If you have the space, and if you prefer a tower, the Monkey Tower is still a good choice. Just use the same drivers, same baffle width, same left/right/top distances of the driver positions on the baffle, and the same xover. Adjust the bass tuning for the larger box volume and you'll get more deep bass extension.
I want to do the tower
So, follow post #41. Does anybody care to give a spec on the port?
Height off bottom (inside) dimension.
Left/right position. Hopefully centered if only one.
Diameter or some part number.
Length and Bends(???) Really should be constant diameter exit from box for aesthetics.
Thanks,
Regards,
Don
So, follow post #41. Does anybody care to give a spec on the port?
Height off bottom (inside) dimension.
Left/right position. Hopefully centered if only one.
Diameter or some part number.
Length and Bends(???) Really should be constant diameter exit from box for aesthetics.
Thanks,
Regards,
Don
Matthias, thanks for response.
You are the expert but I am thinking per post 41 and 10 that this will be an OSMC in a 1200mm overall hight and a front port. I will be using 15 ply baltic birch in 3/4 inch so 1200-36mm for inside. Then 1164mm high by 324mm wide by 378mm deep. All inside dimensions. Some flexibility on height per your judgement. I am reading OSMT thread and just want to do as good a speaker as we can make. Look forward to our comments, thoughts and advice. I guess if it is a failure I can cut it off to OSMC length so risk isn't too bad. Do you think this will be inferior to OSMC? Pfarrell loves his.
Thanks for help.
Best,
Don
You are the expert but I am thinking per post 41 and 10 that this will be an OSMC in a 1200mm overall hight and a front port. I will be using 15 ply baltic birch in 3/4 inch so 1200-36mm for inside. Then 1164mm high by 324mm wide by 378mm deep. All inside dimensions. Some flexibility on height per your judgement. I am reading OSMT thread and just want to do as good a speaker as we can make. Look forward to our comments, thoughts and advice. I guess if it is a failure I can cut it off to OSMC length so risk isn't too bad. Do you think this will be inferior to OSMC? Pfarrell loves his.
Thanks for help.
Best,
Don
That's a box volume of about 140 Litres. Subtract a bit for the volume occupied by the drivers, braces and ports, so let's say 135 L. I used this with an online calculator to see what comes out of it (see attachment).
I am sure there are better (more accurate) calculators out there, but the general impression I get is that 140 L seems to be a bit large for the 12PR20 woofer. Maybe someone with more experience in bass-reflex box modelling might chime in here.
Also, we had long discussions about the best position for the port in the original OSMC thread. I don't recommend to put the port(s) on the front panel in order to reduce the effect of low-midrange sound leaking out of the port. As I see it, the only good reason to put the port on the front baffle is if the speakers are positioned flush to a wall.
I am sure there are better (more accurate) calculators out there, but the general impression I get is that 140 L seems to be a bit large for the 12PR20 woofer. Maybe someone with more experience in bass-reflex box modelling might chime in here.
Also, we had long discussions about the best position for the port in the original OSMC thread. I don't recommend to put the port(s) on the front panel in order to reduce the effect of low-midrange sound leaking out of the port. As I see it, the only good reason to put the port on the front baffle is if the speakers are positioned flush to a wall.
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Hello.
I wasn't gonna go there but the reasons front ports didn't work in the OSMC was obvious to me, and I did post some protests before sawdust was made.
At any rate, 140 liters is a bit larger, but I don't see any obvious problems with that other than internal height of the box might induce some modes. May be able to get around that.
Might have time to look at simulations in about 20-22 hours or so, where do you want the port(s)?
Port placement is so important to get just right if you want front firing, and I love a good front firing port, but I won't judge. Want it on the back? Less precision, less worries. (Or perhaps more worries pending on the room.)
I wasn't gonna go there but the reasons front ports didn't work in the OSMC was obvious to me, and I did post some protests before sawdust was made.
At any rate, 140 liters is a bit larger, but I don't see any obvious problems with that other than internal height of the box might induce some modes. May be able to get around that.
Might have time to look at simulations in about 20-22 hours or so, where do you want the port(s)?
Port placement is so important to get just right if you want front firing, and I love a good front firing port, but I won't judge. Want it on the back? Less precision, less worries. (Or perhaps more worries pending on the room.)
I see Kaffimann has already responded. He's the man when it comes to box design! So if he has time to run it through some simulations I would take heed of what he suggests.
For what it's worth, if the form factor of the 120cm tall box is something you want (maybe it fits nicely in your room or whatever), you can always block off an internal section of the box to make the internal volume smaller.
gabo
OSMC minitower
Thanks, Kaffimann:
Look forward to your input. I can do ports wherever you want. Front, side or back. Prefer side to back but I am going to do what you think is best unless you think it is high risk of going backward. I don't want to ruin the OSMC but the reality is the box is the least expensive part of this so a do over is not the end of the earth. And, I can send an email and have a new box show up at my door.
Same goes for volume.
R,
Don
Thanks, Kaffimann:
Look forward to your input. I can do ports wherever you want. Front, side or back. Prefer side to back but I am going to do what you think is best unless you think it is high risk of going backward. I don't want to ruin the OSMC but the reality is the box is the least expensive part of this so a do over is not the end of the earth. And, I can send an email and have a new box show up at my door.
Same goes for volume.
R,
Don
tower update
Great idea gabo. I can put the xovers there and it's a win-win. I'll still take what I can get in the volume department though.
Thanks for responding.
Don
Great idea gabo. I can put the xovers there and it's a win-win. I'll still take what I can get in the volume department though.
Thanks for responding.
Don
Don, I sense you want a quick'n'dirty reply with just the "easy way out" + backfiring port.
And that's ok.
If you get the port as close as possible to the driver without there being any chance of the cone beaming higher frequencies into the port, here's what you might get if you have the perfect room.
Problem as I see it, the perfect room does not exist.
Long story short, you can just elongate the speaker, slam the port on the back far away from the edges of the box and probably around 1m (3.3ft or so) from any and all walls. Should make you reasonably happy.
Same port size and length, only it's round because the proper sized box don't need a lossy port.
It's not big, it's juuuust right.
And that's ok.
If you get the port as close as possible to the driver without there being any chance of the cone beaming higher frequencies into the port, here's what you might get if you have the perfect room.
Problem as I see it, the perfect room does not exist.
Long story short, you can just elongate the speaker, slam the port on the back far away from the edges of the box and probably around 1m (3.3ft or so) from any and all walls. Should make you reasonably happy.
Same port size and length, only it's round because the proper sized box don't need a lossy port.
It's not big, it's juuuust right.
Attachments
I am not sure what is (not) included in this model curve. Baffle loss? Coil inductance? Or just the low-frequency acoustics of the woofer+box? The curve shows a SPL decrease starting at about 150 Hz down to about 40 Hz. If this is due to the bass-reflex tuning (i.e., "just the woofer+box acoustics"), the bass output between 150 Hz and 40 Hz or so will be less than with the original Monkey Coffin box, which has a flat SPL curve in this range.
The SPL decrease could be compensated by the xover by attenuating the SPL above 50 Hz or so. However, this would involve a complete redesign of the entire (!) xover filters.
KaffiMann: just to be sure, could you do a model curve for the original Monkey Coffin and plot this curve together with the one for the Monkey Tower? Comparing the two curves would be useful to understand this better.
And while we're at it: could you also calculate the SPL curve for a 90 L bass reflex box?
The SPL decrease could be compensated by the xover by attenuating the SPL above 50 Hz or so. However, this would involve a complete redesign of the entire (!) xover filters.
KaffiMann: just to be sure, could you do a model curve for the original Monkey Coffin and plot this curve together with the one for the Monkey Tower? Comparing the two curves would be useful to understand this better.
And while we're at it: could you also calculate the SPL curve for a 90 L bass reflex box?
Matthias, it's not "less bass", it goes deeper. Sub 30hz vs barely 40hz is a major difference.
Passive eq at sub 300hz (not to mention 100hz) is crazy expensive and impose huge losses, please don't.
Those sims will have to wait until tomorrow evening, I'm a bit overworked and need to go sleep.
Passive eq at sub 300hz (not to mention 100hz) is crazy expensive and impose huge losses, please don't.
Those sims will have to wait until tomorrow evening, I'm a bit overworked and need to go sleep.
I couldn't agree more, and I didn't mean to imply "less bass" (whatever that may mean). I meant "lower SPL" between 50 -- 150 Hz.
30 Hz vs 40 Hz is almost half an octave, which is a lot.
Ha, don't worry! I am not going to redesign the xover, and I am surely not going to kill the SPL output (efficiency) from 50 Hz all the way up to the tweeter just to equalize for flat bass SPL response.
Sleep, yes. Should do the same. Good night!
tower update
"Don, I sense you want a quick'n'dirty reply with just the "easy way out" + backfiring port."
@ Kaffimann,
What I "want" probably isn't what I asked for. What I was (am) looking for are your thoughts on how to do this. I am just cautious about how much to ask for. I am open to everything you want to contribute. Any time and effort you spend on this is greatly appreciated. Hopefully the community will have a great speaker option as a result.
Regards,
Don
"Don, I sense you want a quick'n'dirty reply with just the "easy way out" + backfiring port."
@ Kaffimann,
What I "want" probably isn't what I asked for. What I was (am) looking for are your thoughts on how to do this. I am just cautious about how much to ask for. I am open to everything you want to contribute. Any time and effort you spend on this is greatly appreciated. Hopefully the community will have a great speaker option as a result.
Regards,
Don
Hello, some feedback from my side. Maybe it can help.
I did some simulation of a BR on infinite baffle with larger volume (and other fB) than the Monkey Coffin.
In the SPL and impedance plot:
- red curve: VB = 68 L, FB = 38 Hz; this is actual Monkey Coffin
- green curve: VB = 120 L, FB = 28 Hz; larger volume and same port as Monkey Coffin (lower fB)
- blue curve: VB = 120 L, FB = 38 Hz; larger volume and same FB as Monkey Coffin (shorter port)
- violet curve: VB = 120 L, FB = 35 Hz; larger volume and other FB and port as Monkey Coffin (shorter port).
In all cases with larger volume, you have to adapt the RLC circuit parallel with the woofer, because the location of the higher impedance peak is different.
I did some simulation of a BR on infinite baffle with larger volume (and other fB) than the Monkey Coffin.
In the SPL and impedance plot:
- red curve: VB = 68 L, FB = 38 Hz; this is actual Monkey Coffin
- green curve: VB = 120 L, FB = 28 Hz; larger volume and same port as Monkey Coffin (lower fB)
- blue curve: VB = 120 L, FB = 38 Hz; larger volume and same FB as Monkey Coffin (shorter port)
- violet curve: VB = 120 L, FB = 35 Hz; larger volume and other FB and port as Monkey Coffin (shorter port).
In all cases with larger volume, you have to adapt the RLC circuit parallel with the woofer, because the location of the higher impedance peak is different.
Attachments
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