FAST build with an Alpair 7.3 and a 12" Peavy Pro 12 woofer - diyAudio
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Old 26th July 2012, 08:05 PM   #1
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Red face FAST build with an Alpair 7.3 and a 12" Peavy Pro 12 woofer

Hello all,
I am looking to build a FAST system that could be run off of a tube amp.


Objective Goals:
1. Learn more about building speakers and DIY audio in general
2. Each Speaker should Run under 20 Watts
3. Bi Amp
4. Symmetrical response between the Full Range and Low Frequency driver
5. Do Not Break The Bank


Musical Goals:
1. Instrumental separation
2. Not looking to find fault in music that is being played
3. Good Imaging
4. Warm midrange

Equipment
1. MiniDSP for crossover
2. 4 Channel 30 Watt Amplifier (Will Build)
3. Tube Preamp (Will Build)

Peavy Pro 12 Main Cabinet Dimensions



Internal
  1. Height = 47"
  2. Width = 10"
  3. Depth = 22"
External
  1. Height = 49"
  2. Width = 12"
  3. Depth = 24"
Alpair Cabinet Dimensions



Internal
  1. Height = 8"
  2. Width = 6"
  3. Depth = 4"
External
  1. Height = 10.6"
  2. Width = 8"
  3. Depth = 5"
Speaker Drivers



Alpair 7.3 Gen3
  1. Sealed Box
  2. F3 114.6
  3. 4 Ohm
  4. 84.5 dB 1w/1m
Peavey Pro 12
  1. Vented Box
  2. F3 37.78 Hz
  3. 8 Ohm
  4. 94.3 dB 1w/1m
Questions:
1. What would be the best xover freq?
a. 500H Hz
b. 250 Hz

2. How well does a side firing woofer work in a FAST system?

3. Do you believe matching the Peavy Pro 12 with an Alpair 7.3 is a good match?

4. Is there anything that I may not have accounted for?

5. The SPL between the two drivers is almost 10dB difference, the max that the Alpair 7.3 can get too is around 96.5 dB and at the same power the Peavy Pro 12 is around 103 dB. Is this going to be a problem?


What I am really asking does this make sence?
Thanks for the responces
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File Type: jpg PA2.jpg (86.0 KB, 434 views)
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File Type: jpg PA4.jpg (108.0 KB, 431 views)
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Old 26th July 2012, 08:13 PM   #2
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Location: Ladysmith, BC
I'd suggest the 250hz cross over. EDIT - this depends on the type of cross over you use. If using 6db/oct then maybe the 500hz is better, but then I'd be tempted to front mount that Peavy.

Side firing is fine, just delay the alp7 as required in the minidsp.

The SPL difference is fine, just offset the Peavy as required in the minidsp.

Is there anything I may not have accounted for?... Well, have you accounted for how you will:

1. Deal with Baffle step compensation?
2. Define the cross over parameters?
3. How the side firing polar response of the Peavy will affect the room?

As for #3, if you're listening beyond 90 degrees, most of the information in around 250hz will come from the room unless you toe in the speakers so you have a line of sight to the woofers. Or face the Peavy inwards instead of outwards. This isn't necessarily a bad thing, just something to be aware of. Alternatively you could reduce the depth of the cabinent/baffle the Peavy is on and it would stay a little more omni.

Last edited by tuxedocivic; 26th July 2012 at 08:16 PM.
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Old 26th July 2012, 08:37 PM   #3
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Join Date: Aug 2011
The development is still in the exploritory phase.



Quote:
Originally Posted by tuxedocivic View Post
1. Deal with Baffle step compensation?
2. Define the cross over parameters?
3. How the side firing polar response of the Peavy will affect the room?
For the front baffel I will be rounding off the strait edges. I am still working on the crossover and will post more information when I comes in.

For # 3, I am not sure how to answer this. Can you give an example or point me in a place to learn about how to deal with Polor Responce?

Thank you for the reply,
Golgi
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Old 26th July 2012, 08:54 PM   #4
chrisb is offline chrisb  Canada
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Join Date: Aug 2002
Location: victoria BC
Quote:
Originally Posted by golgiapparatus View Post
Hello all,
I am looking to build a FAST system that could be run off of a tube amp.


Objective Goals:
1. Learn more about building speakers and DIY audio in general
2. Each Speaker should Run under 20 Watts
3. Bi Amp
4. Symmetrical response between the Full Range and Low Frequency driver
5. Do Not Break The Bank


Musical Goals:
1. Instrumental separation
2. Not looking to find fault in music that is being played
3. Good Imaging
4. Warm midrange

Equipment
1. MiniDSP for crossover
2. 4 Channel 30 Watt Amplifier (Will Build)
3. Tube Preamp (Will Build)

Peavy Pro 12 Main Cabinet Dimensions



Internal
  1. Height = 47"
  2. Width = 10"
  3. Depth = 22"
External
  1. Height = 49"
  2. Width = 12"
  3. Depth = 24"
Alpair Cabinet Dimensions



Internal
  1. Height = 8"
  2. Width = 6"
  3. Depth = 4"
External
  1. Height = 10.6"
  2. Width = 8"
  3. Depth = 5"
Speaker Drivers



Alpair 7.3 Gen3
  1. Sealed Box
  2. F3 114.6
  3. 4 Ohm
  4. 84.5 dB 1w/1m
Peavey Pro 12
  1. Vented Box
  2. F3 37.78 Hz
  3. 8 Ohm
  4. 94.3 dB 1w/1m
Questions:
1. What would be the best xover freq?
a. 500H Hz
b. 250 Hz

2. How well does a side firing woofer work in a FAST system?

3. Do you believe matching the Peavy Pro 12 with an Alpair 7.3 is a good match?

4. Is there anything that I may not have accounted for?

5. The SPL between the two drivers is almost 10dB difference, the max that the Alpair 7.3 can get too is around 96.5 dB and at the same power the Peavy Pro 12 is around 103 dB. Is this going to be a problem?


What I am really asking does this make sence?
Thanks for the responces

in no particular order:

yup the general approach makes a lotta sense

side firing woofer(s) can certainly work well in such a configuration - and coordinating XO frequency with baffle dimensions can eliminate the need for BSC / EQ (in the case of one we built a couple of years ago with Fostex as mid/tweeter, we used 330Hz)

pro woofers are generally more rugged than small FR drivers such as the Alpair7, and one factor not yet mentioned is the room size /placement constraints - both factors which could affect SPL levels sustainable with any safety margin for the Alpairs

I personally prefer the sonics of the Alpair 7.3 in aperiodic / resistively vented enclosures, or MLTL if attempted close to full range ( i.e. XO lower than 100Hz)

As much as I love the 7.3 with a nice SET, to match the dynamics and tonal signature that you'll likely achieve with the Peavys , I'd be inclined to think about a pentode or U/L P/P ( such as EL84/6BQ5 - I've yet to hear one I couldn't live with ).

In spite of their higher rated sensitivity, the Peavys might well be better served by SS amp of 60-80 wpc.


IINM the Alpair 7.3 REVC= 5.4 Ohms, but that would likely only be of significance if you were considering adding passive high level filters - with miniDSP and active amplification, this point is probably moot

Will there be multiple signal sources ahead of the miniDSP? If not, with high enough source signal level and input sensitivity on the direct coupled amps, you might not really need a pre-amp, tube or otherwise.


edit: consider side mounted push/push woofers - you might well be able to achieve equal or better results with smaller diameter drivers - i.e. 10" or even 8" .
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Last edited by chrisb; 26th July 2012 at 08:58 PM.
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Old 26th July 2012, 09:24 PM   #5
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Location: Burlington, NC
Here is mine. XO will be done this week....hopefully
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Old 26th July 2012, 09:29 PM   #6
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Join Date: Jan 2011
Location: Ladysmith, BC
Quote:
Originally Posted by golgiapparatus View Post
Can you give an example or point me in a place to learn about how to deal with Polor Responce?

Thank you for the reply,
Golgi
I can't think of a resource off hand.

Basically, what I mean is, the baffle is going to block direct sound if you're behind the baffle. Unless the wavelengths are longer than the baffle dimensions. It's the same principle as baffle step.

That's a large baffle the Peavy is on, so most of the 250hz content is going to be pushed sideways in a hemisphere (2pi). If you aren't in that hemisphere, then you're hearing the sound power from the room. At those frequencies, that's not to big of a deal at 250hz. At 500hz, it is.

To address this, you could:

1. Live with only hearing the room sound power and not the direct sound;
2. Place the Peavy inwards;
3. Shrink the baffle the Peavy is on;
4. Decrease you cross over point even moreso; or
5. Place the Peavy on the front baffle.
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Old 2nd November 2012, 12:07 PM   #7
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Location: Bristol
How is this project getting on?
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