This is such an interesting thread. I'm currently making some full range bookshelf speakers with corian boxes and No Rez interior. But while that is being completed I'm also looking at making a band pass subwoofer enclosure. Before reading this I thought ok just use baltic birch ply. But now this "reshape" polyurethane material the Mr Geddes mentions seems very very interesting. Does anyone know the other brand names this material goes by? Also I see there are different densities, 34lb, 37lb, 41, 42, 43, 48 - How does one know which material is the right one to use? And if the material is self dampening - Does that mean that something like No Rez is irrelevant?
It's Renshape and Google will give you all you need to know. If the price doesn't bother you then there is no comparison. Use 1" for a sub enclosure, cross brace and you will be fine.
This thread has been one hell of a read... I was most surprised to see there was only minimal discussion about magnet mounting versus basket mounting. Linkwitz goes into some detail about the benefits of magnet mounting the driver (midranges) instead of rigidly mounting the basket to the baffle. It seems magnet mounting in conjunction with good bracing technique and skyhook damping (I believe that's what Earl called it) would be great starting points for new designs.
I just took the test set to full range speaker and the T. Chapman music with headphones straight out of the Dell laptop audio jack and that resulted in a score of -30dB. Redid the test with the J. Stone music and got the same result. Never heard either of those songs before, but neither of those sound clips sounded good... Maybe it's my laptop or headphones
Regardless, the test makes a great point about the audibility/perception of distortion. I know that when firing up a new set of speakers or amp for the first time there is also a bit of euphoria that further masks any distortion
I just took the test set to full range speaker and the T. Chapman music with headphones straight out of the Dell laptop audio jack and that resulted in a score of -30dB. Redid the test with the J. Stone music and got the same result. Never heard either of those songs before, but neither of those sound clips sounded good... Maybe it's my laptop or headphones
Regardless, the test makes a great point about the audibility/perception of distortion. I know that when firing up a new set of speakers or amp for the first time there is also a bit of euphoria that further masks any distortion Greetings......
Wow after reading the whole thread, I'm wiser, confused and energized...lol
I've been looking at these 1/4" thick cement boards as the second layer inside the
existing speaker box, the first layer would be a high viscosity carpet glue that will stay soft and pliable. Any thoughts?
Wow after reading the whole thread, I'm wiser, confused and energized...lol
I've been looking at these 1/4" thick cement boards as the second layer inside the
existing speaker box, the first layer would be a high viscosity carpet glue that will stay soft and pliable. Any thoughts?
Hi All,
A good evening to you from Scandinavia - hope things are well where you may be
As it is I'm moving in the direction of finishing the accelerometer I bought & mentioned here earlier - and thus actually getting it ready for use (the ADXL001 from Analog Devices - weight 154 mg). To this end I wonder how I may best mount the wires going from the accelerometer so that they influence the measurements to the least degree.
The accelerometer itself is quite small - 5x5x2 mms - and has its pins oriented as shown in the attached illustration. The actual accelerometer measurement direction is indicated with an arrow in the image.
Given a reasonably stable PSU (will be a LiFePO4 battery) the local decoupling needed on the accelerometer itself is a 100 nF capacitor which I intend to be of 0603 size glued (with silicone probably - epoxy or something else better?) to the bottom of the accelerometer. This is the black angled rectangle.
The OUT+GND and the VDD/VDD2+GND (PSU) wires I then intend to be two sets of very thin twisted enamelled wire that are suspended e.g. in a couple of rubber bands e.g. 10 cms from the ADXL-001 and then connected to an ADC.
The two twisted pair wire sets are shown in the illustration as two circles - one blue, the other reddish-brown - going out perpendicularly from the bottom center of the ADXL-001 ... I hope this is reasonably clear ....
In my thinking about it this may be the connections that influence the free movement of the accelerometer to the least extent ... Any of you seeing it differently?
I've also attached an illustration of the rod I a.o.t. am going to measure. I would like to use the accelerometer to measure the rod's vibrations, however, another option is to use a small microphone placed closely to the rod. I already have one of the small Panasonic electret microphones (WM-68 I think) that I may use for this purpose - and actually am a bit pre-disposed towards it because using it would mean practically no influence on the rod's vibrations - something the accelerometer cannot quite achieve.
Might you have experiences with what works best in practice?
Thanks for any feedback
Jesper
A good evening to you from Scandinavia - hope things are well where you may be
As it is I'm moving in the direction of finishing the accelerometer I bought & mentioned here earlier - and thus actually getting it ready for use (the ADXL001 from Analog Devices - weight 154 mg). To this end I wonder how I may best mount the wires going from the accelerometer so that they influence the measurements to the least degree.
The accelerometer itself is quite small - 5x5x2 mms - and has its pins oriented as shown in the attached illustration. The actual accelerometer measurement direction is indicated with an arrow in the image.
Given a reasonably stable PSU (will be a LiFePO4 battery) the local decoupling needed on the accelerometer itself is a 100 nF capacitor which I intend to be of 0603 size glued (with silicone probably - epoxy or something else better?) to the bottom of the accelerometer. This is the black angled rectangle.
The OUT+GND and the VDD/VDD2+GND (PSU) wires I then intend to be two sets of very thin twisted enamelled wire that are suspended e.g. in a couple of rubber bands e.g. 10 cms from the ADXL-001 and then connected to an ADC.
The two twisted pair wire sets are shown in the illustration as two circles - one blue, the other reddish-brown - going out perpendicularly from the bottom center of the ADXL-001 ... I hope this is reasonably clear ....
In my thinking about it this may be the connections that influence the free movement of the accelerometer to the least extent ... Any of you seeing it differently?
I've also attached an illustration of the rod I a.o.t. am going to measure. I would like to use the accelerometer to measure the rod's vibrations, however, another option is to use a small microphone placed closely to the rod. I already have one of the small Panasonic electret microphones (WM-68 I think) that I may use for this purpose - and actually am a bit pre-disposed towards it because using it would mean practically no influence on the rod's vibrations - something the accelerometer cannot quite achieve.
Might you have experiences with what works best in practice?
Thanks for any feedback
Jesper
Attachments
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Moment of truth ...
Hi again,
Just a brief feedback on the ADI ADXL001 accelerometer that I've mentioned before ... I finally got around to assembling the accelerometer, i.e. mounting capacitors on its backside, and using it for my first measurements.
It's a bit tricky to measure the accelerometer's actual final weight due to the wires attached but it ended up weighing less than 0.2 grams - quite fine I think from the point of view of not influencing the measurements. Should you be interested I've attached a picture of the accelerometer with capacitors and wires (tiny The capacitor lying next to the accelerometer is a 1206 size).
However, the accelerometer is excessively noisy - so much that even with a quite restrictive band-pass filter I reckon that it will only be marginally useful for (any) measurements that does not involve major excursions and fast accelerations. I've had this high noise level confirmed on ADI's webpages so, well, "moment of truth" this time was not too useful.
Just would like to mention it should one of you consider such an accelerometer.
Cheers,
Jesper
Hi again,
Just a brief feedback on the ADI ADXL001 accelerometer that I've mentioned before ... I finally got around to assembling the accelerometer, i.e. mounting capacitors on its backside, and using it for my first measurements.
It's a bit tricky to measure the accelerometer's actual final weight due to the wires attached but it ended up weighing less than 0.2 grams - quite fine I think from the point of view of not influencing the measurements. Should you be interested I've attached a picture of the accelerometer with capacitors and wires (tiny
The capacitor lying next to the accelerometer is a 1206 size).However, the accelerometer is excessively noisy - so much that even with a quite restrictive band-pass filter I reckon that it will only be marginally useful for (any) measurements that does not involve major excursions and fast accelerations. I've had this high noise level confirmed on ADI's webpages so, well, "moment of truth" this time was not too useful.
Just would like to mention it should one of you consider such an accelerometer.
Cheers,
Jesper
Attachments
Hi George,
I would say that it is white noise - the twisted pair cables appear to be quite effective in terms of 50 Hz attenuation. The ADXL001 in itself is quite noisy as discussed in this thread:
https://ez.analog.com/docs/DOC-15747
Cheers,
Jesper
P.S.: If you are interested I can send you the accelerometer assembly with the cables as shown for testing. I can see that you have been working with accelerometers before so, well, if you are interested in trying it out feel welcome to let me know.
I would say that it is white noise - the twisted pair cables appear to be quite effective in terms of 50 Hz attenuation. The ADXL001 in itself is quite noisy as discussed in this thread:
https://ez.analog.com/docs/DOC-15747
Cheers,
Jesper
P.S.: If you are interested I can send you the accelerometer assembly with the cables as shown for testing. I can see that you have been working with accelerometers before so, well, if you are interested in trying it out feel welcome to let me know.
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Hi,
If it is white noise, I don't think that there is something to do.
If it was 50 Hz, I have found that a very effective solution is to wrap a very thin aluminum foil (like the one used in cooking) around the accelerometer and connect this to the ground.
Of course in your case, first you should use something (like a thin plastic membrane) to isolate the active parts from the aluminum.
The added weight is not much and you can measure without the disturbances from the 50 Hz line.
regards
George
If it is white noise, I don't think that there is something to do.
If it was 50 Hz, I have found that a very effective solution is to wrap a very thin aluminum foil (like the one used in cooking) around the accelerometer and connect this to the ground.
Of course in your case, first you should use something (like a thin plastic membrane) to isolate the active parts from the aluminum.
The added weight is not much and you can measure without the disturbances from the 50 Hz line.
regards
George
You might want to look into one of Measurement Specialties' AH-01 piezo accelerometers. Broadband, high output, has internal FET buffer (like an electret mic uses). Not too expensive.
1-1001220-0 Measurement Specialties | Mouser
ACH-01-04/10 Measurement Specialties | Mouser
Hi George & bwaslo - thanks for your replies & suggestions ...
@bwaslo: I've actually already looked at the ACH-01 but I will be measuring structures that are microphone/headphone sizes so I assessed that it - due to its weight - would influence the measurements. As it is I think I will go with a measurement microphone - I already have a couple of B&K 4133 capsules which should be usable for this.
@gdan:
Cheers,
Jesper
@bwaslo: I've actually already looked at the ACH-01 but I will be measuring structures that are microphone/headphone sizes so I assessed that it - due to its weight - would influence the measurements. As it is I think I will go with a measurement microphone - I already have a couple of B&K 4133 capsules which should be usable for this.
@gdan:
... I'll keep this in mind should I run into 50 Hz issues ;-)
Cheers,
Jesper
Hi ... This would be interesting to me as well as I'm about to inquire about samples from obo-werke. In my context the a moulding compound would also be most relevant - so if you have a suggestion here as well I'd appreciate this ...
And then about accelerometers etc.: Would it be (maybe an even better) solution to use e.g. a Panasonic WM-61A microphone capsule instead of an accelerometer? Noise levels probably would be much lower and the weight of the capsule is only 70 mg higher than the ADXL-001 which I reckon is already low weight (the WM-61A weighs 0.22 grams). And it may also be connected with low weight wires and should not be more difficult to mount on the DUT than an accelerometer ...
Any comments on this?
Cheers,
Jesper
Sorry for the necroposting, but gotta do an electronics final test in a few hours and gotta "distract" my mind, XD.
I think we can take this problem as a damped spring mass one. What matters to us is the correlation within the enclousure and driver systems. Cabinet resonances are fixed and driver excite different frecuencies depending on aplication. The worst case scenario would be of course that at which driver and cabinet have the same resonant frecuency. Much below that point the system responds in phase and the amplitude will be aprox dictated by the driver movement. Much above resonance the system responds inverted in phase and the movement will reduce as the frecuency increases.
So, the system will oscilate the most when the driver hits the enclousure resonant frequencies. To reduce oscilation below res stiffnes dominates, in res, damping dominates and above that, mass dominates. I said dominates because the three variables are correlated. For example, damping index is inverse proportional to mass and stiffnes is direct proportional to natural res frecuency of the enclousure. I guess mass matters only for tweeters cabinets at which the frecuencies of the driver are above cab resonance.
So, it seems that a too much stifff cabinet would move the resonance up wich may or may not be good depending on the situation. For example, in a sub, if we can get the the resonance of the enclousure further than the intended max freccuency it will reproducce, it could be nice, as the enclousure would be "planar" in its response, although, it may or may not radiate sound depending on the other variables.
In cases at which the resonant frecuency of the cabinet will be in the frecuency reproduced by the driver then damping is our natural ally. As the damping increses, the resonance amplitude decreases, BUT the amplitude at higher frecuencies increases, or seen in other way, as Freq rises we obtain less attenuation. So, damping seems to be the way to go for fullrangers or midwoofers, as increasing stiffness here would move the resonance to a more auditory sensitive part of the spectrum. In fact, yo may even reduce stiffness to move the res down the lowest frecuency the driver is intended to reproduce.
To finish, if the enclousure has many resonant frequencies the damping should be enough for the intended attenuation at the LOWEST one, as the others will always have better attenuation.
This was all deduced from the basic theory of machinery acoustic isolation and the book "engineering vibration" of Daniel Inman is the more complete in this matter that i know. It may be all wrong, this was just a mental exercise and i´m not really sure how one could increase damping of a cabinet structure (maybe putting some rubber pads somewhere where it matters?)nor how to calculate the structure resonant frecuencies (maybe pink noise and FFT?). Anyway,
All the best,
regards!
I think we can take this problem as a damped spring mass one. What matters to us is the correlation within the enclousure and driver systems. Cabinet resonances are fixed and driver excite different frecuencies depending on aplication. The worst case scenario would be of course that at which driver and cabinet have the same resonant frecuency. Much below that point the system responds in phase and the amplitude will be aprox dictated by the driver movement. Much above resonance the system responds inverted in phase and the movement will reduce as the frecuency increases.
So, the system will oscilate the most when the driver hits the enclousure resonant frequencies. To reduce oscilation below res stiffnes dominates, in res, damping dominates and above that, mass dominates. I said dominates because the three variables are correlated. For example, damping index is inverse proportional to mass and stiffnes is direct proportional to natural res frecuency of the enclousure. I guess mass matters only for tweeters cabinets at which the frecuencies of the driver are above cab resonance.
So, it seems that a too much stifff cabinet would move the resonance up wich may or may not be good depending on the situation. For example, in a sub, if we can get the the resonance of the enclousure further than the intended max freccuency it will reproducce, it could be nice, as the enclousure would be "planar" in its response, although, it may or may not radiate sound depending on the other variables.
In cases at which the resonant frecuency of the cabinet will be in the frecuency reproduced by the driver then damping is our natural ally. As the damping increses, the resonance amplitude decreases, BUT the amplitude at higher frecuencies increases, or seen in other way, as Freq rises we obtain less attenuation. So, damping seems to be the way to go for fullrangers or midwoofers, as increasing stiffness here would move the resonance to a more auditory sensitive part of the spectrum. In fact, yo may even reduce stiffness to move the res down the lowest frecuency the driver is intended to reproduce.
To finish, if the enclousure has many resonant frequencies the damping should be enough for the intended attenuation at the LOWEST one, as the others will always have better attenuation.
This was all deduced from the basic theory of machinery acoustic isolation and the book "engineering vibration" of Daniel Inman is the more complete in this matter that i know. It may be all wrong, this was just a mental exercise and i´m not really sure how one could increase damping of a cabinet structure (maybe putting some rubber pads somewhere where it matters?)nor how to calculate the structure resonant frecuencies (maybe pink noise and FFT?). Anyway,
All the best,
regards!
For a sub, it is a no-brainer. Subs made of MDF are not sane.
And what you say is true, but you also have to keep in mind that as frequencies go up the amount of enerfy to excite a resonace decreases, so if it is high it is less likely to get excited (also related that the material thinkness compared to the HF wavelength makes for more material for the wave to travel thru so HF are killed faster. If you can get the Q of any potential resonance high enuff at a high enuff frquency than there will neve rbe any piece of music that can geenrate an input in a narrow enuff band for a long enuff time to excite the resonce.
So follow the math and there is a potential resonace there, but if it is never excited it is as if it is not there at all (except maybe when you tap it with a hammer).
dave
I like your aproach!
Another advantage that it seems to have is that the movement (but i'm not sure sound radiation) of the enclousure would be in phase with the signal for a wider bass band.
That about the hammer implies transient response wouldn´t be the best for a high stiff no damped material? Does that influence the characteristics and color of the percusive sounds
one usually finds in music?
Got a 6" full range driver project in hands (my first electroacoustic one actually), got to meassure TS parameters and then make the enclousure. Simulation in leonard audio app showed that a teardrop like cab would really help to minimize node antinode difference, but hell, those doesnt seem easy to build. I was thinking about doing it out of a "cast" technique, the way one would do it out of plaster for example, with just some rustic external wood structure. But that would be fragile and probable resonate, other option is ceramics, but again i`m concerned about same issues. Has any one tried some kind of resin or epoxi or more plastic like consstruction with this method? could one paste together wood and spray foam modular shapes to get the final enclousure?
regards!
Another advantage that it seems to have is that the movement (but i'm not sure sound radiation) of the enclousure would be in phase with the signal for a wider bass band.
That about the hammer implies transient response wouldn´t be the best for a high stiff no damped material? Does that influence the characteristics and color of the percusive sounds
one usually finds in music?
Got a 6" full range driver project in hands (my first electroacoustic one actually), got to meassure TS parameters and then make the enclousure. Simulation in leonard audio app showed that a teardrop like cab would really help to minimize node antinode difference, but hell, those doesnt seem easy to build. I was thinking about doing it out of a "cast" technique, the way one would do it out of plaster for example, with just some rustic external wood structure. But that would be fragile and probable resonate, other option is ceramics, but again i`m concerned about same issues. Has any one tried some kind of resin or epoxi or more plastic like consstruction with this method? could one paste together wood and spray foam modular shapes to get the final enclousure?
regards!