[jonirvine]

Hello all!  I'm new to this forum but it looks like there's some good OB conversation!  This will be my second OB project ever so bear with me if I'm way off.  I'm looking for advice on this setup:




Any thoughts?  Ideas?

[JohnR]

Interesting setup  One thing to consider may be the Alpha 15 impedance, I believe they are 8 ohms, so with two of them you will be driving a 4 ohm load from the woofers amps (in mono mode) which they may not be very happy about (per specs). Or, connected in series you will have a 16 ohm load so reduced power.

The other point to note that the lowpass filter is 18 dB/octave. I'm not sure if that will integrate well or not.

[jonirvine]

You know John I had similar concerns but when I emailed the Parts express guy he replied with:

Your best bet, if using two amps, would be to run one channel of each amp to each woofer. If you wanted to use one amp, you could run the two woofers in each speaker in parallel. This would present a 4 ohm impedance to each channel.

Regards,
Technical Advisor
Parts Express

So I didn't know I was misunderstanding something or if the amps would be able to handle sending (2) 4ohm loads to (2) 8ohm speakers (again, I'm a newb at this)

How would that 18 db/octave effect the sound?  Do you have a better suggestion on how to amp this setup?  Maybe some different amps or an easy crossover?

[Poultrygeist]

I use a Denon AVR-1905 in stereo mode to drive four Alphas with a low pass 80 hz XO from PE on each. The Denon has terminals for 2 pair of mains. I paid $35 for this older non HDMI AV receiver which seems more powerful than the two Dayton APA 150's I use in another system. It's also nice to have a remote to control the volume.

Since the Denon has a DAC I am able to send a digital signal to it from my CDP while sending the analog to my integrated SET thereby avoiding the need for a preamp.

[Poultrygeist]

If you go with the Daytons here's a manual that gives other connection options. The Dayton's were formerly sold by Emotiva.

http://emotiva.com/manuals/49_emotiva_bpa_manual_final_v1.0.pdf

[Angaria]

You'll definitely need a low pass filter for the alpha 15's - they have some nasty peaks.  Assuming you can get the mids down to 200hz, a cheap way to do this would be with some small plate amps with a filter built in.  GR has some designed for OB.  Also, the stock zaph crossovers were not designed for such a wide baffle.

[AJinFLA]

The Alphas are near ideal for a passive system due to their very high Q.
However, for an active system, as proposed above, they are IMO, an inferior solution.
I would suggest instead 2 x http://www.parts-express.com/pe/showdetl.cfm?Partnumber=269-087 per side and 2 x http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-805. Mount the amp in the main baffle or in the floor base to support it (if you are cloning the 909). You will get far cleaner, deeper, more powerful bass, with greater flexibility/control. And it costs less too.
More problematic is the dipole/baffle effect on the midbass. You will want some form of highpass on the midbass, as well as a bit of eq to tame the baffle peak. You should have that ability (eq) with your computer source. So the question would be the highpass on the midbass.
Btw, there also now zero excuse for not measuring. Any modern computer with a mic input can measure. The calibration mic that comes with HT receivers will work just fine and most everyone has those. So zero hardware to buy. And plenty free software.
Heck, there are even iPhone/android etc apps that allow RTA measurements, not perfect, but way better than flying blind over mountains.

cheers,

AJ

[Poultrygeist]

The Alphas are ideal in my bi-amped Tang Bands/ H-frames. I drive the TB's with a 2a3 and the Alphas with two Dayton APA150's. MJK likes them

[tryman]

Hi Look at your set up sub woofer will maximum down to only 150Hz(freq on the sub plateamp show)   but for 5 inch on mid woofer I think is very difficult to reach 150 Hz(in open baffle without EQ) . normally 200 hz is lowest for that 5 inch .

thanks

[JohnR]

You know John I had similar concerns but when I emailed the Parts express guy he replied with:
So I didn't know I was misunderstanding something or if the amps would be able to handle sending (2) 4ohm loads to (2) 8ohm speakers (again, I'm a newb at this)

Hi, you would have less output power that way. The specs don't give power into 8 ohms, but probably 40-45W per driver. And you need more cables.

How would that 18 db/octave effect the sound?  Do you have a better suggestion on how to amp this setup?  Maybe some different amps or an easy crossover?

It would be a question of integration - slope (and accompanying phase) will affect how the woofer output interacts with the mid. I like using a DSP crossover and separate amps because of the flexibility. However the suggestions by AJinFLA look good.

[jonirvine]

Thanks everyone for the advice! Very helpful and kind to offer your wisdom.

Well, since I've already ordered the Alpha's and the 1" MDF sheets have just come into the plywood store (special order amazingly enough), I've had to make some major decisions here.  I've modified the plan to get rid of the Zaph's and instead go with  my original plan and go with some TB W8-1808's (similar to your setup Poultrygeist but without the h-frame). I know, I know, this won't make for a very good 909 "clone" but in the end, I was worried that the untested Zaph's would lack in mid and also mix weird with the Alpha's since they had a much lower SPL.

I've also decided to passively cross over the alpha's with the seemingly simple design mentioned in MJK's legendary article http://www.quarter-wave.com/OBs/OB_Design.pdf.

This will open up a variety of options for ampage which I will still meditate over while I build the baffles.  I think I could still end up going with the Dayton's but I'd just nix using that active low-pass.  I think the advice about the subs needing to reach 200hz is a good reason not to use any active pass on the amps.

I'm still considering the Peachtree Decco, Decco2, or Nova to power the full ranges and be my DAC.  I like this all-in-one solution because it keeps things simple and clean.  I may experiment with a high pass c/o on the full range like in MJK's article as well. 

Here are some other amps I'm looking at for the subs:
Mitsubishi DA-A15DC - http://portland.craigslist.org/mlt/ele/2855425888.html
(2) Marantz MA-500 - http://portland.craigslist.org/mlt/ele/2851822075.html
Hafler DH-220 - http://portland.craigslist.org/mlt/ele/2859970931.html
*The problem with all of these is that they're all power amps with no volume control (like the Daytons).  Poultrygeist, that's not a bad idea running the Alpha's with an integrated amp.  I may consider that.  Actually I have a Harman Kardon avr25II laying around that may do the trick but for some reason I feel weird about using these modern home theater amps for this sort of application. 

Any other ideas on a good amp solution for the Alpha's?

[JohnR]

Any other ideas on a good amp solution for the Alpha's?

Pro amps usually have input attenuation (and plenty of power).

[grsimmon]

The 2 flagship Jamos are on my list (but can probably never afford them!). That's way cool your doing a DIY version.   My humble suggestion:  add a rear firing tweeter.   Best of luck however you decide .

[jonirvine]

My humble suggestion:  add a rear firing tweeter.

I've seen this done before but I'm not sure I understand the concept, sonically speaking.  Can you explain briefly and/or point me in the direction of an online resource? 

[scorpion]

It's a pity that people still walk right into the Alpha15 trap. This unit is markedly inferior soundwise, for instance also to Beta15 and others which many people now have witnessed about, some exapmles: http://hi-fiworld.co.uk/index.php/loudspeakers/68-technology/138-open-baffle-loudspeaker-design-part-16.html .

I wonder what kind of music really is listened to if clarity and articulation is not the valued asset. The Alpha15 does colour the whole music appearance.

/Erling

[Poultrygeist]

For the price of the NOVA or less you can buy a SET and an outboard DAC for your Macbook. I'm pretty sure you can even buy a USB SET. I promise you the full range Tang Bands will sound so much better with a SET and I would not use an evil passive XO on them as there's no need if you bi-amp and use the Daytons. Bi-amping with active XO will get the most out of this design. This is the approach MJK uses in his "Alpha Experimental OB Design" article which we're likely to see more of it in his "Designing An Active Two Way OB System Coming Soon" article.

The Alphas sound the same to me whether I'm driving them with the Daytons or the Denon AVR. I like the Alphas for their fast transients and over all bass weight which adds a much needed foundation to all the full range speakers I used them with. I run the Alpha H-frames topless when I want more bass for the Frugal Horn Mk3's.

[Rudolf]

Erling,

with due respect for your controlled and measured personal findings and preferences: the second link in your previous post is a typical example for misleaded "knowledge", false "deduction" and poking around in the dark.

The thread opener has no clue about dipoles, can't do measurements, but knows that the driver is the culprit. When switching to another driver, things improve.

I don't see how anybody can learn anything trustworthy from such an "experiment".

Rudolf

It would be VERY helpful, if you could show with some distortion diagrams or CSD, where and why the Alpha 15 is inferior to the IB 15.

[Poultrygeist]

If you daisy chain the Daytons together ( as shown in the Emo link ) each Dayton can drive two Alphas so there's no need to connect the Alphas in series and you'll have a 8 ohm load instead of 4 ohms.

[scorpion]

Rudolf,

You are right I removed the last link.

Regarding measurements I think there are better resources available, here is a measurement of the IB15's distortion at 100 dB from the known 'drivervault':
http://493531664873718246-a-1802744773732722657-s-sites.googlegroups.com/site/drivervault/driver-measurements/15/ae-speakers-ib15/non-linear-distortion/HD_sweep.PNG?attachauth=ANoY7cqUnxOLBHiHIcYsnGEDUEcHcIXHJt5ir7TEYNS4FrPxz_ASDiy5LCUMOt2rkDQSkN3j36yTD4IDq_vp58n7fJqyisEWDmzaQn4XFA9Wwit6HIHZ0lB9_yciwdarMMuOEjbzOhk6VMoDmDuM1rP4LRnVoW-I5_G-lHwIZB-_sMQIjvGtSIiqflAA4VELVqSV4TpWQYYHYkzPBE4tk6OCX9VsOpcSNuds_PhEqzm6skjLiEsqaj2oZTVwI8yOtdXQgJ1PIEwO96C1kwU_cENBhpAFcXqY_hCc2oUHNZjfG1fcOU70BoM%3D&attredirects=0 and I don't know of any similar for the Alpha15.

It is enough that I felt tricked myself when I realized the big difference in sound when the better unit was put to use.

/Erling

[opnly bafld]

If you daisy chain the Daytons together ( as shown in the Emo link ) each Dayton can drive two Alphas so there's no need to connect the Alphas in series and you'll have a 8 ohm load instead of 4 ohms.

The way Jon has it in his diagram is fine (the end result will be the same), he can use a female to male Y at the sub amp end and run one Alpha on each channel.