Speaker placement, reflections, cancellations, modes - making the best of a bad job
Posted: Sat Oct 16, 2021 10:28 am
First off I want to say I am nowhere near an authority on this. Some may say they are not overly bothered about such things but I believe it is worth trying to understand the issues so you can make the best of a bad job. Can't polish a turd though.
Many of us here are semi omni lovers but we face the same problems as the point and squirt brigade. Also as filter dodgers and prone to complexity dodging we don't have any baffle step comp circuitry to enable the speakers to be away from the wall where they usually sound the best. They have to be close to the front wall to get the level of bass we need to marry with the higher frequencies.
As we have chosen semi omni then I presume imaging is not the be all and end all for us. But even so, why not make the best of what we have - there is no harm in that is there ? Early reflections are bad for imaging (Haas effect) yet our speakers need to be close to the front wall and the up firing mid bass is producing very early reflections off the said wall. Nothing we can do about it really apart from treatments on the wall. That would help with the frequencies down to a point . But we need the later reflections otherwise we will only hear sound which is of a purely omni directional nature. So keeping the speakers away from the side walls if possible is probably going to help.
Then we have destructive cancellation from sound waves bouncing back from a boundary (walls, ceiling, floor) and combining with the front wave out of phase causing a dip. There is nothing worse than following your favourite bass players lovely flowing parts and suddenly one or more notes disappear or are severely reduced in level. Then there are room modes which cause peaks at certain frequencies making the whole thing even worse. This might not bother you - it annoys the hell out of me. These cancellations can occur higher up than the bass as well depending on distance to the reflection point and the wavelength of the frequency concerned. They can be calculated but I guess nobody here has gone to that length or are even bothered.
Floor bounce from a woofer can be a pain in the arse and it can affect mids as well - high frequency is often mopped up by a carpet or rug if you have one. Doc always referred to Roy Allison's work on boundary effects. He was known to put the woofer as close to the floor as possible, cross it over low and put the mid near the top of the baffle with the tweeter. A compromise was made here as the woofer and mis are a long way from each other but it was crossed low which is better for keeping the centre to centre distance within a quarter wavelength at the xover frequency (speed of sound divided by distance divided by four ?)
Cube users can't get the bass driver at floor level but you can get it close to the front wall which should help with cancellation in the bass but it will move higher up in frequency. It may have to reflect off at least one other boundary (the ceiling) to reach your lug holes as the mid bass is usually above ear height in order to get the front firing tweeter to ear height.
Point and squirt users can't get the centre of the bass driver as close to the front wall as cubes and maybe they don't need to and have adequate bass a little further out into the room. But the destructive cancellation will be at a very noticeable frequency. The general advice is either get the speaker as close to the wall as poss or over a metre out into the room. I can't live with speakers that far out so I am stuck with wall placement
I have tried my speakers near the centre of the room well away from walls and the listening position being nearfield. The worst place to be seated is against the back wall especially if the speakers are tight up to the front wall. I situated my chair as far from the wall as I could. It was the best sound I have ever heard in this room. With conventional cubes that are not baffle step compensated I expect the bass will be too far down in level due to lack of boundary reinforcement. Room gain will help but it will probably not be enough. They will sound thin and fatiguing. In my case I got away with it because the bipolar up and down firing mid bass provided very good levels of bass due to it's inherent baffle step compensation and I have tweeters pointing in various directions. I was absolutely in love with the amazing clarity of the sound. I even moved the two speakers next to each other so they only had a mm or two between them. No stereo imaging and not much sound staging but I loved that even more. It is a real shame that this set up can't be accommodated in my living room at home
So what can we do about these problems? Ignore them ? That is a possibility but with a little effort we can make the best of a bad job. DSP is all the rage these days - music killers as Doc would say New devilry imo. I could live with the idea more if the chain was all digital before it but converting an anologue signal to digital andthen back to anologue is just all wrong in my book.
We could invest in room treatments but who in the real world would go to the effort, expense and prospect of row inducing aesthetics . Bass traps have to be ridiculously large to have an effect. Panels for higher frequencies at first reflection points may be acceptable to some but not me though. The best option imo is to fill the room with the possessions of life - some of us who don't have a dedicated listening room with extremely directional speakers and a single chair with vice to hold your head still (a very unsociable and selfish way to listen imo) have to live in the same room as the hifi. Shelves full of books, cd's, vinyl and the clutter of life can act as diffusers for higher frequencies.
Have a carpet or at least a rug at the first reflection points. If you are listening with a family present spread across several sofa's then the right thing to do imo would be to carpet the whole room. If it's just you then a rug would probably suffice. I once thought of filling the voids in my sofas with bass absorbing material. Then I realised the sofa would have to be a frame type so a fruitless exercise in my case.
I would say that there is nothing we can do about ceiling reflections and as semi omni lovers we need the ceiling. My ceiling is textured (Artex) but no idea if that helps at diffusion at all or even if it is desirable with up firing drivers.
You often read of hifi nut's swapping speaker after speaker and very rarely find something they are truly happy with. That is a shame imo. If only more were in to diy speaker building as it really is an excellent way to design and make a speaker system which suits your ears and room. Different aspects can be changed. Too much bass right against the wall - make the box bigger or change the driver for a slightly lower efficiency one and cross over to the mid at the middle of the baffle step transition. Or use a dedicated amp for the bass driver and give it it's own volume control Or even buy an amp with tone controls
Lately I have been trying to get the down firing bass driver as close to the floor as possible (going to try as close as an inch) for boundary reinforcement and to try and minimise any floor bounce cancellations. That is what is pointing me in the direction of going to a three way as having mid frequencies rattling about down there doesn't sound like a good idea to me. The mid can be up firing into my tweeter sphere.
Another thing I found which helps with room modes is to set up your speakers across a corner with each speaker on a different wall. Works a treat in my room with my gear. It has the added bonus of making the sound field/ stage seem deeper as you have some distance behind the mid point between the speakers.
Failing this just go open baffle if you have the room, dsp and some muscle amps. Or buy some of them Dutch & Dutch, Devialet, Buchard or similar whatsits that can also make you a cup of tea and wipe your arse at the same time. Your fooked if they go tits up though.
Many of us here are semi omni lovers but we face the same problems as the point and squirt brigade. Also as filter dodgers and prone to complexity dodging we don't have any baffle step comp circuitry to enable the speakers to be away from the wall where they usually sound the best. They have to be close to the front wall to get the level of bass we need to marry with the higher frequencies.
As we have chosen semi omni then I presume imaging is not the be all and end all for us. But even so, why not make the best of what we have - there is no harm in that is there ? Early reflections are bad for imaging (Haas effect) yet our speakers need to be close to the front wall and the up firing mid bass is producing very early reflections off the said wall. Nothing we can do about it really apart from treatments on the wall. That would help with the frequencies down to a point . But we need the later reflections otherwise we will only hear sound which is of a purely omni directional nature. So keeping the speakers away from the side walls if possible is probably going to help.
Then we have destructive cancellation from sound waves bouncing back from a boundary (walls, ceiling, floor) and combining with the front wave out of phase causing a dip. There is nothing worse than following your favourite bass players lovely flowing parts and suddenly one or more notes disappear or are severely reduced in level. Then there are room modes which cause peaks at certain frequencies making the whole thing even worse. This might not bother you - it annoys the hell out of me. These cancellations can occur higher up than the bass as well depending on distance to the reflection point and the wavelength of the frequency concerned. They can be calculated but I guess nobody here has gone to that length or are even bothered.
Floor bounce from a woofer can be a pain in the arse and it can affect mids as well - high frequency is often mopped up by a carpet or rug if you have one. Doc always referred to Roy Allison's work on boundary effects. He was known to put the woofer as close to the floor as possible, cross it over low and put the mid near the top of the baffle with the tweeter. A compromise was made here as the woofer and mis are a long way from each other but it was crossed low which is better for keeping the centre to centre distance within a quarter wavelength at the xover frequency (speed of sound divided by distance divided by four ?)
Cube users can't get the bass driver at floor level but you can get it close to the front wall which should help with cancellation in the bass but it will move higher up in frequency. It may have to reflect off at least one other boundary (the ceiling) to reach your lug holes as the mid bass is usually above ear height in order to get the front firing tweeter to ear height.
Point and squirt users can't get the centre of the bass driver as close to the front wall as cubes and maybe they don't need to and have adequate bass a little further out into the room. But the destructive cancellation will be at a very noticeable frequency. The general advice is either get the speaker as close to the wall as poss or over a metre out into the room. I can't live with speakers that far out so I am stuck with wall placement
I have tried my speakers near the centre of the room well away from walls and the listening position being nearfield. The worst place to be seated is against the back wall especially if the speakers are tight up to the front wall. I situated my chair as far from the wall as I could. It was the best sound I have ever heard in this room. With conventional cubes that are not baffle step compensated I expect the bass will be too far down in level due to lack of boundary reinforcement. Room gain will help but it will probably not be enough. They will sound thin and fatiguing. In my case I got away with it because the bipolar up and down firing mid bass provided very good levels of bass due to it's inherent baffle step compensation and I have tweeters pointing in various directions. I was absolutely in love with the amazing clarity of the sound. I even moved the two speakers next to each other so they only had a mm or two between them. No stereo imaging and not much sound staging but I loved that even more. It is a real shame that this set up can't be accommodated in my living room at home
So what can we do about these problems? Ignore them ? That is a possibility but with a little effort we can make the best of a bad job. DSP is all the rage these days - music killers as Doc would say New devilry imo. I could live with the idea more if the chain was all digital before it but converting an anologue signal to digital andthen back to anologue is just all wrong in my book.
We could invest in room treatments but who in the real world would go to the effort, expense and prospect of row inducing aesthetics . Bass traps have to be ridiculously large to have an effect. Panels for higher frequencies at first reflection points may be acceptable to some but not me though. The best option imo is to fill the room with the possessions of life - some of us who don't have a dedicated listening room with extremely directional speakers and a single chair with vice to hold your head still (a very unsociable and selfish way to listen imo) have to live in the same room as the hifi. Shelves full of books, cd's, vinyl and the clutter of life can act as diffusers for higher frequencies.
Have a carpet or at least a rug at the first reflection points. If you are listening with a family present spread across several sofa's then the right thing to do imo would be to carpet the whole room. If it's just you then a rug would probably suffice. I once thought of filling the voids in my sofas with bass absorbing material. Then I realised the sofa would have to be a frame type so a fruitless exercise in my case.
I would say that there is nothing we can do about ceiling reflections and as semi omni lovers we need the ceiling. My ceiling is textured (Artex) but no idea if that helps at diffusion at all or even if it is desirable with up firing drivers.
You often read of hifi nut's swapping speaker after speaker and very rarely find something they are truly happy with. That is a shame imo. If only more were in to diy speaker building as it really is an excellent way to design and make a speaker system which suits your ears and room. Different aspects can be changed. Too much bass right against the wall - make the box bigger or change the driver for a slightly lower efficiency one and cross over to the mid at the middle of the baffle step transition. Or use a dedicated amp for the bass driver and give it it's own volume control Or even buy an amp with tone controls
Lately I have been trying to get the down firing bass driver as close to the floor as possible (going to try as close as an inch) for boundary reinforcement and to try and minimise any floor bounce cancellations. That is what is pointing me in the direction of going to a three way as having mid frequencies rattling about down there doesn't sound like a good idea to me. The mid can be up firing into my tweeter sphere.
Another thing I found which helps with room modes is to set up your speakers across a corner with each speaker on a different wall. Works a treat in my room with my gear. It has the added bonus of making the sound field/ stage seem deeper as you have some distance behind the mid point between the speakers.
Failing this just go open baffle if you have the room, dsp and some muscle amps. Or buy some of them Dutch & Dutch, Devialet, Buchard or similar whatsits that can also make you a cup of tea and wipe your arse at the same time. Your fooked if they go tits up though.