Recommended QTS for infinite baffle Car subs 0.5 to 0.7 or higher than 0.7??

I doubt that you can find an infinite baffle application inside a car.
The concept of IF applies to the propagation of sound around the box, as the model is a monopole with no boundaries. Once you move from 4pi steradians, you'll get reinforcement from the boundaries - according to the wavelenght, of course, and that explains why it's easy to talk about pressurization inside a car.

Qtc indicates the kind of rolloff and what happens at the 'knee' around Fb.
It's mostly Fs related, as you want to design to have the lowest extension with good punch, so highish Q against 0.7 or lower.
 
please see the attached image.
Trying to find suitable Qts drivers for this application.
 

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I see a finite baffle, about 1x0.3m ; two huge woofers and two tweeters at the sides. A back chamber with high losses. Qts is derived from electrical and mechanical Q. Any speaker designed for car should do the job. For subwoofers, the restricted BW calls for lower sensitivity, so a dedicated amplifier with electronic crossover is the norm...or you're gonna go with the example that you gave, 25 cm woofers, that have about 90 dB/W/m sensitivity.
 
I see a finite baffle, about 1x0.3m ; two huge woofers and two tweeters at the sides. A back chamber with high losses. Qts is derived from electrical and mechanical Q. Any speaker designed for car should do the job. For subwoofers, the restricted BW calls for lower sensitivity, so a dedicated amplifier with electronic crossover is the norm...or you're gonna go with the example that you gave, 25 cm woofers, that have about 90 dB/W/m sensitivity.
You are right !!!
Ideally it's a finite baffle with high losses. But I want to go this way to have more space for luggage. It's. a compromize
 
That pioneer sub is huge! I wouldn't put it in my room, go figure in a car's inside!
High losses is a joke, I imagine pressure would make the sound spill from every fessure!
And what about the rest of the set-up?
Subwoofer covers only the first octave ( even less) and can be easily be forgotten when/if the system plays fine.
OR
If you wish to use two of them as woofers, those are said to work good till 125 Hz, so you need two fullrange or midwoofer and tweeter to play the rest ( of audio spectrum).
 
High Qts isn't as important as you'd think in this situation. Reasonable efficiency and excursion is. I've had great success with low Qts (0.2-0.3), low Fs drivers in rear package trays.

I consider this much less of a compromise than a boxed woofer stuffed inside the trunk, you may be pleasantly surprised.
 
Right, Ideally we want a flat response, so need a 0.707 Qtc alignment to blend to the cabin's 2nd order rise, but need to measure the cabin gain to figure out what driver Fs, box tuning [Fb] is required to match up to it, which often requires a lower Qts driver than one would think and why premium JBL, etc., mobile audio woofers have < 0.5 Qts to match up with differing size cabins, rear box volumes [Vb].

That said, with the amps, electronics available today, probably best overall to use a ~0.5 Qts driver for transient perfect response as the mean and let cabin gain combined with parametric EQ allow sufficient latitude for tailoring it to one's 'taste' based on windows up/down and/or different music genres.

GM
 
That said, with the amps, electronics available today, probably best overall to use a ~0.5 Qts driver for transient perfect response as the mean and let cabin gain combined with parametric EQ allow sufficient latitude for tailoring it to one's 'taste' based on windows up/down and/or different music genres.

Exactly. Even careful adjustment of LP frequency and amplifier level adjustments alone can transform things quite a bit.
 
The Pioneer speaker has a 4 cm voice coil. This is good for, maybe 100W rms. Not really a sub woofer, seems to be a cheap junk design rip off. 350 W rms look for a, at least, 75mm VC.

The Qts for an "free air" woofer should be around 0.6-0.8 Low resonance frequency around 30 Hz is fine, too. So look for 12" woofer or larger with these parameters.
"free air" is what you call a in car installation which is close to infinite baffle, where the volume of a box can not be calculated, because it is more or less open= very high losses. The virtual volume of that cavity may even change with frequency.

A woofer with a Qts lower than 0,7 may need some boost, which explains the need for high power in car installations.
A lot of cheaper PA speakers will work inside a car, as long as you keep it dry.
I even had dedicated car speakers rusting away, so all day, all year use off a car HIFI installation may need some attention.

A funny thing about large cone diameter /displacement in a car with closed doors/ windows, is the point where the car becomes a pressure chamber. Car HIFI is so far away from "normal" Hifi, some even think it is no Hifi. Which in many cases may be right. Like these Pioneer woofers...

If you do not want to measure your results with a microphone, a good indicator you make some serious bass is when the number plates start making noise and you have to glue them down.
 
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We don't know what the rest of the system is, so it's a guessing game as to what the OP needs to integrate well. But with a claimed 96dB sensitivity, if the Pioneers can deal with anywhere close to 100W RMS, they'll be more than enough if the goal is listening to music.

If he just want to rattle his tag or annoy people as he drives by, then ya'll go ahead and knock yourselves out.