GRIMM Audio LS1c & SB1 DSP Speaker Review

[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.

The interesting thing is we only get this type of measurement resolution with the NFS, which let us see the effects of the frequency dependency of the acoustic center when using a fixed measurement coordinate system.

 

[kimmosto]

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.

Yes sure - slightly below 0 dB assuming that responses are calculated to 2 m (/CTA-2034). But not for example -5 dB at 25 Hz with conventional box concepts. That requires quite significant calculation error or noise or whatever. As already said, that's usually insignificant because many readers have knowledge about speakers. Problem is that readers should be able to trust the results - especially if the measurement system is continuously praised to be the best available and better than large anechoic at LF. I'm a bit allergic to that kind of conflicts.

 

[kimmosto]

Better continue tomorrow and nobody gets hurt?

It's just midday in Finland

 

[BeeKay]

It's just midday in Finland

 

[Lars Risbo]

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.

yes, i use that routinely. the limitation is that it does not include the baffle step and the internal standing waves (modes) in the box causes errors as you move up in frequency. For a high sensitivity box (ie large but does not go deep) this is a problem since the lowest box mode is too close to the bass corner frequency.

I showed an example in the spk16 blog post.

 

[Lars Risbo]

NFS results looks systematically unreliable below 40 Hz if some LF radiators such as ports are in rear panel. For example, DI could jump to -5 dB without any possibilities to do that in real life.

maybe not systematically but often it’s seen that the speaker is not omni at the lowest frequencies. I suspect that NFS requires a well defined acoustic center for the spherical harmonic series and a large speaker with multiple woofers and ports can be a challenge. As i said, would be good to understand the limitations better. NFS is definitely very useful but of course not perfect.

 

[Heinrich]

On "mic in the box method"

yes, i use that routinely. the limitation is that it does not include the baffle step and ...

I really don't get why people are that sensitive to bass extension and or bass volume as measured in a (hypothetical) neutral room. As I said before, the big tower Revels show a very similar response to the Grimm. Nobody of the actual users (!) complained about lacking bass, afaik. Can't we transfer this experience from the Revels to the Grimm orderly? (As I said before, with studio monitors the circumstances are different, from extensive, quite costly room treatment down (up!) to the actually knowing studio technician, who takes professional care of things.)

Today bass management is crucial for every room, every speaker box, every user's taste. Even if it is just a shelf-boost/cut, we know how much the bass may in case contaminate the mids with smear.

But, the very parameters of bass are notoriously ignored: capability after equalization. Reflex limits, sharply, bass extension, and that cannot be equalized. That's why Harman tunes to 30Hz or below. Exceptions apply, namely that bass needs a lot of spl to be heard by a human, and smaller speakers hardly deliver. These want to be cut, not to be pushed - another call for actively shaping bass.

The Grimm is quite gracefull in that regard, as it is of sealed design. For "perfect" bass one needs additional subs anyway in order to cope with the room's standing waves. See the Grimm's as halfway a sub, halfway a woofer in between.

 

[Robbo99999]

Suit yourself, my reading of the data shows the Grimm goes lower and will need less manipulation in room, but keep those knickers twisting away

Well, they're not twisted though, ha! We don't have to agree on all points. I do understand your "less manipulation in room" point anyway, so I actually agree with that, which I've said a couple of times already.

 

[kimmosto]

maybe not systematically but often it’s seen that the speaker is not omni at the lowest frequencies. I suspect that NFS requires a well defined acoustic center for the spherical harmonic series and a large speaker with multiple woofers and ports can be a challenge. As i said, would be good to understand the limitations better. NFS is definitely very useful but of course not perfect.

I was aware of separate multi-way module for larger constructions with multiple radiators/ways. But I'm here just a simple reader who might expect that authors use modules and methods giving the most accurate result at 20-20k, or informs or removes unreliable bands. Focusing to 1 dB directivity variations while 5 dB measurement errors exist does not increase plausibility. I could even hope that Klippel or someone else could design and deliver system which calculates to any point in space at 1-30 m, any directivity concept at LF and tower-sized up to 2 m etc. Just click Go button and see the result.
Ok, for example this kind scale cropping hides DI error at LF:

but error can be revealed somewhere else

 

[Purité Audio]

Well, they're not twisted though, ha! We don't have to agree on all points. I do understand your "less manipulation in room" point anyway, so I actually agree with that, which I've said a couple of times already.

I would rather have the output and worry about the ‘manipulation’ ( which is now really straightforward) later.
Keith

 

[Pearljam5000]

Why is Finland making so many good speakers?

 

[Robbo99999]

I would rather have the output and worry about the ‘manipulation’ ( which is now really straightforward) later.
Keith

That's also my preference. But I did say that I understand how this rolled off Grimm might sound better in room than a linear extended bass speaker if you're not gonna RoomEQ them, which was my point of agreement with @Frank Dernie .

 

[Frank Dernie]

I would rather have the output and worry about the ‘manipulation’ ( which is now really straightforward) later.
Keith

Straightforward for a single listening position yes.

 

[Lars Risbo]

On "mic in the box method"


I really don't get why people are that sensitive to bass extension and or bass volume as measured in a (hypothetical) neutral room. As I said before, the big tower Revels show a very similar response to the Grimm. Nobody of the actual users (!) complained about lacking bass, afaik. Can't we transfer this experience from the Revels to the Grimm orderly? (As I said before, with studio monitors the circumstances are different, from extensive, quite costly room treatment down (up!) to the actually knowing studio technician, who takes professional care of things.)

Today bass management is crucial for every room, every speaker box, every user's taste. Even if it is just a shelf-boost/cut, we know how much the bass may in case contaminate the mids with smear.

But, the very parameters of bass are notoriously ignored: capability after equalization. Reflex limits, sharply, bass extension, and that cannot be equalized. That's why Harman tunes to 30Hz or below. Exceptions apply, namely that bass needs a lot of spl to be heard by a human, and smaller speakers hardly deliver. These want to be cut, not to be pushed - another call for actively shaping bass.

The Grimm is quite gracefull in that regard, as it is of sealed design. For "perfect" bass one needs additional subs anyway in order to cope with the room's standing waves. See the Grimm's as halfway a sub, halfway a woofer in between.

well, the anechoic response of a loudspeaker is the most revelant characterisation (and no this is not a ‘neutral’ room whatever that means ). you buy a speaker and not a speaker and room. The anechoic response can be used to give an idea of how it works in a room.

With that said, i fully agree that the response of a speaker in the particular room cannot be ignored. also agree that having multiple woofers is the only way to effectively kill offending room modes in the sub 100Hz range where treatment is not very effective.

But again, the anechoic a response is relevant for a given speaker.

 

[NTK]

At the extreme low end, because of signal to noise ratio (low loudspeaker output, high noise), the NFS measurements are not very accurate.
[Edit] Attached a higher resolution version of the slide in the zip archive.

 

[Lars Risbo]

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.

good point. Maybe some of the DI not going to zero issues are simply due to the 2034 prescribing a 2m mic distance and for a large speaker the acoustic center may shift quite a fraction of this distance. It would help to evaluate the spherical function extrapolation at a very large radius. 2m is the absolute minimum of you want to be out of the near field for even just a stand mount speaker.

 

[a4eaudio]

On "mic in the box method"

I really don't get why people are that sensitive to bass extension and or bass volume as measured in a (hypothetical) neutral room. As I said before, the big tower Revels show a very similar response to the Grimm.

well, the anechoic response of a loudspeaker is the most revelant characterisation (and no this is not a ‘neutral’ room whatever that means ). you buy a speaker and not a speaker and room. The anechoic response can be used to give an idea of how it works in a room.

@Heinrich - I think there are two distinct conversations going on. One is about the Grimm speaker and it's measurements. The other is about accurate low frequency measurements in general (which realistically should be in a separate thread on measurements).

Accurate low frequency measurements are relevant for the speaker designer so that he/she can verify that the speaker is working as intended and to convey an accurate and standardized metric for the end user. This may not be that difficult for a two way bookshelf with an F3 of 45Hz, but for a large ported tower, with two woofers and an F3 of 30Hz it is hard to confirm. The discussions so far are that a real anechoic chamber may not be able to do it. A Klippel NFS may be imprecise. Ground plane measurements are a valid option but have to be done correctly and are inconvenient. So, mic in the box is a 4th option, that is not discussed often.

 

[Heinrich]

... the anechoic response of a loudspeaker is the most revelant characterisation (and no this is not a ‘neutral’ room whatever that means ). ... anechoic response can be used to give an idea of how it works in a room.

I was kidding. The neutral room was a sidekick to the predicted ... from the CES wxyz standard, or the listening window ... . But again, why should I care about any estimation taking unknown room properties into account (impossible). From a practical standpoint I have to e/q anyway.

What I regularly cannot alter is the reflex tuning. It defines limits. People ignore it. Maybe because it is not taken in consideration, as speakers are auditioned unequalized, for "the truth" to reveal. Actually, without my experience as a far and out experienced DIYer, I wouldn't be able to say that. A blind spot, and nobody knows it's there. The most prominent (hidden?) feature of blind spots. So, who cares? Peace!

@Heinrich - I think there are two distinct conversations going on. One is about the Grimm speaker and it's measurements. The other is about accurate low frequency measurements in general (which realistically should be in a separate thread on measurements).

I get that. You see, my argumentation is about both. It is not the shape of the bass to be most relevant, if for the sake of good sound equalization is to be used in room anyway. It is the output capability after e/q. The latter is missing in a) evaluating the Grimm, and b) with speakers in general.

 

[Lars Risbo]

But again, why should I care about any estimation taking unknown room properties into account (impossible).

I meant the anechoic response meaning a full polar. I did specifically not mean the PIR which is a somewhat arbitrarily weighted average. So seems we agree here

 

[Lars Risbo]

bass response: anyone who can explain why the anechoic NFS shows about -15dB at 20Hz and the out door 3 way boundary measurement is only 3dB down at 20Hz? based on what i elaborated earlier it’s hard to envision a shelving correction of more than 6dB?