One of the very first questions I posed on this forum was about qts and enclosure size. Unfortunately, I'm still struggling with my understanding of the thiele-small specs, but I believe you are basically on the right track.

There have been some good posts recently on the subject. And, for what it's worth, here's what I think.

Higher qts lends itself to IB intalls. The lower qts drivers do better in some size of enclosure, whether sealed or ported. My sr6500 set has a high qts and sounds good and punchy right down to roll off, even though it doesn't have deep bass. It's also too low in it's mid-bass perfomance for me, but it's nice and even (flat) sounding.

I think the manufacturers mostly make drivers for the speaker builders, and mostly for enclosures. This makes sense, since the DIY community isn't their real customer and there isn't a lot of IB design for obvious reasons.

Look over some of the other posts here, especially the more recent ones.

My thoughts.

 

In an infinite baffle, a speaker with a QTS of 0.7 will measure flat, with no peaking or drooping until you reach the F3.

The problem with focusing on QTS alone is that the car is anything but an anechoic environment. Typically you see massive peaks and dips, due to reflections.

Check out some of my threads - I'm kind of obsessive about dealing with the reflection and diffraction that occur in an automotive environment.

In a nutshell, there isn't a magical value of QTS that will work perfectly every time. Even worse, these reflections in the car vary when you move around the cabin. So you can't just EQ them away - you have to consider the response at multiple points in the vehicle.

Sorry for all the bad news

If I were working on your car, I wouldn't replace the speakers. I would take polar measurements at various locations, get an idea of how the speaker is playing INSIDE the car, then apply EQ to null out the midbass hump. Again, the key is measuring the polar response.

 

Sorry sorry sorry....

I wasn't very clear about my setup. I've got the 6.5" Peerless SLS's in a .07 cubic foot enclosure, not a qts of .07

I wasn't clear at all, my fault.

With that small of an enclosure I'll get a huge peak at 180-220hz like I said above. The SLS's want a bigger enclosure than that, but .07 cubic feet is the absolute biggest I can go. I've got an s10 with kick panels I made myself and I've used every cubic inch of room down there. This is why I'm looking at new midbass that either wants a really small enclosure, or no enclosure at all.

I just want to know what to look for in the t/s parameters that will tell me if the speaker needs an enclosure or not, that is, if it's possible by just looking at the t/s parameters.

Hopefully that clarifies my situation a little better.

 

I can guarantee PB and all of us understood what you meant because you said it perfectly.

But he was saying take a look at the qts of the speaker to understand how it will behave.

You can also check out zaph's reviews for clarification on what really works in IB and why.

 

Well, before you throw them out, try stuffing the box with cotton and/or punching a hole in it and letting the woofer breathe some.

 

I've got most of it stuffed with cotton, and I've already tried cutting out the back of the kick panel to get rid of the spring effect that an enclosure has on it. When I do this, the SLS's just get very loose and sloppy.

Oh yes, forgot to mention, to get the right bass response in an older Sonoma, I had to drill the metal in the kickpanel area out so the speaker vented to the fenders. This also helped the big magnet fit properly as well, so it was a double-necessity. Sometimes you gotta just "do" it. you could consider installing aperiodic membranes in the metal of the kick area and vent it, which may be the ultimate ticket for your existing speaker and your goals.

lol...... funny you say that....