Dimensions for sealed 18" sub box - Page 14

I should be making an IKEA run this weekend to West Chester if you want me to swing a 12 spoke basket by (Fi built). Shoot me a pm we can work out the details

Any info on whether or not there's going to be a box in the 2.5-2.75 ft^3 range?

at that point, you are going past the point of driver protection and just making the enclosure inefficient.

in cars where you get a whole boatload of pressure vessel gain, very small sealed subs can be okay.

in a home theater/home media room, you just end up needing twice the amp in the smaller enclosures which raises the price of the system quite a bit.

the 18-ho is 107db at 20hz in model in 4 cubic feet.

the 18-ho is 103db at 20hz in model in 2 cubic feet.

that is 3-4 times the power (figuring in a hair of compression) for the same output.

not recommended.

Hey LTD02.

The Dayton 18" HO in 4.5cuft is limited to about 300 watts if Dayton/Eminence's claims of 12.8mm xmax are to be followed. I would rather shrink that box since watts are cheap nowadays to allow for more power handling. You can go as low as a 2.5cuft box for a single driver and with advanced DSP nowadays like the MiniDSP or Audyssey you don't have to worry about the box Q before these awesome inventions.

But not always avoidable I'm afraid. Aesthetics, placement considerations -- and various other factors -- often dictate enclosure size. That's the case here. FWIW... I was actually looking at the 15", not the 18". 2.5 ft^3 does seem a little constrained for an 18" driver, unless it's the Cap S1 of course...

"The Dayton 18" HO in 4.5cuft is limited to about 300 watts if Dayton/Eminence's claims of 12.8mm xmax are to be followed."

ricci just measured them to at least 20mm. 4 cubic feet at 1000 watts takes them to 20mm excursion at 10hz. i was edging on the conservative side and knocked it down 1/2 a cubic foot.

"Aesthetics, placement considerations -- and various other factors -- often dictate enclosure size."

agree. i was just saying that for the same performance in the tiny enclosure, you'd need twice the amp or more. if that is a good tradeoff in your system, cool.

With cheap watts and DSP nowadays I like a smaller box so you can turn up the volume down low with an LT/shelf filter for sealed boxes which is essential for good performance. The added travel is gravy but unless I am wrong isn't xmax were the driver begins to reach about 10% THD or the bl begins to fall off? Of course there can be added travel but you don't always want to model to that point as that is when distortion begins to rear it's ugly head.

From personal experience I have always had better performance from a smaller box than a larger trying to get to that magical .7 enclosure Q range which is just not needed in the age of cheap watts and DSP. Even Ricci's enclosure Q is going to be up there with his 9 cuft dual opposed XXX 18" which is normally the size for a single XXX 18" in sims.

Personally I think 3cuft would be a better all around size for the 18" HO and if you had enough power and DSP knowledge you can go a little smaller. You get more natural low end from a bigger box but you lose out on power handling which is needed for a boost down low for sealed designs.

"You get more natural low end from a bigger box but you lose out on power handling which is needed for a boost down low for sealed designs."

yeah that is kind of the myth that i was talking about. it isn't so much that tiny sealed subs have twice the power handling as they are half as efficient so they require twice the power for the same performance.

Myth, really? When you can get close to 2000 watts from the EP4000 bridged in the $300 range it's not like trying to catch a unicorn

"Myth, really? When you can get close to 2000 watts from the EP4000 bridged in the $300 range it's not like trying to catch a unicorn"

not sure about the unicorn reference, but yeah, that is what i was talking about.

if it takes twice the power to reach the same spl, then the system can be said be 1/2 as efficient.

instead of being able to "take twice the power", a better statement might be that it "requires" twice the power for the same spl down low.
Edited by LTD02 - 11/6/12 at 12:05am

I have built multiple boxes for the same driver but feel that the advantages of a smaller box with the availability of cheap watts and DSP should be taken advantage of now, I guess you disagree. Your point is true but is not necessary as it was in the past when big amps were too expensive and DSP was not readily available to the DIY'er.

There really is no reason to argue the point with you anymore, I have read enough posts between you and Bosso to know this is going nowhere.

So would the Dayton 18" HO in a 4-4.5 cu ft box and a 500w bash amp be sufficient? Or would I need more than 500w (I already have a 500w bash amp sitting doing nothing).

Xmech on this driver is 32.25mm. Useful excursion is about 20mm. Geometric xmax is 12.75mm.

In a 4.2 cubic foot sealed enclosure this driver will take all of a 1400w amp channel without issue. Put it in 3 to 4.5 cubes sealed and give it 1000-1500w of amp. EQ to taste. Done.

One thing that is often missed with very small sealed boxes is that your excursion peak ends up being not at 5Hz or 10Hz or anywhere in the low bass and instead ends up being much higher in frequency depending on the particular sub. This despite what models might say about the excursion. They do not include the driver behavior and non linearity inherent at 2.5" peak to peak excursion. So while your driver may be safe in the deep bass it may not be at the excursion peak which could be at 20Hz or even 25Hz.

X100000!

Erich - From the sounds of it, this is going to be a very popular combo! I'm going to order a handful of these soon and I'd be happy to be a test bunny,.

Hey, Josh. When I use the T/S numbers you derived from the 18HO in Unibox and plot out for a 4.2cuft sealed box with 1,400w I get this:



Seems like one would get pretty close to Xmech with that much power. Did I mess something up? Does this seem reasonable? To me it seems like it would be a good idea to skip out on 1dB ~10hz and use a 3.5cuft cab with that much power.
Edited by Scott Simonian - 11/6/12 at 3:00pm

I was seeing the same things Scott, this is why I was lobbying for a smaller flat pack. I also thought a smaller flat pack would allow for lower costs so 3 to 3.5cuft would make more sense.

The sweet spot seems to be between three and four cubic feet, imo. I wouldn't go any smaller for home use personally. 3cuft sounds good but it really depends on how one plans to power them. I've pondered a cheap multi-driver system for a rear subwoofer in my room with these drivers powered by a single ep4000 which gives roughly 400w per driver. In that case I could easily go with 4cuft or more with no worries. If someone wants to put +1,000w into each driver... no more than 4cuft, for sure.

"Xmech on this driver is 32.25mm. Useful excursion is about 20mm. Geometric xmax is 12.75mm."

holy crap. that is a nice fat margin of error for safety. great data josh.

scott, like ricci mentioned, once you start moving the driver in and out of the enclosure 30mm, it is going to start to run into things like significant air spring effects, significant bl rolloff, etc.

the thiele small numbers are for "small signals". all kinds of other schlock occurs when "large signal" are run through a driver. it is how a driver responds to large signals that is one of the principal reasons for klippel analysis.

That's true. I guess I model in the direction of some safety. Don't mean to come off like a know-it-all but I know better but not everyone will. Don't need people destroying their drivers ala recent LMS-U builds.

'test bunny' or 'dead duck'? Your wife is gonna string you up someday! What on earth do you need more subwoofers for? Dual Caps not enough any more?

See my thread in this section.

"Don't mean to come off like a know-it-all but I know better but not everyone will. Don't need people destroying their drivers ala recent LMS-U builds."

+1.

Do my eyes deceive me? You're moving the Caps out of the basement HT??? You'll be labeled a heretic/turncoat/pagan/defector by Archaea!

Guess that means your wife hates every last one of us for planting this seed in your mind, eh? I suppose no more GTG's at your house now...

Winner winner chicken dinner.

Let's just say I'm doing some experimenting. Archaea is aware I'm getting the urge to try some new things, although he might not be too pleased.

So far my wife hasn't really complained...might as well schedule the next event now before it's too late?

Might not be a bad idea. At least this way we can all get a chance to see your 'experiments' before she changes her mind...

They are not the same (weight) but I'm not going to drag this out anymore...I cannot speak precisely for the plywood you're using though because I haven't seen it.

Every 4x8 3/4" sheet of TRUE BB I've ever handled/used hasn't weighed more than 85lbs (most are around 82)...it varies a bit on the type and amount of adhesive used, but certainly no more than a few pounds, tops. Yes I have a scale in my shop and can easily weigh them.

That said, virtually every sheet of 3/4" MDF on earth weighs at LEAST 94lbs with many nearing 100lbs depending upon species/adhesives utilized- with more and more poplar thrown into the mix, that has added a few more pounds per sheet.

Check here: http://www.wolstenholme.com/pdf/Baltic%20Birch%20Plywood%20Specifications.pdf

Check the MSDS' on either product.

Pick up a 4x8 sheet of either.

They do not possess the same mass.

But thanks again for all of the work you're doing.


James

Correct...If you are using more power move towards the smaller box, if using less power move towards the larger box.