Overcoming Room with REW

Discussion in 'Subwoofers' started by L4_Isoside, Jun 30, 2019.

  1. L4_Isoside

    L4_Isoside
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    Hi,

    I finally managed to setup REW and have taken some measurements. In my lounge / setup I am very limited with subwoofer placement, currently using a Monolith+ as shown in the attached diagram.

    It's a rectangular room with part of it blocked out (as seen by the black box) and I am sitting on the long length of the wall. It's about the best friendly / home cinema layout I could come up with and for the most part I'm really happy with it.

    Current sub position is giving me REW results as attached under 'original position'. (Sub woofer is placed to my right hand side)

    I would like to add a second sub but it gives much worse results (attached 'second position') This subwoofer would be on my left hand side the same distance from MLP and the first sub.

    If I average the two results in REW I get the third result 'average of two'.

    Would adding a second sub be a terrible idea? Both subs are basically touching the couch and very close to MLP..

    I am considering building some sealed subs and wondered if there was any worth in building a second one knowing it can only be placed really in that second position?

    Thanks.
     

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  2. Conrad.

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    I would ask what you're hoping to achieve with a second sub? What do you feel you're not getting with a single Monolith that you'd like to improve upon?

    Can you set the graph to the standard measurements of 45dB - 105dB with 5dB increments.

    You've got a wide (20Hz) deep (-15dB) trough centered on about 42Hz. That'll be taking quite a bit of the punch out of the room. It's hard to see if the second sub would be much of an addition with the two separate graphs, can you overlay them onto a single graph? It looks like the second sub is also -15dB at that frequency, so I don't know it'll help you.

    The average of the responses will give you an idea, but remember it'll be affected by where the subs are in phase and are summing their outputs, giving you an increase in output, or where they're out of phase so you'll end up with a different dip. Even though your AVR has a single sub out, the monolith has a phase control, so you should be able to identify the bset combination of settings.

    EDIT: Is it an FF or a DF? If it's an FF have you tried turning it around? It might not look ideal but you'll be able to see if the dip changes.
     
  3. L4_Isoside

    L4_Isoside
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    Thanks for your input.

    It is a FF monolith, however, I will be building (well planning to) a sealed 18" sub to replace it. As we all want - more output is the goal! However, ideally, I would like a bit more low down stuff and more importantly more of a 'punch'. Also it would be nice to know that my sub response is as accurate as possible (in terms of a flat-ish response).

    I have adjusted the screenshots to as you have asked (I think Ive done it correctly!) and attached.

    The reason for the second sub would be to have one left and one right of MLP, because the sub is so close I can tell that its there and hope that two would also even that out.

    EDIT: Currently my sub is to my right hand side. I will try turning it around and checking the measurements when the lounge is free.
     

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  4. Conrad.

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    As I understand it, you're dealing with three issues there: depth, slam/punch, and tactile response.

    Two subs won't go lower than what you have now. To do that you need to move more air, which your 18" sealed will do. You'll get a benefit from having two monolith's but they're never going to get down into the low teens.

    For punch, you need that upper bass dip eliminated, which is placement. The second sub, where you're planning on putting it, won't do much. It'll improve things, but I'm not sure it'll give you what you want. Someone with more experience might know better.

    The tactile response is what you're feeling from the sub being so close. A second sub at the other side of the couch won't eliminate that. It could make it worse. I guess if you've got two and you can turn them both down you might minimise it, but if it's right next to the couch then you're likely going to feel it at any decent output.

    My recommendation would be to focus on the 18" and see what that does to your response. Subs of different sizes and different brands are about the hardest combination to integrate, but it's not impossible.
     
  5. L4_Isoside

    L4_Isoside
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    Again thankyou.

    The cost of building 1 vs 2 cabinets for the subs is minimal so will be having two. The biggest cost will be an additional driver, however if it simply does not work, I could sell it on, so I guess suck it and see will be the best bet!

    Yeah I do quite like the tactile reponce from the sub but I can hear its coming from one side vs the other. When I had it up front in another house I lived in, it felt like it was coming from everywhere. If that makes sense. I'm kind of hoping two bigger drivers (even if they are very close) will help with that.

    When I get the new ones built I'll not be using the monolith I don't facy trying to implement two different types of subs.
     
  6. Conrad.

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    2 x 18" will definitely get you lower than the monolith. Each one has over twice the driver area (not the only factor, but an significant one). It's a good sized room you're filling too.

    I guess your costs will go up around the amplification as well? Or does the amp you're planning on running the sub with handle two subs?

    If possible, arrange it so that the driver points away from the couch. Even the air moving across the side of the couch could allow you to localise the sub. One of my subs fires across the back of my couch and I can feel them when they get going.

    Without fixing that hole at 40Hz though, I don't know that you're going to end up with what you want.
     
  7. L4_Isoside

    L4_Isoside
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    Yeah it's a shame. The front end of my setup is pretty well fixed and to place subwoofers there to try and get rid of that null would mean a significant change to the LCR + cabinets etc that were fitted when I first moved in. Even smaller / thinner subs such as the Arendal sub 2 etc wont fit pretty much anywhere without modification.

    Would placing sub woofers on the other side (well over to the left of the room) help at all, even if they where there just to fix a null? It would be relatively far away from the MLP though.

    Will have to see how the new sealed sub responds, either way should be a good upgrade to what I currently have.
     
  8. Conrad.

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    Yeah, room placement issues are a fact of life, unfortunately.

    Agreed that what you're looking at building will be an upgrade, it just won't change response shape much if you put it in the same place.

    Given that the sub is pressurising the whole space, there's a chance that putting one of the new ones down at the other end of the room would help. Room sim says that a sub to your right will give you a big suck out at 42Hz, which is what you've got, but a much smoother response at the other end of the room. That's without the closed off area, of course.

    To try it, stick the sub as close to your listening position as you can and go and walk around the other end of the room or, for the price of a 15m amazon basics subwoofer cable, try it out. Even if it's for a little while.
     
  9. L4_Isoside

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    Yup I have a long cable but ordering another longer one to make it easier to place the sub all across the room. :smashin:

    Looking that this new position in the room sim, where the sub is over to the right but closer to the front wall (only just enough room and partially blocks the door but could work), you think this helps the null? I will certainly try it and post some results when I can.
     

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  10. Conrad.

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    Amazon basics and prime are just amazing. I just decorated and put the room back together yesterday only to find my HDMI cable had failed. Orderd last night, arrived today, and watched a movie this afternoon!

    Anyway. How have you got your mains in there, are they listed as subs too?

    For me, in that same location about a meter from the front wall the dip at 40 is gone but another narrower dip at 60 appears. Any chance you can move it to about 1.5m from the front wall along that side wall, so in the middle of the right wall?

    Also, it looks like you're mounting the sub to the ceiling!

    Is there no chance you can try the sub to the left of the left front speaker? That seems to give the best response, but this is all without the blocked off section being taken into account.
     
  11. DodgeTheViper

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    Try adding 1m to the distance and see if that affects the 55hz to 70hz dip.
     
  12. L4_Isoside

    L4_Isoside
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    :facepalm: Yup that's what happens when you rush together the EQ sim!

    Corrected the height and took out the mains as they will be crossed at 80hz and not worrying about them for the time being.

    I will try a few difference positions tonight! There is a single-seater couch there that takes up a chunck of that wall then a rear right speaker in the corner. The couch is way bigger than we wanted but made the mistake of ordering it online without seeing it and its going nowhere now SWMBO likes it. :rolleyes:

    To the left hand side, I have the front left speaker, then a door to the kitchen, then that blacked out bit, which is a load bearing wall that for some reason they set lightly further in to the living room (giving more room in the kitchen that isn't needed).

    Also yes cable ordered on Amazon coming Tuesday all being well.

    I'm going to have to ask how I add 1m to the distance !
     
  13. Conrad.

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    I didn't think distance did much to change a single speakers response shape. I always thought that it was about the combined arrival times at the mic/MLP. Is that wrong?

    It's a free test though, so why not.
     
  14. DodgeTheViper

    DodgeTheViper
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    That extra cable will certainly help in trying different locations for sure. The distance thing will be within the AVR.
     
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  15. L4_Isoside

    L4_Isoside
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    Ok I have re-measured the original sub position, plus the new position suggested in which it is 1m from the front wall on the right-hand side this is about as far as practical as I can get it.

    The line in red is the new position, brown is original. Would having a sub in each position then optimized give a better response? It looks slightly better to my untrained eyes :confused:.

    EDIT: Adding or subtracting distances to the sub made no difference that I could see at all. I made a few other tweaks that did little to nothing as well.
     

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  16. Conrad.

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    Absolutely it should. As long as you can get the phase right one sub should help where the other falls short, that’s the whole point.

    Let’s see what the other end of your room looks like when you get the longer cable.

    How does the new position sound? It should sound quite different with that 42hz hole filled, but it’s missing some top end with that 60-90hz dip.

    What are your main speakers and where are you running your crossovers?
     
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  17. L4_Isoside

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    Awesome thanks. I tried the sub to the left of the front left speaker and to the left of the rear surround speaker and both gave awful results.

    I'll admit, that new position, is actually the position I first placed the sub when I moved in and set up this room in around October last year, and at that time I did not like it compared to where it is now. The reason for this is that I felt like it was "pressurizing" my right ear over my left and it made it very localizable, however, I didn't spend a lot of time trying to sort that out and moved it quite quickly. Also I was using the Denon with x32 and not Dirac etc. I didn't spend any time testing it last night, I might try doing some actual listening with it there again.

    Extra long sub cable arriving tomorrow, so I will try the sub in the same place but on the opposite side of the room (or as close to as possible). I could even corner load it there. The issue im thinking about is that it would be around 4.6m from MLP vs 2.5m when placed to the right. Would this large difference in sub placements cause an issue seeing as one will be working harder than the other?

    Thanks again for your advice it is really helpful :thumbsup:.

    EDIT; Mains are;

    Tannoy DC6T Signature floorstanding left and right
    Tannoy 6c Precision centre
    Tannoy DC6T Revolution floorstanding for rear left and right
    S2 atmos ceiling mounted (crossed at 100hz) for Atmos duties

    All crossed at 80hz.
     
  18. Conrad.

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    I'm not sure. One way to test though is to play some bass heavy content and go and stand at various points at the other end of the room. If you get decent bass response there, then the inverse should be true. It's the same principle as the "sub crawl method".

    If you want to be really thorough, take a laptop with a mic to that end and use the RTA in REW while playing white noise. That'll show you what response you're getting without having to hook everything up to run a sweep. (you could also run sweeps with a long lead to your mic/spl meter).
     
  19. Ultrasonic

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    What makes you say one will be working hard than the other? Being further away won't cause this.

    So long as you aren't reaching the maximum delays you can set to get phase matching right I wouldn't give any thought at all to how far away different subs are. Just focus on getting the frequency response right.
     
  20. Ultrasonic

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    In case this isn't clear, when making a measurement of a single sub on its own, changing distance settings in a AVR won't make any difference at all to the amplitude response that you're looking at. Distances/delays become important when considering how the sound from multiple sources adds up.

    Having had a quick read through the thread I'm not quite sure where you've got to now. Could you post a picture showing the positions you are considering, and the mdat file containing the corresponding measurements?
     
  21. Ultrasonic

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    Is a layout anything like this a possibility?

    upload_2019-7-1_14-4-48.png
     
  22. L4_Isoside

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    My reasoning for thinking one would be working harder than the other is my general lack of knowledge :rotfl:.

    So I have attached a picture of room sim and the 4 locations that I could place the subwoofer.

    1) Is the current position and the appropriately name 1 file has been attached - download here
    2)Was my choice for a second sub to be positioned (when I have a second sub, at the moment I am using just one) - download here
    3) Is the position suggested in this thread - placement here i tend to find 'pressurizes' my right ear and not my left ear when in use, and so it makes its self very obvious - download here
    4) is the position i will be trying when I get a longer subwoofer cable. In fact, anywhere along that left-hand wall is fine.

    EDIT: The issue with the rear corner as you have suggested is that there is a floorstanding surround speaker right in the way. Placing a subwoofer there would mean moving that speaker, which would need mirroring on the opposite side and will either bring them much closer to MLP or further forward of MLP and this losing the surround effects. If i am desperate I may try this.
     

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  23. Ultrasonic

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    I'm confused by your position 4, since in your first post this is within the black box region that I'd taken to be a region 'blocked out' by walls?

    Rather than your dropbox files it would be far easier for everyone if you saved all of the profiles in a single mdat file, and then uploaded this as a single attachment here (using the 'Upload a File') option.
     
  24. Ultrasonic

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    Actually just trying myself I see this forum doesn't like .mdat attachments. My bad.
     
  25. L4_Isoside

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    Yeah sorry, this was my first option but the forum didn't like it.

    You are correct the 'indented corner' to the left is 58x236cm rectangular indentation in to the room. So that position 4 would be placed at least 58cm in to the room. I re-attached the positions to more accurately describe my senario.
     

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  26. Ultrasonic

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    To give you an idea of the sort of result you could get from two subs combined, below is a possible result using the sum of your positions 1 (orange) and 3 (purple), with 1 being delayed by 2 ms. The result in black is better than either on their own.

    The other benefit of two subs is that each won't be pushed so hard to achieve the same volume, which should reduce distortion.
    upload_2019-7-1_15-8-14.png
     
  27. Ultrasonic

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    Out of curiousity, do you have a particular DIY design in mind?
     
  28. L4_Isoside

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    Awesome, thank you.
    Yeah, 20" cube with a bms 18n862 8ohm driver. Powered most likely by a nx6000amp and using a minidsp 2x4hd. I've gotten the order in for the cabinet. :thumbsup:
     
  29. Ultrasonic

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    I'll be interested to hear how you get on. Good luck with the project :smashin:
     
  30. Conrad.

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    I still can’t wrap my head around this. I know it’s correct, but still. Taking room interactions out of the equation (not really possible, I know - let’s say standing in two places that give the same response) we’re saying that standing next to a sub or standing 50ft away should make no difference to the perceived volume.

    And it’s because of the way bass is felt and not heard. I get it all, it just seems wrong.
     

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