Huge (-10 dB) dip between 200Hz and 300Hz in my room.

[abdo123]

Hello,

I have this huge 200Hz to 300Hz dip in my room and I don't really know why or what to do about it.

The speakers are measured on this forum, they're flat so I would rule out the speakers.

they're rear ported and placed in a bookcase; However, there is more than enough room for the port to function. I manage the bass boost just fine.

the dip is so huge, that boosting it makes acoustic guitars sound 'clipped' or 'chopped off'. So perhaps i'm over driving the speakers by boosting the dip?

leaving it the way it is makes low and mid bass very prominent even if they're 'within target'.

Any opinions on what causes dips right at the transition frequency?

 

[daftcombo]

Hi,

I would never boost a dip based on in-room measurements, or at least never more than a few dB and with Q < 4 . Some do, but I only get rid of narrow peaks.

Can you try throwing some carpets and clothes on the floor between the speaker and you, and measure again?

 

[oursmagenta]

I wouldn't exclude SBIR. Especially if your speakers are in a bookcase.
I guess that if the front speaker is at a distance of 40cm from the front wall, that should produce a dip around these frequencies (~250 hz).

Edit: I re-did my computation.

 

[abdo123]

Hi,

I would never boost a dip based on in-room measurements, or at least never more than a few dB and with Q < 4 . Some do, but I only get rid of narrow peaks.

Dirac is very smart about this too, as you can see it does not correct dips in bass. but since it's right above the transition frequency it's not treating it as a standing wave and is boosting it anyway (Which it should arguably do?).

I wouldn't call the boost a bad thing, Dirac is only boosting roughly ~5dB out of the necessary 10 dB so the bass wouldn't sound completely hollow.

I will try the carpet advice and let you know, I have the time to do more experimenting tomorrow.

 

[abdo123]

I wouldn't exclude SBIR. Especially if your speakers are in a bookcase.
I guess that if the front speaker is at a distance of 40cm from the front wall, that should produce a dip around these frequencies (~250 hz).

Edit: I re-did my computation.
View attachment 122786

Okay, the rear port is roughly 10-12 cm away from the rear wall, which makes the woofer 35-40 cm away from the wall.

does these calculation consider the distance to start from the center of the woofer of the rear of the cabinet?

 

[oursmagenta]

Okay, the rear port is roughly 10-12 cm away from the rear wall, which makes the woofer 35-40 cm away from the wall.

does these calculation consider the distance to start from the center of the woofer of the rear of the cabinet?

It's starting from the center of the woofer/tweeter.

 

[flipflop]

but since it's right above the transition frequency it's not treating it as a standing wave and is boosting it anyway (Which it should arguably do?).

It should not make any corrections above the transition frequency because there's a risk of the direct sound being degraded as a result.

 

[abdo123]

It's starting from the center of the woofer/tweeter.

can you please share the link for the calculator so i can put the dimensions of my room?

 

[abdo123]

It should not make any corrections above the transition frequency because there's a risk of the direct sound being degraded as a result.

Dirac has a way of separating early reflections from direct sound. it cannot handle late reflections though.

What you're seeing here is more direct sound than it is early reflections. Which is why the speaker shows almost no high end roll-off.

 

[oursmagenta]

can you please share the link for the calculator so i can put the dimensions of my room?

Ah yeah sorry forgot to put it in the previous post.

 

[abdo123]

Ah yeah sorry forgot to put it in the previous post.

Sorry, you attached an empty 22 bytes archive.

 

[oursmagenta]

Sorry, you attached an empty 22 bytes archive.

(I edited my previous post, it should work)

 

[abdo123]

(I edited my previous post, it should work)

Okay this is not cute, What can I do about SBIR?

 

[oursmagenta]

View attachment 122794
Okay this is not cute, What can I do about SBIR?

Absorption panel just behind the speakers, at these frequencies the GIK Acoustic Alpha series 4A should work, or at least help.

 

[vavan]

Dirac is very smart about this too, as you can see it does not correct dips in bass

it's not so simple and sometimes it does, or at least tries

 

[Bullwinkle J Moose]

What exactly are you measuring?

Right Speaker?
Left Speaker?
Both?

 

[flipflop]

What can I do about SBIR?

Another option than the one proposed by oursmagenta is to make sure there's no boundaries within 50 cm of the sides and rear of the speaker. You might have to invest in some stands.
Putting a speaker in a bookshelf is just about the worst thing you can do when it comes to placement.

 

[vavan]

It should not make any corrections above the transition frequency

for me full range dirac correction sounds better than limited one

 

[abdo123]

What exactly are you measuring?

Right Speaker?
Left Speaker?
Both?

just one of the two speakers.

 

[Bullwinkle J Moose]

now measure the other

and then measure the other in the same location as the first

Rule out the possibility of one bad speaker that does not match the first

If both measure the same and location is bad, then move them