A compromised IB?

[jagman]

It is late for you... here it's just the middle of the afteroon. Kind of funny how the internet brings people from such great distances together.

As you suggested, I already have the sub amp set to zero attenuation. And, as you suggested, the upper frequencies had to be attenuated with the BFD. Now I'm doing your other suggestion... boosting the lower frequencies and adding yet more attenuation to the upper ones. For whatever reason my room doesn't have that much low frequency gain. Part of it I'm sure is all the bass traps. But that only accounts for part of it; there is a 3m^2 opening to the rest of the house and 4.5m^2 of windows. They must contribute.

I am concerned about bottoming out the subs. I have a certain threshhold of which I won't turn the volume dial past. As long as they don't bottom out at that point I'll be in the clear. It is a bit worrisome, though. Especially with discontinued speakers from a company on shaky ground (pun intended). Then again, these bad boys have 27mm one way Xmax so they should be OK. I'm thinking about climbing up into the manifold with it playing to see how much they move. I'll need some heavy duty hearing protection to do that. I may just have to waddle up the ladder with both palms over my ears. That will be funny to watch.

[kramskoi]

jagman wrote:

It is late for you... here it's just the middle of the afteroon. Kind of funny how the internet brings people from such great distances together.

As you suggested, I already have the sub amp set to zero attenuation. And, as you suggested, the upper frequencies had to be attenuated with the BFD. Now I'm doing your other suggestion... boosting the lower frequencies and adding yet more attenuation to the upper ones. For whatever reason my room doesn't have that much low frequency gain. Part of it I'm sure is all the bass traps. But that only accounts for part of it; there is a 3m^2 opening to the rest of the house and 4.5m^2 of windows. They must contribute.

I am concerned about bottoming out the subs. I have a certain threshhold of which I won't turn the volume dial past. As long as they don't bottom out at that point I'll be in the clear. It is a bit worrisome, though. Especially with discontinued speakers from a company on shaky ground (pun intended). Then again, these bad boys have 27mm one way Xmax so they should be OK. I'm thinking about climbing up into the manifold with it playing to see how much they move. I'll need some heavy duty hearing protection to do that. I may just have to waddle up the ladder with both palms over my ears. That will be funny to watch.

It'll be movies like BHD and WOTW that will have you holding your breath. In places, these movies sport single-digit infrasound at varying levels and will certainly test the mettle of any subwoofer system attempting to reproduce it...trying to produce these infrasonics at palpable levels will certainly test a driver system which does'nt have airspring support...of course the amount of infrasound that will pass through the system will be largely determined by the inherent electronics roll off amongst the different components of the system...be certain to have good headroom with the amplifier(s) for movies like this...

[jagman]

The infrasonics are exactly what have me worried. I've played BHD and WOTW turned up to what I would consider loud and the drivers don't pressurize the room. I'm taking that as they aren't moving all that much. I'll be sure to take a peak at their movement before I add in too much boost. I'm hoping to get good movement while still having some headroom for piece of mind. There's nothing like the fear of the unknown... will they or will they not bottom out? Such deep thougths . I just don't think I'm getting all that I can out of the drivers. Since don't move that much and the amp isn't getting anywhere near clipping I think I have quite a bit of room to play with.

[Chrisbee]

Doesn't it strike you as odd that one has no idea of the peak bass levels and frequency on DVDs?

Most HT systems have subwoofers these days.

One ought to be able to quick-scan the disk for max bass peaks before playing.

It is is possible to scan for peaks on CDs on some CD players...

Perhaps some sort of numerical code for max/F could be applied to DVDs by the manufacturers to protect subs?

[jagman]

One would think disk manufacturers would want to display that info. Freaks like us would snatch up DVDs with VLFs in spades like there's no tomorrow. It would potentially save a lot of people from destroying there subs, too.

[Chrisbee]

I finally managed to get some REW playtime testing with my new meter.

The soft-look meter correction curve is much less flattering of low frequencies than my old analogue model. (which is what I have always suspected)

This is my latest curve using the new meter and 7 BFD filters including a +16dB @ 20Hz with 120 B/W.

Will someone please confirm that the black like represents the usual correction curve for this meter?
The old meter correction curve had a much steeper LF roll off.



Here's the no BFD curve with the new meter:



Here's the no BFD plot using the old analogue meter:

[brucek]

Will someone please confirm that the black like represents the usual correction curve for this meter?

Yeah, looks correct for the new analog meter.

That's a very unusual house curve? I thought convention was to raise the level from the crossover down to about 30Hz and then flat from that point down.

The old meter correction curve had a much steeper LF roll off

There have long been reports that the old analog meter enjoyed a large variance between units, and so the common correction file can't address that issue.
I think the two new meter types are more accurate between units. You were probably wise to get a new one.

The one aspect of your two plots comparing the meters that has me baffled is how the response in all areas appears different. Did you do this comparison with the same setup and the two mic elements close together with as many other variables removed?. It seems strange that at even 100Hz (where both old and new meters essentially track a standard c-weight), that they are so different? They show about 12dB difference. Did you ever drop your old meter?

brucek

[Chrisbee]

Hi brucek

The old meter plots were taken some months ago. I always suspected this meter flattered the VLFs after tests on four different subs over the years. Though I have used a variety of correction factors over the same period.

Over the last 12-15 years the old meter may well have suffered the odd drop test though not to my knowledge.

I suppose the real answer is to retest with new and old meters in the same position using their own correction files. I set up both meters on a tripod at ear height at the listening position. There can't have been more than a couple of inches of variation in exact meter position.

The new curve sounds deep on organ music but unchanged on film.

Is there any way to save the REW filter settings box as a jpeg for future reference? I usually scribble them down longhand then lose the paper.