Identical subs with different frequency response, time domain and SPL

[Love4sound]

I have dual LV12F and ran into a problem with one sub. Both subs at same location and gain values are having a different frequency response, gain and delay values.Reached rythmik support who acknowledged this is not normal and have agreed to ship a new amp from us. So to explain in detail about the issues, I have one sub A in front and sub B at the rear. Both are rythmik LV12F. When I swap and measure them there is variations with the base frequency respone and gain which makes it difficult for dual sub calibration.so I have 4 images below. Image 3&4 is the biggest problem for me.How can identical subs have such variations. Let’s see how rythmik resolves this issue.

Image 1

Sub A(orange graph)and B(red graph) kept in the exact same location in the front. Same gain values,cables but variation of 3-5 dB and sub B and also see how attenuation is at 28hz. It doesn’t go all the way like sub A to 20hz.

Image 2

Sub A(orange graph)and B(red graph) kept in the exact same location in the rear. Same gain values,cables but variation of 3-5 dB with sub B

Image 3 and 4

Combined response of sub A and B. Red graph is with Sub A at front and Sub B at rear. Blue graph is both subs swapped but huge variations with frequency response. I need to change delay values to get better response

Image 5

Measured both subs at front with the u-mik kept close to the sub and not MLP. Here also same issue where sub B has 2-3 DB variation and starts to roll off at 28 DB.

 

[Decadent_Spectre]

Have you tried closemic?

 

[Love4sound]

Have you tried closemic?

What’s closemic?

 

[insane79]

Could be the Subwoofer cable? i have read even the subwoofer cable can be at fault for lesser output.

Give it a try.

 

[Love4sound]

Could be the Subwoofer cable? i have read even the subwoofer cable can be at fault for lesser output.

Give it a try.

I guess you have not read or understood my post completely. Please read clearly. Power chord, sub,gain,cables all are the same. Issue is gain, response is different when subs are swapped at the exact spot. This affects time domain. Rythmik support is very responsive. They kept replying to all my emails and with their guidance did back to back tests and based on the graphs shared they agreed for changing amp. Will take a month for it to arrive from us

 

[keith_correa]

What’s closemic?

Near-field [which your post indicates you've already done] as opposed to Far-field!

 

[Love4sound]

Near-field [which your post indicates you've already done] as opposed to Far-field!

Yeah which is in image 5. Rythmik support was very particular only with the near field response. Based on those graphs only they finalised on amp replacement. Already shared the graph and mentioned it in the post which is in image 5. Sharing again the graph and how I measured.

 

[Decadent_Spectre]

I'd suggest not moving the mic between the swapping of the subs and keeping it 6-8" from the center of the cone. Keeping the mic in the exact same position and the sub in the exact same position will give more accurate readings that are directly comparable. You did mention close to the sub but no other details were provided. The LF bump could possibly be explained by more output from the port (if this is a ported sub) reaching the mic, if the positions of the mic and the sub were not exactly the same. Does the subs amp have gain settings? I'm sure the upstream settings were not touched but sometimes the gain on the sub amp can be overlooked if it has one.

 

[Love4sound]

I'd suggest not moving the mic between the swapping of the subs and keeping it 6-8" from the center of the cone. Keeping the mic in the exact same position and the sub in the exact same position will give more accurate readings that are directly comparable. You did mention close to the sub but no other details were provided. The LF bump could possibly be explained by more output from the port (if this is a ported sub) reaching the mic, if the positions of the mic and the sub were not exactly the same. Does the subs amp have gain settings? I'm sure the upstream settings were not touched but sometimes the gain on the sub amp can be overlooked if it has one.

Yes the subs and mic where at the exact same positions. This graph also clearly explains the issue. This is the combined response of both the subs at MLP. Blue is sub B at front and sub A in the rear. Red is with the subs swapped. Having a boost of gain is different to the FR rolling off at 28.

 

[Decadent_Spectre]

I'd pay closer attention to the close mic, if indeed there were no anomalies in the testing and it was measured without moving the mic at 6-8" from the center of the cone then it is indeed strange. The MLP graphs are not useful in this scenario IMO.

 

[Love4sound]

I'd pay closer attention to the close mic, if indeed there were no anomalies in the testing and it was measured without moving the mic at 6-8" from the center of the cone then it is indeed strange. The MLP graphs are not useful in this scenario IMO.

I took countless measurements to make sure there is no errors.Placements where 100% same cause I have marked them in a manner that when ever I place the sub the foot rest will be at the exact location. The variations in MLP is what caught my attention. Cause same subs swapped giving different response. A mild variation in gain and response is fine but this variation indicates both subs are not performing the same even though they are identical. Look at the response at MLP in image 3 in the first post

 

[Decadent_Spectre]

In general troubleshooting is always done closemic to eliminate the room. Preferably outdoors. In domestic cases that is not always possible so closemic is used.

 

[Bloom@83]

Forget measurements for a sec , how much of this problem is audible when you are watching a movie ? And to what extent ?

 

[sandeepmohan]

You have not explained where or how your sub is receiving a signal? Is it from one or two pre outs of the AV receiver or have you used a Y splitter from one pre out terminal?

Also; what else have you tried measuring with those u-miks? This is only to rule out the mik's have not lost their calibration. Its unlikely to be the case but worth a check.

When you listen to each sub woofer by ear, do you hear any difference at all? If those graphs are to be believed, you're surely going to hear it.

 

[Love4sound]

Forget measurements for a sec , how much of this problem is audible when you are watching a movie ? And to what extent ?

Yes it is audible. Some scenes sound very flat

You have not explained where or how your sub is receiving a signal? Is it from one or two pre outs of the AV receiver or have you used a Y splitter from one pre out terminal?

Also; what else have you tried measuring with those u-miks? This is only to rule out the mik's have not lost their calibration. Its unlikely to be the case but worth a check.

When you listen to each sub woofer by ear, do you hear any difference at all? If those graphs are to be believed, you're surely going to hear it.

Before rythmik and the dealer finalised to replace the sub amp they did want to make sure and made me do all the tests. I measured directly from avr and also through mini dsp. Do note since cable, power chord
,gain settings where all the same and if there was issues with anything in the chain or the Mic the measurements wouldn’t be consistent.

 

[keith_correa]

Also; what else have you tried measuring with those u-miks? This is only to rule out the mik's have not lost their calibration. Its unlikely to be the case but worth a check.

Why would the microphone behave uncalibrated for one subwoofer and not the other?

 

[sandeepmohan]

Why would the microphone behave uncalibrated for one subwoofer and not the other?

I did say thats unlikely. To further confirm that it isn't the case, you can run the calibration on just about any speaker in the room. If it all lines up right, you rule it out.

 

[keith_correa]

It really doesn't matter if the mic's calibration is broken or not. In this case, he's measuring frequency response for BOTH subs with the SAME mic just to compare the SPL between both. Calibrated response is moot!

 

[spirovious]

Are those sub's from same batch? Few different parts in other sub may result little different curve. I hope all measurements are taken after burning in both subs for same hours.

 

[Love4sound]

I did say thats unlikely. To further confirm that it isn't the case, you can run the calibration on just about any speaker in the room. If it all lines up right, you rule it out.

Measurements are consistent so no issues with mic. I did measure LCR and the measurements are consistent

Are those sub's from same batch? Few different parts in other sub may result little different curve. I hope all measurements are taken after burning in both subs for same hours.

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.