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Blocking up the bass ports on Nearfield monitors

Discussion in 'Monitoring / Headphones' started by Sean G, Sep 13, 2015.

  1. Sean G

    Sean G Well-Known Member

    I would like some advice from members on the topic of blocking the bass ports on nearfield speakers.

    I have a set of KRK Rokit 5 Gen2 (I know, I know, before you get started they were cheap and I was on a budget at the time and have'nt upgraded yet) pictured below, which have a front bass port below the driver at the front.
    Although the pic does not show it, I have them sitting on neoprene mouse pads to isolate them from my desk, I do plan to pick up some speaker feet early next week to replace said el cheapo isolation option.

    These are situated around 6 inches from the wall behind and I have acoustic tiles which are 2 inches thick behind said monitors.

    I have read differing opinions on whether or not blocking the bass ports is a good idea, bad idea, better /worse, so I experimented with a piece of high density memory foam cut and placed into the front port to see if I could hear any difference.

    To my ears the difference is very minimal, but I would like to know the following from those in the know:-

    a) does it tighten up the bass sound ?

    b) Does it effect the driver response by restricting the air pressure / flow thereby limiting the driver travel or slew the response?

    c) Would using something like the HD memory foam I have used allow air pressure to escape as opposed to something more solid such as, dare I say it, styrofoam?

    c) What effect would this have on say EQ and the overall sound / how it translates?

    d) Any other thoughts or considerations I would need to take into account?

    Thanks in advance for any advice on the matter.

    Edit - I am not running a subwoofer with these as the room is not that large (11ft x 15ft)
     

    Attached Files:

  2. pcrecord

    pcrecord Don't you want the best recording like I do ? Well-Known Member

    I'm gonna follow this thread to read what others think about it.
    Here is my guess : Yes, it will change the frequency response of the speaker but making the bass thighter would be a complete 1 to a million chances.
    Most of what will happen is unbalance it and make things worst. A small piece of foam would more affect low mids than bass...
    Usually bass ports are there to recover some sound pressure created by the speaker to produce bass frequencies otherwise not present in the box.

    In my opinion, messing with it won't correct room accoustic problems and won't make a 100$ speaker sound like a 1000$.
     
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  3. Sean G

    Sean G Well-Known Member

    Thanks for your reply pcrecord

    In my opinion, messing with it won't correct room accoustic problems and won't make a 100$ speaker sound like a 1000$.[/QUOTE]

    I'm not looking to fix room acoustic problems, (the room for what it is has some acoustic treatment at first points of reflection, main walls at strategic spots and some bass trapping & a carpeted floor) or make them sound like $1000 monitors, just wanting to know if it does or does not improve the overall sound of these budget boxes.

    The plan is to upgrade shortly to maybe something like a hs-10 or JBL LS 305P ???, there is a store here in Sydney where you can try out many different sets before you buy, but that does not give you any idea how they sound in your room environment or through your set up

    I have even read of the "old bundle of straws in the bass port trick", I can't say Iv'e tried that one.
     
  4. DonnyThompson

    DonnyThompson Distinguished Member

    I've done this occasionally, but only in situations where the monitors were located in close proximity to walls and/or control room windows; and as Marco mentioned, it's only ever going to be so effective; the larger determining factor is the room in which you are monitoring, and you won't be able to correct that without actually treating the space.

    You might be able to compensate a little bit; if perhaps you are in a space where you have little to no choice about where the monitors are located, and if they are if close proximity to corners or boundaries, and are perhaps creating standing waves because of their location and placement... but you also need to keep in mind that by doing this, you could also be over-compensating too, and perhaps even skewing the monitors for the worse... ending up very far away from their original response/tuning, to the point that other frequencies would also be affected - and they could very well end up being frequencies you might not want to change.

    By plugging the ports, for better or worse, you are changing the way the speakers were designed and intended to be used, and how they were measured in regard to frequency response.

    The only thing you can do is to try it, and then listen to how the mixes sound on other systems, to see how well they translate outside of your mixing space.

    FWIW
     
    Sean G likes this.
  5. DonnyThompson

    DonnyThompson Distinguished Member

    As a follow up Sean -
    I'd personally place a lot more importance on the acoustics of the space over the types of monitors. Put it this way - If given a choice, I'd rather use a pair of "okay" Alesis Monitor Ones in a treated space, than I would a pair of "boutique" Genelecs in an untreated space.

    Now, there have been recent advancements made in room modeling and software compensation, that will allow monitors to be tuned to rooms via artificial modeling processing; and at the rate that Modeling Technology is moving these days, I wouldn't be surprised if at some point, someone comes up with an acoustic modeling program that actually works; something that will allow for accurate frequency compensation in monitors of all types... but I don' think that these companies are there quite yet; so for now, you'll be better off to look into treating the space you are in. as opposed to messing with the original physical design of the monitors you are using.

    Out of curiosity, what monitors are you using?
     
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  6. Sean G

    Sean G Well-Known Member

    Thanks for the advice Donny.
    Monitor placement is situated in the centre of one of the longer 15 ft walls, with monitors around 2 to 4 inches from the wall.
    I have placed some acoustic tiles 2 inches thick behind the monitors, allowing for them to rise with the addition of some speaker feet.
    I have treated the wall behind my monitoring space with 4 x 20x20 inch x 2 inch thick acoustic tiles directly behind me grouped together in a large square, with 2 more placed centre either side of that between those 4 and the corners. I have treated the corners with some bass traps to help cut down the build up of bass frequencies in the 4 corners of the room but due to the limitations with the size of the room compared to the typical wavelength of bass frequencies I am aware that these are limited to what they can cut down. I have also treated the wall behind my desk and above my LCD screen.
    There's also a really heavy 2 seat fabric sofa with a fold out sofa bed inside it directly behind me along that other long wall below those 4 tiles grouped together to help break up the reflection. But as always, I can only work with the environment until circumstance allows me to move up and try to improve things where I can.
    Edit : First points of reflection are treated and so too is the rear of the solid timber door.
     
  7. Sean G

    Sean G Well-Known Member

    They are KRK Rokit 5s' at present. See pic illistrating in the original post.
    Looking to upgrade to something better in the near future.
     
  8. DonnyThompson

    DonnyThompson Distinguished Member

    That's a factor right there, Sean. If you are hearing too much low end, or, are hearing low end as "undefined" of "frumpy" (loose), this would be one of the reasons why.

    Depending on the type of material these tiles are made of, that probably isn't thick enough to handle the frequencies you are having problems with. If you are using something similar to Auralex, 2" will only be effective down to around 500hz or so. It won't attenuate the low frequencies; those that are down around 200hz... and lower.

    When you place a monitor in close proximity to a boundary ( walls, ceilings, floors) some of those various low-frequency and frequency ranges will emanate from the rear of the monitor, and will reflect off of these boundaries.

    Depending on what the distance is, some frequencies will bounce back in phase, resulting in peaks in that frequency range, while others might come back out of phase, and could end up cancelling out certain frequencies, which then ends up giving you "nulls", which can really play havoc with your ears - because what you are hearing isn't what is really going on.

    The short of it is, your ears are being lied to by the frequency response of the room, along with the sound coming out of your monitors in that room.

    Try walking around your room while music is playing, and listen for "hot spots" as well as for "nulls". Hot spots will reveal themselves as a "jump" in level for a certain frequency or range, while nulls will sound much lower in volume, and in some cases, these frequencies can even disappear completely.

    This is where room treatment can help - through Bass Traps ( corners especially) that will attenuate low end frequencies from a certain point on down ( example, 200hz and lower), BB Absorbers ( broad band) which will attenuate a wider range of frequencies ( example 200hz and higher - depending on the thickness/ mass/density of the material used) - and Diffusion, which is meant to "scatter" frequencies, so that they aren't hitting each other ( and your ears) all at the same time.

    You could try plugging the ports on your monitors, but honestly, it probably won't be very effective, and as I mentioned arlier, you could end up with other issues as well. A better, more effective option, and one that is proven because it's largely based on physics and actual calculations - would be to look into room treatment. The good news with room treatment is that it doesn't have to be expensive to be effective. There are many materials available at home improvement stores that are very effective; things like Roxul Safe and Sound, or OC ( Owens Corning) rigid insulation, etc., and because these materials are so light in weight, you don't have to build huge, heavy frames to hold the material in place.

    But, you first need to find out what your room is really doing. If it were me, I'd start by measuring the room; there are some good measurement programs available on the web, some even free:

    http://www.roomeqwizard.com/

    You'll need a measurement microphone... the standard go-to for this is the Earthworks Omni; although it's pricey. Behringer makes an omni-directional measurement mic, the ECM8000; and while I've personally never used it, I have colleagues who have, and with success:

    http://www.zzounds.com/item--BEHECM8000

    So for a grand total of $59 (U.S.) you could measure your room and get a fairly accurate idea of what is happening. The cost of your treatment could also end up being very affordable... you might even be able to do if for under $100; the more handy you are with building frames and installing the treatment, the more money you'd save.

    I guess what I'm suggesting Sean, is that you may very well be able to end up fixing ( or at least greatly improving) your mixing environment for really not all that much money. Not only will this help you with mixing, it could also prove to be advantageous for recording, too.

    FWIW, here's an article on monitor placement that you might want to take a look at:

    http://www.soundonsound.com/sos/mar02/articles/monitors.asp
     
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  9. Sean G

    Sean G Well-Known Member

    Thanks for the advice, much appreciated.
    I have looked at the room EQ wizard after reading another post here on RO, its good advice.
    When I get to that point I may post a thread to get some further advice as to how to correctly measure the room going forward.
    I shall definitely have a read of the article above also...cheers.
     
  10. dvdhawk

    dvdhawk Well-Known Member

    Some questions:

    Are you suffering from too much bass as is?
    Do they have to sit so close to the wall?
    Are they angled inward, or firing straight out?
    Are you using any EQ now to add or subtract bass response?
    How do your mixes translate to the outside world and other playback systems now?
    Have you run any kind of analyzer to identify problem frequencies?

    Plugging the port will certainly restrict the movement of the woofer, which would generally produce less low-end on two fronts. (Neither the woofer, nor the port would be moving as much air)
    I couldn't say it will 'tighten' the bass response, but I would guess it would reduce it some.
    My concern would be that you might over-compensate EQing more lows into everything across the board.

    The engineers at KRK calculated the port size and port depth based on how that particular 5" woofer behaves in a ported box with a very specific volume (in terms of cubic cm or inches). But like everyone else, manufacturers can often fall prey to their own hype and sacrifice accuracy for exaggerated bass. And even though it's ported out the front, bass frequencies are still radiating out the back and sides of the box - frequencies probably too low to be very effectively absorbed by foam.

    This might even be a case where, even though you say your room isn't very large, a subwoofer might be a better way to tighten up the bass by taking some of the burden off the smallish 5" woofer in the KRKs. There is only so much bass you can get from a 5".

    So I don't really have any concrete answers, just more questions to consider moving forward.
     
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  11. Sean G

    Sean G Well-Known Member

    As a side note, I wanted put it on the record how appreciative I am to be part of the RO community, its such a great resource for learning and its a credit to RO members who are openly willing to share their time, knowledge and experience on recording, especially with someone who made the transition from playing to recording late in the game.
    A huge thank you from the Land Down Under.(n)(n)(n)
     
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  12. Sean G

    Sean G Well-Known Member

    Thanks for your input dvdhawk, there are some good questions there.
    I'll see if I can cover them all.
    I can't really say I'm suffering from too much bass, I suppose that also comes down to levels set during the tracking process.
    Some of the work I have mixed so far also is a collection of tracks that I have recorded over a course of some years in different environments, rooms etc, some treated, some not, that have to date been works in progress so to speak. Not a lot of live tracking in this room to date.
    At present, they are close to the wall, probably too close to it for my liking. I am playing with the idea of bringing the desk out from the wall and trying to get my seating position more centred to the room, but not in the centre. Any suggestions on the room size dimensions (11 x 15 ft x 9ft high) you could recommend? - I see from your room build you would be more versed in monitor placement than I would in that department.
    As for EQ, so far it has come down to what tracks I have been mixing but I don't appear to be doing too much either way. Listening to my mixes on other systems such as the car, phone + tablet with earbuds, dvd home theatre are translating well although on a couple of tracks the bass was a little harsh, which supprised me somewhat at first because I thought with the room size it may have been the other way around. My headphones I use as a reference are AKG 701s' which can be somewhat biased in the mid / highs so they could be coming into play also, but I try to mix using a balance of both monitors and headphones (HP mostly in the late hours).
    I have not used an analyser to look for problem frequencies as such but definately now you have mentioned it, theres' something to look at.
    Consideration has been given at a sub, due to thinking about upgrading to a better grade of monitor I have put that on hold for the time being but something worth pondering.
    You are spot-on, theres' only so much low end you can get out of a 5 inch driver. If not a sub, maybe even going to an 8 inch monitor may be worth considering also.
    I know that these are designed by a team who do their research and put the port there for a very good reason, so I'm probably upsetting the apple cart by blocking the port and changing the way the monitors are supposed to sound.
    Having read different pros / cons on the idea of blocking the port, I thought it was worth throwing it out there to see what came back from those in the know.
    I suppose doing a mix with them blocked / unblocked may be worth trying also...

    Edit : they are approx 26 inches apart, angled towards my seating position, directed at ear level height and I'm in the sweet spot with each monitor 26 inches from each ear.
     
  13. DonnyThompson

    DonnyThompson Distinguished Member

    Ya. I have the same concern(s) Hawk... as well as what might else occur by altering the physical properties of the cabinet - in regard to the way the cabinet was originally designed and tuned for... although I have to be honest and admit that I wasn't aware that the KRK's he has are front-ported...

    Remember Sean... in regard to room treatment, that the effectiveness of frequency attenuation - and in your case, low frequency attenuation - is determined by the thickness/mass/density of the material being used.
    (Side note: There is also the possibility that you can increase the effectiveness of the material's attenuation properties by providing an air gap in-between the treatment material and the boundary it is attached to... Again, this is largely dependent on the material being used )

    And because of the density and mass - or more accurately, the lack thereof - your current use of 2" "acoustic" tiles placed behind the monitors, (or anywhere in the room for that matter) isn't doing anything to help those lo end frequencies. It will help with mids and hi's, and tame some flutter echo and "pinging" in the room, but it's not doing anything for problematic low frequencies.

    As Hawk mentioned, the low end on the speakers will emanate in all directions, so... even if the material you are using would be dense enough to be effective, placing the treatment behind the monitors is only one area of many that you need to be concerned with.

    I think your best bet would be to measure the room before you look into upgrading your current monitors ( you may find out that your current KRK's will work just fine once they are used in a room that has been acoustically adjusted)... and I certainly wouldn't just start randomly installing various materials to your walls and ceilings ( or your floors) until you get an idea of just what issues you are treating for.

    I don't think you'd be doing anything wrong by installing some corner bass traps, I think most experts (of which I am most definitely NOT) would tell you that you'll likely end up having to treat your corners anyway, but beyond that, I wouldn't just start throwing up 1" or 2" Auralex / Sonex tiles "randomly"... I think you need to figure out what your problems are before you start adding treatment to the room.

    Brien ( @Brien Holcombe ) is our resident bad-ass when it comes to acoustics. Perhaps he can chime in here with further info regarding port-filling and speaker placement, along with perusing the thread and making sure that I haven't given you inaccurate info ...

    You've mentioned your room dimensions being 11 x 15 ft x 9ft... I'm pretty sure that Brien will probably also want details of the shape of the room, dimensions of certain walls... and probably also an idea of the materials that the room is made of ( plaster, wood, drywall, windows, doors, drop ceiling, wood floors, carpet, etc). Pictures and drawings showing the room's layout can also be very helpful.

    FWIW

    -donny
     
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  14. Sean G

    Sean G Well-Known Member

    Thanks Donny, all sound info there to take into account.
    Thats also worth considering, no good throwing money into new monitors until I look at how to improve the room treatment with regards to doing it right.:D
     
  15. Brien Holcombe

    Brien Holcombe Well-Known Member

    Back in the day we heard that sticking a potato into the tailpipe of a car would create a buildup and shoot the potato out. Sometimes it changed the flow and the vehicle would sputter for a while and then die.

    Come to find out, it was just a bad idea and caused an other wise well tuned system to behave poorly or cause damage or both.

    So would I do it? The potato...hell yes! The bass port...no way.
     
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  16. Sean G

    Sean G Well-Known Member

    Thanks for your opinion on the matter Brien.
    I'm thinking now its not such a good idea to change something that has been designed by experts with a specific purpose of improving the efficiency of the speaker at low frequencies compared to a similar sealed unit :rolleyes:
     
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  17. Sean G

    Sean G Well-Known Member

    Brien, I may ask you for some expert advice regarding room treatment in this thread shortly if you don't mind.
    I shall endeavour to draw up a room diagram as suggested by Donny with dimentions and construction materials of the room and if its OK I'll rack your brain on which way would be the best way to improve the room in regards to treatment with thought going into the rooms use (ratio @ mixing 60 % to live tracking 40%).
    I'm sure that different specific treatments may be required for each scenario in regards to room use, while I'm trying to kill two birds with one stone due to space limitations, I'm sure this may be a determining factor in what would be the best way to make / improve the room for a dual purpose use over my current set-up, which is pretty basic and coupled with the limited knowledge on the subject I have gained before starting this thread..
    Your advice as recommended by Donny would be wise before I even consider spending a cent on acoustic treatments, let alone consider upgrading my current monitors, if this is required at all.
    Many thanks to everyone who has shared their knowledge & thoughts up to now.
     
  18. Brien Holcombe

    Brien Holcombe Well-Known Member

    Sure...you can start with this here link. http://recording.org/threads/newbie-control-room-acoustic-treatment-help.55413/
    Some knucklehead called "Space" gives a great introductory on basic mix positions. Its good stuff and can be trusted, no testing involved since that has already been handeled by the Masters we follow.

    Also, go to http://www.bobgolds.com/Mode/RoomModes.htm and plug in your room measurements. With a 1,400 cubic foot room like yours, you still have low frequency issues but they start to become not as bad as a typical 9X11X8 bedroom. So bass trapping is still needed at least in front of the mix.

    The Bonello curve on your existing space is nice and smooth...that is considered a good thang :)

    Oh, and get Sketchup... http://www.sketchup.com/
     
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  19. Sean G

    Sean G Well-Known Member

    Thanks Brien, I shall go work on the sketch and get it posted ASAP.:D
     
  20. DonnyThompson

    DonnyThompson Distinguished Member

    Attached Files:

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