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Author Topic: The 35 hz cut off ?  (Read 10911 times)

Alan Star

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The 35 hz cut off ?
« on: December 07, 2006, 10:33:40 pm »

Just wondering if anyone can tell me ... how does the labhorn provide amplification of frequencies below 35 hz when you cut off there ?

I understand that it's necessary in order to put large amounts of amp power safetly into the labhorn but aren't you then missing some of the lower frequencies ?

I don't doubt that it still works and that you gain lower extension by clustering the cabinets but would be great if someone could explain how it works ?
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peter.golde

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Re: The 35 hz cut off ?
« Reply #1 on: December 08, 2006, 10:33:08 am »

I believe the 32-35Hz cutoff was the original design parameter agreed upon by the LAB community for a sub to be used for live sound reinforcment.
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Nathan Lehouillier

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Re: The 35 hz cut off ?
« Reply #2 on: December 08, 2006, 11:20:21 am »

Hi Alan,


First what kind of program material are you playing?
Second how many lab's are you using?
I believe that the lab has a low corner of 28hz with 4-6
cabs.

Nate KDS&L
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peter.golde

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Re: The 35 hz cut off ?
« Reply #3 on: December 08, 2006, 11:52:36 am »

Nathan Lehouillier wrote on Fri, 08 December 2006 11:20

I believe that the lab has a low corner of 28hz with 4-6
cabs.



There is a big difference between 28Hz and 35Hz especially with this horn, I would not want to run a group of 4 down to 28Hz at high levels.
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Raj Sookraj

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Re: The 35 hz cut off ?
« Reply #4 on: December 08, 2006, 03:49:21 pm »

Eminence: You must use a high pass filter set to 35 Hz and that has a slope of at least 24dB per octave to realize the real potential of the design.   Many people are using huge power on these cabinets day in and day out, but they are the ones who run steep high pass filters on them.
Alan Star wrote on Fri, 08 December 2006 03:33

 I understand that it's necessary in order to put large amounts of amp power safetly into the labhorn.


Why is that?  Is it because below 35hz the speaker approaches it's mechanical limitations?  How does sub 35hz affect the speakers thermal capabilities?
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David Trotter

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Re: The 35 hz cut off ?
« Reply #5 on: December 11, 2006, 02:45:09 pm »

the reason why you need a 35hz filter is because below this frequency the horn does not load the driver and its excursion skyrockets.

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Alan Star

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Re: The 35 hz cut off ?
« Reply #6 on: December 21, 2006, 10:59:01 am »

I guess what I am asking is ... are we not missing those very low frequencies then or does it just not really matter or are they somehow gained through clustering the boxes and the coupling effect created ?

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Kevin McDonough

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Re: The 35 hz cut off ?
« Reply #7 on: December 21, 2006, 01:58:14 pm »

hey

All speakers have a "lowest point" on the frequency scale, and trying to produce frequencies below this will result in the speaker exceeding its mechanical limits (Xmax and Xmech).

This limit will be a combination of both the properties of the driver itself and also the cabinet design (air volume for reflex or horn length, compression ratio and chamber sizes, among other things, for horns)

If your only playing at extreamly low volumes it wont matter as much. It still wont produce those frequencies below its low point very well if at all, but the power will be low enogh that it does no long term damage.

When you start putting any sort of power into a speaker though you have to filter out the frequencies below this point otherwise you'll blow the speaker.

All sound systems will (or should!) have this.

Alan Star

I guess what I am asking is ... are we not missing those very low frequencies then or does it just not really matter


Well yes, technically your cutting out the frequencies below what the horn can safely produce, but this happens with ALL sound systems.

In general, horns will only get down to around 40 or so before they begin to become, relativly, pretty huge like the lab or Quake or a couple of others. Reflex may get down to low 30's (or maybe high 20's at a push) but wont have the same horn provided efficiency. Below these points all the frequencies are always high-passed out to save the speaker.


Alan Star

are they somehow gained through clustering the boxes and the coupling effect created ?



Kind of.  Horn speakers, subs in particuluar, have a particuluar advantage though that you dont get from reflex ones. Until it reaches the open air, the air moving in the horn can only expand in a very limited direction (i.e. down the horn) and so is "harder" to move. This creates a bit of pressure against the movent of the speaker and acts like a spring, adding extra suspension and helping to keep the movement in check at the low end of the frequencies. How much it does this is affected, among other things, by the length of the horn and the cercrumference of the mouth.

Now, when you stack several horn speakers right next to each other, their horn outputs combine. For a small distance in front of the horn the air flow still follows (is coupled to) the path of the horn and the aparent horn length that the driver 'sees' is increased. Also, so therefore is the mouth area.

In practice, what this all means is that when the horns are stacked together you gain a length and mouth area on the horn and so a few more hertz, and can move the cut-off point of your high pass filter down a few hertz.

(I don't know the specifics of the Lab, i've never made one, thats just general for all horns.



k
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Kevin McDonough

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Re: The 35 hz cut off ?
« Reply #8 on: December 21, 2006, 02:20:32 pm »


EDIT: double post, sorry!  Rolling Eyes
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Mike {AB} Butler

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Re: The 35 hz cut off ?
« Reply #9 on: December 21, 2006, 02:29:32 pm »

Alan Star wrote on Thu, 07 December 2006 22:33


I understand that it's necessary in order to put large amounts of amp power safetly (sic) into the labhorn but aren't you then missing some of the lower frequencies ?


The answer is: Yes, you will miss the lower frequencies.. but remember that even with a 24dB / oct rolloff.. you can still get a fair amount of output at 30 hz, anyway. With Live sound reproduction, I'm not sure you want be attempting to reproduce too low (this HAS been discussed further down at great length), as building and fixture damage increase rapidly (see Dan Fowler's post about these dudes..). And if you're building home Hi-fi stuff, why would you even consider these for sub - 30 Hz.. there are other choices out there that are better designed for that kind of genre.
Regards,
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