How to figure a subwoofer cab size...

halo71

....when you know the brand but not the model sub? I have 2 Pyle Driver 10" subs that I used several years ago in my truck. Nothing at all special about them. But I already have them, MDF, plywood etc and would like to "try" to use them. So I would like to build a cabinet and put them in my daughters room. Along with a set of Mirage M590i's.

I need help figuring out what size cabinet(s) to make. I do not have the original boxes nor remember their size. The Mirage are great sounding speakers but pretty weak in the bass department. This may just be a shot in the dark but anyone have any ideas?

FTGV

If you can get the model # then you might be able to do a search and get the T/S paramters like Qts,Fs and Vas.If you do obtain those specs then you determine a usable volume by entering the data into a simple calculator program like http://www.mh-audio.nl/ClosedBoxCalculator.asp or a more involved one like this.http://www.linearteam.dk/default.aspx?pageid=winisd

ShinAce

Unless you test the specs yourself, all you can do is build multiple boxes and choose the best sounding one, or use manufacturer suggested specs.

If they're going in a car, the design is usually a high Q(sloppy bass) design.

If you do build a box yourself, build one bigger than you think is needed and then start filling it with sealed water bottles to get the volume down progressively. That way, you build one box and test many volumes.

Likely more work than they're worth. More of a bonding with kids type project than a useful one.

edit: FTGV's second link is a great piece of software with a HUGE database of drivers. Still, specs can change from one batch to another, and even from one speaker to another in the same batch. They're not foolproof.

FTGV

ShinAce wrote: »

Still, specs can change from one batch to another, and even from one speaker to another in the same batch. They're not foolproof.

True ideally one would want to measure the parameters of each driver but the manufactures spec's should get you in the ball park and let you figure out something usable.Without parameters as Shin suggest's a sealed box and guestimating it's volume will be your only option.

F1nut

T_unit recommends an Amsoil box. I believe a hole was optional.

dorokusai

I certainly wouldn't waste time building multiple boxes for a Pyle driver. I'd compile as much information as you can about it, average some other generic drivers of the same size and make a good guess. You can always play with the internal volume a bit to tweak it as its just for your daughters room anyways. I'm sure it will be fine for that application.

Don't overthink it....but most people do anyways, see above. You should bookmark the links at least.

Jstas

You should ask the car audio guys. They build sub boxes all the time.

halo71

Thanks guys. I will play around with a box size. I have a box built from a project last year that was going to be a toy box that never got finished. Cabinet grade plywood with oak trim. Thinking I may cut it down and adapt it to fit both the 10" drivers.

She wanted my Monitor 10's. I told her she could have them if mommie would let me get some SDA's.:D

Mommie said no.

kawizx9r

^ lol

Have fun with it I'd say. Make it look like a piece of furniture!

Should see the Rubik's cube sub on Rythmik Audio, or a few other builds on the DIY Forum

Good on the little one wanting those Monitors! Next thing you know she'll want your MIT speaker cables and more haha

halo71

kawizx9r wrote: »

Good on the little one wanting those Monitors! Next thing you know she'll want your MIT speaker cables and more haha

She is 11 and I have had no luck so far trying to turn her onto jazz, blues, classic rock.....or just about anything I like. Sadly she is into the hip hop stuff. :rolleyes: She does kinda like Candy Dulfer and Sarah Mclachlan, so ALL hope is not lost I guess.

Funny you mention the MIT cables. My father-in-law saw them the other day and asked what the hell I had wired up that needed so much power to warrant such big cables! :rolleyes:

Jstas

OK, now that I have more time and it seems no one has given you the accurate answer, I'll esplain.

Vas
Measured in litres (L) or cubic metres, is a measure of the 'stiffness' of the suspension with the driver mounted in free air. It represents the volume of air that has the same stiffness as the driver's suspension when acted on by a piston of the same area (Sd) as the cone. Larger values mean lower stiffness, and generally require larger enclosures. Vas varies with the square of the diameter. A typical factory tolerance for Vas spec is ±20–30%.

Vas is a Thiele-Small Parameter. Essentially, it is a measure of, like the quote says, stiffness. But not stiffness of the cone in a conventional sense.

Air is made up of gases. Gases compress. But, at a certain point, the energy needed to overcome the resistance of the gas to compression is greater than what the driver can produce through mechanical means.

Think of it this way. Blowing up a beach ball with your mouth, it's really difficult to pop it by overfilling. This is because your lungs do not posses enough volume of air, enough CFM or enough compression force to fill the beach ball beyond it's physical limits. An air compressor on the other hand, well it can pop it like a zit if you want it to. But it has 20 times the volume, CFM and pressure you do.

A speaker driver moves air, just like your lungs. That's how it makes sound. It moves air by oscillating the cone. The cone movement compresses the air in front of it to create a pressure wave which then hits your ear drum. Your ear drum vibrates from it and your brain translates it in to sound. We know that, right?

Well, "volume" is known as SPL which is sound pressure level. It is a physical limitation of the driver to be able to produce a certain amount of pressure in that pressure wave at a given power level. You know, measured at 1 watt at 1 meter?

Well, that pressure wave can only move a certain amount of air. It can only compress the air so much. When you compress a gas, resistance goes up exponentially as compression increases. At some point, like blowing up the beach ball, the pressure in the enclosure gets to be too great for that driver to work without distorting. That's "stiffness".

When building an enclosure, you want that pocket of air behind the speaker to be large enough to provide enough volume that it matches what the driver's suspension can act on when controlling the motion of the driver. It essentially acts like a trampoline and assists the motor structure of the driver in controlling the cone. If you make the box too large, you can over extend the driver because it cannot build enough pressure in the back wave to compress that air pocket to it's Vas rating. It makes for a boomy, **** mess and lotsa port noise. If you build it too small, you pressurize that pocket of air too soon and you can actually truncate the performance range of your speaker. It makes for tight, accurate, punchy bass but not very loud bass.

So, if you want to know how large to build a box, your internal volume should be as close to the Vas as possible. However, Vas does not take in to account the volume of the driver in the enclosure. So, if you have a driver that is .13 cubic meters in volume and a Vas for that driver of .53 cubic meters then you need an enclosure that is .66 cubic meters internally to get the .53 cubic meters you need to get the ideal Vas for that driver.

Make sense?

Wikipedia actually has a good article on Thiele/Small parameters:

http://en.wikipedia.org/wiki/Thiele/Small

Also, http://www.math.com is a good site with lotsa tools for helping you out with calculations. I use it all the time.

Jstas

Here, to find the info on your Pyle drivers: http://www.pyleaudio.com/mdownloads.asp


If you can't find the info, usually Vas is pretty common among drivers. Since it's a physical measurement, unless it's some super exotic material like titanium or aluminum or carbon fiber or even fiberglass, a 10" driver will typically have a Vas of around .45-.65 cubic feet plus the volume of the driver. A 12" sub will typically have a Vas of about .65 to 1.3 cubic feet plus the volume of the driver.

Lighter cones cannot usually compress the pocket as much as heavier cones. But lighter cones are easier to move so sensitivity is higher. So if your sub has a sensitivity rating of 97 dB then it's a light cone, flexible motor structure and surround and a moderately sized magnet. If your sub has a sensitivity of 85 dB then it's likely a heavy cone with a massive magnet, beefy motor structure and heavy surround or maybe even multiple voice coils.

Pyle drivers are far from the top echelons. They are usually fairly sensitive and easy to drive so they will make a bunch of noise for you. I wouldn't go super big on them. Maybe around .65 cubic feet total. Basically, build the box to .65 cubic feet or as close as you can get to that and that should be enough to push the driver. That's if you are going sealed. If you are going ported, .85 cubic feet at least, maybe even 1.0-1.2 cubic feet.

If you want to build a box to mess around with, make it on the larger side. Then, to change volume inside the box, just cut some pieces of wood with, say, .1 cubic feet of volume each. Then, if you want to change the volume of the inside of the box by say, .5 cubic feet, screw 5 of those .1 cubic foot blocks inside the cabinet, remount the driver and test again. Once you figure out the size, build a new box with your figured size and go to town.

ShinAce

Vas is not the best box size. It is a measure of the speaker's compliance. As explained earlier, it is how much 'spring' the speaker has. For example, you can inflate a car tire and it doesn't change size much. A tire has a tiny Vas and is not compliant. A balloon can stretch easily with a little air pressure. A balloon is very compliant.

A mix of Qts and Vas gives you the 'ideal' box size. Ideal having a Q factor of 0.707 when it's mounted to the box. All this is different for vented boxes.

Again, not worth your time. Use manufacturer suggested specs if you can find them.

Jstas

ShinAce wrote: »

Vas is not the best box size. It is a measure of the speaker's compliance. As explained earlier, it is how much 'spring' the speaker has. For example, you can inflate a car tire and it doesn't change size much. A tire has a tiny Vas and is not compliant. A balloon can stretch easily with a little air pressure. A balloon is very compliant.

A mix of Qts and Vas gives you the 'ideal' box size. Ideal having a Q factor of 0.707 when it's mounted to the box. All this is different for vented boxes.

Again, not worth your time. Use manufacturer suggested specs if you can find them.

Really? Care to explain what this "mix" of Qts and Vas are? I mean, since you are so knowledgeable, maybe you could help the rest of us out? Or are you just regurgitating what one of the calculators out there tells you?

'Cause I know what the math is. Do you? Do you even know what values and measurements you need to find Qts? Is Qts a measured value or derived?

Or do you mean Qtc which explains the value of the resonance of the entire enclosure, including driver?



If you want to find Qts, you need to calculate it from measured values. Qts has no units because it's not measured but derived. You need the Fs which is the free-air resonance plus the Fh and Fl, the high low range of the resonance on a -3 dB slope. Ideal enclosure volume is related to but not directly proportional to Qts. Qts changes as Fs changes. Fs can change with the amount of air space allowed for the driver. The "Q" is the ratio of electrical resistance to mechanical reactance.

An example of deriving Qts: Qts = (Qes * Qms) / ( Qms + Qes )

Qtc = Qts * [ ( Vas / Vb ) + 1 ]^1/2

Qms = (2pi * Fs * Mms)/Rms

Qes = (2pi * Fs *Mms * Re)/(Bl)^2

Technically, Vas is not the most descriptive term either. However, Vas is measured and has physical properties. It won't totally define how large your box size should be but in the absence of other measurements, it's a good place to start.

What will really tell you the needed size of the enclosure is Vb. Wanna know how to get that?

Here, an example: Vb = Vas/{(Fb/Fs)^1/0.31}

I'm not going to go in to this any further 'cause I don't have the characters I need available to me to write it all down properly.

You want to learn how to build enclosures and you don't want to have to listen to people on the Internet? Get this book:



http://www.amazon.com/Loudspeaker-Design-Cookbook-Vance-Dickason/dp/1882580109

It should be in every DIY'ers library even if it's just for reference. I learned alot from my copy (if I can find it again, think someone stole it, it was a 2nd Edition though) and I've managed to build competition winning subwoofer boxes with the methods and concepts presented in that book.

halo71

Jstas, thanks for the infor and the link!
My problem there is that these drivers have no serial or model numbers on the back. Just the Pyle logo. I bought these sometime in the early 90's. And from what I understand the earlier ones are of "better" quality than the later ones they made. I use "better" very lightly there! lol

ShinAce wrote: »

Again, not worth your time. Use manufacturer suggested specs if you can find them.

Thanks, but I got more time than money. I already had these drivers.

halo71

Was playing around with different cabinet sizes. The bottom half was about twice this size and the bass was rather loose and boomy. So I cut the cab size down and came up with this. The XO tweeter and midrange are from a pair of old Cannon TLS speakers from the late 80's I had. Overall they sound much better than I had imagined they would! I will probably go back and shorten the baffle moving the mid and tweet lower.

So go ahead and laugh! Its my first attempt at building something like this.

Joe08867

Awww isn't that cute. Just playin,

Are you having fun? That is all that matters.

Did you use any fill in the box? Could help with the looseness.

ShinAce

Jstas wrote: »

Or do you mean Qtc which explains the value of the resonance of the entire enclosure, including driver?

Do you understand than you just proved me right?

Jstas

If it's loose and boomy, two issues might be there. One, the enclosure is just too big for the woofer. By the look of your pictures, that might be true.

Two, the enclosure might leak. Even a small leak can vent enough pressure so that the air pocket that the enclosure contains never gets pressurized enough to reach that Vas number which is where you want to be for optimum performance.

When I'm building a box, I glue all joints and nail or screw them together. Nails are good for plywood or solid wood but MDF requires screws. When the box is done, I run a bead of caulk along every corner inside the box and smooth it off with my finger. Provides a good seal and helps eliminate sharp corners which reduces standing waves and uneven pressure inside the cabinet. I also make sure any terminal cups are sealed and I will typically make my own gasket for the sub mounting ring because, aside from Polk Audio, most companies send junk with their subs.

So if you're just testing right now, that's fine but don't be too concerned over a bit of loose and boomy. If it's a crazy amount, change the box size. If it's not, and it just gets muddy on certain material, finish off the box and seal it up. That should help it out.

BTW, polyfil doesn't get rid of boominess. Polyfil is a defractive material and it slows down the backwave. This basically makes the enclosure take slightly longer to pressurize the airspace. It essentially makes the box perform like it's bigger than it is. A small amount lining the sides can help with taming resonances or even slowing down port speed in a vented enclosure but if the box is boomy to begin with, polyfil will only exacerbate the problem.

ShinAce

Jstas wrote: »

If it's loose and boomy, two issues might be there. One, the enclosure is just too big for the woofer. By the look of your pictures, that might be true.

Two, the enclosure might leak. Even a small leak can vent enough pressure so that the air pocket that the enclosure contains never gets pressurized enough to reach that Vas number which is where you want to be for optimum performance.

When I'm building a box, I glue all joints and nail or screw them together. Nails are good for plywood or solid wood but MDF requires screws. When the box is done, I run a bead of caulk along every corner inside the box and smooth it off with my finger. Provides a good seal and helps eliminate sharp corners which reduces standing waves and uneven pressure inside the cabinet. I also make sure any terminal cups are sealed and I will typically make my own gasket for the sub mounting ring because, aside from Polk Audio, most companies send junk with their subs.

So if you're just testing right now, that's fine but don't be too concerned over a bit of loose and boomy. If it's a crazy amount, change the box size. If it's not, and it just gets muddy on certain material, finish off the box and seal it up. That should help it out.

BTW, polyfil doesn't get rid of boominess. Polyfil is a defractive material and it slows down the backwave. This basically makes the enclosure take slightly longer to pressurize the airspace. It essentially makes the box perform like it's bigger than it is. A small amount lining the sides can help with taming resonances or even slowing down port speed in a vented enclosure but if the box is boomy to begin with, polyfil will only exacerbate the problem.

Dear god no!

Boominess is usually from the box being too small. This raises Qtc and causes a peak around resonance. Hence the boom.

Adding fill does make the box 'look' bigger to the driver, because it changes the air inside the box from adiabatic to isothermic. By absorbing heat changes, the air is more compliant(looser, let's say).

So if the box is too small, adding fiberglass will smooth out the boominess.

Might I suggest you read the book you're referencing?

Best bet is to shoot for a box that is too big and then add stuff inside it to bring the volume down. Once you reach a point where it sounds good, take the initial box volume minus whatever volume you've blocked off and that's the box size you want.

p.s. I'm 100% for stuffing sealed boxes. It makes a smaller box act like a bigger one, so helps your wife approval factor. It also absorbs sounds(mostly midrange) bouncing around the inside, so it reduces distortion. If that unwanted sound gets absorbed, it can't come bouncing through the speaker cone and out of the box.

Has anyone seen specs for the speakers? Which model is it?

Jstas

ShinAce wrote: »

Do you understand than you just proved me right?

Do you understand that no where in your post did you mention Qtc and instead referred to Qts as the value that is important and tried to explain with the explanation for Qtc?? Your entire post was wrong because you do not understand the terminology or relationships of the values.

Overall, unless you have the enclosure assembled and are trying to match a driver, Qtc has no bearing on building the enclosure. It defines the resonance of the enclosure and driver together. If you're building the enclosure to match the driver, you can't even determine Qtc because you don't have the airspace measurements needed to calculate the Qtc of the enclosure. It really only matters when dealing with vented enclosures so that the port tuning can be done to compliment the enclosure rather than fight it. Unless you are going for maximum SPL then it's a whole different scenario.

Here's a link for some explanation on Qtc and why it matters:

http://www.carstereo.com/help/Articles.cfm?id=29

If you want to, use the .707 value for Qtc and follow the equations, entering the Thiele-Small parameters for the driver...oh, wait, that's right, halo71 said he DIDN'T HAVE THEM!


The OP stated he was using a sealed enclosure so why would Qtc even matter for anything more than just efficiency of the enclosure? Especially if he's going to test it out before finalizing the design? Wait, you know what? Don't answer that because I know you don't know and you're just going to come back with a trollish response. I'll just put you back on the ignore list.

Face

This is just going to be a garage speaker, right?

FYI, that mid should probably have an enclosure behind it.

Joe08867

Face wrote: »

This is just going to be a garage speaker, right?

FYI, that mid should probably have an enclosure behind it.

I was thinking the same about the Mid but it looks like it is solid backed and not open. Makes a slight difference but still think it should be enclosed though.

Jstas

ShinAce wrote: »

Dear god no!

Boominess is usually from the box being too small. This raises Qtc and causes a peak around resonance. Hence the boom.

Adding fill does make the box 'look' bigger to the driver, because it changes the air inside the box from adiabatic to isothermic. By absorbing heat changes, the air is more compliant(looser, let's say).

So if the box is too small, adding fiberglass will smooth out the boominess.

Might I suggest you read the book you're referencing?

Best bet is to shoot for a box that is too big and then add stuff inside it to bring the volume down. Once you reach a point where it sounds good, take the initial box volume minus whatever volume you've blocked off and that's the box size you want.

p.s. I'm 100% for stuffing sealed boxes. It makes a smaller box act like a bigger one, so helps your wife approval factor. It also absorbs sounds(mostly midrange) bouncing around the inside, so it reduces distortion. If that unwanted sound gets absorbed, it can't come bouncing through the speaker cone and out of the box.

Has anyone seen specs for the speakers? Which model is it?

First off, thanks for "paraphrasing" the post you just referenced as well as my previous post and reiterating what I already said.

Secondly, boominess comes from a lack of control over the driver. If the enclosure is too small for the driver, it restricts performance and drops the efficiency of the driver in the enclosure. It doesn't make things boomy. If anything it makes the driver distort. The amplifier will also have more trouble driving the sub because of the higher load but it won't be boomy. It will just not play at the same SPL as a more efficiently designed box.

As far as your fancy words, again, using terminology you do not understand. Adiabatic refers to a process that occurs without heat transfer. That would be any enclosure, honestly. There is no such thing as an "Isothermic" process. It's Isothermal, it has a suffix and a root that is important. An isothermal process is a change of a system where the temperature remains constant. This change typically occurs when a system is in contact with an outside thermal reservoir and occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange. An adiabatic process is where a system exchanges no heat with its surroundings. Please, let the class know where the external reservoir of heat is? Compression is an endothermic reaction so any heat generated does not come from an external source but within the process itself.

Also, you know why gases get "looser" and " more compliant" when heated? 'Cause they expand. When they expand, it takes more energy to compress them. So if you have a cold box with a Vas of .53 cubic meters and you stuff it with polyfil to change the behavior of the box, you slow down the compression process. It slows down because the air mass now retains more heat and expands creating a more difficult volume to compress. This means it takes the driver longer to reach that Vas number so it can perform at the optimum Qtc. Sure, you can say that the added heat to the system can help the compression efforts but the gas is still trying to expand and creating a greater oppositional force against the mechanical movement of the speaker cone. That greater expansion force against the cone cancels out any pressure building benefit the added pressure from heat expansion would gain.

Lastly, if you are, again, going to reference Qtc, get it straight. F3 increases for values ABOVE OR BELOW 0.707.

You should stop cutting and pasting from websites and talking out your butt before you hurt your brain.

ShinAce

Jstas wrote: »

Lastly, if you are, again, going to reference Qtc, get it straight. F3 increases for values ABOVE OR BELOW 0.707.

You should stop cutting and pasting from websites and talking out your butt before you hurt your brain.

I did. I said "Ideal having a Q factor of 0.707 when it's mounted to the box." That is Qtc! You're the one putting words in my mouth.

My specialty is designing sub boxes. Then followed by a decent understanding of passive crossovers.

The two best pieces of advice in this thread are posts 2 and 3.

I assume the OP will not be measuring an impedance plot of the raw driver and then measuring Vas. Giving him box design advice is not warranted. He can't use it.

Here's one for you. I have a speaker with a Qts of 1/sqrt(2) . It has a Vas of 5 ft^3. What size box do I use to have a Qtc of 0.707?

halo71

I said the cab was rather boomy and loose before I cut it down to its present size. I added fiberglass to the insides. Bass is much tighter and defined now, well as much as one can expect from a cheap driver like these. The cabinet is glued and screwed together with 1 brace inside. And joints are all caulked as well.

Face, the mid is a sealed back driver. Perhaps I am wrong but I was under the impression it didn't matter if it were in a cabinet or not unless it was an open backed driver.

And yes, just garage speakers. The wife seen them yesterday and says...."just in case you were wondering, there is no way in hell those are coming into the house!" :eek:

Face

Ok, I couldn't tell on my monitor, good.

Jstas

You gonna paint them or anything?

If they are going in the garage, I'd cover up the crossover components so something doesn't like fall on one and break it.

Nice deal though. Looks good!

Are those compression horns screechy at all? If so, some acoustic foam on the wood around the outside of the flange can help tame reflections off of the front of the baffle. It'll quiet them down a bit. Kinda like what's on the front baffle of the AR9s.

Face

FYI, those drivers should be grouped closer together. Guessing by the parts count, you're using shallow slopes, which requires the drivers to be within a certain distance of each other for the best integration. For example, if the crossover frequency of the mid to woofer is 700hz, the center to center distance should be 8.5". With steep slopes(4th order+), this is less of an issue.

halo71

Horns are not bad at all really. The XO has a mid/tweet control to tame things. I may paint them black. Not sure yet. Think I am gonna shorten the baffle though and move the tweets and mids a little lower.

On the original cabs, which are trashed now. The mid and tweeter were really close to the woofer. This design also incorporated a 12" PR with the original 12" woofer. I had 2 sets of these speakers, 1 set still complete minus 12" drivers needing refoamed. And the drivers etc out of another set that I used here, except for the 12" drivers. Next project is to buy a refoam kit and redo them.

Jstas

If you want to dress them up, you can get grill stanchions from Parts Express. Get a sheet of 1/2" or 1/4" MDF and cut rectangles to cover the front of the baffle for them. Then cut large rectangular holes, leaving some crosspieces for strength where they won't interfere with drivers. Get yourself some acoustically transparent speaker cloth, 3M trim adhesive and a staple gun (with staples). Cover the grill surfaces that the cloth will be stretched over with the adhesive. It keeps the cloth from slipping or getting tugged unevenly. Then, when the adhesive sets up and the cloth doesn't move, fold it over the side and staple it to the back. You can put adhesive on the sides as well if you want. Drill your holes for the grille stanchions and install them on the front of the baffle.

You could probably build a wood frame from some dowel or rip down a 1x4 or a couple of 1x2s in to 1x1 inch pieces and make a removable framework to stretch some grille cloth over. It'll help keep dust and gunk from the garage off of the backs of the exposed drivers and the crossover network.