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help on theater design (1 Viewer)

Jon Hancock

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Mar 18, 1999
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67



Bryan,

Sounds like you've got a nice big room to work with, but it does present some challenges, though if you can find a DIY setup that meets your needs, that may help with the cost.

But, I'm inclined to agree with some of the others here that you'll have to be careful selecting a speaker setup because of the relatively large room size and listening distance throw.

I used to build some dual 5" TMM 2.5 ways for folks in the Boulder Colorado area many years ago, used in some small studios as nearfield monitors with seperate bass speaker crossed in at ~100 Hz for each channel- this worked pretty well, becuase 5's have great dispersion, and with a listening distance of 1 meter, though 5's have limited Xmax and power handling, 100 dB peak SPL's weren't a problem. Getting 100dB+ level's cleanly at the listening distances you describe will require a bit more oomph...

I'd also be cautions about using just Xmax as a guideline for maximum output. The reason is how Xmax is rated/determined- at the Xmax limit there's already a large BL fall off. XBL2 drivers have a more linear curve, but they manifest this also. What I find, is that even for high linearity long throw woofers like the TC2+, which has a 20 mm Xmax, the really linear "sweet" part of the curve is ~ 12 mm each direction. So, what I've found is that "de-rating" the driver to operating the speaker design just in that region is an important factor in having a speaker with a high sense of "ease" at the higher SPL region, rather than one that starts to sound a bit congested or strained when you push it.


These weren't subwoofers, though, more a high power bass driver with flat response to 500 Hz+, so integration with a 100 Hz crossover was a non-issue. For HT, and "true" subwoofers handling most of the low end, I find a crossover at 75 or 60 Hz more desirable, which places greater demands on the mains and surrounds, considering the response overlap required for good integration. For the text book filters used in Pre-pro's to work well, the drivers involved should have at least an octave of clean overlap.

So, while if you run the numbers in Unibox, you'll see that a dual 5" driver will perform quite respectably down to 100 Hz, even with a slight derating of maximum Xmax at 1 meter distance, a large room like yours will present additional challenges, and I'm inclined to agree with some of the others that for HT in a room this large, you'll need something a bit more robust.

You've had several good DIY kit recommendations so far in this thread, but another one you might want to check out is Jim Salk's HTS system.







He provides these with different baffle step compensation options in the crossover to match your placement requirements. The basic response of these speakers seems quite good, according to his published curves and from folks I respect (haven't had the opportunity to hear them yet myself).




Check them out

here.

These are available as built speakers, in kit form with supplied cabinets, and as component only kits (you build the cabinets).


Regards,

Jon
 

RichardHOS

Second Unit
Joined
Mar 11, 2003
Messages
454
Dannie,

It's one thing to offer knowledge, and quite another to offer your opinion. Both are welcomed, but try to make it clear which is which. i.e., if you are going to start throwing the word "accurate" around as loosely as you do, then sadly it loses a concise meaning.

You speak of dipoles not being "accurate" because they can't localize pinpoint surround sound cues. Perhaps it would help if you mentioned that (movie) surround sound mixing stages use an array of surround speaker along the side and rear walls, and they can't localize pinpoint sounds either. This is the standard we're talking about here, so if you want to casually throw around the term "accuracy" it is fair to say that dipoles more accurately match this standardized mixing stage than direct radiating surrounds, when used in a small home room.

The truth is that there are almost always compromises in any given speaker or system design. Dipoles have problems. Direct radiators have problems. Either can work well given the appropriate room and installation. I wouldn't stick dipolar surrounds in a 40' x 40' room, and I probably wouldn't stick direct radiating surrounds in a 10' x 10' room, though with work you could probably get acceptable results from either.

In a room the size Bryan has described, I'd probably use direct radiators for the rear pair. For the sides, at 17' width, that will depend on the level of acoustic treatment in the room, the width of seating area, and personal preference. Dipolar sides do a bit better with multiple rows of seating, so that would figure into the decision as well.

Bottom line, I think it is worth pointing out that there are many smart people out there that still believe there is a place for dipolar surrounds. Any intelligent discussion should acknowledge that, and then proceed to help Bryan to find the best solution for his room and his preferences.

As for the importance of larger radiating surface areas in rooms of the size Bryan is concerned about, it certainly is an issue that still deserves investigation. Even using a subwoofer, the speakers will have to cover frequencies down to ~100Hz or so. Using the numbers in TomasW's post as an example, the single 5.25" midwoofer with 3mm Xmax would be capable of less than the 105dB reference level into half space at one meter, much less 17 feet away (and even less if in free space when placed sufficiently far from a wall). On the other hand, the 8" midwoofer with 6mm Xmax would be capable of around 117dB at one meter in half space, giving you at least a chance of achieving the 105dB reference level at the seating position in a real room.

Which one do you think will be producing more distortion at moderatly loud listening levels? I personally like small drivers whenever possible to use them, but sometimes those pesky laws of nature have a thing or two to say about what I can and cannot do.
 

Patrick Sun

Senior HTF Member
Joined
Jun 30, 1999
Messages
39,660
The only caveat is that the Salk HTS speakers aren't shielded, so the center channel *might* be a problem with a direct-view CRT display.

I have an early center channel speaker that I built using the Vifa M18's (used in the Salk HTSs) and they were pretty beefy.
 

Hank Frankenberg

Senior HTF Member
Joined
Oct 13, 1998
Messages
2,573
I SWEAR I'm not on Bose' payroll!:D Or Danny's, even though I built a pair of A/V-3's and think they're a great value in a combo HT/Music speaker.

Danny, I disagree a bit on the SIDE surround dipole issue. I say a "bit", because I'm relating specifically to triangular side surrounds. They have the two sides with drivers not perpendicular to the side walls, but 45 degrees away from the walls, and thus don't fire directly towards the front or back walls.
I built my triangular side surrounds, and in my opinion they work better than any direct-firing side surrounds I've heard in any local home theater (or store). A local speaker designer said they are the best surround sound he's heard. For a really large room like Bryan's, direct radiating speakers could work better than conventional rectangular box dipoles . And, of course I would use directs for the rear surrounds for 6.1/7.1.
 

Danny Richie

Stunt Coordinator
Joined
Apr 8, 2002
Messages
171


I agree and have found that the smaller drivers have many advantages over larger ones, and yes, high SPL's at low frequencies does require greater Sd's.

One always has to weigh out what is important to them. High SPL's are not hard to make. Sound quality is a different issue, and where I would focus more effort. That part was just my opinion again. :)
 

Jon Hancock

Stunt Coordinator
Joined
Mar 18, 1999
Messages
67


Well, Pat, Bryan is doing a pretty big room with a 160" FPTV setup, so I suspect sheilding isn't much of an issue. ;)

I'm not surprised to hear your feedback of experience with the Vifa M18's; my only reservation at all with the HTS system is the driver spacing and relatively high crossover frequency the ribbons require.

Still, it's a flexible alternative.

My experience with dual 5" and dual 7" with 100 Hz crossovers indicates the latter will get closer to the SPL's that Bryan will need in a room that big.

That's the funny thing; I see posts from time to time of guys using speakers like X1 SLAMM's for main's when doing HT in a room that large.

If I was doing it for myself on a tight budget, the MTM 8" systems would be something I'd consider carefully, but with an upgraded tweeter, as we've done in several cases. Ported or sealed, they'll hold up down to a low crossover point with very smooth performance on and far off axis, especially for a larger driver- this is due to the crossover design and crossover frequency.



These were done at 15 degree increments, but forgot to use the mic cal file, so the top shows some roll off that isn't there in the actual tweeter. Note the "difficulty" in identifying the crossover point from the off axis plots.

In response to a variety of requests, I'm playing with a new design right now in similar enclosures to the HTS, using two Dayton RS180's, and a ScanSpeak D2904/60000- this should allow quite optimum placement of the tweeters and midwoofers for both a vertical MTM and horizontal MTM center. We're also looking at a two box system design with a "bass unit", something along the lines of Watt/Puppy combo, or the Sophia, regarding bottem end extension. Really, most of what I play with is for music, not HT; i'ts just not sized for small boxes all over a small room. ;)

Jim Salk's HTS system seems to be a good proposition for someone who needs a turn key kit, complete with very attractive enclosures. OTOH, I wouldn't call it DIY. ;)
 

Patrick Sun

Senior HTF Member
Joined
Jun 30, 1999
Messages
39,660
Of course, I was speaking in general terms re: shielded center speaker for those reading who don't have FP.

The M18s seemed to be a little ragged in crossover regions beyond 2K IIRC (which is why you don't see them used as much in 2-way designs, I guess), but I used mine in a 3-way design, so I didn't have to push them too hard past 500-700Hz, but their low end was pretty decent.
 

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