that's not what he's planning. Either that or he doesn't understand how bass traps work. Placing bass traps OUTSIDE the room isn't going to work. I'm just pointing out the fact that straw bales two deep outside the room isn't going to do anything for noise isolation at very low frequencies, and since you brought it up, it certainly isn't going to do anything to resonances inside the room.
Regardless, if used as bass traps the straw bales would need to be INSIDE the room and I'm pretty sure that's not what he's planning. Either that or he doesn't understand how bass traps work. Placing bass traps OUTSIDE the room isn't going to work. I'm just pointing out the fact that straw bales two deep outside the room isn't going to do anything for noise isolation at very low frequencies, and since you brought it up, it certainly isn't going to do anything to resonances inside the room.
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Hi Doggyboy,
Absorption by foam, rockwool, straw bales... are all ¼ wavelength related and not ½ wavelength. It’s not necessary to 'fill up' the entire depth. The cavity between the wall and the absorbent material (at a ¼ wavelength distance) is usually used for hanging width-band panel absorbers and bass absorbers to treat specific problems of the room. The advantage of such construction is that the panel absorbers and bass absorbers can be tuned lower than the depth of the entire 'absorbing wall' to increase the effectiveness without sacrificing too much space of the room. Drywall can be designed/constructed in such way that it acts like a membrane absorber.
There is a lot of info you can find on the web. Maybe it's also interesting for you to check out the gearslutz forum where you can find more info about industry standards and how to get most out of your budget.
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All right.
The requirement: High levels of infrasound on a budget. "Sitting inside the sub enclosure" has been suggested as a way to achieve both goals.
Assume:
- Small sealed room run in pressurised mode.
- 4x FI IB3 18 inch drivers.
Room:
Poured concrete slab floor.
Prestressed concrete slab or cinder block walls (rebarred and concrete filled).
Prestressed concrete slab ceiling.
Airtight door (as used in professional studios / control rooms).
Aircon ducts long enough to tune the room to less than 1 Hz.
Allow enough height and length to add passive damping (straw bales etc).
Although the IB3 drivers are designed for IB, they simulate well in an 800L enclosure. They also just reach Xmax at rated power in this size enclosure. This is probably not a coincidence, given their intended application.
This implies a room about 32 cubic metres, for example 2.5 H x 3 W x 4.5 D.
This should allow room for one or two people, a small desk, a monitor and two near-field speakers, plus up to a metre thickness of damping behind the seats and some on the ceiling, and some on the walls if required.
Assuming the room can be effectively sealed, 4x IB3 18s should produce at least 125 dB down to 4 or 5 Hz. That's also close to their "free air" SPL, which minimises the amount of EQ required.
So, at first glance, the requirements appear to be achievable.
The requirement: High levels of infrasound on a budget. "Sitting inside the sub enclosure" has been suggested as a way to achieve both goals.
Assume:
- Small sealed room run in pressurised mode.
- 4x FI IB3 18 inch drivers.
Room:
Poured concrete slab floor.
Prestressed concrete slab or cinder block walls (rebarred and concrete filled).
Prestressed concrete slab ceiling.
Airtight door (as used in professional studios / control rooms).
Aircon ducts long enough to tune the room to less than 1 Hz.
Allow enough height and length to add passive damping (straw bales etc).
Although the IB3 drivers are designed for IB, they simulate well in an 800L enclosure. They also just reach Xmax at rated power in this size enclosure. This is probably not a coincidence, given their intended application.
This implies a room about 32 cubic metres, for example 2.5 H x 3 W x 4.5 D.
This should allow room for one or two people, a small desk, a monitor and two near-field speakers, plus up to a metre thickness of damping behind the seats and some on the ceiling, and some on the walls if required.
Assuming the room can be effectively sealed, 4x IB3 18s should produce at least 125 dB down to 4 or 5 Hz. That's also close to their "free air" SPL, which minimises the amount of EQ required.
So, at first glance, the requirements appear to be achievable.
Hey Don, now we're on the same page.
I'd use different drivers (data-bass.com says all the FI drivers make weird noises when pushed hard) and I'd use rigid fibreglass instead of straw bales for bass traps, and I'd leave the ducts out completely, but other than that I like your plan. (Instead of ducts I'd pump the temp. control in while the doors are open and live without it when closed since there's no way to make a room airtight if there are ducts to external areas.)
I'd also advise the OP to check local building codes and safety rules and plan some type of direct exit to the outside world. If something like a fire happens and you're inside a room like this, it could be way too late to escape by the regular route by the time you notice. Safety first.
I'd use different drivers (data-bass.com says all the FI drivers make weird noises when pushed hard) and I'd use rigid fibreglass instead of straw bales for bass traps, and I'd leave the ducts out completely, but other than that I like your plan. (Instead of ducts I'd pump the temp. control in while the doors are open and live without it when closed since there's no way to make a room airtight if there are ducts to external areas.)
I'd also advise the OP to check local building codes and safety rules and plan some type of direct exit to the outside world. If something like a fire happens and you're inside a room like this, it could be way too late to escape by the regular route by the time you notice. Safety first.
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Any suggestions for other drivers? Are AE IB15s still available?
I'd use fibreglass instead of straw too, because I don't have a ready source of straw.
Ventilation is essential, otherwise there will be a gradual buildup of CO2, heat, and digestive gases and other odours. Plus, some building codes require it, and it's not practical to open a window. Ducting is easy to do with two 10 to 12 metre lengths of 15cm flexible duct (aluminium, not plastic) wrapped into a coil. One attached at each end of the room. Put standard extractor fans on the "outside" ends, one "sucking" and one "blowing", and wire them in series to reduce the speed (and noise).
I'd use fibreglass instead of straw too, because I don't have a ready source of straw.
Ventilation is essential, otherwise there will be a gradual buildup of CO2, heat, and digestive gases and other odours.
Plus, some building codes require it, and it's not practical to open a window. Ducting is easy to do with two 10 to 12 metre lengths of 15cm flexible duct (aluminium, not plastic) wrapped into a coil. One attached at each end of the room. Put standard extractor fans on the "outside" ends, one "sucking" and one "blowing", and wire them in series to reduce the speed (and noise).
Doggyboy, you should relate more with acoustics and drop the loads of text you deliver (I can measure your posts in meters and inches). It turns everything so confusing. You may think you are learning but for me you are completely lost. You will forget everything that was said as soon as you leave the thread and it's dead. You say you have a barn, or something like it, and you want to compete with the IMAX Theaters types, Todd AO and Danley, Disney and Six Flags. Give me a break! You know it requires tons of amps and tons of money, not 1KUSD. For me, unless you are humble with your visions and commitments, you are losing your time trying to achieve and learn in five minutes what others have spend their lives studding and experimenting.
I'm not too interested in this type of super high excursion driver since I have no personal need for them so I don't keep up to date with them. All I remember is that data-bass.com said all the FI drivers make a clicking or knocking noise at high excursion. (IIRC) Not sure if that's already past the point of xmax or not, and they are not the only drivers with this reported problem either.
I have no idea if AE IB15s are available. ED is gone now. The Stereo Integrity drivers have been mentioned a few times and mach5audio usually has something available (but usually only 1 model at a time these days, and he keeps inventing new drivers instead of stocking older models). Rumor has it that Kevin Haskins might be reviving Exodus as a source of large HT drivers. There's a few models of TC Sounds drivers that could work but they are all expensive. There's a few car audio brands that might work, like RE Audio (especially the XXX line), Sundown Audio, Ascendant Audio, maybe even Sound Solutions, SoundSplinter and Digital Designs and probably a few others I'm forgetting at the moment. (In case you haven't guessed I have no experience at all with ANY of these, and depending on the alignment, some of the car audio drivers might require some eq, but they all have plenty of listed excursion.)
I'd use fibreglass instead of straw too, because I don't have a ready source of straw.
I could get my hands on plenty of straw but I can't imagine it would be anywhere near as effective as rigid fibreglass. If space is an issue, I'd be looking for maximum effect and I don't think straw is the answer.
Ventilation is essential, otherwise there will be a gradual buildup of CO2, heat, and digestive gases and other odours.
Can't argue with any of this, but it seems a waste to go to so much trouble to make the room airtight and then have a big vent hole. But if there's no way around it I guess there's no choice... I'm not sure how the serious HT guys deal with this and I'm not quite interested enough to research.
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It's a rigid, "airtight" (no unintended leaks) enclosure. But you do want pressure equalisation to prevent, for example, the driver cones being damaged by accidentally slamming the door. So you tune the room like you would any other enclosure - add port(s). The trick is to tune the room to a frequency well below the lowest frequency of interest. For a 32 sq m room, two 15 cm x 13 m ducts will tune the room to about 0.5 Hz. For frequencies greater than an octave or so above resonance, a ported enclosure acts like a sealed enclosure.
Wouldn't a door slam be a strong 0 hz pulse? (Positive pressure with no negative component.) If so, you can't tune lower than that.
Anyway this door slam thing would only affect drivers in an IB alignment and IMO it's a good excuse to use more drivers - enough total displacement that a door slam wouldn't hurt them.
If the enclosure is tuned to 0.5 to 1 Hz, a "DC" door slam will bleed out through the port. Standard ported enclosure behaviour - port appears closed above resonance, open below resonance.
Indeed, it would only affect drivers in an IB arrangement, but that's what is being proposed.
Adding another $1K of drivers would certainly help protect the drivers from damage, but would cause significant damage to the OP's wallet. Remember, this is being done on a restricted budget.
If you want to go further down the rabbit hole, you could work out the displacement caused by the closing of the door and see if it exceeded the Xmech-limited displacement of the drivers.
Anyway, hopefully by now the OP has enough info to decide if he wants to take this path. I've been following it because I've had plans for doing something similar for a while. (I have a pair of Altec 15" full-range drivers that simulate perfectly in 1.35 cubic metre enclosures, flat down to 20 Hz. I can either brick up one end of the garage to form the enclosures, or I can "sit inside".
Indeed, it would only affect drivers in an IB arrangement, but that's what is being proposed.
Adding another $1K of drivers would certainly help protect the drivers from damage, but would cause significant damage to the OP's wallet. Remember, this is being done on a restricted budget.
If you want to go further down the rabbit hole, you could work out the displacement caused by the closing of the door and see if it exceeded the Xmech-limited displacement of the drivers.
Anyway, hopefully by now the OP has enough info to decide if he wants to take this path. I've been following it because I've had plans for doing something similar for a while. (I have a pair of Altec 15" full-range drivers that simulate perfectly in 1.35 cubic metre enclosures, flat down to 20 Hz. I can either brick up one end of the garage to form the enclosures, or I can "sit inside".
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Although I have heard of fragile large diaphragm ribbon microphones being damaged when airtight studio doors were slammed, I have not heard of a single bass driver ever being damaged in cars or studios by doors being slammed.If you want to go further down the rabbit hole, you could work out the displacement caused by the closing of the door and see if it exceeded the Xmech-limited displacement of the drivers.
The old VW Beetle was tight enough to float (before it rusted out) and would make your ears feel like they were going to blow up when you slammed the door, but the speakers never got blown out.
I once heard a bunch of Altec 15" playing around 16-20 Hz tone in an art museum.
I thought it was air handling noise, it came and went depending on the standing wave distribution, it was not until coming across the exhibit did the source become clear.
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I haven't heard of a car or studio installation where the drivers were mounted "in the wall", with one side open to the room and the other side open to the outside. Actually, come to think of it, I recall one car installation - Earl Zausmer's BMW 540 - which had the subs vented out into the front wings, although even then the wings were sealed against the body in normal use. Milbert Amplifiers, Most Musical Amplifiers
Mounting drivers between rooms is common practice for members of the "Cult of the infinitely baffled", but in most cases the volume of the room is much larger than that contemplated here and the room is usually quite leaky in the first place. Compare how hard it is to slam a door to a typical listening room against a door to a sealed closet. Consider also that most room doors are relatively light so are hard to slam with any real force, compared with a solid double-thickness studio door.
But the point isn't really the driver protection, the point is the ventilation. Some building codes will mandate it, and in any case it does get stuffy quickly in enclosed spaces. You'll have heat from bodies (about 150 to 200 watts each), from the electronics in the desk and monitor, and from the drivers themselves if the magnet sides face into the room. If nothing else, the moisture from perspiration and breathing will condense on the equipment and damage it. Since ventilation has obvious advantages, and can be done cheaply without compromising the room's function, why not do it?
Edit: Somewhat relevant picture.
Bobby Owsinski's Big Picture Production Blog: A Picture's Worth A Thousand Words
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