ThX Speaker Setup and MCACC (Pioneer)

Discussion in 'Speakers & Subwoofers' started by RobD, Apr 9, 2003.

  1. RobD

    RobD Second Unit

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    I just got a Pioneer VSA-AX10I Amp (Euro version of 49TXI) and am not sure what to set my speakers to. The speakers are Mordaunt Short THX Select ones, the left and rights have subs built in and I have matching di poles correctly placed at the back of the room. I currently have the subs set to THX (No volume control possible on the sub in this mode) and the amp setting at +0.

    Should these speakers be set to Small or Large? Is an 80Hz crossover correct?

    My other question concerns 6/7.1. The room has to the letter layout for THX Ultra/Select but Ultra 2 asks for 2 speakers at the rear. There is only a couple of feet space behind the listening chairs although there is 20-25 feet between the rears, is 7.1 worth it or would 6.1 be better. One point to remember is this speaker range does not have bookshelf speakers.

    Sorry to ask so many questions (MCACC made the system sound worse!)
     
  2. MikeRP

    MikeRP Supporting Actor

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    I'm not familiar with your speakers but if the MCACC makes it sound worse - your doing something wrong!

    Mike
     
  3. Till

    Till Auditioning

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    I am not familiar with the particularities of the built in active sub of what is probably the 500 series, right?

    I have a 49TXi sso I'll try to help with some of the questions to the best of me knowledge.

    If you set the Sub in the AX's menu to THX the x-over frequency is automatically 80Hz and I believe all speakers are automatically set to small including the fronts. This is THX spec and since your system is specified to be THX that should be alright. The difference between select ultra and ultra 2 is afaik in power requirements and room size but not so much in the basic principle of things.

    There is a Boundary gain compensation for THX subs in the expert menu. You might want to try that out. OTOH your subs are inside your main speakers so they are probably not positioned to close to any boundaries, read walls.

    I hope you get good sound with not too much boomy bass if no volume control is possible. The correct position for your phase switch on the sub is the one that has more bass. If you don't hear a difference but it on 0 rather than 180.

    Most people are probably using their systems in the long axis of the room, i.e. main speakers and TV or PJ are on the short wall. If this is the case for you that would mean that your short wall is still 20 to 25 ft. long, right? That is a very big room after all if the long wall is around 30 ft long. So you would be rather in Ultra 2 specs for the room size. If your room is that large it does make sense to have two back surrounds because a) you get more sound pressure level and b) you get a more even soundfield from the back.

    Channel 6 and 7 (the back channels) get exactly the same signal, as you know. There is a function related to Ultra 2 in the expert menu that lets you choose the distance in which the back speakers are mounted to the wall. Use it. Besides the fact that it might be hard to buy a single speaker because they always come in pairs it might be a good idea for the above reasons to go with two back speakers. Now, you must decide whether you want direct radiating or dipole speakers for the back. I know that Ultra 2 says you should take directs. But you will be sitting very close to the back wall, if I understand correctly. And your back sp. will be either set quite close at a 4 ft distance form each other or farther apart. In any way they will be further apart than your ears and if you are to close the sound will radiate so that it just passes by. Like sitting directly between your fronts and not at the correct distance of the stereo trianlge. Therefore, you might consider another pair of dipoles for the back which will give you a more even soundfield which is especially desirable for movies.

    Hope this helps,

    Till
     
  4. RobD

    RobD Second Unit

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    Till,

    Thanks for the really helpful response.

    The speakers are the 500 series. Direct radiation bookshelves speakers arent available in the 500 series so Iam limited to dipoles or a rear centre. I didnt think of using dipoles, will look into it.

    When the subs are in THX mode, volume control can be done using the amp channel adjustment, at + 0 the bass is heavy but not out of control (Subs have no problem wih the DTS Intro at +10 volume - about as loud as I ever go). The setting for the REL sub is difficult however, it produces deeper bass than the integrated subs but nowhere near the volume, I was thinking of enabling it's built in filter and setting a 60Hz or similar rolloff.

    The screen is on the long wall, the room is about 2600 foot cubed. As I said volume isnt a problem, is it really a problem that MCACC messes up the sound?
     
  5. Till

    Till Auditioning

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    Rob,

    sorry for not getting back earlier. If I understand correctly, you have built-in subs in the Mordaunts and an extra REL. Right? You like bass, he? And you say despite all that you don't get enough bass?

    You might have a room cancellation problem with the REL at a certain frequency, so that this particular frequency is canceled out or subdued. Moving around the sub and trying out which position sounds best should help. Corner position usually gives up to 6db more volume. A 60Hz crossover is recommended since you already have two subs at 80 and at 60 you shouldn't be able to localize the REL. By the way, how do you hook up three subs? There are only two sub outs on the Pio. Do you use a Y-cable?

    Read my post in this thread on more sub info:
    http://www.avsforum.com/avs-vb/showt...36#post2014736


    Usually the surrounds should be two or three feet over your head to avoid localisation. But if the rear wall is so close you could lower them because of the described sitting-between-the-speakers-effect. Dipoles are actually a good idea in this case, or even bipoles (both speakers are in phase).

    Holy crap, as they say here in Texas, dts trailer at plus ten is super loud. Don't try that with the THX moo trailer, you'll be deaf.

    Till
     

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