How low to go, ht sub

[Pashley]

I do not think I need a sub for music. My main speakers are Thiel cs 3.5 with a -3 dB point of 28 Hz. They come with an EQ that makes it 20 Hz. I've tested with music (Doors, Pink Floyd etc.) and cannot hear a difference with/without the EQ.

For home theater, I think I want (need?) a sub. Run the mains without EQ, play with preamp's variable crossover to find a point (probably in 40-60 Hz range) that works well.

First guess at design is sealed boxes with two 15" or four 12" drivers and a Linkwitz transform (Linkwitz Transform Subwoofer Equaliser) to get low enough cleanly. I won't know exactly until I do some modelling.

How low is it useful/necessary to go in HT? Presumably it would be possible to design something that goes down to, say, 8 Hz but I suspect that would be silly.

[freax]

How big is your HT? If its large, 20Hz, if its average size, 50Hz.

No point in producing 20Hz and wasting power on that frequency when you can't even hear it because you aren't far enough away from the subwoofer.

[Pashley]

Originally Posted by freax

How big is your HT? If its large, 20Hz, if its average size, 50Hz.

Now, small but i want to design something that will work in a large living room eventually. Up to, say, 6 by 10 m with 4 m ceiling.

Are you saying clean reproduction to 20 Hz is all one needs for topnotch HT? I thought sound effects went somewhat lower.

[chris661]

Originally Posted by freax

No point in producing 20Hz and wasting power on that frequency when you can't even hear it because you aren't far enough away from the subwoofer.

How did you arrive at that conclusion?

[Juhazi]

5.1 and 7.1 source material (movies mainly) makes a meaning for a separate sub. The .1 (LFE=low frequency effect) channel has up to 120Hz content mixed in too, specially in movies. That's why many sub plate amps have a switch for LFE, which bypasses the highpass filter.

AV amps (the dsp) have the option in speaker configuration to drive LFE to all speakers, if you don't have a sub. But then you can easily clip your amp or break your drivers when the dino jumps or cannons fire.

LFE in movies means that you must set up your system (AV receiver/dsp and sub-amp) differently for best performance/quality of 2ch music and 5.1 or 7.1 music and movies. Or have two different systems just in case you don't remember to change the setting's every time! Personally I have a HT system in the living room and two separate systems in the home theater room

[m R g S r]

Budget? If you were considering two double 15" boxes (it's unclear from your post how many cabinets you want) then maybe you would consider two of these boxes...

New HT subwoofer. Dayton Ref 18"

$250 each driver, wood glue stain etc, looking at right around $400 per box. $800 for a pretty powerful clean 20hz output! (Assuming you already have sufficient amp power and ability to EQ down below 40hz).

[GM]

How, low, loud for a given room size depends on how much of the LFE gain BW some movies have: The New Master List of BASS in Movies with Frequency Charts

For some folks this means output to near DC, so huge IBs or at least multiple sealed EQ'd, with kilo power feeding them. At this level, the ability of the room's, building's construction to handle such acoustic output becomes a major issue as to what the practical limit is.

GM

[Pashley]

Originally Posted by m R g S r

Budget? If you were considering two double 15" boxes (it's unclear from your post how many cabinets you want)

I don't know. Part of that depends on how low it is useful to go for the HT LFE channel. Do movies normally include useful content below 20 Hz? How far below? Is a -3 dB point of 18 Hz likely to be good enough? Or 12? Clearly the lower I go, the more drivers, power & expense. What i am asking is how low it is useful to go.

I probably want two cabinets for flexibilty in placement, preferably not huge. Ideally, each a single 12" or 15" or a pair of 10" or 12". even that i am not sure of yet because I do not know what I'm aiming at on the low end.

[GM]

Look at the charts in the thread I posted. Red is where the most bass is, then you decide if large sealed or 10-20 Hz vented will suffice.

GM

[norman bates]

wow.
I think F3 27hz ported is fine..................
Especially at 120db !!!!

But I do appreciate a good low sealed system also.
Maybe someday I'll try a 20hz ported.......

My eye is on the epic 12's either sealed (3ft3) with 12db of boost to make F3 around 25hz, or twice the sized box but ported at 25hz.
I know the ported will be cleaner, but the sealed should go way lower adding a nice low level feeling.

Or a pair of dayton 390hf in a sealed qtc .707 (11ft3 total) giving fsb=fs=31hz.