Bass Reproduction in a Small Room - Floyd's Book

[parodielin]

I am reading Floyd's Sound Reproduction - a bit challenging for a first timer but a good read. Based on the book, he suggested that it's best to use a system of subwoofers in a "small" room rather than having 5 or more full range speakers b/c of the room modes and standing waves. Without a system of subwoofers, the bass will vary among locations and it's a hit or miss.

Well, that suggests that I need to have a receiver that can do bass management and I should use subwoofers to match speakers. Full range speakers are probably not needed. But many two-channel amplifiers do not have bass mgmt function and we're still building full-range speakers.

What did I miss?

I do not have a specific room in this context. I am trying to understand what Floyd is discussing. His "small room" definition is like average family room or home theater room (Carnegie Hall is a big room and car cabinet would be a "smaller" room). His argument is that to reproduce frequencies under the room's transition frequency (e.g., 300 hz) will be governed by room modes.

He also said 2-channel is "antisocial" b/c only one spot (or very few) can have the correct bass reproduction. Different position will have different bass responses unless room modes are considered and a system of subwoofers are positioned accordingly.

If I follow Floyd's suggestions, I should build sealed speakers tuning to like 50Hz, add one or two subwoofers, and let the receiver do the bass mgmt. When I read the Amazon review, Linkwitz said Floyd's book did not fully explore the potential of 2 channel. Linkwitz's Comment But I am not sure if I understand fully.

That said, I do not have 100% level understanding of most Floyd's materials.

[Deward Hastings]

Well, that suggests that I need to have a receiver that can do bass management and I should use subwoofers to match speakers. Full range speakers are probably not needed. But many two-channel amplifiers do not have bass mgmt function and we're still building full-range speakers.
There's nothing new about the observation that the best position for a subwoofer (or subwoofers) is not necessarily the position in which acoustic or other (most commonly other) considerations place the L, R and C speakers. This lack of position optimization may, in fact, extend well above what we generally regard as "sub" . . . but for localization (and other) reasons we just have to live with discrepancies above about 80 Hz. When designing for "audio only" there is often some flexibility regarding speaker placement . . . for HT you are much more likely to face "and the speakers go *there*", whether *there* is acoustically optimal or not. Sometimes we get lucky . . . historically it's been "hit or miss".

Most of the time, though, the sub (or subs) will sound better in the listening area (listening "position" *is* "anti-social") if located elsewhere than with the "mains", and to get proper integration between the two does require "bass management", in the form of a continuous "phase", or "distance", adjustment (sometimes a couple of parametric equalizers will help too). Most analog crossovers don't offer that, and many digital receivers (that could) don't either. The answer there is simple, and cold . . . only buy a receiver or pre-pro that does.

Room response and subwoofer integration used to be one of the understood-but-unsolved problems of bass reproduction. It's still not completely solved . . . but we now have much better tools for dealing with it than we did even a decade or two ago. If full range speakers work in the position which nature or she-who-must-be-obeyed has chosen for them . . . count your blessings. Otherwise count your change, and be grateful for the technology that now lets us deal with the problem.

[Dirk]

If full range speakers work in the position which nature or she-who-must-be-obeyed has chosen for them . . . count your blessings. Otherwise count your change, and be grateful for the technology that now lets us deal with the problem.

Bump, set, spike. Great post, Deward.

[Cinemadesigner X]

One thing to look for in your amplifier is a main in -pre out where you can place a processor like the Behringer DCX2496, or BSS BLU-160, now you can manage up to 6 subs or more, the Blu series will allow you to apply a seperate EQ for each sub-woofer, most processors will allow you seperate slopes, and delay to match room and sub requirements.

Cambridge Audio & Arcam have main in -pre-outs in the middle to higher end models


Harman Kardon and Denon stereo receivers have been known to have these connections too.

[seriousfun]

... he suggested that it's best to use a system of subwoofers in a "small" room rather than having 5 or more full range speakers b/c of the room modes and standing waves. Without a system of subwoofers, the bass will vary among locations and it's a hit or miss...

I agree with his conclusions.

A full range speaker system simply has to play 20-20,000 Hz from each channel (and 20-100 or-so from the dedicated LFE channel). There are two ways to make a full range speaker system: integrating a subwoofer with limited range speakers, or using true full-range one-box speakers.

I can assure you that it is nearly impossible to find flat frequency response at the listening position from five speakers positioned properly around the vast majority of rooms (small rooms - a big room would be commercial theater sized, at least 12,000 cubic feet). 1 in 100 rooms probably can support this, so it's not impossible, but highly unlikely.

General problems happen below 80 Hz (and other modal problems below 300 Hz as he said, but these are less noticeable and harder to address), so even if your speakers go lower you probably should choose a crossover point somewhere around there, and not much lower (go much higher, and the subwoofer will start being more localizable and have other problems).

This overall approach can address any number of speakers/channels from one to infinity.

Many subwoofers have two channels of crossover - bass management - built in (few have 5.1 bass management). Use that loop! Take a preamp out from your receiver or preamp go through the subwoofer back to your main-in or power amp.

[DS-21]

I am reading Floyd's Sound Reproduction - a bit challenging for a first timer but a good read. Based on the book, he suggested that it's best to use a system of subwoofers in a "small" room rather than having 5 or more full range speakers b/c of the room modes and standing waves. Without a system of subwoofers, the bass will vary among locations and it's a hit or miss.

Well, that suggests that I need to have a receiver that can do bass management and I should use subwoofers to match speakers. Full range speakers are probably not needed. But many two-channel amplifiers do not have bass mgmt function and we're still building full-range speakers.

What did I miss?

Nothing. The common approach is wasteful and poor-sounding compared to doing it right.

The only minor I can see that you may have missed is that it is possible to do two channels and multisubs, either by using a separate preamp and inserting a crossover/EQ between the preamp and amp, or by using tape monitor loops or preout/main-in loops on an integrated switcher/amp.


He also said 2-channel is "antisocial" b/c only one spot (or very few) can have the correct bass reproduction.

It is also antisocial in that only one tiny spot can have the correct midrange balance, in the case of poorly designed speakers. (Any speaker that does not control the directivity of the HF driver at the bottom of its range, i.e. any speaker with a tweeter slapped flush on the baffle, is "poorly designed.")


If I follow Floyd's suggestions, I should build sealed speakers tuning to like 50Hz, add one or two subwoofers, and let the receiver do the bass mgmt.

Your sealed mains don't need to go down to 50Hz. An F3 of 80-100 is probably sufficient. Also consider the possibilities that open up. Instead of building inefficient speakers to get maximum bass extension in a given cabinet volume, you can build efficient speakers with weaker bass and the same cabinet volume. All else equal, a more efficient speaker is superior to a less efficient speaker, because it will suffer less from power compression. Also, more efficient speakers result in lower energy consumption, if only marginally so.


One thing to look for in your amplifier is a main in -pre out...

Good advice. The only problem is, except at the stupid-expensive range, preout/main-in loops seem to have disappeared in modern consumer receivers. That is unfortunate, because they are useful in that they both allow greater flexibility and extend the useful life of gear. (Hmm...maybe that usefulness explains their disappearance....) However, most modern receivers do have preouts for all channels, which means one can do all of the processing required in a separate box, but needs to buy a separate amp.