This turned out to be a bit more long-winded than I initially wanted, but posts with request for help or advice with lacking information irk me, so I tried to be thorough.
First thing, my speakers are DIY designed and built and are comprised of AE TD15M's in 5cu.ft bass reflex tuned to ~32Hz and a QSC waveguides with BMS 4550 on them, actively bi-amped with miniDSP and 4 channels of 50ASX2 ICEpower. The bass alignment makes for a shallow roll-off that reaches fairly deep, with an overall dry presentation, which is what I was going for and what I enjoy. The miniDSP crossover setup is fairly standard, hi-pass, lo-pass, BSC, mass roll-off compensation and time-align, all done with measurement using Holm Impulse and a calibrated UMM-6 mic.
An older picture, then without phase plug and in their old room:
I used to have these in an 11' x 13' room, 8' ceilings and bass was nice pretty much everywhere in the room, but the small dimensions forced my sitting position close to a backwall, therefore slightly re-enforcing bass.
In the new home, these are in a basement room, which is 11' wide, 19' long and a drop ceiling is at ~7'6" high. The floor is concrete with vinyl tiles glued on it, both 11' walls and one 19' wall are the concrete foundation (perhaps up to ~6'-7' high), but are finished in a standard manner, 2x4's, insulation and gypsum board. The other 19' wall has rooms on the other side of it, so it's a standard internal wall with two doors.
I have the speakers located on a short wall, symmetrically, woofer centers perhaps 30" from side walls and a bit more from the back wall, the enclosure itself placing them perhaps ~18" up from the floor. The opposing short wall (at my back) is a staircase leading up to the first floor, perhaps adding ~3' acoustically to the 19' room floor length. I have some freedom as to where to place my chair and not being close to a backwall does some good for midrange and HF IMO.
The bass problem is as follows: there is this "stratum" roughly 5' up from the floor, underneath which bass is weak, in most of the room, except if I get my head against a wall or get ridiculously close to the speakers. As I am sitting when listening, my head is a good way below this. Pretty much anywhere in the room though, if I stand up, I hear the bass just as I like it and can also feel it, perfect. When sitting, I suppose I do hear most of it in a way, but there is absolutely nothing being "felt", the otherwise punchy TD15M feels somewhat anemic and low bass is non-existent.
I moved both speakers and listening chair around and can not get things the way I like. EQ'ing the bass in miniDSP does not sound like the right solution either, assuming there is one.
Is this normal from a mostly concrete basement? It's this 5' bass stratum effect that puzzles me most.
I will appreciate any tips or knowledgeable explanations. 🙂
First thing, my speakers are DIY designed and built and are comprised of AE TD15M's in 5cu.ft bass reflex tuned to ~32Hz and a QSC waveguides with BMS 4550 on them, actively bi-amped with miniDSP and 4 channels of 50ASX2 ICEpower. The bass alignment makes for a shallow roll-off that reaches fairly deep, with an overall dry presentation, which is what I was going for and what I enjoy. The miniDSP crossover setup is fairly standard, hi-pass, lo-pass, BSC, mass roll-off compensation and time-align, all done with measurement using Holm Impulse and a calibrated UMM-6 mic.
An older picture, then without phase plug and in their old room:
I used to have these in an 11' x 13' room, 8' ceilings and bass was nice pretty much everywhere in the room, but the small dimensions forced my sitting position close to a backwall, therefore slightly re-enforcing bass.
In the new home, these are in a basement room, which is 11' wide, 19' long and a drop ceiling is at ~7'6" high. The floor is concrete with vinyl tiles glued on it, both 11' walls and one 19' wall are the concrete foundation (perhaps up to ~6'-7' high), but are finished in a standard manner, 2x4's, insulation and gypsum board. The other 19' wall has rooms on the other side of it, so it's a standard internal wall with two doors.
I have the speakers located on a short wall, symmetrically, woofer centers perhaps 30" from side walls and a bit more from the back wall, the enclosure itself placing them perhaps ~18" up from the floor. The opposing short wall (at my back) is a staircase leading up to the first floor, perhaps adding ~3' acoustically to the 19' room floor length. I have some freedom as to where to place my chair and not being close to a backwall does some good for midrange and HF IMO.
The bass problem is as follows: there is this "stratum" roughly 5' up from the floor, underneath which bass is weak, in most of the room, except if I get my head against a wall or get ridiculously close to the speakers. As I am sitting when listening, my head is a good way below this. Pretty much anywhere in the room though, if I stand up, I hear the bass just as I like it and can also feel it, perfect. When sitting, I suppose I do hear most of it in a way, but there is absolutely nothing being "felt", the otherwise punchy TD15M feels somewhat anemic and low bass is non-existent.
I moved both speakers and listening chair around and can not get things the way I like. EQ'ing the bass in miniDSP does not sound like the right solution either, assuming there is one.
Is this normal from a mostly concrete basement? It's this 5' bass stratum effect that puzzles me most.
I will appreciate any tips or knowledgeable explanations. 🙂
A couple suggestions. First have you tried raising them up off of the floor? Being a much larger space room modes will be totally different, especially the low flexible ceiling that tends to suckout bass. Solution most likely is a multi sub placement. If possible add one and position it high, near the ceiling. Check out REW's room simulator. It's a bit basic but should give you a much better idea on placement.
Way back in the 70's when I was just starting down this road my nextdoor neighbor had similar issue. His parents built out an unfinished basement and turned ~40% into his apt (not bad for a 14y old kid 😉
Two rooms either of which could be used as a bedroom with a open livingroom between. Getting his (Acoustic model 310 3ways) speakers up off the floor was a big help. Placing an additional sub we concocted solved the anemic bass when standing. Dr Geddes has invested considerable study on this subject and agree with his findings.
Way back in the 70's when I was just starting down this road my nextdoor neighbor had similar issue. His parents built out an unfinished basement and turned ~40% into his apt (not bad for a 14y old kid 😉
Two rooms either of which could be used as a bedroom with a open livingroom between. Getting his (Acoustic model 310 3ways) speakers up off the floor was a big help. Placing an additional sub we concocted solved the anemic bass when standing. Dr Geddes has invested considerable study on this subject and agree with his findings.
A single subwoofer is not something I ever really wanted, as I like the bass the speakers can and do produce, much less a multi-sub approach, but I knew the suggestion would come if I started this thread - and rightly so I suppose. 🙂 It is to be considered if nothing else solves it.
As for getting them up from the floor, this is already on my list. The waveguide and the on-axis point of the drivers' vertical beam would benefit from a bit of a raising as well - good if it helps bass as a bonus. I've had a mind to build simple structures with 2x4's and ply to test this out.
As for getting them up from the floor, this is already on my list. The waveguide and the on-axis point of the drivers' vertical beam would benefit from a bit of a raising as well - good if it helps bass as a bonus. I've had a mind to build simple structures with 2x4's and ply to test this out.
As a test, you could flip them upside-down (and perhaps also put them on a pedestal to correct the tweeter height) to hear if it affects the bass.
Two ways to smooth out bass/subbass in a room is to use multiple subs or use room treatmetns. In your case bass traps. Two up in the front corners from floor to ceiling and one or two in the back of the room from floor to ceiling if possible. You are experiencing peaks and nulls but in the verticle instead of the horizontal.
In my old room, in my listening chair the bass was perfect, but sitting is the chair to the left, there was no bass, in the chair to the right, there was overwhelmiing bass.
Traps will solve your issue and not mess with the system the way you like it.
In my old room, in my listening chair the bass was perfect, but sitting is the chair to the left, there was no bass, in the chair to the right, there was overwhelmiing bass.
Traps will solve your issue and not mess with the system the way you like it.
I don't see how bass traps can cure the core problem. Greebster beat me to posting the core problem and the typical way to solve it is to mount the speakers same as in a recording studio control room, but I doubt he wants to install such heavy speakers up at the ceiling line and mass load the ceiling tiles. At the very least the woofers/vents need to be up in one of the vertical's odd harmonics.
Multiple subs will compensate if enough of them is used, but the lossy suspended ceiling and real ceiling act similar to an under-damped, closed terminus of a plane wave tube [PWT] with the floor as the closed [driver] end except in this case, the driver are offset along the line at wherever the woofers are vertically off the floor, modifying the room's vertical harmonic structure in ways that's hard to predict.
GM
Multiple subs will compensate if enough of them is used, but the lossy suspended ceiling and real ceiling act similar to an under-damped, closed terminus of a plane wave tube [PWT] with the floor as the closed [driver] end except in this case, the driver
GM
Raising the LF has worked for me in the past it caused bass to spread out more evenly.
Its a lot of work and money but some type of false floor out of 2x4 and fiberglass pink in between can really help a basements acoustics. But make sure to dampen well where they make contact to the concrete itself. We used a type of cork underlay. We set out to warm toes and in the process warmed sound up to so it was win win. Concrete must be the worst material from a sound aspect.
Its a lot of work and money but some type of false floor out of 2x4 and fiberglass pink in between can really help a basements acoustics. But make sure to dampen well where they make contact to the concrete itself. We used a type of cork underlay. We set out to warm toes and in the process warmed sound up to so it was win win. Concrete must be the worst material from a sound aspect.
rearrangement
If possible, try reversing your listening position vs where the speakers are by 180 degrees. Place your couch, or chair almost against the back wall, and construct a very large acoustic absorbent panel on the wall right behind your head.
If possible, try reversing your listening position vs where the speakers are by 180 degrees. Place your couch, or chair almost against the back wall, and construct a very large acoustic absorbent panel on the wall right behind your head.
Bass traps don't work very well, so discard that idea. Multiple subs EQ'd with a miniDSP (or equivalent) is the only highly effective answer that I think you are likely to find. If you do try damping put as much as you can only behind the speakers - do the whole wall with very thick drapes - and do not have the speakers against that back wall. But nothing is going to be as effective as multiple subs - works every time.
I don't know if the lossy drop-ceiling is behind that odd "stratum" effect, at least I didn't think it'd be an issue. I never really had a sound system in a room with such a ceiling.
If I check my room modes according to the dimensions 19' x 11' and assuming 8' for the height, I get:
Length: 29.6Hz / 59.1Hz / 118.3Hz / 147.9Hz
Width: 51.2Hz / 102.4Hz / 153.6Hz / 204.8Hz
Height: 70.3Hz / 140.6Hz / 210.9Hz / 281.2Hz
I feel bass performance is relatively fine above 100Hz or so, even when I listen below that "stratum". This might leave me with 4 problematic modes, if I exclude 29.6Hz as it's outside of my speaker's BW. 2 length modes, 59.1Hz and 88.7Hz, one width mode at 51.2Hz and one height mode at 70.3Hz.
I understand it's not a good idea do drive the room at nodal points. To avoid this for the two length modes, I'd need to either have the speakers less than 38" (h2 - 88.7Hz node) from the wall, or out more than 57" (h1 - 59.1Hz node) into the room. For the height, it'd seem like having the woofer close to the floor would be best as getting them higher approaches the central 48" node - but that's not proving really good at the moment, so I'm not sure here, perhaps due to that lossy ceiling?
As for room width, this may get a bit more interesting. That 51.2Hz main mode is driven fairly into antinodal points, but out of phase as I see it, not being an odd harmonic. Does it work this way or is that not an issue? It is the only room dimension for which the speakers are at different points along its axis.
I could see using one or two subwoofers at some point if nothing else works out. Bass traps, I don't know - I never felt I needed them in any of my previous setups, not do I think it'd solve the issue here. This remains a familly room too and I don't really want to prop it up with a ton of gizmos if I can avoid it. I still appreciate the suggestion and I have to read more about bass traps anyway, never really having done so.
I though about that, but it might make for an awkward room layout the way the stairs come down and where the door to other rooms are located. Non-theoretical rooms are no fun! 🙂
Thanks for the input. I've read some of your multi-sub articles in the past, might be wise to freshen-up on them. What about this effect where I barely hear nor feel bass below ~5', even with my head to the floor? As I said, the floor is concrete with thin vinyl tiles glued on, so as hard/rigid as it gets, while the ceiling is lossy. Perhaps that's the hearth of it. Or perhaps I'm making too big a deal of this one perceived issue, where it might only be a series of different compound issues.
I have a very similarly dimensioned basement listening room, the one big difference is I have acoustical fibreglass ceiling (not suspended type) installed on firring directly mounted on the first floor floor joists. Floor is concrete with tiles and rug, walls are 2 x 4 construction with sheet rock...
You want want to look at redoing that ceiling with something more rigid.
My biggest problem was room modes with a huge peak between 40 - 60Hz, a dip around 100Hz, and another huge peak between 140 - 200Hz. Room EQ proved surprisingly effective fixing this.
I'm running 11 cu ft Onken bass boxes with 16 inch iconic 165-8G woofers, tuned for an F3 of around 35Hz.. Bass quality is very good.
Interestingly the general consensus amongst my audio oriented friends is that this is a good room.. (Not convenient for more than a couple of listeners however.)
I have 4 RPG corner bass traps (63Hz tuning) which helped some - enough that I will keep them. The jury is out on the two diffusers, not sure I need them..
You want want to look at redoing that ceiling with something more rigid.
My biggest problem was room modes with a huge peak between 40 - 60Hz, a dip around 100Hz, and another huge peak between 140 - 200Hz. Room EQ proved surprisingly effective fixing this.
I'm running 11 cu ft Onken bass boxes with 16 inch iconic 165-8G woofers, tuned for an F3 of around 35Hz.. Bass quality is very good.
Interestingly the general consensus amongst my audio oriented friends is that this is a good room.. (Not convenient for more than a couple of listeners however.)
I have 4 RPG corner bass traps (63Hz tuning) which helped some - enough that I will keep them. The jury is out on the two diffusers, not sure I need them..
Imho your room is probably so full of room modes that you don't recognize the sound field between the modal frequencies. As I see it, you forgot to calculate the diagonal and oblique modes, but that wouldn't answer your question either.
I disagree on the opinion that bass traps would not work. But they do certainly not cure the problem 100 percent. It's a cheap solution (if you build them yourself)however that enhances the quality of any sound (reproduction) in the room, whereas multisub approach only regards the stereo set. The best way to proper acoustics is a combined active-passive approach as most multisub-solutions will not address all room modes either. Floyd Toole wrote interesting stuff (known by many here, I presume) on the theme, by the way.
I disagree on the opinion that bass traps would not work. But they do certainly not cure the problem 100 percent. It's a cheap solution (if you build them yourself)however that enhances the quality of any sound (reproduction) in the room, whereas multisub approach only regards the stereo set. The best way to proper acoustics is a combined active-passive approach as most multisub-solutions will not address all room modes either. Floyd Toole wrote interesting stuff (known by many here, I presume) on the theme, by the way.
Theoretically, the bass should be enhanced near a very rigid boundary so something in what you say does not seem right.
In my experience we can all go round and round about the modes, where they are what's causing what, there are hundreds of things that can, and probably are, happening all at the same time. So I just ignore all that, put in several subs, make some measurements, setup the DSP control and in virtually every case the bass is great. The endless discussions about the whats and the whys that could be going on will not really ever get you to an "understanding". Just "do the right thing" and move on.
I got the bass in my basement music room pretty much perfect with those variables:
location and number of subs (1x room corner 2x on different walls), EQ (minidsp) and location of listener.
I went earls way first, but had to make some compromise to the listening location in addition to this, as most were just horrible - leading to way too much EQ needed to compensate. I blame the pure concrete with minimal openings to the outside world for that - and not my imcompetence 😉
location and number of subs (1x room corner 2x on different walls), EQ (minidsp) and location of listener.
I went earls way first, but had to make some compromise to the listening location in addition to this, as most were just horrible - leading to way too much EQ needed to compensate. I blame the pure concrete with minimal openings to the outside world for that - and not my imcompetence 😉
I'd recommend doing all of the obvious things first like checking to make sure that the speakers (woofers) are operating in phase.
That they are. 🙂 Along the same lines, I'll start with the easier stuff and will try and play some more with location, including elevation.
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