Room response measurements

[SteveR750]

My sound pressure level meter arrived this morning, bought primarily to set my sub up, for which it has been essential. What I didn't expect was the huge variation in sound level by position and frequency. There are several "hotspots", each frequency dependent. I've now moved my chair backwards by a couple of feet to benefit most from the addition of the sub. Unfortunately there is no practical spot that avoids both the 40hz null and the one at 110hz, I suspect it might be in the garden.... I think the Dspeaker antimode is probably the only cure given the massive dips; as much as 15dB variation across the room.

Have to admit, it sounds fabulous now. Took a while to find the phase sweet spot on the sub, and to make sure it was volume level matched (a lot less than my ears believed to be right) to the 40s. Best £12 upgrade I've made!

 

[Thompsonuxb]

Suppose it's cheaper than carpet......

Seriously you need a sub with those speakers and that amp?

 

[Jota180]

Suppose it's cheaper than carpet......

Seriously you need a sub with those speakers and that amp?

Big room apparently.

 

[Frank Harvey]

Room EQ won't (and shouldn't) address nulls, but obviously their magnitude can be reduced by reducing the peaks that usually appear either side of them, but of course the bull will still be a null. Adding a second sub will more effectively address nulls. If, as already stated, the room is rather large, a single 10" driver may not be sufficient.

 

[matt49]

Room EQ won't (and shouldn't) address nulls, but obviously their magnitude can be reduced by reducing the peaks that usually appear either side of them, but of course the bull will still be a null. Adding a second sub will more effectively address nulls. If, as already stated, the room is rather large, a single 10" driver may not be sufficient.

+ 1

If you can be flexible with positioning of the sub, you should be able to fill the null. Unfortunately domestic bliss is usually incompatible with a well positioned sub. If so, a second sub will be needed. *sorry2*

 

[SteveR750]

Room EQ won't (and shouldn't) address nulls, but obviously their magnitude can be reduced by reducing the peaks that usually appear either side of them, but of course the bull will still be a null. Adding a second sub will more effectively address nulls. If, as already stated, the room is rather large, a single 10" driver may not be sufficient.

+ 1

If you can be flexible with positioning of the sub, you should be able to fill the null. Unfortunately domestic bliss is usually incompatible with a well positioned sub. If so, a second sub will be needed. *sorry2*

Ah the n+1 law!

I've managed to mostly mitigate the 40hz null, which was the annoying part with the sub, and another movement of the listening chair has helped overall. Thankfully the big peaks are nowhere near the listening position.homson

Thomson, the amp has no effect on room response, irrespective of its power, it's an interaction between the room and the speaker. Adding watts or damping factor won't fix it. The SCM40s are a sealed box, and roll off gently so that they are - 6dB at 48hz so if you want to hear a 4 string bass at the same volume as the rest of the band then you need a sub.

 

[Thompsonuxb]

Carpet!

Get some decent quality carpet with underlay.

Include the cost of vacum cleaner in your budget.

If the sub is to take up the slack below 48Hz you'll still suffer with the same issues if you have 'level' matched the sub so not to over power the speakers.

If you are finding the sub helps. ...that's good but maybe a ported design would be more suited to your room.

 

[Vladimir]

Stereo subs is a great idea.

 

[Andrewjvt]

Yes 2 subs in stereo would be very very good but just thinking of how much it all costs. A sub that can partner with the atcs is not cheap i expect. Think you better just get those atc scm 50 actives

 

[SteveR750]

Yes 2 subs in stereo would be very very good but just thinking of how much it all costs. A sub that can partner with the atcs is not cheap i expect. Think you better just get those atc scm 50 actives

Well, they will help, but a sub would still help. I don't necessarily agree that I need two subs, there is no more than 3-4 dB variation from 100hz to 40 hz in my listening position, which given its a lounge in which a family lives is pretty good. I'm not sure below that as I don't trust the accuracy of the meter, and it's about feeling things as much as hearing them at those lower frequencies.

 

[andyjm]

My sound pressure level meter arrived this morning, bought primarily to set my sub up, for which it has been essential. What I didn't expect was the huge variation in sound level by position and frequency. There are several "hotspots", each frequency dependent. I've now moved my chair backwards by a couple of feet to benefit most from the addition of the sub. Unfortunately there is no practical spot that avoids both the 40hz null and the one at 110hz, I suspect it might be in the garden.... I think the Dspeaker antimode is probably the only cure given the massive dips; as much as 15dB variation across the room.

Have to admit, it sounds fabulous now. Took a while to find the phase sweet spot on the sub, and to make sure it was volume level matched (a lot less than my ears believed to be right) to the 40s. Best £12 upgrade I've made!

Steve,

I could highly recommend 'room equalisation wizard' which is a free software download. If you couple it with a measurement mic (the Minidisp guys in Honk Kong sell a good one with USB output), then you can put your SPL meter in the bottom drawer. I find it much easier to mess around with room acoustics using a computer generated sweep and a frequency response graph than fiddling around with multiple SPL measurements every few Hz - which is a complete pain.

If you get the bug, REW will produce room correction files to allow some pretty sophisticated dsp room equalistaion.

As mentioned above, you can't fill in a null, but you can tame some of the nasty resonances.

 

[SteveR750]

Thanks Andy, that's useful to know. I've only undertaken a very basic survey, walking slowly (quietly) around the room whilst playing a fixed test tone, so far only at 40Hz 80Hz and 110Hz. Latter two were simply arbitrary higher bass frequencies that I suspect are still in the flat response of the ATCs. 40hz is specifically a frequency I wanted "flat" as it's low E on the bass guitar, and it's the crossover f setting on the sub.

I'd like to try a more comprehensive freq sweep analysis, it could only work if the mic has a long cable as I've only got one laptop at the moment. I'll certainly download the software though and see if I can get it to work. Do you have a link for the mic?

 

[RobinKidderminster]

Ordered mine from France.

http://www.minidsp.com/products/acoustic-measurement/umik-1

 

[SteveR750]

Thanks for the link.

Meanwhile, I did some decending step tests and got the following averages after 5 runs, all measured from my listeing position:

200Hz - 71dB

150Hz - 67dB

100 Hz - 63dB

90 Hz - 64dB

80Hz - 60dB

70Hz - 55 dB

60Hz - 50dB

50Hz - 58dB

40Hz - 44dB

30Hz - 48dB

I'm not too worried about sub 50Hz, as I suspect the accuracy of the meter is questionable, and it sounds OK, however; boith the meter and my ears detect a noticeable drop between 60 and 80Hz. I've added a little lift in the J River DSP but the EQ is pretty crude, so +2dB added at 60Hz and +1.0dB at 170Hz. I'm not sure yet how to set up J River with a finer / thinner EQ lift. I'll order the mic and see what that reveals, but already it's clear that there is more going on than I suspected. The dip could of course be due to the ATCs, but I think its reasonable to assume they are not out of spec.

 

[RobinKidderminster]

REW software has a room simulator. Based only on room measurements I used it earlier to adjust crossover and sub delay. Must be the crudest tool to use to set up a system but it seems to have firmed up the bass. Expectation bias maybe but for 30mins work and only a tape measure it may be worth a punt.