[tonytopshed]

Hello all! I'm a newbie to speaker deign - and this forum; I've built a couple of TL kits and have felt that whilst good, there is always that 'box' effect. I've been trawling the internet  and am delighted to find a forum dedicated to OB's!

I took out the drivers and crossover from one of the TL's and mounted them on laminate flooring board so I can experiment by adding widths just by clicking together. This is purely experimental to decide if OB beckons - it does!

As I'm new to speaker design, much is over my head, I'll build, listen, tweak and hopefully pick up theory as I go along - and help from the forum would be appreciated!
What I'm looking at to get going is a two or three way OB  with passive crossover. There seem to be two main ideas here -
1. A small  (3 - 4") full-range driver with a largish (12 - 15+") bass woofer and possibly a tweeter.( MJKing, Manzanita, mh-audio project)
2. Two 10- 12" drivers and a tweeter. (Hestia)

I doubt if I'd be popular with herself if I went larger than a 12" driver, even that might need an awful lot of Brownie points!

My amplifier is an Arcam 38 and I listen mainly to classical music.
So what ideas do you all have on this? Feel free to encourage or rubbish me!

[matevana]

Hi Tony,

A few folks are building the Hestia V Dome project. It exploits the wide range capabilities of the 3" Seas MU10RB-SL and augments the part of the spectrum where this driver starts to peter-out. It works well at moderate volume levels and would be an easy load for your Arcam.  The largest driver is 10" in diameter, but actually looks a bit smallish because it is rear mounted. This helps with the acceptance factor! A ready made baffle and stand are available at a nominal cost to give you that completed project look. (The parts are CNC cut and milled on maple veneered plywood). You can choose to build the top section only (as several have) and opt to add a single or dual LF cabinet at a later time, only if desired.

Even w/o the LF section it is very balanced, clear and transparent. In this configuration, it excels in classical quartets, small orchestral pieces, and acoustic jazz. 

[tonytopshed]

Thanks. Can you explain please how an amplifier's power output (rms) interacts with a speaker's? The Arcam is 100W (per channel I think) the 10" B102 is 200W. Is that what it can take, or does it mean it would never run at maximum volume from the Arcam? Then what is the situation with a speaker of less power than the amp? The Hestia has 4 speakers (I don't suppose the tweeter takes much power); how many speakers can you have in one channel before an amp lies on its back with feet in the air crying "enough, enough!"?

You can see how little I know! - If I knew a little of the little you know I'd know a little!

I've been attracted by the Jordan Eikona, it seems to be well regarded. Despite its price is it worthy of consideration? I know MJK used it with the Eminence 15" - I'm hoping to keep the width of the baffle down to Hestia proportions though.

Being in the UK I feel that I'd be better to build my own version than import the Hestia components, postage and tax can be quite expensive!

[matevana]

Perhaps of greater importance is the load that any speaker system presents to an amp, and the relative ease in which that amp will drive the speaker. This is a factor of the combined impedance of the drivers that make up the system, as well as the impedance "swing" over the speakers operating range. While you can typically combine as many drivers as practical and maintain an average load (8 or 4 ohms), it is a bit harder to manage the stability of the impedance. A well designed crossover can help. A speaker that is said to present an "easy load", is one that generally will tax an amp less, and will afford greater power on-hand for response to transients in the music, etc. When the drivers have a high combined sensitivity, they will also play louder at the same RMS output from your amp, compared to drivers that are less sensitive.

RMS power is somewhat less useful in the example you mentioned, in my opinion.

Hope this helps.     

[tonytopshed]

Thanks, I'll digest that.
 I've been looking for a 10" available in the UK to go with a full range, basing my plan on the Hestia OB series. I came across the Faital Pro 10 FE 200 A; would this be a suitable candidate to get me started?

24 cm bass-midrange driver with paper cone. •power handling (continuous/programme) = 150/300 W
•frequency range = 50-4000 Hz
•resonance frequency fs = 55 Hz
•impedance R = 8 Ohm
•DC resistance Re = 5,9 Ohm
•force factor BL = 8,2 N/A
•voice coil inductance L = 0,42 mH
•effective piston radiating area Sd = 332 cm2
•effective mechanical mass incl. air load mms = 24,5 g
•equivalent volume of compliance Vas = 53,4 l
•total Q factor Qts = 0,69 (Qms=11,3, Qes=0,74)
•voice coil diameter = 37 mm
•maximum peak linear excursion vibration xlin = +/- 4,67 mm
•mounting diameter d = 233,8 mm
•overall diameter d = 256,8 mm
•mounting depth (not countersunk) t = 102 mm

•mass m = 2,2 kg

They're asking for 57.80 Euros (plus shipping) which seems reasonable. I've uploaded the FR gragh

[matevana]

Pro sound drivers can be hit or miss for OB in home audio, even when their T/S parameters appear to be quite good. For example, the priorities for many pro sound manufacturers can be different, and include things like material choices that stand up to moisture and extreme temps.  As a result the cones and suspensions are often very stiff and can emit mechanical noises, especially in the nearfield. While this isn't much of a concern in an enclosed PA cabinet, it can be very distracting to the home OB enthusiast.

I once had a pair of B&C 10" neo drivers. They were fairly expensive, had great specs and the build quality appeared to be first rate. But the motors were noisy and could easily be heard above the music during softer passages. I sold them to someone who put them in a ported box and absolutely loved them. 

If you can somehow listen to them first, I would highly recommend it. 

[tonytopshed]

I e-mailed Faital this morning and asked them  if there is any motor noise at low volumes of music. The (prompt) reply is -" The 10FE200’s motor has no cooling holes in it and is totally sealed, therefore we do not expect any noise to come from the motor itself."

Does this answer the question?

[matevana]

That sounds like a good endorsement. A bit unusual that neither the magnet nor the spider isn't vented when trying to deal with heat in a pro sound environment, but for home OB heat isn't much of a concern. There's a customer review on the PE site and he/she seemed to like them.

[ThePriest]

Hi Tony,
I also started building OB's, inspired by Matevanas Hestia OB.
Infound out that you can order the MCM 55-2981 from farnell uk. They will then send it from their Newark storage, but delivery was quite fast.

Good luck with your project.

Regards,

ThePriest

[tonytopshed]

I'm going to try the Faitals and see (hear?) what happens. After all, it's all about having fun in investigations!

[tonytopshed]

Trying to get my head around crossovers! A second order XO has a roll off of 12db with an inductance and a capacitor. At 400Hz L= 4.5, C =35 (Butterworth, from an online calculator). I understand that without the cap it's a first order (different L). What would be the effect without an inductance? Just the parallel cap on its own?

Also - I bi-wire my present two way speaker, one to tweeter, one to woofer. What do we do in a 3 way set-up with one amplifier? Tweeter & mid on one wire, bass on the other? Or mid & bass together?

[JohnR]

What would be the effect without an inductance? Just the parallel cap on its own?

That would not be a good idea, as it will present a short-circuit to the amp at high frequencies and could damage it. (And at low frequencies, it will do nothing.) You always need something in series with the driver in a crossover.

[matevana]

And if you combine that parallel capacitor with an inductor (parallel LC combination) you wind up with a "tank" circuit which can be a very useful filter. The tank circuit will have a lot of impedance at resonance, allowing the signal to get to the load with minimal attenuation. Under or over resonant frequency, however, the tank circuit will have a low impedance, shorting out the signal and dropping most of it across the circuits resistance (i.e., voice coil of a woofer).

[tonytopshed]

Ah, yes ...Which is how a high pass works. What I was really in the back of my mind, was, with the inductor fixed, what's the effect of varying the cap?

[JohnR]

It will "stagger" the crossover, so you get a first order rolloff which then becomes steeper. It can be useful for tweaking the response. (That's making it smaller - making it too much larger isn't a good idea for basically the reason mentioned before, the impedance as seen by the amplifier will drop.)

[tonytopshed]

Here are some pics of my trial OB; the laminate flooring looks better than plain mdf! I've no idea what the speaker TS parameters are, they and the crossover are straight out of my old TL speakers. The best sounding variant is the wide one with 3 boards.

[Russell Dawkins]

The best sounding variant is the wide one with 3 boards.

Shades of the PHY open baffle design:
http://www.phy-hp.com/openbaffle.html

[mcgsxr]

Looks like fun experimentation!

I might be tempted to try an angle across the top of the baffle, it helps to spread the frequencies where the driver is affected by edge diffraction.

I'd try a mildly smaller inner wing too, might help with imaging.

Good fun!