Multiple Small Subs - Geddes Approach

[dwk123]

Originally Posted by Pallas

Summed response S1+S2+S3, after just optimizing levels and delays on the miniDSP,

Which minidsp plugin are you using for this multi-sub application ? Would the 4-way Advanced be the right choice? It's not entirely clear from the datasheets whether all of the high/low pass settings are completely independent or not.

[Pallas]

I'm using the Advanced 4-way.

The high and low pass settings for each output are independent, and one can do a bandpass filter on each output.

I'm not using the crossover section here, though, except for a highpasses down low to protect the S1 Perhaps I could improve things further by adjusting the lowpass slopes independently. I'm redoing the setup (mostly because by building subs to fit the room as opposed to using pre-existing stuff I can completely hide all three subs, but also because I want to use sealed subs and some of my Aurasound underhung drive-units) and I will probably play with the crossovers as well.

[Jimmy154]

The more I read this thread (only on page 16) the more I realize I need to build two subwoofers instead of one and the more I feel like life would be easier if I could just smack these modes in the mouth and they could all fall into line. Is this normal? Maybe it's an uniquely American form of thinking, I'm not sure.

[AllenB]

Perhaps the attitude, Jimmy, but the frustration is universal I'm sure

Just begin with one. Put it somewhere until things measure better. Forget it's there. Put in another one....eventually if you've done things right you'll forget your troubles.

[bentoronto]

Originally Posted by dolphinamica

[SIZE=3][FONT=Times New Roman]Just a word of caution on those PE/Dayton plate amps. I bought a Daton 250 wt plate amp and it hums and buzzes like a huge pissed off bumble bee....

For my cottage, I found a second-hand sub. It is a box with 4 inch legs, passive radiator on bottom, plate amp, sold under a dozen names with prices from $15 (my price at Goodwill store) to like $750. Sure hums.

So I had visions of taking phenolic casting resin and entombing the transformer in it, like the Chernobyl reactor. Prolly would start a fire or at least melt down the transformer, like the Chernobyl reactor.*

Finally took it apart yesterday and with plate amp resting on the floor and a big gaping hole in the box, hum is vastly reduced.

So my conclusion is that the underlying problems with some of these subs that are sold cheap (or should be) are (1) you don't want to mount a transformer on the wall of your woofer and (2) many of these systems are pretty resonant in the 60 Hz region (which makes both the residual amp output hum and the physical transformer hum louder).

Ben
* Need a laugh? Want to hear about the stupidest design ever? This sub has a remote. Sound useful? It controls volume and cross-over freq.... as it you EVER touch these once you figure out the right settings to match the rest of your system after much measurement. Worse, the settings are volatile and disappear when the power flickers briefly. So you are back to re-setting each time!!!

[bentoronto]

Originally Posted by bentoronto

...and (2) many of these systems are pretty resonant in the 60 Hz region

Which brings me to my next point: the relationship of mic-derived sound loudness and perceptual experience. Since there is hardly any musical instrument making (or making any too often) sounds below maybe 35-40 Hz, no kidding, aiming for good performance in the 120-40 range is prolly the important thing you can do.

I think several threads at this forum have generally veered to favoring curves rising in the bass, not flat.

Ben

[DBMandrake]

Originally Posted by bentoronto

Which brings me to my next point: the relationship of mic-derived sound loudness and perceptual experience. Since there is hardly any musical instrument making (or making any too often) sounds below maybe 35-40 Hz, no kidding, aiming for good performance in the 120-40 range is prolly the important thing you can do.

The "there's not much musical content below 35-40Hz" claim is often repeated but really doesn't hold true in my experience.

If all you ever listen to is acoustic recordings of "real" instruments, then perhaps, maybe, but even then the lowest fundamental on a piano is (from memory) 28Hz, not to mention that ambient noises in large acoustic spaces can produce low level sounds in the <30Hz range that help give a sense of space of the venue.

If you don't just restrict yourself to recordings of "real" instruments, there is a ton of music out there with a lot of content below 40Hz, down to at least 25Hz, and the difference listening to it with speakers that go down to 40Hz vs speakers that go down to 25Hz is very big indeed.

(I find on my current small speakers and limited room size which together give a cut-off of around 35-40Hz that the lowest bass notes of some of my favourite songs are "missing in action", so I can certainly tell the difference compared to when I had a system that went down to about 24Hz)

I think several threads at this forum have generally veered to favoring curves rising in the bass, not flat.

Anechoically flat bass response to below 40Hz is a disaster in room because of the effects of both room gain and modal distribution. Typical room/speaker positioning will boost bass below ~40Hz at least several dB, but at the same time standing wave cancellations will typically suppress bass in the 80-160Hz range by several dB causing a large downwards tilt (with increasing frequency) at the listening position which sounds really poor.

An upwards sloping anechoic response is just giving a closer to flat in-room response when "typical" room effects are considered. I prefer a speaker with an early gradual rolloff at the bottom end for this reason (rather than something like a flat then sudden drop-off B4) to help combat the low end rise and also having the woofer close to the floor to minimize the cancellation induced loss in the 80-160Hz range. The two together tends to give a flatter in room response before any EQ is applied.

[bentoronto]

Give me a minute to figure out where to begin a reply.
Ben

[weltersys]

Originally Posted by bentoronto

Since there is hardly any musical instrument making (or making any too often) sounds below maybe 35-40 Hz, no kidding, aiming for good performance in the 120-40 range is prolly the important thing you can do.

Ben,

Though I agree that 40 Hz to 120 covers most bass requirements, the low "A" on a piano is 27.5 Hz, the low "B" on a 5 string bass is 32 Hz.
Without considering pipe organs, which have 16 Hz low notes, many pop recordings often have plenty of musical content down in the 20 Hz range, and movie soundtracks have effects well below that.

The octave from 10K to 20K contains no musical fundamental frequencies, the octave from 20-40 Hz contains many.
No one seems to argue that the top octave is not needed, leaving out the lower octaves makes no sense when they are now easily attainable.

For $10 in speakers, a few more dollars in screws, glue and wood anyone can hear the difference that octave makes for themselves.

$10 (plus wood) 18Hz ISOT-TQWP Sub

Art Welter

[bentoronto]

Good points from weltersys.

I have quite a big collection of organ music and many other goodies and I have spent a lot of time watching this music on a spectrum analyzer. Pretty rare for anything that low. Betcha if you hit that bottom key on the piano, there's not much fundamental present. Likewise for organ pedals which mostly have proxie tones, not the advertized frequencies.

Anyway, your brain reconstructs those fundamentals just fine although I'd love to see one of those debunking ABX blind experiments done with and without output below 35 Hz. Many times I've run while the sub is out of action - 140 Hz crossover and very sharp. You'd be amazed at how little is missing, not that I'd like to live without that missing part, of course.

True, there are fireworks and disaster movies with low notes.

As far as I know, your brain does not add the upper partials and their absence is easily sensed, unlike bass.

True, not expensive to make bass with a sub and electronics these days. But if you add bass, your system will sound lousy unless you also ensure the treble is strong.

A lot of this discussion is vague because we are throwing around Hz's as if a woofer played zilch below 37.5 Hz or whatever. Relative.

Ben
BTW, no such thing much as "room gain" unless you lived inside a sealed propane cylinder. Anyway, a mic picks up "room gain" as well as your ears do... so it isn't some extra mystery benefit not visible on acoustic curves... even if it existed.