frequency response testing

[csuzor]

I have been playing with frequency tests (using sweepgen) on my 704 fronts, very interesting... I notice that between 45 and 54Hz, response drops off (I don't have a meter, just my ears), and it picks up again between 37-44Hz, and then drops off slowly down to 30Hz
Looking at the specs, it should have been relatively flat down to 40Hz...

Has anyone made similar (or serious) frequency response analysis, on these or similar speakers?

I'll be using this technique to setup the sub (asw700, soon)... I am tempted to avoid setting up the sub according to a meter, but only to my ears (which are most probably far from a flat frequency response!)... If there is a partial drop-off of response on the 704 as I believe, it'll make setting the cut-off frequency tricky...

Especially if the partial drop-off of response is purely the human factor (my ear!)

Here's the software

http://www.hitsquad.com/smm/programs/SweepGen/

Thanks
Christophe

[PewterTA]

I imagine your real problem is you have a null right at that frequency due to room acoustics. You might want to try moving the speakers a little bit and see if that fixes the problem (if they are right up against the walls, move them away from them).

That might fix the problem. If you ran a frequency sweep test with the speaker outside on a flat piece of wood with the microphone 1 meter away and nothing within a good 3 meters of the speaker, you'd find that the response is very flat.

To me, your room is causing the issue. Though once you get the sub, you can divert everything from 80Hz down to the sub, which will allow for more flexibility in moving the sub around to get the best response.

I HIGHLY recommend calibrating the sub with your meter, then if you want a little more "oomph," raising it 2 - 4dbs to get it how you like it. But calibrating with a meter makes a world of difference.

[csuzor]

You're right, PewterTA, it's all about room acoustics.
I put the speaker outside, ran the frequency sweep, and everything is as expected, with a good response down to 37Hz. I can sleep easy tonight.

I am not an expert, but some simple math points to room acoustics problems at that frequency (speed of sound = 300m/s, @50Hz => soundwave = 6m, which is the size of the room!).

Now I hope that the sub will help fill the gap between 45 and 54Hz and below 38Hz. I hesitate to crossover everything below 80Hz to the sub, which defeats the purpose of floorstanders, and would supposedly lose all stereo imaging below 80Hz...
I will first try to fill the frequency gap with the sub, and leave the full range to the 704.

Thanks
Christophe