How high should a subwoofer play?

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Hi there,

How high can the subwoofer play without the listner being able to localise the bass? I belive the THX spec calls for speakers to go as low as 80hz and then the subwoofer takes over. At this frequency the bass is not "localizable".

I will be building some NSB line arrays that will be OB. I therefore don't expect them to play low and definately not down to 80Hz. Do I need to consider adding additional woofers making each speaker a 3way? I would rather stay with 2way OB if its possible to combine with a subwoofer in a way that will work for HT.

I was thinking of doing dipole bass for the subwoofer. Then maybe a boxed subwoofer for the very low frequencies.

Please advice.

Regards,

Exipnos
 
80 Hz would be the rule of thumb.

It depends on the subwoofer, placement, roomacoustics, distance between sub and tops, distance from sub, etc.

The highest I could ever cross a subwoofer without localizing was 120 -130 Hz and only in downfire position.
Which crossover frequency do you think you're going to use?

The higher you cross, the closer you should place the tops to the sub(s).

Wkr Johan
 
Thanks for the reply.

I don't know the crossover yet, but I doubt that the open baffled NSB will play as low as 120-130!

What do you mean with subwoofer should be placed close to the "tops"?

The more I think about it the more I see a need for 3way if I will do OB. If I go ported then I can probably go lower with the NSB and stay with 2way.
 
What do you mean with subwoofer should be placed close to the "tops"?

The tops would be the speaker or set of speakers you use above your sub frequency-wise. In this case the OB.

By placing the woofer and mid close together you prevent having a "gap in the sound image". Close would be within 1/4 wavelength of the frequency you cross at.

Johan
 
just an FYI but 80Hz was chosen by THX because it was the best compromise found by playing a variety of sources. In the end, it turned out a recoding of a male humean voice revealed limitations of crossing over any higher and the playback seemed to lack any lower.

On a lot of other forums, the members are crossing at 50Hz. I use 80hz but also designed my speakers (Sub/Sat) around that frequency...

Mark
 
I've see mentioned here and there that THX made some misstakes when setting their specifications. If I was to design the speaker/subwoofer combination whats the best compromise in todays world? Should I design HT speaker to go lower then 80 and then the subwoofer to be crossed over at that frequency?

So the general concensous is to cross 80 or lower. I guess that forces me to investigate woofers to complement low end on my line array.

Cheers,

Exipnos
 
I've see mentioned here and there that THX made some misstakes when setting their specifications.

I wouldn't exactly call it a mistake, but a compromise. It works for the majority of program, with some program needing a lower crossover and other stuff wanting a higher frequency. In the end though, your ears will determin wat is right for you. What crossover (to the sub) will you use, and is it built into an audio visual receiver or it an external device?

Mark
 
I have listen to subwoofers that where cut at more then 300hz without any placement problem. The woofers where placed in corners and where time aligned to the main speakers, with a delay line for the main speakers (A digital crossover/roomcorrection are mandatory, fx. Tact RCS). I think the time aligment is the main factor for succes.

claus
 
Also consider how accurate the driver is up that high. I find better performance when I cross low ~ 40 Hz or so. I have tried crossing up at 80 Hz with a 4LR and didn't like the result. IMO you need a very good driver to cross higher than this for anything other than home theatre LFE use.

I don't know anything about that driver you linked, but it does look good for OB line array use. Perhaps make it a 3 way OB then cross to a sub in the midbass somewhere ~ 40 - 60 Hz. If you make the woofers a U frame you can get an fequal down to 60 Hz without it being too big.
 
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