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I am trying to work out a design for my Alpine 1243D sub cab. I like the low end from a large sealed cab. What about tuning a vented cab for ~25hz or lower?? Anybody try this in a largish sedan? Thanks. Id like to go really low, mimicking a nice large sealed cab, but with vented efficiency. I already know I need a LPF.
 

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How much power do you have available? If you want efficiency, class D is your friend. There's no need to give up all your trunk space either.

My Infinity Perfect 12 plays flat down to 20Hz in a 1 cubic foot sealed enclosure with 320RMS and some good processing power.

Here's my post from a very similar thread a week ago:


It's easy to get a 12" sub to play flat down to 20Hz in a sealed box - you just need to do it right. The idea that sealed subs only play as low as 40-50Hz is a myth based on too many people who don't do it right.

You need 4 things:

1) A decent sub
Specific requirements are decent power handling, decent xmax and that the sub is designed to work well in sealed box. I'm using an Infinity Kappa Perfect 12, but something like an Alpine Type R 12 would do just fine. You don't need to go spending a fortune on a sub to do this. You will need some $ for processing if you don't already have it.

2) A decent sealed box
Check the manufacturers specs. 0.9 cubic feet will be just fine for that Type R - you'll still even have most of your trunk space left!

3) Lots of power
Sealed boxes are more accurate than vented, but need more power - especially if you want to play low. Low frequency sound has more energy than higher frequency sound of the same amplitude, hence requires more power. I'm using 320RMS and it does a pretty decent job. I'm about to try 800RMS, just to see if the extra headroom makes any difference, but I wouldn't consider this necessary.

4) Equalisation (an RTA to help is a bonus, alternatively test tones and an spl meter)
Because of the natural roll off of your sub in its box, you are going to have a big peak around 40-50Hz that you need to deal to. There are a couple of different ways you can go about this.

The first is to use your eq - assuming it's got enough gain and cut to do the job. You might have 12db of difference between 20Hz and 40Hz that you need to flatten out. If you've only got 6db of gain in one band under 50Hz (like my old CDA-9835 had), that's probably not going to cut it. If you've got enough eq bands and gain to do this by boosting 20-30Hz and cutting from 40Hz up, that's great - your sub will now play flat down to 20Hz.

If you don't have enough equalisation gain/cut to do this, then you have one more option that might save you having to buy a new head deck or processor (some of which are rather cheap these days mind you - eg mini dsp looks pretty cool for for $125). If your LPF will go low enough (25Hz or lower), you can actually use it to equalise out that nasty 40-50Hz bump in your FR.

Let's say, for your sub, the difference in output between 20Hz and 40Hz (1 octave) was 12db. That is a 12db per octave roll off from 40Hz down.

If you run your LPF at 12db per octave from 20Hz, this is a 12db per octave roll off from 20Hz up.

What happens when you combine these two effects? Flat response from 20Hz to 50Hz. Your nasty 40-50Hz peak is gone and your sub is now playing flat down to 20Hz! (or use 18db/octave and have a really fat bottom end!)​
 

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What happens when you combine these two effects? Flat response from 20Hz to 50Hz. Your nasty 40-50Hz peak is gone and your sub is now playing flat down to 20Hz! (or use 18db/octave and have a really fat bottom end!) [/INDENT]
Nice idea, but I am afraid it's bad for integration with a typical 2-way front stage. A lot of subwoofers have just enough midbass to integrate well with front speakers. If 40-50Hz region gets cut, higher bass region obviously will get cut even more. I might try it once I get some kind of SPL meter. I don't think I could do this right by ear. However, my HU's crossover goes down to only 30Hz. Setting LPF at 12dB probably will not cut enough in 40-50Hz range and I wouldn't use a steeper slope because I still need reasonable integration with the front stage. (BTW, I got a Kappa 120.9w in sealed box).
 

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Zakow, I appreciate what you are saying about midbass integration. If I understand you correctly, you are talking about the hole in the FR between say 50Hz and 80Hz (or wherever your components crossover is set).

To many peoples ears, a FR with more output below 40Hz than above it is actually desirable, so when the sub is turned up further, the hole between 50Hz and 80Hz dissapears.

I personally like to run my components pretty low 50-60Hz, so I don't have too much of a hole to fill. My sub integrates beautifully - all of the bass sounds in front of me. (TA helps too obviously)

I actually did some TrueRTA measurements on my sub over the weekend, which I'll post up soon - once I figure out how to get images into my posts...
 

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b.t.w you are right 12db doesn't quite cut it - with no crossover or eq, my sub is actually 18db down at 20Hz (compared to 40).
 

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what is the FS on the sub. becuase if the fs is to high on that particular sub, it just won't play thre low hz that ur looking for no matter what enclosure ur looking at running.
 

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what is the FS on the sub. becuase if the fs is to high on that particular sub, it just won't play thre low hz that ur looking for no matter what enclosure ur looking at running.
Sorry, I don't think that is correct. I have proven otherwise in my experience.
 

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Type-R or Type-X?

Either one has pretty poor low extension performance because of high fs and high qts values. You get very uncontrolled movement below fs and the qts indicates it just wants sealed box or really high tuned ported (what sounds like s***).

I quickly modeled type-r using winisd and flattest response I got was 3.3cu box with 23.5Hz tune and F3 being at 21Hz. Try at your own risk but that driver is not going to sound that good probably.

My tempest plays really well in big W210 sedan. I just need to mod the rear shelf the let more pressure in the cabin, or put port through it. It's in 6cu enclosure at about 26hz tune. Would tune it lower but port lenght is a big problem. Plays well below 20hz even now.
 

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I took some measurements on my Infinity Perfect 12 over the weekend just gone. It's in a 1 cubic foot SEALED box, with 320RMS available.

Here it is with an 18db/octave Low Pass at 50Hz. As you can see there is a large peak at 45-55Hz and it is actually 18db down at 20Hz - not pretty, horrible one note bass.


------------------------------------------------


Shift the 18db/octave low pass filter to 22Hz. Much better, but not quite flat - now only 8db down at 20Hz


------------------------------------------------


Quickly apply some eq and presto - a good looking FR (still needs fine tuning, but pretty good)

22Hz 18db low pass with eq
 

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most of what you are saying make no sense. lowpass at 22hz? seriously? you have a nice flat box because you have nothing left! everything above 40 hz is gone! do not do this! is will sound horrible! you can not EQ stuff back in that you have cut out and have it sound good.

You want to speak about myths! ported designs are NOT less accurate than sealed unless you have no idea how to biuld them correctly. sealed are certainly easier to build. build box, put in woofer, done! ported actually takes a little skill.

OP please do not listen to anything this guys says! boosting EQ is bad idea if you are boosting 12db+ to get back music that you cut out by putting in a ridiculous low pass filter.

a sealed box WILL roll off sooner than a ported box, this is how they work! no way around it. they will play lower than a ported box, but ussualy because they roll off sooner, they will be quieter at the lower octaves. ussualy a sealed box will be smaller than a ported one, so if space is a premium sealed might work better.


if you want a ported box, then make sure you buy a sub that will support a ported box and will sound good tuned that low. there are alot of em! you will be required to use a SSF with a ported box to keep it from unloading below that tuning freq, but if you tune at 25-30hz, your SSF can be set pretty low, 20-25hz. if you biuld it correctly it will sound fine if you set the lowpass to about 80 or so as a starting point. you will have to adjust it to taste ;)

best plan is to model the sub in different boxes before you biuld to see if it will work well in a box you want. extremerevolution has a modeling service here or you can PM me and I can either show you how to do it or model it for you.
 

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I am trying to work out a design for my Alpine 1243D sub cab. I like the low end from a large sealed cab. What about tuning a vented cab for ~25hz or lower?? Anybody try this in a largish sedan? Thanks. Id like to go really low, mimicking a nice large sealed cab, but with vented efficiency. I already know I need a LPF.
after loving bass in vehicles for 30 years, my understanding is that to get the results you really want, is an exact science, there is 1 person i know of who understands how to get the bass to perform the way anyone wants in any vehicle, i havent used him yet, but i think i will one day soon

after trying to find fault with his thinking, i cant, i believe he knows and understands many things about bass in vehicles most other people have no idea about.

i think for $50 he will design you a box that works optimally in your vehicle, to your specifications, with your equipment, and send you blueprints.

"The cornerstone function of an enclosure is to impedance-match the speaker’s electro-mechanical properties to the air mass between the source and the target listening point–and to do so along a specific bandwidth"



PWK Designs
 

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most of what you are saying make no sense. lowpass at 22hz? seriously? you have a nice flat box because you have nothing left! everything above 40 hz is gone! do not do this! is will sound horrible! you can not EQ stuff back in that you have cut out and have it sound good.

You want to speak about myths! ported designs are NOT less accurate than sealed unless you have no idea how to biuld them correctly. sealed are certainly easier to build. build box, put in woofer, done! ported actually takes a little skill.

OP please do not listen to anything this guys says! boosting EQ is bad idea if you are boosting 12db+ to get back music that you cut out by putting in a ridiculous low pass filter.

a sealed box WILL roll off sooner than a ported box, this is how they work! no way around it. they will play lower than a ported box, but ussualy because they roll off sooner, they will be quieter at the lower octaves. usually a sealed box will be smaller than a ported one, so if space is a premium sealed might work better.


if you want a ported box, then make sure you buy a sub that will support a ported box and will sound good tuned that low. there are alot of em! you will be required to use a SSF with a ported box to keep it from unloading below that tuning freq, but if you tune at 25-30hz, your SSF can be set pretty low, 20-25hz. if you biuld it correctly it will sound fine if you set the lowpass to about 80 or so as a starting point. you will have to adjust it to taste ;)

best plan is to model the sub in different boxes before you biuld to see if it will work well in a box you want. extremerevolution has a modeling service here or you can PM me and I can either show you how to do it or model it for you.
I support everything said here 100%.

And don't worry about midbass.

Or a HPF...

Even though a Sealed will play "lower" because it does not roll off as fast, at some point you have to draw the line and ask where?

For example....



I can assure you that not a **** was given about the efficiency below 22 cycles when looking at the up to SIX DECIBELS of GAIN where I really needed it.

The supermonkey is right.
 

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"The cornerstone function of an enclosure is to impedance-match the speaker’s electro-mechanical properties to the air mass between the source and the target listening point–and to do so along a specific bandwidth"
OK, I have to admit I like Pete's designs but that statement is overly complex and actually obscures the truth. Maybe that is part of his marketing gibberish (and all successful companies use marketing gibberish) but it just pisses me off. You can use physical/acoustic transformers to BETTER impedance match the driver to the atmosphere but all that means is using a box/speaker location that provides a better load for the woofer (e.g. ported, bandpass, tline, or horn/corner loading, rear facing ports, etc.). This becomes important when you are trying to wring every last bit of performance out of your sub system.

IME - I would rather just go IB with some large woofers and an EQ. It saves me a ton of weight which translates to a better handling car with better gas mileage. For me these are important. For others they may not be.

Again I do like some of the exotic designs but statements like "there is 1 person i know of who understands how to get the bass to perform the way anyone wants in any vehicle" do a dis-service to many of the qualified professionals in the car audio industry.
 

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OK, I have to admit I like Pete's designs but that statement is overly complex and actually obscures the truth. Maybe that is part of his marketing gibberish (and all successful companies use marketing gibberish) but it just pisses me off. You can use physical/acoustic transformers to BETTER impedance match the driver to the atmosphere but all that means is using a box/speaker location that provides a better load for the woofer (e.g. ported, bandpass, tline, or horn/corner loading, rear facing ports, etc.). This becomes important when you are trying to wring every last bit of performance out of your sub system.

IME - I would rather just go IB with some large woofers and an EQ. It saves me a ton of weight which translates to a better handling car with better gas mileage. For me these are important. For others they may not be.

Again I do like some of the exotic designs but statements like "there is 1 person i know of who understands how to get the bass to perform the way anyone wants in any vehicle" do a dis-service to many of the qualified professionals in the car audio industry.
not everyone can go IB, so many need to use a box, a box inside a small car performs very differently to the same box inside a much bigger car.im sure you understand the physics way better then me, but if scott B won 1st with a quad of 6.5s in a pwk design,

there must be some reason?? and no-one can argue with good science.....

from what i see, no one else considers the internal volume and shape of a vehicle like pwk does?

"Big congratulations to Scott Buwalda from Hybrid Audio! He attended this year’s USACi World Finals–held in Shreveport, LA–and secured first place in his class using four Hybrid Audio I6SW drivers in a PWK Designs enclosure.
(An interesting side-note to this setup is that it’s also a replacement for a pair of 18″ drivers, and with noticeably better results.)"

and after watching several of pwks other videos, i have to give him props, he speaks very clearly and openly about the science of car audio,. no gibberish, no bs, just cold hard facts.

seems to me he understands aspects of car audio few have even considered.

and he has the equipment to test and prove his thinking,

http://www.youtube.com/watch?v=VNIvlXA8CxM

many pretend ......
 

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lol, 120.8dB out of a free air 6.5" lol. I am surprised it lasted that long, lol.
 

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The fact that he plugs speakers into the 120VAC line.. And used the term "Assuming it held an 8 ohm impedance" while it was plugged into said source. Caused me to completely lose ANY respect I had for him....
 

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The fact that he plugs speakers into the 120VAC line.. And used the term "Assuming it held an 8 ohm impedance" while it was plugged into said source. Caused me to completely lose ANY respect I had for him....
well he has no way to measure that, so he has to assume it will. since line voltage is pretty closely regulated to 60hz it will play 60hz. what part of what he said do you think is wrong?
 

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well he has no way to measure that, so he has to assume it will. since line voltage is pretty closely regulated to 60hz it will play 60hz. what part of what he said do you think is wrong?
I mentioned nothing about frequency.... but I did have to go look because you made me think my old brain farted.

As for impedance, he DOES have a way to determine it... Set the gating and look at current and voltage. Which is easy to do assuming 60 cycles, which is going to be tits on. :D
 
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