Chances are you don't need stuffing at all with a box that small. As for the booming that's generally caused by a peaking response in the lower midbass, usually indicative of a box that's too small. The Beta 15 in 100l sealed models out with an f3 at 55Hz and a response peak at 90-100Hz, so a boomy response is just what I'd expect you to get. This driver is simply not capable of response below 50 Hz from a box that small; 400l would be the minimum. Using electronic means to flatten the response would lower the broadband SPL to an almost unuseable level.
You must have missed Matt the first time around. We all know he's crazy with that sub of his 
You can't really do any calculations unless you are a maths professor and know the absorptive properties of the pillows. What you can do is measure the Fc and Qc of the box to see what it's changed to. You did measure Fc and Qc before designing the LT, didn't you?
You can't really do any calculations unless you are a maths professor and know the absorptive properties of the pillows. What you can do is measure the Fc and Qc of the box to see what it's changed to. You did measure Fc and Qc before designing the LT, didn't you?
Bottomline is that below 100 Hz there is for all intents and purposes no absorbtive value of stuffing, and the wavelengths are so long compared to internal box dimensions that damping serves little, if any, purpose anyway.
Porpoerly executed his transform might work, but the sensitivity will be so low that he'd need 400W to get anything out of it at 30 Hz or lower, which will be rather taxing on a 200W driver.
Porpoerly executed his transform might work, but the sensitivity will be so low that he'd need 400W to get anything out of it at 30 Hz or lower, which will be rather taxing on a 200W driver.
To determine the effect of stuffing on the response of the sysstem, you could measure Q the way Linkwitz did, before and after stuffing. You can then use the results to tune up your Linkwitz transform circuit. The link shows how to measure the Q.
http://www.linkwitzlab.com/images/graphics/f0Q0.gif
http://www.linkwitzlab.com/images/graphics/f0Q0.gif
Wow, I didnt expect that much of a response so soon. DIYAudio must have changed...
I didnt actually measure the Qc or Fc, WinISD calculated it for me.
The LT is calculated perfectly, but as the Q and Fs have changed due to the stuffing, the response is messed up.
pblossom: Thanks for the links. How do I calculate f1 and f2 described in the Linkwitz image?
Hopefully if I can measure the Fc and Qc accurately enough to re-calculate the LT and get it working properly again.
Should I just take the stuffing out? Do I gain any advantage from the stuffing?
I didnt actually measure the Qc or Fc, WinISD calculated it for me.
The LT is calculated perfectly, but as the Q and Fs have changed due to the stuffing, the response is messed up.
pblossom: Thanks for the links. How do I calculate f1 and f2 described in the Linkwitz image?
Hopefully if I can measure the Fc and Qc accurately enough to re-calculate the LT and get it working properly again.
Should I just take the stuffing out? Do I gain any advantage from the stuffing?
Using figure 18 from my first reply, measure Rmax with the measurement setup in figure 19. You also need to measure the dc resistance of the driver using a VOM. From that you can calculate the square root of Rmax*Rdc. Then tune the oscillator both above and below the frequency of Rmax to so that the meter reads the "square root" to find f1 and f2. At this point you should have all the numbers you need to calculate the equation on the right of Fig. 18, which will give you the Q of the system. That, along with F0 can be plugged into the calculations for the Linkwitz transform circuit to tune it up.
As an aside, if you are going to stuff the box, stuff it full to get the maximum benefit. THe nousaine article can be used as a guide for the amount needed.
As an aside, if you are going to stuff the box, stuff it full to get the maximum benefit. THe nousaine article can be used as a guide for the amount needed.
Matt,
Whether you go for stuffing or not, you should measure Fc and Qc as manufacturers specs are often out. This can be down to poor measurement technique and/or production tolerances.
One danger that I think a lot of DIYers fall prey to is not measuring T/S paramaters properly. I ought to write a webpage for it, I've emailed that many people now I'm getting a bit fed up of writing it! Basically you should calibrate your setup first by measuring every 5Hz or so from 20-100Hz. You will find that with most DMMs the voltage falls relative to 60Hz or so when you start going down in frequency.
I'd recommend you getting hold of a good book like Vance Dickason's Loudspeaker Design Cookbook. I am selling one if anybody is interested! Looking for a fiver for it, and it's in perfect condition.
Whether you go for stuffing or not, you should measure Fc and Qc as manufacturers specs are often out. This can be down to poor measurement technique and/or production tolerances.
One danger that I think a lot of DIYers fall prey to is not measuring T/S paramaters properly. I ought to write a webpage for it, I've emailed that many people now I'm getting a bit fed up of writing it! Basically you should calibrate your setup first by measuring every 5Hz or so from 20-100Hz. You will find that with most DMMs the voltage falls relative to 60Hz or so when you start going down in frequency.
I'd recommend you getting hold of a good book like Vance Dickason's Loudspeaker Design Cookbook. I am selling one if anybody is interested! Looking for a fiver for it, and it's in perfect condition.
pblossom said:
Adjust the frequency of the signal generator until the resistance is equal to the square root of the Rmax*Rdc equasion to get f1 and f2, right?
richie00boy said:
Im interested.
E-mail me your address and i'll post you a fiver. Or I can send you it over paypal if you use it. matttcattt@gmail.com
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