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Discussion Starter #1
This is a writeup in the footsteps of lycan, Patrick Bateman, and so many others here at diyma, which intends to answer a specific question regarding sub-bass reproduction down to 20 Hz. How do you do it in a subcompact car, without taking up the entire cargo area? Everyone's seen that walled-off CRX stuffed with MTX jackhammers or MMATS juggernauts. Or that civic with some kind of tapped horn / t-line enclosure that hits like a pissed off Irishman. But what if you actually want to carry passengers, or maybe a bag of groceries? And what if you want to reproduce that low cleanly? What compromises can be made?

Patrick Bateman started an excellent thread last year entitled, "BASS! How Low Can You Go?" (this thread is kind of trying to pick up where he left off), where he states:
To sum it up, if you're speakers only go to 30hz, you're probably not missing a whole lot. Almost all the "bass" energy is in the octave from forty to eighty hertz. But there *are* a handful of tracks with synthetic bass lines that can only be heard properly if your speakers are flat to 20, or even 18hz. And yes, there's even bass down to 3hz.
Later, he posted:
I went to the Skrillex / Knife Party show in Vancouver last week, and that had to be, without a doubt, the most bass I've ever heard in my life. ... Anyways, Skrillex was doing thes same trick, but to the whole damn venue. I have no freaken idea how much power and subwoofers it takes to do that, but it was EPIC. Even if you hate Skrillex, hate Dubstep, and think that dance music is for douchebags, it was a neat trick.

When I was walking up to the venue you could see the walls flexing. That is an absurd amount of power. This is the kind of sound system that could probably damage a venue. I wouldn't be shocked to hear that it could actually crack a wall.

Also, I want to stress that it wasn't that the show was loud. It was that there was a level of subharmonic bass that I've never seen attempted. My home subs do 15hz, and I have a train that goes by my house twice a day. So I know the difference between a 40hz bassline and a 10hz roar. You hear one, and FEEL the other.
I saw Skrillex in December and can confirm everything Patrick says above. My pants legs were flapping from all the sub-bass, and could literally feel the floor shake. I'm pretty sure a few pair of britches got crapped in that night :surprised: If you haven't experienced such an event, get out of your mom's basement and do so, right now.. this post will be here when you get back.

Love it or hate it, Dubstep and other fledgling electronic genres of music including Complextro, Moombahcore, and Glitchhop will make your system work harder than just about any other type of music out there. And IMO there is definitely some overlap between the Bass-Head and the SQ junkie.. They are not mutually exclusive. I will wholeheartedly agree that classic rock sounds like **** when the bass is boosted. This is because the information was never there in the first place, and the tonality goes to hell when most "bass boost" circuits increase the bands from 40 to 100 Hz. The genres mentioned above, however, were mastered to include sub- and infra-sonic bass down to DC, and don't need to be boosted at all. So the tonality is still there. Combined with a great three-way setup, and a rear-fill with Logic-7 style phase steering, these tracks sound positively amazing. A quick note about the rear fill.. There's a lot of out-of-phase content mixed into electronic tracks these days -- If you have Logic 7, listen to Rusko - Hold On (feat. Amber Coffman) (Sub Focus Remix), I can't imagine listening to it with only a front stage.

I am still somewhat of a newb, but here are the facts as I understand them (I am over-simplifying some of them for sake of brevity):
  • Hoffman's Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). The obvious implication is that to reduce the cutoff frequency by a factor of two, e.g. from 40 Hz to 20 Hz, while still retaining the same system efficiency, you need to increase the enclosure volume by 23=8 times! In other words, to reproduce ever lower frequencies at the same output level you need an extremely large box! -- quoted from a PB thread
  • More often than not, larger subwoofers reproduce lower frequencies more easily than smaller ones, while being more efficient. Consequently, larger drivers require a larger enclosures.
  • Ported enclosures sacrifice low end extension for efficiency higher in the passband. Most other exotic enclosure types work in the same way, and therefore aren't well suited to infra-sonic duties.
  • Making an enclosure smaller will reduce low-end frequency response.
  • Multiple subwoofers may offer better performance than a single subwoofer due to power compression. Everything else being equal, the multiple driver setup can play 3 dB louder with the same xmax.
  • Playing a a sub near or past its xmax will usually start to develop non-linearities that results in harmonic distortion. Some speaker models use shorting rings and other "tricks" to reduce non-linearities
  • Isobarik designs attempt to reduce non-linearities by using a set of matched drivers in push-pull configuration. I've heard mixed results on how well this actually works.
  • Sub-bass frequencies take considerable power (wattage) to reproduce. For a small car, class D amps are the way to go.
  • Cabin gain = free bass, and you get a lot of it in a subcompact. My R56 gets around 27 dB on the low end.
The short story is... Bass needs space. If you got the space, sub-bass is a piece of cake. If not, you will have to work around a serious set of compromises. Cabin gain is the only silver lining in an otherwise bleak and hazy future.


And to quickly dispel one of the most common myths. For anyone that says there's not a lot of content down at 20 Hz, I give you this, a random dubstep mix out of my iTunes library. It's a spectral plot of Excision Shambhala 2010 compilation, at around 1:19:20.



Here's another track entitled Scatta by Skrillex and Foreign Beggars. I consider this to be a excellent sub-bass reference track. Definitely worth a listen if your system is up to it.


For comparison, here's Hank Williams Sr. singing Your Cheatin' Heart, recorded in 1952. There's literally nothing past 40 hz.


So in the case of the first two tracks (and many others), the information is there waiting to be played. For my next post, I will explain the current setup I'm using and the measurements that I came up with.
 

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Discussion Starter #2
A Mini Cooper S has 5.7 cubic feet of cargo space in the hatch area (compare that to 21 cubic feet in a 2012 Ford Explorer). Before I had a sub box, there was barely enough cargo room to get a load of groceries home without folding down the rear seat. Adding even a small box is a huge compromise with an area this small.

So, with 5.7 cubic feet to work with, that's:

  • Room for 1x of your average 12 in a false-floor configuration, with room for your groceries..
  • Barely enough room for two ported JL 12W7's, with no usable cargo room.
  • Room for multiple drivers in a false-floor configuration, as long as they're designed to work in a small enclosure space.
  • No way in hell of getting any amount of 15's back there.
  • The last option is to keep the cargo area and put a set of 15's where the rear seats are. The vehicle is now a two-seater with the stock cargo area.. No way to fold the seats down or get anything big in the vehicle. Also, the middle of the car isn't a great spot for them (no corner loading)
After enlisting XtremeRevolution and Pete from PWK, I was presented with a false floor sealed enclosure, designed to fit four 8" drivers with 0.3 cubic feet per driver. I went with the Alpine SWR-843D's, as they were the forum boner at the time.



We knew compromises had to be made... So it was decided that the Alpines could hit greater xmax cleanly (thanks to the shorting rings and other trickery), and by having four of them, the surface area to xmax ratio would be favorable. The main advantage is that the box is extremely small and flat, and hides in the floor of the hatch area. The main disadvantage, however, was the F3 rolloff at 53 Hz. The first thing I did after the box was built and wired was to take some RTA measurements to see how bad the harmonic distortion would be below the F3. Here are my results:


This was my test setup. Three of the four subwoofers wired, as I'm currently missing an amp. TrueRTA is running on the laptop, with the M-Audio MobilePre's Microphone #1 input connected to a Behringer ECM8000, and Line Output #1 connected directly to the amplifier subwoofer channels. I'm doing this outside the car, as I'm currently only interested in measuring harmonic distortion, and the rattles in my car would make that quite hard.


100 Hz sinewave. Very clean.


60 Hz sinewave (just above the F3 cutoff). Still very clean.


30 Hz sinewave. The harmonic distortion is very obvious on the RTA display, and is somewhat audible. The 2nd harmonic is 14 dB down.

No picture at 20 Hz. At low volumes, it's masked by the ambient noise, and a higher volumes it sounded like utter crap. Lots of flappy noises from the driver suspension. No need for an RTA plot when it's that obvious.

When placed in the car, the cabin gain helped tremendously. I didn't really come up with any decent RTA measurements, however. The subs seem capable of shaking the car to pieces, but will do so with rich harmonics that sound offensive to the ear.

The jury is still out on this one. While this design meets three of my requirements (small, low, and loud), it doesn't meet my third (to do so cleanly). I'm tempted to temporarily mount the subs in Isobarik configuration to see if the non-linearities go away.
 

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30 Hz sinewave. The harmonic distortion is very obvious on the RTA display, and is somewhat audible. The 2nd harmonic is 14 dB down.

No picture at 20 Hz. At low volumes, it's masked by the ambient noise, and a higher volumes it sounded like utter crap. Lots of flappy noises from the driver suspension. No need for an RTA plot when it's that obvious.
I'm curious - did you take the measurements at the same drive level from the amp, or did you take them at the same SPL level (which would mean that you increased the amp's output for the lower frequency measurements).

Note: A sine sweep measurement with HolmImpulse will give you a quick idea of the THD across the range of the subwoofer's response.


I'm tempted to temporarily mount the subs in Isobarik configuration to see if the non-linearities go away.
The non-linearities in your measurements appear to be mostly odd-order. Isobaric mounting is likely not going to reduce this by much.
 

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Interesting thread. I wanted to get low, so I went simple. I bought a JBL P1224, and built a big low tuned ported box (2.5 cubes @ 25 hz) wherein the port takes up a third of the box (port makes a 90 degree turn and then a 180 degree turn). The result is zero in car rolloff all the way down to 20 hz and below. If anything, it gains steam as it gets subsonic vs rolling off. Never been happier, and did it with a single 12.

Edit: I'm thinking it's possible to sell off 2 of the Alpines, and use the rest of the space for box and port, and tune stupid low and go as big as can fit, and thus low bass in minimal space.
 

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Im going to be watching this thread closley i love the shambala mixes and i want to make sure i can feel it in my truck and i have similar space requirments. However im looking at a single 10 but not sure if its gonna be enough
 

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I like the idea of this thread and the Patrick Bateman thread you linked, which I've read. Hopefully these discussions can help people understand a) inaudible bass is out there in professional tracks but only if you're searching for it b) the compromises we all make become much more severe, if that word is appropriate, if we choose to emphasize the less audible bass frequencies.
 

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Edit: I'm thinking it's possible to sell off 2 of the Alpines, and use the rest of the space for box and port, and tune stupid low and go as big as can fit, and thus low bass in minimal space.
I'm with Dan here. Before you give up on these subs you might as well spend another $50 & get a ported design from Pete. Maybe he can give you some input on if there will be much of a benefit going with 2 ported over the 4 sealed.
 

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Discussion Starter #8
I'm curious - did you take the measurements at the same drive level from the amp, or did you take them at the same SPL level (which would mean that you increased the amp's output for the lower frequency measurements).

Note: A sine sweep measurement with HolmImpulse will give you a quick idea of the THD across the range of the subwoofer's response.




The non-linearities in your measurements appear to be mostly odd-order. Isobaric mounting is likely not going to reduce this by much.
I was adjusting the gain on the MobilePre and was looking for the distortion to increase at higher levels. The screenshots were taken at approximately the same SPL levels. Probably not the most scientific method, admittedly. I'll be doing more measurements in the days/weeks to come. I will look into the Holmimpulse application, thanks for the advice.

As for the Isobaric configuration, I'm still reading some papers on it to dispel any myths I might have come across.. I will heed your advice in the meantime.
 

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Discussion Starter #9
Interesting thread. I wanted to get low, so I went simple. I bought a JBL P1224, and built a big low tuned ported box (2.5 cubes @ 25 hz) wherein the port takes up a third of the box (port makes a 90 degree turn and then a 180 degree turn). The result is zero in car rolloff all the way down to 20 hz and below. If anything, it gains steam as it gets subsonic vs rolling off. Never been happier, and did it with a single 12.
Interesting setup. I might have to model something like that myself. It would take up over half my cargo area, but might be worth it if it gets low cleanly.

And come to think of it, I haven't really tried researching what it takes to port a box that low.. Most of the vented enclosures I've dealt with are tuned much higher. I will make a note to look into this..
 

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Discussion Starter #10
I'm with Dan here. Before you give up on these subs you might as well spend another $50 & get a ported design from Pete. Maybe he can give you some input on if there will be much of a benefit going with 2 ported over the 4 sealed.
One of Pete's original comments was to try exactly this. I resisted at the time, since the subs had already been purchased, and because it would have taken more cargo space than the design I ended up with. In retrospect, I should have made a compromise on cargo space, and just listened to Pete :blush: It was naive to think that I could get that much bass out of something that small. Newb mistake I guess.

My next detailed post here will be an analysis of a dual ported enclosure with an extremely low tuning frequency, including calculated response curves including cabin gain. Pete's designs are great, but quite slow, so I'll be trying my hand at WinISD and some other tools / spreadsheets. From my sealed box measurements, I can gather that the harmonic distortion of the 843D's only gets bad at high xmax, so if I can keep that down on the ported box model, it should stay pretty clean. I'll also be auditioning some other sub models, including (for kicks and giggles), the new HAT I8SW / I10SW. Likely not a bass monster, but worth throwing in for good measures.
 

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Interesting setup. I might have to model something like that myself. It would take up over half my cargo area, but might be worth it if it gets low cleanly.

And come to think of it, I haven't really tried researching what it takes to port a box that low.. Most of the vented enclosures I've dealt with are tuned much higher. I will make a note to look into this..
Yea, I have to stuff groceries around the sides of my box, as I intended for the cone and the port opening to only be about port width or so from the back of the trunk lid (to avoid any wave cancellation), so not much useable trunk space.

If, in your car, you would be willing to take your box to just under the rear window line (with a stealth cover), you could do nearly anything you want.

My first ported box was 4 cubes @ 36 hz for a Digital Designs 1515 sub. I despised it so bad I just grumbled every time I got in the car. Kinda glad I toasted it trying to force it to play anything lower than 30 hz. Look on caraudio.com. 99% of the ported sub stage guys there are tuned to like 32-38 hz. That creates a hideous peak around 45-55 hz, and the subsonics sound like a box fan. No thanks. Not even a 30 hz tune sounds good to my ears. That still creates a peak in the wrong place so as to make you think your box won't hit the higher bass frequencies.

But... when you drop your tuning down to 23-26 hz, something magical happens, and you get it all - tight SQ like a sealed box, but without the high F3, unreal subsonic response, no need for a SSF, and effortless, efficient output from below the threshold of human hearing up to wherever your particular sub likes its LPF to be. I reject all these claims that low tuned boxes need to be low passed at like 50 hz or whatever. Mine is crossed at 110.

Bad news is you might have to load groceries in the back seat lol
 

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One of Pete's original comments was to try exactly this. I resisted at the time, since the subs had already been purchased, and because it would have taken more cargo space than the design I ended up with. In retrospect, I should have made a compromise on cargo space, and just listened to Pete :blush: It was naive to think that I could get that much bass out of something that small. Newb mistake I guess.

My next detailed post here will be an analysis of a dual ported enclosure with an extremely low tuning frequency, including calculated response curves including cabin gain. Pete's designs are great, but quite slow, so I'll be trying my hand at WinISD and some other tools / spreadsheets. From my sealed box measurements, I can gather that the harmonic distortion of the 843D's only gets bad at high xmax, so if I can keep that down on the ported box model, it should stay pretty clean. I'll also be auditioning some other sub models, including (for kicks and giggles), the new HAT I8SW / I10SW. Likely not a bass monster, but worth throwing in for good measures.
One thing that converted me to preferring a single sub ported from a past of always going multiple sealed is that, no matter how many sealed subs you add to increase the first octave response, the actual response CURVE stays the same. Basically, I wasn't satisfied at the prospect of having to cut a bunch of mid to high level sub bass (45ish - 80ish hz) just to match the first octave response, even considering the general cabin gain vs. rolloff balancing act. I like to roll down and open every window I got in the the summer months, so there goes most of my cabin gain to level things out.

But, dang those groceries...
 

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Discussion Starter #14
If, in your car, you would be willing to take your box to just under the rear window line (with a stealth cover), you could do nearly anything you want.
Not sure exactly what you mean by placing the box under the rear window line… That is assuming up-firing drivers and up-firing port? I'm pretty ignorant with ported boxed, what exactly would that do?

But... when you drop your tuning down to 23-26 hz, something magical happens, and you get it all - tight SQ like a sealed box, but without the high F3, unreal subsonic response, no need for a SSF, and effortless, efficient output from below the threshold of human hearing up to wherever your particular sub likes its LPF to be. I reject all these claims that low tuned boxes need to be low passed at like 50 hz or whatever. Mine is crossed at 110.

Bad news is you might have to load groceries in the back seat lol
Exactly… Bass is easy to get if you have the space for it! That was the whole purpose of this thread: Where is the compromise point between flat output to the lowest octave, and smallest enclosure possible, given all of the other factors? In a car analogy, if the standard large ported box is a Chevy 350, what I am after is something more like a Porsche 911 engine… Just as fast, half the weight, and tolerances are a lot tighter.

One thing that converted me to preferring a single sub ported from a past of always going multiple sealed is that, no matter how many sealed subs you add to increase the first octave response, the actual response CURVE stays the same. Basically, I wasn't satisfied at the prospect of having to cut a bunch of mid to high level sub bass (45ish - 80ish hz) just to match the first octave response, even considering the general cabin gain vs. rolloff balancing act. I like to roll down and open every window I got in the the summer months, so there goes most of my cabin gain to level things out.

But, dang those groceries...
That's a good point that I should have included in my first post. From the beginning, I always knew that my 4x sealed enclosure would need a lot of equalization, and I was okay with that, it was one of the compromises I was willing to make. As for rolling the windows down -- I don't think my town is ready for the level of filth that is Dubstep :eek: I'd better keep them up!
 

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Not sure exactly what you mean by placing the box under the rear window line… That is assuming up-firing drivers and up-firing port? I'm pretty ignorant with ported boxed, what exactly would that do?
Oh, sorry. I meant to make your box height less high than the window line so as to make it less visible, but still be ample box.

Exactly… Bass is easy to get if you have the space for it! That was the whole purpose of this thread: Where is the compromise point between flat output to the lowest octave, and smallest enclosure possible, given all of the other factors? In a car analogy, if the standard large ported box is a Chevy 350, what I am after is something more like a Porsche 911 engine… Just as fast, half the weight, and tolerances are a lot tighter.
Yea, sorry I got away from that a little on your thread. But, IMO, the way to get that is to be willing to sacrifice a little bit of the actual output and just scale down the setup, but you can effectively get your curve and response right in return. For example, 2 of your Alpines in as big and low tuned of a ported box as they can function well in vs. the same configuration for a pair of 12 inch Type Rs. So, like (guesssing) 1.5 cubes vs. 4.5 cubes.

Another compromise is to stay sealed, but use as large a sub as possible, with as low of a Fs as possible, in as big a sealed box (always smaller than ported) as possible so as to get as close as possible to a .7 to .8 Qtc. I did that with a RE Audio SE/x 15 (has a Fs of 22 hz) in a big sealed box. It caught some sick lows for sure.

That's a good point that I should have included in my first post. From the beginning, I always knew that my 4x sealed enclosure would need a lot of equalization, and I was okay with that, it was one of the compromises I was willing to make. As for rolling the windows down -- I don't think my town is ready for the level of filth that is Dubstep :eek: I'd better keep them up!
lol Filth? I admit I know nothing about dubstep. I have a low bass capable setup, yet I play anything from death metal to bluegrass on it. Got some old school bass albums for some roof flex when I'm in the mood lol. BTW, I'm fascinated with your RTA results. I've never used or even so much as seen one.
 

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Discussion Starter #16
Yea, sorry I got away from that a little on your thread.

lol Filth? I admit I know nothing about dubstep. I have a low bass capable setup, and I play anything from death metal to bluegrass on it. BTW, I'm fascinated with your RTA results. I've never used or even so much as seen one.
No worries. I've got a ton of informative stuff now to keep me busy for a few days. Thanks for the advice.

As for Dubstep.. if you can handle death metal, you may have an ear for it. And at the very least, it will exercise the low end of your system. A few tracks if you want to give it a listen:

That should be enough to wear out an alternator or two :D
 

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Neil,

Another option to keep your box size down would be the use of passive radiators.
 

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Could someone explain more indepth on passive radiators and if one would work with a good 12? Say a w6/7 or the wgti mkII im loving this thread and i hope it will help me figure out my sub and box set up.
 

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Tried some of the tunes you linked to and they sounded pretty dang good,even to my 56y/o ears.
And after reading this thread,it seems that I might be more satisfied with my SWR12/sealed or one of my unused RF HX2 10's in a ported box. It might need that 4" vc to play some of that stuff..
 

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Some of my favourite tracks there:)

Have you read PB's thread "does anyone understand cabin gain". Some interesting points in it but the main ones (paraphrased) you should be thinking about:

Below FB of a vented enclosure cabin gain begins to drop off as the rear wave and front wave are basically acting against each other and cannot produce pressure.

Sealed boxes extend further, with the front and rear wave separated they no longer cancel each other below FB so maintain pressure.

So, either tune low with a big ported or forget ported and go sealed. I've fitted 2x SWR1243 into a 2003 Cooper S boot (pretty sure your boot is the same) in a sealed enclosure, that fitted underneath the factory parcel shelf-no room for shopping but you can't have both!
 
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