Bi-amping open baffles

leer0y

New Member
Hi, all,

Hoping someone might be able to provide me with some advice.

I recently built a pair of open baffle speakers with the assistance of Martin King (MJK) and his mathcad worksheets. I used Eminence Alpha 15A woofers and Alpair 7 full-range drivers on 18" x 24" baffles. I also build some simple 2nd order crossovers (1 inductor and 1 capacitor per driver).

Basically, this is the first time I've heard an open baffle and I'm blown away (even though drivers etc are not even run-in yet). I am using my Elekit TU-8200DX valve amp (8 watts per channel). However, I am being advised by a lot of people that I can achieve much tighter/deeper bass with a more powerful solid state amp. The issue I have is that I love the tube sound and don't particularly want to stop using my current amp (which I built myself just a year or two ago).

I had a couple of questions:

1) I have been reading on this forum about horizontal bi-amping, but it is not something I know much about. It would seem on the face of it like this could be the perfect solution for me - use my valve amp for the full range drivers and buy an additional more powerful solid state amp for the woofers to achieve stronger/tighter bass. What would I need to achieve this? Do i need some sort of active crossover (e.g. DBX)? Do I need a pre-amp?

2) any people who can offer opinions on powering open baffles (with similar high efficiency 15" drivers) using similar power valve amps? Am I really losing out on the bass side?

Thanks,
Lee
 

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A couple of additional photos of the speakers
 

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I am very interested to hear what is advised here as well. I have a small set of beautiful bookshelf speakers that I want very much to be a part of my system and I need to restrict the frequency response to them so they can shine where they perform best and let the main speakers handle the rest.

From what I gather some sort of active crossover and a dedicated amp for the little guys should work but I know very little about crossovers.
 
I had some OBs for a while with Eminence Alphas, and later Delta 15's and a Fostex FE206en 8" for mids - with a fostex horn tweeter.

I found that bi-amping worked a treat - and it doesnt really matter what drives the bottom end driver - tube or SS. Note that you should take the "tighter, deeper bass" comments with a grain of salt as this can always be a weakness of OB's - simply due to the baffle design.

I tried passive filters etc to roll the woofer off but I could never get great results, plus you may also be getting volume level mis-matches between the 2 drivers. You also lose far less signal if you actively EQ - and as you are giving the fullrange driver all frequencies - you only need to filter the amp thats powering the woofer. Yes it sounded cleaner to me.

So a great "mix" here (and how I currently power my KEF 103.4's) is use a SS state amp to power the woofer - its an Eminence with ridiculously high sensitivity - so you dont need tons of power - so theres no reason why even 20 watts of valve power to power the woofers couldnt work either.

Try to get an active EQ to filter the signal to this amplifier - this puts you in the realm of hunting for professional PA gear - but I would warn against skimping with this ( I have had bad experiences with both Behringer & Alesis gear - try dbx).

then you can use a nice tube amp to power the fullrange driver. I use a vintage ECL86 amplifer, or if not that, then one of my VFET amps.

Yummy. Its so worth it once your setup is right.
 
At the moment your passive crossover is 2 pole at 12dB/octave roll off. With an active unit such as analogue units from DBX, Behringer et al you will have 24dB/octave roll off. If you go digital you will generally be able to alter the roll off for each driver and create asymetrical crossover bands. Also you would have parametric EQ at your disposal as well. I use a pair of Behringer 2310s running as 3 way mono units. I have replaced the power supplies (their apparent weak link).
Also, while setting things up you can vary crossover frequencies and relative gains using front panel controls rather than replacing expensive components.
 
Since you have a crossover in place which you presumably like, you really don't need an active crossover.

There are plenty of folks who add a cheap Class D amp for the bass drivers in an OB system....not just because they're cheap, but because they generally do a hell of a job tightening up the bass.
 
Yeah, I've found that myself recently. After getting my treble working right I find bass to be a bit short so will be using a S.M.S.L. SA98E for bass. I'll just need to install another pair of speaker terminals :)

My crossover is even simpler than yours with a single cap (+bypass cap) on the tweeters, my 10" Zenith 49CZ running full range and a single inductor on the bass woofer.
 
Note that you should take the "tighter, deeper bass" comments with a grain of salt as this can always be a weakness of OB's - simply due to the baffle design.
Yes, I agree. SS amps can go down to almost DC but your OBs won't get anywhere near that. Yes, some valve amps can be soft and woolly in the bass, but not all. A switch to a solid state amp won't guarantee an improvement on bass.
You also lose far less signal if you actively EQ - and as you are giving the fullrange driver all frequencies - you only need to filter the amp thats powering the woofer. Yes it sounded cleaner to me.
My opinion - which isn't universally shared on AK - is that if you have a driver which is handling bass, it makes sense to make life easier for the smaller driver by not feeding it with bass frequencies. It's performance will be cleaner if it isn't trying to handle frequencies that the bass driver is handling anyway.

As for an active crossover, it doesn't have to be strictly active but it makes life easier if it is. It is possible to have passive filter networks between the preamp and power amps, but you have to be very careful about source and load impedances.
Another possibility is to make a DIY active filter, and I'm sure there's plenty of information online if that's something you want to do.
Or it's probably a lot easier to just buy an active filter, though I wouldn't know which one to recommend.
 
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