Rears: Specs and performance vis-a-vis Mains

[A9X]

Hi All,

I'm an experienced designer and builder of speakers and have a set of large JBL and BMS based mains* designed and will begin construction soon.

Once these are done, I'll turn my hand to a set of rears, and I need some advice to what sort of performance I should aim for with regard to the mains so I can set a spec and start fiddling with the design before I begin the build in the latter part of the year. In the meantime my first series Realistic mach Ones will serve that duty.

A designer I respect greatly, Lynn Olson, suggests the rears should ideally be the same as the mains to integrate properly and to get the best performance. Intuitively, this seems correct, but the mains will be very large, the drivers took ages to source and I'm not sure I could get another set easily or cheaply. However I will if need be.

So, what I'm after is some idea from the more experienced DIYers as to where to set the performance spec for the rears for the best all round performance. I'd rather do it once and then just use them for several years.

Should I just build another pair as close as possible to the fronts?
Would a similar tonality with less LF extension be OK? How much less?
Some have suggested OB's. I have drivers that will work for a large OB dipole but they would sound good, but dissimilar to the mains. Comments? Suggestions?

* The mains will be an WMTMW on a wide baffle similar in appearance but substantially larger than Troels Gravesen's Poor Man's Strad and Acapelle WB

http://www.troelsgravesen.dk/Acapella_WB.htm

Driver complement is JBL 2225 60-250Hz, JBL 2123 250-1k2Hz and BMS 4592 and OS WG > 1k2Hz. It'll all be active and multiamped.

Rears would also be multiamped active, but I'll build them into the enclosure and remote switch them on so there's only a powercord and signal cables running to them.
Current room is a bit small, 6.5m x 4m x 3m but after I finish with school and my work contract, I'll move back to my home which is basically a huge open plan living/ dining / kitchen so they'll need to be able to fill a lot of space well as the previous horn system did.

System will be Mains + rears + subs. Never found the need for a centre.

Any or all help is welcomed and suggestions gratefully received.

[ThomasW]

Is this for multichannel Hi-Rez music? HT? Both?

What are your multi-channel sources, type of decoding, etc.?

[A9X]

Is this for multichannel Hi-Rez music? HT? Both?

Both. Music will mainly be 2ch, though I use the reciver to set up a pseudo 4ch for listening casually or wandering around. Main close listening to the rears will be for HT.

What are your multi-channel sources, type of decoding, etc.?

Currently DVD is the only multichannel source, a Pioneer DV686A fed via a properly made coax to a Pioneer VSX1015 receiver.
When finished I'll use the pre outs of the receiver to go to a multichannel switcher and stepped attenuator (I would call it a pre but it'll have no gain or active cmponentry) and then to my xovers and amps.

[ThomasW]

If you're running 4 discrete channels then I agree with the need for identical speakers all around. For ambient-fill or so called 'effects' speakers one only needs to match the timbre of the mains.

For example, I have large ESL/planar/leaf tweeter mains. These are 3' wide and 8' tall. For HT/rear effects speakers I run a modified pair of Magnepan MMGs.

[Deward Hastings]

As Thomas notes, it depends on your source. I have well over a thousand music recordings, and exactly none with discretely recorded rear channels. The rear channels in every movie I’ve listened to were entirely (and generally obviously) synthetic . . . even on those (rare) occasions where there is recognizable dialogue in the rear it is generally colored or muffled *in the soundtrack*. What is it that you are trying to reproduce?

There are two experiments that I’d suggest:

1) go outside and find a localizable sound source . . . a car, a lawnmower, kids playing. Listen to it carefully. Turn your back on the source. Does it sound the same? Especially are the highs the same?

2) back inside put on a movie with sound effects that you consider important to the film. Set your normal listening level. Turn off the front speakers and subwoofer. Listen to what’s back there. If it’s not too difficult route those rear effects to your front speakers (same level) and listen again (don’t forget to turn your back . . . we’re pretending they’re your rear speakers now).

If it’s possible you might arrange a visit to your local cinema . . . find out what speakers they have beside and behind the screen, and what they have in back and on the sides. That speaker complement is, after all, what film soundtracks are mastered for, and provides what movies are expected to sound like . . . (nobody imagines that they sound “real”).

[---k---]

Note to a potential lurker, I think this is a good separate thread. Lets not go there.



I'm currently debating this myself. My rears are scheduled to be upgraded this summer.

There is a reason you build BIG mains. It is to give the music dynamic power and bass authority. You know this already.

For surrounds, it depends on your goals. I love listening to the Blue Man Group DVD "Audio". It is 5-channel DTS. Lots of dynamic big drums, etc. I also have one or two 5-channel SACDs that I recently acquired. For these recordings, having rears to match my fronts would be optimal, but a divorce in the making. Therefore, I'm willing to compromise some dynamic ability and bass response for size.

Currently,the small 2-way rears (Ascend 170SE) I'm using could use a crossover in the 80 - 100hz range, while my mains I cross to the sub at 50hz. So, that presents some challenges. They clearly don't have the midrange capability as my mains. But, for the most part, I haven't been disappointed with the current setup - even at some house shaking levels. Sure, I think I notice a drop off in quality of the rears to the mains when listening to the hi-res SACD's but it isn't enough to stop me from enjoying the the music.

I do most of rear usage with DVD movies. And never with a movie have I noticed issues with the rears. However, I'm often paying attention to the movie and not listening for compression or distortion. I also think that with movies and many audio recordings, that they are engineered / mastered with limited rears in mind. Ambiance on subtle effects that are usually found in the rear channels, arn't going to push the speakers to the limits that would require big speakers.

Subwoofers also take the bass requirements off of rears, and therefore can be a big factor in what you want to do.

So, I think the bottom line is: Remember why you built big front speakers??? Are you willing to give this up in your rears?

I'm likely going to build the in-wall versions of the NatP or ModulaMT for my rears. I think it will be a good balance.

[A9X]

If you're running 4 discrete channels then I agree with the need for identical speakers all around. For ambient-fill or so called 'effects' speakers one only needs to match the timbre of the mains.

I'm beginning to think that if I get the general timbre and extension SPL capabilities close, I probably won't notice that much. More details in the next two posts below.

For example, I have large ESL/planar/leaf tweeter mains. These are 3' wide and 8' tall. For HT/rear effects speakers I run a modified pair of Magnepan MMGs.

Helpful analog. My mains will be nearly as tall and wide, but a bit deeper (~400mm) so another identical pair will take up a lot of space.

[A9X]

Apologies in advance for the long response: I'm thinking in print to try to work out what I need and want and where to cut the spec with minimal loss from a 100% approach and maximum return for all the $ and work inout into it.

As Thomas notes, it depends on your source. I have well over a thousand music recordings, and exactly none with discretely recorded rear channels. The rear channels in every movie I’ve listened to were entirely (and generally obviously) synthetic . . . even on those (rare) occasions where there is recognizable dialogue in the rear it is generally colored or muffled *in the soundtrack*. What is it that you are trying to reproduce?

Excellent points. I decided to review the listening requirements and source material.

Sitting In The Chair:
Music: 2ch from CD or vinyl - about 45%
Movies: multichannel DVD about 45%
Music DVD's: about 10%

The last group is mainly concert type footage, rock, jazz and Motorhead, so it's processed and the rear channels are 'effects' not to accurately portray the recording space. I am getting into classical as I get older, so there may be MDVD's or even some SACD's that I get in that genre later where the rear channel information is 'real'.

When wandering around the house I often have a CD or FM on in the background and will switch the receiver into a pseudo surround. In this mode, I don't see it matters much the exact spec of the rears, so long as they can keep up and don't sound awful. Just seems to fill the house a bit better than 2ch.

I have tried some of your suggested experiments, and will do more later today.

[A9X]

Sorry again for the length of the post.

Note to a potential lurker, I think this is a good separate thread. Lets not go there.

Que?

There is a reason you build BIG mains. It is to give the music dynamic power and bass authority. You know this already.

When I was thinking about the rears initially, the Pragmatic Engineer part of my brain switched off, and the Petulant Audiophile voice took over and demanded that I must have the biggest, loudest, most excellent looking speakers that would accurately reproduce the seimic events in movies, the full bombast of an orchestra and the subtle nuances of Lemmy's voice (at 120dB). The sort of speakers that would make women leave damp patches on my couch and other audiophiles quake in fear before their incredible awesomeness and wish to declare me their new God.

For surrounds, it depends on your goals. I love listening to the Blue Man Group DVD "Audio". It is 5-channel DTS. Lots of dynamic big drums, etc. I also have one or two 5-channel SACDs that I recently acquired. For these recordings, having rears to match my fronts would be optimal, but a divorce in the making. Therefore, I'm willing to compromise some dynamic ability and bass response for size.

I do most of rear usage with DVD movies. And never with a movie have I noticed issues with the rears. However, I'm often paying attention to the movie and not listening for compression or distortion. I also think that with movies and many audio recordings, that they are engineered / mastered with limited rears in mind. Ambiance on subtle effects that are usually found in the rear channels, arn't going to push the speakers to the limits that would require big speakers.

Your comments are appreciated and reflect my thinking as I look more closely at usage and real expectations. I more or less replied above to Deward and explained my usage; seems we're similar in that regard.

Subwoofers also take the bass requirements off of rears, and therefore can be a big factor in what you want to do.

I will have 2 tapped horn subs in the small room in Sydney. When I get back to the larger room, I'll add 2 or 4 more depending upon what I find I need. I have the drivers already, a Quest QA3004 that will drive them.

I'm checking the drawings and getting ready to mark out the TH subs today, and will hopefully cut them next weekend.

So, I think the bottom line is: Remember why you built big front speakers??? Are you willing to give this up in your rears?

Perhaps some of it, but I'm certainly not going to step down to a 6.5" 2 way.

I couldn't sleep last night so I tried to put the Pragmatic Engineer cap back on and did some simulating in Unibox of what I have on hand and what I can get easily and cheaply.

I have two pairs of new coaxes: some PAudio BM8CX, which is actually a nice little speaker and some EV Pro12B. I can also get a hold of 4 NIB PAudio C15-300MB from an aquaintence who didn't need them for a project. He tells me they measure well and sound good and used 2/side in 120L net in a low Q ported alignment gets me good LF and it should sound similar enough to the fronts that it won't be an issue.

I already have a DDS 3way stereo analog xover sitting idle and a Yamaha P7000 that doubles in my bass guitar rig that I could use for the LF, <250Hz when it's not doing BG duties and my old Rotel RA840B for the HF >1k8. Add a Behringer A500 for the mids (cheaper than building my own) and some time (already own the ply), as well as $A800 total and I'll have a set of rears that will likely be good enough, better then most, even if it is a bit of a hodge-podge system. The other drawback is it'll take a bit of rack space rather than be built into the enclosures. An advantage though is that I can build them into a smaller footprint so they don't become room dividers in themselves. I have no WAF issues, but I don't want the room to be single use as it's still the living room.

Even if I can get another set of JBL's, and the first set took 2 years to gather, it will be considerably more expensive than what I proposed above unless I can find them locally and even then 3x more. The only alternatives I like are some 18Sound units, and they'll be even more expensive again.

I can fund all of the above by selling off a lot of audio parts I don't need. Sound like a feasible plan?