Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems The HH2 guide to bass management and MRC

The following are some notes I took from the "How to get the best from your system with Des 'n' Rhonda. The subject of bass management and MRC was handled, in the context of an MConfig run through, by (Saint) Des Ford, Head of Support.

Bass Management

Subs: Use narrow. I reckon most of us will have figured that one out. The Wide setting for subs means that anything above the sub crossover will be thrown away by the sub. Wide isn't used much these days with modern subs which have line-level crossover bypasses.

Main speaker size: Meridian would normally treat 5200s as "large" speakers. A 5200C would normally be treated as "small" to force it to do less work. This is critical given that a centre speaker typically handles 70% of the front duties. The main point here was that you shouldn't be afraid to set a physically big speaker to "small" and use the processor's crossover to re-direct the lowest bass to a sub.

Bass heavy: This "is not hifi". It corresponds to twice the bass vs. the reference level and was introduced due to market demand. Lots of people with expensive subs want to hear them working all of the time. Also, it does help sell a system to people who want the bass to sound "like my mate's system".

Bass *is* left/right directional due to time differences in the wavefronts hitting the ears. There was some discussion that I missed a bit of where Des said that M usually recommends to its dealers to use chained mono subs rather than stereo left/right subs, but I can't remember the reason why. It might have been because Meridian processors are restricted to eight output channels and that, if you have stereo subs, you can't have a 7.2 setup, only 5.2. Can anyone help me out here? I certainly intend to try a 5.2 setup at some point.

The angle of the rear speakers in the MConfig diagram is used for the "THX EX" presets (only). I'm not sure if this includes the "THX Ultra2" preset. You can see the angles if you print your settings out in MConfig. I discovered for myself that you can also see them (and change them) in the MConfig XML files.

The room aspect ratio is used by the "Ambisonics" and "Super Stereo" presets (only).

Metric or imperial for specifying distances? Imperial is probably best as it is the primary unit in the software, chosen because one foot nicely corresponds to one millisecond of delay. Metric inputs always get rounded to the nearest six inches (even though this might not appear to be the case with G91/92 distances!!!).

Room Correction

1) Signal to noise

Firstly, irrespective of reported S/N, if you get through the MRC process and it builds filters, you have had a successful MRC run.

The main problem with S/N is spurious noises being measured such as: rattles, house noises, road traffic, other people in the house, etc. (Note: I have seen this with my boiler kicking in and out). You may be a bit stuffed if the walls themselves are rattling.

Meridian believes a single Radio Shack mic is perfectly adequate. Whilst the *magnitude* of a room mode varies with listening position, the *decay time* of a room mode is the same at different listening positions. There would be a problem, of course, if the measurement position is in the null of a particular room mode; such a mode would not be corrected properly, if at all. Meridian recommends using the listening position to start with.

Most sound meters have a 1V RMS maximum output, so the 1V sensitivity setting in MConfig is a good starting point. Ditto the 90dB meter range. However, be prepared to try different settings!

If there are problems, you need to experiment with the many variables at your disposal, including moving the measurement position, shooting the cat, adjusting the processor mic input sensitivity and adjusting the sound meter's sensitivity range. Des did say that with experience, he can tell if the speakers sound "loud" during MRC and that changing the meter range to 80dB is appropriate.

2) Small room acoustics:

a) Emphasizes frequencies.
b) Some notes ring on too long.
c) *Pitch changes during the decay of a note.
d) *Changes in pitch of short notes.
e) Beat and echo effects.

* Once the actual note has died away, you hear the resonant frequency close to it, that it has excited, and which has a longer decay time. With short notes, you may never hear the correct pitch because it's gone so quickly.

3) Target decay time

We know that MRC corrects frequencies only below 250Hz. However, MRC measures up to 2kHz in order for it to calculate the target decay rate. In other words, the decay time for frequencies up to 2kHz are used to work out the room's natural decay time.

Critical point: MRC attempts to bring the problem frequencies in line with this all-frequency room decay time.

My thoughts: We didn't get into a further discussion on this, but if you choose a target decay time which is less than Meridian-calculated all-frequency decay time (to control the bass to your satisfaction), this *might* indicate that you should spend some money on improving the room. On the other hand, I reckon that a little extra attenuation of the resonant frequencies might help with the pitch change issues (i.e. kill the resonant frequency before the the actual note decays).