Hi Loren, could you (whenever you have some spare time) run the simulations I asked in post #228 for the boxes of 120 liters?
Also see the question regarding the vents with both sides flushed?
That would give me the final word on the smallest size box I need to use. It seems like the 120 liter has almost the same response on the lower frequencies as the 150 liter one and that will give me a little more manageable size to work with.
Thanks.
Leo
Also see the question regarding the vents with both sides flushed?
That would give me the final word on the smallest size box I need to use. It seems like the 120 liter has almost the same response on the lower frequencies as the 150 liter one and that will give me a little more manageable size to work with.
Thanks.
Leo
Here are three different runs. All have 50% fill, which is a lot.
The first is the 120 liter box:
Note. I don't like this because the port tube almost hits the back wall. You also get a cabinet resonance spike at 400 Hz
The next is the 808 mm X 500 mm by 309 mm box:
This is the rectangular port and it is much further from the back wall. Notice the resonance is better.
Finally, this is the same box as above, but with two 4" round ports:
Last is a composite SPL graph of all three designs:
Blue is the first design, magenta is the second design with rectangular port, brown is the design with the two 4" round ports.
My conclusion is the smaller box helps with internal resonances. The internal volumes are absent of any bracing. I would figure out the bracing volume and adjust the final cabinet volume upward to account for the bracing you use.
I figured on a wall thickness of 3/4" and all dimensions are external.
The simulation is in Full-Space (4∏), which is the same as an anechoic chamber. The simulation will give you an SPL curve that takes both edge diffraction and baffle step loss into account. In your actual room you will have some room gain at the bottom end and the baffle step loss will also be not as bad as shown here. So, in reality the bass will be more pronounced than seen in these plots.
All cabinet dimensions are external.
Pay particular attention to applying filling material on the back wall. This is the wall that will resonate the most. Keep fill away from the port(s) so they are not blocked. The remaining walls should have a 1" or less layer of fill. Consider adding some sort of cabinet resonance damping material such as roofing felt (staple about 2 to 3 payers on the inside wall) under the filling material. The front baffle should be two layers ideally. Remember to alter the external dimensions to account for all braces inside. I would brace the box pretty well, but all that energy from the driver must go somewhere, so the fill material and roofing felt will convert that energy into heat.
The woofer is mounted above the port(s). Ideally, all drivers should be mounted asymmetrically on the baffle.
You can reduce the effect of edge diffraction a lot by rounding over all four edges of the baffle a minimum of 2" radius. If you round the edges you should not need to mount drivers asymmetrically. GedLee does this with his loudspeakers.
The first is the 120 liter box:
Note. I don't like this because the port tube almost hits the back wall. You also get a cabinet resonance spike at 400 Hz
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The next is the 808 mm X 500 mm by 309 mm box:
This is the rectangular port and it is much further from the back wall. Notice the resonance is better.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Finally, this is the same box as above, but with two 4" round ports:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Last is a composite SPL graph of all three designs:
Blue is the first design, magenta is the second design with rectangular port, brown is the design with the two 4" round ports.
An externally hosted image should be here but it was not working when we last tested it.
My conclusion is the smaller box helps with internal resonances. The internal volumes are absent of any bracing. I would figure out the bracing volume and adjust the final cabinet volume upward to account for the bracing you use.
I figured on a wall thickness of 3/4" and all dimensions are external.
The simulation is in Full-Space (4∏), which is the same as an anechoic chamber. The simulation will give you an SPL curve that takes both edge diffraction and baffle step loss into account. In your actual room you will have some room gain at the bottom end and the baffle step loss will also be not as bad as shown here. So, in reality the bass will be more pronounced than seen in these plots.
All cabinet dimensions are external.
Pay particular attention to applying filling material on the back wall. This is the wall that will resonate the most. Keep fill away from the port(s) so they are not blocked. The remaining walls should have a 1" or less layer of fill. Consider adding some sort of cabinet resonance damping material such as roofing felt (staple about 2 to 3 payers on the inside wall) under the filling material. The front baffle should be two layers ideally. Remember to alter the external dimensions to account for all braces inside. I would brace the box pretty well, but all that energy from the driver must go somewhere, so the fill material and roofing felt will convert that energy into heat.
The woofer is mounted above the port(s). Ideally, all drivers should be mounted asymmetrically on the baffle.
You can reduce the effect of edge diffraction a lot by rounding over all four edges of the baffle a minimum of 2" radius. If you round the edges you should not need to mount drivers asymmetrically. GedLee does this with his loudspeakers.
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Thanks Loren for the calculations and plots. But I think there is a problem. The dimensions I gave you were internal. If you calculate the first (120 Liter) box dimensions as externals they will give you a 105 Liter box approximately if I am not mistaken. And the second one around 96 liters?
Now, the smaller the better for the design of the box so I am not complaining
but the 150 liter box I think was giving us an Fb of around 41 Hz. BUT if it is ok to go with a slightly higher Fb as far as the response on the lower frequency is close to the 150 liter one, then I will be more than happy because I decided that I will look for a suitable ( 18 inch as Thorsten suggested) subwoofer to add in the near future.
Let me know what you think.
Can you compare the one you considered the best of these latest plots with the original of the 150 Liter box to see if the lower frequencies are suffering too much?
I have the pictures but they seem to be done in a different way since they dont match at all.
Thanks again a lot for your help.
Leo
Now, the smaller the better for the design of the box so I am not complaining
but the 150 liter box I think was giving us an Fb of around 41 Hz. BUT if it is ok to go with a slightly higher Fb as far as the response on the lower frequency is close to the 150 liter one, then I will be more than happy because I decided that I will look for a suitable ( 18 inch as Thorsten suggested) subwoofer to add in the near future.Let me know what you think.
Can you compare the one you considered the best of these latest plots with the original of the 150 Liter box to see if the lower frequencies are suffering too much?
I have the pictures but they seem to be done in a different way since they dont match at all.
Thanks again a lot for your help.
Leo
Hi,
These boxes are really too small. You need to tune them higher for this too work (which means still huge boxes with no bass whatsoever) or make them bigger.
I really think 150 Liter (net) is needed.
As for the resonances, you can subdivide the Box into several small sections with acoustic lowpass filters inbetween.
Ciao T
These boxes are really too small. You need to tune them higher for this too work (which means still huge boxes with no bass whatsoever) or make them bigger.
I really think 150 Liter (net) is needed.
As for the resonances, you can subdivide the Box into several small sections with acoustic lowpass filters inbetween.
Ciao T
Thanks Loren for the calculations and plots. But I think there is a problem. The dimensions I gave you were internal. If you calculate the first (120 Liter) box dimensions as externals they will give you a 105 Liter box approximately if I am not mistaken. And the second one around 96 liters?
Now, the smaller the better for the design of the box so I am not complaining
Let me know what you think.
Can you compare the one you considered the best of these latest plots with the original of the 150 Liter box to see if the lower frequencies are suffering too much?
I have the pictures but they seem to be done in a different way since they dont match at all.
Thanks again a lot for your help.
Leo
They don't match because these are plotted in 4∏*space, so it includes diffraction effects, which the original runs did not, they were 2∏.
I'll run some more with an actual net of 150 liters for comparison (both in 2∏ and 4∏ space).
Cool, thanks everybody. Thorsten, yes I understand for what you guys have told me that the 150 liter box will be the best possibility but I just wanted to make sure that the smaller one will not be a decent alternative.
Even if I get a slightly worse lower frequency response with the 120 or 100 liter box and the F3 is maybe 5 to 8 Hz higher also, if I add later a dedicated Subwoofer ( a good 18 inch driver as you suggested ) do you think that will be ok to compensate for it?
I mean compared to doing the bigger 150 liter box now and just use the small subwoofer I have already?
Because it will be better for me to be able to do smaller main boxes and then have just a single bigger subwoofer box that as you also said, can be done as a table or something to "disguise it".
Leo
Even if I get a slightly worse lower frequency response with the 120 or 100 liter box and the F3 is maybe 5 to 8 Hz higher also, if I add later a dedicated Subwoofer ( a good 18 inch driver as you suggested ) do you think that will be ok to compensate for it?
I mean compared to doing the bigger 150 liter box now and just use the small subwoofer I have already?
Because it will be better for me to be able to do smaller main boxes and then have just a single bigger subwoofer box that as you also said, can be done as a table or something to "disguise it".
Leo
Easily. You are talking about splitting hairs here because the Peaveys get you down to at least 60 Hz comfortably. Any sub would pick up from there downward.
The 18" sub would be a fun project, but you will get a lot more bang for the buck with multiple smaller subs. Having multiple subs will help even out the room acoustics so that the bass is consistent over a greater area of the room, rather than one sub that will have hot and cold spots.
I would consider two, three, or four smaller subs to fill in the room. The system would kick butt.
Hi,
So that is why they are looking so wrong.
Running Simulations for 4PI is useless for home audio as no speaker for home audio ever operates in fee space with large distances to all walls.
In fact 2PI is unrealistic in the bass for most situations. If the speaker is closer than 1/4 wavelength to a room boundary we can effectively include taht room boundary into the spatial load. The same holds if the distance to a room boundary is less or similar to that of the baffle width.
So a more realistic spatial loading for the woofer in it's large baffle and likely placed close to the floor is probably 2PI above around 250Hz which increases progressively to Pi at 125Hz and Pi/2 at 63Hz.
So at the minimum run all sims in 2PI and for Leo, add mentally 3dB at 125Hz and 6 dB at 63Hz (and 12dB at 31Hz).
Ciao T
So that is why they are looking so wrong.
Running Simulations for 4PI is useless for home audio as no speaker for home audio ever operates in fee space with large distances to all walls.
In fact 2PI is unrealistic in the bass for most situations. If the speaker is closer than 1/4 wavelength to a room boundary we can effectively include taht room boundary into the spatial load. The same holds if the distance to a room boundary is less or similar to that of the baffle width.
So a more realistic spatial loading for the woofer in it's large baffle and likely placed close to the floor is probably 2PI above around 250Hz which increases progressively to Pi at 125Hz and Pi/2 at 63Hz.
So at the minimum run all sims in 2PI and for Leo, add mentally 3dB at 125Hz and 6 dB at 63Hz (and 12dB at 31Hz).
Ciao T
To make sure we are on the same page, 2∏ looks like this in LEAP5:
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Another shot from the rear:
An externally hosted image should be here but it was not working when we last tested it.
This is essentially an infinite baffle. There is another variation called Half-Space, which is the same as if the cabinet was sitting on the floor of a huge gymnasium.
That would yield a response similar to the Full-Space 4∏, but include floor bounce.
I really don't want to get into trying to model the room because that is not only beyond the scope of LEAP5, but every room is different, so it becomes an exercise in futility.
I would suggest the infinite baffle would be the most representative since DIY measurements really can't measure below a few hundred Hertz due to the proximity of walls and floor in their environment. At that point the only way to measure below that is with near-field measurements and stitch that together with the 1 meter measurements above the gating time.
Hi,
Yes. Remember Leap uses theoretical concepts. In practical terms the spund from a low frequency driver is omni directional. If the distance to the floor is shorter than quarter the wavelength of the tone reproduced the floor is our "infinite baffle". Assuming a speaker around 40cm above the floor (acoustic center) we have "2PI" loading from the floor below around 220Hz even if the baffle does not extend to the floor.
Then Leap models wrong if the response is similar to 4PI.
At sufficiently low frequencies there are no differences between halve space and 2PI. Differences become appreciable at higher frequencies, which we are not interested in.
Then, for most speakers you must not model the so-called baffle step either.
So the bottom line is you model as 2PI and use an "average room curve" as an adequate fudge to estimate the room-gain of real rooms.
This is around 3dB @ 80...100Hz, around 6dB at 40...50Hz and around 9dB at 20...25Hz, if the room is of sufficiently solid construction. If it has too much glass and sheetrock and wood instead of solid building techniques these numbers reduce, often significantly.
Yes, agreed. So 2PI curves please. And keep in mind for this project, around 6dB boost at 40Hz from the room.
Ciao T
Yes. Remember Leap uses theoretical concepts. In practical terms the spund from a low frequency driver is omni directional. If the distance to the floor is shorter than quarter the wavelength of the tone reproduced the floor is our "infinite baffle". Assuming a speaker around 40cm above the floor (acoustic center) we have "2PI" loading from the floor below around 220Hz even if the baffle does not extend to the floor.
Then Leap models wrong if the response is similar to 4PI.
At sufficiently low frequencies there are no differences between halve space and 2PI. Differences become appreciable at higher frequencies, which we are not interested in.
Then, for most speakers you must not model the so-called baffle step either.
So the bottom line is you model as 2PI and use an "average room curve" as an adequate fudge to estimate the room-gain of real rooms.
This is around 3dB @ 80...100Hz, around 6dB at 40...50Hz and around 9dB at 20...25Hz, if the room is of sufficiently solid construction. If it has too much glass and sheetrock and wood instead of solid building techniques these numbers reduce, often significantly.
Yes, agreed. So 2PI curves please. And keep in mind for this project, around 6dB boost at 40Hz from the room.
Ciao T
Thorsten,
Here is a 150 liter cabinet tuned to 38 Hz. Let me know which way you think I should adjust it.
I have included the previous two plots as guide curves for comparison (magenta and blue lines).
An externally hosted image should be here but it was not working when we last tested it.
Hi Loren,
No need to adjust. Looks fine. Maybe tune to 42Hz or so, but in principle this is fine, basically flat between 100Hz and 500Hz and with a gentle rolloff that our roomgain will largely compensate, with 6dB roomgain at 40Hz the response will be basically flat to 40Hz in room and have a quick rolloff below that.
So keep that as a "reference" curve for something that will go more or less flat in room down to 40Hz.
The previous curves for smaller boxes include other effects which make them poorly comparable. If you can instead add them in using the same room loading as the 150 Liter curve we can see the differences between the different alignments, so we can see how much we really loose by reducing the volume.
Ciao T
No need to adjust. Looks fine. Maybe tune to 42Hz or so, but in principle this is fine, basically flat between 100Hz and 500Hz and with a gentle rolloff that our roomgain will largely compensate, with 6dB roomgain at 40Hz the response will be basically flat to 40Hz in room and have a quick rolloff below that.
So keep that as a "reference" curve for something that will go more or less flat in room down to 40Hz.
The previous curves for smaller boxes include other effects which make them poorly comparable. If you can instead add them in using the same room loading as the 150 Liter curve we can see the differences between the different alignments, so we can see how much we really loose by reducing the volume.
Ciao T
Well, the last plot with the guide curves were from the following designs:
Plot #5 (Blue) is a 100 liter cabinet tuned to 45 Hz.
Plot #6 (magenta) is a 90 liter cabinet tuned to 50 Hz.
This plot below is a 120 liter cabinet tuned to 42.5 Hz. It looses about 2 dB at the bottom end due to the smaller size as compared to a 150 liter cabinet.
An externally hosted image should be here but it was not working when we last tested it.
Hi,
Yup. Same SPL at 50Hz, 2dB less at 40Hz.
I suspect by the time you are at 90 liters net you have another 2dB loss.
My take here is to keep 50Hz at or above 93dB.
The only issue as said is that there is strong content around 40Hz in much modern music, so if push the tuning much higher we end up with a more distortion at the bottom than neccesary, unless bass management is used.
Ciao T
Yup. Same SPL at 50Hz, 2dB less at 40Hz.
I suspect by the time you are at 90 liters net you have another 2dB loss.
My take here is to keep 50Hz at or above 93dB.
The only issue as said is that there is strong content around 40Hz in much modern music, so if push the tuning much higher we end up with a more distortion at the bottom than neccesary, unless bass management is used.
Ciao T
Hi,
Well, it seems the best compromise to get reasonably low and loud. Smaller box means either less loud and equalise the system to make up for the bottom end rolloff or less LF extension full stop and add a subwoofer.
Ciao T
Well, it seems the best compromise to get reasonably low and loud. Smaller box means either less loud and equalise the system to make up for the bottom end rolloff or less LF extension full stop and add a subwoofer.
Ciao T
Okay. Here are the rest design files for a 150 liter cabinet tuned to 38 Hz:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The last plot is cone excursion at 100 Watts. At about 30 Hz we reach xmax:
An externally hosted image should be here but it was not working when we last tested it.
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