Dustcover Blues

@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.

Mike, You sure get up early in the morning.  More important or at least as important in conceiving a supplementary woofer or subwoofer is the cabinet design. The choice of cabinet type would affect the choice of woofer, I would think.  So what are you going to build, acoustic suspension, bass reflex or other ported design, open baffle, or what?  (I can't be sure from your photos what type of cabinet you are presently using, either, and I don't see 4 woofers.  Where are the other 3?) For me, I don't care much about frequencies below 30Hz.  I much prefer a "fast" woofer that can mate well with an ESL around the crossover point.  A seamless blend is hard to come by, even if using an 80db/octave slope, or especially so if using such a very steep slope.  I have no dog in this fight; I'm just curious to learn. I long ago decided on a fast, smallish woofer in a Transmission Line enclosure as my ideal for mating with a full-range ESL or an ESL that needs help at low frequencies.  If I wanted more oomph (as in SPLs) I would use two or more of such agile woofers per channel.

By the way, I agree with you, everything can be measured.  But sadly, once you've done that and technically perfected the frequency response in room, I have yet to hear a system that was obviously benefited by such contouring. (On the other hand, in the past several years, I have not auditioned that many systems other than my own.)