Soundlab (Chinese) 204mm (8") drivers in open baffle array - Page 2 - diyAudio
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Old 15th July 2011, 08:22 PM   #11
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Quote:
Originally Posted by sreten View Post
...

9.5" wide baffles ?????!!!!!! don't what planets theory your coming
from but not a chance in hell even domestically for decent bass.
You won't even get upper bass + lower mids, nevermind bass....
Come on Sreten, tear him down without offering any ideas of making it better?

Tim,

The width of the baffle (or more correctly the distance from back of driver to front of driver) determines where the dipole roll-off starts. With a 9.5" baffle, the EQ needed to flatten the response will likely reduce efficiency to more like 80 dB than 100. Not to mention the dramatic amount of excursion.

Also to follow up on Jim's comment, with 4 8" drivers in a row, the issues in the HF is going to start really low. Well into the midrange.

With 10 drivers i can think of better ways to get the most out of them (it would end up being a 2-way and use 5 drivers/side).

You can go ahead with your scheme, be a good learning price, but i'm all too afraid that it will disapoint.

dave
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Old 15th July 2011, 08:47 PM   #12
godfrey is offline godfrey  South Africa
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If there's too little bass, you can always add wings to the sides of the baffle later. Attaching them with piano hinges would allow them to be folded for slightly easier transport and also let you play with the angle to get the best sound.
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Old 15th July 2011, 09:02 PM   #13
Rudolf is offline Rudolf  Germany
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It would have been good practice to do some EDGE simulations before cutting wood
Anyway - here is what you can expect:

Click the image to open in full size.

Both sims account for the floor/ground reflection by assuming a mirrored baffle with four added drivers. The diagrams only show the baffle loss in the bass area. You have to subtract the bass loss of the drivers from that too.

If you pool the four drivers in the upper part of the baffle, you will have a dip around 500 Hz. If you distribute the drivers along the length of the baffle, this dip will vanish, but there will be more dips above 2 kHz. Choose your poison.
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Old 15th July 2011, 10:13 PM   #14
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As a separate thought, in order to sort out the potential HF problems...

A reasonably sturdy compression driver, crossed in at, say, 4kHz might alleviate some of the comb filtering problems.

The only way to find out is listen, though. You might find that you're happy with the "smooth" (ie, rolled off treble) sound that all 4 would have to offer.
You could try crossing the lower 2 over, so they're not reproducing HF that would interfere with the output from the upper drivers.

Chris
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Old 16th July 2011, 10:23 AM   #15
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Hi, with 4 of these drivers, you'll probably have sufficient cone area to reproduce some reasonable bass.
That is what I am hoping for. The total area should be approaching the equivalent of a 16 inch driver.

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If you find them to be lacking, a small (4ohm or less - you'll need to experiment) series resistor can, by altering the T/S parameters, give more bass on open baffles.
Thanks for that. I don't understand why though. Is this specific to open baffles?

Here is the little Lepai amp powered up from the batteries. There is a reassuring click of a relay around half a second after switching on. I will mount the amp & battery pack on the rear of one of the baffles to make the speakers 'active'. The source will be an old iPod mini connected with a 1/8" lead.

The last time I made speakers was before CDs let alone iPods, class-D amps and line arrays.

I have just bought 100m 79-strand 2.5 sq mm speaker wire for 13 (from Wilkinson Plus). I am sure this was almost 1 a metre 30 years ago. With a nominal rating into 8 ohms of 3.2KW (!) it should not interfere with the transients.

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Best of luck,
Chris
Many thanks!
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Old 16th July 2011, 11:00 AM   #16
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Chris, Dave, Godfrey and Rudolf,

Many thanks for your input. Actually those frequency response curves don't look too bad to me! I didn't actually know that such modelling software existed so that is fascinating and thanks again. These are low-cost drivers and are very much an unknown beast. The limited parameters that the manufacturer supplies cannot really be relied upon so it will very much be trial and error. I hadn't considered moving the drivers apart but the modelling is very interesting. I have given the project my best initial shot. In the end there will almost certainly be some modifications to compensate for the actual weaknesses of the system - perceived, measured or both.

I was thinking that if the top end is lacking, I may add some piezo tweeters (this will probably provoke even more outrage!) The reason being that I could still avoid using a crossover. However, my hearing falls off quickly over around 14Khz so these drivers may just be OK for me as they are. The comb filtering effects should lessen with distance but that also means they will start to behave like a point source and the SPLs will drop off - perhaps this is good so as not to annoy the neighbours we haven't invited. Old as I am, almost everyone at the party will be even older. This is turning out to be quite a specialised project - a music system for old people at a garden party without a power outlet :-)

I just wish the drivers would arrive. DFB don't have the fastest delivery service. They may be on a slow boat from China.

Tim.

Last edited by timmillea; 16th July 2011 at 11:23 AM.
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Old 16th July 2011, 03:22 PM   #17
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Quote:
Originally Posted by Rudolf View Post
Click the image to open in full size.

Both sims account for the floor/ground reflection by assuming a mirrored baffle with four added drivers. The diagrams only show the baffle loss in the bass area. You have to subtract the bass loss of the drivers from that too.
I am still studying this modelling. It is fascinating. Sadly Edge is Windows only. Does anyone know of anything similar for the Mac or is web-based?

My understanding that this is showing the effects of 1) constructive & destructive interference due to there being 4 drivers + ground reflections, 2) baffle boundary and diffraction effects at various frequencies and 3) the dipole interference, i.e. rear waves interfering with front waves. Is this correct?

I expect that the response curve alters drastically - e.g. to the opposite peaks & troughs shown here - depending upon precise listening position. As Rudolf pointed out - this does not show the effects of the actual driver response - a sobering thought. The major complications are that a listener has two ears in significantly different places, listeners will be in a wide range of positions and there will be two arrays in different places. In most recorded music, there will be single elements of the mix panned somewhere between right & left - hence more interference. This acute localisation may be one of the perceived qualities of an open baffle array. The psychology of sound quality is much more complex than its engineering!

We know that linear arrays suffer terribly from interference in order to achieve their overall cylindrical dispersion pattern. Yet they work. I am not bothered in the least by a 6 dB trough or peak in one modelled position. The brain is remarkably adaptable to this. I think by removing the boundary effect lift from around 1 Khz down to around 60Hz (through a minimal baffle and ground reflection), and avoiding crossover-induced phase shifts, the design principles are sound even though the calculated (and actual) frequency response in any one position may look horrific.

The proof is in the pudding. I wish you could come to the party!

BTW I tried out the Lepai amp with small box speakers today. It sounds absolutely great! There was no perceivable noise and oodles of power. I have had some expensive hi-fi in my time but this is the best sounding amp I have ever listened to. Soooooooo looking forward using it with the new speakers.

I will have two 8" drivers left over. These are candidates for the bookshelf version!

Tim.

Last edited by timmillea; 16th July 2011 at 03:51 PM.
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Old 16th July 2011, 05:49 PM   #18
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I may add some piezo tweeters (this will probably provoke even more outrage!) The reason being that I could still avoid using a crossover.
Done right a piezo can be a quite good. And you won't be eliminating an XO, just using the one built-in caused by the capacitive nature of a piezo impedance. The reason piezos get trashed is from those instances whem people do not add additional XO components,

dave
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Old 16th July 2011, 06:14 PM   #19
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You will need tweeters of some sort.
Nothing to be afraid of there.
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Old 16th July 2011, 08:08 PM   #20
sreten is offline sreten  United Kingdom
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Come on Sreten, tear him down without offering any ideas of making it better?

dave
Hi,

No. It simply won't work at all and the application of "theory" is simply wrong.

Contrary to what you say, I posted how to use the drivers for the application.

Somebody "complaining" about their ideas being criticised isn't even listening.

I'll repeat, it simply won't work at all as it stands. The drivers are very likely
too low Q and lack excursion capability. By all means build it if you want to
pretend it will be allright, it wont, it will be terrible for the intended purpose.

rgds, sreten.

With a 10" wide baffle effective cone area will plummet in the bass. a 15"
driver in a 24" baffle is about equivalent to a single 8" in a box, here you
will end up in the bass with the equivalent of 4 x 2" drivers, it will not work.
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Last edited by sreten; 16th July 2011 at 08:23 PM.
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