NGD: Line6 PowerCab, questioning if it is working properly

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

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!