Dustcover Blues

My problem is occuring just above the cutoff frequency.

@mijostyn Filter theory says that the greater the filter slope, the greater the hump is prior to cutoff- and the closer to the cutoff frequency. A digital filter might behave differently (some do, some don't) but a simple solution might be to move the cutoff down a few Hz so as to get the turntable resonance out of the filter bump that occurs just above cutoff.

That should be easy- worth a try.

@atmasphere , I can do that easily. I'll give it a go tomorrow. 

@limomangus , I'm not quite sure what you are saying. You have had a number of turntables and you have used them with the dust cover on and off and do not have any problems with either?

Dear @mijostyn :  If you are using paper cone I think that you have to stay that way ( btw, I cross too at around 100hz. My Velodyne HGS are heavy modified by me because its electronics design: input and crossover are very poor but great all other design/build. ). Stay away of other cone material on subs.

Now, I think that you are not measuring what you need to measure ( I don't know what you need to measure. ) or you are doing not in the rigth way.

In theory everything can be measured " problem " is what to measure and you have to " figure " out about instead to use your time in this thread.

R.

Mike--you say the bass frequency response is pretty much the same all along the TT shelf--is the bass response pretty much the same all along the left wall?  or could you possibly slide the entire cabinet one way or the other to find a bass null at 20-30 Hz---or would that be a real PITA?

@wyoboy , several issues. The first is that the cabinet is built into an alcove so it is definitely not moving. The second is that I designed the room so that it has no back wall. It is broken up between the kitchen and dinning room, the nearest solid wall being about 75 feet away. I also use line arrays which limit dispersion so as to minimize room effects. There is some modal behavior but it is very weak in comparison to the usual situation. The bass at both side walls is very much determined by the boundry effect. In order to get the turntable to a balanced frequency response environment I would have to put it out in the middle of the room. 

@rauliruegas , I owned Velodynes for perhaps a decade in the 90's and I got them working tolerably well but I was using an outboard crossover.  IMHO the major problem with subwoofers is not the cone material but the enclosure and positioning of the drivers. Any good subwoofer driver 12" and up is capable of beating 0.5% distortion it not over driven. Everything else comes down to enclosure resonance and shaking. For commercial subs Your Velodynes are not bad but (and I really mean this politely) they are not near as good as what I am using now never mind. what I have in store. I aim to build the most accurate subwoofers possible with current drivers and I will do it. (or go broke trying)  As for measuring. How do you know what and how I am measuring except the tools I have mentioned in these threads? The only part of a HiFi system that is not measurable is the human mind. Everything else is easily measured with the right tools. The bane of speaker design has for decades been the room they are placed in and even that is measurable. Any problem you identify can be fixed. If you can't identify it it becomes a mystery and something you "can't measure."  

As for my dustcover problem. That has been fixed by sealing off the space under the turntable with a skirt. I can now bury the volume with the dustciver down and it will not feed back. I put a picture of the solution up on my system page. The final solution is a new plinth which I will get around to when I find that special plank.