Maximize a Scanspeak 18M/4631 T00 Revelator midrange for a 3 way

[jawen]

Zoom into the x axis to have around 10 ms of total length

Like this you mean?

 

[stv]

Exactly, you can see a first reflection at -1.5 ms (4.5 ms after the peak, purple graph).
Now adjust the right window to -1.5

 

[jawen]

And is Ref Time setting -6 correct?

 

[IamJF]

How do you get an impulse at negative time? That's not easy ...

Do you use 2 channel measurement with a reference channel to get delay of the interface corrected? Can you take a pic of your speaker setup + Ref mic? A negative time should not be cause sound needs some time to travel ...

Try to get your speaker (about) center/center/center in your room, best put it on a narrow stand which doesn't influence (alternative - solid stand which makes a larger front baffle when that is how your speaker will look later). Try 50cm distance of speaker and mic to get more time before your first reflection.

You have a few very short timed reflections in your measurement - any corners/surfaces near the speaker? Avoid that!

Step by step ... it's not extra hard but you need to do it right and there are a lot sources for mistakes.

 

[raymondj]

Post 63 you do seem to have some small reflections at -1.5, 1, and the big one at 4.5mS. Consequently if you moved the window end to approx. -2 that should remove the reflections. Which would give you 4mS of gated measurement.

 

[jawen]

How do you get an impulse at negative time? That's not easy ...

My bank account is also always in the minus area with red numbers, hahaha
When i start up REW it did a update, and -6 was default in IR Window settings Ref Time?

Never understand exact how IR window works, but understand "the basic".
For me in-room-mesaurements are the most importent, because people use their speakers there.
Then low distortion even in high SPL, my head and ears screem STOP otherwise.

The sound from the SS M18 is nice and relaxing....a form of real nice paper-cone sound.
Threw together a quick 12dB LP/HP xover ( with not perfect values) and did a first mesauring.

But my head must rest now a while, because my 2 braincells are angry on eachother hahaha

Regards John

 

[jawen]

Speaker at the back at the table pointing up, lying on filt..
Ca 3,5 m from table to roof, roof have 18 degree slope.

My lamp is about the only near reflecting surface when mesaure.
But will try to mesaure outside tomorrow.

 

[stv]

Speaker at the back at the table

You should keep the speaker clear of any nearby surfaces, also the back of the speaker!

 

[raymondj]

Nice to see you are working the issues and making physical progress at the same time.
Good luck as you refine it more.

 

[IamJF]

My bank account is also always in the minus area with red numbers, hahaha
When i start up REW it did a update, and -6 was default in IR Window settings Ref Time?

The RefTime is correct - but the impulse should not start before 0ms!

For me in-room-mesaurements are the most importent, because people use their speakers there.
Then low distortion even in high SPL, my head and ears screem STOP otherwise.

For designing the crossover you need the speakr response, not the in room response! You need to check crossover additions and phase etc. without room influence! THEN you do in room measurements and alter to your liking.

Speaker at the back at the table pointing up, lying on filt..
Ca 3,5 m from table to roof, roof have 18 degree slope.

As already written - the table behind the speaker explains these nasty, very early reflections. It needs to stand completely free. Get closer with the mic.

 

[jawen]

Okey now i have done some outside mesaurements.

But was about to smash the computer with an axe, when REW crashed 2 times with 6 hours of work totally gone.
Seems to happend if you take a paus (doing setup for a while), and have to make the Preferences settings again.
When you then hit the "Start" button REW crasches!

LIve 18 m from a road and 120 m from the railway, and many Sweden cars still have winter tires with studs (making a lot of noice)
Also a Pheasant around my house screeming for "lowe" as a maniac, and 10 other species of birds in all the bushes and trees that want to meet a mate.

Had the first fantastic day in Sweden yesterday, 20 degrees warm & sunny, but my goal was outside mesauring in silence.
Build a fake-baffle 38 X 60 cm W & H ( as the Dayton 390ho wooferbox will be), to see the respons.

Here is outside mesaurement mic 50 cm with and without that fake-baffel No smooting!
And outside mesaurement mic 100 cm & 50 cm with and without that fake-baffel No smooting! (don´t have 50cm without fake-baffle)


And the SS 93000 and SS M18, No smooting
SS 93000 curve, dist and spectogram
for you to analyze because I do not have sufficient knowledge.

I'm very tired after yesterday, as my health can't really handle such long periods.

Regards John

 

[jawen]

What "happens" if i have 7 liter netto box for the SS M18 insted of 4 liters?
Is it still good for 150-2400 hz or does it creates "problem" ?

Never really understand how "big/small" box a midrange need, and what happens if the box is to small or big.
Will soon post some progress in construction pictures

Regards John

 

[raymondj]

7 - 10 litres closed box should be fine, you will loose a little bit of a bass hump, but it will be a flatter response with the resonance frequency coming down slightly lower, at the same time.
You should still be able to hit your targets of 150 - 2400 Hz.
Going bigger the volume of air in the box increases which means it has become a softer spring/cushion for the drivers cone movement, consequently the driver will move more freely which eats into you overall power handling a little bit. A bit of a simplification, but maybe it helps, i would not go any bigger than 12 litres with the amount of power you have at hand. Have fun.

 

[jawen]

you will loose a little bit of a bass hump, but it will be a flatter response

Going bigger the volume of air in the box increases which means it has become a softer spring/cushion for the drivers cone movement, consequently the driver will move more freely which eats into you overall power handling a little bit.

Thank you so much Ray, it was exactly that information i was after .

Earlier in the thread Lojzec suggested about 4 liters sealed 140 hz LR4 well damped to Qtc=0.74, and what I understand now is that there will be a maximum hump with a smaller box.

 

[jawen]

Okey here come some building pics on the 91 liter netto Dayton rss390ho vented box tuned to 25 hz.
W 38 H 64 D 56 cm, MDF 22 + 16 mm baffle ( to use all left over mdf pices laying around, and thickening the baffle)
Port 35 cm 102 mm inside homemade endings.

Trying to imitate Walnut with 2 different wood stain on the MDF, and make some type of "design" with the "ribbs".
Lacquer tomorrow with 2 layers of Polyuretan to get high finish.

Regards John

 

[raymondj]

Skill and ideas to the max there. I also like the fact that you can make a mess. Is the final picture a veneer or your staining skills?

Going back to mid box size, I don't think Lojzek was wrong, and in the driver literature from scan speak they suggest 3 Litres with their caveat to read their design notes. The reason I think scan suggest this is it has a natural 2nd order roll off of its own, it comes with the box size.

So a larger box will allow a little more Hz of bass to be produced, this in turn takes up more cone movement, and power handling. There is always a trade off with the parameters. So the 3 or 4 litre box help protects the mid woofer from bass and comes with its simple low pass filter saving you at least one inductor and one capacitor.

Now in a larger box you can have a slightly flatter response but you will need to add a 2nd order High pass at say 150-170Hz into the crossover.

Your driver is in the VituixCad database, if you go to tools/Enclosure./scan speak 18W/4631T00 and tick the box for your driver then select closed you can move the box volume to your hearts content so as to get a feel of what is going on especially response shape and resonance plus excursion. You can additionally add HP filter frequency and see how that re draws the lines.

 

[jawen]

Skill and ideas to the max there. I also like the fact that you can make a mess. Is the final picture a veneer or your staining skills?

Yes, I always seem to "overdo" things!

It was a really big job to make the "ribs" from small leftover pieces of mdf, would have been much easier with a large piece of MDF and draw a circle and then saw them into "ribbons" and use the jig saw to make them follow 15 inch driver.

And thank you for your kind words, it is my first try of using 2 different staincolure (and experimented me forward in the progress)
First Rosewood colure oilbased stain, and worked it in with a small cloth so I saw that the mdf was quite saturated.
Then one more side "the same process", then back to the first again whit a thinner layer of black oilbased stain,and work it in with a cloth (you se when the mdf get saturated, and the the surface becomes darker)

The use the black stain with a smal brush, and make black "lines", and work that black stain with the cloth drag from top to bottom & bottom to top only....and make the fake wood grains like you want and also improve them several hours later with a little more black stain.

Will study your VituiXcad and try to experiment in VituiXcad.
Maby its better with a 3-4 liter box, as you know i play real loud

Regards John