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Old 14th May 2005, 05:36 PM   #1
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Default Line array dilemma for 7.1 HT (Long)

Hi

I desperately need some help from the experts to figure out what to do. I'm just learning about speaker building so bear with me if there are obvious errors in my thinking.

Iíve read up on some of the line array threads here at DIY and Iím sold on making line arrays as my first speaker project. The speakers would be used in my dedicated home theatre which is another of my DIY projects. The room size follows Sepmeyer's golden room ratio and would be 6.524m (21.4 ft) long and 4.48m (14.69 ft) wide and 2.8m (9.2 ft) ceiling height. I will hopefully have two rows of four seats each. I will also acoustically treat the room and build columns and proscenium to hide the 7.1 speakers.

Iím no audiophile but would like good sound that would impress my friends which also are no audiophiles. Enough background now to the questions

1. Does it make sense to have line arrays in home theatre? Many are using arrays for two front speakers but I have not found anything that discusses using 7 identical arrays for all channels. I read that the sweet spot from arrays is far larger then point source and I hope that this would lead to decent sound in all seats. If it will sound good then this is what I would like to do.

2. Cost! Since I need 7 speakers the costs run up dramatically. This brings me to the driver selection. Iím pretty much sold on using 16 Partsexpress 49cents NSB drivers for the midband and this would keep the cost down and still get good sound. Tweeter line. This is where the problems start. I would love to use the PT2 planar tweeter but probably need 10 pieces. At 25$ a piece its 250$ for each array at a total of 1750$ for the tweeters. That makes me cringe and I need something cheaper. Partsexpress has the onkyo buyout and there are some cheap tweeters there. I also found the ApexJR tweeter at 85cents each. To match the NSB array I probably would need in 40-60 small tweeter which will cost around 50$. Would this be good sound for a HT? Is the 5 times difference in cost justified? Another strategy would be to go with single high efficiency tweeter in the middle of the array just like Griffins Needles or something like chipco3434 line arrays with two PT2 Planars. But then I loose the line array benefits on the tweets. What solution would give me the best sound in most seats for the HT? Line or point?

3. Bass. The NSB will not give me any bass and would need help. I was either thinking of dedicated subwoofers or 1 or two 12Ē large drives in the base of each array. Would subwoofer be enough or do I also need the bottom drivers in order to cover the full range?

4. Open or closed: Many people rave about the open baffle sound and I would like to try it. But my placement would be in columns right up against the wall. Is this at all possible? I was thinking of covering the sides of the columns with speaker cloth but will this be enough to give the OB benefits?

5. Crossovers: I wanted to do something fun and go active since I like to play around and learn about that. Iím going to use a HTPC for source and was therefore thinking of using 2 7.1 soundcards and use bruteFIR to do crossovers and room Eq. Is this overkill since I am using such cheap drivers? Will I still get benefits?

6. Amps: I plan on using gainclones for all the channels. Am I right that I would need 14 amps plus subwoofers in order to go fully active and biamp? If I need the 12Ē drivers in the base of each array, would this require 7 more amps?

7. Final question. Ruff cost estimate of building all the speakers will run up to anything between 700 (cheap tweeters) and 2100 (planar tweeters). Would I get better sound then a packaged deal or would I surpass store bought sound.


I know its much but please try to help out where you can.

Cheers,

Exipnos
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Old 14th May 2005, 06:31 PM   #2
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Exipnos,

I don't think it's usually good practice to ask a huge multi-part question like that- you might not get a lot of replies. Nevertheless, here are some of my opinions.

1 and 2- i have no experience. Search the forum for line array stuff; this has been discussed a lot, and the if it works for stereo it will work for surround. Also- do NOT do a horizontal center channel!

3) It is generally stated that by 100hz, bass becomes directional. My experimentation with the NSBs leads me to recommend at the very least to go with stereo subs crossed over 100 hz. A 4th order crossover at 150-300 hz should improve the sound of the NSBs by reducing their excursion, and allow you to find a woofer that can handle the passband gracefully.

4) I think you should have at least a couple of feet from the back wall for open baffle to have its full effect. I tried the NSB with a cardboard open baffle, and I found that if it was too close to the back wall, it wasn't as good.

5) A good active solution is what will ALLOW you to get great effect from cheap drivers. However, it will be quite a challenge to process 7 channels actively. If you tri-amp them, that's 21 amps, not counting the .1! If you have to do passive crossovers to avoid the need for lots of sound cards and amplifiers, do the tweeter to mid crossover passively, and the bass to mid actively. Note, if you buy and build in steps, you can used your sound cards to prototype your passive crossovers before building them.

6) see above- good luck with this!

7) It's all in the implementation. There are corners that would be worth cutting... perhaps you could forget the woofers for the side, center, and rear speakers, just have the bass come from the front. Most of the really neat surround effects (in my opinion!) are in the directional tweeter and mid. Another note- when you start getting above $1,000 system cost, it's really worth paying attention to room interaction. It might be worth hanging something on the wall or ceiling.

A lot of the satisfaction of this comes from saying "I made this!". It's true that you can get an awesome bang/buck ratio- but only if you enjoy working on it and don't mind putting i the hours to get results. That includes doing the homework first.

I hope that was helpful. As a closing comment, I'd like to say that by asking a big quesiton about a cool system, you are pretty much obligated to post pictures and details when you're done!
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Old 14th May 2005, 06:48 PM   #3
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Arrays are far better for large images because they give you a large sound image along with the larger sweet spot that you definitely need with that much seating. Unless you have a large family, you may want to rethink the seating and base it on how you will really typically use the theatre. I always opt for more space and comfort instead of extra seats that are rarely used.

To me it make no sense to mate a bunch of expensive tweeters with $10 in main drivers when the main drivers carry most of the load. Go with Dr Griffin's single more efficient tweeter approach, it's much easier and cheaper. The only benefit of an array of tweeters is the SPL vs distance advantage and you can balance that out with a higher efficiency tweeter that is adjustable.

Forget the center channel. It just doesn't work with projected images. The sound has to come from the top or bottom which doesn't sound right unless you use the supposedly sonically invisible screens which have lower image quality and aren't sonically invisible anyway. You can't turn an array on its side either. Just let the mains carry the center channel load which works perfectly well. The separate center channel was invented only to make everyone buy new equipment and IMHO provides zero benefit as long as you don't place your mains too far apart.

Home theatre guys will tell you that the sonic mix wasn't done for dipole to work right. I think the resulting more natural sound especially with dialogue makes the compromise worthwhile in going OB at least for the mains. Just don't go pure dipole and put some polyfill batting on the backside for some attentuation to make closer wall placement work. With dipole and arrays you can focus your room treatment on the bass frequencies where they are needed the most. If you add some bass drivers to your array, don't just add a couple to the bottom. You'll have a sub, so deep bass isn't necessary, but you'll want the array effect to include the bass that the arrays play. Use 5 smaller bass drivers with the topmost higher than you mid array and bottommost lower and space them evenly. They don't have to be close together due to the longer wavelengths and you want that array to be as long as possible to get a good nearfield projection distance in those frequencies. If you plan your cabs to decide later about going sealed or OB, then you can compare the two and decide for yourself. Just put a removeable back on one pair and do a real world comparison before making the final decision.

It sounds like you are willing to put the effort in and yes it will be rewarded with better sound and lower cost (as long as you don't factor in the value of your time or go crazy with those tweeters) than store bought. Also arrays will be far superior for your planned setup.
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Old 14th May 2005, 10:11 PM   #4
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thanks for both replies. Its amazing how people on this forum are willing to help newbies like myself..

center channel - if array is used then it would be standing behind a transparent screen. I would prefeer not to have transparent screen since a good one will be quite expensive. I'll try ghosting the central channel and see if that works.

Tweeters - I'll forget about an array of PT2 planars, tooooo expensive! johninCR- I saw on another thread that you recommend a Pyle bullet tweeter and at 19$ is fits in my price range.

http://www.partsexpress.com/pe/showd...number=272-115

The question still remains though, should I go with a single tweeter or do the array of ApexJR tweeters just like tom1356 did in

Ouch! $100.00 for brass mounting hardware

I probably will stick to only mid and tweets but I would like to fill in the lacking bass from the NSB, and therefore might try the suggestion of a few small bass drivers. Any recommendations about cheap small bass drivers that would work?

As far as pictures goes I will definately post when things start happening.
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Old 14th May 2005, 11:22 PM   #5
RJ is offline RJ  United States
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I know that this is not your intended Line Array.
With this setup I don't need a Center Channel nor Subs.
It's only driven by a 75 watt rms amplifier.
Jurassic Park & Lord Of The Rings just literally shake the room.
As far as seating goes, anywhere on the two couches in the room are fine. There is no sweet spot, just a sweet area. In fact I prefer to be on one side or the other.
Just letting you know a line array is ideal for home theatre.
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Old 15th May 2005, 12:36 AM   #6
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RJ .....what drivers are you using ? And is that a closed system ?
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Old 15th May 2005, 01:01 AM   #7
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Only with a cost no object array or an array for use with a large audience would I use an array of tweets. The only advantage I see of a array of tweets vs a single high output tweeter is that up close and far away the speaker will have a different tonality using a single tweeter since it's SPL decreases by 6db per doubling of distance vs 3db for the array. In your HT you're not going to be doing a bunch of moving around, so you set the tweeter output to be balanced with the array at your listening position and forget about it. You just need tweeters that have a higher sensitivity than your array, and you'll be fine. With an array of tweeters that aren't a continous line like a ribbon, then you aren't going to be able to overcome the center-to-center spacing issue at the highest frequencies (which will surpress the high end) and you have the issue of multiple sources of high frequencies being different distances from your ears which can only partially be offset by power tapering. Throw on top of that the extra work, wiring, and cost and for me it's a no brainer if a single $20 tweeter does the job.

For the bass, you might consider just using more NSB's. Add another column (or 2 columns) plus some extras at the top and bottom for bass only duty and match their HF roll off to the main array's rolloff. Keep in mind that you only need them flat down to where the sub can take over which isn't that difficult even with OB since you'll be bi or tri amping.
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Old 15th May 2005, 01:50 AM   #8
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every now and then someone will put some 8'' or 10'' drivers on sale. I got a bunch a while back for like $8 a piece. (plus they have a qts of close to .7 which is perfect for OB)
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Old 15th May 2005, 03:16 AM   #9
RJ is offline RJ  United States
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MadMike2, They're 5 1/4" Dayton Aluminums;
http://www.partsexpress.com/pe/showd...number=295-330
With 6 Dayton Planars per side;
http://www.partsexpress.com/pe/showd...number=275-085

It's a closed system with a Qtc of 0.59
Crossover is 4th order Bessel at 2500 hz.

I didn't buy the drivers all at once, I would buy 5 drivers a month.
It took a while but it was well worth it.
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Old 15th May 2005, 06:42 AM   #10
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Iím no audiophile but would like good sound that would impress my friends which also are no audiophiles.

It seems that you want to impress people not really interested in
audio, so why bother with the esoteric line array HT design
for all channels? Seems like an overly complicated design to satisfy
noone. /hehe

Do you think they want high SPL that a line array can offer when
watching movies? Most people will probably tell you to turn down
the sound because they are getting punished by too much volume.

If you want the line array then one idea would be to build two line
array towers using good speakers no cutting corners like many people do and obviously add a seperate subwoofer.

NSB's with treated cones I consider good speakers in spite of the
low cost. PT2's are good speakers. Don't be afraid to mix them
as they integrate very well together. I have 10 PT2's and 16 NSB
per tower and the NSB's still overpower the tweeters by just
a bit. I have the NSB's wired for 2 ohms and the tweeters under
1 ohm. It's almost a perfect match, but I have an active setup so
it's easy to adjust to make it sound perfect.

The NSB's are ported tuned to 100hz and there is plenty of midbass
for the normal person. A subwoofer is needed. If you listen to
rap or heavy metal music then you probably need a little bit more
midbass punch and a bass array would be interesting.

This will give you good 2 channel audio, also works for HT, then do
the rest of the loudspeakers using simple designs in smaller boxes. Most theaters much greater than your room don't have line array
surrounds and they can generate SQ with SPL with the simple
designs.

Here is work in progress pics of the array I'm doing. If you pay
attention to detail the sound can be amazing. I didn't skimp
on cabinet construction, dampening and sound conditioning
inside the chambers. The NSB are treated with lacquer to smooth
out the sound. The ported NSB's work well. The idea was to
build a matching bass array with eight Dayton DVC 8" woofers
for ~ $22 each, that will come later.

http://home.pacbell.net/lordpk/robarray/Picture14.JPG
http://home.pacbell.net/lordpk/robarray/Picture15.JPG
http://home.pacbell.net/lordpk/robarray/Picture16.JPG
http://home.pacbell.net/lordpk/robarray/Picture17.JPG
http://home.pacbell.net/lordpk/robarray/Picture18.JPG
http://home.pacbell.net/lordpk/robarray/Picture19.JPG
http://home.pacbell.net/lordpk/robarray/Picture20.JPG
http://home.pacbell.net/lordpk/robarray/Picture21.JPG
http://home.pacbell.net/lordpk/robarray/Picture22.JPG
http://home.pacbell.net/lordpk/robarray/Picture23.JPG
http://home.pacbell.net/lordpk/robarray/Picture24.JPG
http://home.pacbell.net/lordpk/robarray/Picture25.JPG


For center channel do a horizontal NSB array with the high
output tweeter as mentioned already, horn or bullet. Because
NSB's and these tweeters are low cost build a test box
to make sure you get the desired sound before committing
to the final design.

If you like it, then make a mini array for surrounds, maybe 4 NSB
and a good tweeter. You can do whatever you want with surrounds,
big or small.
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