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Old 26th March 2014, 10:55 PM   #1
soren5 is offline soren5  Denmark
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Default 3-way for bookshelf (in-wall/on-wall)

I need your help fellow DIYers!

A friend of mine is going to have his living room completely redesigned and a custom bookshelf made to fill the entire lower part of one end wall. He has asked me if I wanted to build some speakers for his new setup. The idea is to have the speakers hidden inside this bookshelf. I have attached a 3D rendering of what it’s going to look like. The two red arrows are where the speakers will be.

I know that most speaker design are tuned with BSC to be placed away from the back wall. In this setup however, the speakers will almost be in-wall when the bookshelf is filled up with books etc. Most speakers will sound bloated in the mid bass if positioned here. Are you aware of any good designs out there that would work for this setup?

Additional info: The room is quite large at about 60m2 and 3m to the ceiling. Each bookshelf is big enough to have a speaker of 50 litres internal volume. I will take part in the construction of the bookshelf and make sure it will be stable enough to support the speakers and not vibrate.

I was hoping there was a good 3-way bass-reflex design out there that would work in this setup? Budget is 1000 EUR.

Suggestions and recommendations are welcome.

Thanks!
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File Type: png StuenHIFI.png (314.7 KB, 621 views)

Last edited by soren5; 28th March 2014 at 08:48 PM.
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Old 26th March 2014, 11:42 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

Its debatable how much BSC they would need,
more than inwall IMO, but less than normal.

You can argue until the cows come home but IMO
Zaph|Audio - ZDT3.5
you could do a lot worse the the centre version x/o,
noting the design axis is 12" above the tweeter.

40L to 50L vented is ideal for the design.
No subs I'd low tune vented, i.e. simply use
one of the shown vents instead of two.

YMMV but I don't think you'l find a better design.

rgds, sreten.
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Last edited by sreten; 27th March 2014 at 12:03 AM.
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Old 27th March 2014, 12:22 AM   #3
soren5 is offline soren5  Denmark
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Quote:
Originally Posted by sreten View Post
Hi,

Its debatable how much BSC they would need,
more than inwall IMO, but less than normal.

You can argue until the cows come home but IMO
Zaph|Audio - ZDT3.5
you could do a lot worse the the centre version x/o,
noting the design axis is 12" above the tweeter.

40L to 50L vented is ideal for the design.
No subs I'd low tune vented, i.e. simply use
one of the shown vents instead of two.

YMMV but I don't think you'l find a better design.

rgds, sreten.
Thanks for the input. That looks like an interesting design. I was previously on the parts-express forum where CJDs In-Khan-Neatos design was recommended, which also uses Dayton drivers. I tend to avoid Dayton (and other American brands) since theyre much more expensive here in Europe compared to over there. I was hoping to find a design using SB, Peerless, Vifa, ScanSpeak, SEAS etc, but perhaps this is unrealistic (?).

Anyway, back to your suggestion. If using the ZD3C I guess I would need to modify the baffle layout and place the tweeter above the midrange since the speakers will be placed slightly below listening position. Actually the tower option baffle layout would be more suitable for my application, although I would need to change the port placement to make it all fit on the baffle, which need to fit inside the hole of the bookshelf, about 68 cm tall and 34 cm wide. But after changing the baffle layout, do you think Zaph's XO will be any good?

I'm concerned about Zaph's comment on the ZD3C:
It's worth noting here that some builders may be wondering if it's a good idea to just build 3 of this design and use them turned upright for lefts and rights also. In a word, no. There's too much in the design that is specific to center channel usage but not suitable for mains. Controlled vertical off axis with wide horizontal off axis, along with low BSC are perfect for a center, but turn into serious shortcomings when used for an upright left and right.

Last edited by soren5; 27th March 2014 at 12:26 AM.
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Old 27th March 2014, 12:55 AM   #4
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You may want to take a look at some of the other Zapf designs. Some indeed use other drivers. I highly respect his design methods. Zaph|Audio
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Old 27th March 2014, 12:55 AM   #5
sreten is offline sreten  United Kingdom
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Hi,

Zaph comments are pretty pointless, as they address the stupid,
and don't address the clued. Yes its a very bad idea to simply
turn the centre upright for L&R but that is totally clueless.

Of course I'm implying using the centre x/o with the normal
L&R vertical baffle layout and it will work then as implied.

Is obvious you need to maintain vertical mid / treble.

rgds, sreten.
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 27th March 2014 at 01:04 AM.
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Old 27th March 2014, 10:45 AM   #6
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Quote:
Originally Posted by soren5 View Post
I was hoping there was a good 3-way bass-reflex design out there that would work in this setup? Budget is 1000 EUR.
The location is not only on-wall but also on-floor. A woofer at the bottom of your baffle will radiate into a quarter space. I doubt you will find any popular designs suitable for this location. However the woofer is going to be efficient in this location.

The speakers are a bit low and so the tweeter will have to go at the top and probably a bit too close to the top edge. A waveguide would help but may be impractical. Perhaps the SEAS DXT?

The midrange may need to be largish or perhaps doubled if you are to run with an efficient design. Again a waveguide on the tweeter may help.

There may be some sound quality issues from the bookcase cavities, cancellation due to reflection off the back wall and structure-borne radiation from the large surface area of the bookcase. The latter would be improved by normal soffit mounting techniques but not sure much can be done about the others.

It looks like a nice project and it will be interesting to see what you come up with.
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Old 27th March 2014, 12:25 PM   #7
soren5 is offline soren5  Denmark
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Join Date: Jun 2011
Location: Copenhagen
Quote:
Originally Posted by sreten View Post
Hi,

Zaph comments are pretty pointless, as they address the stupid,
and don't address the clued. Yes its a very bad idea to simply
turn the centre upright for L&R but that is totally clueless.

Of course I'm implying using the centre x/o with the normal
L&R vertical baffle layout and it will work then as implied.

Is obvious you need to maintain vertical mid / treble.

rgds, sreten.
Gotcha. So you reckon it would be okay to take the baffle layout of the ZDT3.5 tower and then use the XO of the ZD3C? I will have to widen the baffle slightly as well, and have front-firing ports. Something like the attached drawing?

A thing to consider though is that the RS52 midrange dome sticks out about 2cm from the baffle, and because I will need to attach grille cloth the speakers will have to be pushed into the bookcase a couple of cm, which Im sure wont have a positive effect on the sound?
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Old 27th March 2014, 12:42 PM   #8
soren5 is offline soren5  Denmark
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Quote:
Originally Posted by andy19191 View Post
The location is not only on-wall but also on-floor. A woofer at the bottom of your baffle will radiate into a quarter space. I doubt you will find any popular designs suitable for this location. However the woofer is going to be efficient in this location.

The speakers are a bit low and so the tweeter will have to go at the top and probably a bit too close to the top edge. A waveguide would help but may be impractical. Perhaps the SEAS DXT?

The midrange may need to be largish or perhaps doubled if you are to run with an efficient design. Again a waveguide on the tweeter may help.

There may be some sound quality issues from the bookcase cavities, cancellation due to reflection off the back wall and structure-borne radiation from the large surface area of the bookcase. The latter would be improved by normal soffit mounting techniques but not sure much can be done about the others.

It looks like a nice project and it will be interesting to see what you come up with.
Thanks for pointing out the issues related to having the speakers close to the floor. You suggest a waveguide, but without a design suggestion (or least a starting point) I’m in a bit of a loss here I have built speakers before, but always based on a proven design.

For this project I initially thought of some of the 70s classic 3-ways, which were designed with less BSC for the purpose of near-wall / bookshelf placement. Does anyone know of a modern design based on these speakers? I asked Troels Gravesen about his 3-Way Classic, but he told me the 3WC was designed for away-from-walls placement and wouldn’t recommend the design for my setup.

By the way, I recalculated the bookshelf dimension and could actually accommodate speakers with an internal volume of 60 litres.

Last edited by soren5; 27th March 2014 at 12:46 PM.
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Old 27th March 2014, 03:20 PM   #9
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Quote:
Originally Posted by soren5 View Post
For this project I initially thought of some of the 70s classic 3-ways, which were designed with less BSC for the purpose of near-wall / bookshelf placement. Does anyone know of a modern design based on these speakers? I asked Troels Gravesen about his 3-Way Classic, but he told me the 3WC was designed for away-from-walls placement and wouldnt recommend the design for my setup.
Your location will boost the bass a lot and mean both the in-room and on-wall "baffle step correction" circuitry will be wrong in existing designs. It also means that the choice of sensitivities for midrange and woofer in existing designs is likely to be less than ideal. If you choose to design the crossover yourself then you have the opportunity to make a significantly more efficient speaker with the benefits that brings. Alternatively you could make an existing design intended for an on-wall or in-room location and then electronically equalise it for your location.

I would expect a standard 3 way to be more appropriate for your location than multiple small drivers in a narrow baffle design. Are you looking at 10" or 8" sized woofers? Something like the cited 3 way classic using easy to work with drivers from the standard SEAS or Scan-Speak range might be a good place to start for your own design.
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Old 28th March 2014, 03:03 AM   #10
soren5 is offline soren5  Denmark
diyAudio Member
 
Join Date: Jun 2011
Location: Copenhagen
Quote:
Originally Posted by andy19191 View Post
Your location will boost the bass a lot and mean both the in-room and on-wall "baffle step correction" circuitry will be wrong in existing designs. It also means that the choice of sensitivities for midrange and woofer in existing designs is likely to be less than ideal. If you choose to design the crossover yourself then you have the opportunity to make a significantly more efficient speaker with the benefits that brings. Alternatively you could make an existing design intended for an on-wall or in-room location and then electronically equalise it for your location.

I would expect a standard 3 way to be more appropriate for your location than multiple small drivers in a narrow baffle design. Are you looking at 10" or 8" sized woofers? Something like the cited 3 way classic using easy to work with drivers from the standard SEAS or Scan-Speak range might be a good place to start for your own design.
Well, Im intrigued by the idea of designing my own 3-way for this project, but Im doubting whether I can expect as good results as e.g. the modified ZDT3 sreten suggested?

Anyway, I was looking at the Scan-Speak Discovery range and there are some interesting drivers. What do you think of something like this?

Sealed 3-way WMT, 55 litres, F3 ~40Hz:
  • Woofer: 10'' 26W/8534G00 - 8 ohm - 89dB
  • Midrange: 5.5 15M/4624G00 - 4 ohm - 92.4dB (400-2500Hz)
  • Tweeter: 1 D2604/830000 - 4 ohm - 92.1dB
If I choose to go this way, I would need some help with the XO design including adjustments for the unusual position of the speakers.
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