# Does speaker Qts matter in IB door installations?



## mda185 (Dec 14, 2006)

I have been a member of this forum for a few years but only started posting frequently in the last month. The subject of this post is something that has been bothering me for a while because I can't find any test data to shed light on the answer. I have asked a similar question over on DIYAudio forum. 

A lot of folks talk about buying raw speakers from Parts Express and Madisound that have 4 ohm impedance and using them as midbass drivers in car doors. I have been building home speakers for a long time but stayed away from serious car audio upgrades for the last 15 years because I did not have the time to do it right. (Kids, home projects, job changes, etc,) Now, I want to attempt some upgrades on my cars but I want to do it based on good design principles as I have learned them in home audio speaker building. 

The basic question is has anyone on this forum installed raw DIY drivers in car doors and measured the resulting Qt and frequency response? Does a well constructed door install approach the response of a ported or possibly an aperiodically damped design? I always thought conventional wisdom was that a car door was closer to an infinite baffle and that drivers with Qts in the 0.30 range were not suitable unless crossed over to a subwoofer 1 or 2 octaves above their installed resonant frequency. I thought you needed a Qt of something between 0.70-1.0 to get good tight bass response in a car door. I don't see many DIY drivers with Qts this high.

I am about to conduct some experiments with raw drivers in the door of a 2001 Pathfinder but I am looking for information from anyone that has already gone down this path. Does anyone out there have some real world experience to share?

IIRC, the problems that might crop up using DIY drivers in IB door installations are caused because there is inadequate damping on the voice coil and cone assembly. The air in a sealed or ported enclosure acts as an additional spring that helps control the excursion of the cone and enable the speaker to approach its electrical power handling capability without running out of voice coil travel. I remember Madisound folks telling me > 10 years ago that they would not honor warranty claims for drivers that had voice coil damage because the mechanical limits had been exceeded in a car stereo install. I had damaged a Morel MW244 driver running it in a rear deck IB install and I was not pushing it with high power, high spl at the time. They explained that a woofer designed for car audio would have stiffer suspension and a raised bump plate to allow longer voice coil travel without physical contact between the voice coil former and the back plate of the magnet assembly. 

Having said all of that, I want to find out if today's generation of DIY drivers are more suitable to IB installations in car audio systems and if the speaker Qts is an indicator of suitability. Without test data, it seems to me that running a DIY 6.5" woofer in a door without crossing to a subwoofer could still result in a damaged driver. That is exactly what I want to do in my family car. I don't want the hassle of making room for a subwoofer enclosure in my Pathfinder. I can live without extremely low bass response if the 6.5" drivers will get down to 60 Hz region without running out of mechanical excursion capability at moderate to high sound levels (~95-98 dB SPL). 

My approach is going to be this:

1. Build MDF baffle plates to attach the DIY drivers to my door structure.

2. Apply sound deadening to the door skin and the inner panel. Seal openings in the inner panel to best of my ability.

3. Measure installed Fs, Qt, and frequency response with the door open and with the door closed. The difference between door open and door closed should give the cabin gain. I am curious to see if cabin gain offsets the early roll off you get with a low Qt.

4. Repeat this process with as many different drivers as I can get my hands on. To start, I will look at Dayton RS180, Peerless SLS 6.5", Dynaudio 17W75, Adire Koda 6, and Dynaudio MW160. 

5. Try to model cone excursion based on the installed measurements to see where these drivers run out of travel. I don't want to test to destruction.

I will be using Praxis to take measurements and LEAP to do the modeling if I have the time.

I have not been able to find any evidence that anyone in the DIY community has taken a systematic approach like this to evaluating drivers and published the results. The closest thing to this I could find is Geo's excellent review of the Peerless SLS 6.5" where he talks about audible indications of mechanical stress with a Scan Speak driver and lack of it with the SLS.


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## captainobvious (Mar 11, 2006)

Im very interested to see your results. Door installs Ive always considered IB as well. They are leaky by nature anyway with drain holes and the window seal so a true sealed door is pretty much impossible without building a self contained sealed enclosure inside the door.
I always thought that the cabin gain/transfer function is what made a lower qts driver seem to have more output and midbass response that what it would appear to produce by the numbers.


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## Brian Steele (Jun 1, 2007)

mda185 said:


> Having said all of that, I want to find out if today's generation of DIY drivers are more suitable to IB installations in car audio systems and if the speaker Qts is an indicator of suitability.


It depends .

If you're NOT going to be using a subwoofer, what's going to be most important is how the driver reacts when it receives large signals, which you will be feeding it at low frequencies to compensate for the higher noise level in-car. The typical t/s parameters don't cover this, as they're small-signal parameters. Larger Xmax is better, but even then Xmax doesn't tell you how that driver will behave if it receives a signal that sends the cone beyond Xmax. 

In terms of frequency response, the drivers I'm currently using are both low Qts and Low Fs. The rolloff is shallow and easily compensated for by the cabin gain. Bass is very clean, and I think it should be possible to run them full range at "decent" levels, but I don't drive them below 100 Hz because I like to turn the volume up and I don't like buzzing door panels and distorted low bass .


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## mda185 (Dec 14, 2006)

Brian,

Does that mean you high pass the door speakers at 100 Hz and don't have a subwoofer? I just visited your web site and it seems that if anyone would use a sub, it would be you.  LOL


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## Brian Steele (Jun 1, 2007)

mda185 said:


> Brian,
> 
> Does that mean you high pass the door speakers at 100 Hz and don't have a subwoofer? I just visited your web site and it seems that if anyone would use a sub, it would be you.  LOL


LOL - two 12's in the rear


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## schmiddr2 (Aug 10, 2009)

4 weeks gone by. Anything yet? This is some info I might need soon.


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## michaelsil1 (May 24, 2007)

I used to think so, but now I'm not so sure.


I was having a very hard time getting the Mid Bass to sound right (SEAS W18NX IB in Doors) I thought that it was because they have a low QTS. I've been hit lately (IASCA) for having too much Mid Bass; I now having it pumping out the Bass. So I guess I'm going to say it's harder with a low QTS to get it to sound right. I'm sure someone can find fault with my logic since I really haven't played with that many Drivers.


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## Patrick Bateman (Sep 11, 2006)

If you don't like the QTS of your driver, just change it. I've done it both electrically and mechanically. Check out this thread:

diyAudio Forums - Tapped Horn for Dummies - Page 1


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## michaelsil1 (May 24, 2007)

Patrick Bateman said:


> If you don't like the QTS of your driver, just change it. I've done it both electrically and mechanically. Check out this thread:
> 
> diyAudio Forums - Tapped Horn for Dummies - Page 1


That's interesting.


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## Jroo (May 24, 2006)

very interested in this for two reasons. First I am starting an install in a 04 pathfinder and second been looking for midbass drivers. Are you going to install in doors with the door panel on or off? The reason I ask is that I am being told that drivers like the dayton rs 180 will be hard to fit in the door without major cutting and baffles. I would like to do a 7" or 8" but am hearing that it must me less than 3" to fit a path door. The Mpyre was high on my list, but getting hard to find so I would also look at the Daytons if they fit and actually produce decent midbass in our doors


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## Hernan (Jul 9, 2006)

A car door install is very diferent to a home bafle install. You must use a HP electrical filter on the midbasses whatever QTS the driver has.

Cabin gain distort the frecuency response so much that is a real challange to have anything near a flat midbass response. 

Driver selection is still important, output capability, installation...

Today i pull out my Mpyres because they have TOOO much midbass output, even with heavy EQ... I install a more conventional woofer with higher QTS and they are easier to dial up.


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## Patrick Bateman (Sep 11, 2006)

michaelsil1 said:


> That's interesting.


The nice thing about using resistors is that you can tune it. Basically install the speakers in your car, add a bit of resistance, and continue to increase it until you get the response that you're looking for. I have a pair of home theater subs that use this, and they've been running great for a year. I thought I might fry the resistor in that time, but so far, so good.


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## mda185 (Dec 14, 2006)

*Update*

jroo, 

I plan to install in doors with the door panel on. I believe the Dayton rs 180 will fit in the door without major cutting but it needs custom baffles. The factory plastic mounting brackets will not work with most decent quality midbass drivers. There is a Pathfinder build log on here by ***** that describes the process of making mounting rings in great detail. Mounting depth does have to be less than 3" to fit a path door or the magnet will hit the window. The driver that worries me is the Peerless SLS 6. I think it is too deep to fit even with custom mounting rings if I want to keep the stock door panel. 

Current status is that I have all the drivers I intend to test and I have cut several mdf and mdf/plywood combination mounting rings. I am stalled while I try to figure out the best way to make mounting rings for the different screw hole patterns for all the drivers I want to test. I did not want to make completely different mdf adapters for each different driver but drilling multiple screw holes in one adapter will probably make it weaker and lead to problems down the road. 

I can state that custom mounting adapters are essential. The pathy door sheet metal is very flexible and needs reinforcement for any decent quality midbass installation. I will get some pics up of the adapters I cut tomorrow.


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## mda185 (Dec 14, 2006)

*Non speaker related update*

One of the reasons for the delay in getting the door midbass review finished also led to a pleasant surprise. I replaced the stock Bose head unit with an Alpine DVA-9860 and old school PPI PAR-225 preamplifier in the dash. The Alpine is not a great SQ unit but it has optical output and ability to control an H701 signal processor. (Something I plan to use in the future.) I also like that it plays MP3 and WMA ripped to DVDs. The Alpine preamp outputs are rated at 2 volts RMS but even that is optimistic. Before I installed the PAR-225, the sound coming out of the Bose amplified speakers was terrible. I believe the factory head unit drives the Bose amplifiers with speaker level outputs. (The factory system sounded pretty bad for different reasons. This is clearly not one of the better Bose OEM systems.) The PAR-225 gives me 5 bands of quasi-parametric EQ, an auxiliary input, and a very clean preamp section to drive the amplifiers down stream. It also has RCA outputs that are isolated from ground. 

When I used an oscope to set system gains, I found that the Alpine HU was clipping before it got to 2 volts. This meant that I had absolutely no headroom at high volume with just the HU. The PAR-225 allowed me to set the system up with 9 volts peak to peak driving the Bose amplifiers in the doors. This cleaned the sound up tremendously. It actually made the Bose speakers listenable. It is not what I would consider great SQ but for a family car, this is probably good enough for many folks. My wife is the primary driver of the pathfinder and this upgrade is definitely good enough for her. 

Bottom line is that a head unit upgrade with high voltage drive capability will improve the sound of the stock Bose speakers significantly. I want more than this so this trip will continue.


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## ChrisB (Jul 3, 2008)

I am getting ready to do a set of **THESE** IB in the doors of my 2006 Rustang. Hopefully they will handle from 200 Hz on up just fine.


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## mda185 (Dec 14, 2006)

Those Tang Bands should work fine IB if you cross them over 24 dB per octave at 200 Hz. Moving the crossover up to 250 or 300 will probably buy you a little better power handling. 200 is probably the lowest you want cross these without an enclosure.

This touches on a point that has been explained in other posts on DIYMA. If you cross the midbass over at a frequency 1 octave or more away from its resonant frequency, then Qts does not matter much. 06BLMUSTANGGT is planning on crossing over the the Tang Band 4" drivers at 200 Hz and the free air resonant frequency is 75 Hz. The Qts of the Tang Bands is 0.46. This means a gradual roll off in the low end that starts at about twice the resonant frequency or 150 Hz. To me, the most significant aspect of Qts in this instance, is when does the driver start to roll off and how steep does it roll off? The answer here is that the roll off is gradual and smooth. A 200 Hz crossover point should work OK. I would prefer 250-300 Hz. The slope must be 24 dB per octave or the driver response around its 75 Hz resonance will become an issue.

The reason I am going through the trouble to measure drivers with different Qts, is that I want to know how important it becomes when I want to run a 6.5" driver full range or cross it over below 120 Hz.


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## mda185 (Dec 14, 2006)

I did some test fitting today with the the RS 180 and SLS 6. The good news is that both will fit. The bad news is that it is not as easy as I hoped. The first pic is the OEM Bose speaker and amplifier assembly mounted on the door. The second pic shows the back side of this assembly. It extends 1 1/2" into the door. The depth of the assembly outside the door is 1 5/8" including the speaker. Pic 3 shows the door with window down. Max depth to the window is 1 7/8" in the center of the hole and 1 5/8" to the shallowest spot near the bottom of the window. The difference is because the window is mounted at a slight angle. Pic 4 is one of the mdf adapters I made after tracing the outline of the OEM Bose unit on cardboard to make a template. This particular adapter is a composite of 1/2" plywood and 3/4" mdf. This adapter comes close to matching the OEM unit in depth and with it, the Peerless SLS 6 fits. It is very close to the window but it fits. There is no room for a water shield. When I stack two pieces of 3/4" mdf to make a 1.5" spacer, both the Peerless and the RS 180 fit. That is the good news.

The bad news is that there is interference with the plastic speaker grill that is part of the door panel. Pic 5 is the inside of the plastic grill. The ring that protrudes from the perforated area is going to have to be cut down with a dremel and the opening in the door card will also have to be trimmed to fit around the speaker adapters I made. If I made speaker rings that were circular instead of following the contours of the OEM plastic mount, I could probably get away with just cutting down the ring around the inside surface of the grill. I wanted to make my adapters as strong as possible and that is why they are not circles. If you look up *****'s thread in the build section of this forum, you will see that he made his adapters circular but used polyurethane cutting boards for material. I don't have the equipment to cut that material efficiently and will have to find a way to do this with wood.

Bottom line is that large magnet 6.5"-7" midbass drivers will fit if you are willing to modify the door card. Forget about 8" drivers without major surgery.

There is one more issue that may cause problems. The SLS 6 magnet is very close to the diameter of the cutout in the door sheet metal and the magnet sits squarely in the middle of the cut out. This is bound to cause air restrictions for the back wave from the driver and I expect to see it show up in the measurements. Hopefully, it will cause frequency response problems at a higher frequency than I intend to operate these midbass drivers and won't choke it down low. (The SLS 6's are really more of a subwoofer in terms of construction.) The PE RS-180 has a smaller diameter magnet and it will be less of a problem in terms of air restriction. The Dynaudio drivers (MW160 and 17W75) both fit without any issues. 

That's all I could get done this weekend. The heat has been oppressive and I have been a single parent with two young kids this past week. My SO has been in Vancouver on business trip. I spent most of my time with the kids at the beach.


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## mda185 (Dec 14, 2006)

*Re:Tuning Qts with resistor*

Patrick,

I am not ignoring your suggestion. That has some very interesting possibilities. I just want to get the basic driver installs completed and make measurements before looking at mods like that.


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## Patrick Bateman (Sep 11, 2006)

mda185 said:


> Bottom line is that large magnet 6.5"-7" midbass drivers will fit if you are willing to modify the door card. Forget about 8" drivers without major surgery.
> 
> There is one more issue that may cause problems. The SLS 6 magnet is very close to the diameter of the cutout in the door sheet metal and the magnet sits squarely in the middle of the cut out. This is bound to cause air restrictions for the back wave from the driver and I expect to see it show up in the measurements. Hopefully, it will cause frequency response problems at a higher frequency than I intend to operate these midbass drivers and won't choke it down low. (The SLS 6's are really more of a subwoofer in terms of construction.) The PE RS-180 has a smaller diameter magnet and it will be less of a problem in terms of air restriction. The Dynaudio drivers (MW160 and 17W75) both fit without any issues.


Intuitively, a big hung of metal reflecting off the back of the basket is a BAD THING. The funny thing is that the closer it is, the less it screws up your frequency response. Strange but true.

If that hunk of metal near the basket is half an inch away, it will cause a dip in your frequency response at 6750hz. But if it's two inches away, it will cause a dip at 1688hz. Obviously, it's a bigger problem if it's two inches away.

I didn't even realize half this stuff until I started doing a lot of speaker measurements. That's why Bose can get away with using that plastic doo-hickey on the driver, the reflections are out of the pass band.


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## Patrick Bateman (Sep 11, 2006)

*Re: Tuning Qts with resistor*



mda185 said:


> Patrick,
> 
> I am not ignoring your suggestion. That has some very interesting possibilities. I just want to get the basic driver installs completed and make measurements before looking at mods like that.


Too bad the car is in New Jersey and the wife is in Vancouver - I do all my measurements at my house, 30 minutes south of the 'Couv... Would be happy to help.


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## Rob J (Jul 18, 2010)

Interesting thread. too bad it kind of got lost. Bringing it back TTT.


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## stream (Mar 24, 2009)

Rob J said:


> Interesting thread. too bad it kind of got lost. Bringing it back TTT.


+1. I'm also interested on results.


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