GRIMM Audio LS1c & SB1 DSP Speaker Review

[Heinrich]

Then the mic is not fit for the job. Use a better mic. How is it not predicted during the design process?

Find a mike that is (at least in level) linear up to 150dB. That's a valid caveat, as I said three times now. But the "room" is not.

Then please explain what the subwoofer is supposed to do, when the disturbance (e.g. door slam) was already heard by the listener ...

That's exactly the point. The woofer is not to equalize at the listener's ears, but at its own cone alone. Targeting the listener's ears? How would an accelerometer do that?

 

[NTK]

Have you worked with the Mic-in-the-box method?
Information seems to be pretty limited on the "typical" forums, but it is well-enough known to be included in REW and VituixCAD.

The height of the wedges need to be 1/4 of the wavelength. At 50 Hz, it means 1.7 m ( = (343/50)/4 ), so the box need to be at least 2 × 1.7 m per side, plus room for the test piece and mic and some distance in-between. This box is going to be huge, and still only works to 50 Hz.

 

[NTK]

Find a mike that is (at least in level) linear up to 150dB.

If no mic exists that is fit for the purpose, either develop one or find another way.

That's a valid caveat, as I said three times now. But the "room" is not.

That's exactly the point. The woofer is not to equalize at the listener's ears, but at its own cone alone. Targeting the listener's ears? How would an accelerometer do that?

Wasn't this the point @gnarly made? Then why was his take on why it won't work flawed?

 

[Heinrich]

Was this the point @gnarly made? Then why was his take on why it won't work flawed?

For starters simply because he didn't consider the original problem statement. He pushed the theoretically possible solution to different grounds in changing the problem and then quoted Meyer Sound on that other problem. Something around that lines.

The feedback loop is from the input of the amplifier to the sensor. The woofer is the actuator. In case the sensor senses the actuator's output as sound. It may pickup sound from the room, but that is just noise, and is attenuated by the negative feedback, at the woofer!, because it is not part of the input. This works as long as a) the sensor is true, b) the delay of the actuator's output in regard to the sensor's (negative) input is neglegible.

Spoiler: (One may argue that the room is part of the amplification. Please go ahead and derive a mathematical formula to describe the effect. Maybe there is a constellation, that generates undesirable behavior. I personally don't see any. Go ahead, I can read and understand advanced mathematics, and I'm perfectly willing to change my mind.)

 

[amirm]

NFS results looks systematically unreliable below 40 Hz if some LF radiators such as ports are in rear panel.

As I explained, that happens in anechoic chambers. For NFS, this was fixed a few years ago. And the issue wasn't that the port was in the back but that it was very far from the acoustic reference point (usually near tweeter/midrange).

For example, DI could jump to -5 dB without any possibilities to do that in real life.

Anechoic measurements are not "real life." Real life rooms, even high treated or EQed ones won't have even bass response. So this comment is neither here, nor there.

We measure anechoically as to remove the room impact from the measurements so that the data can be compared and analyzed. It also instructs preference in listening tests.

 

[Heinrich]

... may pickup sound from the room, but that is just noise, and is attenuated by the negative feedback, at the woofer!, ...

Spinoff: Sennheiser, Bose especially ... they have active noise cancellation with headphones. Now think of a big, bold woofer with a microphone before its cone. The mike provides the only input signal to the woofer. In a (negative) feedback loop the woofer would attenuate all sound in front of it. There you have it, active room mode cancellation. The woofer would act like a 'black hole' for sound, within its limits in frequency mostly.

Practical design: a huge sheet of neoprene driven by a bass shaker ... for the die-hard DIYers, have fun!

 

[dfuller]

Spinoff: Sennheiser, Bose especially ... they have active noise cancellation with headphones. Now think of a big, bold woofer with a microphone before its cone. The mike provides the only input signal to the woofer. In a (negative) feedback loop the woofer would attenuate all sound in front of it. There you have it, active room mode cancellation. The woofer would act like a 'black hole' for sound, within its limits in frequency mostly.

Practical design: a huge sheet of neoprene driven by a bass shaker ... for the die-hard DIYers, have fun!

This exists, actually. PSI makes them.

 

[Ilkless]

One of the most tiresome trends on ASR right now is perhaps, ironically, this rise of technically-proficient yet pedantic, dogmatic and nihilistic users that tend towards an overly stringent definition of technical merit than evidence supports.

To them anything short of a waveguided 6" dome and cone LR4 2 way is a scam.

 

[kimmosto]

Anechoic measurements are not "real life."

I was talking about DI result. Of course you can twist it to something else than real life.

For NFS, this was fixed a few years ago.

It does not look so.

 

[amirm]

I was talking about DI result.

DI result? In bass??? Why on earth you would concern yourself with that?

 

[kimmosto]

DI result? In bass??? Why on earth you would concern yourself with that?

It's not about my concern about DI. In many cases I know what it is, but NFS gives wrong result. I don't have religious faith for it and need to be so defensive.
P.S. you seem to need some studies and experience about significance (in practice) of DI at low frequencies.

 

[amirm]

P.S. you seem to need some studies and experience about significance (in practice) of DI at low frequencies.

You say you are not concerned about DI and then go on and say you are concerned about DI in low frequencies. When you make up your mind and can come back with actual data on shortfalls of NFS, we can talk. Until then, I suggest you lay off FUD on system operation.

 

[kimmosto]

You say you are not concerned about DI and then go on and say you are concerned about DI in low frequencies. When you make up your mind and can come back with actual data on shortfalls of NFS, we can talk. Until then, I suggest you lay off FUD on system operation.

Why don't you calm down and have some sleep and try to wake up less defensive and twisting others messages.

 

[Arindal]

Since bass frequencies are almost omni, it takes just a few low order basis functions to describe it. This means NFS computes this in its sleep.

If bass frequencies are almost omni (with conventional monopoles), and the NFS has no problem with calculating that, why is it possible that the direcitivity index calculation result is occasionally well under 0dB, particularly at lowest frequencies? In my understanding, a speaker with an omnidirectional radiation pattern would not go below 0dB of d.i. with very long waves.

A potential explanation might be that drivers which are closer to a sufficient number of spherical microphone positions will be accidentally calculated with higher SPL at longer assumed distance, as if the drivers were at reference position. Is the true microphone distance to reference position always fixed, like 1m, or can it be partly extended to 2 or 3m? How would the d.i. calculation and bass FR look like if the subwoofer would be positioned at reference position instead of the midrange?

 

[mcdn]

One of the most tiresome trends on ASR right now is perhaps, ironically, this rise of technically-proficient yet pedantic, dogmatic and nihilistic users that tend towards an overly stringent definition of technical merit than evidence supports.

To them anything short of a waveguided 6" dome and cone LR4 2 way is a scam.

There’s an ignore feature for that

 

[NTK]

You will only measure a DI of 0 dB for a true omni source if the origin of the measurement coordinate system aligns perfectly with the acoustic center. Where is the acoustic center? It moves around depending on which driver/port is active at the frequency. If the acoustic center is behind the measurement origin (with respect to the reference axis), you get a DI of <0 dB.

 

[mcdn]

You say you are not concerned about DI and then go on and say you are concerned about DI in low frequencies. When you make up your mind and can come back with actual data on shortfalls of NFS, we can talk. Until then, I suggest you lay off FUD on system operation.

Jeez Amir, it’s Kimmo, we can presume he’s got a valid point!

 

[amirm]

Jeez Amir, it’s Kimmo, we can presume he’s got a valid point!

His comment reminds of my late father in law, may he rest in peace, looking at his food and saying, "it needs salt!" On ASR, we come with data and references. We don't claim this and that looks wrong and hope to have that have any value.

 

[amirm]

Why don't you calm down and have some sleep and try to wake up less defensive and twisting others messages.

Why don't you watch your manners. Watch it.

 

[BeeKay]

Better continue tomorrow and nobody gets hurt?