HT Newbie looking for guidance regarding speaker cabinets. - AVS Forum
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post #1 of 6 Old 07-20-2012, 11:57 PM - Thread Starter
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Hello,

I am a car audio nut who is looking to make the transition to HT. I want to build a 7.1 surround sound system for my living room and plan on building from the ground up. I plan on testing out several speakers including some car audio speakers(Focal Utopia be#7) since I already have a connect for them. The model I plan on basing my cabinets around are the Focal Viva utopia(fronts/center) and the Diablo utopia(surrounds); with 6 1/2s instead of 8's of course!





Anyways, my questions

1. I've been browsing around here for a while and I've noticed that all of the DIY speaker cabinets are a common chamber shared among all mid and high freq drivers. Is there a disadvantage to running each driver in their own sealed/ported chambers in a cabinet?

2. I picked up a used Denon 4311 for a good price, so I definitely plan on using it as my AVR. Can I expect the 4311 to realistically provide 120 rms/channel? My living room is about 600sqft. Is that power adequate for a room this size or do I need to look into an amplifier.

I am not looking for an IMAX/RPX experience, but a nice system with some balls! I build enclosures regularly, so I'm not concerned with the actual creation of the cabinets/sub enclosure, I just want to get some insight on cabinet design theory.

Matt
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post #2 of 6 Old 07-21-2012, 12:52 AM
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Originally Posted by gibsonm21 View Post

1. I've been browsing around here for a while and I've noticed that all of the DIY speaker cabinets are a common chamber shared among all mid and high freq drivers. Is there a disadvantage to running each driver in their own sealed/ported chambers in a cabinet?
No matt, you have gotten that wrong or misunderstood what's going on.

Many people here are using compression drivers for the high midrange and up, and these drivers have their own sealed chamber at the back so that the LF driver cannot influence it. Do not use standard open frame drivers with the LF (woofer) and midrange in the same enclosure. If you do do this the LF driver will create much larger pressure differences inside the common enclosure and effectively drive the midrange through this pressure, causing considerable distortion, so you must use separate enclosures for each.
Dome tweeters, like compression drivers, have their own sealed rear chamber for exactly this reason.

I particularly like the Focal multi box look and am building my surrounds in a similar manner - but I doubt my finish will be anywhere near as good. This is a quick Sketchup I did to help visualise it. The woofer is a 15".

Surrv2crop.jpg
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post #3 of 6 Old 07-21-2012, 10:04 AM - Thread Starter
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Many people here are using compression drivers for the high midrange and up, and these drivers have their own sealed chamber at the back so that the LF driver cannot influence it. Do not use standard open frame drivers with the LF (woofer) and midrange in the same enclosure.

Thanks for clearing that up. Alot of the build logs I looked at didn't seem as if each driver was isolated.

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I particularly like the Focal multi box look and am building my surrounds in a similar manner - but I doubt my finish will be anywhere near as good. This is a quick Sketchup I did to help visualise it. The woofer is a 15".
Surrv2crop.jpg

Aww, the big boy. You can get that high gloss finish, its just going to be alot of sanding and painting over and over and over................


What about the issue of power? Is receiver power usually satisfactory?
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post #4 of 6 Old 07-21-2012, 05:48 PM
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Originally Posted by gibsonm21 View Post

What about the issue of power? Is receiver power usually satisfactory?

It all comes down to the efficiency of the speakers and (or?) using a subwoofer to take the LF load off the receiver. You've got plenty of power if you have the right speakers - right generally meaning bigger and often with pro-audio drivers.
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post #5 of 6 Old 07-22-2012, 03:19 PM
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Aww, the big boy. You can get that high gloss finish, its just going to be alot of sanding and painting over and over and over................
I'm not doing high gloss finishes.
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What about the issue of power? Is receiver power usually satisfactory?
Wrong person to ask as I use active designs, so I have 3 amplifier channels per speaker. The only time I've used a passive set up with the internal amps (Pio 1015) was in a small bedroom system.
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post #6 of 6 Old 07-23-2012, 01:45 PM
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Quote:
Originally Posted by gibsonm21 
Hello,
I am a car audio nut who is looking to make the transition to HT. I want to build a 7.1 surround sound system for my living room and plan on building from the ground up. I plan on testing out several speakers ...
1.... common chamber shared among all mid and high freq drivers...
2. ...Denon 4311 ...provide 120 rms/channel? ...600sqft. Is that power adequate for a room this size...
I am not looking for an IMAX/RPX experience,

Your plan to build from the ground up is good, but what do you have in mind for speaker testing? Are you serious about cloning the Focals you show, or is the goal equivalent sonic performance?

Here's the scoop. You can design a world class speaker yourself. But I guarantee your first speaker won't be world class, and it's up to your skill and learning ability when (and if) you get to the point where you can design at the world class level. Your first $200-500 expenditures will be for test equipment, and you'll need to find and understand the several measurement threads before you start driver selection. Then you can start on the speaker design books, so you can understand the speaker design threads...

Or you can use available data to choose drivers, and look for a "proven design" using those or comparable drivers. Here's the master list.
http://techtalk.parts-express.com/showthread.php?211558-Links-to-existing-DIY-speaker-designs

If you choose a proven design, there are two things to look for in the design family.
- is there an on-wall/in-wall design?
Any speaker placed near flat surfaces, like under a TV screen, will sound boomy if not designed for that location.
- is there a center channel design?
Center channels have unique program content (i.e. dialog) and so benefit from voicing for dialog intelligibility.

The ideal option if you want to hear a lot of different drivers and speaker designs is to attend a DIY event. There are a bunch around the US.

As to your questions,
1 has been addressed quite well.
2 is personal taste.

Adding 8' ceilings, you have 4800 cu ft. to fill - big room. Easy to have 4 meter speaker distances, but you'll also have 7 speakers. Distance costs 6dB every time it doubles, so you're -12dB at 4m. But, a second speaker doubles cone area (+3dB) and doubles amp power (+3dB), and you double speakers 3x so you're +18dB with 8 speakers. Note all this assumes direct sound field only; the reverbrent field will be a major contributor, so we can safely say: "Loudness at your listening position will be approximately equal to the sensitivity of the speaker x power applied."

A 140W amp adds ~21.5dB above 1W, If you want to achieve 105dB SPL at your listening position, you'll need speaker sensitivity greater than 105-21.5=83.5dB@1m, 1W. Practically, aim for 85-90dB sensitivity and you'll find reference levels are within reach. You will be adding subwoofers, right?

I will note that none of this is cabinet design theory, which I see stretching from how to build a dead box to unique cabinet designs (eg. dipole, band pass) intended to achieve specific objectives. Slanted baffles, angled baffles as you show, all have deisgn goals. In many cases, the major goal being to "look good" as it's well known that pretty speakers sound better.

Thus, the caveat that fancy cabinet design theory may influence your opinion of the sound, even if it has no sonic effect whatsoever. Beauty speakers sound better... but only if you can see them.

Have fun,
Frank
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