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1st Open Baffles; Need help!

So I'm really far from an expert on these things, but I was able to score an active crossover on BT for $100. A rane; used pro gear.

With that you can really play around with your crossover points.

My $0.02
 
mr_RBG said:
I made my first OB using Alpair 10.2 and alphas 15. I have some problems and I would appreciate any help. I use 24x48 baffle with 11" from the bottom to the center of the alpha and 8.5" from the top for the 10.2, two inches from a center line. I've tied different types of filters: 1st and 2nd. Different x-over points. My impressions so far:
1) I have no idea why, but the speaker is so inefficient. I have troels PMS clones and they are so much louder. It was the most important point for me: make efficient easy to drive speakers.
2) I just can't mate Alpair10.2 and alpha. It doesn't sound coherent, fils like some part of lower mid is missing. Maybe they are too far apart? Or maybe you need something bigger to match 15".
Here is the photo:
View attachment 426877
Click to expand...

Don't know much about your set up but I would use one amp for the 87db Alpar ( 20 wpc or greater ) and a separate amp for the Alphas ( inexpensive plate amps or whatever of at least 100 wpc ) and a 2 way electronic crossover. The baffles aren't the problem.
 
Based on having built MJK's small, passive OB project: my best guess is you will still need to pad down the Alpha 15a by about 2 dB, assuming it is crossed at 150 Hz 2nd order. The XO point for the Alpair 10 should be 500 Hz. 2nd order. Polarity should be the same for both drivers, although you can try switching it if you like.

Cheers, Jim

PS: Qts of 0.35 doesn't matter, as you are using the Alpha 15a for bass.
 
Thanks Jim! I was trying to go upper for the alpair like 500hz, and even with 1st order I can hear that so many details are missing. I will try again. Another thing, what do you think of using 2 alphas per speaker? Do you know what impedance value to expect than?
 
mr_RBG said:
I made my first OB using Alpair 10.2 and alphas 15. I have some problems and I would appreciate any help. I use 24x48 baffle with 11" from the bottom to the center of the alpha and 8.5" from the top for the 10.2, two inches from a center line. I've tied different types of filters: 1st and 2nd. Different x-over points. My impressions so far:
1) I have no idea why, but the speaker is so inefficient. I have troels PMS clones and they are so much louder. It was the most important point for me: make efficient easy to drive speakers.
2) I just can't mate Alpair10.2 and alpha. It doesn't sound coherent, fils like some part of lower mid is missing. Maybe they are too far apart? Or maybe you need something bigger to match 15".
Here is the photo:
Click to expand...

I think that the Alpair 10.2 and the Alpha 15A should work on an OB, the crossover design is the key.

1. What type of crossover are you using, passive or active?

2. What type of amp(s) are you using, tube or solid state?

3. How did you design your crossover frequencies and slopes? Did you run any simulations to see how they would combine?

All you should need is one Alpha 15A, two would provide too much bass. When I have had a poor performing OB system it has always been improved by using the correct crossover and matching the on baffle SPLs of the drivers (balancing the response). The other lesson I have learned is that a passive OB system is not tube amp friendly, many tube amps do not like the wide swings in electrical impedance that occur in the 100 to 500 Hz range produced by the crossover circuit and the driver impedances.
 
Amps: I am using different Pass amps. Low power 25w firstwatt mostly except f5t which can drive everything.

For the cross over I did not use any simulations, but I should. I just do not know where to start: what software?
So OB systems are hard to drive/control? That was actually the main point I wanted to try it. I have a clone of troels PMS, but was thinking that OB will be easier on my amps. Apparently not? PMS plays much louder. I would appreciate if you can direct me so I can make some simulations before buying parts for a x-over. Thanks!
 
Electronic crossovers make life less complicated and can be less expensive than passives. There are many articles that claim sonic advantages for actives.

Ashly XR-1001 ( components similar to $$$$ Marchand - no slope control but it's response control is close ) - $250 from Parts Express

dbx 223 - $150 ( good reviews )

Behringer CX2310 - $89 ( cheaply made but decent reviews and good enough to get your feet wet )

Behringer DCX2496 - adjustable slopes and does everything - entire forum sections devoted to it's use - high dollar Emerald Physics OB's come with their own programmed Behringer. - $300

Minidsp - inexpensive and gets high praise

Used Ranes and Ashlys can be found on ebay for around $100. Some have 12 db slopes. There are also vintage electronic crossovers made by Pioneer and Sony. Pass sells a high end electronic crossover designed specifically for OB.

You may need XLR to RCA cables but they are very inexpensive and of high quality at monoprice.
 
mr_RBG said:
Amps: I am using different Pass amps. Low power 25w firstwatt mostly except f5t which can drive everything.

For the cross over I did not use any simulations, but I should. I just do not know where to start: what software?
So OB systems are hard to drive/control? That was actually the main point I wanted to try it. I have a clone of troels PMS, but was thinking that OB will be easier on my amps. Apparently not? PMS plays much louder. I would appreciate if you can direct me so I can make some simulations before buying parts for a x-over. Thanks!
Click to expand...

It isn't true (AFAIK) that OBs are an easier load on the amp than other designs. Single full range drivers are easier loads (generally) because they don't have XOs, so the amp deals directly with the driver. The complexity of the load is usually due to XO, although some types of speakers, such as electrostatics, exhibit very low impedance which will stress an amp.

One way around problems with passive XOs in the speaker is to use a line level XO--either passive or active. Active offers much flexibility in tuning.

Cheers, Jim
 
mr_RBG said:
Amps: I am using different Pass amps. Low power 25w firstwatt mostly except f5t which can drive everything.

For the cross over I did not use any simulations, but I should. I just do not know where to start: what software?
So OB systems are hard to drive/control? That was actually the main point I wanted to try it. I have a clone of troels PMS, but was thinking that OB will be easier on my amps. Apparently not? PMS plays much louder. I would appreciate if you can direct me so I can make some simulations before buying parts for a x-over. Thanks!
Click to expand...

I don't know anything about a Troels PMS speaker so I cannot comment.

The Alpha 15A has an efficiency of about 90 dB/w/m in an OB crossed over in the 100 to 200 Hz range.

The Alpair 10.2, according to the frequency response plot at Madisound, is about 85 dB/w/m dropping to 82 dB/w/m above a few hundred Hz.

In most OB two way designs the problem is getting efficient enough bass to match the full range driver, you situation is exactly the opposite.

I see two options. If you want to stay passive replace either the woofer or the full range driver so that the SPL's match better. Or step up to an active crossover which will give you the adjustability to dial in the crossover frequencies and slopes and matching the levels without continuing to buy more passive parts. If you already have several amps this may be the best and cheapest solution.

There is a good list of active crossovers above. I would add the dBx Driverack PA to the list. In general spending a little more will provide more adjustability and flexibility for your system, I think it is worth the extra dollars to get a decent active crossover. Once you have an active crossover then you can in general match any two drivers in any type of speaker system.
 
What did MJK say about the woofer needing to be louder than the FR? Wasn't it supposed to be 4-6db? If so... This combo is just about right. One more time: MiniDSP solves all your problems. Dial it in using MiniDSP and when you have it - build a passive xover.
 
I am a little bit worried about letting all these x-overs in my system. It is a very nice system, so it is hard for me just put some semi digital x-over in it. Without knowing what's inside and how it works. I would really like to stay passive for some time until I become familiar with active stuff and how it works. I would prefer to DIY an active crossover then :-).
 
mr_RBG said:
I am a little bit worried about letting all these x-overs in my system. It is a very nice system, so it is hard for me just put some semi digital x-over in it. Without knowing what's inside and how it works. I would really like to stay passive for some time until I become familiar with active stuff and how it works. I would prefer to DIY an active crossover then :-).
Click to expand...
Have no fear. My suggestion would be to acquire an inexpensive active crossover that will meet your needs and experiment.

I use two Behringer CX3400's in my main system, one to filter low-mid-high and one for subwoofer duty. I use different combinations of amps including Pass F5's, JBL, Kenwood, QSC, and others. Speakers are DIY MLTL Altec Model 19's with Heil super tweeters, sub is DIY 15" sealed. I haven't sought out better crossovers since the Behringers hit most of my spots pretty well. At some point, I'll probably upgrade to a programmable active crossover, just to get every last bit out of the system.

I've heard the dipole subs (H frame) in one excellent system. I believe they were doubled Peerless 12" woofers. It was a well integrated subwoofer system.
 
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