# Advantages of low QTS woofers?



## Fellippe (Sep 15, 2006)

Curious what the advantages of low QTS woofers and subwoofers are, given all the hype towards high QTS?

Is it that high QTS is superior for IB (a popular thing on this forum for both trunk mounted subs and door mounted woofers)?

I get this impression that low QTS drivers are meant to be in enclosures....and when put in enclosures give a warmer, fuller bass sound than it's high QTS counterparts...?

Just want to sort this out as there has to be advantages to low QTS drivers....otherwise there'd be no need for them.


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## npdang (Jul 29, 2005)

Low q drivers tend to have higher efficiency, and more suitable box requirements for ported applications.

The q of the system is usually more important in determining if it's "warm" or "fulller" than the q of the driver itself.


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## Fellippe (Sep 15, 2006)

npdang said:


> Low q drivers tend to have higher efficiency, and more suitable box requirements for ported applications.
> 
> The q of the system is usually more important in determining if it's "warm" or "fulller" than the q of the driver itself.


When you say more efficient, are you referring in general or certain frequency ranges? Higher Q drivers seem preferable for midbass applications....at least free air. 

And I agree that the QTC is the final factor, not the QTS. However when comparing drivers, if driver A has a QTS of .72, and driver B has a QTS of .37, driver A's QTC will most likely only go as low as .72 (most likely up), whereas driver B can be as low as .37 but can be brought up to .6 or .7 or higher by putting it in a small enclosure.

That flexibility I felt was the big advantage. 

And when you referred to the Scan Speak being more robust than the Seas Excel....was this what you were referring to? It's lower overall Q?


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## npdang (Jul 29, 2005)

I'm not talking about the low end sensitivity, but the overall efficiency of the driver.

When referring to the Scan Speak vs. Excel, I think it has far more to do with the nonlinear distortion performance as well as dampening and stiffness of the cone/suspension that account for those differences.


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## DS-21 (Apr 16, 2005)

Low Qts is generally an advantage in car-fi because a lower Qts woofer will generally yield a lower sealed Qtc in a smaller box, with a relatively high F3. The higher F3 is a huge component in why lower-Qts woofers often sound better, because some woofer's low-end rolloff dovetails nicely with the average car's transfer function. That leads to relatively smooth LF response (though EQ is always a very good idea). One of the most common SQ-killers in car audio is excessive and lumpy VLF, caused primarily by a fundamental mismatch between the acoustic (or assisted) rolloff of the enclosure and the car's transfer function.

Note also that woofers with low and high Qts can model and sound damn near identical in similar enclosures if they're designed to meet a given response profile in a certain sized enclosure and have similar motor designs. An example of that is the "home" Peerless XLS and the "car" Peerless XLS; the "car" one has a much higher Qts, but if you model them both it's really hard to tell apart the graphs.

Also, high Qts doesn't make a woofer better for I-B installs. What it does is reduce the need for LF EQ compared to a similar woofer with a lower Qts. I can't think of an 8" driver I'd rather use as a midbass in an I-B install (or any other) than the B&C 8NDL51. It has a Qts of 0.44 (which is actually about .2 more than I thought it was), but because of its high Fs (66 Hz) it needs considerable EQ to reach down to 60Hz or so in an I-B. By contrast, consider the Peerless SLS8, which has a Qts of around 0.5 and an Fs of about 35Hz. In an I-B install, an SLS8 will give you an F3 in the low 40's without any sort of EQ. So if you're a minimalist when it comes to processing, higher Qts is indeed better. But if you're not averse to loading up your midbass with EQ, then you can possibly do better by using a lower Qts (or higher F3, or both) driver with a superior motor design.


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## ocuriel (Oct 7, 2005)

Interesting subject. Keep it coming guys.


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## audionutz (Dec 22, 2005)

Good discussion so far  
in my experiences with regard to Qts, the main reason to seek a higher Q sub for IB, and more specifically, a woofer with a higher Qms, is that a woofer in IB operates in an "unloaded" state and therefore must rely on it's own mechanical suspension stiffness to control cone motion and/or prevent over excursion. Qes is a contributing factor as well, but basically ALL free-air -specific subs have something in common>>>Higher Qts (usually around 4.75-6.0), and higher Fs (usually 40-50Hz). 
THe Fs of a free-air specific sub belies it's actual performance, as in-car frequency response extends EASILY below the natural "anechoic" Fs of the driver when installed properly. A sub "rated" at F3 of 45Hz, for example, can easily play down to 20Hz if installed properly, maybe even lower!

On the flip side, if you use a Low Q driver in freeair application, the sub will have a limited power handling ability (as suspension can easlily reach Xmax) and careful EQ will need to be applied to try to prevent overexcursion. Sonically, a LowQ woofer in IB will exhibit good deep bass response and not use a lot of amplifier power, but that response is often mistaken as "a great IB performance" because the amount of low bass extension overshadows the fact that sub bass resolution has been diminished, midbass and transient response is sacrificed, and overall tonal accuracy is adversely affected. In layman's terms, you'd have a lot of "bass", but to an audiophile it will be "sonic slop".

Using a higher-Qts driver for IB with a higher Fs yields a vast improvement in tonal accuracy and transient response campared to the low Q driver in IB, and the resolution of adjacent tones especially in the bottom octave become much more easily rendered and discerned. So, in a freeair application, some call this a "dry" sound, whereas a lowQ woofer would be called "boomy".

Of course, you throw these subs in an enclosure and things change drastically! 

Of course I am not dismissing other performance findings as false, merely sharing my personal "hands-on" with ya


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## legend94 (Mar 15, 2006)

so what would be an ideal qts of a mid woofer for a factory door location, lets say in an acura legend?


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## Fellippe (Sep 15, 2006)

My guess is somewhere between .5 -.7...

BTW, speaking of Acuras , I was told that the Integra has a great midbass hump for car stereo.....


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## npdang (Jul 29, 2005)

Depends... what is the ideal target response???


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## t3sn4f2 (Jan 3, 2007)

npdang said:


> Depends... what is the ideal target response???


When you say that, do you mean for the whole range of 20hz or 30hz to 4K or for a more narrow range more in the bass region.


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## ocuriel (Oct 7, 2005)

audionutz said:


> Good discussion so far
> in my experiences with regard to Qts, the main reason to seek a higher Q sub for IB, and more specifically, a woofer with a higher Qms, is that a woofer in IB operates in an "unloaded" state and therefore must rely on it's own mechanical suspension stiffness to control cone motion and/or prevent over excursion. Qes is a contributing factor as well, but basically ALL free-air -specific subs have something in common>>>Higher Qts (usually around 4.75-6.0), and higher Fs (usually 40-50Hz).
> THe Fs of a free-air specific sub belies it's actual performance, as in-car frequency response extends EASILY below the natural "anechoic" Fs of the driver when installed properly. A sub "rated" at F3 of 45Hz, for example, can easily play down to 20Hz if installed properly, maybe even lower!
> 
> ...


I like your asnwer.


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## npdang (Jul 29, 2005)

It's akin to saying what is the ideal shirt to wear? Well, it would depend on alot of things wouldn't it


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## caver50 (Sep 2, 2007)

The Beyma SC-500 (5.25") has an FS of 70HZ and a QTS of 1.0 So if my understanding is correct, that should be an ideal speaker for IB. Is that correct?


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## 14642 (May 19, 2008)

Qts = (Qms*Qes)/(Qms + Qes)

Since the Qes is usually a much lower value than the Qms, the equation above reveals that the motor is more responsible for the Qts value than the suspension. Taking that a little further will also reveal that the job of the suspension is to prevent the coil from moving too far and for IB applications is important in making sure the speaker isn't destroyed. The motor determines the shape of the roll-off and the behavior above that roll off. In the speaker's passband, the suspension has no almost effect on the frequency response.


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## Hernan (Jul 9, 2006)

i've just change my midbasses from a low Qts (0.35) to a medium Qts (0.55).
They show less bass and much more controled midrange. They looks better for a car door install.


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## ~thematt~ (Sep 14, 2007)

Simply put, you can raise the Qtc up to your desired level, starting from Qts, but you can never lower it. 

If you want a Qtc of say, 0.60, it cannot be achieved with a woofer of Qts of 0.7.

However, if you want a Qtc of 0.6, it CAN be achieved through the enclosure design with a woofer of Qts (for ex.) of 0.4


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## Hernan (Jul 9, 2006)

~thematt~ said:


> Simply put, you can raise the Qtc up to your desired level, starting from Qts, but you can never lower it.
> 
> If you want a Qtc of say, 0.60, it cannot be achieved with a woofer of Qts of 0.7.
> 
> However, if you want a Qtc of 0.6, it CAN be achieved through the enclosure design with a woofer of Qts (for ex.) of 0.4


But what happends at the car door? It has enought air volume to act as IB?
If so, you can not raise the Qtc of the driver.


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## caver50 (Sep 2, 2007)

In general, would a midbass with a higher QT have a stiffer suspension with less excursion? This is a little hard for me to understand. I thought the higher QTs would always be better suited for IB. Now I'am a bit confused. Perhaps QT has nothing to do with excursion. It's just making it more difficult to make a purchase. I hope someone could clear this up without making it to techinal.
Thanks in advance for any help I can get.


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## 14642 (May 19, 2008)

If you'll use an electronic crossover for the midbass in the door and the frequency of the crossover will be slightly above the resonance of the speaker, then none of this matters much as long as the Qts of the driver is below 1 or so.


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## James Bang (Jul 25, 2007)

I think this is a great thread with very beneficial information regarding the QTS of woofers. This info would greatly help people save time with trial and error with purchasing drivers for their specific needs. It's definitely helped me with my purchases.


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## SSSnake (Mar 8, 2007)

Steve,

First I LOVE the CDs.

As always though I have questions... go figure.



> Sonically, a LowQ woofer in IB will exhibit good deep bass response and not use a lot of amplifier power,


Agree completely!



> but that response is often mistaken as "a great IB performance" because the amount of low bass extension overshadows the fact that sub bass resolution has been diminished,


How has bass resolution been diminished?



> midbass and transient response is sacrificed,


Again how? I always thought that the lower Q approaches had superior transient response 



> and overall tonal accuracy is adversely affected.


Agreed the low end is typically too strong but with proper EQ you can achieve falt response with a large increase in efficiency in the area that consumes the most power.

Again Steve, I'm not throwing stones justr trying to understand. Why? I have a low Q IB application that sounds bad. Everything that I believe says it should sound much better. It doesn't and I need to find out why...


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## ANS (Sep 23, 2011)

Andy Wehmeyer said:


> If you'll use an electronic crossover for the midbass in the door and the frequency of the crossover will be slightly above the resonance of the speaker, then none of this matters much as long as the Qts of the driver is below 1 or so.


Sorry for reviving such an old thread, but have a question regarding this. Am I understanding this correct that is you cross above the resonance of the speaker than the qtc curve does not matter as much given you now have influence on the curve with the set crossover point? Would it not be of the total resonance of the system (speaker + enclosure)? 

On a side note, would a higher or lower ebp be more ideal for a speaker working in an infinite baffle?


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## t3sn4f2 (Jan 3, 2007)

ANS said:


> Sorry for reviving such an old thread, but have a question regarding this. Am I understanding this correct that is you cross above the resonance of the speaker than the qtc curve does not matter as much given you now have influence on the curve with the set crossover point? Would it not be of the total resonance of the system (speaker + enclosure)?
> 
> On a side note, would a higher or lower ebp be more ideal for a speaker working in an infinite baffle?


Yes, but influence in the sense that your passband is now above the point where the QTC affected response is. Since the change in enclosure volume only affects the response next to the resonance point, then crossing over in that area will attenuate the response to a point that it does not affect the summed response with the the driver it is mating to. Take the example below.


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## ANS (Sep 23, 2011)

t3sn4f2 said:


> Yes, but influence in the sense that your passband is now above the point where the QTC affected response is. Since the change in enclosure volume only affects the response next to the resonance point, then crossing over in that area will attenuate the response to a point that it does not affect the summed response with the the driver it is mating to. Take the example below.


Thank you! Completely understand now


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## Patrick Bateman (Sep 11, 2006)

ANS said:


> Sorry for reviving such an old thread, but have a question regarding this. Am I understanding this correct that is you cross above the resonance of the speaker than the qtc curve does not matter as much given you now have influence on the curve with the set crossover point? Would it not be of the total resonance of the system (speaker + enclosure)?
> 
> On a side note, would a higher or lower ebp be more ideal for a speaker working in an infinite baffle?


Keep in mind that all of these discussions about qtc are based on measurements in an anechoic chamber. In a car, cabin gain will have a larger effect on frequency response than QTC will.

Basically you have to look at the loudspeaker and the car as a system, and factor in the influence of the car.

For instance, I'm running some B&C eights in a bandpass box in my car for midbass. According to the sims, the drivers should have a fourth order rolloff around 180hz. But once you add cabin gain into the equation, their rolloff is much shallower than fourth order, and the output extends all the way to 100hz.


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## oabeieo (Feb 22, 2015)

npdang said:


>




I miss this guy posting


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