SLOB project

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Nick
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Re: SLOB project

Post by Nick » Mon Jan 20, 2020 6:50 pm

One last question I couldn't solve so far: Why does nobody (at least I couldn't find anything) use servo controlled woofers in OB designs
I think like rats, we have a advanced form of Neophobia
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Re: SLOB project

Post by Wolfgang » Tue Jan 21, 2020 2:54 pm

I don’t want to use this thread for a topic that is not directly related to the SLOB. Just a quick last note because the results are simply so good.

It worked amazingly well to use “sound matching” for EQing the bass/lower mids. Of course I didn’t expect to get miraculously OB bass out of horns but I would say from listening to an A/B comparison just between the two bass recordings after matching that the sound of the Klipsch La Scala bass horn is about 30% closer to the OB bass “sound” (from video) than before.

The real amazing stuff happened in the overall sound after adjusting some frequencies with DSP (only from 50 to 400Hz, x-over point between the horns is at 200Hz). This was an incredible improvement in the bass but mostly in the full midrange as some “smearing” which was there disappeared completely. There is a stunning clarity and openness which was not there before with these speakers in my listening room despite sweet spot EQing and acoustic room treatment.The most interesting part was that the suggested corrections looked at first rather “wrong” and counterproductive.

If anybody wants to try this at home but doesn’t have the programs in order to do it I am offering to do the matching for the new EQ settings. The only thing I need are two bass audio files (ideally high resolution/5-10sec): one with the target sound and one with the target sound played with the audio system that needs to be adjusted. A simple but good near field recording of the bass is enough (I used a Zoom H5 at 96/24 for this purpose). Of course the audio system needs to be connected to some DSP device or analog EQ. No need for very steep PEQs it all happens with rather low Q filter settings.

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Re: SLOB project

Post by Ray P » Wed Jan 22, 2020 8:18 am

Wolfgang, there's a lot of technical stuff (that I've only skimmed through) in the thread you linked to, along with, perhaps, an element of 'willy-waving', so like the initial poster, I don't have an understaning of the 'science' but I think Nelson Pass's last paragraph in post #16;
In any case, these days I have settled on a design which floor-faces one large woofer, as
seen at the last two BAF's. It gives a consistent asymmetry difference from 30 to above
100 Hz and sounds very good. I think I'll build some and put the Definimax 15's and
Lowthers in them.
is sufficient justification to give the SLOB a try as it is a sentiment I've seen supported by others with experience of the results.

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Re: SLOB project

Post by Wolfgang » Wed Jan 22, 2020 3:24 pm

Ray, I don't question the SLOB. I think N.Pass does really cool stuff from what I have seen. I am sure it will work.
My point was rather that if the OB bass can sound so good why not make some additional efforts and solve all/most existing problems around OB bass with a servo controlled woofer? Because at least some big part of the discussion in this thread was about OB bass-loss and how to deal with this problem and there was no clear statement/explanation from N.Pass IMO that slot-loaded bass would really improve the bass SPL at the listening position. But with servo control and powerful amp one can force theoretically and to a high degree also practically a woofer to do almost everything better (SPL, low frequency, quality).

What N.Pass means with "asymmetric difference" is not really clear to me.

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Re: SLOB project

Post by IslandPink » Wed Jan 22, 2020 3:29 pm

Wofgang - I really don't know enough about servo-controlled woofers. My understanding is they are mostly used for high power applications in PA. Do they sound any good at normal room HiFi levels ? It would probably need to bi-amped, as I have no idea what it's parameters would look like in a conventional crossover. My experiences have been mainly in the series-crossover applications with low power drivers which I favour for my own listening.
"The bass is the king of the instruments - it has no known natural predator" (Wobble)

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Re: SLOB project

Post by ed » Wed Jan 22, 2020 5:22 pm

I like/understand this explanation but don't know whether it's valid for simple home listening...

https://www.genesisloudspeakers.com/our ... advantage/
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Re: SLOB project

Post by Wolfgang » Thu Jan 23, 2020 12:04 am

I really don't know enough about servo-controlled woofers. My understanding is they are mostly used for high power applications in PA. Do they sound any good at normal room HiFi levels ? It would probably need to bi-amped, as I have no idea what it's parameters would look like in a conventional crossover. My experiences have been mainly in the series-crossover applications with low power drivers
For PA active speakers (not all are servo controlled)are used for different reasons. For example long distances(long cables) between mixing console and speakers and the need for setting delay times for aligning acoustically clusters of speakers makes it necessary to use active systems. There is also better control over the driver which is especially necessary at high SPLs.
Active systems need one amp per driver. Main benefits are better control of each driver (even without servo control) which cannot be achieved with a passive x-over and one amp for 2 or more drivers.

Servo controlled active woofer adds some really cool features: it controls the driver's movement by analyzing what the driver does in comparison to the input signal. In case there is any discrepancy (bass signal peak is over but driver's still trying to settle) the amp would actively stop this movement rather than let the driver's suspension or the compressed air in a box do their job. Rythmik Audio has a very good and short explanation:
"Direct servo can be thought of as an adaptive equalization system. To be more specific, it performs a transformation on the physical T/S parameters into a set of virtual T/S parameters. By doing so, the amplifier adjusts its output so that the frequency response behaves as if the driver possesses these virtual T/S parameters."

Servo controlled woofers sound noticeably better (independent of volume levels...but the louder the better because there is no audible distortion added by misbehaving drivers), like "tight" instead of "sloppy", bass sounds more "dry" which opens up the whole midrange with its subtle information ( mostly in the upper bass/lower midrange ) about the acoustics of the recording venue/studio etc.

Interestingly enough: What I tried with the "sound matching EQ transfer method" (I just named it like that) is based on the same principle of an "adaptive equalization system". Of course it cannot be as effective as servo control but follows the same principle. But instead of controlling the movement of the woofer by analyzing its actual movement I set fixed EQ parameters derived from a "dry" sounding woofer which makes the actual woofer operate as if it would have different parameters like those from a dry sounding woofer. These parameters look counter-intuitive compared to DSP adjustments of room acoustics like in the case of too much or "bloated" bass and don't include room acoustics as a result of near field recording.
I like/understand this explanation but don't know whether it's valid for simple home listening...
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Re: SLOB project

Post by Ray P » Fri Jan 24, 2020 7:19 am

Interesting OB project using Lii Audio drivers...

http://www.modelpromo.nl/The%20Liiondia ... peaker.htm

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Re: SLOB project

Post by Nick » Fri Jan 24, 2020 8:51 am

Much like my plan but the bass using the supravox should avoid having to padd the 10 inch down.
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Re: SLOB project

Post by Ray P » Fri Jan 24, 2020 12:17 pm

Yes, I thought that. Shame the two Lii units have the disparity between their sensitivity specs.

I though these might be a good match for the Lii 10inchers

http://greatplainsaudio.com/wp-content/ ... -Sheet.pdf

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Re: SLOB project

Post by simon » Fri Jan 24, 2020 12:51 pm

Very interested to hear these Lii full rangers...

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Re: SLOB project

Post by Nick » Fri Jan 24, 2020 1:37 pm

Is the servo limited to pistonic notion though. Once the cone starts to breakup all bets are off.
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Re: SLOB project

Post by Wolfgang » Fri Jan 24, 2020 4:18 pm

The Liionidas OB looks like very interesting project.

With all these options it's very hard to make the right choices.I am really torn right now what to do. Building a H-frame bass with 2 servo controlled woofers and test it first with my existing PM6A horns (one channel only) or simply follow a plan and trust that it will fulfill my expectations. Right now it's all about the bass what drives me.

Is the servo limited to pistonic notion though. Once the cone starts to breakup all bets are off.
I assume this is about the Rythmik Audio drivers? I know from Backes&Mueller active speakers and my Velodyne sub that the piston mounted cotrol works really flawlessly. But in my understanding Rythmikaudio uses an even better way with their sensing coil next to the driver coil.

http://www.rythmikaudio.com/technology.html

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Re: SLOB project

Post by Nick » Fri Jan 24, 2020 6:12 pm

Wolfgang wrote:
Fri Jan 24, 2020 4:18 pm
Is the servo limited to pistonic notion though. Once the cone starts to breakup all bets are off.
I assume this is about the Rythmik Audio drivers? I know from Backes&Mueller active speakers and my Velodyne sub that the piston mounted cotrol works really flawlessly. But in my understanding Rythmikaudio uses an even better way with their sensing coil next to the driver coil.

http://www.rythmikaudio.com/technology.html
Neither and both. It was about the general idea.
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Re: SLOB project

Post by IslandPink » Fri Jan 24, 2020 6:47 pm

Nick wrote:
Fri Jan 24, 2020 8:51 am
Much like my plan but the bass using the supravox should avoid having to padd the 10 inch down.
I don't understand why the Lii bass unit is such high Qts ( ie. low magnet strength). If it had a slightly stronger magnet it would be 94 or 95dB and maybe 0.45 or 0.50 Qts and that would be perfect for passive ( non-equalised ) use on an OB.
"The bass is the king of the instruments - it has no known natural predator" (Wobble)

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