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Small 2-way speakers with linear on-axis and power response characteristics (Scan Speak and SB Acoustics drivers). H&V off-axis measurements included
- Thread starter XMechanik
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Gregoire90
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Finishing up my build on these, rounded over the edges a bit, first time building a speaker from scratch. Thanks again to @XMechanik for providing this design for free. Can’t believe how cool people are on the internet.
Thinking about slapping a gel stain on these, but it looks kinda bad on test pieces. Honestly might just apply a semi gloss clear coat and call it a day. I like the raw look of the birch.
Thinking about slapping a gel stain on these, but it looks kinda bad on test pieces. Honestly might just apply a semi gloss clear coat and call it a day. I like the raw look of the birch.
Gregoire90
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Thank you! I will try this
And here they are in our farmhouse kitchen, mounted high on the walls in the food prep area.
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Gregoire90
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I want to steal your idea, love the black front baffle. Looks incredible
lazorade
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Guys, is this too much damping if I'm also planning to damp the whole side walls and the top wall, and also fill the cabinet with polyfil? Is there a better plan?
It's not really apparent from the photo but I would be losing quite a lot of inside volume were I put the damping on all sides. I'm trying to get a balanced sound and not deaden it too much.
Thank you
It's not really apparent from the photo but I would be losing quite a lot of inside volume were I put the damping on all sides. I'm trying to get a balanced sound and not deaden it too much.
Thank you
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I would be interested to know if and how anyone has put speaker grilles on the Mechano 23s. Here is my effort which is black hessian (burlap in the USA) circles (3mm ply) attached with magnets to the driver screw heads. I don't detect any change in sound although hessian/burlap seems not to be rated highly in DIY circles as a grille material. It comes in lots of colours though and might be fun to experiment with other colours.
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Inertiaman
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I've been considering a grill for my build using Guilford of Maine FR701 fabric, a relatively transparent burlap-ish acoustic fabric which is available in 40+ colors. Its does have some attenuation, but I think its acceptable if one also wants an "attenuated" appearance.
I prefer a traditional rectangular grill. Have been thinking about embedding some magnets in the corners of the baffle to accept a magnetic grill. Am hung up a bit on how to best execute a frame that is low profile but still stiff enough. Might try some 6mm foamed PVC.
In addition to any attenuation from the fabric, I assume the grill frame will have some impact on directivity.
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- Thread Starter
- #373
This made me wonder where my belief in the effectiveness of polyfill came from. I've recalled one of my early design where polyfill application did the job perfectly, so I stayed for longer with that method. That was a slim floorstander design and below you can see the effect of polyfilling Mechano23 that I've just measured.
Port NF signal. Red: with polyfill, green: no polyfill.
So it still seems to work quite well, some of the internal modes and port resonances are attenuated even up to 20dB.
What may make a difference is the amount of filling, in my case it's c.a. 70g.
It should be noted that this method is suitable for damping standing waves inside the enclosure and reducing the coupling between the driver and the port resonance in the midrange, but is rather ineffective for damping enclosure modes.
Interesting, thanks XMechanik. As a relative newcomer to DIY I have been completely confused by the different arguments around the effectiveness of various damping materials in terms of what materials to use, how much, where and in which types of speakers. DIY Audio has dozens of threads on the topic (such as this recent one) as well as a number of speaker-building books. There seems to be no consensus between any of them. I feel that this is a part of the hobby that needs further research (or at least an existing expert with good communication skills) incorporating the latest damping materials and speaker types. If there is already a definitive and current guide to speaker damping out there somewhere (including measurements), please could someone let me know.
What I can suggest though based on our tests is not to rely only on polyfil (alone) as a damping material but to first line the inside walls with a natural material such as wool felt. In Australia acoustic felt is hard to find so we used (believe it or not) 'saddle felt' which is used between saddle and horse in horse riding to keep the horse comfortable. Apparently several Australian commercial speaker builders use this to good effect. The key (according to speaker designers at DIY Audio) is to use natural fibres rather than articificial ones (such as nylon or polyester), since natural fibres have more complex strands and are therefore better at 'trapping' waves. It could be that you needed a relatively high density of polyfil to compensate for its 'uncomplex' strands? From what I have seen polyfil is used in closed boxes and transmission lines but less so in ported speakers where wall-lining is more common.
At the same time it seems you need to be careful no to overdo it - too much of any material can 'muddy' the sound or interefere with the drivers. That's why we built one speaker with a removable back so that we could try out a variety of damping solutions. As I mentioned, using felt alone gave the best outcome for us (on all internal walls except the baffle and floor where the crossover was). But to my ears at least these changes were minor compared to the huge impact of strong cabinets, good driver choice and a well-designed crossover (for which thank you again!). So if you do have the luxury of a removable back it would be interesting if you could replicate our results with felt.
What I can suggest though based on our tests is not to rely only on polyfil (alone) as a damping material but to first line the inside walls with a natural material such as wool felt. In Australia acoustic felt is hard to find so we used (believe it or not) 'saddle felt' which is used between saddle and horse in horse riding to keep the horse comfortable. Apparently several Australian commercial speaker builders use this to good effect. The key (according to speaker designers at DIY Audio) is to use natural fibres rather than articificial ones (such as nylon or polyester), since natural fibres have more complex strands and are therefore better at 'trapping' waves. It could be that you needed a relatively high density of polyfil to compensate for its 'uncomplex' strands? From what I have seen polyfil is used in closed boxes and transmission lines but less so in ported speakers where wall-lining is more common.
At the same time it seems you need to be careful no to overdo it - too much of any material can 'muddy' the sound or interefere with the drivers. That's why we built one speaker with a removable back so that we could try out a variety of damping solutions. As I mentioned, using felt alone gave the best outcome for us (on all internal walls except the baffle and floor where the crossover was). But to my ears at least these changes were minor compared to the huge impact of strong cabinets, good driver choice and a well-designed crossover (for which thank you again!). So if you do have the luxury of a removable back it would be interesting if you could replicate our results with felt.
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HighFutility
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I placed the order for the PCB, drivers, and crossover. Waiting impatiently for build time. Thank you, @XMechanik, for all your contributions.
- Thread Starter
- #376
My enclosure is all glued and changing polyfill to felt would be a bit problematic. On the other hand, if you have the NF BR port measurement of your implementation, it would be interesting to compare.
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HighFutility
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I just received the crossover parts and PCB. Drivers are probably a week out, give or take. I will be making the cabinets out of MDF and using veneer.
I have not purchased the port. Looking at the comments, it looks like a few individuals changed the dimensions and port tuning, and a member built one with PR. What is the consensus on cabinet volume and optimal port/ports? I can build out of 5/8 or 3/4 MDF but will have to change dimensions. Does this unit need bracing? I think if time and budget permit, I could build a few versions.
I have not purchased the port. Looking at the comments, it looks like a few individuals changed the dimensions and port tuning, and a member built one with PR. What is the consensus on cabinet volume and optimal port/ports? I can build out of 5/8 or 3/4 MDF but will have to change dimensions. Does this unit need bracing? I think if time and budget permit, I could build a few versions.
- Thread Starter
- #378
3/4' is 19mm so very close to 18mm. If you want to compensate this 1mm difference you may consider making the cabinets few mm deeper. I don't think it would make much difference.
As for bracing, there is a small cabinet resonance in the 300Hz region. Some tips on how to try to deal with it: #336, #334.
Regarding BR dimensioning and tuning, some good points have been raised, e.g. here: #74. Consider increasing the port diameter, especially if you're plan to use it at high volume. You could even try not increasing the port length, which would result in an increase of tuning frequency, which may also be a desirable effect according to some opinions. But I haven't tried it tbh.
Inertiaman
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I've been contemplating my port dimensions, thinking perhaps this is one area that we could improve on the original spec. One challenge/obstacle is a lack of available port options between the original 1.375" port and widely available 2" ports which would require too much length. Finding something 1.75"-ish and long enough proved challenging.
Eventually I found PVC Class 200 IPS pipe, which is used for irrigation, which I may ultimately choose. The nominal 1.5" size is actual 1.9" o.d. and 1.7" i.d. That's 50% greater cross sectional area than the 1.375 port . . . enough to meaningfully impact potential port noise, but small enough to keep the length reasonable.
I'm considering lengths in 200-230mm range, with a corresponding slight rise in tuning.
Of course implementing a port w/ basic pipe adds a degree of difficulty for the build. I'll probably roundover the port hole on the back panel, and use a heat gun and wine bottle to flare the interior end of the pipe.
Eventually I found PVC Class 200 IPS pipe, which is used for irrigation, which I may ultimately choose. The nominal 1.5" size is actual 1.9" o.d. and 1.7" i.d. That's 50% greater cross sectional area than the 1.375 port . . . enough to meaningfully impact potential port noise, but small enough to keep the length reasonable.
I'm considering lengths in 200-230mm range, with a corresponding slight rise in tuning.
Of course implementing a port w/ basic pipe adds a degree of difficulty for the build. I'll probably roundover the port hole on the back panel, and use a heat gun and wine bottle to flare the interior end of the pipe.
- Thread Starter
- #380
The key is the port area. If you make port area equivalent to desired (smaller) pipe diameter you can use port length for the smaller pipe diameter. For changing port area you can glue in slats or something.
Making a slot port would be another option. With this approach you could freely adjust port area (as you're not tied to any specific dimensions) so balancing port area vs port length would be easier.
Attached example of a slot port implementation. This is equivalent to 35mm pipe diameter (as the woofer was 12cm in that case).
