Subwoofer for REW and Room acoustics

[bowl_actually]

Not sure exactly where to put this question as it applies to subwoofers, and REW, and room acoustics. But since what I'm looking for is a subwoofer, I'll start here.

What I'm looking for is a portable system for doing room acoustics that can give me more accurate results. I have a PC and a sound card and a couple of different amps that are pretty portable. So my initial reaction is to DIY build a passive sub.

However, these days there are so many powered "mini" subs that maybe that's a better way to go. Certainly a powered sub is more convenient and with built in DSP maybe there are some good candidates.

I need something that will play fairly low, preferably to 20hz, although most systems excite very little below about 30hz. and fixing room issues below 30hz is also a big challenge. It also needs to play loud enough to give me a reasonable S/N ratio. Maybe a sub that isn't really big enough for general use in a large room would still generate enough signal for testing if things were pretty quiet in the room. It also doesn't need to be perfectly flat, of course it's always better, but a few db variance is small potatoes compared to room modes and boundary interference.

It would be great to get a KEF KC62, but spending $1500 is out of scope for a dedicated box to carry around and do room measurements. I need something in the "below $300" range.

What suggestions do you guys have? Does anyone else here do something like this and have experience with a portable room acoustics setup?

 

[Sonnie Parker]

I think it's going to be tough to find something at that price that will be very good down to 20Hz, unless you find something in the used market. I think your initial thought of a DIY sub might be the way to go. Perhaps look at some of the Parts Express subpacks and drivers. Or get the driver and build your own box for the least expensive route. They have a lot of drivers to choose from, but their Dayton brand is very good. I've had a few of those in the past. Something like this 12" driver might work well in the right enclosure: https://www.parts-express.com/Dayto...ce-Series-HO-DVC-Subwoofer-295-467?quantity=1

With this subpack, you'd be at around $350 or so: https://www.parts-express.com/Knock...io-12-Reference-Series-HO-300-5014?quantity=1

Treating room acoustics below 100Hz is also a challenge. I always think of huge Helmholtz resonators. I spoke with a guy years ago who worked with a company that did room treatments below 100Hz. I can't remember the company and don't know if they are still in business. I know COVID put a lot of small companies like his out of business. They would come to your home, do sophisticated measurements, and determine where to place these huge panel traps. They would be full wall height and vary in width and depth, with a slot on one end. The location and size depended on what frequencies you wanted to tame at certain listening positions.

 

[bowl_actually]

Thanks for the response, I agree that maybe the DIY approach might be best.

As for controlling those frequencies, I like to use Limp Mass Absorbers that I build using MLV that I can buy from Amazon. Here's a very old thread about how to build them. They are not very big and if you build a number of them like Tim describes in the thread, it works very well.

Tim's Limp Mass Bass Absorbers - Gearspace

Over the years I have had great success fixing smallish room bass problems with limp mass absorbers. As there are so many threads here about this very

gearspace.com

Another approach that I might try, before buying or building a sub is to use a "clapper" device to generate an impulse. Here's an investigation of using such a device.

A simple impulse sound source for measurements in room acoustics

A simple impulse sound source for measurements in room acoustics

www.academia.edu

There is a company called Larson Davis that makes a commercial one, the BAS006. But I can't find where I can buy one of those. I want to make a few prototypes, clap them and use REW to measure the response I get. Can probably do that outside so I can get reasonable results. If one of these things will generate a good response, then it might be as good or better than a sub. Certainly more portable!

 

[Sonnie Parker]

That limp mass absorber is interesting. I don't remember seeing it before now.

 

[bowl_actually]

They are the best I've found for controlling low frequencies. They have a wider range than a typical hemholz and are much smaller. One of the keys is to make them about the size he lists in that thread, so about 24"x15" and depth depending on what you want your center frequency.

But with those sizes you need to do quite a few of them, he says a minimum of 4, but I think a minimum of 8 is best. For the corners if you alternate different depths, you can cover a wider range of frequencies.

I like to do maybe 4 panels at each of 30hz, 50/60hz, 85/90hz. Or if you have the room scans from REW you can choose appropriate center frequencies, doing at least 3 different depths under 100hz.

All that would be better posted in the acoustics forum... maybe I'll move over and do a thread there as I would also like to explore the "clapper" for an impulse source. I actually also need to do a bit of REW work as I don't think I've ever tried to start with an impulse! These days you generally start with sweeps or with white noise. I'm assuming it's straight forward to do a clap/baloon pop/or one of these clappers.

FYI, I found another clapper design that is round, with a hole in the center that claims to be better. It's made of MDF, is 35cm in diameter. They tested it and got usable frequencies down to 20hz. Easy enough to build something like that and test it, so I may go that route first and see what I can come up with.

 

[Sonnie Parker]

I use Dirac Live ART in my room for the sub-bass and overall room response. It does a wonderful job. A couple of years ago, I removed about half of my acoustic panels.

It sounds like you got it figured out for those who may need it. I hope you can find a solution for your subwoofer.