I have a 12 inch no-name PA bass driver with no T/S parameters whatsoever. Only 600Watts and 40Hz to 7KHz
I have put it in a sealed 2 cubic feet enclosure to try but Frequency responds starts to drop sharply around 50Hz and going to null around 30Hz.
Is is possible to lower the Fs of the driver by adding mass to the speaker cone of Dust cap, or both.
I don't mind lowering the sensitivity of the driver if it means getting better response @ 30Hz. I can always dial up the power on the dedicated amp.
By adding mass I was thinking about using epoxy glue, wood glue etc (any idea welcome). mostly around the dust cap. Is this completely stupid and will I just damage the speaker beyond repair or will this have a chance to work?
Thierry
I have put it in a sealed 2 cubic feet enclosure to try but Frequency responds starts to drop sharply around 50Hz and going to null around 30Hz.
Is is possible to lower the Fs of the driver by adding mass to the speaker cone of Dust cap, or both.
I don't mind lowering the sensitivity of the driver if it means getting better response @ 30Hz. I can always dial up the power on the dedicated amp.
By adding mass I was thinking about using epoxy glue, wood glue etc (any idea welcome). mostly around the dust cap. Is this completely stupid and will I just damage the speaker beyond repair or will this have a chance to work?
Thierry
What you plan to do is quite irreversible so the advise to first measure your loudspeakers makes eminent sense. Understand what you want to do before you start doing it.
BTW, PA speakers typically don't go very low. 50 Hz is not that bad at all. When you increase the weight of the cone, it is not just the efficiency you will change. You will also increase Qt, which means that your enclosure needs to be larger than it used to be. If you don't at the same time increase the size of the enclosure, you might not notice any change in low frequency response. Another issue is Xmax. If you weigh up the driver, you might improve the bass response somewhat, but at the risk of the driver bottoming out. To reproduce 30 Hz requires a lot more Xmax than 50 Hz for the same SPL.
BTW, PA speakers typically don't go very low. 50 Hz is not that bad at all. When you increase the weight of the cone, it is not just the efficiency you will change. You will also increase Qt, which means that your enclosure needs to be larger than it used to be. If you don't at the same time increase the size of the enclosure, you might not notice any change in low frequency response. Another issue is Xmax. If you weigh up the driver, you might improve the bass response somewhat, but at the risk of the driver bottoming out. To reproduce 30 Hz requires a lot more Xmax than 50 Hz for the same SPL.
I roughly doubled the moving mass of my PA speaker to get the new shape of the vented roll off I wanted.
BTW,
I used lead sheet, beaten into a thin foil, stuck on with double sided tape. And retested the T/S params.
In the process I threw away about 6dB of sensitivity in the midrange and upper bass, to maintain sensitivity in the lower bass.
I reported some of my experiments in a Tannoy B950 post.
I considered it a great success going from 101dB/2.83V@1m to ~95dB/2.83V@1m
BTW,
I used lead sheet, beaten into a thin foil, stuck on with double sided tape. And retested the T/S params.
In the process I threw away about 6dB of sensitivity in the midrange and upper bass, to maintain sensitivity in the lower bass.
I reported some of my experiments in a Tannoy B950 post.
I considered it a great success going from 101dB/2.83V@1m to ~95dB/2.83V@1m
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Ok, thanks everyone. I thought this "might" work, but I don't want to risk ruining the driver completely. Xmas does not seem to be very high :S but this PA driver has very stiff suspension that wont seem to mind a little weight on the cone, or so I think.
I think it is a 97db driver. I won't mind going lower.
I have an idea that I'll just try sticking some Blue-Tack around the dust cap (and even sticking lead to the blue-tack itself) and measure to see if it changes for the better. I can easily remove the Blue-Tack if does not work.
I'll also see if I can gather the courage to understand how to measure T/S for a driver.
I think it is a 97db driver. I won't mind going lower.
I have an idea that I'll just try sticking some Blue-Tack around the dust cap (and even sticking lead to the blue-tack itself
) and measure to see if it changes for the better. I can easily remove the Blue-Tack if does not work.I'll also see if I can gather the courage to understand how to measure T/S for a driver.
Ok, thanks everyone. I thought this "might" work, but I don't want to risk ruining the driver completely. Xmas does not seem to be very high :S but this PA driver has very stiff suspension that wont seem to mind a little weight on the cone, or so I think.
I think it is a 97db driver. I won't mind going lower.
I have an idea that I'll just try sticking some Blue-Tack around the dust cap (and even sticking lead to the blue-tack itself
I'll also see if I can gather the courage to understand how to measure T/S for a driver.
You can certainly add mass to a driver to change it's FS and sensitivity. However, if you are at all concerned about frequency response and longevity of the driver you'll want to work to get that mass right at the apex of the voice coil and cone.
Check out the link in my signature...I've actually added mass to a 5.5" woofer in a two way design. A cheap, easy way to make a mass ring is to use heavy gauge copper wire. All the details are in the DIYRM-A design guide at the link.
If you add it to the dustcap I'd be concerned about rocking modes and "oil-canning" at high excursion. The woofer can actually start rocking up and down, and depending on how tight the gap is, you can start making contact between voice coil and the hard parts of the motor.
Once you measure the T/S parameters of the woofer you can use basic algebra to work out how much mass to add to get the response you want. I have a spreadsheet that I can send you if you get stuck.
Scott
Even if you get the LF response you want, the HF may be useless. If you change the profile or stiffness of dustcap and/or the apex of the cone, the high end response will change. The highs radiate from the center. If you planned on crossing over where you are supposed to (where everything is pistonic, and the dispersion is not narrowing) then it would be fine. If you planned on pushing past this, the resposne you get may be an unpleasant surprise.
wg_ski,
The impact on the shape of frequency response from mass added to the apex of the cone is minimal to non-existant. Please see the measurements I took on a Dayton RS150P, in the document linked in my sig. The *only* practical change is sensitivity
I agree if you add the mass to a dustcap, or if you let the mass get too far up the cone towards the surround it can change the breakup modes of the speaker.
If done properly...it really won't change anything.
Besides, it sounds like he's using this for a subwoofer...so it may not matter.
Scott
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Back in the early '70s, I was working for Infinity, and we did add "Permagum" a putty-like substance to all of the woofers for the 1001 speakers, just to improve bass performance. The stuff was a sticky, putty-like substance that stuck well, and could be removed. We did this in production to hundreds of speakers. . . Mostly 12" CTS drivers.
They have TSP's! ...
and even if they were published, you should still measure them for the drive(s) you have. Start with the enclosure(s) you have, and determine the TSP's of the driver(s) needed. Once armed with that information, you will be in a better position to know how to proceed. The driver(s) you have may be incapable of meeting the mission you have planned for them. The need to add mass to the moving system, contraindicates driver suitability for this mission. Typically mass increases are sustained to increase driver [sd] and/or [bl] while lowering [fs] as well. It may be easier to swap out these driver(s), than to rework them.
Regards,
WHG
and even if they were published, you should still measure them for the drive(s) you have. Start with the enclosure(s) you have, and determine the TSP's of the driver(s) needed. Once armed with that information, you will be in a better position to know how to proceed. The driver(s) you have may be incapable of meeting the mission you have planned for them. The need to add mass to the moving system, contraindicates driver suitability for this mission. Typically mass increases are sustained to increase driver [sd] and/or [bl] while lowering [fs] as well. It may be easier to swap out these driver(s), than to rework them.
Regards,
WHG
I have a 12 inch no-name PA bass driver with no T/S parameters whatsoever. Only 600Watts and 40Hz to 7KHz
I have put it in a sealed 2 cubic feet enclosure to try but Frequency responds starts to drop sharply around 50Hz and going to null around 30Hz.
Is is possible to lower the Fs of the driver by adding mass to the speaker cone of Dust cap, or both.
I don't mind lowering the sensitivity of the driver if it means getting better response @ 30Hz. I can always dial up the power on the dedicated amp.
By adding mass I was thinking about using epoxy glue, wood glue etc (any idea welcome). mostly around the dust cap. Is this completely stupid and will I just damage the speaker beyond repair or will this have a chance to work?
Thierry
Don't.
You said it is a "cheap" driver.
Cheap driver = will not handle much power.
Adding mass will lower the F3, and as noted drop the sensitivity. Which means you will crank it more, and either clip the amp (more than it already is) and/or over power the driver, which will cause it to flame out. x__x
Anything cheap that says "600 Watts" on it really means that they spec'd the overhead lights in the warehouse at 600 watts each and used that figure. You can count on a solid 100watts maximum. Unless you get/got lucky.
_-_-bear
You said it is a "cheap" driver.
Cheap driver = will not handle much power.
Adding mass will lower the F3, and as noted drop the sensitivity. Which means you will crank it more, and either clip the amp (more than it already is) and/or over power the driver, which will cause it to flame out. x__x
Anything cheap that says "600 Watts" on it really means that they spec'd the overhead lights in the warehouse at 600 watts each and used that figure. You can count on a solid 100watts maximum. Unless you get/got lucky.
_-_-bear
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