Car Subwoofer Sensitivity
In a recent exercise, I took a long search of available 12" drivers available on the market to try to find the best DIY for the buck. Although I ended up going with a used 410 for economy reasons, I thought it would be interesting to note a few findings and address the blanket statement that always come up when it comes to car subs and their efficiency.
For the most part, the blanket statement that car subs are inefficient is true of any subwoofer (vs. a woofer). To get useable output at or near 20Hz, the cone has to have a low resonant frequency (added moving mass) among other necessary design specs that make for a very inefficient speaker (Sensitivity in the mid to high 80's).
However, there are exceptions. Some subs out there have efficiencies in the low 90's. A decade ago, Cerwin Vega and Lanzar used to put out highly efficient subs - but by design they had very little excursion, requiring large banks of them to move any air below 40Hz without bottoming out. Mutually exclusive design properties are a beeyatch. Other brands had efficient subs that could go low somewhat efficiently - if you put it in a box the size of a walk-in closet.
These days, there's a LOT of deceptive practices in sensitivity listing. Rather than stick to the standard 1W/1M (as flawed as many think that is), many companies are now listing their driver sensitivity at 2.83V regardless of speaker impedance. When most speakers were 8 ohms, 2.83V was equivalent to 1 Watt. But these bastids are using the 2.83V standard on 4 ohm and even 2 ohm voice coils, padding their sensitivity numbers with up to +6dB. Pretty crappy for those who aren't familiar with circuit theory. The giveaway is that their 2 ohm voice coil model magically has double the sensitivity of their 4 ohm model.
So now you can rate a subwoofer at it's arbitrary resonance peak at say 1KHz, giving you a +6db gain over the actual frequency range it's intended for. Then you rate it at 2.83V which inflates another +3dB on a 4 Ohm speaker. That's a lie of +9dB, making your 86dB speaker look like it has a sensitivity of 95dB! Major suckage.
I should mention that the other design parameters of the Lanzars and Cerwin Vegas of decades past put them more in the category of woofers than subwoofers. They typically went into ported alignments that dropped off below 45Hz.
And woofers make for good bas cabs, Eminence Kappalite 3012LF being a great example.
Car audio speakers, of any sort, are intended to reproduce recorded music, and thus, are never any good for musical instrument applications. All specs aside, the general topic comes up here often enough, and anyone seriously considering building a bass rig would do best to skip these drivers altogether.
Hi RickenBoogie, this is a statement that I have heard many parrot but I I'm not a fan of blanket statements. Live music can definitely have more dynamic range than recorded music (which is usually compressed), but that doesn't mean a car speaker can't perform if it's suited to the task.
Basically, if the dynamic range and volume level exceed the speaker's limits, one of three things happen:
1. The voice coil melts (this is more likely with compressed music than uncompressed live music),
2. The excursion is exceeded and the speaker bottoms out (car subs are actually less likely to bottom out than bass cab woofers because they're usually designed for lower frequencies and have more excursion built into them),
3. The cone breaks up due to high SPL at higher frequency than design. This is where many car subs can run into trouble when used for live music, IF they're not crossed over at a low enough frequency.
There's nothing magical about live music and there's nothing about a car speaker that makes it not work outside of a car. If a design takes into account the strengths and weaknesses of speaker, it can work in the application.
But based on my discussion above, ANY subwoofer is sub-optimal in a live music application unless it's designed like a woofer, OR it passes off the midbass load to another driver at a relatively low crossover point if the cone can't sustain high output at frequencies above its intended range.
My recent foray into building bass cabs with leftover car subs I had sitting around the house was a hit/miss experience.
For my first design, I tried to use a 10" Polk MM series speaker combined with a soft dome tweeter. Its midrange response wasn't able to adequately bridge the gap to where the tweeter output was significant, giving me a permanent mid scoop. Fail.
My second design paired an old school 12" JL sub with a 6" Eminence Alpha midrange, which allowed me to cross it over at 800Hz. This is now my home practice speaker, and I'm VERY pleased with its tone, accuracy, and low excursion for dropped tuning.
However, the low sensitivity (86dB) of the JL relegates this to living room use only, which is what it was intended for. This cab will kill any 50W practice combo out there (it should since I'm pumping in 175Watts) in terms of crisp transient response, clarity of tone, and low B response that rattles the rafters.
Again, it's a matter of design expectations and real world limits. No voodoo needed.
+1 on the suitability of car and HT sub drivers for home practice. They are built take a real beating. With a mid crossed over in the mid-upper hundreds they can make a great practice cab. An added benefit is that their relatively low efficiency allows a moderate-power amplifier (like my GK 400RB run into 8 ohms) to be overdriven at less than insane spls.
By the way, after my tour of available speakers, I came to the conclusion that if I decide to build a bass extension cab down the road to supplement my 410, the only real choice is the Eminence Kappalite. It has the best balance between efficiency, price, cabinet size, and good low frequency extension to 40Hz. But that's only down the road if I find myself craving more bottom end for some reason. And I'd cross it over to eliminate the proverbial "dice roll" to ensure it doesn't interfere with the active range of the 410.
Welcome to the world of marketing.
Car subs are woofers that are optimized to work in... cars.
Cabin Gain is integral to their design.
A sealed 10" (Rockford RFR-2210) has a dismal sensitivity of 85 SPL but it performs very well... in a car.
Moving up to the 15" RFR-2215 requires a much larger box at 5.7 cuft, and a slightly better sensitivity of 92 SPL.
These do get down very low, but are big, heavy and power hogs.
In 2000 I biamped four of the 15", plus E110 tops, and can tell you they are a giant PIA to handle.
The boxes are so big, and the output is so anemic I am better served with a bass horn.
Today, three of these drivers are now back in the boxes and their cabs destroyed.
The fourth lives in my storage unit for some future grand purpose such as End of Days...
Both the 10" and 15" do very well, in a car, in sealed boxes that capitalize on cabin gain.
Sealed boxes are easy to build and practical for vehicle use.
Outside of a vehicle, these don't have much use.
And no, not all car woofers are made only for sealed boxes, just as not all of them are true inefficient subs designed for near subsonics. Blanket statements and rhetoric don't change the fact that you need the right tool for the right job, which is a driver that matches what your goals are.
My secret is this: when I use a car subwoofer, I lie to it and tell it my living room is actually a car. Then it doesn't fail on me, and works like a champ! ;)
Inefficient in general for "sub woofers"? http://www.usspeaker.com/definimax4018lf-1.htm
Not hard to find well designed efficient sub drivers at all. That was just two random mouse clicks. If you are happy playing to your TV that is great. Kids coming here trying to find cheap ways out with low power amps, your post does no service to? IMO
It's like everyone is making the sign of the cross on themselves when someone mentions "car speakers," even though it has nothing to do with cars and everything to do with woofers vs. subwoofers.
I only linked subwoofers. Those designed for use under 1KHz. The 4018LF is 200 Hz and under. (Sub) woofer, low/mid range woofer low/mid bass are all design choices and none are bound to be inefficient by the "use" chosen in design.
Several times kids come here with the "great, new" idea of using "car" subs as bass guitar speakers and it always ends as a fail. It may only be time and material wasted, but why provide incentive to do such is my personal concern. I am a big believer in making what you have work so long as the outcome is reasonable and don't come out swinging saying those that know better are "making blanket statements that don't hold water".
We have a difference of opinion here clearly and will just need to respect each other's views. :)
IMO swamp_bass provided a good rational discussion of the use car & HT subs for bass cabs, something that is a taboo here at TB. He concluded that as a class of drivers they are generally too inefficient for bass cab use, and that the few moderately efficient ones require very large cabs and usually have small Xmax. He also found that they make a nice practice cab when crossed to a mid.
bgavin pointed out the role of cabin gain in car subs, and suggests that car audio sub drivers are designed (ts parameters) to work with room gain. Therefore, they are not very useful in a non-car environment.
B-string pointed out that we shouldn't encourage the use of car & HT subs for gig-worthy cabs because they are far too inefficient. Then mentioned that there were in fact some relatively efficient subs available.
There is a problem with nomenclature here. In the car-audio and HT world a sub is a driver/cab that provides useful response down to the 20-40 Hz range. In the pro-audio world, a sub is a driver/cab that provides response in the 40-60Hz range. In the pro-audio world a woofer is expected to go to about 60Hz. The drivers that B-string offered as examples of relatively efficient subs are just that in the pro-audio world, but are quite lacking (deep bass) in the car audio and HT worlds.
If we simply view these drivers as transducers with engineering parameters that may or may not be useful for a particular application, a number of car audio and HT sub drivers are seen to be potentially useful for low spl, practice bass guitar applications. Again, these are not gig-worthy drivers/cabs, but they sure can sound great (with a mid) for practice at home.
These competition 15" drivers are 90 dB at 1 watt 1 metre each with an fs at 30Hz as there are 12 of them in my son Henry's Hexa horn port design, he gets a British championship winning just under 169 dB at 10,000 watts at 30Hz.
As soon as you get a few of them coupling in a well designed and tuned enclosure the sensitivity comes up by a good amount.
The real issue here is they are best crossed out at 24dB per octave at only 80Hz.
So as a decent bass guitar cab like an Ampeg 8x10 is starting its LF performance where Henry's Hexa Horn Sub is being crossed out.
You might as well have just got another 8x10 Ampeg and another 300 watt tube amp instead.:bassist:
The fact that my home practice cab sounds great is very clearly balanced by the fact that I have to pump in 175W to match the sound level of a typical 50W combo. Therein lies the rub for anybody considering building a gig-worthy cab based on these massive subs: it will take half the western power grid to run them.
Building a bass cab with a car subwoofer is like building an airplane with wrought iron instead of aluminum. The strength is in a mostly irrelevant category.
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