@jmascreen
This room response shows your "room modes" as they are called (standing wave frequency and its harmonics, as a result of speaker positioning and the spot you have measured the sweep). They will cancel out a frequency at one spot and at the same time amplify the same frequency at another spot.
It is not depending on your speaker, so don't touch that.
FACT: Each room has room modes, you can't prevent that for the simple fact that a number of frequencies have a wavelength that matches either the length, the width or the height of your room of a combination of those. This wave will be canceled or amplified by the returning wave, observed depending on where you are in the room. As an experiment to start understanding all of this subject, play a 40 Hz tone and start walking slowly around the room, note that this tone (with a fixed dB level by the speaker will change depending on where you are. Mark the spot you think there is hardly any difference between the output of the speaker itself and what you hear at that spot. That woud be a good listening position for 40Hz. NEXT ALL other frequencies until around 200 Hz, higher can be treated in a more simple way as explained at the end of this poetry. You could also listen and music you know really well and listen to the whole spectrum with focus on the lows. The higher you get, the more standing waves we get, the less you hear a difference.
There is a number of combinations of length / width and height that are most optimal (the least amount of room modes), check if your room is in that safe area. The are room mode charts on the internet that shows a figure for this. If not, you will find treatment even harder or choose NOT to use that room if possible. Changing room dimensions is another alternative, but don't start there.
This is complex stuff to handle, you would need to have serious acoustic measures to reduce this, you CAN NOT take it away completely as that would require to much acoustic treatment material to begin with filling most of the room you want to be in (and even then impossible).
I am NOT an expert, but browse the internet for some background info (look for room mode treatment), a lot of technicians are breaking their head over this subject. Some commercial companies promise wonders by you buying their acoustic panels and hang it on the wall, it takes much more than that believe me. As we know, you can't get rid of standing waves as that requires the complete cancelation of the return wave which is impossible (but you can decrease the magnitude of them), their are other basic steps to start improving your room or better said, improve at your listening position. What you need to look for in the end is the least number of room modes with the least magnitude, that takes a lot of effort but still there will be room modes. So get the best of this bad situation. You will be very happy to get within +- 3dB improvement on the room mode frequencies at best and can call yourself a specialist.
Common approaches:
0 - Do the wheelchair listening test and choose the best to your liking. If you have a very good listening capability (very good ears) you can start with sitting on a chair with wheels and slowly move along that measurement middle of the room line until you have found a nice balanced sound field in the low frequencies. Then mark that spot as best ears 1 and rate it from bad to very good, move the speakers and redo listening while moving your chair over that same line. Repeat until all speaker positions have been listened to. Pick the position that has the best rating and you're done. Some find this a good enough check, other may argue as it is not measured but observed, I like this approach as it is simple and will take max 2 hours. Listen to various material you know VERY well how it should sound for reference.
1 - Measuring to get detailed facts. Place you speakers in a first best position where you want them (fairly close to the wall that faces the opposite at the length of the room) not less than 2 meters apart or something in that range and measure like you did (REW with a measured mike and compensating table, along a line in the middle of the room(width / length depending on how your speakers play), a fixed delta of positions (so 10 cm, 20 cm, 30 cm, etc.) while you start the first measuring position at the triangle position where the sound of the speakers cross each other while both facing inwards.
Put a mark at each position so you can use the same position further down the procedure.
2 - After having done your first set of measurements at each delta measurement position, move both speakers the same distance along one line to the outside of the room or to the inside, depending where you started (near each other or as far as possible away from each other near both opposite walls). ALSO put a mark on each speaker position as you move the speakers.
3 - Repeat the some measurement along that same measurement line as in step one.
3a - Write down each measurement in an overview and name each measurement related to that speaker and measurement position. Make sure it is 100% correct noted down.
Once you have done this for 5 - 10 iterations, find the most optimal one - so the less dips / standing waves and /or this least scale of the dip. The combination of that speaker placement and measuring position is your "kind of optimal" listening position.
BAD spots for speakers is dead in the corner / along a 45 degree line from that corner into the room, stay away from that line.
BAD spot for listening position is dead middle of the room, in a corner or on the same 45 degree line.
What about EQ ?? As we know it is room modes, treating you speaker with an EQ has no effect what so ever, it kills your good sounding speakers and you only put more or less energy in your speaker at a room mode (standing wave). If you reduce the amount of dB at that frequency (as we think that will fix the standing wave to occur) of course you are decrease the energy for that standing wave, but as you cancel the frequency you also want here it (now not because of fixing the room mode but because of EQ). As your problem is that this frequency is not played as loud as the others, you have achieved nothing. Increasing the dB on a room mode frequency (as we think we can overshoot the standing wave killing, it will still result in a (even louder) standing wave but as your EQ never works just at that single frequency it will change the end result in a more chaotic frequency plot around that frequency, while the dip will be bigger as it still cancels out that frequency at a more intense level. Room EQ wizards / tools only partially work in well treated rooms to flattening peaks, they don't / can't solve room modes.
4 - Once you found your optimal positioning, MARK THAT SPOT and keep you measurement mike a that position. You need to start treating the room (if you feel you need to), with what is called bass trapping where you try to tame the standing waves. That takes a lot of material to do the damping, meaning a lot of room space to get lost in treatment material. Good place to start is corners and ceilings. Corners is EVERY corner area, so floor to wall, wall to ceiling and wall to wall. Use 12 cm thick at least of damping wool (or other effective high density material with a width of 60 cm (at least) and a length from each opposite area (so floor to ceiling, wall to wall) which leaves you with some trapped air behind that sheet of damping material (a triangle volume that cover the whole corner length / width / height) that is.
After each change in material applied measure at your MARKED listening position and compare before and after. Also hang a few peaces of this damping sheets at least 12 cm (Same as the thickness of the material from the ceiling over you listening position (200 by 200 cm at least) and measure again.
What is often seen is people buying a set of acoustic foam with egg crate shape to do low frequency damping. It can not be said enough, THAT IS USELESS. These type of sheets only do an average to poor job on mid & high frequency absorption which you only need to do as a last step when for instance your room is to lively / echoing or to bright sounding (the more hard material you have in the room to bigger this gets). Don't waist your money if you work on low Frequency standing waves.
If all else fails, just ignore these room modes, you could question if you really hear them just by ear or now you have seen the plot it's drawing your attention. Perfect rooms don't exist, good rooms are complex and expensive. If that room is your living room, the people you may live with do not always approve / like all this acoustic stuff all over the place. They may even don't here its benefit and don't understand what you are trying to achieve (I know from personal experience so I am building my own man cave and do what I like.
This room response shows your "room modes" as they are called (standing wave frequency and its harmonics, as a result of speaker positioning and the spot you have measured the sweep). They will cancel out a frequency at one spot and at the same time amplify the same frequency at another spot.
It is not depending on your speaker, so don't touch that.
FACT: Each room has room modes, you can't prevent that for the simple fact that a number of frequencies have a wavelength that matches either the length, the width or the height of your room of a combination of those. This wave will be canceled or amplified by the returning wave, observed depending on where you are in the room. As an experiment to start understanding all of this subject, play a 40 Hz tone and start walking slowly around the room, note that this tone (with a fixed dB level by the speaker will change depending on where you are. Mark the spot you think there is hardly any difference between the output of the speaker itself and what you hear at that spot. That woud be a good listening position for 40Hz. NEXT ALL other frequencies until around 200 Hz, higher can be treated in a more simple way as explained at the end of this poetry. You could also listen and music you know really well and listen to the whole spectrum with focus on the lows. The higher you get, the more standing waves we get, the less you hear a difference.
There is a number of combinations of length / width and height that are most optimal (the least amount of room modes), check if your room is in that safe area. The are room mode charts on the internet that shows a figure for this. If not, you will find treatment even harder or choose NOT to use that room if possible. Changing room dimensions is another alternative, but don't start there.
This is complex stuff to handle, you would need to have serious acoustic measures to reduce this, you CAN NOT take it away completely as that would require to much acoustic treatment material to begin with filling most of the room you want to be in (and even then impossible).
I am NOT an expert, but browse the internet for some background info (look for room mode treatment), a lot of technicians are breaking their head over this subject. Some commercial companies promise wonders by you buying their acoustic panels and hang it on the wall, it takes much more than that believe me. As we know, you can't get rid of standing waves as that requires the complete cancelation of the return wave which is impossible (but you can decrease the magnitude of them), their are other basic steps to start improving your room or better said, improve at your listening position. What you need to look for in the end is the least number of room modes with the least magnitude, that takes a lot of effort but still there will be room modes. So get the best of this bad situation. You will be very happy to get within +- 3dB improvement on the room mode frequencies at best and can call yourself a specialist.
Common approaches:
0 - Do the wheelchair listening test and choose the best to your liking. If you have a very good listening capability (very good ears) you can start with sitting on a chair with wheels and slowly move along that measurement middle of the room line until you have found a nice balanced sound field in the low frequencies. Then mark that spot as best ears 1 and rate it from bad to very good, move the speakers and redo listening while moving your chair over that same line. Repeat until all speaker positions have been listened to. Pick the position that has the best rating and you're done. Some find this a good enough check, other may argue as it is not measured but observed, I like this approach as it is simple and will take max 2 hours. Listen to various material you know VERY well how it should sound for reference.
1 - Measuring to get detailed facts. Place you speakers in a first best position where you want them (fairly close to the wall that faces the opposite at the length of the room) not less than 2 meters apart or something in that range and measure like you did (REW with a measured mike and compensating table, along a line in the middle of the room(width / length depending on how your speakers play), a fixed delta of positions (so 10 cm, 20 cm, 30 cm, etc.) while you start the first measuring position at the triangle position where the sound of the speakers cross each other while both facing inwards.
Put a mark at each position so you can use the same position further down the procedure.
2 - After having done your first set of measurements at each delta measurement position, move both speakers the same distance along one line to the outside of the room or to the inside, depending where you started (near each other or as far as possible away from each other near both opposite walls). ALSO put a mark on each speaker position as you move the speakers.
3 - Repeat the some measurement along that same measurement line as in step one.
3a - Write down each measurement in an overview and name each measurement related to that speaker and measurement position. Make sure it is 100% correct noted down.
Once you have done this for 5 - 10 iterations, find the most optimal one - so the less dips / standing waves and /or this least scale of the dip. The combination of that speaker placement and measuring position is your "kind of optimal" listening position.
BAD spots for speakers is dead in the corner / along a 45 degree line from that corner into the room, stay away from that line.
BAD spot for listening position is dead middle of the room, in a corner or on the same 45 degree line.
What about EQ ?? As we know it is room modes, treating you speaker with an EQ has no effect what so ever, it kills your good sounding speakers and you only put more or less energy in your speaker at a room mode (standing wave). If you reduce the amount of dB at that frequency (as we think that will fix the standing wave to occur) of course you are decrease the energy for that standing wave, but as you cancel the frequency you also want here it (now not because of fixing the room mode but because of EQ). As your problem is that this frequency is not played as loud as the others, you have achieved nothing. Increasing the dB on a room mode frequency (as we think we can overshoot the standing wave killing, it will still result in a (even louder) standing wave but as your EQ never works just at that single frequency it will change the end result in a more chaotic frequency plot around that frequency, while the dip will be bigger as it still cancels out that frequency at a more intense level. Room EQ wizards / tools only partially work in well treated rooms to flattening peaks, they don't / can't solve room modes.
4 - Once you found your optimal positioning, MARK THAT SPOT and keep you measurement mike a that position. You need to start treating the room (if you feel you need to), with what is called bass trapping where you try to tame the standing waves. That takes a lot of material to do the damping, meaning a lot of room space to get lost in treatment material. Good place to start is corners and ceilings. Corners is EVERY corner area, so floor to wall, wall to ceiling and wall to wall. Use 12 cm thick at least of damping wool (or other effective high density material with a width of 60 cm (at least) and a length from each opposite area (so floor to ceiling, wall to wall) which leaves you with some trapped air behind that sheet of damping material (a triangle volume that cover the whole corner length / width / height) that is.
After each change in material applied measure at your MARKED listening position and compare before and after. Also hang a few peaces of this damping sheets at least 12 cm (Same as the thickness of the material from the ceiling over you listening position (200 by 200 cm at least) and measure again.
What is often seen is people buying a set of acoustic foam with egg crate shape to do low frequency damping. It can not be said enough, THAT IS USELESS. These type of sheets only do an average to poor job on mid & high frequency absorption which you only need to do as a last step when for instance your room is to lively / echoing or to bright sounding (the more hard material you have in the room to bigger this gets). Don't waist your money if you work on low Frequency standing waves.
If all else fails, just ignore these room modes, you could question if you really hear them just by ear or now you have seen the plot it's drawing your attention. Perfect rooms don't exist, good rooms are complex and expensive. If that room is your living room, the people you may live with do not always approve / like all this acoustic stuff all over the place. They may even don't here its benefit and don't understand what you are trying to achieve (I know from personal experience so I am building my own man cave and do what I like.
Sorry I seem to have lost my photos and I don't own the speakers now. All ai found was the CAD I made some years ago.
Guys a hopefully quick unrelated question - what software is suitable for modelling a folded TL? Hornrest and (I think) M. King mathcad sheets treat all sections as a straight line varying in cross-section. I don't want to treat it as a straight line I need to consider the possibility of reflections from the boundaries and change in vector of propagation.
Is AKABAK a reasonable way, using ducts? I've heard that BEM is not very accurate for small volumes especially where resonance is happening.
Is AKABAK a reasonable way, using ducts? I've heard that BEM is not very accurate for small volumes especially where resonance is happening.
Tenson, Martin's software is capable of accurately modeling a folded line provided the user correctly inputs the actual areas along the line's length. I know because I've done it many, many times. His Sections software is best used for this but it can also be accomplished with one or two others once you realize out how.
Paul
Paul
Well my room size is 10(h) X 13.5(w) X 18.5(l) and have simulated it in amroc and found the places where the room modes exists, but it doesnt suggest on how and what way one can treat it. Also what I read and from your inputs that its almost impossible to treat bass below 80hz.
I tried speaker placement with various method of cardas, golden ratio, 1/3, 1/5 each positions I find a dip in bass region so none of them working as expected.
Let me try your approach and revert
So this will be somewhere in middle of the original 5.25" driver and my 7" RS180 driver?
You could probably use same dimensions as RS180 driver - not sure if that 1/2in is really different. I mean a “7in vs a 6.5in” driver for all intents and purposes is the same class driver. It’s all marketing.
Because the Dayton 7in has Sd of 127cm^2
Whereas the Purifi 6.5in has Sd of 132cm^2
And my OEM XBL 6.5in driver (same bezel size as Purifi) has Sd of 133cm^2.
The Dayton is actually the smallest of the three but claims to be a 7in.
Because the Dayton 7in has Sd of 127cm^2
Whereas the Purifi 6.5in has Sd of 132cm^2
And my OEM XBL 6.5in driver (same bezel size as Purifi) has Sd of 133cm^2.
The Dayton is actually the smallest of the three but claims to be a 7in.
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Here is the complete xover schematic and also attached all the requested file in zip format
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