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Alpair 10p Build
Alpair 10p Build
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Old 18th January 2019, 07:33 PM   #1
AudioGeek is offline AudioGeek  United States
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Default Alpair 10p Build

After much thought and consideration i have decided to go ahead with the Alpair 10p.

I really want to do something like this:

TLb -- Table of Contents

Run a couple per side in a transmission line bipole. Should i run the rear one full or throw an inductor on it? I assume the size of the inductor will be relative to the size of the baffle? How does one calculate this in a bipole configuration?

Thoughts on this design?

Thank you!
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Old 18th January 2019, 08:19 PM   #2
chrisb is offline chrisb
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Good gosh that takes me back, the project page was I think much earlier than the 2007 date listed in the edit, and Iím sure if any actually got built? The bipole configuration is something that Dave has played with many times since, and Iíve built at least 6 of the numerous designs - almost of which were for smaller diameter fullrangers, 4Ē mid-bass , or 6 - 8Ē woofers. My favorite ended up being a variation with one driver top mounted at an angle at the sealed end of the line - i.e. the Castle Microtower.

Personally I consider a single A10P quite capable by itself but Dave might have already considered revisiting this particular topology, although Iíd suspect it might include one of the smaller Alpair metal cone models - such as Alpair5.2 - rather than a soft dome, and active bi-amping.
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Old 19th January 2019, 02:24 AM   #3
BJosephs is offline BJosephs  United States
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I don’t know anything about this particular speaker approach but I will say I built pensils with 10p speakers and I like them very much. I’ll be following.
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Old 19th January 2019, 04:08 PM   #4
Jim Griffin is offline Jim Griffin  United States
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I have built several bipolar MLTL speakers which have been documented here on diyaudio. One design featured CSS FR125S and WR125S drivers. As with any bipole you have wrap effects around the cabinet which cause a resonance dip in the forward radiation pattern near frequencies which are half wavelength apart. In my case a 5-6 dB dip showed up about 400-500 Hz. You can mitigate that dip by rolling off the rear driver of the pair before the resonance frequency.
For details see:

Bipolar MLTL Speaker with FR125S/WR125S

Another dipole design had the drivers offset in an attempt to better address the wrap around resonance and to better disperse in-room effects. My design had the drivers spaced high and low in their front to back baffles. This approach will yield results akin to the castle arrangement suggested by Chris.

Offset Bipolar MLTL with CSS EL70 Drivers--Part 1

I like dipoles as they effectively double the in-room bass output of a speaker.

Last edited by Jim Griffin; 19th January 2019 at 04:22 PM.
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Old 22nd January 2019, 07:29 AM   #5
Jim Griffin is offline Jim Griffin  United States
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I should have caught these two mistakes:

First 'dipole' should be 'bipole' in the second paragraph.

Second 'dipoles' should be 'bipoles' in the closing sentence.

I will stay after school and write 'bipole' 100 times to clear my mind of 'dipole'.
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Old 24th January 2019, 05:25 PM   #6
AudioGeek is offline AudioGeek  United States
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I am just trying to figure a way of keeping up the sensitivity of the A10P and doing away with a BSC.

The bipole transmission line configuration looked interesting especially with its relatively simple enclosure design and pretty good performance.

I was just wondering where to roll off the rear driver and how would that interact with the response of the transmission line... it at all.

or should I forget this method and just go with a simple BR A10P with a BSC?

Thanks!
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Last edited by AudioGeek; 24th January 2019 at 05:28 PM.
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Old 24th January 2019, 11:44 PM   #7
Jim Griffin is offline Jim Griffin  United States
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AudioGeek,

The bipole configuration would naturally address the BSC if you view the polar plots of a bipole speaker. A bipole configuration radiates the same amount energy into the forward 180 degrees and the rear 180 degrees. Hence, it would work best away from the wall behind the speaker-- say 4-6 feet space spacing from the wall.

The wrap around effect needs to be taken into account if you wish and I have included how to take do that in my second link above. Assuming that you have connected the two drivers in parallel and have a 4 ohms overall impedance (two 8 ohms drivers in parallel for lower frequencies). The connection for a bipole speaker with the wraparound mitigation is for the rear driver to have the inductor inserted in series with that driver. Thus it would have an 4 ohms impedance for the bass/low mid area and transition to an 8 ohms speaker impedance as the wraparound inductor takes effect and chokes off the rear driver.

Now another way to go for BSC with two drivers in the box is to use a 1.5 way arrangement (see photo below) and connect such as I did for my two TangBand 3.5" drivers. Essentially, the two drivers are placed on the front baffle and electrically connected such that they both radiate forward for their bass frequency area. For the bass range the two drivers are essentially connected in parallel. One driver--say the lower front driver--with a series inductor connected in series similar to the bipole configuration so that the lower front driver rolls off at the BSC corner frequency point. Hence, you get the bass enhancement for the two drivers at low frequencies yet the upper driver radiates full frequency. The impedance goes from 4 ohms for bass and increases to 8 ohms for the upper frequencies.

http://www.patcave.com/diy2002/sjgc6958.jpg

Finally, if you go with the transmission line approach for two drivers I would go with a Martin King based MLTL design for the two drivers A10p vs. the older transmission line approach you mentioned in Post #1. Several A10p MLTL design are listed in the diyaudio forum.

Jim

Last edited by Jim Griffin; 24th January 2019 at 11:58 PM.
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Old 25th January 2019, 12:23 AM   #8
chrisb is offline chrisb
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+1 to Jimís recommendation for an MJK worksheet calculated design, MLTL or otherwise. If your budget can afford dual drivers per side, I wouldnít be surprised if Dave/Scott didnít already have something sketched out with 2 front facing A10Ps - there was certainly something like that for the A7.3.
Frankly, though Iíve never personally found a single A10P to be deficient in either sensitivity or LF extension in the enclosures Iíve used - Pensils and FHXL - but then Iím no longer running low powered tube amps, so the sensitivity is not an issue. Also, neither of my listening rooms are huge, and Iíd long ago lowered my average listening levels to the mid 80s at most. The Woden Silbury is also worthy of consideration, but they are a more elaborate build, and certainly the opposite of a compact stand mount monitor.

Woden Design | Silbury
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Old 25th January 2019, 04:07 PM   #9
AudioGeek is offline AudioGeek  United States
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just a thought... A10P in a BIB?
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Old 25th January 2019, 05:53 PM   #10
chrisb is offline chrisb
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Sure, but the antithesis of stand mount / bookshelf BR / MarKen
Not likely to need BSC, I think
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