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Old 4th March 2011, 08:34 PM   #1
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Default Trying to understand speaker position...

Hi folks, I am a certified lurker until today.

Background: I am about to undertake a speaker building project using the Greg Monfort (thanks Greg) Alpair 10 cabinet design. It seems straightforward enough and the design appeals to me. The driver I have chosen for this the MarkAudion Alpair 10 generation 2. The cabinets will be constructed of 3/4" baltic birch ply with a zebrawood veneer. I also intend to put a flared base to give the speakers a wider stance for stability reasons.

Question: As you can see by the attached drawing provided by Greg Monfort the driver is placed about 2/3 up from the bottom of the cabinet. I would like to have the driver placed just 1.5 inches from the top of the cabinet if, everything else being equal, it doesn't affect the sound/performance of the speaker.

This change is just for personal taste and if it makes a difference I will be driving these with the Elekit TU879 S, an 8.5 watt @ 8ohms tube amp.

Your thoughts kind members would be most appreciated.
Also I did look for related information here at diyaudio but have come up empty handed.
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Old 5th March 2011, 01:13 PM   #2
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Old 5th March 2011, 01:17 PM   #3
Pano is offline Pano  United States
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Old 5th March 2011, 01:20 PM   #4
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Seeing as what you've got there is a transmission line, moving the speaker will impact the sound.

This is a good overview, and includes in-depth references:

Quarter_Wave_Resonators
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Old 5th March 2011, 01:29 PM   #5
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Keriwena, Thanks for some information. I am not sure I understand how to make adjustments though.
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Old 5th March 2011, 04:35 PM   #6
zman01 is offline zman01  Bangladesh
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Nauralmystic, I am no expert, but I think it will have an impact - trust that Greg Monfort made that exact placement of driver becasue it was optimal for his design.

If you prefer the driver a bit higher from the floor, using spikes you will gain 0.5" on height.

Also are you sure that Alpair 10.2 will work well in this cabinet? AFAIK Alpair 10.2 is new (2nd Gen) and improved version of Alpair 10. The plans are for Alpair 10, and using Alpair 10.2 might need slightly different considerations. If you already have and answer to that, great. If not you can post the question at the Markaudio section of the forums.
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Old 5th March 2011, 04:51 PM   #7
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zman01, You make an excellent point. I had not considered that there are differences between the 10 and 10.2. I have posted a more general question about which driver to select in the MarkAudio section. Once I get some response to it I will address the cabinet design more specifically.

THanks to all who have taken their time to respond.
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Old 5th March 2011, 04:58 PM   #8
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I bet that you can move the driver higher without completely impacting the design. Typically you just need to adjust the amount of stuffing.
Someone took a TABAQ and moved the driver higher and it worked just fine.
What you need though, is to model you design. Someone who has Martin Kings software could model it for you.
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Old 5th March 2011, 05:43 PM   #9
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The driver offset is important to the design. It kills the 1st objectionable harmonic, allowing for less damping and a net gain in bass reinforcement. The offset is not ~2/3 but likely carefully placed to within fractions of an inch.

If you end load the driver you will need more damping and will end up with less bass or more ripple.

ML-TLs are typically fairly tolerent, A10.2 will probably work just fine (althou starting from scratch you would probably end up with something slightly different)

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Old 6th March 2011, 03:53 PM   #10
Squeak is offline Squeak  Denmark
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Consider doing a ML-TQWT if you want the driver at sitting down ear hight (1 to 1.10 metres, is a good compromise). A slanted wall within the cap will give you the driver displacement effect.
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