This ^^^^
You can follow my journey… amply documented in this thread. I need to build stuff.. and want to try something open baffle FR down-facing-15”-woofer speaks like the Pass SLOB, totally different animal need to bi-amp etc.… I have been assured by those I trust, yes build them (because you are nuts) but don’t think for a second they will be “better” since I built my last speaker first. Haha.
Re: Sensitivity… We have a nice room, 22x12’ with an L-shaped extension off one long side. Vaulted canted ceiling, a natural bass trap opposite the speakers and above the listening sofa. Giant glass window on one short side. No room treatment other than throw rugs on the wood floor. Muses volume control in the pre-amp (no screen so I don’t know level exactly), and any number of ~25W Pass monoblocks… the speakers positions have had to follow the mandatory redo of our fireplace with a serious wood stove (they can’t be near the stove obviously). They had to move to the extreme of the long length of the room (40’ cable run under the floor)… they sound even better now! I sit them on the Xover boxes, much better defined bass when up off the floor. (and no shortage of bass here no matter the input).
We use the full DIY system as general movie/music machine but it’s really set up for vinyl playback…. point is: we can’t be in the room if I crank the volume to max/clipping. Oh and the WAF that comes up here a bit due to their size? My wife got it immediately… came rushing into the room, I’d only put one speaker into play since I was so excited, the other one needed wiring! I did involve her in the cabinet design/finishing. Cartridges and these speakers… the 2 biggest YES factors. (but everything matters)…
I’ve said it many times here in various ways… if you have the skills (or know someone that does ;-) there’s zero risk here. Just build them.
Worst case… you learn a ton…. and have loads of fun….
Thanks for the nice notes and info @pfarrell and @planet IX. It is reassuring to hear your praise after living with the speakers for a long time. To the point about placing the speakers on top of the crossovers...the Monkey tower version has some appeal in that no stands would be needed and the crossovers could be built into the bottom part. Guess I will start looking for deals on parts 
I like the flexibility of the separate boxes, and the look we did here personally....building the Xovers was insane levels of fun, and I like to be able to see them when I want to, or make the few tweaks Matthias made here and there.... But certainly, go big or go home—I'd be very interested to hear a comparison, of course related to bass extension...Thanks for the nice notes and info @pfarrell and @planet IX. It is reassuring to hear your praise after living with the speakers for a long time. To the point about placing the speakers on top of the crossovers...the Monkey tower version has some appeal in that no stands would be needed and the crossovers could be built into the bottom part. Guess I will start looking for deals on parts
I can see the appeal in easy access. For a tower version, a plexiglass covered crossover compartment, accessibly from the back, could be possible - a little component jewelry and easy access. I would love to go for the ATC look, but my wood working skills may not extend that far. From a brief exchange with Matthias it seems a front port is feasible but I don't know if that type of front baffle would mess with the dispersion?
I think the slight step in such a front panel wouldn't do very much to the acoustics.
I'd guesstimate the size of the step to about 4 cm, and they will be irrelevant for frequencies with wavelengths larger than this (frequencies well below 8.5 kHz). In other words, anything coming from the woofer and the midrange will not be affected much by the steps. For higher frequencies, most of the sound is kept away from the edges/steps by the wave guide of the tweeter (and the same could be said for the upper midrange).
Go for it!
I'd guesstimate the size of the step to about 4 cm, and they will be irrelevant for frequencies with wavelengths larger than this (frequencies well below 8.5 kHz). In other words, anything coming from the woofer and the midrange will not be affected much by the steps. For higher frequencies, most of the sound is kept away from the edges/steps by the wave guide of the tweeter (and the same could be said for the upper midrange).
Go for it!
It would change it slightly. The ATC in the picture have a stepped baffle which is not a desirable feature in general. The stepped baffle is there to have a place for the chamfered dustgrille, that can reduce baffle edge diffraction.
The issue of port location was about something else… from memory… putting it at the centre is the best location if the enclosure is not optimised. The design brief asked for a simple enclosure so we have parallel walls causing standing waves. Their speed is lowest at the mid point between walls so that’s why it’s the best port location. Someone please correct/amend the technical details if necessary. My impression was that in order to move the port, the enclosure would need to be redesigned (eg like B&W or Magico Mini) except for the baffle.
You might want to look at what Erin Hardison measures with his Klippel NFS. Those are 4Pi conditions at 1m distance using 2.83V.
https://www.erinsaudiocorner.com/loudspeakers/
In the first part of his review there are usually specs for passive loudspeaker by manufacturer. Use that to compare with measurements Erin made and then to measurements at 4Pi for OSMC. 93dB/2.83V/1m sensitivity at 40Hz is usually reserved for 15" woofers.
There are manufacturers that are flat out liars (like Klipsch, i think that they just invent a number based on nothing) and there are honest ones like Revel, JBL and Kef.
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My build is slowly progressing. The hybrid plywood/aluminium structure of the cabinet, as per a previous post, is not exactly making things easier.
But it is now the time to consider the crossover and I have questions @mbrennwa/anyone regarding inductor selection vs changes to the DCR values as specified in post 931. For now I am only looking at inductors in series with the drivers:
Finally, also @mbrennwa, regarding the Basotect, I am aware of the pictures of your build but I also vaguely recall that you removed/thinned some of it later on. Can you give an up to date description of what foam type/thickness you used where?
But it is now the time to consider the crossover and I have questions @mbrennwa/anyone regarding inductor selection vs changes to the DCR values as specified in post 931. For now I am only looking at inductors in series with the drivers:
- For the woofer there is limited choice. To achieve comparable DCR values of Lw1, Lw2, only cored inductors work. The combined DCR of 0.28Ω is possible with Mundorf BS180, Mundorf I-core CFS12 and Jantzen C-Coils. The latter option even allows for a combined DCR of 0.1Ω if the largest C-Coils are chosen. Do these small differences in DCR values matter?
- For the mid dome, Lm1 and Lm2 are in series to the driver, and options are plentiful thanks to their small values (1.2mH and 0.33mH) and the relatively high DCRs (total 0.54Ω) of the suggested components. Using e.g Goertz copper foil 14AWG inductors, I get 0.303Ω. Would I need to compensate with resistors?
Finally, also @mbrennwa, regarding the Basotect, I am aware of the pictures of your build but I also vaguely recall that you removed/thinned some of it later on. Can you give an up to date description of what foam type/thickness you used where?
For the woofer series inductors, I'd go for the lowest DC resistance. With the mid inductors, I'd think your suggestion should be fine. You can always xperiment with adding a small extra resistor later on. For the caps, just don't use anything containing fairydust or other glitter. Figure 6 in the OSMC Paper shows how I did the Basotect
That Basotec stuff is available in different thickness, 3cm and 5cm.
If you get some of both, you don't have to cut anything. I think I posted pics of it here...
Hi, again –
As mentioned above, I have been thinking about a tower version of the OSMC. To fit into our living space, and not be larger than the current speakers, 100cm would be a good height. Keeping the width and depth of the OSMC, I sketched the following and wonder if I am missing anything or making silly mistakes? Assuming 18 mm nominal thickness for the 3/4" Baltic birch available here in the US, the volume would be about 106l.
The two upper braces would be identical to the OSMC ones, and a third brace (or more) could be placed below the woofer. This brace could also be the top or bottom of a small crossover compartment. Any issues with the third brace or crossover compartment?
I would love to make this front ported to not have the speakers too far into our living room. Port placement/height could be centered between the woofer and the bottom, or closer to the woofer. Any insights on port placement on the front? Port dimensions is another question.
Unless I can find Baltic birch thicker than ¾” (18mm nominal), I would likely put a layer of MDF on the back of the front/baffle to accommodate the min depth of 20 mm for the Volt752. Would it be beneficial to add an MDF ‘lining’ this to the rest of the cabinet if using 18mm Baltic birch? This would further reduce the volume and add some heft to the cabinet.
Any insights and suggestions will be greatly appreciated!
Cheers,
Soren
As mentioned above, I have been thinking about a tower version of the OSMC. To fit into our living space, and not be larger than the current speakers, 100cm would be a good height. Keeping the width and depth of the OSMC, I sketched the following and wonder if I am missing anything or making silly mistakes? Assuming 18 mm nominal thickness for the 3/4" Baltic birch available here in the US, the volume would be about 106l.
The two upper braces would be identical to the OSMC ones, and a third brace (or more) could be placed below the woofer. This brace could also be the top or bottom of a small crossover compartment. Any issues with the third brace or crossover compartment?
I would love to make this front ported to not have the speakers too far into our living room. Port placement/height could be centered between the woofer and the bottom, or closer to the woofer. Any insights on port placement on the front? Port dimensions is another question.
Unless I can find Baltic birch thicker than ¾” (18mm nominal), I would likely put a layer of MDF on the back of the front/baffle to accommodate the min depth of 20 mm for the Volt752. Would it be beneficial to add an MDF ‘lining’ this to the rest of the cabinet if using 18mm Baltic birch? This would further reduce the volume and add some heft to the cabinet.
Any insights and suggestions will be greatly appreciated!
Cheers,
Soren
Yeah, if at all possible make a "prototype" version to test out your build "issues" you have in mind, like the mdf double front you are wondering. It is a chance to test your building ideas/methods but also about how the enclosure works acoustically.
As the enclosure has long internal dimension it's highly likely the port outputs some unwanted midrange sound, either schuffing sounds or it could resonate, or leak some sound from inside. It would be advantageous to you to be able to play with the port size and also position (inside the box) in order to check there is not severe issues with it. If you do not do this, it's left for luck and you might get it nice, or not. Worst case unwanted mids are louder than the Helmholtz resonance itself, which pegs question why use a port at all.
Another thing you can test with prototype is that how much the box gives coloration in general, whether your bracing / damping / stuffing scheme is fine enough. Area of panels is much greater than area of the woofer, and any vibration of the panels could be quite loud so this might be another critical thing to be able to tune.
Prototype is quite much extra work and money, but you'll learn a ton and it is pretty much quaranteed a prototype gives you better end result by many counts. You might be able to "fix" at least one thing from construction side for better looks as well and you already have that much better end result even if the audio was fine, but you could have spotted multiple things that result in so much more better end result. And learnt thing or two. Of course everything relates to how interesting this stuff is to you, most important thing is to be motivated the whole way through to get some end result so do what feels relevant to you Have fun!
As the enclosure has long internal dimension it's highly likely the port outputs some unwanted midrange sound, either schuffing sounds or it could resonate, or leak some sound from inside. It would be advantageous to you to be able to play with the port size and also position (inside the box) in order to check there is not severe issues with it. If you do not do this, it's left for luck and you might get it nice, or not. Worst case unwanted mids are louder than the Helmholtz resonance itself, which pegs question why use a port at all.
Another thing you can test with prototype is that how much the box gives coloration in general, whether your bracing / damping / stuffing scheme is fine enough. Area of panels is much greater than area of the woofer, and any vibration of the panels could be quite loud so this might be another critical thing to be able to tune.
Prototype is quite much extra work and money, but you'll learn a ton and it is pretty much quaranteed a prototype gives you better end result by many counts. You might be able to "fix" at least one thing from construction side for better looks as well and you already have that much better end result even if the audio was fine, but you could have spotted multiple things that result in so much more better end result. And learnt thing or two. Of course everything relates to how interesting this stuff is to you, most important thing is to be motivated the whole way through to get some end result so do what feels relevant to you
Have fun!
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Hi Guys,
Thanks for the input!
@tmuikku your suggestions make good sense but seem a little daunting for a first time speaker builder I can imagine a few approaches that would enable me to tweak the cabinet along the way, even if not fully reversible. MDF is inexpensive in the context of this build - are there downsides to making the cabinet from two layer/sandwich walls, other than weight?
If a volume of about 100l is too large, I suppose it may be possible to close off the upper part of the cabinet, or part of it, above the woofer? One could also make the crossover compartment in a 'bottom' compartment. Both would shorten the effective cabinet space if this is desirable.
If I think too much about it, I will end up building the OSMC as designed ...
Cheers,
Soren
Thanks for the input!
@tmuikku your suggestions make good sense but seem a little daunting for a first time speaker builder
I can imagine a few approaches that would enable me to tweak the cabinet along the way, even if not fully reversible. MDF is inexpensive in the context of this build - are there downsides to making the cabinet from two layer/sandwich walls, other than weight? If a volume of about 100l is too large, I suppose it may be possible to close off the upper part of the cabinet, or part of it, above the woofer? One could also make the crossover compartment in a 'bottom' compartment. Both would shorten the effective cabinet space if this is desirable.
If I think too much about it, I will end up building the OSMC as designed ...
Cheers,
Soren
Well, my purpose is not to scare you
Thought to write about prototyping on a coffee break as it has been single most useful advice I've thought myself, and could pass on to anyone, without knowing any specifics. It is a way to save time and money and especially have fun all the time, although it might seem counterintuitive
Thought experiment: If you go into great effort building pair of quite expensive and laborous big speakers, make some mistakes on the way building just because it's first time and we are all humans not robots. Spend some time fixing them up, tweak and polish, and then comes time to listen and there is a glaring issue but nothing you can do about it now as you had no idea about it and could not plan it in advance. If this unlucky chain of events happens there is no option than to butcher the projecy and start over.
It hurts a lot if this happens as you've now two boxes you invested lot of time and money in and they'd still need work, what a let down.
If you instead built single quick one with mentality there might be some issues that I'm gonna learn to tackle. If lucky it would be alright and all you have to do is to build another one. By now you might already have two polished speakers without obvious issues, and be rocking sooner than without prototyping mentality. Worst case you had lot of problems, but instead of scrapping two polished enclosures you only need to scrap one cheap and it's not too bad of a bump to self esteem.
Hence, if it is your first build you could assume end result depends some on luck as it isn't entirely paint by numbers project, and count on it. If you take it as such, embrace it by making a prototype assuming there is going to be some difficulties and it is a chance to learn, you'd get better outcome by definition, right? If you were lucky and there was no issies, you spent some extra money. If not you saved some instead. Most importantly you never felt let down!
Have fun!
Thought to write about prototyping on a coffee break as it has been single most useful advice I've thought myself, and could pass on to anyone, without knowing any specifics. It is a way to save time and money and especially have fun all the time, although it might seem counterintuitive
Thought experiment: If you go into great effort building pair of quite expensive and laborous big speakers, make some mistakes on the way building just because it's first time and we are all humans not robots. Spend some time fixing them up, tweak and polish, and then comes time to listen and there is a glaring issue but nothing you can do about it now as you had no idea about it and could not plan it in advance. If this unlucky chain of events happens there is no option than to butcher the projecy and start over.
It hurts a lot if this happens as you've now two boxes you invested lot of time and money in and they'd still need work, what a let down.
If you instead built single quick one with mentality there might be some issues that I'm gonna learn to tackle. If lucky it would be alright and all you have to do is to build another one. By now you might already have two polished speakers without obvious issues, and be rocking sooner than without prototyping mentality. Worst case you had lot of problems, but instead of scrapping two polished enclosures you only need to scrap one cheap and it's not too bad of a bump to self esteem.
Hence, if it is your first build you could assume end result depends some on luck as it isn't entirely paint by numbers project, and count on it. If you take it as such, embrace it by making a prototype assuming there is going to be some difficulties and it is a chance to learn, you'd get better outcome by definition, right? If you were lucky and there was no issies, you spent some extra money. If not you saved some instead. Most importantly you never felt let down!
Have fun!
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I wouldn't bee too worried about midrange leakage. The x-over filter cutoff for the woofer is about 300 Hz, and the taller box will not introduce any new resonances above this frequency.
Hi, yeah, I've had problems with my ports but it doesn't mean everyone would, just that I'd want to prototype or plan for tweakable port if not sure it's not a problem. Same with "box sound".
Example simple estimations if someone is interested. If 100cm was the longest internal dimension, first three modes would be ~171Hz, ~343Hz, ~514Hz. These could all be audible worst case. Third one is likely already attenuated by damping material inside the box, the lowest one is perhaps non-existent due to the woofer being midway of the long dimension, the second one is fully excited woofer being at a pressure node, luckily the port is roughly at velocity node of that one. Worst place for port inlet would be at the end of the long dimension as it's all pressure node there ready to leak. Perhaps the current location is just fine, perhaps it would be better bit closer to the driver further from the end of the cab. It's possible that there is a leak or not, move 5cm one direction and situation reverses, can be quite fiddly. Could be tweaked with damping material and so on, so perhaps not necessary to make extra prototype box. I'd still opt in some tweakability and measure before finishing, and so on
Example simple estimations if someone is interested. If 100cm was the longest internal dimension, first three modes would be ~171Hz, ~343Hz, ~514Hz. These could all be audible worst case. Third one is likely already attenuated by damping material inside the box, the lowest one is perhaps non-existent due to the woofer being midway of the long dimension, the second one is fully excited woofer being at a pressure node, luckily the port is roughly at velocity node of that one. Worst place for port inlet would be at the end of the long dimension as it's all pressure node there ready to leak. Perhaps the current location is just fine, perhaps it would be better bit closer to the driver further from the end of the cab. It's possible that there is a leak or not, move 5cm one direction and situation reverses, can be quite fiddly. Could be tweaked with damping material and so on, so perhaps not necessary to make extra prototype box. I'd still opt in some tweakability and measure before finishing, and so on
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