Dustcover Blues

@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.)

Dear @mijostyn  : Thia is what I posted:

"" 

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 in ""

You posted: " sealing off the space under the turntable with a skirt. "

You with all your measure tools still does not know what happened down there with out the skirt.

" The final solution is a new plinth... ", yes that's the easy road to go that not necessary warranty success: maybe yes or maybe not.

R.

Dear @lewm   : "" 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..""

Who told you all that including that no sense " fast " woofer or your statement came from your first hand experiences and I said " first hand experiences " because you are totally sure about. Could you explain it?

Btw, please read this link:

http://www.soundstagenetwork.com/maxdb/maxdb061999.htm

R.

@lewm , It can work either way. I think the majority of people building subwoofers come up with a design concept, then choose an appropriate driver and finally given the parameters of the specific driver tweak the dimensions of the enclosure to suit. 

If you look at the picture of my system on the floor you will see a woofer to the outside of each panel then in the center those two boxes on the floor are subwoofers. They are pointed at eachother. These woofers have 200 lb sealed enclosures with a Q of 7.6. 

The new design is a decagon cylinder with 1.5 to 2" side walls (they vary). There will be a 12" driver mounted in each end. They will also be sealed. There is no reason to resort to ports when you have advanced "room control" which is really speaker control. With enough power you can make a subwoofer do just about anything. I would have liked to use larger drivers but space will not allow.

The tonality of a system is debatable and we all have our own preferences. What is not is image and detail. DSP allows you the adjust the frequency response of the channels individually so that they are exactly the same. This gives the best image and with it detail. Every audiophile that has heard it goes out and gets a processor and I am not kidding, every single one. 

Lastly, there is no such thing as a "fast subwoofer" when a woofer is not fast enough it's high frequencies roll off. Usually, the cone breaks up first.  Even 18" drivers can make it to 500 Hz. I think what people really mean by this is muddy vs well defined. Mud is coming primarily from the enclosure. Then there is the amp's ability to control the driver. Some amps are good at it, others not so hot. You need a powerful amp with a very low impedance output stage. Transmission lines are a way of effectively doubling the size of the driver at certain frequencies. They are very difficult to make and require a lot of trial and error tuning. It is much easier to use large drivers or a multitude of small ones.