Building the Nathan 10

[FrankWW]

This is it in a nutshell, I think. Thanks

At LF's the period of the waves and certainly the time it takes for our hearing to react and recognize a LF signal are actually on the order of the reverb time in a small room. Thus there is no decorrelated signal for our hearing to process at LF in a small room, its basically completely correlated. As I studied this situation I came to realize that it was the modes in the large room that decorrelated the LFs and extended the time of their presence thus yielding a psychoacoustic gain in their perception.

I thought that if we could do this electronicaly at LF for the subs then maybe we could get the sound more like the large room.Turns out that the filter to do this is called a decorrelation filter...

Going to make a bunch of small subs. My present subs are just too big to use here. I've three integrated stereo amps and a DCX so making cheap, tiny subs I can stash away makes sense.

[pjpoes]

Maybe I'm nuts here but isn't a decoralation filter pretty easy to design in the analogue domain. Isn't it nothing more than a lattice-ladder filter, as in the same filters we use for creating signal delay? If I'm thinking right this could be achieved with 2 opamps and a small handful of resistors and capacitors mounted on strip board (i.e. a very simple circuit).

[gedlee]

Simple delay was not my idea and I don't think that the filter that you describe would create a decorrelated signal. It would still be highly correlated but at a delayed time.

You need a back of these filters, all with different delays and random levels. This will decorrelate the signal. Easily done digitally, but a lot of analog circuitry.

[gedlee]

Originally posted by noah katz
I don't mean to be tiresome, but it seems that the simple explanation is that larger rooms have higher mode density at low freq.

Yes, of course, large rooms have it and small rooms don't. But how do you get this in a small room?

I hypothesized an electronic simulation of a bank of added room modes. When I did this I found that the LF sound field smoothed out almost like that at HF. Then I found that this filter was called a decorrelation filter - also know as a reverberator. But We don't want to do this at HFs, just the LFs.

[auplater]

Interesting reading.. thanx all..

My experience in my rather largish room 25' x 30' rectangle + 15' x 15' open to kitchen 2 story, maybe 15,000 ft^3 SCREAMS don';t put ANY subs in the corner... else HUGE standing 32 hz wave at the ceiling/floor peak ~17.5 feet that dominates the bass response.

After years of moving first one sub from one corner to another (either room boom or total suckout, depending on the corner) my current setup has 2 12" sonotubes ~1/2 way along shorter walls 2 - 3 ' out, and yields smooth extended bass to below audible freqs. at floor rattling (and drywall joint splitting) levels for both audio and movie HT listening at a large arc maybe 15' across 15' back at the viewing/listening position.

Corner loading in this setup is just plain stupid.

Mathematical calculations may be good for guidance, but with all the assumptions/deletions re: boundary effects or not, trial and error seems to be the best approach. I've tried most of the different setup motifs, and this current setup is by far the best.

Not all of us are limited to small rooms with low ceilings. I'm driving 7.1 surround with 140 wpc on the mains and surrounds, and 300 w/sub for the 2 sonotubes. Not for the faint of heart. Definitely envelopes one into the movie...

I'm not sure how much better this could get, but I'm open to suggestions (short of rebuilding the room w/o windows, drywall, etc.



John L.

[gedlee]

I have a sub in the corner of my HT and I get pretty good reviews of my system - by other people. I always put a sub in the corner and I always get good impressions by others. Never put two subs in the corners.

[noah katz]

"I hypothesized an electronic simulation of a bank of added room modes."

Ah, so fill in the spaces between the natural modes w/synthesized ones.

This is good for smooth response, but what about overhang from the long reverberation times?

[winslow]

Like I said, we know a guy who supplies the furniture mills and he gives us great pricing on wood. There is a 6' tall stack of 3/4" MDF at the shop now. We get anything from 1/4" to 1 1/4". We are a car audio shop and build a lot of sub enclosures for our customers and other shops.

Ultimate goal is to get a Shopbot.

Originally posted by John_E_Janowitz


$10 per sheet?!?! Is this possibly for only 1/4" mdf? We're paying nearly $25 a sheet wholesale now for 3/4" MDF. If you would be able to PM me or email me(john at aespeakers.com) with a contact for the lumber yard I would love to have it. If it really is $10 per sheet I'd seriously consider buying a full truckload and bringing it up here.

John

[Fosti]

Originally posted by pedroskova
..... Buying some active crossover off the shelf is not much different than buying an Eminence 2nd order ready made passive x-over from Parts Express.

Excuse me, but that is a lot of a difference!

Markus and aubergine, that wasn't meant to be rude. I'm a scientist, too, but most people here are hobbyists and that may lead them to take such statements from a scientist with acoustic expertise like gedlee for granted without thinking about it.

I have no problems with the "high gain" of pro-gear but a lot with the sold "aura" of some highly prized consumer gear It is "professional" to have a high amplification at an early stage in the signal path, that's an old rule in communications engineering!
My 8024 runs between the CD player and my Sony AV Receiver with no problems. But one time I will change the Sony "consumer" receiver with its "unprofessional" unbalanced connections aganist this for example with professional balanced connections:
http://www.d-mpro.com/users/folder.a...7&SubCatID=165

[auplater]

Originally posted by gedlee
I have a sub in the corner of my HT and I get pretty good reviews of my system - by other people. I always put a sub in the corner and I always get good impressions by others. Never put two subs in the corners.

Glad it works for you... doesn't work in my room.

Many other listeners agree with this. Changing the phase, changing the sub, putting the sub in the listening location and mapping the room by ear or meter, all yield excessive modal sound vs. mid-wall side loading at the preferred listening locations. So generalizations about stimulating the maximum # of modes don't always work.

John L.