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3803, speaker sizes, subs and resonance

Discussion in 'AV Receivers & Amplifiers' started by chrisgeary, Aug 21, 2003.

  1. chrisgeary

    chrisgeary
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    i have the Denon 3803 which I am setting up. I have a pair of B&W DM620 mains, a 2000IFS centre, some RAM bookshelf rears, REL Strata III and REL Quake II. My room's primary node is 33hz. My mains quoted response is 56hz.

    Using AVIA, I have done some sweep tests and I know that my mains work down to the rooms main node. I also know that the node is so strong that the sub cannot possibly operate anywhere near it. My mains do nothing below the main node. Thus, I have my mains set to large, LFE to LFE+Mains and the Strata out of phase with respect to the mains set to Coarse 1, Fine 1. Thus its crossover is at 22hz. This prevents too much loading of the room at 33hz whilst the out of phase configuration works since the speakers are not actually driving the same frequencies. But of course, the mains tickle the main node and so does the REL, so being out of phase largely sorts that out (actually in reality it doesnt enough hence the Quake, located at the other end of the room quietly controls that node and damps it to boot!).

    Further, I set the rears to small, did some frequency tests and discovered that anything below the denon crossover of 100hz was routed to the sub. Naturally I heard nothing because IT is set to 22hz. Hopefully you understand the reason why i have set it to that. Anywho.. This is also true for the centre channel. I can get away with large for the rears, they reach surprisingly deep for bookshelves, but the centre cannot.

    My question is, have i missed something in the denon that it cannot cope with a sub that is set to 22hz. I thought since I had LFE+Mains set that, as i think it says in the manual, anything below the crossover point is routed to the sub (and the mains if LFE+Mains is set). I had a Yamaha A3090 previously, and it did it just fine, thus it could cope with my slightly unusual subwoofer deployment.

    Anyone have any ideas about this one?

    Cheers

    Chris


    in addition, i have just discovered that when speakers are set to large, the lowest frequencies are output by the sub as well, even when running a sweep on the rears or centre (LFE+mains mode). is that right? not a problem, i can live with that, in fact in some ways it helps me out.
     
  2. lmccauley

    lmccauley
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    Chris, I'm a little confused as to what you are actually asking.

    I think I understand about why you have your mains going down to around 56Hz and your sub picking up again at 22Hz (because of the room node at 33Hz).

    But, I'm not sure what it is you are asking about the Denon 3803. Possibly this is because I've never used that particular amp, so maybe someone else can chip in.

    Have you thought of setting all speakers to small, using the .1 input for the Strata, selling the Quake and buying a Behringer Feedback Destroyer as a parametric equaliser to cut out you room nodes? You should also have enough spare cash over to buy a few DVDs.

    Cheers,
    Liam
     
  3. Jase

    Jase
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    How have you got the Rel's connected to the Denon? Via both High & Low level? Low Level only????
     
  4. chrisgeary

    chrisgeary
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    Liam: actually i used to use an Alesis MEQ230. it does help with resonance, but has two problems. 1. it introduces noise of its own. 2. you cut one band and it has knock-ons to bands adjacent to it. using a frequency sweep from my AVIA test disc, i found this to be more trouble that it was worth. The Quake actually does the same job, only better. No noise added, controls resonance AND damps that resonance too! A much better solution all round.

    Jase & Liam: Yes, low level only which brings me to another problem (although in an ironic twist of fate, i have solved it). The denon has only 1 sub output. This isnt impossible to get around, but when using quality cable, you cant just stuff two into one phono plug. What im doing for now is:
    (oh btw, my centre is now a Dynaudio Audience 122C - flat to 45hz +-3db)
    Mains, large
    Centre, small
    Rears, small
    Sub crossover 40hz
    Sub mode LFE+Mains

    This allows the centre and rears to deploy down to 40hz, at which point they get rolled off, avoiding the rooms main node. Below that the REL handles, it rolls off from 22hz upwards. Because the LFE+mains mode is set, the centre and rears sub 40hz stuff should get routed to the mains as well as the strata. In practice, i dont believe that happens, which I also believe is wrong. (cant remember actually, correct me if im wrong). (remember im doing that as i cant set the mains to small and cross them at 40hz too since then i cant feed the quake with resonance controlling audio so the strata has to be out of phase with the mains to stop them over exciting the node). So I have the quake plugged into the left front pre-out on the basis that with LFE+mains set, what hits the sub will also hit the mains, and in that case it matters not which front channel i use, it should be largely the same audio (plus the full range mains which doesnt matter cos the quake filters it out anyway). Anything above 40hz is done by the centre and rears (which all do quite comfortably), and then the sub takes the rest.

    In short (phew), it actually works really nicely now, but without the depth of the 122c centre, i couldnt have made this work, which i believe is a big failing of the 3803. its flexible, but not flexible enough. 2 sub outs please, (my old yam had 3!), and please route the bass below the crossover to the mains if lfe+mains is set, that just seems to me to make sense.
     
  5. Jase

    Jase
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    Plugging the Quake into the Front Pre Out means it will be receiving a full range unfiltered signal. So I assume you are using it's crossover at some point????

    Don't forget that the amps crossover is not a brick wall filter it will have bass above and below the chosen cutoff frequency.
     
  6. Jase

    Jase
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    As Liam has mentioned ;) you might find it a lot easier to buy a Y-Splitter cable and attach that to the Denon's Sub Pre-Out, set all speakers to small, all bass to sub with the subs crossovers ignored and set the amp crossover to 80hz. Then buy yourself an equaliser and attack it from that angle to iron out any bass peaks etc.
     
  7. lmccauley

    lmccauley
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    Is there an echo in here, Jase? ;)

    The Behringer Feedback Destroyer I referred to is used in many high-quality sub setups in the US, and over here now, too. If you search for BFD on these forums, you will find tons of information about it. You can specify the equalisation gain and width to get pretty specific adjustments (although you are right - you do have to check out all your measurements again to see which other frequencies ended up being affected).

    Cheers,
    Liam
     
  8. chrisgeary

    chrisgeary
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    jase: yeah im using mode 3 and its variable crossover set to (im guessing) around 60hz or so.

    im not sure about the y-splitter.. it would need to be a decent one. i only use OFC grade cable (i have a reel of it and i make up connectors myself using gold plated phono plugs). do you guys have any suggestions for decent grade splitters?

    i have near full range speakers capable of reproducing down to 50hz or so. the strata will over power the room at 33hz so i really have to set the crossover low on it; no higher than 22hz. thus i cannot set all my speakers to small and cross them at 80hz, there would be a huge hole in the sound! actually what i would love to do, and what would solve the problem i believe, is to set all to small (thus sub to LFE only), cross at 40hz, and use the y-splitter for the subs. that way the strata and quake get the same info and i can control that pesky room node, the mains wont get sub info they cant reproduce.. ah i have just remember why i cant do that. when watching a movie, the discreet LFE channel will be somewhat attenuated by the strata's crossover unless also sent to the mains. thus i have to have the mains set to large. im working on the principal that the main's lowest extension and the sub when run out of phase cancels out the room node enough - and that the LFE channel on DVDs is 80hz and lower. some kinda diagram is in order..

    mains
    56hz +-3db
    in my room they audibly work to
    30hz
    sub phase at 180 degrees
    works up to 35hz
    22hz crossover

    so the mains dont interfere with the sub below 30hz and vice versa. whilst at the frequencies they share, they cancel each other out (results in control of room node)

    ive been down the EQ route before and im not convinced its sonically the best route forward plus EQ can never take care of damping. a 33hz tone may be quieter with an equaliser but it will still take time for the room to resonate and time for that to decay once the tone has stopped. the Quake takes care of that restoring the timing as well as the amplitude.

    my original question was more to do with how the denon routes bass information based on the setup parameters. having done some further testing, i still dont think it does it right, but having now upgraded my centre speaker, it matters much less now. i just wish that if you set mode to LFE+mains, it would do just that. any bass information below the xover point should be sent to the sub, and since the sub mode is to output to the mains too, then surely anything below the xover point from the centre or rears should ALSO be output to the mains, not just the sub.
     
  9. Jase

    Jase
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    As I understand it the Denon does the following.

    All speakers set to small, all bass to sub = LFE and all bass below the amps crossover point is routed to the subwoofer.

    Fronts to large, all others to small, bass to LFE & MAIN = all bass below the amps cutoff frequency is routed between the sub and the front speakers, same for the LFE.

    All speakers set to large, sub for LFE (assuming you have sub selected) = all channels receive full range signals and the LFE is routed to the sub only.

    The Denon THX amps have a further option which is LFE & THX which means only the LFE and the bass from the channels set to small is routed to the sub.
     
  10. slyborg

    slyborg
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    Can I ask a real audioNoob question?

    What is the room node and how do you find out what it is?
     
  11. chrisgeary

    chrisgeary
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    the room node is the rooms natural resonant frequency. there are a number of mathematical ways of finding out what it is for a given room, i can post an excel spreadsheet (that i personally dont understand) that will do it for you. frequencies have wavelength, i dont remember what is what, but 33hz is something like 10 metres. so if my living room is 10 metres long, when a 33hz note is played from my speakers, it will sound way louder than it should, and also take time to build and time to decay as the room resonates.

    its normally easy to find without any maths: you will notice certain bass notes are louder than others when you play music, and some are almost non existant. the note that is the loudest of all is your rooms main node. there will be others too all across the frequency spectrum, but they are typically noticable in the 100hz and below region.

    walk through your room and you'll find that that node is only noticable in certain places. in the middle of the room, it will be almost inaudible, whereas towards the back of the room and also at the front near the speakers it will be very loud. this is why speaker placement is very important. you can follow the guidelines set out by the manufacturer and advice from the web, but only trial and error in your own room will tell you where you should place speakers. if it sounds right.. then it probably is :)
     

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