ART Cleanbox frequency response

[Ilkka]

Since the ART Cleanbox is often recommended to those having low signal level problems with their pro amps, I thought to try it out. For my disappointment, it turned out to be less than adequate for my needs.

Here's its frequency response (measuring system is flat).

As you can see, its FR starts to roll off already at ~200 Hz. Here are some numbers:

Frequency / "Down" at that frequency
100 Hz / -0.4 dB
50 Hz / -1.5 dB
20 Hz / -5.4 dB
10 Hz / -10.3 dB
5 Hz / -15.9 dB
2 Hz / -22.6 dB

So unless your system definitely needs some extra protection down low, or you have too much "room gain", I wouldn't recommend using it. It's like adding an extra ~1st order high pass filter at ~30 Hz.

I also found out that it adds some noise (low S/N ratio) into the system.

My ART Cleanbox is for sale. Anyone?

[Sonnie]

This doesn't sound good at all for Mr. ART...

[SteveCallas]

Another one bites the dust and another valuable piece of real world info from Ilkka. Now imagine if someone was using a Velo SMS with an Art Cleanbox in the chain coming from a HK receiver......wow, instant HTIB subwoofer

What's the fix, I have been debating on the ep 2500 or the carvin hd1800. I have read there were no problems with the preout voltage on the Carvin but have heard of problems on the ep 2500. If the real world watts on the ep2500 is about 2000 what is the real world watts of the carvin?

[brucek]

I have read there were no problems with the preout voltage on the Carvin but have heard of problems on the ep 2500

The input sensitivity of the EP2500 is +4dBu. That's a standard output level of retail equipment. I can't imagine that there would be a level problem...

brucek

[crackyflipside]

Wow!

[Sonnie]

I have no problems and no one else does that I know of with the EP2500, but I suppose the receiver could make a difference.

[Chrisbee]

I am running my Naim stereo preamp straight into my sub's EP2500.

I don't even have the Behringer's control knobs set at full on. Currently 28 out of 34 full scale.

[soho54]

I knew I had some major loss somewhere below 15Hz, but I never checked there. It never even crossed my mind. I just gave up. I feel the tweaking urge again. I don't know if I should thank you, or punch you.

Now I know why I can run my RS Sonos at 0dB all day, without killing them. Everything below my tuning is "well" dampened.

[Sonnie]

I suspect there are quite a few people using this piece of equipment that have no idea what it is doing to their signal.

[FlashJim]

brucek wrote:

The input sensitivity of the EP2500 is +4dBu. That's a standard output level of retail equipment. I can't imagine that there would be a level problem...

brucek

I didn't know that. Thanks!

[brucek]

Here's its frequency response (measuring system is flat).

Yeah, that's not too good a response.

The line driver I use is a Paradigm X-30. It offers about +13dB variable voltage gain along with two subwoofer outputs, one with full phase control. It also allows mono or stereo input and mixes the signals together. It even has three high pass outputs if you need them.

It's only fault I find is that there isn't a bypass switch to defeat the crossover when it's not required, although you can dial it fully clockwise and it takes it past the bass management that most people would use.

I use this device when my processor is in bypass, because the subwoofer signal is a full range analog mix of the left and right channel and requires bass management. When I'm in HT mode I dial the crossover fully clockwise.

Here's a response curve (since we're posting them). The crossover was set at full.



brucek

[Kevin_Wadsworth]

I’ll add one more thanks, Ilkka. I’ve seen this recommended several times – it never crossed my mind that it might affect the frequency response of the sub.

Perhaps a dumb question, but if you already have some type of PEQ in the chain, could you just apply a reverse filter to correct the signal loss from the Cleanbox?

[brucek]

if you already have some type of PEQ in the chain, could you just apply a reverse filter to correct the signal loss from the Cleanbox?

Gain filters reduce dynamic range and S/N ratio. In addition the lowest filter the BFD can use is 20Hz....

brucek

[Chrisbee]

This means I should really eliminate my CX2310 active crossover for unwanted (unknown) bass roll-off.

Would somebody please share the simplest method of measuring an active crossover using REW?

It would also be fun to see the variable frequency curves graphed if possible.

[brucek]

Would somebody please share the simplest method of measuring an active crossover using REW?

Ensure soundcard.cal file is loaded.

Ensure C-weight unchecked.

Ensure meter calibration file cleared.

Loop cable from line-out to line-in and ensure flat response is achieved.

Include the device under test in the looped cable and set up REW levels and measure....

The graph will be the response of the device....

Also see this thread on measuring the response of processors. Substitute your crossover for the processor.. You can measure any line level device as long as you can control its gain to 1:1 (unity)..

brucek

[Ilkka]

Chrisbee wrote:

This means I should really eliminate my CX2310 active crossover for unwanted (unknown) bass roll-off.

Would somebody please share the simplest method of measuring an active crossover using REW?

It would also be fun to see the variable frequency curves graphed if possible.

It's really easy. Make sure your measuring system is calibrated flat i.e. perform a sound card calibration. Unload mic cal file and uncheck C-weighting. Then put the device to be measured in the path between the line output and input. Take a sweep and there's your FR. Move the line so that the "flat" part reads 0.0 dB. That way it's more easier to read it.

And yes, every piece of device adds its own FR, whether it's flat or not, into the chain.

[Ilkka]

thylantyr wrote:

See figure 14. High pass filtering.

There's the formula and same circuit as the Rolls and probably the Art.
I calculate 33.85hz high pass, oddly enough this correlates with Ilkka's
comments of -> "~1st order high pass filter at ~30 Hz." from the Art.

We can probably guess that both the Art and Rolls are similar in design
and have similar performance numbers. Perhaps the 30hz high pass is ok
for pro audio use because that seems like a common number in high pass
filtering.

To modify the circuit then just replace that 0.047uF input capacitors
with a 0.47uF capacitor and you should have a 3.3hz high pass or
choose whatever you want.

You can examine the Art to see if it's like this and for a few cents,
swap out the caps and redo your measurements. Maybe you get lucky.

That's interesting. Maybe I will test it some day.

[bobgpsr]

thylantyr wrote:

If you can get Art cleanbox schematic or reverse engineer the circuit, I bet you
can do a simple mod to improve performance, most likely replacing a few
signal path capacitors.
...
To modify the circuit then just replace that 0.047uF input capacitors
with a 0.47uF capacitor and you should have a 3.3hz high pass or
choose whatever you want.

You can examine the Art to see if it's like this and for a few cents,
swap out the caps and redo your measurements. Maybe you get lucky.

I agree. I took mine apart and there are 0.047 uf mylar caps in series to the input gain pot. 1.0 uf and 47 uf electrolytic caps elsewhere. Would be easy to change them. I need to draw out the exact schematic and measure the pots, but will not be too hard. Standard 4558 op amps and a simple one layer ciruit board.

But no deliberate high pass filter like the TI app note. Just the accidental one from the simple input circuit.

[brucek]

As an aside, nobody ever would have to chain one of these with an SMS-1.

It would be interesting to see the frequency response of this device taken by REW......

brucek

[Chrisbee]

Thanks for the test methods.

Now I just have to work out how to get from XLR to minijack.

Edit: They do adaptors.

[ccdoggy]

I would love it if someone that actually knows what you are doing does some testing and gets reasonable results i would love to mod mine to improve it. Just need some reasonable directions and list of needed stuff to do it. I am totally clueless when it comes to detailed wiring and how it all actually works.

alas i am forced to use it so im always interested in upgrading and moding.

[Ilkka]

brucek wrote:

It would be interesting to see the frequency response of this device taken by REW......

brucek

"Slartibartfast" over at AV Talk forum has measured the SMS-1. I doubt the REW would show any different results but I can measure it when I get back home.

http://www.avtalk.co.uk/forum/index....&SQ=1182931696

Using the lowest setting...
-1.0 dB @ 20 Hz
-11.5 dB @ 10 Hz
-29 dB @ 5 Hz

So actually it's even worse than the Art Cleanbox...

[Sonnie]

:holycow: That's almost unbelievable coming from a sub manufacturer. How do they get away with charging as much as they do for it?

[brucek]

So actually it's even worse than the Art Cleanbox

Yeah, I'll stick with my BFD + X-30 combo...... haven't seen anything beat it yet.....

brucek