A question about EQ

[br??]

So I recently got hold of an ECM8000 and REW to take some measurements of my room. With it being moderately treated I was curious to see where I should go next. Apart from some minor ringing in the 60 Hz region (can't fix it with sub placement - more traps?) and general flutter echo annoyances (due to the bare side walls which I don't know if I should treat), the most obvious and unsurprising result was a 10-15 dB suckout around 74 Hz.

After doing some tinkering I figured out that increasing the gain on the SB2000 (crossed over at 80 Hz) by about 25% would fill in the hole, but leave a 10-15 dB peak from ~60 Hz down. I also figured out that I could then use REW (w/ Equalizer APO) to EQ out this new peak, producing an essentially flat bass response. My question is -- have I cheated some rule of acoustics and/or sound reproduction?

I can provide any other helpful information if needed.

Thanks.

 

[highfigh]

So I recently got hold of an ECM8000 and REW to take some measurements of my room. With it being moderately treated I was curious to see where I should go next. Apart from some minor ringing in the 60 Hz region (can't fix it with sub placement - more traps?) and general flutter echo annoyances (due to the bare side walls which I don't know if I should treat), the most obvious and unsurprising result was a 10-15 dB suckout around 74 Hz.

After doing some tinkering I figured out that increasing the gain on the SB2000 (crossed over at 80 Hz) by about 25% would fill in the hole, but leave a 10-15 dB peak from ~60 Hz down. I also figured out that I could then use REW (w/ Equalizer APO) to EQ out this new peak, producing an essentially flat bass response. My question is -- have I cheated some rule of acoustics and/or sound reproduction?

I can provide any other helpful information if needed.

Thanks.

Ringing and flutter can't be EQ'd out without killing sound quality and deep EQ control differences between adjacent bands makes good sound impossible. If you want to get rid of the flutter, you either need to block the path with furnishings or use some kind of treatment- artwork with absorptive materials behind works. Fire up REW and move things around- you'll be able to see the effect in real time. If you have a piece of furniture that's tall, dense and oddly-shaped, like a book case that can fit into a corner, this can help with the bass issues.

 

[WaynePflughaupt]

After doing some tinkering I figured out that increasing the gain on the SB2000 (crossed over at 80 Hz) by about 25% would fill in the hole, but leave a 10-15 dB peak from ~60 Hz down. I also figured out that I could then use REW (w/ Equalizer APO) to EQ out this new peak, producing an essentially flat bass response. My question is -- have I cheated some rule of acoustics and/or sound reproduction?

It’s bad form to use an equalizer as a volume control. Equalizer filters accomplish frequency response changes by shifting the phase of the signal passed through them (see this article for a more technically detailed description). Using an equalizer as it’s intended, that’s not a big deal because it’s essentially counteracting phase issues caused by the room that are altering a speaker’s perceived response (i.e., sound bouncing around the room and arriving at the listening position at different times). But that’s not the case when you try to use the equalizer as a volume control by using a bunch of filters. Each filter is introducing phase, but none of them are counteracting anything from the room. You’re just needlessly adding artifacts the signal that don’t need to be there.

The 74 Hz trough may be a phase issue from the crossovers between the mains and sub. The SB2000 has a continuously-variable phase control. Use REW’s RTA feature to get a real-time reading and see if makes a difference when you adjust the phase control.

Regards,
Wayne A. Pflughaupt

 

[br??]

Thanks guys. I'll fiddle around with your suggestions when I get time and report back.

 

[gene]

So I recently got hold of an ECM8000 and REW to take some measurements of my room. With it being moderately treated I was curious to see where I should go next. Apart from some minor ringing in the 60 Hz region (can't fix it with sub placement - more traps?) and general flutter echo annoyances (due to the bare side walls which I don't know if I should treat), the most obvious and unsurprising result was a 10-15 dB suckout around 74 Hz.

After doing some tinkering I figured out that increasing the gain on the SB2000 (crossed over at 80 Hz) by about 25% would fill in the hole, but leave a 10-15 dB peak from ~60 Hz down. I also figured out that I could then use REW (w/ Equalizer APO) to EQ out this new peak, producing an essentially flat bass response. My question is -- have I cheated some rule of acoustics and/or sound reproduction?

I can provide any other helpful information if needed.

Thanks.

Loudspeakers are min phase devices which means that EQ can work to reduce resonances. At low frequencies, rooms also behave min phase. If you have reduced seat to seat variances in bass using multisub, then you can EQ the peaks and it will fix the time domain response as well and benefit ALL the seats, NOT just one listening position.

See: https://www.audioholics.com/room-acoustics/history-of-multi-sub-sfm

Also see how I used multi-sub and mDSP with REW to fix the bass response in my room using NO bass traps!

https://www.audioholics.com/home-theater-calibration/bass-optimization-for-home-theater

 

[gene]

Ringing and flutter can't be EQ'd out without killing sound quality and deep EQ control differences between adjacent bands makes good sound impossible. If you want to get rid of the flutter, you either need to block the path with furnishings or use some kind of treatment- artwork with absorptive materials behind works. Fire up REW and move things around- you'll be able to see the effect in real time. If you have a piece of furniture that's tall, dense and oddly-shaped, like a book case that can fit into a corner, this can help with the bass issues.

That simply is NOT true. EQ is completely valid below the room transition frequency and I'd suggest you read the 2 articles I linked up in my last post. I'm surprised a few regulars here have NOT read these articles yet.

 

[br??]

Thanks Gene. Are you saying that my method of flattening out the enormous peak I created is valid so long as I don't try the same thing above the transition frequency of the room? Having a quick read of your mDSP article it seems like you did something similar in step 5 of your quick and dirty guidelines, but I doubt it was as barbaric. Or does the technique only apply to multisub?

For context my room is slightly rectangular and on the small side of medium with only 1 seat.

 

[highfigh]

That simply is NOT true. EQ is completely valid below the room transition frequency and I'd suggest you read the 2 articles I linked up in my last post. I'm surprised a few regulars here have NOT read these articles yet.

Fair enough- how many here have a parametric equalizer? I should have been more explicit- I meant that a simple graphic EQ won't work in most cases (unless the slider frequencies happen to coincide with the problem frequencies). When Dr Toole found a way to cure the problem in his room, he matched the frequency and Q of the mode and most just don't have that kind of equipment. It's too bad so many manufacturers have sold people on graphic EQ rather than parametric, but I guess it wouldn't be the same if users couldn't make a Happy Face with the sliders.

However, as Dr Toole states, his solution only worked when the system was in operation and my personal goal is to make the room work for music AND other uses. Passive treatments do counteract the energy and yes, it does require more from the audio system, but an acoustical space shouldn't be unpleasant when the music isn't playing and small rooms with hard surfaces suffer from flutter in mid-range frequencies, making music sound bad when percussive and even some sustained sounds are part of the material.

Can we define the size of a "small room"?

 

[br??]

My room is 3.7 x 2.7 x 2.3 = 23 cubic metres (~812 cubic feet).

 

[gene]

Thanks Gene. Are you saying that my method of flattening out the enormous peak I created is valid so long as I don't try the same thing above the transition frequency of the room? Having a quick read of your mDSP article it seems like you did something similar in step 5 of your quick and dirty guidelines, but I doubt it was as barbaric. Or does the technique only apply to multisub?

For context my room is slightly rectangular and on the small side of medium with only 1 seat.

Yes EQ will flatten that peak and restore the decay time as well but only for one position unless you reduce the seat to seat variances by deploying multi-sub. Once you reduce the variances, then EQ will be effective for all the seats.

 

[gene]

Fair enough- how many here have a parametric equalizer? I should have been more explicit- I meant that a simple graphic EQ won't work in most cases (unless the slider frequencies happen to coincide with the problem frequencies). When Dr Toole found a way to cure the problem in his room, he matched the frequency and Q of the mode and most just don't have that kind of equipment. It's too bad so many manufacturers have sold people on graphic EQ rather than parametric, but I guess it wouldn't be the same if users couldn't make a Happy Face with the sliders.

However, as Dr Toole states, his solution only worked when the system was in operation and my personal goal is to make the room work for music AND other uses. Passive treatments do counteract the energy and yes, it does require more from the audio system, but an acoustical space shouldn't be unpleasant when the music isn't playing and small rooms with hard surfaces suffer from flutter in mid-range frequencies, making music sound bad when percussive and even some sustained sounds are part of the material.

Can we define the size of a "small room"?

Agreed. It pisses me off when receiver/processor companies give you auto-EQ and a GEQ rather than an adjustable PEQ down to 20Hz.

Yes passive treatments (even in the form of throw rugs and couches) are very necessary above bass frequencies especially in rooms with hard floors, and glass.

I would define a small room as one where sanding waves dominate the low frequency behavior.

 

[highfigh]

Agreed. It pisses me off when receiver/processor companies give you auto-EQ and a GEQ rather than an adjustable PEQ down to 20Hz.

Yes passive treatments (even in the form of throw rugs and couches) are very necessary above bass frequencies especially in rooms with hard floors, and glass.

I would define a small room as one where sanding waves dominate the low frequency behavior.

In the '70s, the manufacturers started their specs race, with all kinds of audio magazines spouting various terms and data, without doing much to explain it in a way that most people might understand. This resulted in a steady stream of people coming into the store to ask questions like "How many Amps does this put out?", "What's the slewing rate?" and wanting to buy a 60W/ch receiver to replace their 50W model because they didn't think they needed twice as much power.

It was hard enough to be able to take time to explain what they needed to know when so many were like the kids in my High School Math classes, who asked "Why do I need to learn this? I'll never use it once I graduate". Explaining a parametric or the odd 'Para-graphic' EQ. Then, they spewed graphic EQs in car audio and created a lot of business for those of us who had to replace the blown speakers when they realized the system was a lot louder when all 5, 7, 9 or 12 bands were jacked up all the way. Ugh. I thought it was interesting that the frequency display on Audio Control's SA3050 RTA coincided with the controls on their equalizers. I always wanted to see what was happening between the round, red LEDs.

Give me a 4 band parametric and I'm happy.