Information Line array speakers for under $40K???

[DaveBn]

Hi, new to the forum and new to DIY for audio . I have been researching speakers for a while now and I am interested in building a 7.1 speaker system using 7 line arrays. I don't think I have the ability or confidence to design my own system so I was thinking of getting a kit with the components and I could build the cabinets.

The reason why I was thinking line array was b/c they seem to be very dyanamic and able to handle great SPL with low distortion. But I was concerned as to how they would react in a small room that is 17' wide by 20' long by 8' high. The room is a dedicated home theater and I have the room designed by a professional for the room acoustics so it will be heavily treated.

The kit I have been looking at has 9 X 5" mids and 8 ribbon tweeters. What kind of bass could I expect from a speaker like this? What would be the around about equivalent in say 10" or 12" drivers for air movement? (I can't find anything that I could calculate this) I am planing on having the speakers crossed at about 80hz if this design can do it, but the main thing I want is none of that mid bass punch lost. I will be putting in 4-8 18" TC sounds LMS ultras for subs which should be good for 120db at the listening postion up to about 120hz. I currently have some LCR's that each have two 12" woofers and an 8" coaxial driver, each speaker has 2000w capabilities which makes a 6000w front stage. I am looking for something to come close to this setup at the moment (I may have to get rid of this system now for reasons that will take a long time to explain) I don't have a budget but would like to keep it below $40K for the speakers, not including the subs and amps for the speakers.

And thoughts or suggestions would be very much appreciated.

[thomasjefferson]

If you have a 5" midwoofer that has a cone surface of 85 cm^2 and 5mm linear excursion, multiply by 9 (per speaker) and then by 7 (# speakers), that's about the same volume displacement as four 12" woofers with 12.5mm linear excursion.

The bass from a speaker like this may be decent but you're better off handing off the bottom two octaves to a subwoofer, as you suggested. There should be no shortage of output above 80 Hz, to beyond what your ears could endure. One tower with nine 5" mids could generate 110 dB at 80 Hz.

You would have to be choosing very high-end parts to get anywhere near your budget.

[StigErik]

B&G RD-75 is "just" 750$ at Parts Express. You could run it nearly fullrange and XO to the subs at 120 Hz or so. That should be possible with a fairly wide open baffle for the RD-75.

[StigErik]

ALSR - The RD75 Dipole Baffle Study - The Auditorium Measurements

[Pano]

If you are looking into line arrays, you should certainly check out the work of Don Keele.
Don Keele's CBT (Constant Beamwidth Transducer) Page It's a curved, shaded line array and it works very, very well. I spent some time with it (and Don) over the past weekend.

[dublin78]

Dedicated home theatre room. Seven of these? Nowhere near your high budget:

The Murphy Corner-Line-Array Home Page

[DaveBn]

thomasjefferson, thanks for that quick calculation.

And thanks for all the information guys. Those links are great, but I don't have the smarts to design and impliment that design myself.

So is the line arrays the best choice to build a HT with. Like I said before I want something with huge dyanamics and not lose any of that mid bass punch. I am worried that I will encounter problems with the surrounds, is the worry founded?

Theoretically speaking if all was equal, am I correct to assume that if 2 speakers have range of 40hz to 20khz with a sensitivity of 95db, it would not matter if that sound was comming from a couple of 12" drivers or an array of 5" drivers, 100hz at 100db with sound the same?

Anyone got any opinions of what speakers to use for HT , when it is 100% movies only.

Good to hear that it should not cost me as much as I was expecting.

[gedlee]

Originally Posted by DaveBn

Theoretically speaking if all was equal, am I correct to assume that if 2 speakers have range of 40hz to 20khz with a sensitivity of 95db, it would not matter if that sound was comming from a couple of 12" drivers or an array of 5" drivers, 100hz at 100db with sound the same?

This is most certainly NOT true. The polar response from those would be completely different and the resulting sound would be as well. The "too wide" directivity of a line array is precisely why I do not use them in any of my home theaters.

[DaveBn]

Originally Posted by gedlee

This is most certainly NOT true. The polar response from those would be completely different and the resulting sound would be as well. The "too wide" directivity of a line array is precisely why I do not use them in any of my home theaters.

I would have thought that was a good thing, have a wide sound stage?

[gedlee]

Originally Posted by DaveBn

I would have thought that was a good thing, have a wide sound stage?

There is a lot of debate on that point, but for film, I think that its clear that the directivity should be narrow. For two channel there is a stronger case for wide directivity. Film is always mixed and presented with very narrow directivity sources. Just look at any theater, or film mixdown facility. For two channel wide directivity adds spciousness by compromising imaging. But for multi-channel the spaciouness is in the channel mix.