Diss Posted November 29, 2003 Share Posted November 29, 2003 My TV sits in a recessed area in the wall, from the back of the center speaker is 15" to the wall, about 40" to the top of the area. The hole is 64" wide. I was thinking of maybe building a sub to place back in there since I dont have any room for another that is suitable, My RSW-15 is already beside a open wall. Would the cubby hole hurt any sub in there or how would it react. Does it hurt for a sub to be elevated that high? http://f2.pg.photos.yahoo.com/ph/bkp_80@sbcglobal.net/vwp?.dir=/STEREO&.dnm=TV.jpg&.view=t Thanks Quote Link to comment Share on other sites More sharing options...
TheEAR Posted November 30, 2003 Share Posted November 30, 2003 As long as the sub can breathe easy,at least six inches of space around it.And first try to place your sub there and see(hear)if you like the result. Quote Link to comment Share on other sites More sharing options...
formica Posted December 1, 2003 Share Posted December 1, 2003 In theory, you may loose a little output (SPL) but it might actually have a flatter response. Mathematical room simulations are kinda complex but like the green elf said, you have nothing to loose by trying it. Let us know how it sounds... Rob Quote Link to comment Share on other sites More sharing options...
Diss Posted December 1, 2003 Author Share Posted December 1, 2003 I could probably place my sub in front of the tv an try that, but there no way I could place it as high as I want the new subs by my self. I dont even think I have a table around that I could try setting it on. Does elevation hurt it, if not then maybe I could take the Tv out of thehole and place my sub in there and try that? Thanks Quote Link to comment Share on other sites More sharing options...
fabulousfrankie Posted December 1, 2003 Share Posted December 1, 2003 ---------------- On 12/1/2003 10:43:11 AM Diss wrote: I could probably place my sub in front of the tv an try that, but there no way I could place it as high as I want the new subs by my self. I dont even think I have a table around that I could try setting it on. Does elevation hurt it, if not then maybe I could take the Tv out of thehole and place my sub in there and try that? Thanks ---------------- Elevation does nothing to a sub but only experiemtation will let you know whether it works well. Do you have an SPL meter, MS Excel, and a disc with test tones or at least access to a CD burner so you can burn your own tones? Quote Link to comment Share on other sites More sharing options...
Diss Posted December 1, 2003 Author Share Posted December 1, 2003 I have all but a test cd, but I do have a burner, just not any test tones. Quote Link to comment Share on other sites More sharing options...
fabulousfrankie Posted December 1, 2003 Share Posted December 1, 2003 I ask because I've found that if you place the subwoofer in the listening position and you measure the frequency response at the potential subwoofer location the frequency response when the two(subwoofer and SPL meter) are switched back, the two frequency response curves mimic each other closely. If all you need are tones, then download this Excel document which will graph your frequeny response. I imagine it's easier to put the sub in your main listening position rather than above the tv, so just do that and place the SPL meter in the location you want to place your sub(set the meter to slow & c-weighted). All you need to do is download the appropriate tones from here that match the freq's on the chart. Then just play the tone and enter the number into the "RAW SPL" column and the Excel doc will automatically compensate for the meter's imprecision and creat the graph. You can see whether this would be an acceptable location without the hassle of putting the sub there first. That's what I would do before I did something permanent. If you do this I'd be interested in seeing what the graph looks like. BTW, I've had experience putting a sub in a similarly sized cubby hole in my fiancee's room and it helped boosted the low end quite a bit when compared to it's previous location which was close to midway on the front wall. I'm not sure whether it was the cubby or just because the cubby was in the corner(could have been both) but I think the boost in the low end was more dramatic than it should have been with just normal corner placement so it could be beneficial. LMK, if you have any questions on the graphing process. Quote Link to comment Share on other sites More sharing options...
Diss Posted December 1, 2003 Author Share Posted December 1, 2003 I was hoping it would boost the bass some, but wont the measurements be diffrent since the the bass would be coming from inside a cubby hole vs from a flat wall? When I get home I will see what I can come up with, the wife wont be home till later. Quote Link to comment Share on other sites More sharing options...
fabulousfrankie Posted December 1, 2003 Share Posted December 1, 2003 ---------------- On 12/1/2003 3:55:38 PM Diss wrote: I was hoping it would boost the bass some, but wont the measurements be diffrent since the the bass would be coming from inside a cubby hole vs from a flat wall? ---------------- What I was saying is if you put the sub where you normally sit and place the meter where the sub is going to go, the graph you get will be close to what it would be if the two were flip flopped around. Does that help? Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 1, 2003 Share Posted December 1, 2003 having an elevated sub will introduce the "boundary cancelation" effect. here is a great article that will describe more than you want to know: http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm and here's a short part for lazy folk like myself: "Many local bands and sound companies are unknowingly victims of a type of low frequency cancellation known as boundary cancellation. This phenomenon occurs when a loudspeaker is 1/4 of a wavelength away from a boundary. Assuming that the boundary (like most walls or floors) absorbs little or no energy, the reflection off of the boundary plays against the energy still coming from the speaker source. Here is a thought experiment that is a good analogy. Imagine a subwoofer that is placed 1/2 of a wavelength, at certain frequency, away from another sub, and the second sub has had its polarity reversed. It is easy to imagine that the loudspeakers will be opposing each other because one will be moving inward while the other moves outward, causing mutual cancellation. A similar thing occurs when a loudspeaker is placed 1/4 of a wavelength away from a boundary. It is as if the boundary is not there, but there is a phantom speaker 1/2 of a wavelength away that has had its polarity inverted." Is this phenomenom really that big of a concern? I have no idea. Depending on the room, elevating your sub might actually have beneficial results. Just remember that boundaries near 3ft start cancelling frequencies near 80Hz, and 80Hz just so happens to be one of the "more important" frequencies. Quote Link to comment Share on other sites More sharing options...
Diss Posted December 1, 2003 Author Share Posted December 1, 2003 What I was saying is if you put the sub where you normally sit and place the meter where the sub is going to go, the graph you get will be close to what it would be if the two were flip flopped around. Does that help? ---------------- Im so frustrated, I could bite nails in half. I done the test, The first one was with the sub sitting where the couch was( I moved the couch out of the living room and Placed the sub there.), I noticed the reading were lower on alot of the lower freq, but Stupid me didnt think anything of it . So then I moved the furniture back into the living room. And Did the second test where Everything is normal. Well As I was setting the sub back into its home, I notice the volume knob was about 10:00 psoition, when I normally keep it 1 click passed 12:00. That was when It all clicked together . So now im just listening to some music to sooth the angry feeling. So basically my first test, which required all the moving of furniture, is void . But thanks For your Help, I will try to take the other test again, since you went out of your way to help me do this. Thanks Quote Link to comment Share on other sites More sharing options...
fabulousfrankie Posted December 1, 2003 Share Posted December 1, 2003 The boundary cancellation effect has nothing special to do with elevating the subwoofer specifically, it happens all the time with subs placed on the floor. There's no need to move furniture out of the room. Just keep everything like it will be when you normally listen to music or watch a movie, including your main speakers playing because they will have a big impact on the low end frequency response as well. Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 2, 2003 Share Posted December 2, 2003 by elevating a sub off the floor, the floor becomes a new boundary where this cancellation is significant. yes, it still happens when the sub sits on the floor, but the frequency involved is above the range the speaker is trying to reproduce...6 inches would be about 1130Hz. 1ft = 283Hz 2ft = 141Hz 3ft = 94Hz 4ft = 71Hz 5ft = 56Hz 6ft = 47Hz 7ft = 40Hz 8ft = 35Hz 10ft= 28Hz Also, your cieling acts as a boundary as well, so if the sub is in the middle of an 8ft tall room, you're subtracting 70Hz twice. The only reason I bring it up is because I have found that it can make a huge difference. My system boosts signals in the 70Hz region...I moved the woofers 4ft off the wall and everything flattened out. was it soley due to the boundary effect? i can't say for certain, but it does correspond to the math. I have no idea if I'm applying the concept correctly because I have no idea if the enclosed space of the room might end up having different effects. maybe artto might chime in as he's the room acoustics master Quote Link to comment Share on other sites More sharing options...
Diss Posted December 2, 2003 Author Share Posted December 2, 2003 Ok I redid the test, and with the volume on my VSX-43TX @ -20. And the Subs volume @ 1 click past 12:00. I figured it would be easier for you to put the values in your self since I dont have anyway to host the file for you to redownload. I tested up to 89 Hz, didnt do 100 cause I forgot it when I burned the cd. With the Spl meter at C weighting slow response and with sub in normal position(on side wall midways between cubby hole and listening position)and SPL meter siting on couch, pointed at cubby hole(or straight ahead). 10Hz = --- 12.5Hz = --- 15Hz = 59 17.5Hz = 64 20Hz = 79 22Hz = 89 25Hz = 91 28Hz = 93 32Hz = 95 36Hz = 84 40Hz = 93 45Hz = 96 50Hz = 92 56Hz = 97 63Hz = 100 71Hz = 95 80Hz = 90 89Hz = 93 With the Sub rearrange so that it is where the couch is, and measuring from on top of my center channel in the cubby whole. 10Hz = --- 12.5Hz = --- 15Hz = 60 17.5Hz = 71 20Hz = 81 22Hz = 85 25Hz = 95 28Hz = 100 32Hz = 103 36Hz = 99 40Hz = 98 45Hz = 101 50Hz = 101 56Hz = 104 63Hz = 85 71Hz = 96 80Hz = 103 89Hz = 103 During this test at 63 hz you can see a big dip, While I was measuring these, I left the cd player on repeat, and just walked back and forth measuring and writing, and switching tracks. During the test all of the notes except 63 was quiter while I was in the middle of the room, but 63 hz was louder in the middle of the room and quieter close to the couch and close to the cubby whole. I thought that was weird how that one tone acted different. The levels were overall higher with the sub rearranged, so I guessing that would be a allright spot to place a sub? THanks Quote Link to comment Share on other sites More sharing options...
fabulousfrankie Posted December 3, 2003 Share Posted December 3, 2003 Are those the raw spl numbers or corrected? It's much easier to see what's going on as a graph. Email me the excel files and I'll post the graphs. fabulousfrankie@hotmail.com Quote Link to comment Share on other sites More sharing options...
Diss Posted December 3, 2003 Author Share Posted December 3, 2003 There raw numbers, let me put together the excel files. ok emailed. Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 3, 2003 Share Posted December 3, 2003 how's this? Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 3, 2003 Share Posted December 3, 2003 How's this? Normal is your sub placement on the floor and New is your placement above the TV. Quote Link to comment Share on other sites More sharing options...
Diss Posted December 3, 2003 Author Share Posted December 3, 2003 Nice and simple , what did you use to make the graph, and btw I think there off by one increment. The dip should be at 36 HZ on the normal postion line. Nice job though. Now My question, being a newb that I am, what does this info tell me? That it would be ok to use the hole for a sub? Thanks Quote Link to comment Share on other sites More sharing options...
fabulousfrankie Posted December 3, 2003 Share Posted December 3, 2003 I definitely would not use the cubby hole, that dip at 63Hz is pretty severe(~20dB down from 56Hz). You would notice a very dramatic drop in impact and even though your low bass would still be there it would lack the punch the RSW subs are known for. There is a bunch of content in the range of your dip so I don't think it's a wise idea. BTW, I've had a sub in another room with a similar sized dip centered at 63Hz as well, so I talk from experience about the dramatic drop in impact. Quote Link to comment Share on other sites More sharing options...
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