need help with my measurements

[perxMKII]

Hey there,

so i did my first measurements and now i don't really know how to interpret / fix them.

Obviously i have some big problems with my subs. I'll buy a miniDSP 2x4HD to battle that.

But my bigger concern is in the 180-400 Hz range. I got a big dip there and that's exactly what i hear or "feel". There is some "punch" missing in this region when i listen to music.

Any tipps? Looking at waterfall / spectrogram i can't see any big roommode problems? (except the ones at 20 / 40 hz)

I did some placement changes but couldn't get the 180-400 Hz range up (4 placement options to be seen in this picture):

How did i measure (REW file attached):
mic positioned in the middle of the speakers, right at the position where my ears would be. I measured first all together R + L + subs and after that every channel solo and speakers w/o subs and subs w/o speakers.

Room:
8x4m - speakers sitting in a corner at one of the long sides of the walls.
Space between speakers: 136cm
Space at listening position away from speakers: 220cm
Space behind listening position to wall: 90cm
Space between speakers and wall: 48cm (i tried closer and further to the wall as well - see picture above)

Hope someone can help and my measurements are not totally messy (-:

perx

 

[John Mulcahy]

A filter would deal with the peak at 42 Hz. The dip around 200 - 400 looks to be due to the speakers starting to roll off below 400 Hz, which is unusually high. Assuming you haven't set the high pass for them to a very high frequency they may need to be very close to the wall to have a little more extension.

 

[perxMKII]

A filter would deal with the peak at 42 Hz. The dip around 200 - 400 looks to be due to the speakers starting to roll off below 400 Hz, which is unusually high. Assuming you haven't set the high pass for them to a very high frequency they may need to be very close to the wall to have a little more extension.

no high pass - pure direct. I could try to put them closer the wall but normally Open baffles need to be as far from the front wall as possible.. So i really have no idea why that happens.

In my speaker placement tests (the picture i posted) was the green line the closest to the wall. About 27cm.

did you check the REW file? Could you see a roommode i missed or something?

thanks

 

[John Mulcahy]

Don't think you mentioned they were open baffles. Open baffle speakers roll off at 6 dB/octave below a cutoff frequency that depends on the baffle width. If the baffles are a foot wide, for example, that rolloff starts around 400 Hz. They often have a compensating filter to boost the response to counter that and extend the low end, so that is probably what you need to get them to blend with the sub without a dip.

 

[sm52]

a compensating filter to boost the respons

Is it some kind of active filter? If driver pressure drops naturally, how do you raise it?

 

[John Mulcahy]

Yes, an active filter in the signal path.

 

[perxMKII]

Don't think you mentioned they were open baffles.

Sorry, i forgot about that.

This is the baffle i got:

Seems like there is a "compensating filter" installed. I got it from the manufacturer, so it should be right.. i hope
+ 2x 15" sealed subs

 

[John Mulcahy]

No, there isn't, just a series capacitor for the tweeter.

 

[perxMKII]

No, there isn't, just a series capacitor for the tweeter.

hm i guess it's designed to be without one than?

here is a qoute about the widebands from a review:

The 8Ω widebanders are wired in series for a nominal 16Ω load and run without a filter. A single 1.0µF capacitor serves as high-pass filter to the Gemini tweeter at 11kHz though the decreasing response of widebander and tweeter meet acoustically at around 8kHz. Finally there are two long graphite resistors wired in parallel across each widebander to "...flatten the impedance for tube amps. They also take out some energy in the upper midrange and, important for the Duo baffles (models using two widebanders per side), help together with the series wiring of the drivers to make the drivers behave 100% equal to each other and get a unique wave front. The resistors have a 12Ω value for the Classic drivers and are 15Ω for the Chrystal."​

(can't post the link to the review. It is from "6moons audioreviews: Bastanis mandala")

 

[John Mulcahy]

The roll-off is inherent to an open baffle's structure, sound from the back of the driver starts to cancel with sound from the front. Wider baffles reduce the frequency below which that starts. That might be an acceptable compromise if there is some other feature of an open baffle's sound that is preferred to a box speaker, but it can be countered by filtering the signal that goes to the speaker. The difficulty with that is running out of headroom at anything above modest levels, so the adjustment would need to be limited to a range where the driver can take higher levels. Without some form of compensation there will inevitably be a dip before the sub starts to fill in.

 

[perxMKII]

That does not sound good but thanks, now i have a better understanding of that problem.

 

[sm52]

active filter in the signal path

What additional frequency band can I expect using such a filter?

 

[John Mulcahy]

The open baffle speaker has a high pass response with a 6 dB/octave roll-off, from about 400 Hz in this case. If you generate an EQ filter with such a response you can see the effect other filters have on it. A typical way to deal with that would be a low shelf with a 6 dB/octave slope. A 6 dB/octave low shelf at 100 Hz with 12 dB gain would move the -3 dB point from 400 Hz to 100 Hz, but takes away 12 dB of headroom.

 

[sm52]

That is 100 hertz. 100 hertz, and below in any way with an open baffle. Only if you expand the baffle (a little so that it has an appearance), it can be 90 hertz. So only a sub can save.