nondirectional below 80hz?

I'm upgrading my front stage. I've realized that with my tiny budget, I won't be able to get any decent midrange down to 32Hz, where my sub is low-passed at, so i'll need midbasses. I'm thinking i'll need either 2 8's or 2 10's in the rear to fill in from 32 to about 80Hz.

Is 80Hz and below the typical non-directional frequencies for most people or what? Could I go a bit higher, or if anything, will I need to go lower than 80Hz?

My sub sounds great l/p'd at 32Hz. I have it tuned to about 30Hz, and I try to keep 'sub' bass frequencies to it. This is why I need midbasses.

I love midbass, and my budget for midranges is small, so i'll need midbasses to make up for them.

Sub bass freqs go to about 80 Hz.  You could probably make an argument for as low as 60 Hz, but not 32 Hz.  The point being:  what is a mid and where do you consider its lowest freq?  Keep in mind the gradual fall off slope of your mids which you will hear at two octaves below the crossover point, so always consider this large additional frequency band when deciding on crossover point.  You want the mids to perform without stress at these lowest audible freqs. 

Lower quality mids can't even be crossed at 80 Hz because of this, so something around 100 Hz or higher is chosen when that is the case.

Crossing another set of woofers with the sub at 32 Hz is the same as adding another pair of subs.

80 Hz is almost directional and its hard to pinpoint location below that.  Do some experimenting with your test tones and you'll know at what frequency you hear the sub bass all around instead of being able to locate the source.  The steepness of the LP crossover will have a lot to do with it, as well as any port noise that may occur in a sub setup.  Another source of higher freq noise, and one that a lot of people don't pay attention to when designing a vented enclosure, is the higher harmonic ringing that occurs if the port exhibits resonance within the sub range (including two octaves above the LP point.)   Natch, a sealed sub setup is easier to listen to for pinpointing the freq that localization begins to occur.

"Sub-bass" is the first two audible octaves, from 20Hz to 80Hz.   "Bass" is from 80Hz up to 240Hz.  "Mid-bass" is 240-400Hz.  What your system is missing is bass.  Most acoustic design theories use 80Hz as the beginning of directionality for the average human.  80Hz is the standard Xover frequency for subwoofers.  32Hz is very low indeed, much lower than I can normally recommend, but if it works for you, go for it - although if it was me, I'd change the Xover freq. up closer to 80Hz.

How much do you want to spend for your woofers?

I've got a BostonAcoustics G51044 (dual 4ohm) and a GTR PR. I've got them in a 1.8 cubic ft. sealed box. It's being powered by about 300watts RMS. I've got the 'stage2' weight set in the GTR, in a .5 cubic ft box it'll tune the system to about 35Hz, so with my huge 1.8cubic ft box, and some 19-45Hz test tones, it sounds like it peaks at about 32Hz. The bass is great sounding to me. I love for it to go low.

The 2 6.5's and 2 6x9's i've got in the rear deck are l/p'd at about 160Hz and put off decent bass, but I know some 8's or 10's would do it better. I want to l/p them (8's or 10's) at about 80Hz so when I get my new front midranges I can h/p them at about 80Hz.

So, I raised the lpf to about 40Hz on the sub. I feel it meets the 4 speakers in the back that are l/p'd at about 180Hz.

What my major question is, with the bass like this; Sub and PR l/p'd @ 40, the 2 -soon to be- 8's or 10's bandpassed at 40 and 80Hz (reason for 2 is to retain stereo sound from 40-80Hz), and my front midranges h/p'd @ about 80Hz, will it all sound ok?

You don't need to worry about stereo sound between 40 and 80 Hz.  It's omnidirectional below 80.

stevdart wrote:

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You don't need to worry about stereo sound between 40 and 80 Hz.  It's omnidirectional below 80.

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Cool, so I could actually just get 1 8 or 10" for 40-80Hz and be good, right?

aznboi3644 wrote:

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have you tried turning the subs low pass up to 80Hz and see how that sounds??

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I have, actually. The sub/PR is 'tuned' to about 40Hz, anything above that doesn't sound too great. I mean, it's there and all, but when I do that, it's like it is trying to reproduce too much, so it doesn't go as low as I like. That's why I'd like to add a dedicated 40-80Hz sub.

OK I'm coffused here. The port is at 40 Hz and you say it dosen't sound good above that? Bolow the tuning frequincy the speaker is basicaly at zero resistance box wise and running as if it were infanate baffle...please correct me if I'm wrong on my therory here. Does your woofer have a lot of movement when you are playing it? Dose the speaker move less when playing matterial above 40 Hz?

Always will to learn something new...

Its a woofer and PR (passive radiator) setup, sealed box. The PR is tuned to about 30Hz.

The PR moves more at lower freqs', the woofer at higher ones.

I think my car peaks at about 60Hz, actually. It is pretty bad. It's hard for me to get a flat response down to 20Hz. '95 Cavalier 2dr.

https://i209.photobucket.com/albums/bb103/jmelton86/subbox.jpg

That's a sheet of 1/2" plexi. It keeps the trunk lid from sounding like crap. I actually think it helped with low-end performance.

jmelton86 wrote:

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the subwoofer doesn't seem to like high bass frequencies.

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in what way does it not like the higher bass.

As you move closer the th P/R tuning frequency the P/R will do more work and the powered woffer will do less. But below the tuning frequency say two octives it become unstable. 30 Hz is one octive down now so I'm curious which woofer is doing the work?

jmelton86 wrote:

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I lowered the h/p to 80Hz and upped the l/p to 80Hz. It sounds better from the h/p speakers but I think I need some bass speakers, the subwoofer doesn't seem to like high bass frequencies.

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80Hz is not "high bass."  80Hz is a subwoofer frequency and setting your LP for the sub and HP for your mains at 80Hz is the preferred setup for most applications.  Depending on the woofer you have in a PR alignment it should "like" anything from 400Hz or so down.   I humbly suggest you get your vehicle to a professional shop and pay to have it metered and to have your crossovers properly set for you as it's obvious we are not helping you here.

DYohn] wrote:

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0Hz is not "high bass."  80Hz is a subwoofer frequency and setting your LP for the sub and HP for your mains at 80Hz is the preferred setup for most applications.  Depending on the woofer you have in a PR alignment it should "like" anything from 400Hz or so down.   I humbly suggest you get your vehicle to a professional shop and pay to have it metered and to have your crossovers properly set for you as it's obvious we are not helping you here.

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Something is deffinately not adding up here. DYohn is right the crossover setting 80/80 or even 100/100 are  very typical and should be working for you. So it is possibly time for a second set of eyes to look things over.

I think it's because of the huge 60Hz cabin gain that's throwing me off. I now have the lpf on the HU set to 80Hz, and also 80Hz on the external MTX x-over, so I think it's knocking the cabin gain down a good bit. I'm going to keep my front components h/p'd at 80Hz and tweak the EQ's to my liking. My system's nothing major.

It has taken me awhile to get it right, but I'm going to skip the idea of getting more subs. You all are right, it's pointless. I'll use the G5 to it's fullest -to 80Hz.

Please bare with me, I'm a -very- novice wannabe audiophile. I appreciate everyones input.

hemanjoyman wrote:

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DYohn,

The same applies for HP filters right??? Only use one xover, either the headunit's crossover or the amp's crossover, not both.

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Correct.  Either disable one or set it way out of the passband of the other.

Alright, I'll disable the HU's lpf and only use the RTX01As.

My initial question was -or should have been- is 80Hz the absolute cutoff point for nondirectional sound or can it be a bit higher?

Thanks, everyone, for their input.

jmelton86 wrote:

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My initial question was -or should have been- is 80Hz the absolute cutoff point for nondirectional sound or can it be a bit higher?

Thanks, everyone, for their input.

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THX and most audio theorists say 80Hz is the frequency where sounds begin to become directional.  Some researchers think it is actually a little lower than that.

hemanjoyman wrote:

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Hey DYohn, one more question for you:

My headunit has only a setting for 50Hz, 80Hz, and 125Hz for LP. Should I set the headunit to 80Hz and my amps crossover to 200Hz LP or just turn off the amps crossover, since I can't turn the headunits crossover off??? By the way, I am using the JL Audio 500/1.

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If you cannot bypass the Xover on the amp, setting it up at some higher frequency like 200Hz is the way to go.