Calibration is frustrating

[Egil]

Greetings!

I currently have 2x DIY subs, one with an Rlp15 (tuned to 15.5hz) and one Rlp18 (tuned to 22hz). I finally decided to measure their freq. response, and ended up with this:

Rlp15:

RLp18:

Both subwoofers together:

Rlp18 with phase180

Rlp15 and Rlp18 (With Phase 180)



I got a nasty peak at 26.6hz. I think this can be fixed, just by lowering the SPL on both subwoofers at 26.6hz, on my DCX2496.

It also seems that the Rlp18 has the best freq. response when it's phase is set to 180. But it still drops like a rock below 26.6hz.

Rlp15 + Rlp18 (Phase180) seems to at least have potential for SOME lowend. But from 26.6hz - 40hz there seems to be a null.

I don't know what else to do than to move the subs, until I get a decent flat response from 26.6hz and up to 80hz.

But what im having problems finding out, is where all the SPL goes from 26.6hz and below! I should have good output at least down to 15hz (even though the Rlp18" is just tuned to 22hz.. even that subwoofer should have good output to 20hz). I suspect that there may be something I have configured wrong on the DCX2496 - since it drops like a rock under 26.6hz. On the DCX2496 the Rlp18 is configred to: "BUT48" and "20hz". All my subwoofers are connected to "INPUT C" on my DCX.

Any ideas what might be wrong ?

[brucek]

You have the graphs set to LIN (linear). Change to LOG (logarithmic). The button is call Freq Axis and is located in the top right corner of REW screen.

Also, when measuring a sub, best to sweep to 200Hz.

Phase basically has little effect with a single speaker. It is most noticed in the interaction of two speakers. Adjust your phases with both subs playing together...


brucek

[Egil]

I have stacked the subwoofers again, and in a different position.

And I've taken som new measurements, with correct axis:

Rlp15"

Rlp18"

Both:


If I've done things right now, it finally seems like I got some lowend..! (On each subwoofer that is. not together!)

Only problem now, is how to get rid off that decrease below 26hz, when they are both on. Is phase the answer here? Just play around with phase on one of them, until I find some sweet spot?

[brucek]

Just play around with phase on one of them, until I find some sweet spot?

Yeah, they're obviously cancelling each other at that point.............

brucek

[Egil]

Integrating the 2 subwoofers is really hard.

I manage to get some lowend by setting one of the subwoofers to "inverse". But then I get a bad decrease in SPL from 30-45hz... Adjusting the phase gives minor changes only.

So im going over to plan B... placement!



If you look at the ports, - is there any "theory" of what is optimal for different tuned subs? Im not sure if I should go for A or B.

Each subwoofer weights like 100kg each, so I want to stack them correctly.

Any inputs on how to place them?

[brucek]

Yeah, your thread title about says it all. We continually warn people off trying to mix two different subs, whether it be two different commercial models or simply two subs of a different tune. It's quite difficult to get a smooth and extended response.

Sure, some people get lucky and they use their sample of one to poopoo all the naysayers and recount how simple it is, but it's a shoot and you have to work at it.

It's easy enough to see that if one sub extended flat down to 15Hz, and the second sub was down 20dB at 15Hz, what happens when you combine them. We like to say it dumbs down the better sub to the challenged subs poor response. It's simple math.

Certainly you'll have to do your work with the listening position in mind and do all your measuring and tweaking with the goal of getting the listening position flat. I think your planB of placement is the only way to go with mis-matched subs. Use them against each other in finding the best spots. To make it easier, I would move one sub to my listening position and move the mic around to find a good spot for it (using RTA is best since it's dynamic, then when you find the spot, take a response measure). Then do the same with the next sub and place both responses on the Measured tab to compare. It's easy math to see what the resultant sound will be.

brucek

[Egil]

I have been stubborn thinking it wouldn't be such a big deal to integrate two subs (with different tunings). I was wrong!

I have stressed a lot today, with different positions. I can get a good flat freq. response on each sub, but NOT both subs together. I actually don't think it is possible for me to achieve a flat response when they are stacked. I can't place the subs wherever I want them either, since they are HUGE. So im very limited on where to place them.

I guess I have 3 options:

1) Play some more with the subs stacked, and see if I can get some "compromised" freq. response
2) Place each subwoofer in it's opposite corner. But this means that the RLp18" will be placed nearfield- and last time I had it placed nearfield I had problems setting the delay correctly, not to mention the bass was very easy to localise. BUT I didn't use REW then - so I think I would be able to integrate it better this time!
3) Sell one of the subs.. so that I can build one more sub, and have 2 identical subs

I'll report back when I manage to get something decent out of this!

Thanks for your advice and help Bruce! Much appreciated.

Edit: I actually manage to get it somewhat flat (by using the EQ on the DCX2496.. But when I then play music, it just doesn't sound good to me. It may be because I've gotten used to "car bass" where the area from 30-50hz has been boosted. Or maybe I have just measured things wrong somehow. I also get very flat response like 1m away from the listening position,.. problem is though, that's not where I sit .. hehe

[Egil]

Calibration is VERY stressful. For hours I've tried to get a somewhat compromised freq. response... I was about to give up... when I then read something about my HSU MBM 12 (Yes, I got a 3rd subwoofer also ). In the manual it said, that if I wanted to time align the HSU MBM with the true subwoofer, I had to set the distance on the TRUE subwoofer, NOT the MBM... So I set the distance to 5m on both my DIY subwoofers (they are approx. 5meter away from the HSU MBM). And guess what happened..:

It was suspiciously flat.. and then I noticed the dB range on the graph was very wrong.. dunno what I clicked to get that

The correct graph is like this:

Still not good, but im getting there.

[brucek]

Still not good

Looks OK to me..................... listen for a while

brucek