# Low QTS. midbasses in door, what was your experience?



## nubz69 (Aug 27, 2005)

I have a pair of midbasses I want to try in my doors but they have a low QTS. How have you guys delt with this? Do you just skip over low QTS drivers or have you found ways to make them work?


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## 2500hd (Aug 22, 2009)

Can't you put a resistor at the terminals to achieve a higher qes therefore higher qts? There's lots of stuff you can do to a speaker to make it different search for speaker tweaks and you should be able to find something else to change it


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## Oliver (Jun 25, 2007)

A search for - low qts , brought up 20 pages = DIYMA.com - Search Results


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## nubz69 (Aug 27, 2005)

Hey A$$hole did you even look at what comes up when you do a search or did you just feel like wasting time being an A$$hole? A post like yours does nothing but stymie intellectual discussion. If you look at 99% of those posts they have nothing to do with peoples experiences with mid-basses with low QTS. Most of them are concerned with subwoofers and QTS which has very little to do with what I am talking about. If you have installed low QTS drivers yourself or have personal experience on the subject I would love to hear about it.


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## Candisa (Sep 15, 2007)

Don't worry too much about that.

In real life, it's the Qtc (total Q of the driver in its enclosure) that matters, which is always higher than the Qts, and if you use a high-pass crossover on it, it doesn't matter actually.
I did a simulation recently. 
I took a driver and put it in it's ideal sealed enclosure (Qtc of .707) and in a much bigger one (Qtc closer to .5). By setting the high-pass crossover a little different, it was possible to get the exact same response out of both systems. Same power applied, same cone excursion, same frequency response... same everything!

Low Qtc driver as a midbasswoofer IB in a door? No problem!
There are only 3 things that are important for a midbasswoofer:
- The amount of air it can move (cone area x linear excursion)
- The amount of power you need to give it to move that amount of air
- The amount of power you càn give it (if a driver needs 150W to reach its x-max, but its coil can only handle 100W, you'll blow it before you got the maximum out of it).

What I do is simulate:
- Put the driver in WinISD
- Simulate it in a sealed enclosure of 50litres (door + leaks)
- Apply crossovers
- Apply the power you can give it or (if lower) it's electrical power handling
- Check the excursion.

If the driver doesn't reach its x-max, this means you can lower the HPF and/or put more power on it (without disrespecting the drivers electrical power handling!).

Use WinISD only as a comparison tool, the dB-numbers don't say anything about it's performance in a car, but you can use it to compare different drivers!

Isabelle


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## Oliver (Jun 25, 2007)

nubz69 said:


> Hey A$$hole did you even look at what comes up when you do a search or did you just feel like wasting time being an A$$hole?


Just want to be like you :surprised:


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## Hernan (Jul 9, 2006)

I lived with SEAS CA18rnx at the doors and NEVER sound good.
I made a (huge) sealed kick and they [email protected]!


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## nubz69 (Aug 27, 2005)

Herman could you elaborate a bit?


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## Dangerranger (Apr 12, 2006)

Well Low Qts is only one factor in the equation. The question is what the Fs is. A lower Qts driver like a SEAS excel W18EX or W18NX with enough mass on the driver to have a low Fs will do just fine in a door due to cabin gain. A low Qts driver with a higher fs (think Pro Audio drivers) will lack a lot of midbass. It has to do with where the cabin gain takes over and compensates for the rolloff at Fs when the driver's Qt is lower.


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## Arezump (Jan 6, 2010)

Nice thread! 
anyone here built a sealed box for their scan rev 18w on their doors? or it'll be enuff if i just let it be installed as what they are right now? help & opinions needed!


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## Patrick Bateman (Sep 11, 2006)

Dangerranger said:


> Well Low Qts is only one factor in the equation. The question is what the Fs is. A lower Qts driver like a SEAS excel W18EX or W18NX with enough mass on the driver to have a low Fs will do just fine in a door due to cabin gain. A low Qts driver with a higher fs (think Pro Audio drivers) will lack a lot of midbass. It has to do with where the cabin gain takes over and compensates for the rolloff at Fs when the driver's Qt is lower.


I agree. A few years back I used a pair of Vifa woofers in the doors of my Escort, and it was completely anemic. I believe another problem was that the doors are very leaky.

I've had much better results from a small sealed enclosure.

If I were going to put a woofer in a door, I would use one with a high QTS, or I'd raise the QTS with a resistor or by adding mass to the cone. (Or both.)


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## Hernan (Jul 9, 2006)

nubz69 said:


> Herman could you elaborate a bit?


Technically no. But as I said above, the seas never sound good at the doors.
At a sealed enclosure they shine. Difference is HUGE. They sounds very good.
The kick is big, internal volume is enought for a flat response measured at home. (they have identical or better response than the Vifa woofers at my foorstanders).



HP80 LP600 (I use a HP for comparation because the towers are TL and have much more low end)
Orange: Vifas at a AudioPro FloorStander cabinet (that sound very nice)
Blue: CA18rnx at fiberglass 7(aprox) liters kickpanel enclosures

The bottom lines are 3rd HD. From HolmImpulse.


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## armen818 (Sep 18, 2009)

can you plz explain what u mean

1) resistor ?
2) adding mass to the cone ?




Patrick Bateman said:


> If I were going to put a woofer in a door, I would use one with a high QTS, or I'd raise the QTS with a resistor or by adding mass to the cone. (Or both.)


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## Buzzman (Jul 26, 2007)

Patrick Bateman said:


> I agree. A few years back I used a pair of Vifa woofers in the doors of my Escort, and it was completely anemic. I believe another problem was that the doors are very leaky.
> 
> I've had much better results from a small sealed enclosure.
> 
> If I were going to put a woofer in a door, I would use one with a high QTS, or I'd raise the QTS with a resistor or by adding mass to the cone. (Or both.)


I had always searched for and used a high Qts driver for installation in my doors and use as a midbass. I had excellent results with several Morel woofers (Qts of .55 and higher, Fs around 40 Hz on avg.), and less so with the Critical Mass MB82 (Qts. of about .3 (if I remember correctly) and a Fs of 44 Hz). However, hands down, the best midbass performance I have ever had is with the new Phass MD0875 8" midbasses that Phass developed at my request. I told them they should target a Qts. of .55 or higher to obtain the best results in the application that most people use in their cars - door mounting. Well, after installing these woofers, letting them break in, hearing the results, and reading the T/S parameters, my thinking was realigned. The Qts. is .25 and the Fs is 49.8 Hz, which I wouldn't call "high." Patrick, are you and Dangerranger suggesting that a low Qts. woofer would need a higher Mms in order to operate optimally in a free air/IB application? I don't know what the Mms is on the Seas woofer others have mentioned, but the Mms of the Phass woofer is listed as 17.69, which is quite low. And, as I have said, it's by far the best midbass performance I have ever had in my car. Can the Vas be a significant factor? By way of comparison, the Vas on the Scanspeak Revelator 22W (which has a published Qts. of .3 and a Fs of 23 Hz) is 89 liters, whereas the Vas of the Phass woofer is listed at 41 liters. What role might speaker sensitivity play? The listed sensitivity of the Phass woofer is 95db. Thoughts from those with greater engineering acumen than I would be appreciated.


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## Dangerranger (Apr 12, 2006)

Buzzman said:


> Well, after installing these woofers, letting them break in, hearing the results, and reading the T/S parameters, my thinking was realigned. The Qts. is .25 and the Fs is 49.8 Hz, which I wouldn't call "high." Patrick, are you and Dangerranger suggesting that a low Qts. woofer would need a higher Mms in order to operate optimally in a free air/IB application? I don't know what the Mms is on the Seas woofer others have mentioned, but the Mms of the Phass woofer is listed as 17.69, which is quite low. And, as I have said, it's by far the best midbass performance I have ever had in my car. Can the Vas be a significant factor? By way of comparison, the Vas on the Scanspeak Revelator 22W (which has a published Qts. of .3 and a Fs of 23 Hz) is 89 liters, whereas the Vas of the Phass woofer is listed at 41 liters. What role might speaker sensitivity play? The listed sensitivity of the Phass woofer is 95db. Thoughts from those with greater engineering acumen than I would be appreciated.


It's all relative. There are a lot of ways to skin a cat and realistically, a lot of ways that you can have a low Qts or high Qts or similar. You could have a weaker motor and get a lower Qts by having a "looser" suspension, or less moving mass. A stronger motor and raise the Fs and Qts by installing a suspension that's particularly tight. A stronger motor with a looser suspension and a higher moving mass in order to get a lower Fs and Qts. There are thousands of options in terms of design. Just have to get the balancing act down. So yes, the Vas is a significant factor relative to the other parameters, but not in and of itself 

In your specific scenario, 8" midbasses never hurt  But in addition to that the perceived lack of midbass most people experience isn't below 100hz as much as it is the midbass to lower midrange region. Cabin gain takes care of the lower octaves, where the midbass to lower midrange region has to fight both door resonances as well as the vehicular equivalent of baffle step due to most doors, kick panels, etc having surfaces near enough the driver to provide a boost at higher frequencies, particularly in the right side door as it's more on-axis to you. I'd call 100-300hz the critical range in terms of midbass drivers, and for an 8" midbass driver a lower qts works just beautifully. Just the same as a lower Qts subwoofer works great IB in cars. I personally feel that the smaller the driver gets, the closer you have to get to the .7 Qtc (taking enclosure into account) just due to the frequency range it has to produce. Drivers like the W18NX excel do well due to the fact that they have a low Fs in combination with the low (but not terribly low) Qts, but the other reason they work so well is that they have much more linear excursion than most dedicated car audio drivers so even if you wanted to boost the low bass, it's got the excursion cushion to do so without it sounding like ass


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## ErinH (Feb 14, 2007)

just tossing it out there, but what about lowering the fs by adding mass to the cone via some sort of compound (polyurethane/glue/etc)? 
Then increase Qts by adding a resistor in series of the driver? 

Would this help?

Edit: I’m not a speaker builder. It seems to me that fs & qts are related but the only equations I can find are from wiki and it doesn’t show either as a function of the other:
Thiele/Small - Wikipedia, the free encyclopedia


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## Oliver (Jun 25, 2007)

*Someone has dealt with this before, here are some posts.*



> Using a crossover inductor with a high resistance will raise the Qts, true. The only problem there is that they correspondingly cut sensitivity. It's a little like "adding bass" simply by cutting the midrange and treble.
> _________________________________________________________________
> 
> ... even without a Linkwitz transform. Adding the transform (at least based on free air response) to such a system could result in one of those nasty bass-mobiles and may not be healthy for the woofers.
> ...


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