I got rid of my sub....GOOD RIDDANCE!! (1 Viewer)

[Phil A]

Sorry - Mark - was late and I was just typing away. Dustin, if you know where your problems are that is great. One of the bass treatments I have besides 3 ASC tube traps is made by Acoustics First, www.acousticsfirst.com. The have barrel-shaped traps that are not as pricey. They come in different sizes which help with certain frequencies better. I go into many people homes who buy the ultra-expensive stuff that is great and they don't even have a clue how to use it properly or just buy it because it is the most expensive, not necessarily the best sounding that I guess I get carried away.
I spoke to one of their engineers (Nick?) and actually used my RTA and walked all around the room and send him a video of the readings. They were very nice. He also sent me plans to build your own similar things. Basically you can go to Home Depot and get thin sheets of masonite and make a frame and so that it forms the barrel-type shape with the front middle curved so that it is about several (e.g. 7 or 8) inches from the back. You can fill you the space behind the face of it it with some type of mattress foam or insulation or other acoustical absorbing material and then paint or cover the face of it with fabric of your choice. So for a the cost of a sheet of masonite, a couple of 2x3s or 2x4s, some foam and some fabric you can liklely make something close to a product that is sold for about $260? - from memory. Below is info from their site on the product I am talking about:
ACOUSTICS FIRST Ò
DOUBLE DUTY DIFFUSERTM
(Barrel Shape)
Fiberglass mat saturated with polyester resin molded in a one-piece barrel shape.
Covering - Guilford of Maine FR701 fabric OR white gel-coat finish
Shell of diffuser is 3/32" thick -- Depth is 7".
Standard sizes: 23" x 23" or 23" x 47". Custom sizes available up to 48" x 96"
Class A Fire Rated
Mounting - Wall or Ceiling
Can also be used as bass trap when internal cavity of barrel is lined with 1-1/2" thick absorber layer of glass fiber batts.
Polycylindrical "Double Duty" diffusers will act to scatter sound in any location. Bass absorption will vary with size. A 2' X 4' has maximum absorption at 125 Hz. Increasing size to 4' X 8' lowers the point of maximum absorption to 63 Hz. Mid to high frequency absorption is typically 0.10 to 0.25.
The diffusers exhibit maximum bass absorption when placed across corners. Corner placement eliminates multi-phase, comb filtered, and upper frequency reflections.

 

[Phil A]

Dustin, also keep in mind that the RS meter is a good rough tool but not as good as a RTA as far as accuracy. The lower the frequency in many cases, it is more than likely the RS meter is off a bit. But for about $30-35 it is great. 140HZ aounds like a typical problem area. I have not taken the RTA into my bedroom system yet, just the RS meter. I will need to paint in a year anyway and then I can drive myself crazy with sound treatments or decorations that will help tame the problem areas. The Acoustics First std. (about 4 ft.) Double Duty diffuser actually helped tame problems quite well in the mid 120 to low 130HZ range in my room.

 

[BruceD]

There are a couple points being covered in this thread that are very important, but not quite as clear as they could be.

1) For accurate xover frequency matching of subs and mains 1/6 octave measurements and adjustments are probably the minimum requirement. Typically RTAs with 1/3 octave just don't offer enough resolution to correctly measure or adjust speaker/room/xover frequency effects.

2) Standard THX filters for bass management (what most receivers implement) have specific slopes for both the high-pass and low-pass xover that provide symmetry and are designed to sum to zero.

These slopes are;
1) -24dB per octave for the low-pass
2) -12dB from the receiver's high-pass xover plus an expected acoustic -12dB rolloff from the speaker which added together equal -24dB for the high-pass.

Thus the -24dB for both high-pass and low-pass sum to zero and provide a smooth transition without humps or dips across the xover boundary.

Also, these filters actually start their xover activity before the listed xover frequency so they sum to zero at the specific xover frequency, i.e. no humps or dips.

The basic problem is that unless your main speaker is THX certified, like M&K with an 80Hz -12dB acoustic rolloff, your receiver's high-pass xover won't sum correctly to a -24dB slope.

In fact many ported speakers have even sharper acoustic rolloff slopes; like -18dB or even -24dB rolloffs.

If you xover your mains above their natural rolloff freqency (thus contributing no acoustic rolloff to the total high-pass xover), then the -12dB slope from the receiver's high-pass xover doesn't attenuate enough of the mains bass signal by itself to provide a symmetrical xover with the receiver's low-pass xover to the sub. This is one cause of muddy bass, the mains producing excess bass frequencies and interferring with the sub producing the same frequencies, thus causing unwanted cancellation/reinforcement.

THX certified speakers have designed-in limited dispersion characteristics that I personally don't like, but that's just my own personal preference.

 

[Greg_R]

I would challenge anyone to put your sub behind your listening position and still claim that they are non-directional.

I've done that on separate occasions with a Paradigm Servo-15 and a Stryke HE15-based subwoofer. It's been my experience that perceived bass directionality is caused by other cues (room wall vibration, distortion, port noise, enclosure rattling, etc.).

 

[Dustin B]

Bruce, what about none THX certified processors. Do they usually stick to the THX standard or do they do their own thing? Are there any good resources out there that let you find out what the slopes and corner frequencies of the filters your receiver uses are?

 

[Brian Bunge]

Dustin,

My Sherwood Newcastle receiver (R-945MKII) uses 2nd order high and low pass filters at 100Hz.

Brian

 

[BruceD]

These days most of the bass management in receivers is handled by the standardized software code provided as part of the development package with the DSP processor (Crystal, Motorola, etc.) and is used unmodified by a majority of manufactures.

This code generally follows the THX 4th order low-pass (-24dB) and 2nd order high-pass (-12dB) but is frequently augmented with multiple xover selections (like 60Hz, 80Hz, 100Hz. etc.).

Some do modify or use alternate standarized code to provide different slopes, most don't. Here I'm speaking mostly of the mass market products.

Of course, Meridian, Lexicon and others actually write their own code.

 

[BruceD]

Brian,

I'm curious about your Sherwood. Do you find it difficult to blend a sub with main speakers? Especially for music?

In my experience,I typically find a 2nd order low pass filter (-12dB slope) to be a little too gentle for a sub. It doesn't attenuate the signal quickly enough, i.e. it lets too much of the subs SPL output past the xover frequency. I find it tends to interfere with the main speakers too much.

Also, a 2nd order high-pass plus a 2nd order low-pass won't sum to zero at the xover, but instead will sum to a 3dB peak (3dB SPL increase) at the xover frequency.

 

[Brian Bunge]

Bruce,
I use dual custom built 12" sub enclosures under my mains for that very reason. The only time I really didn't have a problem with a single sub was if I had it firing across the room from right to left instead of towards the listening position.
I'm aware of the 3dB hump at the XO frequency with 2nd order XO's. I'll be building my own 2 or 3 way 4th order L/R crossover once I get my nice big 15" sub completed!
Brian

 

[BruceD]

Brian,

Sounds like a worthwhile project. I bought a Marchand xm9-L 4th order L-R stereo xover kit for my mains to a single sub and I'm really pleased with the results.

Look forward to reading about your results.