How do you know you screwed up in Bass reflex simulation

[oon_the_kid]

Hi,

I have just started moving into the world of simulations for bass reflex. So here is the thing, we know that if a box is not properly designed it might sound boomy or poor transient, etc.

What i would like to know is how do you know you screwed up?

I am presently using this calculator as I am playing with SB acoustics and they already have the database for quite a lot of their speakers.

Speakerbuilder Pro 2.0

It generates multiple graphs of frequency response, speaker excursion etc.

I could tell when you might have some obvious bad design from frequency response, but I intend to equalize by minidsp anyway, so it is not really a concern.

What else could be an indicator? I could think of a few?

1) Transient response? A impulse of a few cycles before going to zero?
2) Port air speed?

I am looking at rule of thumb etc

Thanking all in advance.

Oon

 

[Lojzek]

Simulation software is just a computing program and as such it does not make mistakes. The issues could have their origin in feeding the program with unrealistic data. Simulated FR will not tell you what it may sound like in your listening room. In order to get an optimum result, it is advisable to conduct a couple of experiments by building multiple test enclosures capable of being modified in size and tuning and meet a decision after you do the same with crossovers.

 

[oon_the_kid]

Hi,

I think there is a misunderstanding on what I was looking for. I believe the simulation programs are fairly reliable nowadays.

What I would like to know is how do you know you have a bad speaker design that will sound terrible in real life. It may not be obvious or if the speaker is not optimised.

A few things I figured out so far.

I read somewhere that port air velocity should be kept below 17m/s, higher velocities would require a flared port to avoid chuffing. Which means you would need to simulate at the maximum power you intend to drive it.

Since i intend to incorporate a small bass boost. So i should simulating at different power levels for different frequency. Since I intend to boost at the port tuning frequency, I should ensure the port velocity is sufficient at port tuning frequency. And at a lower power the maximum excursion of diaphragm since it occurs at a higher frequency where it is not so heavily boosted.

Using a bigger box with the same tuning as a smaller box results in a flatter frequency response. The amount of "boost" seems higher. However is there a price to pay for that? The step response seems to last a little longer and at higher amplitude. I suppose that should be bad.

So if you guys who have plenty of experience building and simulating, I would be most grateful if you give me some guidelines on what to look out for in a BR reflex.

Thanks.

Oon

 

[Jerms]

For a 2-way (or say Tabaq TL), the port is oriented by angle or distance away from the driver(s). Any MF/HF that escapes the port therefore has less chance to smear the presentation. In commercial 2 way speakers, that usually means the port is behind the tweeter facing to the rear.

For a subwoofer, build it strong enough and ensure port is at least 1/3 driver SD. Maybe more if driving it harder and lower.

J.

 

[planet10]

Experience helps. A lot.

dave

 

[oon_the_kid]

For a 2-way (or say Tabaq TL), the port is oriented by angle or distance away from the driver(s). Any MF/HF that escapes the port therefore has less chance to smear the presentation. In commercial 2 way speakers, that usually means the port is behind the tweeter facing to the rear.

For a subwoofer, build it strong enough and ensure port is at least 1/3 driver SD. Maybe more if driving it harder and lower.

J.

Thanks. I have always suspected that is the reason. Another question that would pop up is, why not place the port at the bottom. Normally there would be speaker spikes to raise it from the surface. I know that subwoofers tend to do that...

Oon

 

[oon_the_kid]

Experience helps. A lot.

dave

My wife would rather I get it right the first time..

 

[Lojzek]

A rule of thumb could be this. A vented loudspeaker placed in a corner, will benefit from making a non flat vent alignment called bass shelf. Loudspeaker far out in the open space might sound better tuned flat or with a boost.

 

[oon_the_kid]

A rule of thumb could be this. A vented loudspeaker placed in a corner, will benefit from making a non flat vent alignment called bass shelf. Loudspeaker far out in the open space might sound better tuned flat or with a boost.

Hi,

Interesting to hear, can elaborate more on it?

Oon

 

[Lojzek]

Experimenting has taught me that, which still does not mean necessarilly that everyone else may like it as well. Corners add a lot of boost so sometimes it's just too much, depending. Good luck!

 

[ernperkins]

The room size and speaker placement in the room will have a large effect on how the bass sounds. I use Jeff Bagby's "Diffraction & Boundary Simulator" program to estimate the effect. The program is free, but is Excel based. I'm sure there are other similar programs around.