Axiom Home Page Forums General Discussion What's New At Axiom Looking for your input on new video!

Hi everyone,

Our last Axiom information video covered the fairly simple topic of port plugs and we have been very pleased with the discussion that it has generated. In that same vein we are currently preparing for a video on the basics of speaker placement and positioning and would love to get your input on the topic. Is there a question within that subject that you've always wanted to ask but maybe felt it was too basic? You can post your questions in this thread or PM me directly, in case you're too sheepish about asking in public! I can't promise that we will be able to cover everything in the first video, but it would be great if we could make this a regular event as we plan more videos. Answering questions on topics that you're interested in is the purpose of these videos in the first place!

Thanks for your input,

Andrew

Andrew:

Axiom's previous vids have been great. The last one on the Plugs prompted me to experiment with a couple of DIY Plugs that completely cured the excessive bass issue with my M3s.

The subject of basic speaker placement would be most welcome; however, over the years with my systems, WAF & aesthetics seem to rule where my speakers are placed for the best visual impact...

TAM

I'd like to see specific points on dealing with compromises seen and or heard in small or narrow rooms as they relate to the front sound stage.
For example, is it worth while to copy 2 channel listening layouts for the front sound stage in an HT (simply add the center)?

Andrew,

It would be interesting if you could convey the principles that Wilson Audio cover in their manuals.. As seen in section 2.1 starting on page 15.

http://www.wilsonaudio.com/pdf/manual_soph3.pdf

I think this is a wonderful topic for a video, if you're able to convey the true importance of placement.

Toe-in, vertical positioning for bookshelves, first reflection points. You could do a whole episode on center channels.

Should I experiment with facing my LFR1100s the other way so I can see your signatures all of the time?

Hi Andrew, many thanks for bringing this subject up. This isn't a question but did get me wondering just how poor of a decision I'd made concerning my centre channel position so I did a little experimenting.
Took a laser pointer, protractor, tape measure, checked the angle which the centre was projecting into my room, at what height was it really directed.
Was clear it's present position was pointing at the legs of anyone in the first row, fine if you were sitting in a bean bag on the floor, not so much sitting in the chair. So, I have scrap oak laying around from other projects. Used some to fabricate a stand with some height adjustable speaker stand spikes. Can't say I've noticed a night/day difference with the new stand but voices sound better, clearer is the best word to describe the change. So again, thanks for the idea, looking forward to your Video on the subject.
/Jeff

I've always been afraid to ask just what the heck "comb filtering" means. It's mentioned all the time whenever the center channel subject comes up. I've seen/read a couple papers on it, but still don't get it.

I think I've experienced it. Send a test signal sent through the main speakers by using a CD with these tracks on it. Walk slowly across the path of the mains holding a sound meter pointed at the front of the room where mains are at. The reading will vary up and down as you walk across, but will remain steady when you stop at any point.

Using only my ears, I found that experimenting with 3 brands of horizontal WTW types (including my VP100) that there was negligible sound deficits in my room until past 30 degrees off axis.

While 'comb filtering' is certainly present in virtually all horizontal speaker designs, in the real world in most rooms it probably is minimal unless one gets way off axis. I didn't even bother experimenting with my new VP160 because I knew that there would be no or little degradation of sound within our listening area. Perhaps my odd shaped room helps as well...

TAM

I don't even comb my hair anymore

The most straight forward way to put it from a technical point of view is the cancelation that occurs at a single point in space (like a microphone) when identical frequencies arrive at different times. Each frequency where this occurs creates another cancelation tooth in the comb that is visible in the measurement.

It can be caused by playing a pair of speakers and positioning the microphone even just inches off centre or by the reflected sound arriving at a different time from the fundamental. The fact is that we are listening to a pile of comb filtering all the time when we play our audio systems and there is lots of empirical testing that has been done to show this creates a favourable listening experience.

I would say there are three camps of opinion on comb filtering:
There is the camp that believes all comb filtering is bad. Unfortunately the only way to accomplish zero comb filtering would be to listen in mono in an anechoic chamber. Having done this myself I can attest that it is not a great listening experience.

Then there is a camp that tries to separate the comb filtering into two or three groups and rate each group separately as to its effect on the listening experience. The most benign of these groups would be the comb filtering caused by the reflected sound. Next would be the comb filtering caused by using a stereo pair of speakers (or more) and not sitting exactly in the centre. Lastly, and this camp believes this type is bad, is the comb filtering that occurs when two identical drivers (usually tweeters but that depends on the physical spacing) in one speaker are used. I have seen some highly technical explanations of this difference but none that are backed up with any empirical scientific testing.

Then there is the camp that we are a member of which embraces all forms of comb filtering as either favourable or at worst irrelevant. And we have conducted empirical scientific testing to back this up.

Ian:

Thanks for the excellent explanation - good for laymen like me. While it is increasingly rare, it is nice to see that pragmatism & common sense still prevails in some circles.

From the myriad of articles that I've read elsewhere, it seems that much of this theoretical stuff gets blown way out of proportion in relation to what happens in the real world in most HTs out there. I couldn't believe how many posters had been convinced by the 'gurus' that the horizontal WTW is an absolute abomination when it clearly isn't. My amateurish, real world CC experiments proved to me that this is so...

TAM

At the risk of completely underailing this thread, how about some discussion of how to set up speakers for multi-channel music listening? In fact what about a combination of home theater and music?

I was just looking into this and found that the Dolby recommendation for HT is to use bi/dipole speakers for surround but for music the recommendation is to use regular speakers. Then there are different recommendations from THX. That doesn't even get into stereo listening. Is there some reasonable compromise that's good for everything?

Thanks Ian!

I'm thinking visual aids would be helpful. Maybe you could use a white board and pointer, while wearing a long lab coat?

Hi Michael,

Haha, this would be fun. We could even throw some of the related complex mathematical equations on the board to add to the mystique of it all. Kidding aside though we really should try to put together a video, or mini-series perhaps, on this topic. It really is an interesting phenomenon especially if you don’t close your mind to it based on the measurement visuals alone, but rather heed the results of the scientific empirical testing.

What video are you guys working on now?
I'd still hope to pick up a point or two relating to small,narrow and or short rooms.
That and why you might consider raising speakers or subs off the floor.

Andrew, you looked a little nervous...
Great job on these. Thanks for touching on each subject.
FWIW, (it would appear) I'm doing everything wrong and I've never experienced better sound and or imaging.
Guess that should speak volumes about the product, I'm glad I stumbled upon the brand when I did.
I can't wait to start planning my next screen room.

Blair