set the subsonic slightly above fs.

You can play a speaker in resonance, you just don't want full power at resonance.

That's the easy explanation ,


You could also skip the subsonic and turn down 31hz on the eq until it sounds good.

But IB the subsonic will help you in high power situations.

 

Awesome. Thanks!

 

The specs show sealed box volume of 0.5 cu ft, you might be able to make that work on a rear deck if you don't like how it sounds IB

 

The reason I am going free air is that I can't afford to give up the trunk space.

The next thing I am a little confused about...
I am considering the Infinity which shows a frequency response of 35 - 175Hz with a Fs of 30Hz and the guidance I got above was to set the sub infrasonic filter to slightly above that. Easy enough. I figured I'd set it to about 35Hz and be done.

Another speaker I am considering is the Pioneer TS-SW2002D2. It's an easier fit at 8" vs 10" but it has a Fs of 65Hz and a frequency response of 20 - 200Hz. Will this one just not do well under 65Hz or am I over thinking it?

 

In true IB, Fs is the resonance frequency. In a sealed box Fs(c) will increase.

It does matter though, Qts/Fs kind of determines the shape of the rolloff/extension of the response.

Car IB setups are basically equivalent to a large sealed box. Subsonic (highpass) isn't really required with IB and even less so with sealed boxes but as a safety precaution against overexcursion you can put it at or slightly above resonance in this case.


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Hanatsu, can you explain more on what you mean "In a sealed box Fs(c) will increase"? I have always used sealed enclosures but maybe I have been setting my dsp amp up wrong. Do the size of the enclosure change the Fs or what part?

 

When you put a speaker in a sealed box, the free air resonance (Fs) will instead be (Fsc), the resonance of the "system". The smaller enclosure you put it in the more the resonance will increase in frequency and you begin to lose low end extension. How much the driver is affected depends on the VAS of the driver, the lower VAS you got the smaller enclosure you need to retain a given Qtc, this will decrease efficiency however (hoffmans law).

At around 4x the VAS value the driver should "see" an IB config (no longer affected by the air spring in the enclosure).

In a car this matters less than in other environments, we got cabin gain and usually DSPs with decent EQ



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Now does the vehicle type also play a part in determining the Fs(c)? Would a 1cu sealed enclosure have a different Fs than if it were placed in a hatchback or small SUV type?

 

No. Fsc is determined by the speaker and enclosure. Fsc by itself doesn't tell you much though, it's simply the point where the amp needs to work the least to move the the speaker, you could say that it is the point of maximum efficiency.

 

All the parameters in a speaker will change when running it either sealed, ported or IB setup.

 

A single ten in an IB is going to be disappointing. Go big! A couple of twelves is a good start.

If you're going to go IB I would generally use much MUCH more cone area than if you were going sealed or ported.

My Genesis has an eight in an IB and the bass is anemic. My Mazda has a single 12 in a bandpass and it's a good start, but I'll need to add another twelve to get anything close to the level of bass that's acceptable.

 

I can get two of the 10s in back there or three of the 8s. Just need to figure the technical stuff out above.

 

Keep in mind that just because you have a 10" hole in the deck doesn't mean you have to use a 10" woofer. You can use a really high compression ratio on woofers, even four or five to one. That means that if you have a 10" hole in the deck you could mount a 20" woofer and it would work just fine. Air is very compressible.

 

Thanks for all of the great info and education!

Let me throw one more thing out there.
If you:
were unable to go bigger than 10"
could not surrender any trunk space
could not have more than 2 (or possible 3) drivers on the rear deck

what subwoofer would you choose?

Reason for the limitations:
Frequently travel with a full trunk and need every little bit of space.
There is a motorized shade in the rear window limiting how far back I can mount

 

Keep in mind that 2 or 3 drivers IB will likely consume more total volume than even a sealed box for many of the 12" shallow mount small box volume subs.

What vehicle?
Will a pair of the Infinity 10"s fit under the front seats?

A half cubic foot box is pretty ridiculously small. Under front seats can be tricky as you often have to make the box out of fiberglass to fit properly, but again that would be a small box.

What are your expectations on output levels?

 

When space is at an absolute premium, I'd consider a couple of options:

1) Copy the Carver subs. Basically find a driver with a LOT of displacement, combine it with the largest amp you can afford, and use a Linkwitz Transform to get the response you want. This option will cost around $200 for the sub, $200 for the amp, and $100 for a MiniDSP. An example of something like this would be to build a 16" x 16" x 8" box for a fifteen inch woofer like the Alpine Type R 15". That box is way WAY undersized for a fifteen, but that's ok, we'll fix that with EQ. It will be important to make a very sturdy box and get a woofer with a strong cone (Type R is Kevlar) because you're going to be putting a lot of pressure on the woofer cone and the box walls. It will need to be a bulletproof enclosure.

2) The cheap solution would be to purchase three high excursion tens and bolt them to the rear deck. The efficiency of this option will be higher than option one. Alpine Type R 10" is a good candidate, costs about $100 each. This option will likely put out more SPL than option one, but the difference won't be night and day. Option one will be easier and doesn't require you to screw with your car.

 

Absolutely no space for something like that.

The car is a 2001 BMW 750iL. There is no space under the seats. I can go about 2" through the rear deck without causing any problems.

I understand because of my constraints whatever I decide to do is going to sacrifice something in the way bass quality but I am trying to get the most out of that I can. Cost is not an issue (as long as it isn't totally insane) but space is.

I appreciate all of the feedback and guidance!

 

I run a single Boston Acoustics G108-4 in my sedan and anemic isn't a term I would apply. Is plenty for me and that's not even applying a dsp to tighten up the response of the total system yet. Everything depends upon the levels demanded.

 

Is it sealed?

IB subs lose a lot of efficiency in the range of 40-80hz.

 

The sub is IB in the rear deck of a LS400.

 

Hey Dan, I posted some sims. IB looks good and so does sealed. Either will work well. Check out the sims here:

http://www.diymobileaudio.com/forum...advanced-car-audio-discussion/252481-linkwitz-transform-vs-infinite-baffle.html

 

If I remember, the 750il has a full size spare tire? I've seen some build logs where someone incorporated a fiberglass box under the spare, which allows you to retain your spare. Depending on the depth of your spare tire well, this could work, and if you can fit a high excursion 10 or 12 in a decent enclosure, you might get the bass you need.

 

Interesting thought. It does have a full size spare. I know bass carries well but how would that work with a trunk full of luggage over it?

 

Someone else with spare tire well experience may have to chime in, but I know Bing from SiS has done a lot of these builds, as well as other members on here. I don't know that it would be a huge trade off, but I have a feeling that cabin gain would make up for any possible losses.

Anyone? ...Anyone?

 

A single 10" in the rear deck can provide satisfaction. Not understanding some with this if it isn't large or multiples in IB then it's going to suck theory. I say much regurgitation.

Given the right sub is chosen, improvements over stock are most likely. As stated earlier, in my sedan there is provision for a single 8. The stock Nakamichi system had good tonality, but poor output due to driver & amp limitation. The changer also died so that became a good excuse to put a cd/usb deck in the dash, add an amp, and upgrade at the least the sub. First go round was adding a deck & amp (XD700/5) to stock drivers. The door drivers handle it pretty decently with decent gain on output. The sub though very smooth and excellent extension, just couldn't maintain the levels I wanted without overexcursion. Enter an ARC8 (ID8). Good, but wasn't quite there. Tried different coil configurations and decided to try a different sub. Enter the BA sub. Great tonality and power handling. Can easily outdo the doors. So next upgrades are adding the DSP changing the door drivers which all are on hand.


Moral of the story is...... upgrading performance without augmenting the hell out of the vehicle is very realizable with the right gear. Plenty of 10" drivers on the market that can do nicely compared to a single 8" and probably better than that Infinity with it's lackluster xmax of 7.7mm. Not sure what the problem is here other than finding the right one. And for the record.... Fs of the sub isn't entirely detrimental. Subs can & do play below Fs as long as it isn't some ungodly high number. 30hz in a vehicle added with cabin gain isn't a problem.

 

...Plenty of 10" drivers on the market that can do nicely compared to a single 8" and probably better than that Infinity with it's lackluster xmax of 7.7mm....

My issue is that anything other than a shallow mount gets deep enough into the trunk to interfere with the luggage I carry but I am going to take another look. There were a few that weren't that much deeper than the shallow mounts. Maybe I can squeeze something a little deeper in without causing an issue.

 

Looks to be a little under 6"

http://www.aespeakers.com/pdfs/IB10_dimensional.pdf

 

We may have a winner. I am out of town without the car for the weekend but I will definitely take some measurements when I get home.

Thanks for your help!

 

Too bad they don't make an 8", but that's a limited market I suppose.