Bump at 40Hz despite a 80Hz cross over… (Classe Sigma SSP weirdness?)

[Alexandre]

Yes. But ask Alexandre, he's the one who gets to take these measurements! (and hopefully ends up with even better sound when we're done!)

Right, I do think there is a problem between 12 and 24dB slopes: they measure exactly the same so I will inquire with Classe about it. On the other hand, I now feel a lot better about the crossover working in general (albeit with a single slope).

I notice in your pic that the top of those speakers is level with the door handle. Are your seats that low to the ground?

I forgot to answer this one… yes, my sofa is about 12 inches off the ground which means that when I'm comfortably slouching in there my ears are about 32" inches off the floor which is just the height of the tweeters.

 

[Alexandre]

A table set up in the garden don't you have a garden with patio door windows leading to the garden.

Place laptop on table with a chair that you can sit on and make it comfortable for yourself.

Use that grey box to place the speaker.

Look for some extra speaker cable that's in a box and connect the ends to existing cable to extend the length to garden.

Use that little stool to place the microhone or buy a boom stand that are reasonable cheap on ebay that way you can alter the angle or height of the mic on the boom stand.

I do live in San Francisco but it turns out that I am lucky enough to have a garden, that having been said, this will involve moving the amp, the preamp, the speaker downstairs, or I could do it in front of the house in the street which could be a fun exercise.

 

[Alexandre]

I assumed you just mounted separate boxes on the wall that way!
As a stand alone piece they are quite intriguing. I'm not sure how you would do that and it be reasonably sturdy! Nice trick!

I don't want to ruin the magic…

 

[TLS Guy]

First off, I am no expert at measurement, so don't take what I say as gospel. Hopefully someone more experienced will be along before too long, but, in the mean time, I will stick with you and learn as we go!

I think you are expecting a more vertical slope than you should be. If your horizontal axis is spread out, the visual angle of the slope is less.
Here is a graph of the theoretical crossover:

Note the curve is 6dB down at the 80Hz XO point and has a 12dB/octave roll-off (you can see it goes from ~63dB @ 40Hz to ~51dB @ 20Hz).
The 12dB roll-off can only be evaluated where the slope is steady (not where there is any curvature to the chart).

Real world measurements are much more complicated!

However, I can think of no explanation for your 12dB and 24dB curves to be so close other than either the pre-amp is not doing what it should, or you are missing some control which overrides whatever "switch" you are using. You might contact Classe and email them your charts. There ought to be a way to measure the pre-amps output to get the curves before the complications of speaker/room/microphone issues. It seems like you could feed your pre-amp output into you mic input, but for all I know, that might cook the circuits in teh laptop (or whatever you are using).
BTW, I really like you akimbo shelf/boxes! Great idea!!!

The crossover is fine. The speaker rolls off 24 db per octave starting at around 55 Hz. So below that point the lines will come together however the crossover is set. You have to look between 80 and 55 Hz to see the effect of the crossover.

Basically those speakers are good to about 60 Hz.

 

[KEW]

You have to look between 80 and 55 Hz to see the effect of the crossover.

What you say about the speakers natural roll-off taking over at ~55Hz makes sense.
But why would the black and the green lines be virtually identical between 80 and 55 despite having different slopes (per the controls)?

 

[TLS Guy]

What you say about the speakers natural roll-off taking over at ~55Hz makes sense.
But why would the black and the green lines be virtually identical between 80 and 55 despite having different slopes (per the controls)?

The answer is that the Q of the filter is not LR (constant voltage Q 0.49), but most likely Butterworth (constant power Q 0.707). It might just be Chenbychev Q 1.

What the Q determines is the sharpness at turnover, although they all have the same rate of decay after turnover is complete.

The slopes he measured are most compatible with second order Butterworh. It is my understanding that receivers and pre pros usually have Butterworth second order high pass slopes and not LR. In which case in the turnover region, which would be the first half octave, the 12 db and 24 db slopes would look pretty similar.

The bottom line is that in order to define the shape of the crossover response you need three things and not two, namely: - frequency, Q and order.

 

[KEW]

Thank you Dr. Carter!

 

[andyblackcat]

I do live in San Francisco but it turns out that I am lucky enough to have a garden, that having been said, this will involve moving the amp, the preamp, the speaker downstairs, or I could do it in front of the house in the street which could be a fun exercise.

Your not thinking 3D!

Look for the shortest route and what is that? The window!

Like I said get the cable length long enough and toss it out the window to the shortest route to the garden.

 

[Alexandre]

Your not thinking 3D!

Look for the shortest route and what is that? The window!

Like I said get the cable length long enough and toss it out the window to the shortest route to the garden.

I live in a Victorian house on a typical SF plot: the house is 80 feet long and the living room is on the street side… I might have to order some more cables from monoprice…

 

[andyblackcat]

Also got do this on a day that has good weather don't want to get it outside and then next a rain cloud starts pouring down all the electricians will get wet.