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Date: November 19, 2014 at 06:00:46
From: brian in michigan, []
Subject: Re: Volfenhag woofers...

I realize this is so late but cant help myself. I have 2 volfenhag 1247dvx 12s in a vented 3.3ft 26hz box powered by a memphis monoblock 1000w rms at 1 ohm. I bought them used very cheap and am really impressed for what they are. They will bounce the rear view mirror out of place and bounce the roof about an inch. I have never run them hard into clipping have the subsonic filter set at 25hz no to little bass boost and had no issues at all with them. They sound good up to the point that the memphis runs out of power and starts to clip. I highly disagree that they are bad subs. I won't argue they are the best out there but set up right they are a good sub and well worth the money they sold for. I've had them for a couple years now and they often get everything the memphis can throw at them short of clipping. I can't see blowing them short of driving them into hard clipping.

I want to address some misconceptions about vented and sealed boxes brought up here in this thread. A high Qts sub will work in a vented box and often play lower than a low Qts sub but it won't sound as good because the damping will be worse than a low Qts sub in a vented box. The reason any sub blows in a vented box is from not using a subsonic filter set at the box tuning frequency(Fb),not because it's a sealed sub in a vented box. All subs can be damaged playing them below the box tuning frequency. The higher the power the more chance of smoking them. The higher the tuning frequency the more chance of smoking them especially if you listen to music with a lot of low end. playing bass cd's with 20hz tones through a box tuned to 40hz without a subsonic filter is beggin' for blown subs.

At and above the tuning frequency(Fb) the subs barely move and most of the bass is coming through the vent, below it(Fb) its like playing the subs in free air without a box, the subs loose back pressure from the box below (Fb) not good!

Sealed boxes require the subs to move a lot farther than vented boxes for the same spl meaning if you want a lot of spl from a sub in a sealed box you need more Xmax than you would in a vented box. Because they are sealed sub sonic filtering is not a problem as far as damaging subs goes.

There are definitely trade off’s between sealed and vented. Sealed sounds tighter and usually requires a smaller box and no subsonic issues. Vented mostly requires a larger box and you definitely should use a subsonic filter set to the box tuning frequency. But you can gain so much low end and spl from a vented box, especially if you can tune it low like 25hz and still get a relatively flat response.

Its not uncommon to get the same output with a vented box that would take twice the amp power to get out of the same sub in a sealed box. Of course this all depends on the sub, some work good in both and some work way better in sealed or vented.

I've had the same system in several cars, it can and does make a huge difference, the same stuff from one car to another. I think that kinda explains why some people love a sub and other people hate it.

Bandpass boxes are another area where people are highly opinionated and most of them have only heard a generic mass produced band pass with anything that will fit the hole thrown in it. This most of the time sounds terrible with a very peaked response in one area. But when properly built for a specific sub can sound really good and give you a lots of low end. The trade off with a band pass is low end verses spl. Huge low end often means a huge bandpass box and high spl means a smaller band pass box. It can be designed in between to achieve whatever compromise you want to make between low end and spl. A larger vent is needed for best results in band pass and vented boxes. A sealed box sub will work better in a band pass that a vented box sub,

WinISD is a free box program and I have learned as much from playing around with WinISD than from the 4 or 5 books I have on box building. Minimum specs to use WinISD are the subs Fs, Vas, Qts with the rest of them Re,Le,Qms,Qes and others making the calculations more accurate. Sometimes these specs are hard to find, with name brand subs they should be easily found on the company web site. You can simulate the same sub in sealed, vented and band pass, change the box volume and tuning and see how that affects frequency response, group delay (damping) power handling, cone excursion and make somewhat of an estimated guess what's going to work and what will sound absolutely bad. This won't take into account the cars transfer function but you still can learn a lot from playing around with the program. If you know what the cars transfer function is you can build a box to match it to make it sound flat in the car or design a box to get tons of powerful low end.
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