sub woofer enclosure 101

[monty73741]

OK, I said this would be coming, and I found some free time, so here are the the basics on boxes for anyone who wants to know.

I'm writing these threads to expound in detail on some of the more FAQ's around here, not to start debates. Please reply with real questions or information only - we all love to hear different opinions, but I'd like for this thread to be an information source for the beginers, not a debating ground for the old guard. Fellow tech freaks also note - I will not be addressing specific Q alignments and whatnot, this would make a long post a lot longer, and confuse the crap out of the newbies. Feel free to jump in with that stuff in any replies as you see fit. Now -

The job of a subwoofer is to produce the low frequency sound we love so that the smaller speakers in the system don't have to. This is accomplished by creating a pressure differential between the air on either side of the speaker cone. The different types of subwoofer enclosures affect the way that the air inside the enclosure reacts with the speaker and/or the surrounding air to accomplish the desired result, whether it be lower extension, higher SPL, etc. The enclosure also has a tremendous effect on a speakers power handling, because it will have a huge impact on the way that the cone moves. That said - There are many different types of enclosures (boxes), I am going to address the 4 most common - sealed, ported, bandpass, and freeair.

Sealed - Also called "acoustic suspension". The sealed box is the simplest and most popular type of enclosure. It works simply by containing the air behind the woofer to varying pressures, and keeping that wave from interacting with the outside air at all. ANY subwoofer will work in a sealed box of the correct size. It is a commonly stated that a sealed box is "tighter" or more musical than other types, this is NOT always the case. A sealed box can be "tuned" just like any other enclosure by varying the amount of air interacting with the speaker, making it tighter or boomier. Sealed boxes will generally play lower, and have higher power handling capabilities, but are are not as efficient - they need that extra power to play loud. With the way subs are designed now, sealed boxes will usually be quite a bit smaller than other box types. If you are building your own box, or will be putting a given woofer in a prefab enclosure, sealed is the easiest way to go. Just match the manufacturers recomended airspace with the box you'll be building or buying, sealed boxes are pretty forgiving if you're off a little bit.

Ported/Vented - Also called "bass reflex". The ported box is a more sophisticated version of the sealed enclosure. This type of enclosure also works by containing the rear wave, but adds a tuned port that interacts with it in a very specific manner at certain frequencies. The port has a very specific volume of air displacement in relation to the airspace inside the box. This air will provide a specific resistance and resonance when it reacts with the motion of the speaker cone. Technicaly, any woofer can work in a properly built ported box, but due to the drastic effects that this box has on cone motion, it is not recomended by some speaker manufacturers for some of their woofers (the Eclipse aluminum woofers are a good example - in the right ported box, they will POUND - but you greatly reduce their life expenctancy). Ported boxes have a reputation as being "boomy" - this is also not really accurate. Most high end home speaker companies use vented enclosures, they can be VERY accurate if they are designed correctly. A vented box will usually be more effecient, and power handling is exceptionaly high - but in a narrower bandwidth. System tuning is very important to get the most out of a ported box. Ported boxes tend to be larger than todays sealed enclosures, and unless the box is designed specificly for the woofer you're using, prefab ported enclosures are not usually a good idea. You can build your own if you have the right specs, but it's usually better left to the pro's.

Bandpass - Also called by their type, "single reflex" or "dual reflex", by the rolloff, "4th order" or "6th order", or various nicknames, "compression box" is the most common. Bandpass boxes work by controlling the pressure on both sides of the speaker cone using the principals outlined for either or both of the enclosure types listed above. They are INCREDIBLY efficient in the fequency range for which they are designed, gains of 6 to 8 Db vs. a sealed box for the same speaker are not uncommon. However, because of the passive forces that a bandpass box creates on the speaker, power handling is limited. If you're looking for the loudest possible bass with a limited amount of power, they are unbeatable. Sound quality in a bandpass box can be very good, but will always contain more distortion than a single chamber type enclosure. If you only get one thing from this post, let it be this - NEVER USE A PREFAB BANDPASS BOX UNLESS IT WAS BUILT BY THE SPEAKER MANUFACTURER SPECIFICLY FOR THE SUBWOOFER THAT WILL BE USED IN IT!!!! Read that 10 times, never forget it. Bandpass boxes are EXTREMELY picky, and are VERY hard on the speaker if not built right. If you want this type of box, it can be a lot of fun - having two 10's hit like 3 12's is a blast - but I highly recomend having it professionaly designed and built by an experienced installer. Note that bandpass boxes will be quite large, if weight and/or space are factors, this is not the right box. Bandpass is most effective when placed inside the listening area - i.e., in a hatchback or sport utility, etc., so all you Probe drivers are lovin' it. I personaly LOVE to put them in the trunk of a coupe or sedan with the port run to an opening cut in the rear deck, but if you don't want to cut a hole in your car, MX-6 owners should stick with another box type.

Freeair - Also called "infinite baffle". The freeair method works on the simplest possible concept - the air on either side of the speaker has little or nothing to do with the way that the speaker produces the sound in this application. As long as the wave on either side is seperated from the other side to avoid cancelation, it's all up to the speaker to do the dirty work. Because the sub will derive no support from backpressure, power handling and efficiency are VERY limited in this type of system. The majority of subs out there would not last long in this type of mount, if you want freeair bass, you should get a woofer designed for it. Sound quality in an infinite baffle system is EXCELLENT with the right sub - on par with or better than the best sealed boxes and similar to a perfect ported enclosure - but you're not going to get real loud. A lot of the options available for freeair setups are disappearing, and aperodic damping and whatnot is pretty technical stuff anyway. I will let it suffice to say that freeair is great for taking up very little space, and the sound quality is awesome. If you want to build your own freeair setup, it'll be more work than you might expect, but most DIY's could manage with a little patience. The "wall" which will be your mounting point must be VERY solid, pretty much airtight front to back, and you'll probably need a lot of Dynamat or related material to keep things quiet. Amp choice and system tuning will also be very important here.

I'll finish with some notes on box building, those questions also come up a lot....

If you ain't got access to the right tools and materials, don't start till you do. A table or wall saw, a drill and/or screwgun, and woodglue are necessary. Hammer & nails can be used, I prefer to pre-drill & screw things together, and you will need to screw down the sub. A jigsaw or sabresaw is commonly used to make the hole for the speaker, a router will make your life easier. You may want to use a silicone type sealant to make sure things are airtight, but if your cuts are straight the woodglue should hold things tight.

Use 3/4" or thicker MDF or HDF. That's Medium or High Density Fiberboard. There are lots of things you can use, but heavier & more dense is better. Plywood & particle board should not be considered. Flex and resonance are the enemy here. Any surface that'll be more than 18 or so inches long and more than 8 or so wide should be braced internaly - a piece of wood 2" thick running across the large surfaces every 18" or so would do nicely. If you want the box to be REALLY airtight and solid, put a sqaure block of wood along all your right-angle joints as you build the box. This will help ensure proper angles and help seal off the corners from pressure.

To figure airspace, find the volume of your box, Length x Width x Height, and divide by 1728 - that's the number of cubic inches in a cubic foot. If you're metric, do the conversion - just because I think America should switch to metrics doesn't mean I know 'em yet. Remember to find the volume of all the crap that's going in the box, and subtract it from the total space - i.e., a 12" by 2" brace made of 1" thick wood will subtract 24 cubic inches from your volume.

To convert a round port to a square vent for building ease, square the radius of the recomended port and multiply by pi, the length remains the same. So a recomended 4" port 10" long becomes a sqaure or rectanglar or whatever you want vent with 12.57 inches of surface area, still 10" long. The radius of a 4" circle is 2", squared, times pi - 2 x 2 x 3.1417 = 12.5668. Take the port surface area and multiply it by the length to get the port volume, don't forget to subtract that from your box volume!

[MX-SLICK]

In all my years installing, ill pass on a few myths people have seemed to come up with over the years.

1. "bandpass boxes blow your subs"

Well, no...why would they? Bandpass in a reversed sealed enclosure with a tuned airspace.

2. "Ported sounds way better and is way louder"

yeah, in some cases it could sound a bit better, but on average you gain 3 DB total from a ported box.


3. "Stuff your sub box full of insulation or foam"

Aside from fiber particles being sucked up like a vaccum into your voice coil vents in the magnets, this will just artificially increase the box size, making the subs Xmax at lower volumes. Just build it right the first time.

4. (non subs ..but)

"get a cap to solve all of your power problems"

I can think of at least 5 things wrong about this, but a cap is a neutral buffer to avoid sudden surges from heavy bass....not a miracle tube. If your not puting out enough power your not getting enough power.

5. "if you want good subs, buy audiobahn"

if you want good subs, DONT buy audiobahn
alot of people will say audiobahn is awsome because it 'slams' and 'thumps' but so do cheapo pyrmid/pyle/legacy/sony xplodes ...but they dont sound good compared to a quality system, all they do is 'slam'

[TekPmp]

Great write up and facts guys! Got my vote for the FAQs

[reaper of souls]

3. "Stuff your sub box full of insulation or foam"

Aside from fiber particles being sucked up like a vaccum into your voice coil vents in the magnets, this will just artificially increase the box size, making the subs Xmax at lower volumes. Just build it right the first time.

on everything else you said i agree with you but as for stuffing boxes building the box right the first time doesn't all ways work some subs ask for way more air space then a mx-3 could offer so sometimes you have to stuff i on the other hand recomend building a aperodic enclosure if you can't supply the full space. example was on a friend of mines civic we cut out a hole in the floor boards just below the fire wall and installed two 8" kicker comp series subs made a fiberglass box outside the car and placed a verio vent in each enclosure as a controlled leak if you ever want to have a music experice in your car try putting your subs in front of you it'll put the entire sound stage right in front of you . aslo we had to make custom kicks just to get the whole thing time aligned. but stuffing is just a bandaid when it comes to improperally designed boxes i have to agree with you on that much

[manowar821]

I think the stuffing is a good idea in any system where you will be playing the volume at higher levels. I'm not talking about the amount of airspace the sub wants, I am talking about the reflections coming off of the back of the cone, hitting the back of the box and then hitting the back of the cone again. It can get nasty, and stuffing actually solves this problem.

I think that the whole "creates a bigger box effect" is just an illusion caused by other improvements that the stuffing adds.

[Chosenrifter]

I need a Custom Sub Box for my Mx-3 anyone know where I can get one?

[chew*]

I have a few things to add.

Some rules i've learned in my years of doing competiton.

1. You can only output as much power as you input........This doesnt mean you need a 10,000 watt amp it means a 1,000 watt amp usually only outputs 1,000 watts in a pefect world. What this means is you need to upgrade the whole chain. Etc upgrade grounds and power feeds over the stock. Upgrade alternator amperage. Use the largest wire possible, I use 1/0 guage in all my applications sometimes multiple runs. Never ever go from small wire to larger....always go down or stay the same size. I've seen fires caused by this. This goes for wiring in the box also.

2. To increase bass you need more space. The common rule of thumb is whatever your box displacement is you need the same equal volume to get the most sound. For instance a 1 cubic foot sealed enclosure would be best used corner loaded etc fired at a 1 cubic ft corner. In my particular case I use a 4 cubic ft box fired into a 4 cubic ft area in the hatch. If i take away lets say 1 cubic ft and put a spare tire in the spare tire well i lose 3db. So take this into consideration when buliding a box also. A bigger box with more subs isn't always better.

3. 1 speaker is always better than 2. I usually buy the best single sub i can afford versus buying 2 cheaper subs. Running a single sub is more efficient and also alot cleaner.

4. Caps or also known as Capacitors have no place in SPL competitons, so if your interested in SPL don't waste money on caps. Instead invest it in Batteries, this goes hand in hand with #1

5. Sound deadening material such as dynamat is not the SPL miracle that most think it is. It does wonders to stop rattles and improve frequency response inside the harsh confinements of a car but chances are you will not gain 3 db from using dynamat. In fact in some cases you can lose SPL.

6. Amps don't blow speakers. Speakers blow amps. Distortion blows speakers. Incorrect box specs blow speakers. I personally have heard alot of people slam Kickers solo X line of subs and the fact of the matter the speaker is finicky as far as enclosures go and most people build an incorrect box for it and end up shattering the cone......

Also might mention that part of your info on the ported box is incorrect and ill explain why.

"The ported box is a more sophisticated version of the sealed enclosure. This type of enclosure also works by containing the rear wave, but adds a tuned port that interacts with it in a very specific manner at certain frequencies"

The reason why this information is incorrect is that the port in itself acts as a virtual speaker. Also In SPL applications which the port is very critical, the key is to couple the front wave of the speaker with the rear wave of the box, thus a ported box does not contain the rear wave.

[chew*]

I need a Custom Sub Box for my Mx-3 anyone know where I can get one?

http://www.gforceperformanceaudio.com