yes, .707 is considered ideal, but less qtc will start to lack low bass. I have found anything from .7-.9 qtc sounds pretty good. closer you get to the .9, the more low bass you get and more boomy it will sound.

 

There are a lot of reasons why a manufacturer might specify a box that doesn't perfectly match a system q of 0.707.

A smaller box has higher power handling capabilities. Thus, a customer is less likely to damage their sub and remain a happy customer.

I also feel companies recommend a 1 ft box when they can, because there are many pre fab 1 cu-ft boxes on the market. If you were a consumer, looking at two subs.. one requires 1.35 ft and another requires 1.0 ft.. and you can buy a 1.0ft box, but cant buy a 1.35 ft box.. you'll buy the sub that requires the 1 ft box.

And, as far as I'm concerned, anything pretty close to 0.707 is fine. It doesn't have to be exact.

 

Would a Qtc of .76 (manufacturer spec) be noticeably different than 0.67 in SQ and output?

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yes, .67 will be punchier, but lack low end. I think most people, SQ or not, would like .76 much better. fuller, larger sound with more low end.

 

The lower the Qtc, the shallower the slope which will present stronger low notes, but some kick will be lost. Which way to go all depends on what you have up-front not to mention how you're trying to tame the sub's upper end.

I've always preferred a sealed box Q around .6 as well as a roll-off around 60hz. Usually provides upper-end smoothness right down the point where the vehicle starts boosting. Also allows for cuts down low instead of boosting. Depending on the vehicle's acoustics you may want to opt for a sub that has a lower or higher F3hz point. Credence small box 8's roll-off around 70hz with a fairly low Qtc, but mates exceptionally well with small hatchbacks (240SX) without needing any EQ. Put the same box into a 4 door S10 Blazer and no-go.

 

The lower the Qtc, the shallower the slope which will present stronger low notes, but some kick will be lost. Which way to go all depends on what you have up-front not to mention how you're trying to tame the sub's upper end.

I've always preferred a sealed box Q around .6 as well as a roll-off around 60hz. Usually provides upper-end smoothness right down the point where the vehicle starts boosting. Also allows for cuts down low instead of boosting. Depending on the vehicle's acoustics you may want to opt for a sub that has a lower or higher F3hz point. Credence small box 8's roll-off around 70hz with a fairly low Qtc, but mates exceptionally well with small hatchbacks (240SX) without needing any EQ. Put the same box into a 4 door S10 Blazer and no-go.

did I get it backwards?

***edit yup, I had it backwards. lower qtc will give more low end. brain goes all wonky these days, lol.

 

Not really hard to confuse since you will have to aim at the far ends of Q to hear a major difference but it exists.

Trade-offs are usually stronger bass and kick at 60hz and above with a higher Q that actually sounds good on older Pop music (think 80's). Then more extension but starting to trade robust upper bass for less kick and a bit of slop at the lower end of Q.

Of course the happy medium is around .7 which is most sought after, but I tend to look at roll-off just as important as well. Makes the difference if you don't have or want to use EQ down there. Why? Perhaps in the case of not having a separate EQ or flexibility in xover points & slopes for subs, midbass, etc..

 

I have Audison Voce 6.5 components up front with the hpf at 80hz, passively crossed over. Sub is in the trunk of a Mustang. I prefer the accuracy and SQ over volume. Would a Bessel setup be preferable then?

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The only way to tell what would be best for YOU is for you to do testing & modeling based off of your vehicle & gear that YOU have. We can throw hypotheticals in all day, but the final results lies with you and your ears. Using a RTA works best here if you already have a test box/sub with a known open field response. You can then use that data to come up with a plan.

 

Lol... Qtc again. Don't bother messing with "optimal" Qtc. You will most likely hear no difference in the 0,6-0,9 range, any audible difference can be EQed to the same response, it will be more or less efficient - that's all. WinISD model the enclosure using small signal parameters in an anechoic environment, while in the the car, the overall response will be dominated by the cabin (vehicle transfer function). These simple model apps don't take that into consideration.

A lower Q box will have better low end efficiency but less power handling. Imo it's better to have good efficiency in the 40-50Hz range.

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