Fast, fun, Inexpensive OB project

panomaniac said:
...

Green is the original baffle, Red is a 1M tall baffle (puts the tweeter at ear height when sitting).
As you can see, only about a 1.5dB gain.



About 3 months ago, I designed my own full range OB by playing with <Edge> and found that the bottle neck of bass response is mainly at the smallest dimension of the baffle (mostly the width, with regular upright shape).

Most of the time taller baffle (with same width) helps very little.

Eventually I made the baffle 3ft wide by 4ft tall. This is almost the largest width I can handle in that small room. Larger than that would effectively block the doorway. These baffles came out as expected, which I like very much.

Is it only me comfortable with wide speakers? It seems most people like slim desgins, which makes me puzzled.

Almost everybody likes big and wide houses, cars, freezers, TV.... why not big wide baffle? Not sexy?


However, <Edge> does not simulate the floor/wall/ceiling effect. Maybe a very tall baffle in a low ceiling room would be interesting... Then again, with the same height, we surely can get better bass by making it wider.
 
Wow, you guys are very helpful, thanks for all the quick responses. Good to see it wouldn't take much mucking with the crossover at all.
planet10 said:

Given that no-one, not even me has heard the latest version of my B200, comments will be scarce
I guess I jumped the gun a bit on the b200s :). Still, I think my decision is coming down between these and the visaton's. So any comparison, no matter how ill-informed would be helpful.

Oh, and something I forgot to ask, do you think these would do all right if pressed into duty for home theater/gaming use? I really care about quality for music, but I wouldn't want to blow up my fancy new speakers. You guys think a 40hz high-pass from my amp would be sufficient protection?
 
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CLS said:
Most of the time taller baffle (with same width) helps very little.


Yes, surface area is what seems to make the biggest difference. I've played with some big JE/Labs - Wharfdale sized baffles. Good low end, but just too big for my room.

As for the taller version Manzanita, I talked to JB, the designer.

He says you will need to make the crossover cap a bit smaller and play with the tweeter inductor some to bring things back into balance. Drop the tweeter pad resistor to about 20R. An 11mH coil may work better for the woofer.

Not big changes, but you want to tune it a little. The bigger baffle will have the benefits of better dynamics.

So I say- go for it! (You can always put the smaller version on a stand or on legs, you know)
 
"......................has anyone tried to remove dust cup and put phase plug in SLS 830669 ......................"

This got me wondering. I had removed the dust cap from an 8 inch driver and with a phase plug it did sound better than the stock unit . Some of the 'cuppiness' was reduced.
So I took my 12 inch Peerless 831859 driver and wet the glued area of the dust cap ( cloth) with Amyl Acetate. After 20 minutes I put another round of the solvent with a thick paint brush. After another 15 minutes I carefully pried up one end with a sharp pointed rod ( from an old compass set ). You can see it in the picture. The end lifted up after a few tries. Then I pushed it in further till that bit lifted off the cone ( poly prop ). Then I just slowly pushed along the 'needle' all around the edge of the dust cap and the whole thing lifted off. Cool ! I had to clean up the residual glue. It seems to be rubber based or similar.

I have an 18 x 35 inch baffle on which I wanted to try out an OB with either an 8 inch or a 12 inch bass mid. 12 inch for mid seemed a bit tough.
However with what I hear on the 12 inch I think I should try it out.
It sounds better without the dust cap but not enough to work without a crossover. However at average listening levels I don't hear any 'shoutiness'. More 'cuppy' I guess.But not too bad at all.
The pole piece seems to be covered with something black. Could it be a copper disc ? When I tap it ,it is sounds plasticky. Anyway I'll put on a plug and see what happens.

Cheers.
 

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I'll mould a plug out of candle wax first . After I have decided which shape to use I'll make it out of wood or have it turned out of aluminum.
That plastic (?) cap I found is unusual . All pole pieces I have seen so far are bare ( flat ) metal. However I'll stick the plug with double sided tape for now. Only if I decide to make it a permanent fixture will I glue it with something stronger.
 
this has taken an interesting turn.

is there any real reason that a phase plug will improve things?? If it was some sort of 'universal law' that a driver would always sound better with a phase plug then wouldn't there be many more straight from the manufacturers?

Maybe this has already been covered in a dedicated thread. Maybe it would sound different, but all too often in hi fi there is an unrecognised equation going on...different=better, which I don't believe is necessarily the case.

Just curious that's all, and is there any 'rules' to designing a phase plug...if not it's out to the lathe and away I go.
 
terry j said:
then wouldn't there be many more straight from the manufacturers

I'll let the pros tell you the positives and I'll handle the negative. Removing the dust cap exposes the voice coil to the environment. It can't have a positive effect on the longevity as I see it. Mind you, my speakers are often flapping away like a boring guys lips so there's not much chance of Mr Grit getting in there and spoiling the party.

EDIT: Always remember to store your drivers face down. You don't want the gravity monster dropping dust bombs in there.
 
Planet10 : Thanks for that suggestion. Actually I already planned on that but the cap on the pole piece seems to be fairly thick and is non magnetic. So the 'force' is not much on a fairly large sized screw. Maybe it's OK for initial testing if the plug is not heavy.

The plug will affect the HF response. For my tests done by just listening , here is what I found.

1. There is more HF and so music sounds better . Remember this is a 12 inch driver.
2. Some cuppiness in the mid range drops without the dust cap and gets even better with a crude phase plug.
3. A crude phase plug lifts the treble some more and transients sound crisper.
4. My opinion is that voice certainly sounds better without a dust cap and better with a phase plug.
5. You might want to keep in mind that this stock driver appears to have a pretty flat frequency response and no severe cone break up indications on the frequency response graph.
6. The plug should affect the off axis response and I think it should improve it but until I test it I can't say for sure.
7. I can't say now how long the plug should be or it's prefered shape. I've seen convex and concave cones and also long tubes that end up as a stump ! So one will have to try out all aternatives .
Quick guess is a plug with the same diameter of the pole piece and half the vertical depth of the cone ( from the coil top to the front of the cone). Then half or three quarter the length from the front of the plug made into a curved cone . Most are fairly rounded.

Even on a filterless listening test the stock driver sounds pretty good without any 'shouting' or rough sounds in the upper octaves. MANY smaller drivers tend to be 'noisy' beyond their normal operating range. So I'd give this driver a big plus on that .

This model has been discontinued but it's replacement is probably just as good.
 
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terry j said:
is there any real reason that a phase plug will improve things?? If it was some sort of 'universal law' that a driver would always sound better with a phase plug then wouldn't there be many more straight from the manufacturers?

Yes, there are reasons why a phase plug helps in many cases (not in all cases).

Inside the voice coil above the pole piece an oil can resonance occurss. Removing the dust cap decreases this somewhat. The prime purpose of the phas eplug is to fill the hole and leave no room for the resonance to occur.

Further, if long enuff it decreases the distance acrtoss the cone (pushing radial resonances across the cone by an octave, and depending on the shape it will affect the HF dispersion.

Reasons for manufacturers to not fit phase plugs include momentum (big maufacturers tend to be very conservative), they increase cost, and as Cal pointed out, dust.

dave
 
Generally speaking I think it's not a good idea to take off the dust cap if the cone has holes on them as seen in the picture. That's a significant air leak between the two sides of the cone.
Can give rise to audible problems.

Maybe seal them at the rear with thick tape ?