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Discussion Starter · #1 ·
I have 2 rt55 mains, a cs245, and b&w backs. When i do a frequency test 30hz is still good hearable, 40 is even stronger.

When I look at subwoofers they have a frequency from 50 hz to 150 hz. I suppose the crossover frequencies ?

Why should I add a subwoofer with a crossover frequency of 50 hz when I still can hear 30 Hz with my speakers ?
 

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Quote:
Originally Posted by Jogo  /t/1468191/why-a-subwoofer#post_23201691


I have 2 rt55 mains, a cs245, and b&w backs. When i do a frequency test 30hz is still good hearable, 40 is even stronger.

Loud isn't the only dimension of bass. Absence of doubling or harmonic distortion is very important. 20 Hz is part of the audio spectrum.
Quote:
When I look at subwoofers they have a frequency from 50 hz to 150 hz. I suppose the crossover frequencies ?

Why should I add a subwoofer with a crossover frequency of 50 hz when I still can hear 30 Hz with my speakers ?

You must be looking at the wrong subwoofers - sounds like pro audio or low end consumer stuff.


How about this?

http://www.svsound.com/subwoofers/view-all?page=shop.product_details&flypage=flypage.tpl&product_id=267&category_id=1#.UWqbX9aG18E


"Frequency response 20-460 Hz +/- 3 dB."
 

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What does it mean +/- 3db? Thats how we suppose to dial the subwoofer from the reciever?
 

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What does it mean +/- 3db?
+/-3dB is the variance from a test level of output within a defined range of frequencies. If a sub is rated to play "flat" from 20-200Hz +/-3dB at a given test level of output, all frequencies within that range will play at roughly the same level, with a variance no greater than 3dB louder or 3dB quieter.


Any peaks within that range will not exceed +3dB relative to the test level of output; and the extremes of the range (20Hz and 200Hz) will be at -3dB relative to the test level of output.
 

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Quote:
Originally Posted by eljaycanuck  /t/1468191/why-a-subwoofer#post_23201848


+/-3dB is the variance from a test level of output within a defined range of frequencies. If a sub is rated to play "flat" from 20-200Hz +/-3dB at a given test level of output, all frequencies within that range will play at roughly the same level, with a variance no greater than 3dB louder or 3dB quieter.


Any peaks within that range will not exceed +3dB relative to the test level of output; and the extremes of the range (20Hz and 200Hz) will be at -3dB relative to the test level of output.
thanks. good explanation. one more thing, how come after running my aud. all of my speakers when i checked each volume using spl meter each of them register 72-73db spl which is ok, but whn i checked my subwoofer from my listening position it only reads like 60 and above db i thought it should also go to 75db?
 

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Based on recordings made in an anechoic chamber or a room with no sonic reflections.


Unfortunately, +/- 3dB is an accepted dubious standard in that it represents a condition which exists "only" in an ideal playback venue and is not representative of what one can easily expect to have represented by measurements taken in their listening venue.


Sound waves bounce off walls and like small ripples created in a mirror smooth pond by two pebbles simultaneously breaking the surface in equal amounts, the intersecting waves, will cancel each other out. One must take the time to counter this normal phenomenon being created (cause and effect) in their room. The +/-3dB standard needs to be looked upon as "potential." This as opposed to expected results.


If the posted subwoofer specification measurements are accurate, nobody is misleading anybody as this is the "valid" de facto standard used to compare dissimilar subwoofers to each other so the informed consumer can readily draw a valid, snapshot conclusion. That being, at what price will a particular subwoofer serve their intended purpose or potentially, how much sound pressure can one reasonably expect to be created, at what frequency, in a given venue. In other words, from afar (someone in the US, looking to a sub manufactured in the Philippines), one is able to readily understand, which subwoofer, at what price point, will successfully serve their purpose in a given venue, with a given set of sound reproduction equipment.


This of course is based on one taking the time to measure and properly integrate their subwoofer into a listening room's acoustics.


-
 

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Quote:
When I look at subwoofers they have a frequency from 50 hz to 150 hz. I suppose the crossover frequencies ?
Yes, the 50-150Hz you see on the back of the sub is the low-pass filter (LPF) or "crossover".
Quote:
Why should I add a subwoofer with a crossover frequency of 50 hz when I still can hear 30 Hz with my speakers ?
A good sub - one that extends to ~20Hz (or lower) and can play loud cleanly - will play deeper and louder than your speakers can. And by using a crossover of ~80Hz - so that the sub handles everything below 80Hz and your speakers everything above 80Hz - it will "lighten the load" on your receiver.
 

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Quote:
Originally Posted by Jogo  /t/1468191/why-a-subwoofer/0_50#post_23201691


I have 2 rt55 mains, a cs245, and b&w backs. When i do a frequency test 30hz is still good hearable, 40 is even stronger.

When I look at subwoofers they have a frequency from 50 hz to 150 hz. I suppose the crossover frequencies ?

Why should I add a subwoofer with a crossover frequency of 50 hz when I still can hear 30 Hz with my speakers ?

Firstly, if you're looking at "subwoofers" with a freq from 50-150Hz then those aren't really subwoofers. Ideally you want a subwoofer that can go down to 20Hz or even lower.


Secondly, normally when people talk about the crossover freq for a subwoofer that is the upper limit of the bass handled by the subwoofer. So if you say crossover at 50Hz, it means the sub will handle all the frequencies from 50Hz and below and the speakers handle from 50Hz and above.
 

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Quote:
Originally Posted by caloyzki  /t/1468191/why-a-subwoofer/0_50#post_23201896


thanks. good explanation. one more thing, how come after running my aud. all of my speakers when i checked each volume using spl meter each of them register 72-73db spl which is ok, but whn i checked my subwoofer from my listening position it only reads like 60 and above db i thought it should also go to 75db?

What spl meter are you using? Not an spl app on a smartphone I hope.
 

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Quote:
Originally Posted by jchong  /t/1468191/why-a-subwoofer#post_23201998


What spl meter are you using? Not an spl app on a smartphone I hope.
yes smartphone lol.
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by eljaycanuck  /t/1468191/why-a-subwoofer#post_23201928


Yes, the 50-150Hz you see on the back of the sub is the low-pass filter (LPF) or "crossover".

A good sub - one that extends to ~20Hz (or lower) and can play loud cleanly - will play deeper and louder than your speakers can. And by using a crossover of ~80Hz - so that the sub handles everything below 80Hz and your speakers everything above 80Hz - it will "lighten the load" on your receiver.

So your receiver must be able to set frequencies that goes to your speakers, otherwise it has no sense to ad a subwoofer ? Your speakers play at 60 hz and your sub also plays at 60 hz, so there is an overlap what can make bad sound imo.
 

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Quote:
Originally Posted by caloyzki  /t/1468191/why-a-subwoofer#post_23201815


What does it mean +/- 3db? Thats how we suppose to dial the subwoofer from the reciever?

+3 dB represents a doubling of power, and -3 dB represents a halving of power. Sonically speaking +3 dB or - 3 dB is noticeable but not dramatic. It is a commonly-used reference for determining the operational frequency range of a device. If the response variation exceeds +/- 3 dB of that at a median reference point, then it is out of tolerance.
 

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Quote:
the lower -3db frequency is 28 hz, the upper 125hz.
In other words, the sub plays "flat" between 28 and 125Hz: Within that range of frequencies, its output varies from a given test level of output by no more than 3dB louder or 3dB quieter.
Quote:
The crossover is 60hz to 125 hz.


I tought that the crossover frequency was at the -3 db barrier. So not ?
The "crossover" (actually a low-pass filter, or LPF) is variable from 60-125Hz to allow you to blend the sub with your speakers. If you have larger speakers that extend to ~50Hz, you could set the LPF to ~70Hz. If you have smaller speakers that only extend to ~120Hz, you could set the LPF to ~140Hz.
 

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Quote:
Originally Posted by eljaycanuck  /t/1468191/why-a-subwoofer#post_23202466


In other words, the sub plays "flat" between 28 and 125Hz: Within that range of frequencies, its output varies from a given test level of output by no more than 3dB louder or 3dB quieter.

The "crossover" (actually a low-pass filter, or LPF) is variable from 60-125Hz to allow you to blend the sub with your speakers. If you have larger speakers that extend to ~50Hz, you could set the LPF to ~70Hz. If you have smaller speakers that only extend to ~120Hz, you could set the LPF to ~140Hz.
i have towers, but my avr set my LFE 120hz. should i change it to 70hz?
 

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i have towers, but my avr set my LFE 120hz. should i change it to 70hz?
Depends on the extension capabilites of your towers... *BUT* ...if what you're saying is that your AVR has set the LPF of LFE to 120Hz, leave it at that. The LFE channel has its own LPF setting, and the consensus seems to be that setting it to / leaving it set at 120Hz is ideal.
Quote:
Ideally an overlap of 20 hz is good ?
Crossover isn't a point, it's actually a range. Your speakers "roll off" as the frequency decreases, and your sub rolls off as the frequency increases. Rather than set the crossover value to the point where both "roll offs" are at their minimum, you want to set it to minimize the roll offs / any dips or nulls in output.


An overlap of 20Hz should suffice, but you can experiment with more or less overlap and go with whichever crossover setting you find works best with your set-up.
 

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^^^ Also most ppl recommend bypassing the subs own crossover or setting it to the highest possible frequency and ONLY use the cross over in your receiver. For your speakers I would try 60 or 80hz as a cross over.


I have towers that Audyssey set the xover to 40hz, but I changed them to an 80hz cross over and IMO it sounds much better that way.


I would strongly advise looking at internet direct companies for your sub purchase and get one that the -3db point is in the mid to upper teens.
 

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Quote:
^^^ Also most ppl recommend bypassing the subs own crossover or setting it to the highest possible frequency and ONLY use the cross over in your receiver. For your speakers I would try 60 or 80hz as a cross over.
+1.


AFAIK, the sub's crossover/LPF is most often used when you're running a speaker-level connection from the AVR to the sub, and then from the sub to the mains. In this case, since the AVR is not doing any bass management, the LPF on the sub is used to blend the sub with the mains.


When you've got an AVR handling bass management (incl. the crossover between speakers and sub) and you run a connection from your AVR's subwoofer output to a corresponding input on the sub, you don't need to use the sub's LPF, so maxing it out (or disabling it, if the option is available) is the route many (most?) people take.
 
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