Are you (open) baffled yet?

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Konnichiwa,

phase_accurate said:
Is that a Beauhorn in the background ? How does it compare to your open-baffles ?

The smaller Beauhorn on it's own sounds very coherent, well balanced with perhaps a somewhat overly "fat" bottom. The Bastanis Prometheus manages a much wider bandwidth, better detail and much greater dynamic range (plus sensitivity), but slightly the cohesiveness of the Beauhorns (maybe more tweaking will bridge the gap...).

Sayonara
 
Konnichiwa Cat San,

Romy said:

So are any Web sources that you might suggest with the calculation of the open baffles?

Not really. I have pretty reasonable Spreadsheet that gives a good idea how things work, in room. The first thing to note, you require a driver with a Qts of 0.5 or higher to stand any chance of balanced sound.

If the driver has a Qt of 0.5 the output on an INFINITE baffle will be 6db down at the drivers resonance. Using a Driver with a Qt of 0.7 the output will be down 3db at resonance. Using a Qt of > 0.7 will result in a certain peaking of the driver output around Resonance, which can be used to offset the reduced output from open baffle mounting.

So, the baffle size needed relies on a complex relationship. Drivers with a Qt < 0.7 could be said to benefit more or less from as large a baffle as possible (within limits).

The second thing is that Olsons formulas for baffle width are inaccurate. For a simple "ballpark" idea, a plan Baffle with an assymetrically placed driver and a total circumference (all edges of the baffle measured) of 140cm (eg 27cm wide and 44cm high) will provide a +3db peak centered around 400Hz and will have
a -3db point of around 100Hz for the BAFFLE ONLY. The frequency scales with size.

SO if we had a driver with an Fs of 100Hz and a Qt around 1.0 (say a classic German Saba "Greencone" 8" Radio Full range Speaker) on the above baffle the result would be a speaker with a response flat to around 100Hz and then rapidly rolling with a slope a little steeper than 3rd order.

Now if we had a driver on the same baffle with a Qt of 0.2 and an Fs of 56Hz (say a Lowther DX2) we would have a system that is around 12db down @ 100Hz compared to the Midband sensitivity and rolls off below with a slope closer to 2nd order than to third order.

For reference, the Bastanis woofer on the baffle has around 50Hz Fs & a Qt of 0.6, meaning on an infinite baffle the driver will be 4 - 5db down @ 50Hz. The Bastanis Baffle is 36cm X 110cm giving a -3db point of around 50Hz, so as system the Baffle & Driver is around -7...-8db down @ 50Hz and around -2db @ 100Hz, all based on Backmanns analysis & classic TS parameter analysis, but seemingly in line with what I heard ( I have yet to make comprehensive measurements.

I hope this gives some basic datapoints for your work.

Sayonara
 
Konnichiwa,

fdegrove said:
Le vin est un Chateau Bricolo d'un excellent millesime..j'ose esperer.

Well, it was some french 2000 Vintage Bordeux. Nothing to write home about....

fdegrove said:
On a more serious note, alot of credit should go to Steen Doessing of SD acoustics for bringing both OB design and bi/tri wiring back to our attention.

I've owned a pair of OBS2 by SD Acoustics and would like to point to the importance of proper baffle design.

The baffle should be made asymmetrical IMO to reduce IMD.

Hmmm. I agree in principle on the Asymmetry, but the Bastins Speaker has basically a minimal baffle. It makes for a fairly elegant visual design, but less ideal acoustically. Had the baffle been about twice as wide the Subwoofer may very well have become optional....

fdegrove said:
Steen designed an OBS threeway which I can recommend to anyone.
It comprises a bass-reflex rear firing port woofer, the OBS midrange and a ribbon tweeter by Visaton.

I considered buying one of these from a 2nd Shop once, but they wanted silly money. Midrange was a modified Audax PR170M0 IIRC and the woofer also Audax.

fdegrove said:

Some really nice stuff you have there, TL.:cool:

Thanks. BTW, the Bastanis Speakers have surprised me (and a friend) by just HOW GOOD they are....

Of course, haveing 50W EL34 Push-Pull Penthode Watts available makes for an absolutely SILLY dynamic range on these around 96 - 97db/W/m sensitive speakers.... When playing one of the big warhorses (Mahler Thousand, Saint Saen Organ Symphony or my personal Killer favourite Mussorskys "Pictures" on Reference) I am grinning madly, just as on the 15" Tannoys.

Sayonara
 
Sayonara,

Unfortunately I have no knowledge about the Qt and Fs of my drivers but I got the picture, thanks.

Rgs,
The caT

PS: Try to tune yourself off from the Mussorsky’s orchestral version of the "Pictures…" This work is as vulgar in its orchestral rendering as musicality could theoretically be.
 
I´m still wondering what ...

Kuei

thank you for your calculation guidelines. Your spreadsheet seems to be much in line with the practical experience of people as I gathered it from the internet.

Since you emphazise the plan nature of the baffle:
How would you account for any backfolded parts of the baffle like the small wings on the Prometheus?
If I take (as an extreme example) a V-shaped baffle like in the illustration below (view from top) - what distance would be entered in the calculations? The green, blue or red one? Since dipole theory is all about the time difference between the front and back waves of the speaker at the hearing position, the red distance seems to be the valid one. Any ideas about that?
 

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Re: I´m still wondering what ...

Konnichiwa,

Rudolf said:

thank you for your calculation guidelines. Your spreadsheet seems to be much in line with the practical experience of people as I gathered it from the internet.

No profit or recognition to me. Planet 10 send me a copy of Backmans article, I eventually coded the formulas into a decent Excel approximation, no creativity involved.....

Rudolf said:

Since you emphazise the plan nature of the baffle:
How would you account for any backfolded parts of the baffle like the small wings on the Prometheus?

The small wings have the ability to slightly increase the wave radius. Once you take a wave as (sort of) spherical you realise that (short) folded back wings are acoustically nearly invisible. I fitted them merely to make sure the bleedin things stand stable....

Rudolf said:

If I take (as an extreme example) a V-shaped baffle like in the illustration below (view from top) - what distance would be entered in the calculations? The green, blue or red one?

Non of the above. Draw in a spherical wavefront co-inciding with the driver center.

Rudolf said:

Since dipole theory is all about the time difference between the front and back waves of the speaker at the hearing position, the red distance seems to be the valid one.

Almost, except that waves are not square, but spherical....

Sayonara
 
Dear, Mr. Wang

Perhaps you would suggest if the direction I looks is achievable.

I am kind of multi-ways-multi-amps kind of guy and what I am thinking is not something that would substituted my main system but I am kind of look at this project as a complementary system. Nop, not the second system (the notion that I reject religiously) but something that would be melted within my main installation….

I would like to build a mono active speaker that would be able to work from my line level and to cover from 100Hz and up. I am in pursue of the very SPECIFIC AND INTENTIONAL SONIC QUALITIES/ATTRIBUTES with this mono system and now I feel I eventually have found/collected/stolen all ingredients that I need.

The system is 2 ways. The mids will are cared full range by a pair of the 12” active coil 1938 Telefunkens (got two in mint condition) connected in series. The HF will unavoidable 120 degree T350, kicking in at 7kHz with a first order. It driven by two stages with a penthod outside (AM2+AL4) plumbing 8W. The sensitivity altogether will be around 109dB (with 10dB killed in the tweeter).

I certainly would like to make the open baffle as small as possible but here is a dilemma. The 12” Telefunkens 1938 in open air run down to 500hZ and die very sharp. In a sealed enclosure it run very smoothly down to–3 dB at 600 Hz and –6 dB at 100 Hz and then depart from life very quick. The geniuses from Telefunkens found the way to boost 15dB at 150 Hz by placing this driver in their open boxes of those radios from end of the 30s. You have to hear how those enclosures sound themselves just when you knock on them! Those enclosures from those radios sound like an Amati from 1651! I am not kidding! The tone that those Teles enclosure-resonators do is mind boggling!

Now, the question: is any KOSHER ways to get somehow 15dB gain in an open baffle at 150-300Hz or I bound to use those open-box-resonators that Telefunkens used? I intend to use it only as the open baffle and the only chooses would be the original Telefunkens-box- open-baffle or my own flat-large panel. The second it much more desirable but what can I do with 15dB gain at upper bass?

Rgs,
The Cat
 
*** As our samurai friend says, there is unlikely to be any kosher or halal or catholic way to get a passive 15db boost in an open baffle, unless you drop everything by minus 15db and go flat.

Unfortunately to “drop everything by minus 15db” is imposable. First if I kill the 15db. I will not have a power to drive the drivers. Second to kill it possible only with a passive correction circuitry. To use with this driver anything between the secondary and the coil is similar to smelling roses in a gas masks.

*** Why not just use active EQ?

Do you mean not active but line level passive? I thought about it and I do have the second amp to drive it but I would not like to go there. Those drivers are made with ultra-soft and VERY unique paper (with a VERY different tensions radiation within the diaphragm). Presumingly when they designed the coil they assume that it will not see more then necessary LF applied to it. They did assume that 150-500hZ will be boosted acoustically and I wouldn’t like to make those drivers to do what they did not meant to do. How many other years should I spend to fine another pair of the mint Tele’38 drivers?

A freaking quandary….

Probably there is no other ways besides to stick this damn driver back into the place where it should sit.

Rgs,
The Cat
 
Another Baffled Speaker

Konnichiwa,

After major hassle with both Metalworkers (they claimed a maximum of 10 Days but too over a month to cut two simple metal pieces) and Interlink/Parcelline (they where supposed to deliver the metalwork last Saturday) and finding that most of screws holding the wooden box within which the metalwork was delivered having their heads stripped I have FINALLY managed to get my acrylic baffles with the Supravox 215 Signature Bicone playing.....

The design and build is about as straightforward as it gets, speaker cables plug directly into the Driver, one acrylic baffle (appx 2' X 3'6"), one metal L-Piece, 4 Brass screws and nuts - Voila, a most excellent speaker....

Sayonara
 

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Okay, so we have a speaker playing. What's it sound like?

Excellent. The sound is coherent, open, well balanced and these speakers are clearly full range enough to not need either subwoofer or supertweeter. And that is with drivers having minimal play time (no spare Amp's to break them in with pink noise).

In terms of sensitivity I feel they clock in slightly louder than the Bastanis Baffles AND my Tannoy Monitor Red's and NOTABLY louder than the Beauhorn B2.2 Revelation package.

Adding the Bastins based Sub set to 40Hz X-Over, 6db boost @ 30Hz and at rather low levels adds a massive visceral impact, without slowing down the system. Brilliant. You should see my grin....

Again, the system runs without EQ, non needed. Dipoles work well enough in even difficult rooms that room modes do not become a major problem.

So, Supravox Signature Bicone Open Baffle - go for it, it's great stuff. :cheerful:

Just make sure to NOT use any British Companies in the manufacture of the Baffles, otherwise you will be effectively delayed several weeks and under NO conditions allow British Freight carriers to get involved.... If you do the hassle will take years of your life... :mad:

Sayonara
 

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Can you tell me something more aboute the measurements of the baffle and the measurements of the speaker placement. I'm still experimenting with the same sort of baffel at the moment with a Phy-HP 21 cm driver. They are still made out of wood and the driver is placed a bit higher than I see in your picture. Have you experimented with the driver placemant ??
 
Konnichiwa,

Sjef said:
Can you tell me something more aboute the measurements of the baffle and the measurements of the speaker placement.

No, as these are prototypes for a commercial design I am not at liberty to disclose the CRITICAL items.

Sjef said:
Have you experimented with the driver placemant ??

Yes. I might add as possible hint, that having a great deal of knowlegde of and exposure to occult things helps getting the numbers right....

Sayonara
 
Konnichiwa,

Sjef said:
But isn't this a rip off af another commercial design called the "LuiLui"

Try buying LuiLui outside swizerland.... (I know people who tried).

The specific design of the LuiLui does not seem to travel well. This one does. More to the point, there are differences (material ones) especially in the choice of Driver and it's placement. There will also be a larger difference in optics in the finished version.

But yes, LuiLui is the original source, but it is not a simple copy. So what?

Sayonara
 
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