improperly tuned box

You should consider that the sub doesn't need any particular box tuning.  It is the listener that needs the tuning and that his aural need is a combination of the sub, the vehicle, and his expectations of how it should sound with his favorite types of music.  A recommendation of "35 Hz Fb for sub A", as defined by the manufacturer, only indicates this:

• The resultant sound should suit the average user
• The resultant port size / length can fit the box

Depending on who is marketing the sub, the "in car" blend of sub / box sound and cabin gain may or may not have been tested and accounted for.  And if it were, what vehicle type was used for testing?  Hatchback, sedan with sub in trunk, pickup truck, SUV...?  Those all all unknowns if you are being very general in making box tuning recommendations.

What about damage that can occur?  I believe you may be referring to this with your question.  I'll just preface to say that I have never damaged a driver by using it in a box that was improperly tuned, but I know that it can be destroyed when all the wrong things happen.

A driver can be damaged with the box tuned to 35 Hz and it can be damaged with the Fb at 45 Hz.  There's just much more of a chance that the damage can occur if the box is tuned at the higher freq.  The reason is that, unlike a sealed enclosure, a vented box's ability to damp the driver is limited by its tuning frequency.  When a sub is tuned high, the result can be a huge boost in SPL where the full advantage of port output at the loudest freqs can be realized.  Somewhat below that tuning freq, however, the box loses ability to damp the driver's cone excursion.  Of course, there is a lot more content below 45 Hz than there is below 35 Hz.  An SPL competitor will take precautions to enable a filter below that Fb in order to protect from expected damage.

In the ordinary world of street use, I don't see this as so much of a factor.  I believe it is typically a combination of misjudgements and poor installation / setup skills that results in damaged subs.  Combine the high voice coil heat of a clipped signal with an unloaded vented box on a subwoofer that was not built to take such abuse, and there is your fried sub.  With careful setup to all details (except port length) and a reasonably light touch on the volume control, one should be able to continually use the imporperly tuned vented sub although at the expense of listening to a boomy sound output.

So you are actually asking a very different question I see.

First, "boomy" means an unnatural peak in response that causes the system to sound like it's playing one note all the time.   Of course, if you are used to the crap sound of a bandpass system, then you know what this sounds like.  It is very useful to an SPL competitor as their intent is to produce a single tone max dbSPL, but for music or general listening boomy systems tend to sound like a belching blue whale.

Second, as to your use of the earthquake DBX subwoofers, you will need to contact the manufacturer to get the T/S parameters if you care to construct a proper enclosure for them, but since it sounds more like you don't really care (superglue a speaker cone?) then go for it with whatever you want to try.  The info I can find about the DBx 12 indicates is has an fs more like 27Hz, not 35, and they are designed for use in bass reflex (ported) alignments.

Actually to be honest with you, I like the way my bandpass sounds. Maybe its because I have had this box for over 6 years and now I am used to it. It does the bassy music good. i like the way it sounds with rock/heavy metal music. But it just doesnt produce the very low bass.

So what causes "boomy" bass? Is it just a box that is not tuned properly? I seriously would like to test out the sub I had bought from the friend first before I go and rip my subs out. Now since that sub is a dual coil then each coil's RMS is 200 watts. My fiance has a 2 channel jensen I think 580 watts. Could I possibly mount the sub I had bought in one of the ported boxes I made, then run the speaker wire out the front of the port (since I have the box made for a single coil sub) then wire it to her amp and see how it sounds? Or wont that work because of it being tested on her amp and not mine?

Did you not put speaker terminals in your box is this why you want to run it through the port? You can test it on her amp and it will tell you what the sub and box will sound like ran from that amp. 

So what happened to the question about the box being tuned to 45hz because with a tuning frequency that high you will lose out on a lot of lower notes. I generally tune most of my daliy driver boxes to 32hz and have been very happy with the sound output.

The ported boxes I made for my subs only have a single pair of terminals since my subs are single coils. But the sub I had bought from my friend is a dual coil, so thats why I would run those wires out the front of the port. So testing the sub on her amp just to see how it sounds wont help me out much because my amp is alot more powerful than hers?

It doesn't make any difference how powerful the amp is that you are testing with.  You have a volume control on the deck, right?  But a couple of things you seem to be stuck on:

A dual voice coil sub has the same power capacity as its sibling single voice coil sub.  The sub itself is rated to withstand power, not each coil in itself.  Look at the woofer wiring diagrams on this site to see how you should wire the coils to get the desired impedance.  With the coils wired together you will still use the single set of terminals on the box.

You asked what is boomy bass again after DYohn explained that it sounds like "it's playing one note all the time".  Did you miss that?  High tuning tends to do that because the lower freqs are dropped off out of the radar.  When you don't hear the lower freqs and at the same time hear the higher 50-ish Hz freqs amplified by port output, the result is described as "boomy".  That's because, well, its boomy.

Tuning "improperly" does not always equate to tuning too high.  You can tune too low for your expected result.

Your description of having the gains set to about the halfway point tells us that you have no idea how gains are supposed to be set.  Learning that important step is the order of the day when you are working with your system.  But don't mess with the gains on your friend's amp that you are testing with.  If you are testing in his/ her vehicle, just go on the assumption that the amplifier has been set to match the deck output (which is what setting gain is all about).  You don't need to rock the house to find out if the sub sounds the way you would like it to sound, which means you don't necessarily have to crank the volume through the roof while you're testing.  Wrong gain setting problems show up, typically, at close to full volume.

Just make sure you are putting a proper load on the amp when you test the sound of your sub in the vented box.  The amp manual will tell you what its minimum impedance has to be, so use the wiring diagrams and wire the coils together as the diagrams indicate.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

I know I am alittle flacky when it comes to setting gains, I will admit that. But I do know when I am driving an amp too hard. The amp is set at 1/2. It does not clip, It does not overheat. My old amp I had the gain set to 3/4 and for the 5 years that I had it, I never had a problem with it clipping or overheating. I am not going to change the settings on her amp. I just want to see how the sub sounds in the box's I made. I dont have the manual for that amp either so the safest way to wire that amp is 1 coil per channel. That way I dont have to worry about messing the amp up. I will listen for boomy throughout the song. How can I tell if a sub is boomy or not. You said it will sound like its playing only 1 note. Does that mean no matter if its a 50Hz or a 80Hz, it will all sound the same? To put it simple, I just want to see how the sub sounds in my box. I dont have any specs on these subs whatsoever. The box that my friends sub was in, I made 2 exactly the same. He said the sub sounded great when he had it in his car. That was a long time ago so i dont even recall how it sounded. But I dont want to rip my subs out of my bandpass, throw them in the ported boxes and hook them up to my amp only to find out that the box's are junk. Instead I would take the sub he sold me and test it on my fiance's amp in 1 of my boxes. Would I be able to take notice to any "improper tuned" reguardless of the amp I try it on?

Ok, I am going to try and enlighten you here a little, since it seems as though you were not happy with anyone else's responses...

As you probably know from past correspondance, I have a set of the same subs you have (Earthquake DBX12, single 4 ohm coils). These subs are infact better suited to a vented enclosure than a sealed; HOWEVER - the bandpass box you keep touting is not a vented enclosure per se, and as I am guessing it is a pre-fab bandpass box, it is all the more useless. I can tell you with 99.9% certaintly that there is not a prefab bandpass box made that will sound acceptable, let alone good, with ANY speaker installed. There are just way too many design parameters that must be taken into account when building a bandpass box, and they will be speaker/listener dependant - a prefab, one size fits all design is not going to cut it here...

Now, if you'll refer to my origional thread regarding the box I built for my DBX's, it will tell you basically everything you need to know to build a PROPERLY designed vented enclosure for these subs; tuned to ~30hz (not 35hz as I origionaly posted). This is a nice, low tuning frequency that will dig deep and sound good playing all types of music - not just a one not wonder type of box. If you choose to keep your bandpass box, that's fine - people like what they like; just know that is is not the most efficient, or best sounding enclosure you can get for these subs, and you are truly missing out.

Now to answer your last questions; the subsonic filter is used anytime you want to cut the lowest frequencies from going to your subs - a sub being used in a vented enclosure would be a good time to use this type of filter; as you would set it slightly lower than the tuning frequency of the box to protect your sub from unloading itself below tuning. A bandpass box shouldn't need this type of filter, because by it's very design nature, it is already cutting out frequencies below and above a certin range (hence the term "bandpass"...). BUT, this is where your prefab box will let you down - you have no idea what the passbands even are for this box, since it was not designed to work with your application. It could be cutting out everything below 20hz, or everything below 50hz(more likely), and it could be rolling off everything above 80hz, or everything above 150hz - the point is you jsut have no idea, and it is more than likely NOT the exact passband you will want to work with.

Adjusting the amp: yes, you will have to adjust the amp any time you move it from a different type of enclosure; a vented box is loads more efficient than a sealed one, but you will also probably want to setup the subsonic filter in the vented box (again, probably a little lower than the tuning frequency of the box). You will also probably need less gain on the sub in the vented box than if it were in a sealed box.

-Matt

You can get those subs still; I have mine in the fFor Sale section right now (shameless plug...).

You should be safe using either amp on either setup - just watch and listen to make sure the low tones aren't going too low and unloading the sub in the vented box - you'll be able to hear it if it does.

Anyway, I can understand your concern - but there's a reason you like the way her sigle 10" sounds - it's in a vented box and not a bandpass. But if you are seriously in love with your bandpass, so be it...

-Matt

If the subs are in the trunk of a car, they will probably sound better facing the rear, but with the box all the way in the front of the trunk. If it's a hatchback, probably with the subs at the very back of the tunk, but facing up and forward.

Trial and error my friend, trial and error...

-Matt

1 inch between the subs and the truck lid? Eewww... You may have to face them forwards! If you face them rearwards, the surrounds may hit the lid = not too good.

Oh, and from my experience i've had better SQ with them faced forwards and better output faced rearwards.