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I'm trying to understand subwoofer crossover


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#1 of 17 OFFLINE   Donald_S

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Posted November 18 2003 - 03:24 AM

I've bought a Daytona 100 watt sub and Panasonic D912k receiver that I guess is around 80 watts a side. My front speakers go down to 50hz with a sensitivity of 89db (Fluance if it matters). The lowest crossover setting for the receiver is 100hz.

Here is what I don't understand. If I set the receiver for the lowest crossover I can have the sub drive everything below 100hz. Or I can set the receiver for large speakers with no crossover. Would I then set the sub to crossover at 50hz? And which of these makes more sense? Should I make the fronts or the sub work harder?

Thanks bunches guys.

Donald

#2 of 17 OFFLINE   Lee Carbray

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Posted November 18 2003 - 04:12 AM

100Hz is a pretty high crosover but I would still suggest uning that and setting the mains to small. The reason being is that I bet your sub goes a lot lower then 50Hz.
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#3 of 17 OFFLINE   Vince Maskeeper

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Posted November 18 2003 - 04:19 AM

Here is what I don't understand. If I set the receiver for the lowest crossover I can have the sub drive everything below 100hz. Or I can set the receiver for large speakers with no crossover. Would I then set the sub to crossover at 50hz? And which of these makes more sense? Should I make the fronts or the sub work harder?


Keep in mind if you go with LARGE setting, the only thing sent to the sub is dedicated LFE, regardless of the x-over setting on the sub.

The large setting means all full range main signal will go to the appropriate full range main speaker... unless you have your sub wired in line with your mains, the only way you're going to get bass (beyond the dedicated LFE stuff) to the sub is by setting speakers to small.

100hz is not an ideal crossover point- but I think it's better than the alternative.

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#4 of 17 OFFLINE   John Garcia

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Posted November 18 2003 - 04:32 AM

100Hz is OK depending on the main speakers, and since yours are rated to 50Hz, it is practically ideal. Your mains will receive frequencies down to 50Hz, possibly lower depending on x-over slope. I would not recommend setting these speakers to large for the reasons Vince mentioned. If your speakers cannot handle lower bass (30-40Hz) on their own, they are better off set to small. You want the sub to work harder, as that is what it is for.

As for the sub, when you are using the receiver's x-over, you should set the sub's internal x-over as high as it will go to avoid cascading them together.
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#5 of 17 OFFLINE   Jack Shappa

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Posted November 18 2003 - 04:51 AM

Quote:
100Hz is OK depending on the main speakers, and since yours are rated to 50Hz, it is practically ideal. Your mains will receive frequencies down to 50Hz


This statement is misleading. If he sets the crossover to 100hz, the mains will only receive information down to 100hz and everything else is passed to the sub. You probably meant this but I just wanted to clarify it.

a lower crossover of about 80 would be better, to make sure there's no bass directionality, but 100 should be okay... Remember the more signal that goes to the sub the more power is left over for your receiver to power your other speakers.

- JS

#6 of 17 OFFLINE   Lew Crippen

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Posted November 18 2003 - 06:27 AM

Quote:
This statement is misleading. If he sets the crossover to 100hz, the mains will only receive information down to 100hz and everything else is passed to the sub. You probably meant this but I just wanted to clarify it.

Jack, I think that John’s post is correct.

Crossovers are not binary. That is, not all of the information below the crossover is sent to the sub and not all of the information above the crossover points is sent to the mains.

Rather, crossovers are designed so that information above and below the crossover point is sent to both the subwoofer and main speakers. So that at first the split is (for example) 50/50 and as the frequencies become lower, the mix becomes 60% sub/40% mains and then 75/20, and 80/20, until 100% of the information is sent to the sub. It works the reverse way above the crossover point.

How fast this happens depends on the crossover design. But in general you can consider that the main speakers will still be reproducing some of the sound at a frequency that is 1/2 of the crossover point (in this case 50 hz, as the crossover point is 100 hz) and that the subwoofer will be reproducing some of the sound at twice the crossover point (or 200 Hz).

Naturally at these end points there won’t be much sound, but there will be some.
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#7 of 17 OFFLINE   John Garcia

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Posted November 18 2003 - 06:30 AM

Quote:
If he sets the crossover to 100hz, the mains will only receive information down to 100hz and everything else is passed to the sub.

This is not exactly correct. A crossover has a slope associated with it, it does not just cut off all sound at the x-over frequency (depending on design, a steep slope can seem to cut off flat). This means there will be sound for as much or more than one octave below the x-over point, to allow the speakers affected by the crossover to blend together. Even with a 12dB/octave slope with a 100hz x-over, there will be sound information as low as 50Hz, though at a reduced output, as the frequencies will be rolling off starting at 100Hz, and eventually roll off completely. At the same time, the sub will pick up frequencies, also at a reduced level, starting approximately 1 octave above 100Hz, though the sub's x-over is usually steeper than the mains (18dB/octave or greater) to prevent it getting too high into the frequency range.

sorry if I duplicated much of what Lew just said.
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#8 of 17 OFFLINE   Donald_S

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Posted November 18 2003 - 07:10 AM

Man I'm glad I asked. Not anywhere as simple as I thought, but logical if you think about it. I could set the receiver to crossover at 150hz, but even I knew that was too high.

Ok, one more related question. In order to keep my neighbors in the next condo from killing me, I'm putting the sub on the opposite wall from the mains. At frequencies near 100hz is any of the bass directional? Will it seem like it's coming from the wrong place?

Thanks.

Donald

#9 of 17 OFFLINE   Lew Crippen

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Posted November 18 2003 - 07:55 AM

Quote:
sorry if I duplicated much of what Lew just said.

I think that you said with a bit more accuracy, John.
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#10 of 17 OFFLINE   Jack Shappa

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Posted November 18 2003 - 04:37 PM

Hey guys, thanks for the education! I realized cross-overs were on a slope, and that there was some "spillage", but I had no idea the roll-off could go as far in either direction. I thought it was much less, and stand corrected.

- Jack

#11 of 17 OFFLINE   Clem

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Posted November 22 2003 - 10:40 AM

Quote:
Keep in mind if you go with LARGE setting, the only thing sent to the sub is dedicated LFE, regardless of the x-over setting on the sub.


What is LFE? anyone?? Thanks!

Nevermind just saw the glossary..............

LFE (Low Frequency Effects) - LFE refers to bass. That is why you really need a powered subwoofer to truly enjoy DD. The signal generally ranges between 20-150Hz.

#12 of 17 OFFLINE   Bob McElfresh

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Posted November 23 2003 - 04:33 AM

Quote:
That is why you really need a powered subwoofer to truly enjoy DD.

Not ... exactly.

In a nutshell - if you dont have a sub, but have your L/R speakers defined as LARGE, the L/R speakers will produce sound for:

- the .1/LFE track
- sounds from the Center, LeftRear, RightRear that are below the internal crossover.

BASS MANAGEMENT OVERVIEW

Dolby Digital is often called a "5.1" system. 5 channels and ".1" channel of sounds that only go from 20-120 hz (the LFE or subwoofer channel).

But one person can have 5 small speakers and a sub, someone else has 2 large panel speakers, a small center and rears (no sub), and someone else has 5 full-range speakers.

How can the same receiver handle all the different combinations?

DD receivers have something called Bass Management. It is a set of rules about how to handle different combinations of speakers.

Each manufacturer can do things a bit differently, but here are the rough rules:
  • .1 channel - If there is a subwoofer attached, send the .1/LFE signals to the sub.
  • .1 channel - If there is NO subwoofer attached, sent the .1/LFE signals to any LARGE speaker
  • 5 channel - If there are sounds below XX (the internal receiver crossover) going to a speaker, and the speaker is defined as LARGE, let it pass.
  • 5 channel - If there are sounds below XX going to a speaker, and the speaker is defined as SMALL, send these sounds to the .1/LFE channel. (this will use the rules above)
Does this help?

#13 of 17 OFFLINE   Vince Maskeeper

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Posted November 24 2003 - 04:49 AM

In a nutshell - if you dont have a sub, but have your L/R speakers defined as LARGE, the L/R speakers will produce sound for


If, and only if, you have sub set to NONE.
I know Bob knows this, but important element to note.

-V
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#14 of 17 OFFLINE   Bob McElfresh

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Posted November 24 2003 - 04:16 PM

Quote:
If, and only if, you have sub set to NONE.

Good point.

It's important to tell your receiver what mix of speakers you have.

Speakers are either SMALL or LARGE. They are LARGE if they contain a woofer (a large speaker cone - these are called "Drivers") bigger than about 8" in size.

If you have a subwoofer connected to the LFE/Subwoofer output on the receiver, tell the receiver you DO have a subwoofer.

If you have a subwoofer connected by speaker wires, then more speaker wires going to your L/R speakers, tell the receiver you do not have a subwoofer. Instead, tell the receiver you have LARGE L/R speakers.

Running wires to the sub, then to the L/R speakers make the set appear like a LARGE speaker to the receiver.

#15 of 17 OFFLINE   Donald_S

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Posted November 26 2003 - 03:48 AM

I appreciate all the input and clarification, but no one has yet answered my second question. With a crossover at 100 hz, and my sub on the opposite wall from my mains, will the sound seem to be coming from the wrong place? As it's been explained here, there will be some sound coming to the sub above 100 hz. Will there be enough that I'm going to have a directional problem?

Thanks,

Donald

#16 of 17 OFFLINE   Bob McElfresh

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Posted November 26 2003 - 09:31 AM

I dont know if you will have a "Directional Problem" putting the sub at the rear. But if you concentrate, it IS likely you will be able to determine where the sub is located.

It is a bit of a myth that "Bass is directionless".

It IS true that we are much less sensitive to bass frequencies. And a subwoofer generates a LOT of sound from wall-reflections rather than direct.

Both of these mean you are "less likely" to be able to locate the subwoofer in the room. This has led to the myth that you "...SHOULD not be able to tell where the bass is coming from". - more attitude than fact.

Most people do find they prefer the sub up-front with the rest of the speakers. You do feel the sound waves and while not as directional as the mid-range/tweeter sounds, you do get a sense of location. (Kind of like wind - you can tell the rough direction of a breeze, but it's hard to pin-point.)

Donald: you want to know if 80 or 90 or 100 hz crossover would make it less-likely someone could tell the sub is behind them. I'm afraid there is no magic number. I can tell you that 'lower is better', but it's more important you not have a hole between your sub and front speakers.

I'd set the crossover in the 70-80 hz range and try it for a while. This is far enough above your speakers low-end, but low enough that directional issues may not be a problem.

But wall reflections- this will have a bigger impact to 'directionality' than crossover.

#17 of 17 OFFLINE   John Garcia

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Posted November 26 2003 - 10:39 AM

Simply adjust the sub by ear until you minimize any directionality, if you even have it at all. You MAY have phasing problems with the mains, depending on room, but you should be able to adjust that on the sub as well.
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