audio-talk

That;s a shame, I also saw some useful bits and pieces but not £100 worth!

Getting my ducks in a row. I've ordered some PCBs to build a Nelson Pass ACA - 8W of single-ended Class A sand to complement the SE-OTL valve amps. I thought I would try the ACA on the bass driver in the SLOB (I have the option of a 40W chip amp if necessary, in which case it'll still be a nice amp to have around).

Following Nick's revelation that he's also bought some Lii FAST-10S drivers with plans to use them in a Quasar type OB project (coupled with his new Supravox 285s) It seems pertinent to raise a question that I've been mulling over for a few weeks.

Should I extent the 'wings' of the SLOB design vertically as in the Quasar?

The wings in the Quasar are for th ebenifit of the bass mainly, I thought you were using an entirely different approach to bass?

May plan is to start with a flat panel, then add the fast 10, and see what works for that, then repeat with the bass helper, so messing with the side panels is the main thing I guess.

I think you would be safe to extend the side panels up , but slanting down, past the mid driver. You just don't want them to be too deep, ie. much beyond 6" , at the level of the Lii, otherwise you will start to get some ripple from resonances.
I've never been quite sure about how to design the SLOB as a system, but the baffle size still seems to be important, as seen by the schemes Nelson shows.

Thanks gents. The reason I've been thinking about it is based on my assumption that the Lii unit will crossover fairly low down (<200Hz?) so will be producing some upper bass itself.

Yep. My next step with them is to make some simple baffles and see what the new driver is like other than sat on the floor. But I have lots to catch up on and will be away next week till the next Monday, so nothing till then at the least from me. As it is I have to catch up on the backlog of power supplies that need building.

Ray P wrote: ↑Sat Jan 18, 2020 7:03 am Thanks gents. The reason I've been thinking about it is based on my assumption that the Lii unit will crossover fairly low down (<200Hz?) so will be producing some upper bass itself.

It's not really a trade-off relating to the Lii producing upper bass. The extended sides are a way of slightly improving the low bass by further increasing the effective baffle size (width). The downside which limits you to approx 6" depth near the midrange source is colouration in the midrange. At some point it stops sounding like an open uncoloured driver and starts to sound a bit pipe-y . I have tried it years ago and found the limit (approx) as mentioned. I suspect James did the same practical test.

Yes I found the side wings added to the zing of the 208EZ wide band drivers around 2kHz which is why I moved to the simple flat baffle for the 208s and the H frames for the 285GMFs. Definite improvement.

I was wondering if some OB experts could shed more light on what the guy says in the video:



In my understanding the bass is the main benefit from OBs but then again it would need to come from bass drivers ("open source" OB?)that don't operate kind of "ported" like with the SLOB. Is this true?

Any bass from "boxed" systems has indeed a sound of its own which is a little "darker" or pressurized. I disagree, however, with what this guy suggests that OB is the only way (more or less) with which each bass note is clearly distinguishable. One can set up room acoustics perfectly also with other speaker principles and each bass note is clear with no smearing.

The bass in the video is amazing! But with close mic and at low SPL it is of course relatively easy to record perfect bass. Would it really sound like this with high SPL in a room at listening position?

Correct address for the video:

I'll try & check out the video later. briefly one aim of the OB is to get low group delay - OB being close to infinite baffle loading which is the lowest GD apart from a (big) horn, which is very hard to do for the bass.
Also the OB loading on the mid driver for vocals is to my ears the most natural-sounding way of loading the driver in that area. All of this came about from hearing OB's by Steve Shiels and James Doddington in our group here. James's speaker the Quasar (I) appears on Bert Doppenberg's BD design site if you go back far enough. This one is a subtle blend of two carefully chosen drivers on an OB with slanting side-wings, made from Perspex, and uses a series crossover to blend the two driver signatures together either side of crossover ( which is around 160Hz ) .

Wolfgang wrote: ↑Sun Jan 19, 2020 4:03 pm I was wondering if some OB experts could shed more light on what the guy says in the video:



In my understanding the bass is the main benefit from OBs but then again it would need to come from bass drivers ("open source" OB?)that don't operate kind of "ported" like with the SLOB. Is this true?

Any bass from "boxed" systems has indeed a sound of its own which is a little "darker" or pressurized. I disagree, however, with what this guy suggests that OB is the only way (more or less) with which each bass note is clearly distinguishable. One can set up room acoustics perfectly also with other speaker principles and each bass note is clear with no smearing.

The bass in the video is amazing! But with close mic and at low SPL it is of course relatively easy to record perfect bass. Would it really sound like this with high SPL in a room at listening position?

Wolgang, I would take the video with a pinch of salt; as you alude to yourself, at no point are you actually hearing the system in his room but just a facsimile of it.

In my experience from hearing OBs at, for example, our Owston meetings, the primary benefit is operating without a box and in so doing you can get a beautifully engaging, open and natural rproduction. The downside is that you lose bass output lower down so the challenge is to add a bass helper that complements the overall sound to get the overall balance better aligned - I don't think the starting point for an OB is the bass.

I don't think the starting point for an OB is the bass.

Not sure myself about that. Certainly what I find mine does better than box speakers is the bass. Not the extension, but the tonal quality of the bass and its temporal relation to the rest of the music is certainly what I think it does better. They can certainly sound more "open" than say a back loaded horn, as its hard to avoid hearing the horn, but if you are not worried about using just the one driver, then a wide range speaker in a OB will IMHO, sound much the same in a infinite baffle as long as its not broken in the attempt to extend the bass. The dipole nature will add more room reflections from the rear so that will add a bit if you are not near to the speaker.

With the OB bass sound of this video in my head I got so many ideas around this topic that I simply need to do some experiments.

Reading thought the diyaudio thread about the SLOB was rather confusing and somehow showed that slot-loaded bass doesn't add so much benefits regarding SPL as one might expect. (https://www.diyaudio.com/forums/multi-w ... anity.html)

So first I will try to "match" the sound of the recorded bass with a program which I use in my DAW that can match soundpatterns by analyzing frequency bands and transferring these EQ settings to another track. It works actually extremely well. Recording musicians/audio engineers will know what I am talking about. After getting the EQ settings I will transfer it to my DSP of my main audio system. Will be interesting how close I can get! I use my La Scala bass in combination with my PM6A mid BLH which I use right now for listening.

If that doesn't give me satisfying results I will try to build an OB bass unit (H-frame) and use it together with the BLHs. Are there any known problems of such an approach (active x-over)?

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 like for instance the CI series from Rythmik Audio? Wouldn't that solve many OB bass problems like bass loss, accurately stopping a free moving heavy woofer diaphragm, SPL at low freqeuncy etc?