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Discussion Starter · #1 ·
This was sent to Def Tech by a freind of mine who had questions about how to connect his new BP2004 speakers. I was suprised by the response. I would like to hear what some of you think.


To: Definitive Technology

Subject: LFE


Please help put my mind at ease on a subject.


In reading the directions for setting up my BP2004 speakers it said the

simplest way was just hooking up speaker wire and setting the front speaker

settings to Large. If I due this and don't utilize the LFE input will I be

missing any bass in a Dolby Digital 5.1 recorded movie? Some stereo salesman

(who would love to sell me more expensive cables) claim that without using

that input I will not be receiving the .1 of the 5.1 format. I don't have a

preference I just want to make sure that I'm getting maximum performace of

my equipment.


Awaiting your response,



Sir,


Thanks for your recent email to Definitive Technology. You can certainly

connect your BP2004s with speaker wire only. I'd recommend setting your

receiver to large front speakers and no subwoofer. Your receiver will

combine the .1 LFE bass channel and the bass from the front left and right

channels and send it all through the speaker wires to your BP2004s. (You

won't "loose" the LFE or subwoofer channel if you connect your speakers in

this fashion.)


There are no performance benefits to connecting a separate LFE cable to each

BP2004.
 

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One should probably take their advice; they designed the speakers.


It may help to understand that the woofers in the cabinet should perhaps not be considered subwoofers so much as woofers.


Ideally, the LFE should go to a separate sub which can be carefully positioned for best bass performance (something you can't usually do with two large speakers; they have to image correctly).
 

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You said Large. Are you by chance running a Denon reciever?. All that does is basically enable the sub/LFE signal to be sent to the subwoofer crossover @ 80 HZ in small or enables BOTH the subwoofer and the fronts to play sub/LFE signal if set to large. And yes If you tell the Denon unit you don't have a sub it will send the signal to the fronts and let them deal with that signal. The LFE signal is 10dB over reference. I am not sure if this still holds if there is no sub to play the LFE signal but I assume so since the LFE signal is there. Though I will let one of the other peeps answer that ;)
 

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Discussion Starter · #4 ·
Yes he is running a Denon 4800. My concern is that if you set the front speakers to large both the LFE signal and the the speaker level frequencies below 80hz will be utilizing the same sub simultaneously. Would that not create some problems and possiblly create some cancellation or at least cause you to miss some of the LFE.
 

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JCJ1,


No, you won't lose anything when adding the LFE and other bass signals together in the same speaker, so long as you don't crank the volume up so high the speaker is banging against the magnet.


Remember, that's what electronic reproduction of music does: it adds the sound waves of all of the instruments together. You can still tell the difference between a bass guitar and a tenor saxophone, right?


Loss of signal due to phase differences happens when you have several different speakers in the same room generating the identical low frequency sound simultaneously. If the speakers are different distances from you, then the waves add algebraicaly: high pressures add to low pressures to produce inappropriately intermediate pressures (volumes) at your ears.


This is one of the reasons why a single subwoofer is usually the best way to reproduce low frequencies. Room dimensions are comparable to the wavelenght of the low frequencies, which leads to standing waves and diffractive interference patterns which aren't noticable with higher frequencies.


I hope this clarifies things a little.
 

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Quote:
There are no performance benefits to connecting a separate LFE cable to each BP2004.
The LFE line level input bypasses the BP2004's internal crossover. This would only utilize the processors lowpass filter.

I would say this would be the preferred connection for the LFE/SUB signal.


Also feeding the subwoofer sections "Full Range" line level inputs full range R/L Main channel signals will bypass the speaker level to line level conversion done in the speaker.


John
 

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Discussion Starter · #7 ·
Thanks for all of the comments. You realize that both of the speakers have a built in powered sub? I would think that utilizing the F R/L as both full range and sub would create the cancellation that you described.... "Loss of signal due to phase differences happens when you have several different speakers in the same room generating the identical low frequency sound simultaneously. If the speakers are different distances from you, then the waves add algebraicaly: high pressures add to low pressures to produce inappropriately intermediate pressures (volumes) at your ears."


For my personal benefit, can you explain the room size issue more clearly? What size sub is best for what sized room, etc... How would a small room (18X11) react to front speakers set to large (DefTech BP2000) and a seperate sub (DefTech PF15TL+) with Bass Management set to LFE -THX- (Denon AVR5800)? I have had a very hard time getting the sound I am looking for out of this system. Also, I have a DefTech C/L/R 3000 with a built in powered sub (10", 250 watts) for my center channel. Should this be set to large or would I be better off setting all of my speakers to small?


Confused,

JCJ1
 

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JCJ1,


I'm sorry, but I always wind up slipping a decimal place when I try to calculate the wavelengths :) so I won't try to tell you which wavelengths are the worst in your room. It also depends on how the room is constructed, where the doors are, and other physical details you wouldn't notice.


Positioning multiple subwoofers "correctly" is a lot of work. There are two different philosophies.

One is to configure them so they sound the best. That can be extremely subjective: it depends on what you enjoy listening to. It can also be a pain in the back from moving the speakers around.


The other is to try to measure what the sound is doing, adding one speaker at a time. This takes some rather specialized equipment in addition to appropriate sound sources (CDs I mean). Equipment would include an audio spectrum analyzer with a calibrated microphone. This can be either a standalone device or a computer with a high quality sound card and appropriate software.

Wandering around the room with the microphone can be very enlightening -- you'll find that the low frequencies don't become fainter as you get further from the speakers, but do vary in amplitude depending on where you are in the room.

Different frequencies with the same input signal level will have quite different amplitudes at the same location in the room.


Objectivists would say that your goal should be to get the flatest possible response at your favorite listening position.


Rather than try to get more specific here, I suggest you search the AVS forums for articles containing the keywords subwoofer, spectrum analyzer, standing waves, interference, measurement and the like. You'll find more than you want to read, I fear.


Don't forget, though, that the primary purpose of your audio system is to produce enjoyable sound.


I hope this helps a little.
 

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Discussion Starter · #9 ·
Selden,


Thanks for the great idea. I have a B&K (not the same as the audio manufacturer) sound level meter that does octave band measurements. Any recommendations on where to start? I was thinking around 80 Hz.
 

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JCJ1,


One thing you need to realize is that I tend to be like Eyore and see the difficulties with any approach, so bear that in mind for my comments below.


Sounds close to the crossover frequency will be coming from all of your speakers at once. It would

certainly show some of the interactions.


You need to plot the volume from about 20Hz up to about 200 Hz. Doing it manually with tones from a test CD is a good place to start. It can be rather tedious, though, especially if you want to do it for several listening positions.


Some people prefer to use a PC to automate the procedure: generating tones, measuring the amplitude and plotting the results. I've never done it that way myself, but I know there is software available for PCs and probably for Macs.


Handheld sound level meters aren't necessarily the best things to use: they're optimized for measuring the sound level when a broad range of frequencies are present -- like the "pink noise" generated by receivers. Often their response at specific frequencies can vary significantly. For really accurate measurements it can help if you can locate a calibration curve for the model you have. It'll show you which frequencies it's most sensitive to and how much to compensate. A web search and/or a search of AVS should turn up curves that various people have measured.


I hope this helps a little.
 

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Discussion Starter · #11 ·
Seldon,

:eek: That Sounds a bit over my head. While I have always been bit a bit of a gear head, I have never really had any experience with HT setups. I don't have access to the software you are speaking of so maybe I'll wing it with the B&K. I have a lot of experience with this meter. However, it is for an entirely different purpose.


As I mentioned earlier, my room is approx. 18X11 with several doors. Perhaps that is my biggest problem! Maybe I should just build a new house with a more appropriate theater room. What is the ideal size for a Home Theater?


In my current setup I have the subwoofer next to my listening position about 12 feet from the front of the room along the left side wall. Does any of this throw up any instant concerns for you. Keep in mind that I have the Def Tech BP2000TL's up front with 15" subs in each speaker facing twoards the wall. From a pure listening point of view...cetain movies sound really good while others are a bit to boomy or muddy on the bass end. The same circumstance applies to music. I am currently changing the setup for various software. For example; For Phantom Menace and most other THX software it sounds best (but still not as good as it should) to set the Denon parameters at all speakers small + sub. On Gladiator and most other DTS material, everything to Large with THX LFE, and with most music I use the DTS NEO mode setting all speakers to large with LFE+Main bass settings. Last but not least. I seem to always have to adjust the sub volume one way or another.


While I have to admit that I like playing with the equipment, I can't help but wonder if some good tweaking could standardize my set up paremeters somewhat.


I have been reading your many posts on this forum and trust your opinion. Thanks for your help.


JCJ1
 

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JCJ1,


Thanks for the vote of confidence. I think. ;)


Using your SPL meter should be fine. That model seems to be quite a bit better than Radio Shack's.


So far as sound is concerned, my understanding is that the room's dimensions shouldn't be in simple ratios (3:2:1 , 3:4:2, 1:1:1 etc). That causes standing waves of several frequencies to reinforce one another. Ideally, none of the walls should be parallel to one another, either. (a trapezoidal room with a curved wall or two, for example) Other than that, I'd suggest asking in the construction forum for what sizes people have found appropriate.


The main thing that bothers me about your speaker configuration is the number of low frequency sources. The many reflected sounds will cause interference patterns in the room. As a result, what you hear won't be very "clean". I'd like to blame the different qualities that you're hearing for different types of music on the fact that they emphasise different parts of the low frequency spectrum.


Not too long ago I read an article in one of the AVS forums which gave some very convincing reasons for setting all full range speakers to small and using just the LFE output to drive the subwoofer(s). I spent some time just now trying to find it, but couldn't. I'll try to remember its major points.


Don't feel that you're not using your speakers to their fullest. Crossovers aren't "brick walls". Speakers have to be linear well below the crossover frequency, and subs have to produce frequencies above it.


Subwoofers have a much better low frequency extension than the best full range speakers.

(Of course, that may not be true of your DefTechs)


Make sure any crossovers in your subwoofers are disabled. Use the receiver or pre/pro's crossover.


By not having to drive the lowest and most power hungry frequencies, your main speaker amplifiers have more headroom available for the upper ranges. (This doesn't apply so much when using speakers with powered subwoofers built into them, of course.)


When using more than one sub, they should be co-located to minimize the interference patterns.


It's a lot easier to find the best subwoofer position when there's only one involved. One way to locate it is to put the sub in your listening position and then go around the room listening for the best sound. The sound wave reflections travel the same paths in both directions. The sub's final position should be where you liked the sound the best.


I hope this helps a little.
 

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Discussion Starter · #13 ·
Selden, Thank You. Very good info. One more question and this is going to sound stupid...


Please explain "Make sure any crossovers in your subwoofers are disabled. Use the receiver or pre/pro's crossover."


Do you mean use the LFE input? I have the PF 15TL connected via LFE. However, the BP2000's and the CLR 3000 are connected via line level and set to large which as far as know does not bypass the internal crossover.


Thanks for taking the time to help me out. Vey much appreciated.


JCJ1


:)
 

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Sorry, yes, that's what I meant: whatever crossover is built into the sub that's on the lfe output should be bypassed or disabled.
 

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I have a similar setup with def techs and I do have some suggestions for a simpler way to optimize the position of your speakers and seating. 1) do not put your listening position(s) at 50% or 33% of the distance between the front and rear, or between the sides of your room. 2) Start with your speakers a foot or two from the wall. 3) Play some low frequency sweeps from a test source. 3) Using your ears and a radio shack meter, slowly move the speakers forward and back to minimize drastic peaks and valleys in the low frequencies. 4) repeat with the subwoofer turned on.


This made a huge, huge difference when I reached the correct spot. For more details, go to richard Hardesty's web site http://www.audioperfectionist.com./


p.s. Getting biwire cables from bettercables just made a big difference for my def tech system also. It opened up the high end very nicely.


Good luck, Horton
 

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Discussion Starter · #16 ·
Thanks Horton,


That is more good info. Interesting about the biwiring. I have wondered if it would really make a difference.


You say it opened up the high end? I have often wished the DefTechs's were brighter but wrote it off to the limitations of the setup vs. the room.


Unfortunately, my speaker wires were built into the wall and routed to the built in rack when I remodled the room for a HT. In order to bi-wire I will have to run cable along the wall and fiqure a way to get them into the rack.


Did you also bi-wre the center channel?


JCJ1
 
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