Keith's Acapella system

Keith_W

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Mar 31, 2012
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I am having some issues taking measurements with my system at the moment.

The problem: I use an Earthworks M30 and RME Fireface UC. In the past, I have had no problem and it worked perfectly. Recently I noticed I have to turn the gain all the way up when taking a sine wave sweep, and I am unable to get an accurate reading below 80Hz and above 3kHz.

I own 3 microphones - an Earthworks M30, and two Behringer ECM8000's. I also own 3 interfaces - the RME, and a Focusrite 2i2 and a Presonus Audiobox USB. I need the 8 channel capability of the RME, and my only use for the other interfaces is for diagnostic purposes.

Experiments:

Microphones
. I have excluded the mics as the problem. All 3 of my mics work fine with the other two interfaces, although I am only able to sweep 2 channels at a time with those. If I use the RME, both the Behringers fail to register the sweep even with the gain set to maximum. If I use the Earthworks, I can get a reading but I have to increase the gain.

Cables. I have excluded the cable as the problem. A check with a multimeter shows they are passing current correctly.

Interface: Through process of exclusion, the only remaining possibilities are a software issue, or a hardware problem with the Fireface UC.

The first thing I did was check the settings in Totalmix. Everything looked fine.

I ran a loopback measurement (DAC output --> mic input) with a cable. It looked fine.

I checked if it was outputting 48V Phantom Power with a multimeter. It registered 50.1V, so I have confirmed that the mic is getting phantom power.

I can not think of anything else to test. I am convinced it is either a hardware issue with the Fireface UC or a software issue, yet the limited number of tests I can do on the hardware reveals no faults, and looking at Totalmix it looks OK. Replacing the Fireface UC is not a trivial matter because it is so expensive.

I am now thinking of putting the Focusrite in series with the RME, effectively using the Focusrite as a mic preamp for the RME. I will have to purchase a new cable, which I am unable to do over the Easter long weekend.

If anyone has any ideas on what else I can test I would be very grateful.
 

Rensselaer

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Since i'm new here I thought I would post a description of my system. Some of you would know me from other forums and would be familiar with my journey. It has been a rather unique one, and more or less centers around my struggle to get my speakers to work properly.

The Acapella Violon has a plasma tweeter, a horn midrange, and a conventional bass cabinet. When I bought these speakers in 2007, I was aware that the bass was its downfall. It was muddy, indistinct, and noticably slower than the midrange and treble. However, the midrange and treble was unlike anything else I have ever heard - crystal clear, dynamic, and utterly revealing.

At the time, I thought I could cure the bass with a few simple tweaks (e.g. bi-amp, subwoofer, etc) but little did I know! Making this speaker sing has taught me a LOT about audio. Along the way, I obtained a measurement setup, dissected the speakers, tried to understand loudspeaker engineering, bought a subwoofer, bought a crossover, performed some surgery to bypass the internal crossover, learnt how to program a DEQX, and finally got a custom driver manufactured to my specifications. My speaker is completely unique - the drivers I had manufactured are a special one-off, and there are no speakers anywhere else in the world in existence that use the same driver. Many thanks to a local speaker engineering firm (SGR) for many hours in consultation and help.

This is the equipment list:

Source
- Playback Designs MPS-5
- Micro-Seiki BL-99V turntable, MA-505 Mk.2 arm, Lyra Dorian cartridge, RCM phono stage

Amplification
- Cary SLP-05 preamp
- Marchand XM-44 crossover
- DEQX HDP-3 crossover
- Cary CAD-211AE power amp
- SGR EL30S power amp

Speakers
- Acapella High Violon 2001
- JL Audio F110 subwoofers x2

Cabling
- Acrolink 6N and 7N
- Transparent

Here are the pictures:




The vertical panel of lights next to the subwoofer is the DEQX HDP-3. Its sole purpose is to perform subwoofer corrections, however I may have other plans for it.




Equipment stack. SGR rack.


CD collection in 2010


CD collection in 2012. On the top left of the CD rack is my remote receiver. It receives RF from the transmitter (Marantz RC9500) and controls the whole system via macros.

Finally, here is a video of my system:

Would you kindly do another video of your system playing from a pure analogue vinyl LP please, the speakers sound harsh on this video and I suspect it is because of the digital, rather than blaming the horn speakers.
 
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Keith_W

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Thanks. I can't play vinyl now because the system is now all digital. As for why it sounds harsh, there may be all sorts of reasons ... quality of phone microphone, MP4 compression, Youtube compression, etc. And if you think it is because of "digital", well ... if I played back vinyl, it has to be digitized and uploaded to Youtube for you to view it, so you can't escape digital, even if there is an analogue source in there. I don't think you can assess sound quality from a Youtube video :)

But if you want, I can make another video.
 

Al M.

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And if you think it is because of "digital", well ... if I played back vinyl, it has to be digitized and uploaded to Youtube for you to view it, so you can't escape digital, even if there is an analogue source in there.

Please don't overwhelm us with commonsense logic, will you? ;)
 

Ron Resnick

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if I played back vinyl, it has to be digitized and uploaded to Youtube for you to view it, so you can't escape digital, even if there is an analogue source in there. I don't think you can assess sound quality from a Youtube video :)

+1
 

Rensselaer

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Ok then, your speakers sound harsh to me.
 

Al M.

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Ok then, your speakers sound harsh to me.

Agreed, the video sounds harsh.

But isn't this one of your system videos?


It sounds incredibly harsh to me. Intolerable. Also, it sounds brutally thin and bright.

The culprit is (hopefully only) the cheap digital iphone video.
 

Keith_W

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I see I am not going to convince you that evaluating sound quality through Youtube and computer speakers is representative of what systems actually sound like. So aaaaanyway! Let's move on!

Today, I was sent some files which had been pre-convolved with BACCH. If you are not aware, there are several tiers of BACCH. The cheapest tier limits you to inputting the distance between the speakers and the distance from the speakers to the listener. The software then calculates crosstalk cancellation for one listening position only, and you MUST sit in the position that you input to the software to hear the effect. More expensive tiers gives you a head tracker, which is done with a webcam. The software knows where you are and adjusts the effect depending on your position in the room in real time. Even more expensive tiers come with binaural microphones, so you can create your own head-related transfer function (HRTF), headphone corrections, and ... the ability to pre-convolve files.

Someone with the "pro" version processed some files for me, set up for standard equilateral triangle listening. So in effect I got to try out the cheapest tier of BACCH for free, for a few select music tracks.

Before today, I had only read about BACCH and heard one rather unconvincing demonstration. It is said to evoke 3D sound, where the soundstage expands beyond the boundaries of the room, and you can hear things from behind you. With the other demonstration I heard, the soundstage only widened by a tiny bit. Discussion with the owner at the time suggested that it was speaker and room issues that caused the effect to be so disappointing.

Well, with my speakers, and in my room, the effect was incredible. There are very few moments in my audiophile journey where I encounter something that has made such a dramatic difference. I wouldn't say that it worked as well with my system as descriptions elsewhere on the internet, but even then I could hear instruments coming from my right. With my speakers, the soundstage normally only extends as far as a few feet on either side of the speaker. I have never heard it extend so far that it comes from either side of the listening position.

With headphones, the effect was truly mindblowing. Now, the files that were sent to me were configured for speaker playback, so they shouldn't work as well with headphones. But even then, I could hear sounds coming from behind my head. Headphones normally project a limited soundstage and always sound like the sound is in your head. But not with BACCH, the effect that I was in a real room was utterly convincing. The only thing lacking was the physicality of sound which you will never get with headphones.

What was even more impressive was that the tonality did not change. My speakers still sound like my speakers, except that the soundstage is now ridiculously wide and the front half of my room has disappeared and there are musicians there.

I am now totally convinced. I will be getting BACCH, but it will be very hard work to get it implemented in my system because of all the computer stuff involved. Not to mention, I have to buy a Mac - and that comes with its own learning curve.
 
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Keith_W

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BTW, I have solved my wonky measurement problem. It turns out that I have a faulty microphone cable.

I am too much of a cheapskate to buy a long XLR cable for my microphone, so I got that length by joining a number of spare XLR cables together. What really threw me was that the fault was intermittent.

The penny finally dropped when I borrowed a friend's Motu to replace the RME. It immediately developed the same fault as my RME (i.e. not sensing enough gain on the microphone). I knew it wasn't the mic (since I bought a new one), so it had to be the cable.

I pulled out the cable and measured it for continuity with a voltmeter. All 3 pins were fine. Not convinced, I jiggled the cable around a bit more. Presto, no signal on one pin. I then separated them into 5 cables and tested each one. When I found the faulty cable, I opened it up to have a look. Turns out that the insulation was not installed properly, and the bare wire from pins 1 and 3 were making contact when the connector was twisted. This sends signal to the ground, which results in the gain being halved.

I am glad that this frustrating and mystifying chapter is closed. I have since re-measured the system and reinstalled new filters and it sounds incredible now. These speakers have dynamics and clarity like you wouldn't believe, especially since now the tonality has been fixed (now that I am able to take proper measurements) and the drivers are all time aligned.
 

Keith_W

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Now that I am able to do measurements again, I spent a bit of time repeating all the measurements and designing new target curves. These are the two that I came up with:

image.thumb.png.069bd188ed40cc70de21da7c4c917bd4.png

The top curve (in green) is something I copied from a friend after I paid him a visit and heard his system. This has some basis in science - if a speaker measures flat under anechoic conditions, the moment it is put in a room it takes on a tilt at the listening position similar to what is simulated in in this target curve.

The second curve (in red) is a modification of the target curve from Floyd E. Toole's target curve as published in JAES. This particular target curve started off with a flat downwards curve, similar to the one in green. Listeners were then allowed to twiddle with the bass/treble settings to their preference. The composite of their preferences is this target curve.

For those of you interested in the history of target curves, read Sean Olive's AES presentation and the target curve section of Accurate Sound Reproduction Using DSP (Kindle, purchase required).

I am able to instantaneously switch between the two filters using Mitch Barnett's Hang Loose Convolver with zero latency between switching:



image.png.df13cd5759c35e5a0c397c3db306d70f.png


You will notice there is a volume discrepancy between the two filters, which requires gain to be increased for the second Filter Bank. Volume matching was acquired by playing white noise and using an SPL meter.

So what does it sound like?

The straight tilt sounds brighter and a touch bass shy. The red curve has more body but too much bass. In truth, after listening to both of them back to back I think I would prefer something in between. So it's back to the drawing board tomorrow.

BTW you can probably realize the power and flexibility of DSP. I can replicate any target curve I like as long as I know the in-room response of the loudspeaker. This means I can copy the tonality of any system in the world. I can make my system have the slightly lean sound of Magico's, or the chest-thumping sound of Wilsons (the Wilson sound is achieved by having a low Q bass shelf between 60-100Hz). Also on my agenda is to replicate the tonality of my favourite speaker brand - ProAc. For that, I have to analyse a few published measurements of ProAc first.
 
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