SHould I use LFE or low level input - diyAudio
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Old 16th May 2005, 08:08 PM   #1
PeterK is offline PeterK  United States
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Question SHould I use LFE or low level input

I've been interested in building my own sub and just found this great forum! This is the first of many questions I'll probably have.

My listening room is for both HT and music approx 25x14 with a ceiling height of 8 1/2' and the long side walls vault to the ceiling.

Front speakers are Infinity RS5b(pre Kappa 7s), 3-way 10" poly woofers (just refoamed) w/Emit tweeters, Kappa Front Center, Sound Technology rear center, ADS 6" 2-way monitors for rear surrounds, JBL E10 front effects.

My receiver Yamaha RX-V3000(6.1ES) has two mono LFE output jacks that I currently run to the L/R inputs on an Infinity BU-2 sub (it was my first sub, so please no cracks). I plan to put together a 15" sealed enclosure with a plate amp and am confused on whether I should look for a amp with LFE input or just run a Y-cable into the low evel RCA pair?? Trouble with low level is that the gain is not variable with the volume control so I have to keep tweaking the sub volume to keep it in check. I have no need for speaker level inputs or outputs on the sub amp. Most music listening is 8-channel stereo aon the Yamaha with uses the LFE output as well.

The pair that I am considering is the PE 500W and Titanic III 15". I am also considering thre oAudio 500 amp because of the subsonic filtering and BASH technology. The sub will probably be sealed but I am open for suggestions. I am a woodworker, metal worker, etc and will build the cabinet in my shop.

Thanks in advance for the advice.

PeterK
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Old 16th May 2005, 08:25 PM   #2
Did it Himself
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Surely the LFE output varies inline with the volume control? Would be a bit useless if it didn't.

The LFE signal is filtered, usually at 80Hz. It's not really meant for music as it's a discrete channel. Stuff just bleeds through when playing music. The chances of the cutoff frequency matching up with your main speakers is slim. Therefore I say make a speaker level attenuator or look for a plate amp with adjustable filter and that can take speaker level inputs.
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Old 16th May 2005, 08:25 PM   #3
tiroth is offline tiroth  United States
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The only difference between "LFE" and normal input on most subs is that the LFE input usually bypasses signal processing: internal lowpass, etc. This may or may not be desirable--it depends a lot on your setup.
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Old 16th May 2005, 10:24 PM   #4
PeterK is offline PeterK  United States
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Default You're right but

Your're right. My LFE varies with volume control and is cutoff internally - set at 90Hz. Being discrete, it only works for DD or DTS or, in my case, also for 8 channel stereo mode for music which produces a discrete LFE output to the subwoofer from my receiver.

So I could either bypass the crossover on the sub amp (which means OAudio amp becase can't do this on the PE) or run a pair of line outs from the receiver to the low level inputs and let the sub amp set the crossover points which might actually have more granular control. But, with line out to low level is where I have to constantly adjust the sub level to the situation because the line out is not controlled by volume control.

So which is better or does it not really matter (in sonic quality) which input I use? The setting on my receiver is set to "both" subwoofer and mains for LFE since I have 10" woofers in my mains.
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Old 17th May 2005, 08:29 AM   #5
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As I said before, the chances of the preset cutoff frequency of the LFE output matching to your main speakers is slim. As you have 10 inch main speakers 90Hz is way too high.

You need to make an attenuator for the speaker outputs to derive a line level signal then feed this to your sub which has its own filter in which you can set more appropriately. A 1/10 attenuator can be made from a 1.8kR 1W resistor in series with a 200R 0.25W resistor. Take the attenuated signal off the 200R.

Although in all honesty, you should be able to find a plate amp with adjustable filter and speaker level inputs already there without even trying.
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Old 19th May 2005, 08:53 PM   #6
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I can offer you some advice since I use the RX-v3300 and I think they use basically the same bass management. (very limited)
I have tried numerous different setups, but what follows is what I found to be most effective.
I built dual subwoofer boxes that sit under my front speakers. They are each loaded with a pair of 10" audax sub drivers, but you could use a single 12" or 15" driver in each. I have found that I get the best sound and most flexibility if I take the dual mono sub outs from the Yami and run them to a seperate stereo amp which then powers the subs. Set all your speakers to small (I know you want to use those Infinity as full range but trust me you will enjoy both music and HT more with the setup I am describing). The xover in the Yami will provide an adequate blending between your mains and the subs. Having the 2 subs sounded less boomy in my setup , compared to running 1 sub in corner. In this setup, you don't need any special plate amp, just watch ebay for a decent stereo amp, don't overlook the pro audio amps.


By the way, I have never used the front effects speakers, do you like them ?


JM
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Old 24th May 2005, 03:32 PM   #7
PeterK is offline PeterK  United States
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JM -

Thanks for the tip. I tried setting my fronts to small before, and really lost the smoothness of the bass; maybe I can set the cutoff to the sub lower and still keep some bass up front. But my ears didn't like it when I tried. Once I build this sub, I'll try again. The Infinity's are really great speakers with bass down to 35Hz, also nice and bright, but full and solid bass too. I just refoamed them using the low freq oscillator in the Yami to center the foams!

As far as the front effects, it subtle. The front effects use a Prologic-type processor to ectract the effects so it's no a discrete channel, just a little more ambience in the room.

Peter
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