NGD: Line6 PowerCab, questioning if it is working properly

Gear & Tools Talk
1

I got a new amp a couple weeks ago. It has taken me some time to get used to the difference in sound, but I am still uncertain it is working properly. I am looking for advice from others that may have some background looking at frequency response curves. This question will be somewhat technical.

The amp is the Line6 PowerCab Plus. I got this since it is intended as a good mate for my Helix LT.

For several months, I have been using my Helix through a Spark 40. The Spark has always felt a bit thin compared to what I hear from larger cabinets and more common amps in guitar stores. I had created an IR to flatten the Spark response so the models in the Helix were expected to be somewhat accurate once played out the flattened Spark.

The new PowerCab immediately felt bass heavy. I somewhat expected this since I expected it to handle the bass with more air movement. After a couple weeks listening to it, I did start to get used to it, but something still felt off. I decided to run a frequency sweep to see what I could learn.

The setup for the sweep is:

  • computer USB into Helix
  • Helix through with no models and global EQ off
  • AES (6-link) to PowerCab (25 feet)
  • PowerCab in FRFR (full range, flat response) mode
  • budget mic with cal data
  • REW software running the sweep and using the mic cal data (where appropriate)

Measurements proved out my setup looked ok:

  1. Measuring the USB out of the powerCab gave me a dead-flat response, so the Helix was not rolling off the PowerCab input
  2. Measuring the 1/4 inch out on the Helix gave me a pretty flat response (about +/- 1.5dB), so the mic input was not rolling off
  3. Measuring the mic’d speaker out is giving me an unexpected shape, but it does match what feels off to my ear

frfr_pcab_not_so_flat
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There is agood deal of low frequency rolloff from about 130Hz. There is maybe 7-8dB from the A (about 110Hz) to the E (about 82.4Hz). I would not call this “flat response”.
There is also a good deal of rolloff from a peak about 130Hz to around 1.3kHz, which is about the top end of the high E string at 24th fret. Again, not what I would call flat response, but not as harsh as the bottom end rolloff.

So, what should I expect here? is it normal for guitar speakers to have this shape? Can I believe in the models in this PowerCab to give a good representation of the speakers it advertises?

I also measured the individual models in the PowerCab and they have the basic shape seen in the image. It makes them not sound very different to me.

I was able to flatten the PowerCab response with a home-built IR. Using that, it is pretty flat from about 70Hz to 5kHz. It also seems to sound “normal” to me when trying different models from within the Helix rather than using the PowerCab. Maybe my “normal” is based on too much time with a thin-sounding speaker (Spark)?

I’m interested in comments and experience of folks that have some familiarity with what I am talking about. I’m not sure if I need to contact Line6 and get this replaced, or if I am just too new to know what I should get. Right now it is my career as an RF electrical engineer that is suggesting there is something wrong since this is certainly not a “flat response” in anything I have seen in around 40 years in my field.

Kinda long question there, but it required enough background. Thanks for reading through!

2

This is a follow-up on the results of talking to Line 6 about my concerns that the amp is not really flat.

Line 6 was very good with taking time to work with me and answer my questions. Their willingness to answer a clearly unusual concern was pretty good, but not as complete as I wanted. I think this was on the part of the engineering staff, not the customer service staff.

The short answer is that Line 6 engineers have rolled off the “flat response” so that it sounds good when playing guitar through it. They did not address my question about the flat response not being flat, nor did they address my concern that the modeler in front of this amp will already have the same rolloff applied as part of the model. In practice, if I desire a flat response, I have created an impulse response that is loaded into either the Helix or the PowerCab (as I wish) and then I have the neutral canvas for the modeler to play into as I expected to have natively.

Now that I have had this for a few months, I find myself using the PowerCab speaker emulation modes rather than the flat mode with helix models handling the EQ. I don’t use the Helix cabinet models much since they appear to have the associated speakers as part of the cab model. There are a couple of speaker emulations that sound very nice in the PowerCab, and the rolloff built into the PowerCab is necessary for those.

In general, I feel that using less digital manipulation gives me a more enjoyable sound, so avoiding the IR files helps. The PowerCab is pretty expensive for just a few speaker models, and I suspect that the Catalyst would have been just as useful for me at around 1/3 the cost. I’m not dissatisfied with the PowerCab, but it certainly is missing the “flat response” as advertised.