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Old 5th December 2014, 12:43 AM   #1
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Default Help With first build

I am building my first wmt and I want to have the woofer and mid in different enclosures. The woofer is a hi-vi M8n.
HiVi M8N 8" Aluminum/Magnesium Woofer
Product information:M8N Bass-Midrange

These two sites suggest different volume enclosures. I have read that these are excellent when ported but was wondering if porting this woofer in an enclosure that will most likely range from .8 - 1.2 ft^3 is still plausible? I want to use these speakers with no additional sub so I want to have the best low end I can achieve, while keeping the build small. Should I try to port them or have a sealed box?

Also if there are two enclosures, one for the mid and one for the woofer, is there an advantage to placing the tweeter in either one?

Thanks!
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Old 5th December 2014, 03:05 AM   #2
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Sealed or ported is mostly preference but you will get the most bass extension out of a ported box. i wouldn't worry so much about the tweeter sharing an enclosure more so with tweeter placement you will want it close to the mid to keep it in phase. Also with aluminum cones there is resonance problems you may want to go with a paper cone instead. I ran a simulation with WinISD and came up with 2.8 ft^3 at 25.9 Hz
try this link lots of good info The Speaker Building Bible
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Old 5th December 2014, 03:54 PM   #3
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Thanks for the reply! I unfortunately do not have space for a 2.8ft^3 box in my current situation. So I guess my question is if it is possible to port the box to get the most bass extension while keeping it around 1ft^3 or if I should just look for the most efficient sealed volume?

Also thanks for the help with the tweeter placement.
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Old 5th December 2014, 05:14 PM   #4
jReave is offline jReave  Canada
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Without question, I would put the tweeter with the mid. This keeps center to center spacing between the mid and tweeter as close as possible and it helps to isolate both the tweeter and the mid from any cabinet vibrations from the woofer box.

I'm not sure that you understand how box alignments work for either sealed or vented enclosures. There is not simply just 1 box size and tuning (alignment) for every driver, there are many and each one gives a slightly different FR. It's up to you to figure out what is going to work best for your application, in this case, a relatively small box.

You also need to understand that the room plays a role at lower frequencies as well. As the driver goes lower in frequency, the room starts to augment the response depending on the room size and how much absorption vs reflection there is (concrete vs drywall and an open room vs a fully closed one, as examples). So you especially want to tune a ported enclosure so that the driver's FR and the room gain result in a flat overall response. Not doing so is one of the prime culprits in boomy bass. The 1st chart below shows you what the gain might look like in a room with the longest dimension at 20ft and about the usual 65% loss.

The 2nd chart below compares different FR's for your driver in different enclosures to try to help you see what I'm talking about. The blue response is the sealed box and gives you the least bass. Ported in about the same size box tuned to 28Hz will be better.

Increasing box size to something like 50L and lowering the tuning to 25Hz gives a nice gradual roll-off that might work best when combined with room gain, depending on the room size, etc.

Lastly, you'll get the maximally flat response with about 79L tuned to 25Hz. This will be great in an anechoic chamber, but in a room with room gain it's more than likely going to sound boomy unless the room is very large and lossy.

So what size is the room you'll be putting these in?

Note also that box volumes need to be net volumes - so the volume left over after subtracting the volumes of the port, driver, bracing and anything else that will go into the box (except insulation).

Also be aware that just one of these drivers is going to be SPL limited due to cone excursion at the lowest subwoofer frequencies, or in other words, you're going to want to be careful about cranking these with movies.

Btw, do you understand baffle diffraction and how are you intending to design the xo?
Attached Images
File Type: gif Gain 20ft 65%.gif (11.5 KB, 163 views)
File Type: gif pic M8N FR.gif (23.7 KB, 163 views)
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Old 5th December 2014, 05:56 PM   #5
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Quote:
Originally Posted by mayday24 View Post
I have read that these are excellent when ported but was wondering if porting this woofer in an enclosure that will most likely range from .8 - 1.2 ft^3 is still plausible? I want to use these speakers with no additional sub so I want to have the best low end I can achieve, while keeping the build small. Should I try to port them or have a sealed box?
0.8 - 1.2 ft^3 is around the size for a sealed cabinet. A ported cabinet will want to be about twice this size and perhaps a bit more. If 2.5 ft^3 is definitely too big then stick with sealed.

If you want the best low end you can achieve in 1.2 ft^3 then use a 10"-12" subwoofer, a big amplifier and equalisation. This will force the use of a large midrange to enable a low crossover frequency. In turn this may force the tweeter to use a waveguide to cross nicely to a large midrange. Weighting what is important to you and what is less important and then juggling the compromises is all good fun.

Quote:
Originally Posted by mayday24 View Post
Also if there are two enclosures, one for the mid and one for the woofer, is there an advantage to placing the tweeter in either one?
The tweeter generally wants to be at ear height because it beams strongly unless put in a waveguide. It also wants to be close to the midrange so that the distance from the tweeter to the ear and the midrange to the ear does not vary by a significant proportion of the wavelength of sound at the crossover frequency.
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Old 5th December 2014, 06:56 PM   #6
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Default speaker build

hi
i want to build a nice bookshelf speaker and 2 kits i came up with are jeff bagby MANDOLIN or gr research encore xls kit which would have better sound plz help
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Old 6th December 2014, 05:32 PM   #7
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Thanks jReave. That was a very helpful response. I have decided to go with a 29L box. The port size on the graph you provided was 6 cm by 30 cm? Can I create a slot port that has the same length and the same cross sectional area of the round port? If so is there a limit to how small each dimension of the slot port can be (ie. height width)?
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Old 6th December 2014, 07:07 PM   #8
jReave is offline jReave  Canada
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Yes, 6cm diameter by 30cm to 35cm in length should be good. That's with the walls covered with some insulation. When content is down to about 20Hz, you get about 98dB 1W/1m before xmax is exceeded (where distortion starts to increase).

A slot port is fine with the same cross-sectional area and the same length. I'm sure there is a limit to the slot port minimum dimension but I'm not exactly sure what it is. A height of 1" or greater should be fine I think.

Don't forget - 29L net. If you can go bigger, you'll get more bass. Adding more depth is the easiest way without taking up a lot more space as the speaker usually sits out from the wall anyways.
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Old 6th December 2014, 08:22 PM   #9
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Is there a minimum distance the end of the port tube has to be away from the wall?
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Old 6th December 2014, 09:14 PM   #10
jReave is offline jReave  Canada
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With a slot port it has to be at least larger than the height of the slot, otherwise that space just becomes a part of the port, now folded at right angles. Two inches for a 1" port height might suffice but 3" or more would be safer.
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