Identical subs with different frequency response, time domain and SPL

[keith_correa]

Not sure if they are from the same batch but rythmik support confirmed based on the measurements this isn’t normal and suggested the amp be replaced.

Which among the 2 did Rythmik say gives the correct response?

 

[Love4sound]

Which among the 2 did Rythmik say gives the correct response?

Hahah the 2nd sub I purchased after a month. The first sub I purchased has the variations. These variations won’t matter much in a single set up. I am having issues with aligning them in a dual set up.

 

[Love4sound]

Well here you go for those who love to see what’s inside. Tear down of the Rythmik LV12F. In the process of replacing the Amp. Hope the issue of different response in identical subs are resolved.

 

[Love4sound]

So turns out no issues with the amp which I also suspected. Red graph starts to roll of near 24 and the blue graph is the sub which had the amp replaced starts to rolls off at 28hz and has a gain variance of 3-5db. Now this is the same sub which I got first and was very much impressed that I went for a second LV12F. Single performance sounds similar but now because of different frequency response they are having time domain issues. Is this a normal behaviour for an identical sub?

 

[Love4sound]

So finally got the sub replaced. Overall very minor variations which should be within acceptable range unit to unit. May be this variation also will be solved after break in period

Top image Red and Blue- Near field measurements. Blue is the replaced sub. It’s 100% identical in terms of frequency response compared to my sub with only 1db variation in the 20-25Hz region

Bottom image blue and green-MLP response. Green is the replaced sub and is identical with only a minor variation of .5-1db in the 20-25HZ region

 

[Analogous]

I was trying to find the right thread to ask this question. Hope someone with experience with two subs can help shed some light…

I understand two subs can help smooth in-room bass responses and help with smoother integration better than one subwoofer.

I recently got a KEF KC62. This has two drivers on opposite sides.

I am trying to figure out what is going on with these. It sounds pretty good to me on most recordings. On a few there is a hint of booming. I have them placed in the centre between the two speakers pulled 2” away from the wall.

Given the understanding of two subs being better than one, how would this play out with the KC62?

Any thoughts, suggestions, guidance would be welcome.

 

[Love4sound]

I was trying to find the right thread to ask this question. Hope someone with experience with two subs can help shed some light…

I understand two subs can help smooth in-room bass responses and help with smoother integration better than one subwoofer.

I recently got a KEF KC62. This has two drivers on opposite sides.

I am trying to figure out what is going on with these. It sounds pretty good to me on most recordings. On a few there is a hint of booming. I have them placed in the centre between the two speakers pulled 2” away from the wall.

Given the understanding of two subs being better than one, how would this play out with the KC62?

Any thoughts, suggestions, guidance would be welcome.

I have used an osd 12 inch subwoofer which comes with one active driver on the front and dual opposed 12 inch passive drivers on the sides. Both the passive drivers have decent amount of excursions. So the logic behind is to control the cabinet vibrations that leads to distortion. Now my understanding from this is if you have dual opposing active drivers the same theory is going to be applied with higher SPL then a single driver.

 

[Analogous]

I have used an osd 12 inch subwoofer which comes with one active driver on the front and dual opposed 12 inch passive drivers on the sides. Both the passive drivers have decent amount of excursions. So the logic behind is to control the cabinet vibrations that leads to distortion. Now my understanding from this is if you have dual opposing active drivers the same theory is going to be applied with higher SPL then a single driver.

Thanks. Yes, the KEF KC62 has dual drivers powered with two separate amps (500w each) The body is quite inert and heavy. I have this placed so the drivers each face to the sides. Would the same principles of having two separate single driver subs apply?

 

[Love4sound]

Would the same principles of having two separate single driver subs apply?

well logically that’s what I also feel.But one thing to note is having two individual subs at the same spot will cause time delay issues. So manufacturers would have done so much R&D to implement it properly. There are bigger subs with same design principle as well.

 

[arj]

I was trying to find the right thread to ask this question. Hope someone with experience with two subs can help shed some light…

I understand two subs can help smooth in-room bass responses and help with smoother integration better than one subwoofer.

I recently got a KEF KC62. This has two drivers on opposite sides.

I am trying to figure out what is going on with these. It sounds pretty good to me on most recordings. On a few there is a hint of booming. I have them placed in the centre between the two speakers pulled 2” away from the wall.

Given the understanding of two subs being better than one, how would this play out with the KC62?

Any thoughts, suggestions, guidance would be welcome.

I have played around a lot with Dual subs.

The principle of Dual subs is to cancel out Room issues. Ideally it is 4 subs but 2 is not too far away from that. The dual driver for all purposes is one sub but with a larger virtual driver. eg 2 8" drivers is almost a 10" , 2 x10" is approximately a 12" etc etc. what it gives you perhaps is better room pressure due to more air being moved and hence a better tactile impact ( as opposed to frequency extension)

For dual, subs need to be placed symmetrical in the room from opposite corners for the impact and its really very good but getting the right placement can be a pain in you-know-what

 

[Decadent_Spectre]

I was trying to find the right thread to ask this question. Hope someone with experience with two subs can help shed some light…

I understand two subs can help smooth in-room bass responses and help with smoother integration better than one subwoofer.

I recently got a KEF KC62. This has two drivers on opposite sides.

I am trying to figure out what is going on with these. It sounds pretty good to me on most recordings. On a few there is a hint of booming. I have them placed in the centre between the two speakers pulled 2” away from the wall.

Given the understanding of two subs being better than one, how would this play out with the KC62?

Any thoughts, suggestions, guidance would be welcome.

The KC62 appears to be a dual opposed design, the primary benefit of this is that it cancels out cabinet vibrations from the opposing drivers so the cabinet is inert even at high volumes but that is about it. For further distortion reduction you would need to look into a push pull design. For the purposes of smoothing via multiple subwoofers this subwoofer will essentially behave as one subwoofer. To achieve smoothing of the response via this method (if desired) one must place the subwoofers at different locations around the room. Often this will behave as a "fill" for the subwoofer which has a response dip where the other subwoofer may not have a dip and "fills" in the dip, it may also bring down a peak if there is cancellation at this peak (this may measure well in frequency response graphs but will not sound good). There are many possible phase issues with multiple subwoofers and this is something most do not address as the objectively inclined pay less attention to the sound and more to the frequency response graph, the phase response graph is often ignored. Phase issues manifest as sound quality issues, assuming the frequency response is as desired. At times while the frequency may show a smooth response the subwoofers output at the mic may be delayed in ms, this also contributes to poor sound quality. Please note that at time you may see "in phase" but the sound may be a "full cycle" or more delayed. Time delay in ms and phase in degrees is not to be confused, they are related but not the same. Time in ms is regular time, phase measures in cycles of a particular frequency. A last point of note is making multiple subwoofers integrate at the crossover to the mains is tricky as it may be difficult to align both subwoofers, sometimes people have enough troubl integrating one subwoofer.

 

[Analogous]

@Decadent_Spectre, thank you for the clear explanation. You have explained it well. So even though it has two opposite facing drivers, they both are in the same phase, in one enclosure and in one spot. Hence the effect is that of a single sub.

 

[sandeepmohan]

Is this a normal behaviour for an identical sub?

No. Is this the case no matter where you place the sub woofer in the room?
Glad you go the amp and sub replaced. I am curious as to what failed or happened to one of them. If the amp did not fail, you tend to point to the driver and that is rare.

@Analogous
You might to read the Authors experience (Setting up) of using a KC62 here

 

[Analogous]

You might to read the Authors experience (Setting up) of using a KC62 here

@sandeepmohan, thanks for pointing me to this review. I read it before I bought the KC62. Reading it again after having it in my setup for a while is a totally different experience! I can empathise with what the author is saying about this sub and how it sounds. It’s a very good sub and quite easy to integrate with my stand mounts.
An added bonus on re reading Herb Reicherts review was I discovered this exquisite album called “Madar”
Thank you !

 

[Love4sound]

No. Is this the case no matter where you place the sub woofer in the room?
Glad you go the amp and sub replaced. I am curious as to what failed or happened to one of them. If the amp did not fail, you tend to point to the driver and that is rare.

It must be the driver. Even rythmik first thought it was the amp and had it replaced but still there was no change with spl and frequency response.