Bass boost settings on ATC SCM 50 ASLT

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Bass boost settings on ATC SCM 50 ASLT

Postby xtraktz » Mon Dec 25, 2017 9:12 am

Hello everybody,

I found that amp-packs are installed on my ATC SCM 50 ASLT consumer version have sensitivity and bass boost adjustments without any marking. Also I found that bass boost potentiometers have settings to different levels (see screenshots below) and they do not set to reference level 0 dB.
I set both to 0dB, but manual says:
5.5 Bass Boost (SCM “Pro” only): Provides up to
6dB of gain in the region of 40Hz. Use a small
flat blade screwdriver to access the control. Adds more warmth and energy to
the lower frequencies in music, at the expense of accurate transient
reproduction. Note: Adjusting the bass boost without the ability to recalibrate
may leave a pair of monitors unmatched.

Why does my version (not pro) have these adjustments? Why they had different values for each amp-pack and greater than 0dB. How do I correctly set these values to factory default. What about recalibration? Should I do this?

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Re: Bass boost settings on ATC SCM 50 ASLT

Postby darrenyeats » Mon Dec 25, 2017 10:33 am

I advise reading ALL of the following thread before touching anything. The trimmers are easily damaged.
http://atcforums.co.uk/viewtopic.php?f=32&t=6061

Did you buy the 50s new or used? AFAIU the trimmers should be at the reference positions from the factory.

I'd guess these 50s had a previous owner and they were positioned in an asymmetrical room, hence non-matching bass settings. Maybe contact the previous owner or ATC.

If bought new, that's unusual so I'd definitely contact ATC.

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Re: Bass boost settings on ATC SCM 50 ASLT

Postby xtraktz » Mon Dec 25, 2017 10:57 am

I bought new.

I set both bass trimmers to the right stop (reference 0dB). But is it real (absolute) reference 0dB or at the factory the final settings may be different for each speaker and a "right stop" can not always be 0dB ?

To my ears, one speaker played bass louder, in the range of 20Hz-40Hz and in general it seemed to me that the bass was too much. So I decided to check the position of the trimmers , and change it when I noticed their non-standard position.

P.S. Why not make an external reliable knobs with fixed values? Or do not do it at all.
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby darrenyeats » Mon Dec 25, 2017 11:41 am

By resetting back to ref (0dB) at the right stop, you've done the correct thing.

ATC adjust relative level of bass/mid/tweeter at the factory, but internally - nothing to do with this setting. 0dB bass trimmer should be neutral.

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Re: Bass boost settings on ATC SCM 50 ASLT

Postby xtraktz » Mon Dec 25, 2017 12:09 pm

Thanks, I'll leave the bass boost at 0dB. But still I can not understand why they were not originally set to 0db, and also differed from each other. I would like to be sure that my current bass boost settings correspond to factory reference settings of 0dB.

On the one hand we have bass boost tuning, on the other hand - it is absolutely inconvenient.
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby MattSPL » Mon Dec 25, 2017 12:34 pm

Zero should be calibrated as zero.
It’s possible one of your amp packs wasn’t returned to zero after testing at the factory.

I did lots of testing in the past with the bass trims and input sensitivity and found the bass was affected all the way up to 100hz, possibly even higher.
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby xtraktz » Mon Dec 25, 2017 12:59 pm

MattSPL wrote:It’s possible one of your amp packs wasn’t returned to zero after testing at the factory.

Do you mean internal amp settings, which then tried to fix using external trims?
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby xtraktz » Mon Dec 25, 2017 1:01 pm

MattSPL wrote:Zero should be calibrated as zero.

How I can check it now? )))
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby darrenyeats » Mon Dec 25, 2017 1:13 pm

IMV balance of probability is what Matt wrote - the internal calibrations are fine and someone played with the trimmers afterward and forgot to reset.

1. It would make sense they have a process to check the trimmers are at ref before doing internal calibration
2. It would make sense they would check the operation of bass trimmer after doing basic internal calibration (1)

That's my view anyway.

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Re: Bass boost settings on ATC SCM 50 ASLT

Postby xtraktz » Mon Dec 25, 2017 2:10 pm

OK, let it be someone's evil joke with trimmers position and 0db it's really factory reference 0dB)) I sent an email about this issue to ATC support.

Thanks to all.

In which cases should I use a bass boost? How to use it correctly? I noticed that with bass boost more than 0dB, accuracy and speed are lost, and high and medium frequencies do not sound so open and clean. But the bass is more tangible, the sound is warmer, the images are larger.
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby MattSPL » Mon Dec 25, 2017 9:07 pm

Yes, the external trims should be fine and somebody probably just forgot to turn one back to zero.

What you describe about the bass trim effecting the sound signature is exactly what I found. The speakers sound much better with the bass at zero. If you want more bass, you could try moving the speakers closer to the back wall, or add a sub if that interests you.
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Re: Bass boost settings on ATC SCM 50 ASLT

Postby Brad Lunde » Wed Dec 27, 2017 3:30 am

The bass boost/sensitivity settings were in Mark 4 amp pack pro monitors from the beginning I believe. I do know that I remember seeing consumer amp packs that did not have these adjustments. I later asked the factory about it and they said they have now standardized this, so both consumer and pro where the same Mark 4 amp pack. Not sure when this standardization occurred but it would have to be after 2002? 2003?

Discrete amp systems do not have either of these adjustments.

Bass boost was installed in pro systems to compensate for studios with too much absorption, where the room was overly dead and had no low end. They were originally designed for someone to install and then quietly calibrate them once and never touch then again. ATC hid the controls for pro users, once they find them, do two things: turn the bass up to full and ruin the translation of the speaker (mixes come out sounding too thin, lacking bass because you "think" there is more bass than there is) and two, constantly fiddle with it as different engineers have varying degrees of desired bass and then break the PCB pot. Once broken, it breaks the signal path and no more audio! We always tell our clients to use a soft plastic trimmer tool only, this is how best to not damage the speaker for it retains the best "feel" when you re hunting for the tiny pot slot.

A lot of speakers have been damaged in the US and put out of commission by someone sticking a screw driver in there (metal screw drivers reduce "feel" and you cannot tell how hard you are pressing, so they push too hard) and then crack and damage the tiny little pot -which was designed to be set once to the room and never touched again.

The sensitivity control was there for some studios use 1V for full output and some use 2V. If you turn it to 2V the speaker takes more to drive it to full output, so this is confusing sometimes to users as 2V would seem "louder" than 1V.

I've seen threads on here about trying to maximize level on their preamp, the speakers are at full volume at too low a setting. This is a case where turning the sensitivity down to 2V helps.

When I find a user blowing up woofersI usually also find the bass boost was turned up.

Since records vary so much in bass, it would be a mistake to pick one as perfect and adjust to that. It would be wrong for nearly everything else.

I highly recommend that you leave the sensitivity setting to factory and the bass boost to zero. 0dB boost is the only setting that is right for all sources.

Brad
Brad Lunde
Lone Mountain Audio, part of TransAudio Group
ATC Importers USA

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Re: Bass boost settings on ATC SCM 50 ASLT

Postby darrenyeats » Wed Dec 27, 2017 2:15 pm

xtraktz wrote:I noticed that with bass boost more than 0dB, accuracy and speed are lost, and high and medium frequencies do not sound so open and clean. But the bass is more tangible, the sound is warmer, the images are larger.

Without getting into a big discussion, the advice given by ATC in the manual is good:
"Start with them positioned on appropriate stands around 1 metre from the side walls and 2 metres from the back. If the balance is bass-light, the monitors can be moved towards the back walls."

For me in my room, they work best actually rather near the back walls! There's a point where the bass and image size is optimal. Close placement to the back wall is not harmful ... but objects that are not kept behind the speaker baffles AND that are close (<1 metre), such as racks, TVs, furniture may disturb the sound which explains, to my mind, why people disagree sometimes about moving the speakers back. I have my equipment rack behind my listening seats, and use long interconnects.

It's good also to aim for an equilateral triangle between listener and speakers - "ish".

If you're forced to locate them near (<1 metre) to side walls, mitigate with treatments at the side wall first reflection points. I do this.

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Re: Bass boost settings on ATC SCM 50 ASLT

Postby Brad Lunde » Wed Jan 10, 2018 7:06 pm

darrenyeats wrote:
xtraktz wrote:I noticed that with bass boost more than 0dB, accuracy and speed are lost, and high and medium frequencies do not sound so open and clean. But the bass is more tangible, the sound is warmer, the images are larger.

Without getting into a big discussion, the advice given by ATC in the manual is good:
"Start with them positioned on appropriate stands around 1 metre from the side walls and 2 metres from the back. If the balance is bass-light, the monitors can be moved towards the back walls."

For me in my room, they work best actually rather near the back walls! There's a point where the bass and image size is optimal. Close placement to the back wall is not harmful ... but objects that are not kept behind the speaker baffles AND that are close (<1 metre), such as racks, TVs, furniture may disturb the sound which explains, to my mind, why people disagree sometimes about moving the speakers back. I have my equipment rack behind my listening seats, and use long interconnects.

It's good also to aim for an equilateral triangle between listener and speakers - "ish".

If you're forced to locate them near (<1 metre) to side walls, mitigate with treatments at the side wall first reflection points. I do this.


Very good advice!
Brad
Brad Lunde
Lone Mountain Audio, part of TransAudio Group
ATC Importers USA

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