Is this how a Subwoofer Crossover is supposed to work?

imhififan1  Shipping costs returning the subs would be a significant portion of the purchase price.  I would rather figure out a way to make them work for me if possible.

Amazon had this:

https://www.amazon.com/Oatey-33403-Plastic-Galvanized-4-Inch/dp/B000H5T1PI

Cheap and it comes by Monday.  More stuff to play with LOL.

kenjit As you know perfectly well I haven't said anything about how the subs sound and that has nothing to do with my question or this conversation.  

erik_squires I can remeasure with one sub and set the crossover to its 200 Hz high point but I'm not sure the results will show much difference but you can never tell.

I am using a Willsenton R8 tube amp to drive Moabs.  If I want to add subs to level out the room nodes they either have to be connected at the DAC which is why the SW12's looked ideal because they have a balanced input so I use the balanced outs from the DAC to the Sub and the RCA out to the R8.  From their web page I can't figure out how the MiniDSP would fit into that setup.  

I appreciate all the input here although I am less enthusiastic about how this thread has devolved into the kind of digressions and name calling that seems typical of Audiogon.  Also, since these forums don't support true threading it is challenging to actually respond to each of you.

Most importantly though, is my starting question, at its simplest, is really just whether or not subwoofer crossovers are supposed to behave the way the Starke crossover is behaving.  

I'll measure an individual sub later this evening and add a setting for 200 Hz.  But assuming that still shows the rolloff starting from the same place, i.e. roughly 50 Hz, regardless of the crossover setting is that normal?

millercarbon Moabs are great but with caveats.  That discussion deserves a separate topic.

audiokinesis

"Your measurements look to me like they are in the ballpark for a variable-frequency second-order lowpass filter.

I can elaborate if you’d like"

Please do since I don't know what that is.

audiokinesis  Duke, Thank you for that elaboration. Very helpful and informative.  I'll make some measurements of a single Starke SW12 this evening as well as a very cheap Klipsch R-12SW that I have lying around and post those results.

OK. I have taken the suggestions to measure a single Starke SW12 subwoofer near miked in the middle of the room sitting on a padded footrest which is about the best I can do to take out any factors other than the subwoofer. Just for yucks I also measured a Klipsch R12SW with similar settings.

You can see the measurements for the Starke SW12 alone here:

https://www.dropbox.com/s/dwpnt5ndcstr3gu/Starke%20SW12%20Crossover%20Settings%20Near%20Field%20Mic....

And here you can see the Klipsch R12SW alone:

https://www.dropbox.com/s/b5qb4r9f8xsasiv/Klipsch%20R12SW%20Near%20Field%20Crossover%20Measurements....

These were measured with the Sub hooked up to the DAC with an RCA cable. I did also measure using a balanced/XLR cable which provided exactly the same curves but with 7 dB of gain which explains why I was having trouble getting the volumes low enough with the Starke when I had it running on a balanced XLR input. So oldhvymec nailed that one. Getting subs and main speakers aligned seems to require using the same inputs which sucks because I have to believe all those Y splitters degrade the signal quality?

Some observations

1) Boy that Klipsch R12SW is a piece of crap! I didn’t expect it to be good but I certainly didn’t think it was that bad.

2) It is kind of impressive that the Starke is only loses 5 dB from 26 Hz to 17 Hz and has such a flat response out to about 60 Hz depending on the crossover setting.

3) Even though the Klipsch curves are so much worse the crossover seems to be functioning in a fundamentally similar way to the Starke so it could be how I thought crossovers ought to work simply aren’t how subwoofer crossovers are designed.

4) It would be nice to see similar curves for a truly high end Rel sub just to be sure.

5) It looks like the Starke SW12 will be very useful for extending the bass response lower and smoothing any room nodes if I play around with positioning them in the room but only below 60-70 hz. I have crazy peaks and valleys with my Moabs between 50-85 Hz that I’ll have to fix some other way.

geared4me I use the volume controls on the R8 to get the rough level and then the volume control on the DAC to fine tune.  The DAC doesn't have any amplification.  The DAC Volume Control only reduces volume.  BUT it turns out having the Subs hooked up with the DAC's Balanced Outputs runs about 7 dB hotter than if you hook them up via RCA.  So that is where the problem with the sub running too loud probably starts since the R8 only accepts RCA inputs and only has speaker level outputs.

1) So I’m not an idiot. Of course I’m setting the volume of the amplifier at a fixed level that approximates my 75 dB listening level and fine tuning volumes with the DAC that then controls what both the amp and the subs see.

2) If I wanted to spend $2-4K on subwoofers I would have, so all the suggestions about buying "audiophile" quality subs will be respectfully ignored.

3) The bass response on the Moabs is great which is absolutely not the same thing as saying the system wouldn’t benefit from well integrated subs. Here is a chart of the Moabs with and without a very old Velodyne CHT10 subwoofer with a speaker level input. As you can see that sub improves the measurements of the system as well as improving how it sounds. I wanted to see if the Starke’s improved things further although so far I’m not sure that is true.

https://www.dropbox.com/s/bf83tvl57i9l0qw/Moab%20with%20and%20without%20Subwoofer%2050Hz%20Crossover...

That REW graph of the Moabs shows a lot of weird stuff in the response above 200 Hz and that was because the Moabs weren't well positioned in the room when that measurement was taken. Where I have the Moabs now the frequency response is +- 5 dB from 100 Hz to 10 KHz except for a little bump around 325 Hz that might be the crossover.
   
All comments about how subwoofers don’t belong in my system will be respectfully ignored.

4) I didn’t think about the fact that the Klipsch was ported so I guess I’ll reserve judgement. Not planning on using that sub with the Moabs anyhow so I will do no further investigation there. And I’m not going to mess around with the Moab’s ports.

5) I need to do some further investigation about the pros and cons of a) leaving things as they are with the tube amp connected to the DAC’s RCA output and the Subs connected by XLR cables. b) using an RCA Y Splitter to connect subs and amp to the same RCA input. c) Millercarbon’s suggestion to adapt subs to a speaker level input. d) when I bought the subs Starke said you could connect one sub to RCA and use the subs balanced out to connect the second sub with an XLR cable. That sounds weird but I may give it a try rather than having multiple Y splitters.

I will note that there doesn’t seem to be any difference in the curve in the subs response when you switch from RCA to Balanced inputs so it isn’t clear to me why so many of you seem to think it is imperative the subs and the amp use the same input as long as volume is controlled further upstream, i.e. at the DAC level.

6) miniDSP looks interesting and perhaps I’ll get one later but not something I want to play around with right now.

Thanks to all of you who are providing detailed constructive comments.

imhififan Interesting suggestion.  I wish they came in 5 or 7 db attenuation.  -10 starts taking the problem in the other direction LOL.

kenjit "Why would anybody design an electronic lowpass filter with a variable slope and a fixed crossover point? Thats useless. What you want is a variable crossover point and fixed slope." 

That is what I thought also and that is what started this whole thread.  But Starke says the subwoofer is designed properly.  And I haven't been able to find any charts that show how other subwoofers respond with changes in the crossover.

Surely some enterprising soul on Audiogon has performed similar measurements on their sub and can post them or knows of a source showing how a "quality" subwoofer works?

Again, thanks to those of you that are providing constructive input.

1) I've put the system back together, moving one sub to a different location and setting phase and crossover frequencies individually for each sub.  I am still using the DAC to provide fine tuning of volume with it connected by XLR inputs to the subs and by RCA to the tube amp, but now that I have a better understanding of what is going on the volume on the tube amp is set higher and the volume on the DAC is lower which helps offset the 7 dB gain of the XLR inputs vs RCA.  You can see a chart here. NOTE this was measured before adjusting Amp volume up and DAC volume down so the low end bass response isn't actually exaggerated in the system.

https://www.dropbox.com/s/j5a418zmk99zqbu/Moabs%20with%20Starke%20Subs%20Green%2C%20without%20Orange...

Adding the subs provides significant low end extension and a slightly smoother response.  I have significant room nodes at 61, 77, and 99 Hz with steep 10-15 dB valleys that I'm not sure what to do about.  The subs don't help with that and moving the Moabs around hasn't done much either.  I don't hear them so that is good.  Any suggestions about smoothing those room nodes?  I've tried a couple of rockwool panels without much impact.

2) Active crossovers or DSP all seem like good suggestions but things that I would explore at a later time.  I do use the EQ in Roon to adjust for some things but I haven't figured out how to use REW to measure the changes Roon makes.

3) My assumption has been using the DAC to control volume is fine and that there is no change in signal quality with volume set at 100 vs 60. Anybody have any idea if that is true?

4)  mijostyn's idea of subwoofer placement on either side of the speakers is interesting but, as many people do, I have my tube amp right in the middle.  It is on springs and isolation pads etc. etc. but it seems risky to have a tube amp in between, and close to, subwoofers.  Thoughts?

In conclusion, mostly I've roundtripped to where I started.  The system sounds great, the subwoofers extend the bass and increase low end impact without sounding exaggerated or noticeable.  At some point in the future I may explore active crossovers or DSP but not now.  I would still love to see measurements for how changing the crossover frequency works on a Rel or other high end subwoofer.

erik_squires  How would you plug the speaker ports?  There are two of them, each about 4 1/4" in diameter.  The peak at 36 Hz is easy to tame with the parametric equalizer in Roon.  No real need for a miniDSP for that.  But the holes at 61, 77, and 99 Hz are too high for the subs to do much to.  The speakers are in my main living space so I'm limited as to what I can do with bass traps or positioning.  But the truth is the system sounds great. Could it sound better with more treatment?  Probably, but there are limits to what I can and would want to do

There is some trick with REW to measure a signal that REW isn't generating, i.e. played through Roon,  but I haven't figured it out yet..