Multiple Small Subs - Geddes Approach

[markus76]

Originally posted by Tubamark
The Audessey is exactly what I was looking for . . . sounds pricey . . .

No, here's a list of AVRs:
http://www.audyssey.com/products/consumer_ready.html

Originally posted by Tubamark
The Dolby feature linked above is nothing more than a limiter/compressor - Nothing to do with level-dependant frequency spectrum adjustment. Ack. Good for Low-Fi environments.

No again:
http://www.dolby.com/professional/ce...fications.html

Best, Markus

[gedlee]

To be even remotely valid it has to consider the SPL/volt calibration since this can vary by 10 dB or more with different setups. Floyd Toole says that there is some reason to boost bass at low SPLs but there is no justification for changing the HF at all.

[markus76]

Audyssey uses absolute SPLs. Dolby can.

The new ISO standard shows indeed the biggest deviations in the region <500Hz:
http://www.nedo.go.jp/itd/grant-e/re...pdf/is-01e.pdf

Best, Markus

[gedlee]

Good paper, thanks Markus.

[Tubamark]

Originally posted by markus76


No, here's a list of AVRs:
http://www.audyssey.com/products/consumer_ready.html

No again:
http://www.dolby.com/professional/ce...fications.html

Best, Markus

Ah-ha! I stand corrected!
That initial Dolby link was all "consumer friendly" marketing-hype. They missed the opportunity to distinguish the technology from regular compression/limiting -- no mention of spectrum/tonal balance, etc. Shame on the Marketers. Bravo for the technology.

Thanks for (re)pointing me in the right direction!

-- Mark

[markus76]

Yes, Dolby's and Audyssesy's pages are really annoying. But obviously incorrect and/or missing information help sales.

Best, Markus

[gedlee]

The troubling part is just how nieve many consumers are and therefor how easily they are convinced by audio mysticism. It makes it really hard to sell anything honestly as you have a completely unfair advantage when up against puffery and sometimes downright lies.

[audiokinesis]

I haven't spent much time here at DIYAudio recently, and just found this thread last night. Since my system was mentioned in the initial post, I thought I'd put in my $.02.

To briefly recap, I build a four-sub system that I call the Swarm, which is used in some of my complete systems and also sold separately. I got the idea for a scattered asymmetrical multisub system from Earl, and he gave me permission to use it in a commercial product. Of course they can also be set up in a symmetrical Welti or Welti/Toole configuration.

Speaking of Todd, it's great to see him posting in this thread. I must confess that he and Earl are the only ones whose posts I made a point to read (or try to read) every one of. Not that I understood them all!

One of my reasons for using four small subs (each about 1 cubic foot internal volume) is so they can be wired in series-parallel and driven by a single central amplifier, in this case a Parts Express 1000 watt shelf-mount amp that has some nice features (4th order lowpass and a single band of parametric EQ).

Up until I read Earl's posts in this thread I hadn't appreciated how important placing one of the subs in a corner is with an asymmetrical setup. I'll start making that a strong recommendation.

I don't use Earl's overlapping technique because I intend for the Swarm to be compatible with a fairly wide variety of main speakers not having the gentle low-Q sealed box rolloff that Earl's do. Also, I'm not using bandpass subs because I don't know how to design a compact bandpass sub that covers two octaves.

Regarding the ability of multisubs to smooth out the in-room sound, to the best of my knowledge none of my customers have found it necessary to use the parametric EQ feature in their amps. In a case like Earl describes where the lowest fundamental room mode cannot be tamed even by multisubbing, that feature might be useful.

But, I have a question about that: Earl, if I recall correctly, that lowest room mode you desribed is around 30 Hz, and isn't that below the passband of all except your one big ubersub?

Thanks,

Duke

[gedlee]

Originally posted by audiokinesis


But, I have a question about that: Earl, if I recall correctly, that lowest room mode you desribed is around 30 Hz, and isn't that below the passband of all except your one big ubersub?

Thanks,

Duke

The whole concept of "passband" is a free field one. When the subs are in my room they readily excite the 30 Hz mode even though it is theoretically below their "free-field" passband. But then my room measures a flat response down to 15 Hz with the subs that I have and supposedly none of them can do that. This is why I say that what a sub does on paper is kind of irrelavent. What is important is its response in-situ in the room, and that changes everything.

[audiokinesis]

Very interesting - thank you, Earl! This raises even more questions than it answers for me, as I still haven't wrapped my head around thinking in modal geometry rather than Euclidean geometry when it comes to bass propagation in a room.

This flat in-room extension to 15 Hz... isn't that down well below the modal region? Is your room sufficiently sealed to exhibit "cabin gain"?

Can this seemingly free-lunch extension be reliably predicted and thus taken advantage of?

I presume you wouldn't get anything like this sort of extension if you had ported subs, as they'd be rolling off too fast below their tuning frequency... unless they were tuned down around 15 Hz!