[mlundy57]

I have built a modified pair of the Best Speaker Stands Ever. I am using two of the 8" X-sub drivers in each one with a Yung 300W plate amp. These are non-servo drivers. The open back did not work, so I experimented with closing off differing amounts and settled on closing the entire back except for a 2" opening at the bottom.

After building them out I am not getting the results I expected.

First, the volume control on the plate amp can only be set a little above minimum or the bass is way too loud.

Second, with the volume set at almost minimum the drivers will still overextend on very heavy movie effects like at the very beginning of Serenity.

Finally, with the volume set at almost minimum, the bass is still boomy.

In this stand the drivers face in opposite directions. They are currently wired in phase with each other.

What would happen if:

1) I wired the two drivers out of phase
          or
2) I disconnect the bottom driver and let it act as a passive radiator?

Mike

[jcotner]

I'm not the expert, but since nobody else volunteered....
Seems like I remember with two drivers opposing
each other, they should be wired out of phase.
Box configuration may alter this assumption, I'm
thinking this applied to sealed box.
Also is it possible that the amp is being over
driven? I took a glance at the spec sheet for
the amp and they are calling for low level of 210mv
or high level of 3 volts. I'd just grab my o-scope
and measure it, you may not have one but you
can use a volt meter set to AC and drive with
a know waveform (test tone) to get Peak-Peak
voltage.
Also not sure of driver impedance, but remember
series wiring double and parallel wiring halves
the impedance. If the resultant load is too low
it could cause some issues I would imagine.
Maybe this will give you some things to think
about until somebody else can offer something up.

EDIT: Kind of surprised nobody else has answered.
With regards to passive radiator, it will work but
your box needs to be sealed to make it very useful.
So I don't know about the 2" opening and how
much the active driver will modulate the passive.
Maybe somebody else has done that one.

[mlundy57]

Thanks,

I haven't noticed Danny on the board today so maybe he will chime in later. 

Mike

[Captainhemo]

Hey Mike

As you know, in that design I  believe the   drivers are wired  in phase as you have them ( I know your 12's are servo but  are they not also wired in phase ? ).
I am not sure of the specs  for that driver (s), I wonder if they will work in a sealed  enclosure and if so, what would the optimal air space be ?   Have you calculated  what the  space would be if you totally  sealed up the back side of the  wedge ?   
Right now, I'd think by only having  say 1/3 open, it is going to be  acting almost as a port (all be it a crude one) and just incresing the volume which you obviously don't need / want .

Like you say, hopefully Danny will have some ideas , I think no matter what, you're going to need to know that air space
jay

[mlundy57]

Hey Mike

As you know, in that design I  believe the   drivers are wired  in phase as you have them ( I know your 12's are servo but  are they not also wired in phase ? ).
I am not sure of the specs  for that driver (s), I wonder if they will work in a sealed  enclosure and if so, what would the optimal air space be ?   Have you calculated  what the  space would be if you totally  sealed up the back side of the  wedge ?   
Right now, I'd think by only having  say 1/3 open, it is going to be  acting almost as a port (all be it a crude one) and just incresing the volume which you obviously don't need / want .

Like you say, hopefully Danny will have some ideas , I think no matter what, you're going to need to know that air space
jay

Jay,

These stands aren't wedge shaped, they are rectangular. Inside dimensions are 5" x 10" by 24.5" which is appx 0.72 cubic ft.

I disconnected the bottom driver and plugged the port tonight. The bass is tighter but I am still getting bottoming. I don't know if it is the active driver or the passive one that is bottoming though. What I have been reading about passive radiators is that the X-max of the radiator has to be two times that of the active driver. This leads me to think the bottoming is coming from the passive driver but I can't be sure.

Mike

[Danny Richie]

If you wire them out of phase then they will cancel the output at 90 degrees off axis just like an open baffle design turned sideways. So that won't work.

Using one as a PR won't help either.

You might be over driving that amp and then it is over driving the speakers. It won't take much to over drive them in a sealed box, or one tuned that high. Remember the X-Sub had a hugely long port to tune them low and help keep them under control down low.

[jcotner]

If you wire them out of phase then they will cancel the output at 90 degrees off axis just like an open baffle design turned sideways. So that won't work.

Danny since we are on this, I know I've read somewhere there are occasions
where two opposing subs in a sealed box were wired out of phase.
Something to do with magnet facing magnet or both magnets facing rear,
which I guess puts one on the outside of the box.
How does that work?

[Danny Richie]

Danny since we are on this, I know I've read somewhere there are occasions
where two opposing subs in a sealed box were wired out of phase.
Something to do with magnet facing magnet or both magnets facing rear,
which I guess puts one on the outside of the box.
How does that work?

The only reason to run them in a push pull configuration like that is that it cuts the size of the box in half.

Still they will cancel the output at 90 degrees off axis. So one of the woofers must face you.

[jcotner]

Yes that makes sense to me now.
I was having a hard time visualizing
exactly how Mike's boxes were set up.

[mlundy57]

Here's what I was trying to do (these are a picture of the ones Danny built:



However, instead of using the 8" servo drivers and the HX300 amps which these were designed for, I tried building a pair of stands like this using the 8" non-servo X-sub drivers (ported box sub) and Yung 300W plate amps.

The reason was simple, I already had a supply of these amps and drivers. I had bought them for X-Subs which I hadn't got around to building yet so I thought I'd try using what I had. I modified the stands by closing in most of the back. Unfortunately, this did not work. There is simply not enough air space in these stands for the X-Sub drivers to work properly.

I think I have figured a way to salvage these stands. It will require buying two different drivers that will fit the openings and will work with this air space and two passive radiators that will also fit the openings and take the place of the port.

Although this looks like it should work on paper, I won't know until I try.

Mike