Paul, which impedance curve of the Monkey Coffin are you looking at? I just realised the curve shown in Figure 1 of the OSMC paper may be misleading, as this curve was measured with a 141 mm long port. The final design uses a shorter port, and hence a higher fb. I guess I should replace the woofer impedance curve in Figure 1.
I attached a measurement that was taken with a 8 cm long port in the OSMC box (Figure 3 of the OSMC paper). Tuning frequency seems to be approximately 43 Hz. I don't know how to use this data file with Vituix (or anything else) to fit the bass-reflex tuning parameters, but I hope you can use it to determine QA, QL, and QP.
I attached a measurement that was taken with a 8 cm long port in the OSMC box (Figure 3 of the OSMC paper). Tuning frequency seems to be approximately 43 Hz. I don't know how to use this data file with Vituix (or anything else) to fit the bass-reflex tuning parameters, but I hope you can use it to determine QA, QL, and QP.
curves
Well, it certainly doesn't look like we ruined anything. Curves look well behaved. Might have to take Fb with a grain of salt. Regardless, the sound that comes out will be the sound that comes out.
M, if you were going to give a subjective description comparing what we have to the OSMC what would it be?
My guess is it would be pretty darn close to the same. If KaffiMann's comment about the performance of the driver vs volume is correct, it might even be better.
There is clearly a slight shift in frequency around the knee but the area under the curve is larger with both Fb's so we shouldn't be suffering a loss of volume down low I wouldn't think.
One of the objectives of this whole exercise was to not come out worse than the OSMC which has had great revues. And, hopefully with a little more deep base extension. And VOLUME.
It looks to me like you (all) have achieved that.
Don
Well, it certainly doesn't look like we ruined anything. Curves look well behaved. Might have to take Fb with a grain of salt. Regardless, the sound that comes out will be the sound that comes out.
M, if you were going to give a subjective description comparing what we have to the OSMC what would it be?
My guess is it would be pretty darn close to the same. If KaffiMann's comment about the performance of the driver vs volume is correct, it might even be better.
There is clearly a slight shift in frequency around the knee but the area under the curve is larger with both Fb's so we shouldn't be suffering a loss of volume down low I wouldn't think.
One of the objectives of this whole exercise was to not come out worse than the OSMC which has had great revues. And, hopefully with a little more deep base extension. And VOLUME.
It looks to me like you (all) have achieved that.
Don
Matthias
I did use an impedance curve, used at the end of the Monkey Coffin design, and yes it is the same as in figure 1 in the OSMC doc. Indeed that is misleading...
I used now the impedance of the attachement in your last post. I had to edit the txt first, the first frequency in the row did have no impedance values. Something with MATAA??
plot 1 left
Imported the measured impedance of the Monkey Coffin in VituiXCAD, yellow curve, and adapted basreflex parameters for best fit. FB seems to be 43 Hz.
Important, I used a driver model with TSP the same as the Faital driver of Matthias. That driver has fs = 47 Hz, Vas = 77 L, Qts = 0.45
plot 2 right
Imported the measured impedance and corresponding simulated SPL of the Monkey Coffin in VituiXCAD, yellow curves.
Changed VB to 101 L and FB to 41 Hz. This SPL is close to the Monkey Coffin. For a more extended response, FB has to be lower, but the SPL difference 50 to 100 Hz will be more different.
I used again TSP of the Faital driver of Matthias to see the impact of the larger volume.
Simulation with the TSP of the data sheet will be different. Best to do that once Don has its driver at home.
Concerning the port, is the diameter = 14.3 cm and the length = 8 cm? It looks different in VituiXCAD. Then I will look to that also.
Don, in the mean time you did a reply. This post is an answer to the last Matthias post
I did use an impedance curve, used at the end of the Monkey Coffin design, and yes it is the same as in figure 1 in the OSMC doc. Indeed that is misleading...
I used now the impedance of the attachement in your last post. I had to edit the txt first, the first frequency in the row did have no impedance values. Something with MATAA??
plot 1 left
Imported the measured impedance of the Monkey Coffin in VituiXCAD, yellow curve, and adapted basreflex parameters for best fit. FB seems to be 43 Hz.
Important, I used a driver model with TSP the same as the Faital driver of Matthias. That driver has fs = 47 Hz, Vas = 77 L, Qts = 0.45
plot 2 right
Imported the measured impedance and corresponding simulated SPL of the Monkey Coffin in VituiXCAD, yellow curves.
Changed VB to 101 L and FB to 41 Hz. This SPL is close to the Monkey Coffin. For a more extended response, FB has to be lower, but the SPL difference 50 to 100 Hz will be more different.
I used again TSP of the Faital driver of Matthias to see the impact of the larger volume.
Simulation with the TSP of the data sheet will be different. Best to do that once Don has its driver at home.
Concerning the port, is the diameter = 14.3 cm and the length = 8 cm? It looks different in VituiXCAD. Then I will look to that also.
Don, in the mean time you did a reply. This post is an answer to the last Matthias post
Attachments
Last edited:
An Open Source Monkey Coffin in a bigger box will be an OSMC with more bass extension. An OSMC on steroids! I am envious!
Yup. I applied some smoothing to the raw data, so the data points at the end got lost.
Good point! When I played with Vituix earlier today, I blindly used the parameters from the Vituix CAD database, which may be a little different.
The Monacor BR-100HP tube is slightly conical, and has a flared exit:
https://www.monacor.com/media/JPG/1024/G/G1/G128600Z.jpg
At 90 mm length, the internal diameter at the entry is about 96 mm.
Don, I guess you have most information that is needed to go ahead with your Open Source Monkey Tower. The details of the tuning can be adjusted by tweaking the port length.
great thanks
To all,
I do. Great thanks to all who participated in this. I have always liked learning from brainiacs and this was certainly a challenge trying to wrap my brain around the "conversation".
With appreciation, thank you all.
M, if I do a really good job with the build maybe my review will motivate you to "upgrade" your OSMC.
Two questions to start.
1. Is the port placement the same relative to the drivers placement?
2. Could I get any xover part number value changes so I can get that right.
Thank you, thank you, thank you to all.
Regards,
Don
PS, I will post things related to this discussion here and detail specifics and questions related to the OSMC build part on that thread
To all,
I do. Great thanks to all who participated in this. I have always liked learning from brainiacs and this was certainly a challenge trying to wrap my brain around the "conversation".
With appreciation, thank you all.
M, if I do a really good job with the build maybe my review will motivate you to "upgrade" your OSMC.
Two questions to start.
1. Is the port placement the same relative to the drivers placement?
2. Could I get any xover part number value changes so I can get that right.
Thank you, thank you, thank you to all.
Regards,
Don
PS, I will post things related to this discussion here and detail specifics and questions related to the OSMC build part on that thread
Looking to the port dimension calculation in VituiXCAD
- for the Monkey Coffin, VB = 68 L, FB = 43 Hz and port diameter = 9.5 cm, the port length becomes 7.9 cm. That is the same length as in Matthias' speaker.
- for the Monkey Tower VB = 101 L and FB = 41 Hz and port diameter = 9.5 cm, the port length becomes 4.4 cm. That is short. It is better to choose a larger port diameter.
So, for the Monkey Tower VB = 101 L, FB = 41 Hz and port diameter = 12 cm, the port length becomes 9.8 cm. That is already more acceptable.
For the more extended modes, FB is lower and the length will be higher than 10 cm.
It has to be optimized later.
- for the Monkey Coffin, VB = 68 L, FB = 43 Hz and port diameter = 9.5 cm, the port length becomes 7.9 cm. That is the same length as in Matthias' speaker.
- for the Monkey Tower VB = 101 L and FB = 41 Hz and port diameter = 9.5 cm, the port length becomes 4.4 cm. That is short. It is better to choose a larger port diameter.
So, for the Monkey Tower VB = 101 L, FB = 41 Hz and port diameter = 12 cm, the port length becomes 9.8 cm. That is already more acceptable.
For the more extended modes, FB is lower and the length will be higher than 10 cm.
It has to be optimized later.
I would put the port near the middle of the tower, as with the Coffin.
Looking at my Vituix simulations of the impedance curve for your Tower, the upper peak will at about 66 Hz. If this is correct (Paul, please check), I'd suggest C_W3 = 320 uF and L_W4 = 18 mH? (see Fig. 5 of the OSMC paper)
Paul, did you mix up the numbers a bit?
Those port numbers do not make sense to me.
At any rate, I've been away on business for a week and I'll be busy shovelling snow for the next couple of days...
If you guys need any sort of reply for whatever questions you may or may not have, I can probably get around to it saturday morning or thereabouts.
Those port numbers do not make sense to me.
At any rate, I've been away on business for a week and I'll be busy shovelling snow for the next couple of days...
If you guys need any sort of reply for whatever questions you may or may not have, I can probably get around to it saturday morning or thereabouts.
KaffiMann, are you referring to these numbers? I don't see why this wouldn't make sense. I could reproduce Pauls numbers quite nicely with the Vituix calculator. But maybe you were referring to something else?
Hi Kaffimann,
As you can see in previous posts, Matthias and I get the same results in VituiXCAD.
At first we have simulated the SPL of the basreflex system with the same impedance curve and cabinet volume as Matthias' speaker. The port dimensions we get in VituiXCAD are exactly the same as in Matthias' speaker.
Then we increased the cabinet volume to 101 L and adapt FB for the best SPL fit on the simulated SPL of Matthias' speaker, for minimum X-over changes. In this way we get the new port dimensions for the Monkey Tower.
Can you explain which problem you see with the port numbers?
The most important issue is that you have not accounted for particle velocity.
I did not have time to simulate it until just now, but you're exceeding 27 meters per second with 14v from the power amp.
Not a problem for most perhaps, but in the case of wanting to listening to a dynamic kick or some bass for... ahem... "testing purposes" you can easily run into this issue called "port chuffing" the most basic of basic issues.
At the very least double the port diameter. I've used 152cm2 in some sims and get very nice results.
I did not have time to simulate it until just now, but you're exceeding 27 meters per second with 14v from the power amp.
Not a problem for most perhaps, but in the case of wanting to listening to a dynamic kick or some bass for... ahem... "testing purposes" you can easily run into this issue called "port chuffing" the most basic of basic issues.
At the very least double the port diameter. I've used 152cm2 in some sims and get very nice results.
Oh. ok. Sorry, my bad.
Double port area, if you calculate the area of the tube, add another tube or use a bigger tube.
Please don't double the port diameter, that would be a bit excessive
Sorry about that.
More port area also translates to LONGER ports to reach the same box FS, so...
Will you join me in zoom Matthias?
Launch Meeting - Zoom
Online coffee with Kaffi
Or beer, or any other beverage you may prefer.
Everyone welcome!
Double port area, if you calculate the area of the tube, add another tube or use a bigger tube.
Please don't double the port diameter, that would be a bit excessive
Sorry about that.
More port area also translates to LONGER ports to reach the same box FS, so...
Will you join me in zoom Matthias?
Launch Meeting - Zoom
Online coffee with Kaffi
Or beer, or any other beverage you may prefer.
Everyone welcome!
Thanks for feedback Kaffimann.
If we calculate the minimum port area conform the vented-box article of R.Small, the results are as follows.
He recommends a maximum port velocity equal to 4.5 % of the velocity of sound or 15 m/s maximum.
If the port surface Sv is larger than 0.8 * FB * VD with VD = xmax * Sd, then this requirement is fulfilled.
So for the Faital 12PR320, Sd = 489 cm2 and xmax = 7.34 mm --> VD = 3,59 10-6 m3. In the Monkey Tower proposal FB = 41 Hz.
Then Sv has to be larger than 0.8 * 41 * 3,59.10-6 m2 = 117 cm2. Or diameter dv of the port has to larger than 12.2 cm.
With a 12 cm port we are on the limit.
Indeed, we better increase the port diameter to minimum 15 cm, then Sv is 50 % larger than the minimum required one. For FB = 41 Hz the port length will be about 18 cm. For lower FB the port length will become larger than 18 cm of course.
Kaffimann, do you think the diameter even has to be more than 15 cm? With dv = 17 cm, the port area is the double compared to our first proposal with the 12 cm port. Then with dv = 17 cm, the port length is 25 cm for FB = 41 Hz.
If we calculate the minimum port area conform the vented-box article of R.Small, the results are as follows.
He recommends a maximum port velocity equal to 4.5 % of the velocity of sound or 15 m/s maximum.
If the port surface Sv is larger than 0.8 * FB * VD with VD = xmax * Sd, then this requirement is fulfilled.
So for the Faital 12PR320, Sd = 489 cm2 and xmax = 7.34 mm --> VD = 3,59 10-6 m3. In the Monkey Tower proposal FB = 41 Hz.
Then Sv has to be larger than 0.8 * 41 * 3,59.10-6 m2 = 117 cm2. Or diameter dv of the port has to larger than 12.2 cm.
With a 12 cm port we are on the limit.
Indeed, we better increase the port diameter to minimum 15 cm, then Sv is 50 % larger than the minimum required one. For FB = 41 Hz the port length will be about 18 cm. For lower FB the port length will become larger than 18 cm of course.
Kaffimann, do you think the diameter even has to be more than 15 cm? With dv = 17 cm, the port area is the double compared to our first proposal with the 12 cm port. Then with dv = 17 cm, the port length is 25 cm for FB = 41 Hz.