In the first corner is an Alpine SWR-10D2 subwoofer. I really like these Alpine subs, I have four of the Type S and two of the Type Rs. For the money, they're tough to beat. Lots of clean output and they're affordable.

Here's the frequency response of the Alpine SWR-10D2 in a tapped horn with 2.5 cubic feet of air volume. This sim is with 500 watts (4ohm).

Here's some things I see:
1) It has an F3 of 25hz
2) It generates 114dB of output in it's passband, with 500 watts

114dB doesn't sound like a lot these days, and you're probably wondering why that's so low.

The answer to that is "cabin gain." Depending on the dimensions of your car, you're going to pick up as much as 30dB of extra output due to cabin gain. That's how people squeeze 140 or even 150 decibels out of one woofer. (Thanks to Andy Wehmeyer and JBL for the graph. BTW I'm working in Glendale for the next two weeks, so drop me a line if you want to meet up.)

Once we factor in cabin gain, we wind up with a response curve that's getting louder and louder as we go lower and lower. IMHO, this is the main reason a lot of car subs sound "slow." The problem isn't the driver, it's the car. We have too much bass from 20-40hz and it makes the octave from 40-80hz sound "slow" and "thick." It takes a while to realize this, because cars are one of the very few places where you routinely hear 10hz bass, and lots of it!

 

We have too much bass from 20-40hz and it makes the octave from 40-80hz sound "slow" and "thick." It takes a while to realize this, because cars are one of the very few places where you routinely hear 10hz bass, and lots of it!

Yep. Wish more people would realize this.

While it's completely true that displacement equals output, efficiency can still be an issue. If the -f3 (rather Fsc) is too high, we risk hitting thermal rating before Xmax if we use a LT.

 

following along with this, because it makes sense.

 

In the other corner is a Stereo Integrity HT18" subwoofer. The HT18 is possible the best "bang for the buck" subwoofer you can buy today. Check out my "bass race" threads to see what's on top at the moment. The HT18 moves a LOT of air, but it requires a big box.

Or does it?

See, I see this thing as an air pump. Sure, it needs a six cubic foot box if we were using the rules of 1975, but it's 2015 and we don't need big boxes, we have MiniDSP and we can dial in whatever response curve we want.

Here's the frequency response of the HT18 in a sealed box with 2 cubic feet of air volume. This sim is with 500 watts (4ohm).

Here's some things I see:
1) It has an F3 of 50hz
2) It generates 120dB of output in it's passband, with 500 watts

I know that response curve looks "peaky." To get a Qb of 0.7 we would need six cubic feet, and I'm using a box that's one third of that.

The thing is, we can change the Qb, but there's nothing we can do about a driver that can't move enough air.

Once we factor in cabin gain, we wind up with a response curve that's getting louder and louder as we go lower and lower. But unlike the 10" driver, the 18" in a sealed box winds up fairly close to flat. Basically the falling response of the sealed box is offset by the rising response from cabin gain.

 

You can simulate a LT in winISD as well...that way you can keep a check on excursion and power input.

 

I think the lack of excessive low bass is why I like the tonality of pro midbasses and subs in a car...it probably is more flat using cabin gain.

However the excessive bass is easily fixed with an EQ. Anytime you have to cut back output and reduce excursion, you will also lower distortion.

 

I don't think a whole lot of EQ needs to be used on the HT18. It's +/- 3dB from 20hz to 80hz with no EQ at all.

Compared to using a couple of twelves in one cubic foot boxes, the HT18 will have the advantage of more maximum displacement. Basically it won't have to move as far to generate the SPL, because the cone area of an eighteen is so massive. (An 18" woofer has more cone area than two twelves, and almost as much as four tens.)

The big enemy for the HT18 in this box is going to be heat. I nearly bought an HT18 for my car, but I ended up going with a B&C 12" woofer because the B&C had a voice coil that's 4" in diameter, versus 2.5" for the HT18.

Tapped horns are loud as ****. I have one in my home theater, and the main problem with it is that it's so loud, it tends to drown out the other subs. If you like it loud, you'll like tapped horns.

The lowly Alpine 10", in a TH, is louder than the eighteen. So we'll need to apply a "cut" of about 5dB in a broad band from about 15hz to 40hz.

Oddly enough, the Alpine has a larger voice coil than the SI. But not by much, about 2%. OTOH, the Type R woofers have a patented motor that's designed to draw the heat away from the voice coil.

In a tapped horn, the magnet of the woofer has the air from the box moving back and forth over it. Combine that with Alpine's patented motor, and I'm willing to bet that the SWR-10D2 will handle more power... but not a lot more.

 

this is why I'm debating heavily between the stereo integrity ht18 in about 2.5 cuft vs an eminence definomax 4018lf in about 5 cuft ported around 38 hz, I think they'd have similar response but the eminence offering would get a buttload louder. Not simmed it yet so..maybe I'm crazy?

as a favor/test for your own enjoyment (I hope) perhaps you could sim the eminence driver in about 5 cuft or so tuned to 38 hz? would be interesting to see how it stacks up for those who can give up the space and want the efficiency of pro audio drivers.

heres a link in case you get inspired.
Eminence Definimax 4018LF 18" Speaker Driver

 

Here's the cost of these options also:

Alpine SWS-10D2 - $150 online
Stereo Integrity HT18 - $159 online

So the big difference is whether or not you'll need a miniDSP.
The fact that the tapped horn is about 5dB more efficient is a factor too.
MiniDSP is $80.

 

another interesting thing to look at would be the fs of the driver, how much does it play a role in what a driver can handle down low? my reading tells me that above fs the suspension is controlling the driver and below, the motor controls it. if this is true, then it'd be really easy to apply too much power below fs and do serious damage. Is this why pro audio drivers recommend such steep highpass filters to protect them? I know this is kind of ot from the original intent of this thread but I think its right along the same path.

 

The air spring in the enclosure "control" movement. (I should say restrict though). In an IB config this is more of an issue. In a sealed enclosure, Fs = Fsc. We constantly use our sealed enclosure below Fsc.

 

Based on the earlier posts, I saw a trend:

A small woofer in a tapped horn offered the most output, but a giant woofer in a small sealed box offered nearly as much output, but didn't require as much EQ. Basically the TH has *too much* low frequency output.

And the problem with both of those options was the voice coil; each one had a 2.5" voice coil, because they're inexpensive woofers. ($150 and $159, respectively.)

So...

It seemed like the best option would be something with a bigger voice coil.

Here's the response without cabin gain

Here's the response with cabin gain factored in, and the excursion curve

I modeled the B&C 15PS76. Here's what I see:
1) Above 40hz, it's more efficient than the Alpine or the Stereo Integrity
2) By the time we reach 40hz, it's as efficient as the SI, and the Alpine tapped horn is more efficient.

All of this kinda turns into a tribute to Hoffman's Iron Law, it's really hard to get more SPL without losing bandwidth, and vice-versa.

Honestly, all of these options seem viable. The HT18 is easy to build and it will deliver the output. The Alpine is efficient and goes low, but don't bother building it if you can't measure it, because it's going to need EQ. The B&C in a vented box has a response curve that's similar to the HT18. It costs more. But it also has a larger voice coil, and that generally means it will get louder with less power compression.

Decisions, decisions.

I still think using a QTC of 0.7 in a car is a waste of space

 

I really have to get some work done, so I'm going to stop doing sims.

But after running all of this, I think the limiting factor is mostly going to be heat.

The Stereo Integrity has a 2.5" voice coil and it's $159
The Alpine Type R 10" has a 2.6" voice coil and it's $150
The B&C has a 3" voice coil and it's $196

I think the most promising option is the Alpine Type S. ("S", not "R") You can get two of the Alpine Type S tens for under $200. Two of the tens will give you the advantages of the B&C woofer, basically you'll be able to handle more power, because you have two voice coils. But two of the Alpine Type S tens will have more displacement than the B&C, because the Alpine has more XMAX. The Stereo Integrity has more displacement than every single option in this article, but a pair of the Alpines will handle more power.

Winner: Alpine Type S 10D2.

 

Oh, one last thing -

Typically, a Linkwitz transform is an EQ filter that's applied to offset the rolloff of a woofer.

In a car we can't use a "simple" Linkwitz transform, because of cabin gain. Basically cabin gain gives us a Linkwitz transform for free, and we have to use EQ on top of that to get our target curve. So most of these desigs require EQ, but it's not the simple EQ filter we could use at home.

The Sunfire subs are probably the best known example. The box is much smaller than you'd use with a conventional alignment, and then a woofer with tons of xmax, a big amp, and a Linkwitz Transform circuit is added in to make it work.

 

Thanks! Very informative

 

Interesting and reminiscent.

 

I kinda went through this when trying to pick subs for my IB manifolds. I was really worried about qts for IB, since everybody seemed to think .7 qts was ideal since qts=qtc in true IB. The argument was made that they would not get low easily. But then I remembered cabin gain, and it made me rethink the "ideal" sub. So the subs I have are qts .33 and I am using multiples and going for pure cone area of excursion.

 

I probably posted this before, but I got the schematics for a dinky little soundbar/sub from the nineties by Pioneer and they had some pretty wild equalization built into the analog pre-amp of the sub. I believe they maximized the sub's enclosure size by doing something like +9 db narrow band equalization right at tuning, but a subsonic filter too?

seems like this stuff is old hat, or just a re-excitation of the synapses, perhaps because MiniDSP allows custom pre-amp work without the math...

 

That is why I say reminiscent. When you think about it, back in the nineties (if you were there), using a high Q sealed was pretty much the norm although some were better than others. I don't remember having any issues getting low end back then, although the boxes weren't as small either. Still, I'm not sure how the stance on low Q came about. Perhaps when micro enclosures (solobaric) entered the stage and trying to keep a knee response down since the whole objective raised the roll-off point a bit. Again, with enough power & cone area, it could be dealt with easily especially in these times where EQ & DSP are abound.

 

I think it was mostly the Internet's fault. Twenty years ago, people put a speaker in a box and hoped it would sound good. The Internet changed that; in the span of about five years we figured out a lot of exotic enclosures that were 'trade secrets.' I can still remember how amazing it was when that dude from JBL published the articles on modeling transmission lines. (Ausperger or something?)

The problem was, only a handful of people spelled out the effect of cabin gain. I've been using the same graph from Andy W for about a decade now.

IE, we all KNEW that a car made bass louder, but I don't think that everyone understood that it changed the Q too.

 

^ and inexpensive efficient power.

 

I currently use the Hivi 15" X3 subwoofer. It sell for about $125 shipped and I have only found one place selling it (tsgaudio). It has a 3" voice coil and has a 13mm excursion. I will be trying it free air in my next install so we shall see. I do expect to need heavy eqing to flatten the response.

 

heh, I asked you about buying yours a year ago : http://www.diymobileaudio.com/forum/2062208-post22.html