Enclosed Box for DD Subwoofers?

[hispls 5,000+ posts]

Lots of bad advice here. Yes low Q subs are more suited to ported alignment. They will function in sealed box, but generally won't sound great. The difference between even 50% difference in volume in a sealed box isn't really that pronounced so I wouldn't worry so much about doing sealed box(es). If they're in a box now try to screw a block of wood over the port to seal it up and give that a try, if that helps than there you go.

I suspect your box is tuned too high and you're bottoming out the woofer, or pushing your amp into heavy clipping (more likely bottoming out). Sealed enclosure, tuning lower, or using subsonic filter would be solutions.... none of which really optimal since DD is designed for pretty specific alignment.

 

[jonathanengr1 10+ year member]

Tell you what... let me run outside in a few mins and take the measurements so I can post them here. I did drop by the audio store where I bought them, and he measured the box to calculate the volume. He measured the full box dimensions (minus the thickness of the MDF) to calculate the volume. I didn't think you included the port volume, be he says that you do. The port isn't supposed to be considered in the volume, is it?

Anyway, gotta do a few things and I'll post the dimensions back ASAP.

 

[jonathanengr1 10+ year member]

Okay--here are the dimensions... Let me know if you need a drawing and I can whip one up in AutoCAD and save it as a jpg file.

The box is made from 0.75" MDF, and the EXTERIOR dimension are 18.5"x13"x28". The port opening is 4"x11.5" for an area of 46 sq in. The length of the port (length of the internal board creating the port) is 23.5".

Now... what is the "area" of the box? I would assume you do NOT include the port--is this correct? If so, the internal dimensions would be such:

18.5" -1.5" (material thickness) -4.0" (port depth) = 13"

13" - 1.5" (material thickness) = 11.5"

28" - 1.5" (material thickness) = 26.5"

Volume = (13" x 11.5" x 26.5") / 12^3 = 2.3 cf.

Now, if the port SHOULD be included in the box volume, then it's an additional 4.0" x 26.5" x 11.5" / 12^3 for a total of 2.3 cf + 0.7 c.f. = 3.0 cf.

Okay--using the handy calculator for sub tuning, here are the frequencies the sub is tuned to:

If the sub is 2.3 cf in size, the sub is tuned to 43 Hz. If the sub is 3.0 cf in size, it is tuned to 37.7 Hz.

So... any ideas? I guess these are the main questions:

1) What is the actual box volume? Do you include the port volume or not?

2) Is the box too small? Could it be causing the terrible sounds on low frequencies?

3) Is the sub tuned too high?

4) Will a round port, since they are smaller to hit the same frequency, better to reduce distortion since it restricts airflow more (or does it?)

5) Can anyone explain to me why a sealed box doesn't work for some subs? With this one having a Qts of 0.405, you don't think it might work better?

Again--these subs are *loud*, and at middle and upper ranges the sound is actually pretty doggone incredible. I guess I can make a CD of different frequencies and play each one to see where the distortion starts if that helps. Again--it's those bass-heavy and low bass songs that do it. I have to turn it down soooo low to keep it from distorting that you can barely even hear the bass.

As for the 500 being the entry level, true enough. However, I think I've always run the entry level of just about every sub I've ever purchased. I didn't have much money back in my booming car days! The last sub I owned (before the one I have now) was a RF Punch HE that I put into a sealed box I built (a single 10"), and it ROCKED (I think I paid $59 for it). Again--I didn't go for SPL--I just wanted a full range sound out of my stereo. This is--without question--the most I've ever paid for a single sub, and it also has the most amp capacity I've ever owned (I think the old HE I had was only rated for 200 watts, and I used an el cheapo amp to drive it... something like an 80w x 2 or 150w x 1 that I bought at Walmart). Again--it sounded *good* and never had this kind of distortion a low frequencies. The sub I own now is an MTX 4500--bottom of the line--in a custom box to fit behind the back seat on my F-250. It's driven by a Kicker 300 x 1 amp, and sounds very good and clean--no distortion on any of the songs I play that distort on the new box. You can buy the 4500 online for $50.

Again--I've always just looked for a full range sound in my music. I'm NOT an audiophile by any means, but I've always had a decent setup in my theater room/music room and music without bass is unacceptable. The stereo that is on my boat has a head unit and 4 6.5" speakers powered by the head unit. I'm going to be replacing the 6.5's with Polk DB's when they arrive, and have everything hooked to the Kicker 700.5. I just want to have that full range sound that's still audible (and you can hopefully feel!) at higher speeds.

Speaking of which, at higher freq's, you can feel the hum of the bass with this box, but at lower freq's you feel absolutely nothing. Especially when it begins to distort. Don't know if this is useful info or not.

Anyway, sorry to write so much, but I just want to make sure I get the right information to the brilliant speaker builders out there! Let me know if there's more info needed.

 

[chillin 10+ year member]

I'd agree with hispls. The box is probably tuned fairly high and if you put on a cd with lower bass notes and dont have the subsonic filter adjusted properly it will sound bad and quite possibly damage your subs.

 

[jonathanengr1 10+ year member]

Hispls--just saw your post. I'm not sure if I've specifically said it, but you hit on a good point. I'm not looking for loudness here--I just want some good-sounding decent-volume bass to blend (or maybe outdo a LITTLE) the rest of my stereo. Trust me--as loud as those subs were playing at mid and high levels, I could definitely do with less bass... especially if the solution would give me a good, clean low-end.

I actually thought about taking an hour or so to build a 1.5 cf sealed box and trying it out. If it doesn't work, then bore a hole and put in a round vent. I noticed they have "tunable" vents out there (can slide to lengthen or shorten)--are these any good?

My main concern about the sealed box is size. Please don't everyone bash me because I have VERY little experience compared to you guys, but I have never seen a sub that has rec'd sizes for ported and sealed enclosures that are the same size. Most of the time the ported enclosure size is almost double the sealed enclosure size. I don't want to toss these into a ported enclosure the wrong size where they'll sound horrid when they might actually be *perfect* for what I'm looking for at the "right" size. How can I determine what the "right" sealed enclosure size would be? Honestly--they guy I spoke with at DD who told me "the same size " reeeeeeally seemed to be pulling that one our of his ear.

Lastly, when you say the sub might sound terrible in a sealed enclosure, what do you mean? That it won't be as efficient and then quieter than ported, or that it might really have terrible SQ?

I have an SVS Ultra-13 subwoofer for my home theater system, and it is one amazing piece of low-end technology. It is triple-ported, and comes with baffles to "tune" it. Despite its being ported, it is never, ever, ever, ever boomy--even with the baffles completely removed. It just sounds amazingly good, and at loud volumes almost compares to a good massage You said that DD designed the subs for a specific use, so surely they designed it to sound good in their box design and not distort horribly... so confusing!

ONE last note. May be important. I was using a Bazooka MAA1500 amp (500w x 1 at 2 ohms) to drive these subs until my system amp (the kicker) arrived. The Bazooka is no more. It was wired correctly, ran perfectly on Fri, Sat and Sun, and then no bass on Monday. After inspection later that day, I found that all three 20A fuses on the amp were cooked, and even with the stereo turned off (and thus amp should be off based on remote wire) it arced and blew another fuse when I tried to change them.

Geez... amps and subs seemed so simple back in the day! Buy a sub, build a little box, put it in there, wire in the amp and VOILA! You've got a kicking system! Ergh!

 

[jonathanengr1 10+ year member]

Chillin'--did you see my post about what the sub is tuned to? Looks like either 38 Hz or 43 Hz depending on the correct way to size the box interior. I just need someone to check my calcs. I could be waaaaay off! Is there a way to tell how a sub is tuned in real life (other than what it SHOULD be tuned to by calculations)? Should I try to tune this puppy down to 25Hz or 20 Hz? I guess that would be close to having a sealed enclosure, correct?

 

[jonathanengr1 10+ year member]

Chillin'--did you see my post about what the sub is tuned to? Looks like either 38 Hz or 43 Hz depending on the correct way to size the box interior. I just need someone to check my calcs. I could be waaaaay off! Is there a way to tell how a sub is tuned in real life (other than what it SHOULD be tuned to by calculations)? Should I try to tune this puppy down to 25Hz or 20 Hz? I guess that would be close to having a sealed enclosure, correct?

 

[Fiendstolemyamp 10+ year member]

Have you ever tried your subs on an amp other than the one that died? If not maybe that should be your 1st move.

 

[jonathanengr1 10+ year member]

You know--after typing that tidbit of info that did cross my mind. Bad amp, maybe? And no--I haven't tested it yet. Got the Kicker 700.5 in today and will install it *maybe* over the weekend (busy weekend, but will definitely try to make it up to the lake).

I have no idea why that amp failed. It was HOT outside this weekend, and called the manufacturer to see if that could be why, but they said the amp has a temp shut-off at 175 degrees. Thus, supposed to shut off before it gets hot enough to do damage.

 

[jonathanengr1 10+ year member]

Holy cow... doing more searching, I found a calculator at diyaudioandvideo and it has a calculator to determine sealed and ported box sizes based on the speaker specifications (VAS, fs, Qts, etc.). Putting in the values from the DD site resulted in a rec'd sealed box size of 0.4 cf, and a ported box size of 0.82 cf. They also have a "sealed or ported" calculator where you put in speaker specifications (Fs and Qes) and it tells you whether the speaker is best when sealed, ported or either. The 500 series fell into the range of "either", almost right in the middle but a nudge towards ported. The rest of the DD subs fell waaaay into the "ported" realm. Maybe the 500 series, being the low-end of their speakers, would do well ported?

I'm trying to learn here and am grasping at straws. I would very much appreciate someone telling me if I'm somewhat on the right track here. I'll def test the subs with the new amp, but the old one seemed to work pretty well (until it blew!). I'm not holding out much hope that the other one will make it sound better at low freq's.

Either way, can someone tell me if all of the calcs I'm seeing and using online are making sense? As for the speaker, here are the specs for the 510b:

Model 510b

Voice Coil Diameter 2.0"

Magnet Weight 90 oz

Power Handling RMS/Peak 300/1200

Suspension Travel 50 mm

Nominal Impedance 4.0 Ohm

DC Resistance 3.4 Ohm

Rec Box (cubic ft) 1.5

Port Area (sq in) 24

Port Length (inches) 23

Woofer Diameter 10"

Free Air Resonance 38 Hz

Qts 0.405

Qes 0.461

Qms 3.29

Vas 23L

Sensitivity 86.5 dB

Shipping Weight 13 lbs

 

[Kangaroux 5,000+ posts]

i personally would go with the specs on DD's site. a calculator only knows what it's told. 0.8 ported seems very small for a 10, thats what i was using for my 8's.

 

[jonathanengr1 10+ year member]

Yeah--for ported I definitely would follow their specs. I guess I got sidetracked on the sealed box deal and they don't spec a sealed box size for any of their subs. Understandably so for the rest of the series, but the 500 seems fine for ported OR sealed. Geez... I might make a few raw sealed boxes and try the subs out in each one to see what it sounds like. Def need to test with the new amp, though. IMPATIENTLY waiting for the weekend!

 

[Kangaroux 5,000+ posts]

Yeah--for ported I definitely would follow their specs. I guess I got sidetracked on the sealed box deal and they don't spec a sealed box size for any of their subs. Understandably so for the rest of the series, but the 500 seems fine for ported OR sealed. Geez... I might make a few raw sealed boxes and try the subs out in each one to see what it sounds like. Def need to test with the new amp, though. IMPATIENTLY waiting for the weekend!

well what are you doing on here, hook that thing up! lol

the DD will prob sound fine in a sealed box but they are designed for a ported, and unless you run a ported box you're not gonna get it's full potential. build a ported box tuned to like 33-35hz, and if you want to get a flatter response then just use an EQ or something and tweak it that way

 

[jonathanengr1 10+ year member]

I would LOVE to hook that thing up! Bad thing... me here, boat there. I'm about 45 mins from the lake, and with two little kids and a tired mom, you might never see me post on here again (either from traumatic death or, in the least, severe head trauma) if I took off and left her without assistance for the evening

Okay... as for tuning the box... I have blabbered around so much I think people haven't see all of my questions. Soooo... to tune the box...

Here are the box dimensions and port size. I don't know (and can't find the answer) if the port is calculated as part of the box volume. Can anyone tell me this??? It makes sense that it *would not* be. Anyway.... from my above post, here are the calculated volumes including and excluding the port volume, and the resulting tuning. I used the calculator at the12volt to determine tuning. Can someone tell me which box volume (or neither?) is correct, and if my tuning calculations are correct? At present it appears that the box is either tuned to 43 Hz or 38 Hz.

Oh... as for using an EQ, is that not putting a bandaid on a bigger problem? Or would that be an acceptable solution?

 

[Fiendstolemyamp 10+ year member]

Port should not be calc. as part of the box volume. You subtract the drivers displacement as well.