Dustcover Blues

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.

@rauliruegas , I know exactly what is going on. The two chambers above the subchassis are resonating at 24 Hz. This causes the subchassis to bounce at 24 Hz. This is picked up by the cartridge completing the feedback loop. The sub chassis is a solid 1" thick aluminum plate that extends to within 3/32" of all sides of the plinth. Your middle ear has a vent tube to release pressure. It is called the Eustacean Tube. When it gets block your hearing gets damped by up to 10 dB at some frequencies because pressure in the middle ear will not allow the ear drum to move as well. On a hunch I decided to block my turntable's Eustacean Slot with the skirt you see on my system page effectively giving it a hearing problem. It was very easy to test. The first track on Soundgarden's Badmotorfinger gets the feedback going throughout the entire song. With the skirt in place there is none. It is a bit hard to miss. When a 24 Hz feedback loop gets going the entire house shakes.

Right now the skirt works perfectly I just have to dress it up a bit. Yes, I can and will build a new plinth that won't do this when I run across that special plank of wood. If I am going to put in all that effort it has to be very special.