HT: Side and Rear speakers

[Brett]

I'm working on my new combined music/HT system and am running into conflicting ideas about the specification of side and rear speakers. I have read all the Toole papers and others like the JBL Cinema design ideas.


Assuming my Mains are 40-20k, high SPL capability, controlled directivity (will be using Earl's WG's) and there will be enough subwoofery to keep up, I pose the following questions to the gallery;

Q1: Dipole, bipole or directional Sides?
Earl has briefly mentioned dipoles as being the preferred option and states Thom Holman does too. However Toole and Lynn Olson seem to suggest identical Sides.

Opinions and experiences and why you made your choices are greatly appreciated. Design examples, whether commercial or DIY would help too.

Q2: Specification of Sides?
Once you have picked your design type, what level of performance do I need to engineer into them? For example, 6dB less max SPL, only need 60-15k etc.
Any other design specs I need to consider?

Q3: Rears - necessary or worthwhile?
I believe these are generally synthesised in the HT processor and not discretely recorded in most soundtracks, so should I make the effort to design and build some?
Again opinions and experiences and why you made your choices are greatly appreciated.

Q4: Rears- specifications?
Same considerations as for Q2.

Usage will be 2 channel music (45%), movies (45%) and multichannel audio (10%) at a guess.

Please don't worry about budget etc at the moment as I can say add rears next year if I need to save for them. Current room is approx 4x7.5x3m WDH, double brick with suspended floors. I use a projector and screen. System will not be used for TV or gaming.

I will not bore you with the details of the rest of the system as I would like to keep the discussion to the speaker design and implementation.

Looking forward to your comments.
Cheers
Brett

[GM]

I believe if you wade through this fairly comprehensive history lesson you'll understand the complexity of choosing in an 'either/or' sort of way as well as answering your other Qs: http://hometheater.about.com/od/befo...roundsound.htm

GM

[Hezz]

Brett,

I can't give you the last word but I can tell you what has worked well for me.

With the 7.1 setup, which I recommend, the side surrounds do not need to create so much of the illusion of space. Therefore, the idea of using a dipole or bipole as the (side) surrounds is not so important as it used to be back in the dolby surround days. The rear surrounds need not be expensive speakers as they are just low level ambience. The side surrounds are also used for ambience much of the time but then need to suddenly reproduce often loud and dynamic sound effects which can be full range or nearly full range in nature.

Standard monopole speakers work well in the new 7.1 setup with the side surrounds needing to be capable of good dynamics and as full range as is practicle for the installation space. An old pair of small mini monitors or inexpensive custom mini speakers will work well for the rears.

My suggestion is to make the side surrounds as large and sensitive and full range as you can without spending too much money or taking up more space than you have for them. The rears can be old used small speakers or an inexpensive small speaker or wall mounted or ceiling mounted set up.

The reason I suggest higher sensitivity speakers for the side surrounds is that it improves the dynamics of sudden sound effects. This is probably of higher importance than absolute sound quality for the side surrounds. Which when playing music is at very low level.

[pjpoes]

I will Second Hezz on making sure the side surrounds are big enough. I built some M&K clone tripoles, and the originals I made were just tooooooo small. There was a strange shrinking of images passing from behind overhead to the front, or vis versa. It's also good that all of the speakers be tonally matched or you will notice a difference. It's most important for the side surround speakers, however I think it has helped for the rear surround too. It really depends on the movie and how the sound mixer used the surround speakers. A lot of movies today are using them for more than just ambiance.

I also agree that Monopoles work fine for the surround speakers today, however, having the diffused drivers, such as in a Tripole design, does add spaciousness to surround effects recorded for ambiance. I've been impressed with what it adds to most of the movies I watch (I added a switch to turn them on and off), however I don't like what they do for music. I don't really like surround music much, especially that which is recorded to sound like you are in the band, but still, they exist, and dipole surrounds mess that up.

[Brett]

Originally posted by Hezz
With the 7.1 setup, which I recommend, the side surrounds do not need to create so much of the illusion of space. Therefore, the idea of using a dipole or bipole as the (side) surrounds is not so important as it used to be back in the dolby surround days. The rear surrounds need not be expensive speakers as they are just low level ambience. The side surrounds are also used for ambience much of the time but then need to suddenly reproduce often loud and dynamic sound effects which can be full range or nearly full range in nature.

Standard monopole speakers work well in the new 7.1 setup with the side surrounds needing to be capable of good dynamics and as full range as is practicle for the installation space. An old pair of small mini monitors or inexpensive custom mini speakers will work well for the rears.

My suggestion is to make the side surrounds as large and sensitive and full range as you can without spending too much money or taking up more space than you have for them. The rears can be old used small speakers or an inexpensive small speaker or wall mounted or ceiling mounted set up.

The reason I suggest higher sensitivity speakers for the side surrounds is that it improves the dynamics of sudden sound effects. This is probably of higher importance than absolute sound quality for the side surrounds. Which when playing music is at very low level.

Thanks, I thought the same basic thing initially. I also thought that sides that as near as practical matched the fronts in FR, SPL and general tonality would have a less obvious aural transition to the side FX for movies and music DVDs.

I have all the drivers for a JBL based WMTMW (2225, 2123, B&C DE250) system which worked well in a rough mockup with whatever amps I had available, and an old prosound active xover. Ported in an almost SBB4 they went to about 40Hz flat and I have enough amps on hand to do 120dB SPL. I might use these for the sides.
I'm also just about to order some AE TD15 and TD10 to make a similar setup in the front. In identical enclosure (but sealed LF) it should get a similar in room response, and I'll cross to subs below that. These would make better mains and 2ch stereo speakers I think.
I also have some old near mint Realistic Mach Ones which should suit as rears, at least until the bug to build something else overcomes me.

Originally posted by pjpoes
I will Second Hezz on making sure the side surrounds are big enough. I built some M&K clone tripoles, and the originals I made were just tooooooo small. There was a strange shrinking of images passing from behind overhead to the front, or vis versa. It's also good that all of the speakers be tonally matched or you will notice a difference. It's most important for the side surround speakers, however I think it has helped for the rear surround too. It really depends on the movie and how the sound mixer used the surround speakers. A lot of movies today are using them for more than just ambiance.

I also agree that Monopoles work fine for the surround speakers today, however, having the diffused drivers, such as in a Tripole design, does add spaciousness to surround effects recorded for ambiance. I've been impressed with what it adds to most of the movies I watch (I added a switch to turn them on and off), however I don't like what they do for music. I don't really like surround music much, especially that which is recorded to sound like you are in the band, but still, they exist, and dipole surrounds mess that up.

Cheers. I mention above my current thinking for the system. However, I also have 8 Eminence B15 and A15 and may try a dipole later for the sides, as once the monopole sides are built, it would only require a few tweaks in the xover to try, and the enclosures are much less complex. If I like these better, i would still have a use for the monopoles elsewhere, so no loss.

Thanks for your comments guys, it's appreciated.

[gedlee]

I would partially agree with Hezz, with one big difference. I see no reason for the surrounds to carry any frequencies carried by the subs especially if the subs are spread around the room. So I would mostly agree with everyhing that he says except that 150 Hz and up is all that I look for in a surround. And I do like the use of rears.

"The reason I suggest higher sensitivity speakers for the side surrounds is that it improves the dynamics of sudden sound effects. "

And I'm not sure about the assumptions behind this statement, but higher sensitivity is always a good thing.

I whole heartedly agree that sound quality in the surrounds is not nearly as big an issue as it is in the mains. There is no "image" to worry about and colloration of the reverb field is quite common. In fact a HF rolloff will give the subjective impression of the sound source being farther away.

[noah katz]

"I believe these are generally synthesised in the HT processor and not discretely recorded in most soundtracks,..."

I think "synthesized " is going a bit to far, as I believe all of the info comes from the discrete signal.

For instance, in a front-rear pan (or side, depending on speaker location) in a 5-ch system becomes a smoother front-side-rear pan in a 7-ch system, essentially by interpolation.

I also question the strong differentiation made between sides and rears as far as output capability.

While admittedly rare, there are soundtracks that stress sides and/or rears.

[gedlee]

Originally posted by noah katz
[BWhile admittedly rare, there are soundtracks that stress sides and/or rears. [/B]

I've heard those and I find them very disturbing. Music is always in front of me, not to the sides. And in movies the surrounds should barely be noticable. I abhore an obvious surround in either the source or the playback.

[noah katz]

"And in movies the surrounds should barely be noticable. I abhore an obvious surround in either the source or the playback."

I agree 100% for music, but real life has sound sources behind us and so do movie soundtracks.

[HiFiNutNut]

Brett,

Do your "mains" include the centre speaker? I would presume it is identical to the LR speakers.

I had 5.1 before. I never thought that the rear / side speakers were as important. However, I found the centre speakers to be very important. Since I didn't use a projector, there was no chance to use the same centre speaker as the LR. So at the end, I ditched the 5.1 and now only used the LR channels.

Regards,
Bill