subwoofer setup problem

I talked to my brother about TL's and his thoughts were that test data suggests an appr 6 dB per octave roll off. Obviously, this will vary with the specifics of each design. He commented that overall output levels are lower in efficiency than if the driver was used in a sealed design. He also stated that the woofer / mid-woofer increases in linear output as frequency rises i.e. the output on a graph looks more like a very linear but gradual decline as frequency decreases. There aren't any major "hills & valleys" ( impedance peaks ) like those found on most other vented designs.

While all of those comments tend to coincide with the measurements that i've seen and read about, the only one that i would question would be the one about roll-off. I did some digging and came across the following. This was taken directly from Vance Dickason's Loudspeaker Design Cookbook ( 5th edition ) page 73 / 74: "Looking at the response graph in fig 4.1, it is obvious that a TL's frequency response is similar to a sealed enclosure, but with an even more shallow rolloff, probably accounting for the opinion among TL aficionados that TL's are capable of producing very deep bass."

This does somewhat support my brothers' comments although it does not give a specific figure in terms of dB's per octave. He probably arrived at the 6 dB figure after studying various graphs & data.

Vance goes on to say that many proponents of TL's claim superior transient response to vented ( not hard to believe ) and even sealed designs. According to various testing, his conclusion is that they are extremely similar to a sealed box design with a Q of .7 or so. As you and others may be aware, most "fast & tight fanatics" will tell you that the "fastest & cleanest" bass occurs at a sealed Q of .5 or so ( ala Dunlavy and a select few others ). Obviously, TL's are still not quite as fast or clean as fully optimized sealed boxes but are still miles ahead of typical bass reflex designs.

This coincides with my experience in that i do like TL's, but still prefer a sealed design. If i absolutely HAD to choose some type of vented design though, it would be a TL. Sean
>

Sean, I agree, a sealed box of Q 0.5 is very hard to beat, but it's also extremely large if it's going to have good extension. It also has to be shaped and stuffed properly to absorb all the midbass and midrange output off the back of the cone, something that you get "for free" with a TL. Vented enclosures are just plain bad: poor damping and low output in the deep bass, and almost no absorptive material inside, which means the sound bounces around and comes back out through the cone and the port. All for a little extra efficiency? Yuck. I'm with you, for main speakers, give me a sealed box or a TL anyday. For subs, I'll make one exception: RELs with ARM loading, a "damped" form of reflex loading, where the frequency range is so low that it avoids these problems.

Karls, i think that most people don't realize that a vent is only "tuned" or "effective" at the one specific frequency that it is resonated at. As such, they are an absolute "mess" anywhere outside of that range and typically do WAY more harm than good.

Of course, i'm strictly talking about sound quality here as one can show tons of impressive arguments on paper. That is, if all you want is an increase in efficiency and bass extension. Yes, the vent does give you a greater quantity of bass, but it is done at the expense of quality. This can be seen with all of the ringing / poor transient response that takes place with a vented design Then again, i'm sure that i'm preaching to the choir on this one.

Hopefully, this will stir up a few others to check into what we are talking about and bring in some new converts to what is considered "old" technology. What is hard to believe though is that vented designs actually pre-date sealed designs. I guess that after listening to all of those early bass reflex models, they had to do SOMETHING to make it listenable. Hence the "breakthrough" technology of a sealed box.

Thank God for Edgar Vilchur and Henry Kloss !!! Sean
>

Try the passive filters. I use them and find them very transparent. Not only that, they have improved the sound of every main speaker I've tried them with. Because they roll off at a gradual 6db octave rate, they make the transition smoother AND improve the dynamics of the mains. I'll be real surprised if you aren't able to get seamless with the Titan II, my Jaguars are strong to low 30s but with the 85Hz filters and my Titan IIs set around 50Hz it is superb. I was actually able to greatly reduce a major room peak for smoother, more extended bass than with the Jags alone.