Hi All
I just got told (by speaker mnfr) to go somewhere else and ask my dumb question...
I'm looking for a small woof up to 10", that will give f3 below 40 Hz in a sealed cabinet.
My dumb Q: Has anyone tried adding mass to a woofer cone, e.g. by adding a metal ring or epoxy near the dustcap. This would lower the fs and enable operation to lower frequencies in closed box. The cost is higher Q of the driver - bigger cabinet volume, and a loss in sensitivity. By my reckoning, adding about 30% extra mass to one of the Dayton 8" drivers would have the desired effect.
I've not done any detailled calculations but adding mass is simply adding motional impedance to the driver so that the forces etc are not much different, low f excursions might be a little greater, but no more than OB design.
My only concern is that the strange mass distribution might trigger peculiar motions in the driver movement at some point.
Anyway... has anyone tried this?
regards
Rod
I just got told (by speaker mnfr) to go somewhere else and ask my dumb question...
I'm looking for a small woof up to 10", that will give f3 below 40 Hz in a sealed cabinet.
My dumb Q: Has anyone tried adding mass to a woofer cone, e.g. by adding a metal ring or epoxy near the dustcap. This would lower the fs and enable operation to lower frequencies in closed box. The cost is higher Q of the driver - bigger cabinet volume, and a loss in sensitivity. By my reckoning, adding about 30% extra mass to one of the Dayton 8" drivers would have the desired effect.
I've not done any detailled calculations but adding mass is simply adding motional impedance to the driver so that the forces etc are not much different, low f excursions might be a little greater, but no more than OB design.
My only concern is that the strange mass distribution might trigger peculiar motions in the driver movement at some point.
Anyway... has anyone tried this?
regards
Rod
Hi, well how rude of the speaker mnfr 😛 Care to name n shame em ?
Yes it's been done before over the years. The problem would be getting the correct amount to stay put, & not resonate etc ! Plus as you say, it would alter Lots of other parameters also, which could be a time consuming headache, & still not end up with a good design !
Better ways to achieve sub 40Hz are,
1 - Linkwitz Transform
2 - Sourcing a driver with fs = 20Hz or lower
Yes it's been done before over the years. The problem would be getting the correct amount to stay put, & not resonate etc ! Plus as you say, it would alter Lots of other parameters also, which could be a time consuming headache, & still not end up with a good design !
Better ways to achieve sub 40Hz are,
1 - Linkwitz Transform
2 - Sourcing a driver with fs = 20Hz or lower
Thanks Zero D
I'd better not shame - hes really a nice helpful guy 🙂
Will look up Linkwitz Transform
I did find one really good driver - Scanspeak 23W 4557 : fs =21 Hz, Qt=0.47, very good but also very expensive. One of the Dayton drivers is very close, f3=40, and might have to do.
regards
Rod
I'd better not shame - hes really a nice helpful guy 🙂
Will look up Linkwitz Transform
I did find one really good driver - Scanspeak 23W 4557 : fs =21 Hz, Qt=0.47, very good but also very expensive. One of the Dayton drivers is very close, f3=40, and might have to do.
regards
Rod
calculator for adding mass....mh-audio.nl - Home
seems easy and thus tempting to just raise the Qts to get low bass in closed box
........but I would be very cautious with that
also be aware that there may be several reasons for a low Qts
and a few of them could be related to poor design(cheap)
seems easy and thus tempting to just raise the Qts to get low bass in closed box
........but I would be very cautious with that
also be aware that there may be several reasons for a low Qts
and a few of them could be related to poor design(cheap)
It will not improve the low frequency response (aside from the right
around the Q peak), only attenuate the high frequency response...
If you lay before and after graphs upon each other, the extreme left
sides of those graphs would still be identical...
If you had an extreme low Q driver to begin with, only then it might
make sense. But only under the Q peak are you "gaining" anything.
Its always a lossy proposition when you add dead weight.
around the Q peak), only attenuate the high frequency response...
If you lay before and after graphs upon each other, the extreme left
sides of those graphs would still be identical...
If you had an extreme low Q driver to begin with, only then it might
make sense. But only under the Q peak are you "gaining" anything.
Its always a lossy proposition when you add dead weight.
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Indeed, the output is limited by the area of the radiator.
That's why single 8" and single 10" bass only woofers don't work at sensible volumes.
Golf,
have you considered 4off 10" for bass support?
That's why single 8" and single 10" bass only woofers don't work at sensible volumes.
Golf,
have you considered 4off 10" for bass support?
There's something to be said for the Bag End approach: use an efficient driver with a high F3 in a sealed box, then apply a lot of EQ to boost the low end. However, for best results it does need a processor. Initially I assumed that just sticking a filter in the sidechain of a limiter would do it, but that would affect the midbass as well. Bag End's processor uses something like a VCF rather than a VCA to gradually cut off from below. I wonder if that can be implemented using a DCX2496?
Hi all
Lots of questions…
Suppose we start with a driver of given fs and lowish Qts. Such a driver in an infinite baffle might be said to have a weak bottom end. There are two ways we can lift the Q and flatten the pass band.
Firstly, we can stiffen (lower) the compliance by adding a cabinet, which raises the fs and lowers the excursion at low frequencies. The fs rises as sqrt(1/compliance), as does the Q. The excursion at low frequencies falls in direct proportion to falling compliance.
Secondly, we could increase the mass of the cone, which moves the fs down at the expense of loss of sensitivity in the midband. The Q increases as the sqrt(total mass), fs falls also in proportion to the sqrt(total mass) whereas the sensitivity drops in direct proportion to the mass.
The first solution trades the bottom end and bandwidth for flatter midband, the second solution trades sensitivity for bandwidth and flatter midband. No free lunch. The first solution also has the benefit of not burning the driver warranty.
There are a heap of small woofers about that in a sealed box give an f3 just below 50 Hz – some as low as low 40’s. I would be prepared to pay 30% in sensitivity to get f3 below 40 Hz – SPL nominally flat to 40 Hz say (below the lowest note on bass guitar). A 30 % increase in mass would increase Q by 15%, lower fs by 15%, and cost 30% in sensitivity.
Yes the easiest solution is to splash out on a grown-up woofer, but for some of us WAF (wife acceptance factor) is an important specification, and a small ~40 L cabinet has some value – and I don’t feel the need for Richter scale bass. (Could trade the wife I supposeJ)
I was just curious to know if anyone has experience of trying this – any tricks, suggestions?
best wishes
Rod
Lots of questions…
Suppose we start with a driver of given fs and lowish Qts. Such a driver in an infinite baffle might be said to have a weak bottom end. There are two ways we can lift the Q and flatten the pass band.
Firstly, we can stiffen (lower) the compliance by adding a cabinet, which raises the fs and lowers the excursion at low frequencies. The fs rises as sqrt(1/compliance), as does the Q. The excursion at low frequencies falls in direct proportion to falling compliance.
Secondly, we could increase the mass of the cone, which moves the fs down at the expense of loss of sensitivity in the midband. The Q increases as the sqrt(total mass), fs falls also in proportion to the sqrt(total mass) whereas the sensitivity drops in direct proportion to the mass.
The first solution trades the bottom end and bandwidth for flatter midband, the second solution trades sensitivity for bandwidth and flatter midband. No free lunch. The first solution also has the benefit of not burning the driver warranty.
There are a heap of small woofers about that in a sealed box give an f3 just below 50 Hz – some as low as low 40’s. I would be prepared to pay 30% in sensitivity to get f3 below 40 Hz – SPL nominally flat to 40 Hz say (below the lowest note on bass guitar). A 30 % increase in mass would increase Q by 15%, lower fs by 15%, and cost 30% in sensitivity.
Yes the easiest solution is to splash out on a grown-up woofer, but for some of us WAF (wife acceptance factor) is an important specification, and a small ~40 L cabinet has some value – and I don’t feel the need for Richter scale bass. (Could trade the wife I supposeJ)
I was just curious to know if anyone has experience of trying this – any tricks, suggestions?
best wishes
Rod
I remember 'way back when I worked for Infinity, building 1001 model speakers, we used a product called, "perma gum" to add mass to our 12" woofers. Pressed it in at the junction between dust cap and cone. Stuck well, and seemed to be permanent. Back then, we didn't measure stuff (early 1960s), but did it all by ear....
Polydax makes some very inexpensive 10" speakers with an Fs where you are talking about. I would look at the specifications on some of their drivers. The one I am thinking about has a polypro cone and moves plenty of air. Can't remember a model number off the top of my head.
Efficiency go's down a lot of course and an 8" is already not too efficient in the low bass.
If I would do so, for testing purpose, it would be to glue fiberglass all over the cone. Preferably glue that isn't too hard nor springy, for dampening reasons.
You get the weight AND reinforcement. 🙂
If I would do so, for testing purpose, it would be to glue fiberglass all over the cone. Preferably glue that isn't too hard nor springy, for dampening reasons.
You get the weight AND reinforcement. 🙂
Initially just tape or attach some dimes to the cone and measure the reduction in fs as you add weight. If I remember correctly each dime was a gram in weight but would have to check that. After you know how much weight you want to add to increase the mass and lower the fs you can then permanently add your mass to the cone. A ring of silicon around the dust cap cone junction could work and the mass is close to the center so won't be as critical as weight added farther out and causing an imbalance in the cone and voice-coil rubbing. I wouldn't use anything that was rigid to add the weight as that may resonate and make some nasty noises. You could carefully remove the dust cap and put the added mass behind that and reattach the cap which would hide the added mass and you could add all of the mass in the center of the cap. This would have the advantage of not changing the stiffness of the cone in any way.
I once tried to calculate the exstra mass for a 15" PRO woofer to make it suited for closed box
it needed about 100gr
and I decided to try my luck with vented instead
really hate the thought of destroying a fine expencive woofer
and a cheap woofer is never going to make it
seriously, it will just blupper along
but if you have the money and time to waste on experimenting, I guess no harm in trying
who knows, you may be lucky
it needed about 100gr
and I decided to try my luck with vented instead
really hate the thought of destroying a fine expencive woofer
and a cheap woofer is never going to make it
seriously, it will just blupper along
but if you have the money and time to waste on experimenting, I guess no harm in trying
who knows, you may be lucky
tinitus,
Yes most Pro drivers are going to have a very stiff suspension to begin with, a stiff spider and stiff surround and would take a lot of weight to shift the fs much as you found out. But most hifi speakers won't have those stiff suspensions and usually have a fairly light cone to begin with so it is easier to shift the fs by adding weight.. Not saying it is the best way to do this, just that you can. I would rather get a driver with the fs that I was looking for in the first place. That is why I mentioned the Polydax 10" drivers, they are fairly cheap compared to most drivers that go down low and have a good Xmax value.
Yes most Pro drivers are going to have a very stiff suspension to begin with, a stiff spider and stiff surround and would take a lot of weight to shift the fs much as you found out. But most hifi speakers won't have those stiff suspensions and usually have a fairly light cone to begin with so it is easier to shift the fs by adding weight.. Not saying it is the best way to do this, just that you can. I would rather get a driver with the fs that I was looking for in the first place. That is why I mentioned the Polydax 10" drivers, they are fairly cheap compared to most drivers that go down low and have a good Xmax value.
Thanks for that weltersys,
I was off in the weight but they are very consistent from one to another so at least it is easy to use them. It has been awhile since I did that, but they work well when testing to get values when looking at the shift doing testing, made it easy to do some T/S testing with my Cleo system.
I was off in the weight but they are very consistent from one to another so at least it is easy to use them. It has been awhile since I did that, but they work well when testing to get values when looking at the shift doing testing, made it easy to do some T/S testing with my Cleo system.
Interesting. I would have thought our coins would be similar. Apparently not.
http://www.bcscta.ca/resources/hebden/chem/Coin Compositions.pdf
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