Does speaker Qts matter in door installations?
I have asked a similar question over on DIYMobileAudio 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 many years but stayed away from serious car audio upgrades because I did not have the time to do it right. Now, I want to attempt some upgrades on my cars but I want to do it based on sound design principles.
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 2 octaves or so 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?
Great question, and I look forward to your experiments.
I've done some in-door box installs and they definitely work better than the average speaker just mounted in IB. Even inexpensive speakers benefit and can be surprising. But it ain't practical most of the time.
No measurements were ever done on my installs, other than an occasional system RTA.
As far as DIY drivers go, I began using them for car installs in the mid-80's. They worked very well compared to existing car audio components, but you'll have to roll your own crossovers and grilles. Although this adds expense and much more work, you can end up with a very nice product, be proud of your efforts, and still save money over off-the shelf product.
It's been a few years, but the last one I did used 4 Audax 6-1/2" (Qts in the 0.7 range and Fs in the 60Hz range) in the doors and rear side panel factory locations. A true 25Wx4 amp, Peerless tweeters in the front only, and no subwoofers. It sounded very nice with full and solid bass response down to what really sounded like 60Hz, and it didn't diminish with volume. 12dB LP's with Zobels on all four Audax's to keep the garbage above 3kHz somewhat out of the way.
IMO, don't get too hung up on Qts. It certainly matters more in boxless installs, but superior low-Qts drivers should be considered for their own merits.
My own starting point for panel mounted midbass/midrange parameters is to look for Qts of around 0.5 or higher, reasonable efficiency, and then I start looking at upper end frequency response where it will (usually) be off-axis and must overlap with the tweeter.
IIRC in case I mess this up, the qts is how much resonance the sub has, meaning it will be more efficient there. However in turn it does not tune low in a small box everyone wants. So for IB you want it to have some resonance because you have no box....in turn for a small box you need a well damped cone. I have used .4-.6 subs IB with good results, new high power subs with .4 can run IB no problem and you can get substantial bottom out of them....too much for some. And they are less efficient you have to keep an eye on that. I rarely go to the hassle of an enclosure, and today with massive power handling and EQ power it is not that important like it used to be if you use a lesser tuned driver. But, what is fun is to get winISD and try different drivers, it really helps to understand what is changing. That is what I do when I don't mess with them and forget what all the numbers do.
A door is typically large and loose enough to be full IB for most drivers, but you need a solid baffle to get bass just the same as any IB so a good baffle is needed. I also have used those foam guards and tune them with holes, but they don't work as well with powerful high excursion drivers.
I want to expand on the reason for my post.
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 enclusure 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.
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.
I have not been able to find any evidence that the DIY community has taken a systematic approach like this to evaluating drivers and published the results.
There are some issues to consider. One, many drivers today are much higher power handling than they used to be. So one of those can be used with reasonable power IB just because they are so HD. Given you only need about half the power IB as a box can take. Next you have to high pass the driver correctly high enough to stay out of the bass/excursion limits for a given driver. You can use the foam pods to tune them up, but I would still HP them if you have bass distortion/overpowering issues. A woofer will run higher but still a woofer and you will be lucky to touch 80Hz with much power in a 6.5, excepting some expensive ones. I mean how low can a 6.5 get in a home speaker? They can't, not a woofer. Can also get on various forums and people talk about using various drivers. If you need really loud, most home drivers are not going to work excepting some expensive ones that can do near anything. I don't recall running over a 2x75 on fronts, but that was a 12v rated old amp. Driver efficiency and Fs go hand in hand often, but you have to watch efficiency it can require more power for the same output don't ignore that. A lot of people are using the peerless XLS for cars, they are quite capable of getting some bass and still sounding good, but same issue they can't go too high so you have to run a larger mid. A 7" can also be a good compromise and about large as you can go two way unless you run a 3" for a tweeter not a dome.
IMHO unless you need a small box woofer, I have used the cheapest junk sub and they worked fine for reasonable use, SQ use. A sub is a sub. Now you want loud big spl and/or small box SQ then you need to shop more careful. I ran some great sounding pyramids for years that would stand the hair up on your neck and shake the mirrors, and they were just 10s. Most of a sub is in the install, but you need a sub to match a special install or the install to match the sub...if you see what I mean.
Yes a 6.5 is not going to get subwoofer low only at low outputs, the db drop like a brick. I'd always go larger woofer/mid in a door anytime I can. See Euro cars are going to an 8" coax now I bet they have some bass. And a lot of high power drivers are not good at making bass, not sure why, but I find that, but most people have EQs now to change that.
Re: Does speaker Qts matter in door installations?
When it comes to subwoofers, in cars often URPS is used (i. e. under-resonant powered subwoofer, I think). The enclosure is made so small that the resonant frequency is pushed to a point above the low-pass frequency. It takes a woofer with sufficient displacement and power handling. Then it is simply a question of enough amplifier power and adequate equalizing to achieve satisfying performance.
Re: More details
The term "damping" is confusing, because as (1/Q), damping is reduced as box size is reduced. Maximum damping is achieved in IB. Yeah, it's semantics, but it's easily confusing and we don't want to lead others into thinking backwards.
Power handling is indeed greater in sealed and ported boxes over IB. Additionally, the car audio world is indeed much harder on drivers than home audio.
But my own theory, based on my time as an professional installer, is that the added stress in car audio is due to:
-the noisy environment we must overcome;
-the fact that we are isolated in our cars and can really crank it up without disturbing parents, neighbors, etc;
-the operator (and I won't go there);
far more than due to the lack of an enclosure.
I don't blame Madisound for not honoring warranties for products installed in cars. Car speakers get beat on consistently more often, get replaced more often, and that wasn't the game Madisound wanted to play.
I never found indication personally that the raw drivers available were unsuitable for car use. My 17W75's were purchased from Madisound in 1987, and are still in fine shape today. I quit buying "car audio" drivers around 1986. I used products from Vifa, Audax, Polydax, Dynaudio, Focal, Peerless, and others. Sizes ranged from 12" to tweeters.
Professionally I recommended, sold, and installed off-the-shelf car audio speakers until 1993. But, with the sole exception of a pair of Alphasonik plates that I already owned, I never put another "car audio" speaker in MY own car because I like the raw drivers better.
mda185, your planned approach to testing sounds spot-on.
I would humbly suggest testing some inexpensive drivers as well.
My theory has always been that the low Qts and low efficiency of most aftermarket mids was simply to help control the cone due to the abuse most of them see.
I'll go measure the Qts of the factory drivers in my car later; I have a feeling it will be fairly high. Factory driver tend to have a high Qts as a result of using undersized motors and inexpensive soft parts to keep assembly costs down.
I've personally always thought a mojority of factory mids can sound OK if crossed properly and given some clean amplification. I can't say the same for mylar tweeters and a single electrolytic as a crossover though.
Do you have any suggestions for specific inexpensive drivers to evaluate? I just started with drivers that I already have on hand or was getting ready to purchase. The discontinued Peerless CSX 165 C drivers would have been a good candidate but I do not know if there is something comparable in the marketplace now. I actually have a pair of the CSX 165 C and could include it in the evaluation.
As far as progress goes, I installed sound deadening in the driver's door and started cutting mdf baffle rings this weekend. I took photos of the sound deadening install if there is any interest here. I used a product called Brown Bread and some generic foam and sound barrier material purchased from McMaster Carr online.
I forgot to say thanks to everyone for the constructive comments. More to come.
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