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post #1 of 8 Old 06-23-2015, 03:22 AM - Thread Starter
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Need Advice for DIY Shallow Speaker Big Baffle Combo

Hi folks,

I'm a total noob in DIY audio, though I'm an electrical engineer, and I've been researching this project for quite a long time (part of it lurking and reading posts here - lots of information!), and would appreciate your input.

I want to build a hinged contraption that would have an acoustically transparent projection screen on its front, and left/center/right speakers on its back. The contraption will be mounted on the low ceiling of my apartment, which means the main constraint is to keep it all as low profile as possible, so it would not take much of my apartment's precious headspace.

So, the main challenge in this design is to have speakers that would be shallow (but still with the necessary cabinet volume), while at the same time providing good sound reproduction, in a reasonable frequency range (i.e. decent bass, to avoid offloading much of the sonic content to a subwoofer unit).

For the speakers, I've considered adapting various reference designs, finally choosing the ZaphAudio ZDT3.5. From what I read, it's a good choice for movie audio, and it seems to have a good frequency response with a reasonable cabinet volume.

My intended design (see attached images) has a screen-sized baffle, shared by all speakers. The volumes of the ZDT3.5's driven chambers, are maintained, but the dimensions are altered to make them shallow. I also removed the third (undriven) chamber in the reference design, whose purpose I didn't understand, and replaced the round ports with "slotted" ports (whose "lost" volumes are accounted for in the chambers' dimensions).

So, some questions:
  1. Was it a good choice using the ZDT3.5 as a reference design?
  2. Are there any obvious glaring mistakes in my modified design?
  3. I'm planning to use 8mm or 9mm thick plywood panels for the walls of the cabinets. Is it sufficiently thick?
  4. The back end of the woofers is only 7mm away from the back chamber wall, would that be a problem? How much space should I allow?
  5. Is there any problem with rear mounting the RS52AN-8 2" Dome midrange, using the manufacturer's specified baffle cutout? I don't care how it looks, only how it sounds.
  6. What acoustic treatment should I put inside the chambers?
  7. I'm assuming such a huge baffle would completely change the nature of the baffle step response, which I assume I'd need to accommodate for with the crossovers. Any advices how to go about modifying the crossovers?
  8. Any other tips/pointers/articles concerning shallow cabinet designs?
Many thanks in advance for any response.
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post #2 of 8 Old 06-25-2015, 01:15 PM - Thread Starter
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post #3 of 8 Old 06-25-2015, 09:04 PM
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Your "wall" of sound will have similar response to mounting a speaker on a regular wall, for the most part. You need an onwall design as once you change the baffle shape, you're changing the speaker's frequency response.

Plus, 8mm thick ply is mighty thin. You would need matrix type bracing to prevent resonances.

To keep things simple, how about 3 Eminence 8" coaxials for LCR? They're around 5" deep with a compression driver mounted to the rear.
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post #4 of 8 Old 06-26-2015, 03:17 AM
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You could try some coaxial car speakers that are just 2" or less deep. With some eq, they'd sound a lot better than you'd think. I compared some 6.5" JVC car speakers with some Kef60s coaxes, and there's not a lot of difference in it in my room (23 x 11 x 8). They both measure equally bad due to the room, but that's where eq will make a difference. I compared them to a 10" Eminence coax and that was a little better, but not twelve times better which was the cost difference.

To test them, I placed them in an old Kef Cresta ported box, so for a similar result, I'd aim for a similar box volume and port size.

I expected them to sound awful, but they didn't to me. A trained listener would probably identify issues but ignorance is bliss

Gary

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post #5 of 8 Old Today, 07:47 AM - Thread Starter
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Quote:
Originally Posted by Face2 View Post
Your "wall" of sound will have similar response to mounting a speaker on a regular wall, for the most part. You need an onwall design as once you change the baffle shape, you're changing the speaker's frequency response.

Plus, 8mm thick ply is mighty thin. You would need matrix type bracing to prevent resonances.

To keep things simple, how about 3 Eminence 8" coaxials for LCR? They're around 5" deep with a compression driver mounted to the rear.
Thanks for your reply. Regarding the speakers' frequency response, I assume the main change would be in the speakers' baffle step response, which affects the lower frequencies. I'm guessing it's possible to accommodate for that in the XO design.
I'd probably end up however forgoing the huge shared baffle for separate baffles for each speaker cabinet, behind the screen. What would be a reasonable thickness in your opinion for the cabinets' plywood panels in such a project?

Your suggestion to use coaxials is interesting, but I feel a 5" driver is a little too deep for me. I prefer to keep the internal depth of the cabinets to about 4" at most, if possible.


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Originally Posted by Gary Lightfoot View Post
You could try some coaxial car speakers that are just 2" or less deep. With some eq, they'd sound a lot better than you'd think. I compared some 6.5" JVC car speakers with some Kef60s coaxes, and there's not a lot of difference in it in my room (23 x 11 x 8). They both measure equally bad due to the room, but that's where eq will make a difference. I compared them to a 10" Eminence coax and that was a little better, but not twelve times better which was the cost difference.

To test them, I placed them in an old Kef Cresta ported box, so for a similar result, I'd aim for a similar box volume and port size.

I expected them to sound awful, but they didn't to me. A trained listener would probably identify issues but ignorance is bliss

Gary
Thanks for your reply Gary. My understanding is that car drivers/speakers are engineered to be operated in tight spaces and close to the listener, which makes them somewhat of a poor choice for home theater. EQ might fix some issues, but I expect it'll be only to some extent. I prefer to use drivers that are engineered be used as I intend to use them
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post #6 of 8 Old Today, 08:10 AM
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Quote:
Originally Posted by sagsagman View Post
Thanks for your reply Gary. My understanding is that car drivers/speakers are engineered to be operated in tight spaces and close to the listener, which makes them somewhat of a poor choice for home theater. EQ might fix some issues, but I expect it'll be only to some extent. I prefer to use drivers that are engineered be used as I intend to use them
That was exactly what I was expecting to be honest because I'd read much the same thing, but I needed a shallow speaker for side surround duties and for $30 a pair thought I'd give them a try. After measuring I was using them as the L&R in my lounge for a couple of weeks and they sounded just as good (or bad) as the Kef60s home cinema speakers I'd been using. I honestly wouldn't have said they were deficient for a single row of seats in a home cinema.

My main room will be using PA type speakers as LCR with compression driver/waveguide and 15" woofer, as I need them to reach two rows of seats, but the car speakers work just fine for closer range surround duties. Until I measured and listened to them, I was of the same mind as yourself.

Gary

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Originally Posted by elmalloc
Who says Cameron is "right" and why do we care about him so much - lol!

I trust Gary Lightfoot more than James Cameron.
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post #7 of 8 Old Today, 08:36 AM - Thread Starter
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Quote:
Originally Posted by Gary Lightfoot View Post
That was exactly what I was expecting to be honest because I'd read much the same thing, but I needed a shallow speaker for side surround duties and for $30 a pair thought I'd give them a try. After measuring I was using them as the L&R in my lounge for a couple of weeks and they sounded just as good (or bad) as the Kef60s home cinema speakers I'd been using. I honestly wouldn't have said they were deficient for a single row of seats in a home cinema.
I'm not sure I'd like to have a "satellite"-type speaker design from 20 years ago as a performance benchmark for my plans
I'm hoping for a fuller-range solution, although weight issues might force me to compromise. I'll keep in mind your suggestion in case I do compromise, thanks again.
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post #8 of 8 Old Today, 09:01 AM
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I also mentioned I compared them to a current 10" Eminence coaxial driver (10CX), with compression driver (ASD1001) which are more of a benchmark than the Kefs, and they still compared favourably, but you chose to ignore that and gave me a sarcastic reply. Sorry for trying to help, it won't happen again.

Gary

Quote:
Originally Posted by elmalloc
Who says Cameron is "right" and why do we care about him so much - lol!

I trust Gary Lightfoot more than James Cameron.
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