Visaton FR10 in Double Bass Reflex enclosure

[activexp]

I've knocked together a pair of very low cost double bass reflex enclosures from junked bedside cabinets and some sheets of tatty plywood. The design is based on a Fostex plan for the FE127 but as I'd got FR10's going spare I used them instead.

The results were encouraging as far as bottom end goes but not so for the top, rough and unpleasant. The FR10 definitely needs a tweeter for hi-fi usage . Fiddling around with BSC and notch filters didn't improve the sound much.

An externally hosted image should be here but it was not working when we last tested it.

I've done a write-up here:
https://sites.google.com/site/stevesstuffproject/doublebass

Cheers,
Steve

 

[chris661]

Hmmm...

As a thought for those drivers - have you tried taking off the dustcap with a scalpel (adding a phase plug), or removing the whizzer completely?

Visaton's 3" units seem to be better (tried both the FRS8 and FRS8M, which has greater efficiency for use as a mid-high in a 2-way).

 

[mondogenerator]

Its a pity, I have been considering the FR10s for a budget FR project, but the high end response is the fly in the ointment, otherwise, on paper at least, its looks like a fair driver.

If you do go and get a tweeter, have you considered a cheap piezo horn?

I only mention it as i was considering a hi xover type design, and i figured, maybe wrongly, that a horn would keep the sound more directional, or the polar response better, than some other options. However with the FRS8 you probably wont have that problem anyway.......lol

 

[activexp]

Hmmm...

As a thought for those drivers - have you tried taking off the dustcap with a scalpel (adding a phase plug), or removing the whizzer completely?

Visaton's 3" units seem to be better (tried both the FRS8 and FRS8M, which has greater efficiency for use as a mid-high in a 2-way).

I think I read somewhere, maybe on this forum or somewhere else about removing the whizzer from the FR10 or a similar full range driver to tame the top end. Although I'm tempted to give it a try, I'm bit nervous about taking a scalpel to it in case I slip up and damage the cone

Having said that, the phase plug is an attractive suggestion. Any idea where I can get them?

 

[activexp]

Its a pity, I have been considering the FR10s for a budget FR project, but the high end response is the fly in the ointment, otherwise, on paper at least, its looks like a fair driver.

If you do go and get a tweeter, have you considered a cheap piezo horn?

I only mention it as i was considering a hi xover type design, and i figured, maybe wrongly, that a horn would keep the sound more directional, or the polar response better, than some other options. However with the FRS8 you probably wont have that problem anyway.......lol

I've tried a very cheap Skytronic mylar tweeter with the FR10 in my mini t-lines crossed-over at 3.5K (2nd order). Results were OK, certainly an improvement on the FR10 alone but you get what you pay for and the tweeter lacks some smoothness.

Piezo horns are a grey area for me. Am I right in thinking they don't need an XO?

 

[chris661]

I think I read somewhere, maybe on this forum or somewhere else about removing the whizzer from the FR10 or a similar full range driver to tame the top end. Although I'm tempted to give it a try, I'm bit nervous about taking a scalpel to it in case I slip up and damage the cone

Don't worry about it: it's fairly easy to cut things up with scalpels, you just have to take your time with it (says the one that usually rushes and makes a mess). If cone damage occurs, apparently tissue paper and PVA glue is suitable for repairs.

Having said that, the phase plug is an attractive suggestion. Any idea where I can get them?

The voice coil is 20mm diameter. You can get lengths of 18mm dowel (or 19mm if you can find it), then:

Cut off a longer-than-needed piece (go to maybe 2"), drill a long hole down the centre (essential that it is central and straight), put a long screw in, with maybe 3/8" sticking out. Put that into the drill, so the chuck jaws just touch the wood (adds support).
Next, spin the dowel round, and use a file/sand paper to shape the wood (like a lathe, but cheaper). Be careful about burning the wood. A file would be better as it would help to act as a heatsink.

I made them using this method for my FRS8Ms, it really helped, especially in the higher frequencies.

HTH
Chris

Edit - a zobel could help, but I have no experience with them...

 

[activexp]

Thanks Chris, that's most helpful. This might be a dumb question but how are phase plugs actually mounted to the driver? Does the dust cap have to be removed?

Not sure about Zobels. I've only used them on multiway with XO's and in some speakers they've sounded better without them.

 

[chris661]

To mount them, the dust cap does need to be removed. When you've made them and cut them to length (might be an idea to make a few and try different lengths), put a 1/2" wood screw in the bottom, making sure the head is flat to the bottom of the plug. When you put it in, the speaker magnet holds it in place. Make sure there's some clearance around the plug to avoid rubbing, and you're away.

Fair enough about the Zobels.

Chris

 

[activexp]

OK got it, thanks Chris

I've now had an opportunity to try the Monacor SP60 midwoofer in place of the FR10. The results are encouraging and will post more details later.

Steve

 

[activexp]

Monacor SP-60. A contender for full-range?

More on the Monacor SP-60 midwoofer.

An externally hosted image should be here but it was not working when we last tested it.

As the description suggests, this is not a full range driver but I was surprised by the amount of top end energy, similar in many ways to the FR10 being a bit harsh and peaky.

I connected a 0.4mH coil in series to the SP-60 to give a 6db per octave roll-off from 3000Hz with the intention of adding a tweeter. This turned out to be unnecessary to my ears.

The roll-off has tamed the top end without much loss of detail at least when listening on axis. Bass performance is excellent. Overall it's a well-balanced speaker with high WAF

It might also benefit further from a phase plug.

 

[Bigun]

That's a neat looking driver.

You can adjust the response further by placing a resistor in parallel with that 0.4mH choke, try 10 Ohms and work your way down (assuming the choke has a low DCR to begin with).

p.s. I'm liking this DBR enclosure option, it might be a good option for me too (with a smaller driver).

 

[activexp]

Yes, it's a nice little driver. Some specs:

Drilled pole core
Impedance (Z) 8Ω
Resonant frequency (fs) 65Hz
Max. frequency range f3-8,000Hz
Music power 60WMAX
Power rating (P) 30WRMS
SPL (1W/1m) 90dB
Suspension compl. (Cms) 0.8mm/N
Moving mass (Mms) 4g
Mech. Q factor (Qms) 2.10
Electr. Q factor (Qes) 0.64
Total Q factor (Qts) 0.49
Equivalent volume (Vas) 6 l
DC resistance (Re) 6.5Ω
Force factor (BxL) 4.1Tm
Voice coil induct. (Le) 0.3mH
Voice coil diameter 25.5mm
Voice coil former aluminium
Linear excursion (XMAX) ±2mm
Eff. cone area (Sd) 55cm2
Magnet weight 10oz.
Weight 0.9kg

Thanks for the tip regarding adding a resistor and will give it a try. I guess it'll provide some BSC?