SLOB project

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JohnG
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#121 Re: SLOB project

Post by JohnG »

Being the 'eternal optimist' that I tend to be.
Could that mean a accumulation of a Discount to 45%.
Must be worth a Punt, putting the proposition to a Vendor.
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Ray P
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#122 Re: SLOB project

Post by Ray P »

Do 'eternal optimists' not do compound discounts as part of their optimism?

Anyway, why not post the info. so people can mull it over...
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chris661
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#123 Re: SLOB project

Post by chris661 »

rowuk wrote: Mon Dec 30, 2019 9:51 am Surface area x excursion=sound output. You are talking about huge baffles. That creates a large need to either dampen (ugly with transparent materials) or create many isolated “panes” that do not get excited by the single driver. Stiffening the structure just moves the resonance higher up in frequency - makes it more audible. I would think that anything less than 25mm would have audible artifacts unless you can find a good looking decouple scheme.

If you had 2 thinner layers of plexiglass and filled between them with colored sand, it could be attractive and acoustically dead at the same time. The patterns from the colored sand could change over time.
Highlighted by me, for the purposes of dispute (of course).

While the resonant frequency goes up, so does the Q-factor. At higher frequencies, there's also less energy being transferred to the baffle. The net result is that the resonance is actually very difficult to excite, resulting in reduced audibility.

Chris
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rowuk
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#124 Re: SLOB project

Post by rowuk »

chris661 wrote: Tue Dec 31, 2019 9:45 am
rowuk wrote: Mon Dec 30, 2019 9:51 am Surface area x excursion=sound output. You are talking about huge baffles. That creates a large need to either dampen (ugly with transparent materials) or create many isolated “panes” that do not get excited by the single driver. Stiffening the structure just moves the resonance higher up in frequency - makes it more audible. I would think that anything less than 25mm would have audible artifacts unless you can find a good looking decouple scheme.

If you had 2 thinner layers of plexiglass and filled between them with colored sand, it could be attractive and acoustically dead at the same time. The patterns from the colored sand could change over time.
Highlighted by me, for the purposes of dispute (of course).

While the resonant frequency goes up, so does the Q-factor. At higher frequencies, there's also less energy being transferred to the baffle. The net result is that the resonance is actually very difficult to excite, resulting in reduced audibility.

Chris
Hmm. Not my experience. If the Q goes up (depends on how we make it stiffer), then it is even more of a problem. Low Q means wide band noise. Higher Q can even result in single tones - VERY audible. Inside of a box, we can do many things with bracing or like with B&W a matrix. Open back are a different story (which is why I mentioned it). Sand could be a very attractive solution with audible benefits.
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rowuk
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#125 Re: SLOB project

Post by rowuk »

IslandPink wrote: Mon Dec 30, 2019 10:00 pm You make it sound like nobody could get OB to work, Rowuk, but in fact we've had some great sounds over the years from a number of OB projects shown at our meetings.
I'm not a fan of big flat baffles - having (slanted) side-wings to stiffen things up and extend the effective baffle size is the way to go, in my books. I also don't buy this theory that stiffening = higher Freq = just as bad . I've only ever had positive results from stiffening speaker sides or baffles. The amplitude decreases dramatically when you add stiffening ribs or side panels.
Two thinner pieces of Perspex with sand in the middle sounds fine unless you also want the Perspex to make the thing transparent and hence more room friendly - as I do.
Open back can be very compelling. Siegfried Linkwitz followed it his whole life long with wonderful results that he shared with the world. His solutions were well engineered, documented and not prone to unpredictable resonances. As far as stiffening goes, I am sure that there are "rules" to follow. I have heard some VERY bad large open back speaker resonances (even from experienced designers like Wolf von Langa) - which is why that I mentioned it in the first place. "Thick enough" Perspex should also be fine. For conventional speakers and horns that I built I found that the thickness was best when it was the same as I would have used with MDF.

That all being said, I don't understand the criticism of a suggestion. What we get before we cut wood saves us time and money later. I thought that the purpose of sharing concepts/builds like this on line was to get more input (and praise when it works out)...
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Ray P
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#126 Re: SLOB project

Post by Ray P »

I didn't get around to testing the Fast-10S units yesterday as i spent my time working on the 6C33C amplifier build - I need to clear some projects out of the way before I get piles of plywood etc. arriving. Hopefully later today.
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#127 Re: SLOB project

Post by Scottmoose »

Well, on the subject of panel resonance, as Toole points out, the ability to hear a nominal panel mode depends on the ability of the driving signal to actually excite it in the first place. There are plenty of tests out there using pink noise etc., but this is rarely representative of what we usually listen to in a speech or musical signal:

'If the signal is at the correct frequency and lasts long enough, one can hear high-Q resonances; if not, we don’t. Medium- and low-Q resonances have wider “footprints” in the frequency domain, so more frequencies can excite them, and they need not be very long to achieve full effect. Consequently, we end up hearing them more readily. The duration of the ringing, except at low-bass frequencies, appears to be just an interesting engineering observation...'
Toole, F. Sound Reproduction: Loudspeakers and Rooms (London: Focal, 2008) p.449

How much energy is available to excite a resonance also depends on where that resonant mode is, in the frequency domain. Slap-bang around system tuning? Not so good. Higher up, where there is typically less mechanical movement in the driver / arguably less energy being put into the structure? Less likely. YMMV as always of course.
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Ray P
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#128 Re: SLOB project

Post by Ray P »

I'm having a listen to the Lii Audio Fast-10S units as I'm typing this. I've borrowed the kitchen player and squirreled myself away in the spare room - the player is a cheap 'all in one' system made by Sharp so I wasn't expecting revelatory sounds but I now know that the electronics part of the system is far superior to its speakers as the Lii units have transformed the sound.

First things first, both speakers arrived safely as there is no sign of anything being out of alignment, rubbing, etc.

Cosmetically, the cones have a darker patina than in the pictures on the Lii website, where they look positively bleached by comparison. The colour is quite nice in a retro sort of way. The basket is cast and is a little rough in places but it doesn't matter sound wise and will not be seen for the most part.

The cones have clearly been selectively treated, the wizzer and inner part of the main cone are a subtly darker colour and have a slightly tacky feel (but not enough to leave a fingerprint) but the outer sections of the main cones (where the concentric rings have been moulded into them) appear to be untreated. There's a compliant ring around the inside edge of the basket ring (the darker grey ring, seems to be some sort of rubber-like material).

Anyway, sound quality wise I think these units have excellent potential. Even just sitting on their own (see the pictures) they have much more bass than the Sharp speakers (and with no discernible cone movement). Even with the Sharp electronics there's a lot of nicely layered detail and the sound is easy to listen to.

Image

Image
Last edited by Ray P on Wed Jan 01, 2020 4:28 pm, edited 1 time in total.
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Ray P
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#129 Re: SLOB project

Post by Ray P »

And, as we all know, a couple of extra inches makes all the difference - these units seem massive compared with my Lowthers.
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pre65
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#130 Re: SLOB project

Post by pre65 »

Nice one Ray.

Looking forward to further bulletins. :)
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Ray P
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#131 Re: SLOB project

Post by Ray P »

and, as for the Fostex FE167E (rediscovered last evening!)...

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IslandPink
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#132 Re: SLOB project

Post by IslandPink »

Very good. It's encouraging to hear how much they have done to the cone design & treatment. Seems like some work has gone into them.
Extra bass on these will be a lot to do with the relatively high Qts of 0.46 to 0.5.
I'm interested to hear if they sound good on vocals , the 167e's are a useful comparison, they are relatively benign as far as Fostex units go, and I have owned a pair twice (!) However the 167's will be a bit lighter and more up-tilted in response without a baffle to help.
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Ray P
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#133 Re: SLOB project

Post by Ray P »

IslandPink wrote: Wed Jan 01, 2020 4:31 pm I'm interested to hear if they sound good on vocals...
Very good in spite of the limitations of what's driving them.

I'm planning to hook up the Fostex 167's later and I'm expecting them to sound a lot 'lighter'.
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Ray P
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#134 Re: SLOB project

Post by Ray P »

I repacked the Lii units and have just had a short session with the Fostex FE167E drivers. The sound was significantly lighter in weight but then that is to be expected.

First thing I noticed was that to get a 'similar' (i.e. not scientifically measured) volume I had to turn the volume up a bit. Overall, the 167s were really very good considering the context of the test, plenty of detail and voices were well presented. There was a slight edginess to the sound compared with the Lii units but that may be a function of asking the cheap amplifier to work harder or maybe its just because they've been sat completely dormant for a few years?

I think I need to give both sets of drivers a longer workout.
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IslandPink
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#135 Re: SLOB project

Post by IslandPink »

Excellent - thanks. Still very encouraging if the Lii units sound less edgy than the 167e's.
Fostexes do need a little while to warm up, though. keep me posted ( as you will :) )
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