My graphs

[Hakka]

I have 2 DIY sonotube subs using 12 inch shiva drivers, 17.5hz tuning point. They are corner loaded (front corners) in a rectangular room (13ft x 10 ft x 8ft). EQ is a BFD1124P.

I took all my measurements from the right seat (my seat), measuring both subs together and EQing both subs together (in couple mode). When I was finished I measured the left seat and found an almost identical response.


The first graph shows the unEQ'd vs EQ'd.

The second graph shows both seating positions overlaid.

The third graph shows the left sub only, the right sub only, and both subs. This is an interesting graph as each sub on its own has an uneven response but when combined they measure flat.

You will notice the first graph shows a smoother response in the 100hz -150hz range than the other 2, I had already saved the other graphs when I tweaked this filter, so the curve in the 'before & after' graph is what I'm currently running.


I have extended the graphs down to 10hz, as there is quite a bit happening in that region. Who needs bass shakers when you have a 20db hump at 15hz?

All comments welcome.

Harry.

[brucek]

Can't find much fault with that response. Very nice.

The 20dB peak at 15Hz might be a bit scary on a few movies........

brucek

[Hakka]

brucek wrote:

The 20dB peak at 15Hz might be a bit scary on a few movies........

brucek

I've been watching a few of my favorite demo scenes and yes, it is rather scary.

[Hakka]

After watching War Of The Worlds at a rather high volume last night, I think I need the option of removing that subsonic hump. In the scene where the first tripod came up the smoke detector and three vents fell from the ceiling, it sounded like the windows were gonna break and the ceiling was gonna cave in.

Its okay at moderate volume but when I crank it its only gonna destroy the house and off the neighbours.

What equipment do I need to level off this hump/filter out all sub 18hz activity?

Thanks.

[Wayne A. Pflughaupt]

Tough problem. The only thing I can come up with is the Rane PEQ-55, which allows filter settings down to 12.5 Hz. Not going to be a cheap fix, though... Might be cheaper to modify your subs to a higher tuning point.

Regards,
Wayne

[Hakka]

Wayne A. Pflughaupt wrote:

Tough problem. The only thing I can come up with is the Rane PEQ-55, which allows filter settings down to 12.5 Hz. Not going to be a cheap fix, though... Might be cheaper to modify your subs to a higher tuning point.

Regards,
Wayne

The Rane costs $2200 here, thats a little too pricey for me.

If I was to raise the tuning point, wouldn't that make the woofers more likely to bottom out on high spl low freq material? Opening up the subs to change the port length isn't going to be an easy job, they were designed to stay in one piece, I dont think I could do it without damaging them.

If I was to add a wide bandwidth filter at 20hz with a large cut, would that affect the frequencies below 20hz? I was thinking I could do this and then add some more filters to bring >20hz back up to where it was?? Is the BFD1124P capable of this?

Thanks.

Harry.

[brucek]

If I was to add a wide bandwidth filter at 20hz with a large cut, would that affect the frequencies below 20hz?

Yes.

Is the BFD1124P capable of this?

Yes

brucek

[Hakka]

I have done some more testing, this time using a Behringer ECM8000 mic and mic800 preamp, the soundcard output was connected to the AUX input of my Denon 3803 receiver using the bass management circuitry. I used Sonnie's cal file for the mic.

All measurements taken at the right seat.


1st graph shows both mains.

2nd graph shows both mains and subs, phase normal & phase reversed.

3rd graph shows the full range response of the mains.

4th graph shows both mains and subs, with foam port plugs (mains) inserted vs removed.


*main speakers are B&W DM603, set to small with 80hz crossover.


As you can see there are dips around 48hz and 65hz when the subs and mains are interacting. I reversed the phase on the sub amps and these dips disappeared and the response flattened out considerably, but the dip(s) around 80-90 got a little worse.

If you look at the graphs in my first post you will see the response hasn't dropped at 10hz, compare that to these graphs which rolloff about 18hz. The first set of measurements were taken with the soundcard output connected to the BFD, the second set were taken with the signal going through the receiver. So the hump at 15hz is 12db not 20db, just as well or my house would have fallen down already.

[Hakka]

Here's a pic of my room.

[brucek]

Here's a pic of my room.

Looks real good. Love the tubes in the corners. I wonder what the effect of brick on the front wall compared to drywall would be? better, worse? I really don't know. I would think better.

brucek

[Hakka]

brucek wrote:

I wonder what the effect of brick on the front wall compared to drywall would be? better, worse? I really don't know. I would think better.

brucek

I would think bricks would be better on the front wall, the other walls are brick with a layer of concrete over them, and the floor is concrete. It's just a matter of time before I blow the ceiling out . It's a temporary setup in a rental property at the moment.

My Edirol UM-1s arrived yesterday, works perfectly with my BFD, it makes the job even easier than before.

Last night I measured my mains in all possible positions, ended up about an inch from where they were origianlly. No matter where I place them (I only have a few square feet available) I have a large hump at 120-180hz. Is there a material/bass trap available that will absorb these frequencies?



Thanks.

Harry.

[Hakka]

I removed the Yamaha plate amps from my system and replaced them with a Behringer A500. There must have been some serious EQ going on in the plate amps.

The three graphs below are:

1 Both subs with EQ
2 Both subs (with EQ) and both mains
3 Both subs without EQ

If you compare these to the graphs in my first post you will see the massive hump centred at around 16hz is now gone, although I used the BFD to bring it back slightly.

I was surprised by the response in the third graph with no EQ. I only really used the BFD to add a house curve.