Help needed! Where to start with open baffle speakers

[fatmarley]

As the OP who started this thread, I did not expect it to generate such a lively debate. Clearly there are many here on AoS with lots of knowledge...and diverse views!

I'm not ashamed to say this, but most of what you guys are saying has gone totally over my head, but hey, that just shows how much I have yet to learn.

Reading your various posts, I did have a few (more basic) questions:

1. given the wide range of driver/tweeter manufacturers out there - eminent technologies, fostex, seas, scanspeak, vifa etc., is there a combination of woofer and tweeter that goes well in an OB set up (without breaking the bank)?

2. for a first timer like me, should I start with just one woofer and one tweeter for each speaker or have more? (I recognise the answer might have a lot to do with the size of my room and acoustics etc.)

3. should I build my own X-over or buy a ready made one and tweak it? Or maybe no X-over at all and do what Slawa suggests, base on field coil drivers?

My room is about 18ft x 30ft although I sit facing the short length. Walls are fairly bare and ceiling around 15ft high. Floor is suspended wooden slats but largely covered with rugs. So quite a few hard surfaces, but quite airy.

Slawa - glad you joined the thread. It was seeing pictures of one of your OBs for sale on HiFi Wigwam last year that piqued my interest in OBs. Then talking to my friend Dave earlier this year gave me the encouragement to take the plunge. So you are the genesis of this project of mine. Would love to speak to you in person one day and maybe hear your OBs.

Thiha

1. Two drivers that get mentioned a lot on open baffle threads are the Visaton B200 and the Eminence Alpha 15a. QTS Is probably the most Important t/s parameter to look at (you'll find It in the manufacturers data sheets) for open baffle speaker. I'd be looking at a QTS of around 0.7 and higher. Ive heard some people say the Eminence Alpha 15A sounds boomy. I don't know If this Is because of the high QTS (1.26), bad crossover design or the fact that people often mount It almost touching the floor (maybe a combination of all three).
I would'nt worry about the matching the midrange/tweeters. Some of the best speaker designs ever made coupled different driver materials successfully - The old Epos ES14 used a metal tweeter and a plastic mid and Is still very popular now. As long as you use good quality drivers and the crossover Is done right, you shouldn't hear the joins between the mid/tweet.

2. Yes, keep It simple. More drivers will make crossover design much harder.

3. When I tell people crossover design Is hard (assuming you're a beginner), I feel It goes In one ear and out the other. I did some work for a speaker manufacturer once and It didn't matter how many times I told him or even showed him that simple crossovers, done by ear, don't work. He wouldn't believe me (Just to say that simple crossovers can and obviously do work with the right drivers but there was no chance with drivers he chose)
Off-the-shelf crossovers and online crossover calculators are a complete waste of time. They assume your drivers have a perfectly flat frequency response and that the Impedance Is also perfectly flat.
When I say crossover design Is hard, what I really mean Is, If you make one tiny mistake with the whole process of taking accurate measurements, Importing them Into your software and all the things that you need to Input. Your crossover model will not match reality.
If you like a challenge and are willing to put a lot of effort In, I can guide you In the right direction.
Most people just go active because It's so much easier to get the crossover right.

[bumpy]

You have a big advantage with that room but the best way to use an open baffle speaker is to have it firing down the length of the room, not across the width.

The big problem with open baffles is bass cancellation. Bass units go in boxes for a reason, because if you don't put the bass in a box you get cancellation from the return wave and.... no bass or heavily curtailed bass. With 30' to play with you can have the bulk of the room behind the speaker, giving the bass wave a chance to dissipate down the length rather than return. Unlike most rooms you should be able to get pretty good bass from an open baffle by setting them up like that. Have 15' to 20' of the room behind the speakers.

In general terms re open baffles, people do claim that bass sounds more natural etc without the box. I'm not so sure. The various monitoring speakers in studios are not open baffles. Recordings tend to be mixed to sound good on these speakers - not on open baffles. If you listen to a lot of music that has a lot of bass energy below 40 Hz (dance music, electronica, organ and so forth) then I wouldn't recommend going for an open baffle. At least not for the bass. The are not intrinsically better, they are, like all speaker designs, just another set of compromises.

Don't be put off by room restrictions. I have broken all the above guidance in that I fire across the narrow dimension of my room and listen in the near field. Baffles are barely 1m off the rear wall but are angled inwards which I think 'disrupts' the rear reflections reducing cancellations.

[walpurgis]

the fact that people often mount It almost touching the floor

I've noticed that tendency for folk to mount bass drivers very close to the floor. When you consider the wavelengths involved it really has no great benefit at low frequencies.

[fatmarley]

I've noticed that tendency for folk to mount bass drivers very close to the floor. When you consider the wavelengths involved it really has no great benefit at low frequencies.

That's right. According to my simulations. The boost from floor mounting a woofer Is centered around about 150Hz, so not really doing much to help.
Also, with a woofer that low, you can often feel the vibrations of the low frequencies coupling to the floor and adding distortion.

[bumpy]

I've noticed that tendency for folk to mount bass drivers very close to the floor. When you consider the wavelengths involved it really has no great benefit at low frequencies.

But is does maximise the height of the baffle

[Macca]

Don't be put off by room restrictions. I have broken all the above guidance in that I fire across the narrow dimension of my room and listen in the near field. Baffles are barely 1m off the rear wall but are angled inwards which I think 'disrupts' the rear reflections reducing cancellations.

I love breaking the rules. Especially in hi-fi where a lot of them are bollox to begin with. But for a dipole or open baffle you really need as much distance behind it as possible to get optimal performance.

[bumpy]

I love breaking the rules. Especially in hi-fi where a lot of them are bollox to begin with. But for a dipole or open baffle you really need as much distance behind it as possible to get optimal performance.

I am probably helped by the fact I only run my system at mid volume. At low volume late at night its still magic, but I do notice that when friends ask me to wind it up it can get a bit ragged. I do plan to try some sound treatments on the wall behind. The other advantage of running at modest volume with 2 watt monoblocks is that I can run the midrange driver without crossover restrictions above or below. Again a reduction in complexity.

[RothwellAudio]

I love breaking the rules. Especially in hi-fi where a lot of them are bollox to begin with.

Interesting. Which hi-fi rules do you consider to be bollox? I ask because I agree with Scotty when he says "ye canno' change the laws of physics, captain".

[vintage60]

Thank you all.

I went back into my old emails and found one from my friend Dave who tested 5 different woofers including eminent technology alpha 15a but concluded that the best ones were Acoustic Elegance Dipole 15. They are US$359 each is most definitely not cheap! He combined them with AER full range drivers.

Thanks for the advice about not buying ready made X-overs. That's saved me from wasting money.

Keep them coming!

[Arkless Electronics]

Thank you all.

I went back into my old emails and found one from my friend Dave who tested 5 different woofers including eminent technology alpha 15a but concluded that the best ones were Acoustic Elegance Dipole 15. They are US$359 each is most definitely not cheap! He combined them with AER full range drivers.

Thanks for the advice about not buying ready made X-overs. That's saved me from wasting money.

Keep them coming!

That's interesting that there is now a bass unit made specifically for OB use. The lack of suitable bass units and having make do with the limitations of the Eminence units is always a big problem! Back in history there was the Wharfedale SFB3 open baffle speaker which did have a 12" unit they designed specially for the application.