Finally, a functional bass machine.

[parkerbink]

Damn! I forgot about that blower!! damn!!! what would you suggest?

While I am thinking about it how the hell does the blower know when the top is down? I see no sensor but it does not work unless the top is up.

[Jordan]

Take out your rear seat and build a box :)

Convertables are so well sealed of from the trunk, its hard to get respectable bass out of the trunk.

[parkerbink]

Take out your rear seat and build a box :)

Convertables are so well sealed of from the trunk, its hard to get respectable bass out of the trunk.

So obvious why didn't I see the solution! :o

But seriously I like your box because you still have a trunk. I am using a bandpass box that takes up 1/2 of my trunk that was designed for my 92 300ZX it has 2 MTX Orion III's and works great (except that it vibrates the hell out of the trunk outside) I like the idea of having more trunk space & not sounding like some ricer kid.

[StereoInstaller1]

OK, so here is a quick explanation of why Jordan has plenty of midbass...

First, crossovers are NOT a brick wall, they allow frequencies above (in the case of a low pass) or below (in the case of a high pass) the 3db down point (the actual crossover point).

Since the crossover allows other frequencies to pass, guess what rate they are allowed to pass at...wanna bet the 12 db/oct or 24 db/oct has something to do with it?

If we have a 12db/oct crossover set to 110 Hz, we will be down 3db at 110, so 1 octave below 110 would be 55hz...where we would be 12db down.

So now take that sub low pass...85Hz@24db/oct. Figure it out...3db down at 85, means 24 db down at 170.

If someone has the PC skillz, map that out, would ya? You can see that there would be virtually no drop between the 2 crossover points.

Second, we have an interesting function of accoustics known as "room resonance", which is the natural resonance point of any enclosed space...whether that space is the inside of a dixie cup or the cabin of an e30.

If you ran a broadband pink niose fed into a speaker playing in the car, you will find a huge peak (like 15db or more) in the measured response at about 100Hz or so. In other words, the car naturally amplifies sound around 100Hz, so if you had a perfectly accurate speaker, the sound would no longer be accurate due to the room response. Thus the two reasons why Jordan has plenty of midbass. I have a bigger gap in mine, since I use a 24 db/oct (AKA 4th order alignment) at 70Hz, and an 18 db/oct at 120Hz (AKA 3rd order) and believe me, my car has fine midbass...electric bass is my absolute favorite instrument, so I need midbass to be excellent.

Now, on to the speaker fired into the cabin or into the trunk issue...anyone who believes the bass is louder or better in any way having the woofer fire into the trunk need to do some studying.Think of the car as 3 boxes...front (cabin) rear (trunk) and subwoofer Some guys try and bullshit their way into saying the bass has a longer distance to develop...BULLSHIT! a 20Hz wave is about 54 feet long...do you really think the 2 feet you gain will make a difference? The reality is that when you fire a speaker into a corner, you gain about 3db from an old accoustical trick known as "corner loading", because the wave will reinforce itself against a wall. Corner loading is more powerful at lower frequencies. Since what we hear is full range, when the box is fired backwards we hear more effect from the lower frequencies, so in effect, you are using an accoustic equalizer...but it is only a trick on your ears. You lose upper bass, between 50Hz and 100 Hz, you do NOT gain anything. Like comparing a 2 stroke engine that makes all of its power over a small part of its RPM range versus a more powerful electric motor that makes the same power regardless of RPM, the 2 stroke seems stronger because of its big surge in output...in fact, it is weaker. More dramatic, but weaker.Most people prefer the drama, regardless of what they say.

Most people do not expend the energy to make a box completely seal into the cabin....ANY loss of seal at all will cause the wave of the speaker to wrap around the box and cause cancellations withing the trunk. Those cancellations are then corner loded, then reflected back into the cabin 180 degrees out of phase, causing a huge loss in output. This is why some cars have more bass in the cabin with the trunk open...lack of seal. This can not and does not apply to hatchbacks, by the way...for obvious reasons. On cars that arent as well sealed as the e30 have cancellation issues ranging from the rear deck speakers themselves to pressure waves going into the trunk through the rear side panels...the car must be completely divided into a front half and a back half, with all the energy sealed into the front half. I have proven this time and again, and once again in Jordans car.

Anyway, enough typing for now. Back to your normally scheduled events.
Luke

[FrustratedMunky]

Jeez, I wish I understood what you said in the first half of ur post... :? But still, very informative.

[parkerbink]

Great post Luke Thanks!

[Brew]

Wow, thanks for explaining that. I think I'm going to go mess around with my crossover frequencies now.

[Jordan]

I should also mention, there is no audible difference when I set the kicker amp down to 70Hz with the sub on. You can hear a small difference with the sub off.

[rwh11385]

Jordan, so does the port allow all the sound to fill the cabin? Because, yeah, E30 trucks are sealed well, almost too well. Would be a shame to keep music out.

Just confirming.

[Jordan]

Jordan, so does the port allow all the sound to fill the cabin? Because, yeah, E30 trucks are sealed well, almost too well. Would be a shame to keep music out.

Just confirming.

All of the subs output is sealed into the cabin. Both the direct firing of the sub, and the port.

[parkerbink]

Is it better to use the crossover in the amp (sub) or the head unit? My Kenwood KDC-X769 has passthrough or sub xover points of 60,70,80, 100 & 150 the Kenwood amp I am using (don't remember the model) has a variable poteniometer thet goes from 40-200

Currently I am running passthrough on the headunit & 70 on teh amp.

[rwh11385]

Jordan, so does the port allow all the sound to fill the cabin? Because, yeah, E30 trucks are sealed well, almost too well. Would be a shame to keep music out.

Just confirming.

All of the subs output is sealed into the cabin. Both the direct firing of the sub, and the port.

Alright, good to hear, my friend is having a similar problem with his sub in a overly sealed/insulated trunk and hopefully something like this could help. :)

[808BMW]

I was just asking because right now my front comps are crossed at 120hz and the lack of midbass (mainly because I need to deaden my kicks) is starting to annoy me :P

[jimi318is]

Hey Jordan, good move, I'm glad you changed your set up from the original design, this my not be as appealing to the EYE but it's way more appealing to the EAR ;)

[StereoInstaller1]

Thanks for the kind comments about the write up. Sometimes it is hard to express the stuff that rolls around in my head...there is lots of empty space in there.

On the box front, Jims has it...sound first, looks second or third, since ergonomics are far more important. Now on to what I am gonna do, with a 'glass panel inside my box, done in body color, with all box output into the cabin.

There is a bunch of talk about 1 or 2 woofs. I think 1 is adequate for my needs, since I am only looking to achieve like 130 db @ 25hz...and I plan on using a true 1200 watts RMS to do it with. I am thinking 2 10" subs, but not for cone area, but simply to provide enough power handling.

So 2 10" subs, angled towards each other, on a swoopy body colored fiberglass panel, inside of a box with a lexan back panel, neon or LED illumination...sounds gaudy, right? add in the idea of 3 Harman/Kardon CA260 amps and an Infinity Reference 1210A, along with all the auxillary electronics, batteries, caps....what a lot of crap!

Sealed vs. Vented? You gain roughly 3db going from 1 woofer to 2, all other things being equal. Venting a box properly can gain much more, like 6 to 8db, but all focused at lower frequencies. Better cone control above the tuning frequeny, too.

If you people aren't careful, I am gonna explain more in here!
Luke
Happy Labor Day!