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

[jawen]

Midrange appears to be a well behaved unit. On its own high passed at 140 Hz LR4, 4 litres sealed, well damped to Qtc=0.74, without any other consideration, it can be fed with 20Vrms of input and not exceed 2mm of cone travel.
I would have tested it with both HF drivers. Crossing to d2905 conservatively at about 2.3-2.5 kHz.

So I've made a few cabinets......And I'm always overcomplicating things, when all I should be doing is a quick simple box.
SS M18 mid box is now 6.2 liters net with quite a lot of filling. ( can fill it up with MDF to best volyme)

Did the first measurements and Impedace shows FS at 106 Hz? (brand new driver)

You skilled people, what does this look like?

Regards John

 

[raymondj]

Hi Jawen,

I see a Low frequency roll off around 120Hz due to box size and stuffing. A little blip in impedance around 160 and 250Hz. Maybe more stuffing would take care of them?
Diffraction loss of approx. 6dB spread over 400-900 Hz.
Consequently if you intended to use it from 400Hz you will have to deal with that which suggest to me that your your efficiency if you adjust for the loss will be around 82-83dB for the test input level you used.

 

[IamJF]

So I've made a few cabinets......And I'm always overcomplicating things, when all I should be doing is a quick simple box.
SS M18 mid box is now 6.2 liters net with quite a lot of filling. ( can fill it up with MDF to best volyme)

Did the first measurements and Impedace shows FS at 106 Hz? (brand new driver)

You skilled people, what does this look like?

The frequency response has a lot of room influence. Try a nearfield measurement and gated 0,5m distance measurement.

But the problem is the impedance measurement! There should not be dips at 150 and 250Hz! Is this really from the speaker or some humm/whatever?

 

[profiguy]

I agree, there's something not right at 140 ish and 230 ish hz. Could be standing waves at measuring height and distance or the enclosure may have small air leaks. I've seen incorrect applications of dampening material do that as well.

 

[Lojzek]

These impedance blips are not connected with cabinet internal dimensions.

 

[raymondj]

I didn't pick up on the brand new driver aspect.

Maybe gently running them in for a few more hours at 80dB may loosen off the suspension and get rid of the blips you may find the Fs drops a few more Hz as well.

 

[jawen]

Diffraction loss of approx. 6dB spread over 400-900 Hz.
Consequently if you intended to use it from 400Hz

Hi Ray 🙂
Yes diffraction loss is much, and mesaurement make me wonder !
I had the speaker at 1,6 m hight when i did mesaurement, and mic 1 m

I was going to use it from 150 hz 🤔

Regards John

 

[jawen]

Try a nearfield measurement

This is from 0,5 and 0,3 meters.
Speaker at a chair 50 cm over the floor and mic also

 

[Lojzek]

He meant near field like 5 mm.

 

[jawen]

These impedance blips are not connected with cabinet internal dimensions.

This is without 1/48 smooting

Having problems with REW settings to mesaure impedance, never remember the settings between times Grrrrrr
Dont get it to work now when i try to do a new impedance mesaure

 

[raymondj]

Harmonics of 50Hz mains break through via computer or computer PSU?

Although PSU switching frequency should be 100s of Khz?

 

[jawen]

He meant near field like 5 mm.

Blue is mic at 5 mm

 

[jawen]

Maybe gently running them in for a few more hours at 80dB

Without filter or with some filter Ray?
I also tought about that!

 

[jawen]

Harmonics of 50Hz mains break through via computer or computer PSU?

Although PSU switching frequency should be 100s of Khz?

Is there a way to test that?
PC on only batteripower?

 

[Lojzek]

Don't need to worry about that. It'll be high passed. In regard to running the drivers in.

 

[raymondj]

I usually run them in with a few mm of excursions, as these are midranges possibly a mm excursion at around a 100Hz be gentle they are expensive and good.

 

[jawen]

Here is mic from 5 mm without any smooting at all

 

[raymondj]

Always worth a try on battery power only so no mains pollution/interference,

Earthing of cables and pickup could be the other route for noise..

 

[raymondj]

Snap.

 

[IamJF]

This is without 1/48 smooting

Having problems with REW settings to mesaure impedance, never remember the settings between times Grrrrrr
Dont get it to work now when i try to do a new impedance mesaure

This looks like 50Hz hum and harmonics. Ground loop or interference - you need a tidier setup to get rid of these.
Do you also find the 900Hz peak of the datasheet?

The rest looks good.