Port obstruction

Jan 19, 2011
986
52
28
40
Oslo, Norway, Norway
drbentsen.no
If it were me (and it's not so feel free to do as you please), I would give 12dB/oct a try for your crossover, or even mixing slopes just for more consistent time alignment along the coverage pattern. Whatever you've got on top of it is impressively flat.
On-axis that would probably work, but off-axis that would be troublesome I think.
I'ts a MTM design with a fairly high crossover point :)
 

Uwe Riemer

Freshman
Mar 3, 2011
129
5
18
Germany
Made two cabinet dividers, ended up with around 42L per driver.
By listening to the cabinet I hear more low-end, haven't measured it yet.
Impedance plot:

View attachment 209423
So you basically ended with a tuning similar to the suggested B&C design, which is probably a compromise for using the 12" fullrange, where it might be better to have at least some low end.
For Top only application you are still waisting potential low/mid output. So whenever you find yourself having problems with bass guitar or snare, you can remember my words, otherwise forget them :) .
Of course it is easy to tune too high, which will also sound bad, thats the reason every nice curve of the simulation program needs to be evaluated by ear.

Regarding the DATS drive level:
Impedance is a moving target, because it changes with drive level and 10dBU are not enough to provide realistic measurement conditions for a SR speaker IMO.

One last thing: You should look into that 300Hz peak in your impedance measurement_ This could be a sign of serious enclosure resonance
 
Jan 19, 2011
986
52
28
40
Oslo, Norway, Norway
drbentsen.no
So you basically ended with a tuning similar to the suggested B&C design, which is probably a compromise for using the 12" fullrange, where it might be better to have at least some low end.
For Top only application you are still waisting potential low/mid output. So whenever you find yourself having problems with bass guitar or snare, you can remember my words, otherwise forget them :) .
Of course it is easy to tune too high, which will also sound bad, thats the reason every nice curve of the simulation program needs to be evaluated by ear.

Regarding the DATS drive level:
Impedance is a moving target, because it changes with drive level and 10dBU are not enough to provide realistic measurement conditions for a SR speaker IMO.

One last thing: You should look into that 300Hz peak in your impedance measurement_ This could be a sign of serious enclosure resonance
Ok, I'm not sure i follow you here. What were your words? :)
That 300hz peak is on the list, not sure exactly how to look for it right now.
 

Uwe Riemer

Freshman
Mar 3, 2011
129
5
18
Germany
Ok, I'm not sure i follow you here. What were your words? :)
That 300hz peak is on the list, not sure exactly how to look for it right now.
IMO you should reduce the volume for 12" drivers even further, something between 55 and 60 liter. I understand, that this might be difficult to achieve with your actual enclosure.
Experimenting with damping material in different positions will show, if the 300Hz are
 

Uwe Riemer

Freshman
Mar 3, 2011
129
5
18
Germany
IMO you should reduce the volume for 12" drivers even further, something between 55 and 60 liter. I understand, that this might be difficult to achieve with your actual enclosure.
Experimenting with damping material in different positions will show, if the 300Hz are
internal standing waves
 
Jan 19, 2011
986
52
28
40
Oslo, Norway, Norway
drbentsen.no
IMO you should reduce the volume for 12" drivers even further, something between 55 and 60 liter. I understand, that this might be difficult to achieve with your actual enclosure.
Experimenting with damping material in different positions will show, if the 300Hz are
They have around 42L each now. You're thinking 55-60L total, AKA 27-30L each?
 
Last edited:

David Morison

Freshman
Aug 21, 2012
164
12
18
Aberdeen, Scotland
You might need to short the terminals of the unused driver otherwise sympathetic resonance can occur just from the acoustic output of the driver under test, but yes, you should be able to do that comparison. Depending on how loud you need to drive it to get a decent measurement, you might also need to secure the filler material a bit to make sure it doesn't vibrate in the box too.
 

Uwe Riemer

Freshman
Mar 3, 2011
129
5
18
Germany
I'll try to just reduce the volume of one of the 12" temporarily and measure them individually.
Throw some scrap wood in there or similar, I don't think it matters too much what it is as long as it's solid for a simple impedance measure and low-level listening.

Scrap wood is a lot of work to calculate volume, guess how I know.
I´ve used milk ( comes in 1 liter handily ) and hard foam board like used for house insulation.

Davids remark is important.
Shortening the unused driver or connecting it to an amp without signal, probably slightly different outcome.
Also it could be covered with plywood and clamps.