Just had a revelation ! ( how to construct subs )

Audio Playback DIY Speakers
1

i was struggling with the cons and pros of DIY vs Commercial when it comes to subs …

if we look at a subwoofer like JBL VTX G28 - it’s about $10,000 and it’s just two drivers that are $700 each plus about $100 worth of handles and terminals, and a grille.

so about 80% of the cost of that sub is in the cabinet. in that $8,000 cabinet there is only about $400 worth of material, or about 5% of the total cost.

the case for making the cabinet yourself is clear. even if you buy the most expensive tools they will pay for themselves before you finish the first pair of cabinets.

but what if you have an accident and lose some fingers ? then the value isn’t exactly there anymore is it ?

can we do better ?

we can …

2

all of the speakers i built including my TC Sounds LMS Ultra subwoofer were built in a NYC apartment … so how did i even fit 4 x 8 foot sheets of plywood in there ?

i didn’t …

Home Depot at a nominal price ( very cheap ) will cut the plywood to your dimensions for you. now they will only cut it with about 1/8th of an inch precision or so - so it won’t exactly be beautiful but if you modify your construction to allow for those tolerances it can be perfectly structurally sound and acoustically functional ( after sealing the gaps with silicone ).

HD will NOT however make any round holes for you, and i have tools ( both Dremel and Jigsaw ) for that … i should also have a Router but i don’t.

I also have both Circular and Reciprocating and Manual Saws for smaller cuts ( Home Depot has huge jig that is great for making large cuts like 4 foot or 8 foot long cuts )

there is one kind of cut however that i cannot safely do - and that is cutting wedges at an angle … although i could set my circular saw to 45 degree angle i will not risk my fingers for this …

so what can we do ?

3

at one point i had a thought to just ask a Carpentry Shop to build my subs for me based on SolidWorks CAD drawing i would prepare for them ( i had designed many things in SolidWorks before as a hobby ).

but i am reminded about how i tried to build an exercise bench and when i sent the drawing to metal fabricators they quoted me $3,000 plus $300 for powdercoat finish. and that was when gas was like $2 / gallon.

the most expensive commercial exercise bench at the time was $1,300 and i had already spent $400 to buy the materials at that point so the whole custom bench would have cost me 3 times as much as the best commercial bench and i had to bail …

something tells me if i have a carpenter build my subwoofers for me it won’t exactly save me money either …

WAT DO ?

4

well it just fucking hit me and i can’t believe i haven’t thought of this before !

i can have Home Depot do the large cuts for me.

i can do the small and circular cuts myself.

and i can have professional carpenter do ONLY the wedge cuts that neither Home Depot nor I can do.

it is so obvious in retrospect i can’t believe i haven’t though of this before !

i literally only need the wedge cuts for the ports so the final box can look like this:

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without such 45 degree cuts the box would need to be bigger …

i would literally only need a carpenter do FOUR CUTS on two pieces of plywood for me to be able to build this box and it would save me about $5,000.

home depot charges something like half a dollar for a cut. even if the carpenter charges $50 per cut it will be WELL worth it for me !

5

with this approach i would be able to build a box of any size and design and do so on a budget and would not need more space than an average bedroom to build it in …

i guess the reason i haven’t built anything in so many years is i used to have my pops helping me and then my friend Igor and now i don’t talk to my pops and Igor is dead and i am very worried about losing my own fingers to a table / circular saw …

but i think with this new approach both the risk and cost can be managed …

Home Depot will do the big cuts

Carpenter will do the tricky / dangerous cuts

and i will do the easy cuts ( the majority of cuts )

my main task will be to simply design the box first acoustically and then put it in 3D in SolidWorks to create accurate dimensions for all the cuts so that i would be able to delegate the harder cuts out …

6

IMO the best option if you are going to build subs is to just build arrays of sealed subwoofers with decent drivers.

Ported subs and horns/bandpass designs give you more output from your driver, but at the expense of cabinet size, which you could just use for more drivers.

Basically there are three parameters: cost, amplification, and cabinet size. You can only pick one. A big horn gives you the most output per dollar and output per watt, but at the expense of a huge cabinet. A sealed sub gives you the most output per volume, but you need more amplification or subs to make it as loud as the horn.

If we are talking about endgame stuff, cost is really no object. That’s why I’d just build a big array of sealed or small ported subs and call it a day.

7

sealed can take better advantage of room gain versus ported but only assuming there is actual content below tuning frequency …

i listen to electronic dance music which must be playable at events like Coachella

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not much room gain to be had in open air so ported is basically a must.

the best prosound subs are tuned to about 27 hz and assuming they get better over the next 10 - 20 years maybe they will get down to about 23 hz tuning so all i really need is to make a sub tuned to 23 hz today and i’m good for the next 10 - 20 years.

the other issue is that all prosound sub drivers are designed for vented alignment. to go sealed i would have to use something like Dayton drivers …

but yes, lots of cheap sealed drivers is one way to get good bass. you don’t need very good drivers for sealed alignment - you just need lots of surface area, which can always be increased by using more drivers.

this would not work very well outdoors but we are not outdoors. it would also be of no benefit if you only ever played dance music but we also sometimes watch movies.

so i would say both approaches are equally valid.

8

You get the most from pro sound drivers by using a vented alignment, but they tend to prefer huge boxes to get the most out of them. Or horns. You can get a lot of output from them, but that output comes from the box. In an outdoor setting where you basically have unlimited space that doesn’t really matter I guess. In an indoor setting where you might want to be maximizing output per unit of volume it makes more sense to use that space to load up on drivers.

The added benefit with this method is that with more drivers you get more voice coil surface area and hence more power handling and lower compression across the board.

One thing that is mischaracterized about horns is that they are more efficient at every frequency. This is not true. Horns have a highly variable impedance that will dip down to minimum levels at several frequenies along their passband. Depending on the design a horn can actually be less efficient at these frequencies than the same driver in a sealed or ported enclosure. The horn might have high output overall, but it also has high compression at certain frequencies which does not sound good.

With a bunch of drivers in sealed boxes you avoid this problem because the simple impedance profile and because the number of voice coils means that each driver is using less power.

9

it isn’t so much the size of subs that is the problem but their shape.

the key is to integrate them into your room.

the most straightforward hack that people have actually done ( i did NOT invent this ) is build a subwoofer coffee table, which is self explanatory. it’s huge but it doesn’t get in the way - in fact it gives you a place to put your remote and popcorn.

next level up is a subwoofer couch ( my invention ). you would have 4 sections - bottom, back, and two sides. each would be its own subwoofer.

i have actually built a bed for my grandma once - it isn’t even hard. her old bed had failing springs and it was hurting her bad back so i gutted the springs, put in a flat piece of plywood in its place and then an extra layer of foam padding to make up for lack of springs and she used that bed for like 15 years almost until her death at 98. in the last couple months hospice provided her with a motorized reclining and lifting bed, and even then her home attendant continued to use the bed i made and it’s still in great shape today.

i guarantee you if you build a subwoofer couch you will have a lot of respect in the community because of the sheer novelty of such a project - yet it would still actually be practical.

just make sure you don’t glue the 4 parts together. each of the four enclosed volumes should bolt together so they can be disassembled and move to another house.

i had subwoofers in the floor under the front seats in a BMW and it works pretty well.

in addition to my grandma’s bed which used cheap foam i also made my own mattress using very expensive natural latex foam, but even though a decade later it is still super comfortable and i still sleep on it - it wasn’t without issues. the main issue is oxygen is eating the sides of the latex causing them to crumble into fine dust and also the many layers of latex i used ( there are like 5 layers ) shift overtime and need realigning.

but regardless i have some experience with creating comfortable furniture so if you want to build the subwoofer couch i could offer you some guidance. you would have to pay a shop to sew some kind of cover for the foam but it shouldn’t be very expensive.

i will NOT be doing a subwoofer couch myself because i am not short on space.

but in fact if you succeed with the subwoofer couch you could even commercialize it ! i have pretty much all the knowledge needed to make an EXCELLENT subwoofer couch. i just don’t really have a passion for creating things for other people because i don’t believe other people deserve anything good - only i deserve good things.

10

the only way you will NOT get respect is if you admit that it was my idea and design because they all still hate me and would never admit that i am a genius

what you could do is build the subwoofer couch and not mention that i had anything to do with it until they all say it is amazing

THEN you can reveal it was actually my design and it will be too late for them to take their praise back

LOL

11

and so on - you can build a subwoofer TV stand for example.

my TV is actually sitting on top of my LMS subwoofer, which isn’t even connected to anything - it just makes a great stand for the TV.

there is enough space. it’s just about integrating the subs into it.

12

Here’s a guy who actually built a wall of subs with 36 JBL 2242H’s. That is a lot of bass.

What’s more discrete than a wall of subwoofers? If you put a projector screen and speakers in front of it you don’t even notice it.

13

yes so if the subwoofers are INTEGRATED into the room somehow ( whether it is into a wall or something else ) they can visually disappear no matter how large in total cabinet volume.

my issue with his setup is standing waves. when all of the bass is coming from one side of the room there will be extremely strong standing waves.

a room with solid boundaries at both ends has the same standing wave modes as a pipe open at both ends because the wave reflects out of phase at open end and in phase at closed end so two inversions at both open ends is the same as two reflections without inverting ( minus times minus = plus )

so you can just refer to the right side column in the diagram below:

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wavelength at 80 hz is 14 feet so the first mode at 80 hz will be with walls at 7 feet apart. with larger distances you will hit modes at lower frequencies. the only way to push modes up in frequency completely out of subwoofer frequency range is to have a space that is smaller than 7 feet …

YOU CAN ACTUALLY DO THIS by evenly distributing subwoofers in space so that they are always closer than 7 feet to the next one IN ALL THREE DIMENSIONS

that is to say if you were to subdivide a room into virtual volumes smaller than 7 x 7 x 7 feet and put a sub in each of those volumes you would pretty much have EVEN PRESSURIZATION of the entire room with no standing waves …

nobody actually achieves this ideal ( and very few people even understand this is the goal ) but people get HALFWAY THERE by spreading the subs along ALL the walls instead of just the front wall …

this is where the sofa and coffee table subs come in - they bring you closer to the ideal …

if you could also hang the subs on the ceiling above your listening position that would be awesome as it would cancel out the vertical modes … nobody does this in part because they are stupid and in part because it isn’t easy to hang subwoofers on the ceiling ( but nothing is impossible ! )

though frankly with 8 foot ceiling your only vertical mode in subwoofer range would be at 70 hz so maybe it would be easier to just EQ it out but you can’t EQ a mode out in 3D space - only in a single location, or in this case a single horizontal plane … so you would have to have one EQ preset for sitting and one for standing …

on other hand if you laid out one subwoofer grid on the floor ( 7 foot pitch ) and another on the ceiling then you would have perfectly flat bass response in all parts of the room.

think of it as holding up a container filled with water - if you shake it side to side there will be waves - but if you lift the whole thing evenly there are no waves. likewise if you pressurize the entire space of the room EVENLY there will be no waves - just pressure.

14

if you ever had to deal with a single subwoofer in a room you know the sound is different in every part of the room.

it will be almost as bad with a wall of subs because the room is 3 dimensional and you have achieved even distribution in 2 of those 3 dimensions but not in the front to back dimension.

on other hand if you have one floor array and one ceiling array you have even coverage in two horizontal dimensions and you have symmetry in vertical dimension … which means you will still have standing waves vertically but only above a certain frequency based on your ceiling height and you can lower your subwoofer crossover below that frequency easily …

of course you then just kick the can down the road because your mains will still have those standing wave modes … i guess that’s what bass traps are for

bass traps are more effective at higher frequencies than lower so if you can push the problem up in frequency to where bass traps are actually effective that is worth it …

15

essentially without waves you cannot localize the source because even pressure has no direction - so at some point in frequency you have to give up on having an evenly pressurized space to have imaging …

but you certainly don’t need to be able to localize the subs …

and considering how hard it is to damp the standing waves using bass traps you would probably want to cancel out standing waves using randomly placed subs to as high a frequency as you can crossover at …

i believe in most rooms standing waves are a thing up to about 250 hz … but home theater Low Frequency Effects ( LFE ) channel is only 80 hz ? or is it 125 hz ?

i wonder if many processors can mix down regular channels into subs to realize higher crossover point than one built into the LFE channel …

many audiophiles think you get better sound by keeping sub crossover low because they feel the sub is “muddy” while the mains are “clean” … and that may be true for some subs and mains but perhaps with well made and well placed subs optimum XO could be higher … i would experiment with going as high as 120 hz which seems to be the highest setting available with prosound subwoofers.

16

if you can’t randomize subwoofer location the next best thing you can do is keep the sub close to your listening position that way hopefully the flex of the walls will attenuate the standing waves somewhat and direct energy from the sub can overpower the standing waves at the listening position so that any kinds of peaks and dips in response are less pronounced

again, this is where subwoofer sofa comes in …

17

i would also note that if you’re going to have multiple subs whose spacing is less than perfectly even throughout the volume of the room it is nice to be able to EQ each one separately as each one will have different coupling to room modes …

this is an area i was trying to explore on AVS Forum around the time i was banned - i was asking people with very advanced DSP processors and setups if they tried this or had any success with this approach ( individually EQing every single sub to get maximum even-ness of response throughout the room ) but i don’t remember any conclusive answers …

but unless somebody proves that this can’t possibly have any benefit i would err on the side of multi-channel amps for multi-sub setups than a gigantic 2-channel amp where you put multiple subs in different locations on the same channel and then you can only EQ in frequency domain but not in space …

potentially this could get extremely complex because every mode is a function of ALL the subs so when you adjust any of the subs EQ you also affect the modes of all the other subs and if that wasn’t bad enough any amplitude changes you make in frequency will also affect the phase which will complicate the mode distribution even more in both frequency and space … LOL

tuning such a setup without any existing methodology for doing so that i am aware of would be interesting to say the least LOL

still, it would be difficult if not impossible to do worse than what that wall of subwoofers guy did

:slight_smile:

18

The simple solution is to build another wall of subs on the back wall that’s inverted and delayed by the length of the room. It cancels out the reflection so you don’t get any standing waves. This only works if you have a symmetrical room though. Otherwise you could put four feet of foam back there.

19

you’re starting to sound like me - where are you getting these ideas ? if it’s some forum like DIY-Audio, AVS Forum or AudioScienceReview maybe i should come back under a new name … because it sounds like somebody is actually trying to think and that makes me jealous - i don’t want anybody thinking without me ! i want to be part of all that is intelligent.

now as for the idea itself - this would be similar concept to a cardioid subwoofer which are used to direct bass in one direction canceling it out in the opposite direction by using exactly what you said - delayed and inverted signal - so the concept is proven in practice and should work HOWEVER !

however it isn’t without downsides or everybody would be using cardioid subs - and the downside is loss of output at lower frequencies …

in case of a room you wouldn’t lose output - instead you would lose room gain …

assuming perfectly rectangular room your front array would acoustically see a tunnel of infinite length so you would get gain from multiple drivers in close proximity ( as with any array ) and you would see some horn loading gain from the floor, ceiling and side walls creating a horn mouth essentially but you would see NO room gain per se - that is you would never be able to pressurize the room like air is pressurized in an engine cylinder because the volume of the room would never be decreased - it would always stay constant - which means at 0 hz there would be ZERO pressure.

by contrast with my solution you would get FULL pressure at 0 hz assuming perfectly sealed room.

this could be solved by introducing additional crossover point ( continued in next post )

20

assuming 20 foot long room the lowest standing wave longitudinal mode would be at around 30 hz. so what you can do is use VENTED boxes tuned to about 20 hz in the front and back …

the reason you would want vented is because the rear array would essentially cancel out any output much lower than that 30 hz standing wave mode so there would be no point in using speakers that have output much below that 30 hz frequency - instead by going vented you could get extra couple DB of output where it actually is preserved …

and THEN use SOMETHING ELSE below 20 hz …

i would probably go with INFINITE BAFFLE loading for that “something else below 20 hz” application - you could vent the rear anywhere - to the rest of the house or the outside of the house …

that sub 20 hz signal would mostly dissipate in open space but in the tightly sealed home theater room it would build up pressure that you should be able to feel …

and because that infinite baffle sub would operate below all standing wave modes ( assuming the length of the room is the longest dimension of the room ) you could put it anywhere in the room without exciting any modes …