[Bumpy]

I have a pair of these arriving shortly. Does anyone have any tips on their installation in Open Baffles. I am hoping to substitute them as the 8" driver in my current OBs and obviously dispense with the tweeter.

[Bumpy]

Just arrived and really looking the part. The last full range drivers I owned were Lowther DX4s - these look in a different league. Engineering and finish is superb.

Will try to get them connected this afternoon.

[Bumpy]

Now mounted in my baffles.  Its nice to chat.

[Russell Dawkins]

I'm interested in your first listening impressions. Are you high-passing them or running them full range—could you give some crossover details for both the Cubes and the bass driver, please?

[Bumpy]

I'm interested in your first listening impressions. Are you high-passing them or running them full range—could you give some crossover details for both the Cubes and the bass driver, please?

Hi Russell
With these drivers I broke one of my Golden Rules never to buy anything Hi fi unless I auditioned it. Neither do I trust reviews that say things like "These are the best I have ever heard"

But this turned out to be a better product than I could ever have hoped for. I have posted before about other drivers that I had set out to improve on and they did just that.

I am running them full range as intended. I see no need to have a high pass filter unless the driver that sits below can improve on the sound quality in the frequency region you have crossed to.

I am still in the installation phase, but hope to bring the 15" drivers up to just kiss the FC8s. My starting point will be 300Hz using a second order Butterworth low pass of quality single inductor and capacitor.

Until then I am quite happy to run the FC8s as full range drivers.

[matevana]

How do you plan to attenuate the FC8's when matching the level to the 15" drivers that will be crossed at 300Hz?

[Bumpy]

I am not planning to attenuate the FC8s at all - why compromise the SQ?

The bass drivers are 8 ohm and very efficient at 98dB, the FC8s are about 92 dB so in open baffle the volume match is not bad. All speakers are a compromise and this is mine. Others put the bass drivers in boxes or drive them by a second amp or use DSP. I have tried all this and have settled for the sound I get now.

My only concession at present is an REL sub who's output is turned to give a low pass at 40Hz. This gives a firm foundation to the system.

[matevana]

Your assumption is off.  The 98dB you refer to is average sensitivity across the woofer's usable response, and that driver is designed to play higher than most. Adding a 6mH coil and 48uF cap (Butterworth alignment) will likely result in output closer to 88dB @ 300Hz and significantly less below that. I personally think your starting point of 300Hz/2nd order electrical is too high for what you are looking to accomplish. 

An all passive design like this would likely benefit from a steeper/lower xo, which would further necessitate the FC8's attenuation. There are ways to accomplish this without seriously degrading the FC8's SQ.   

[Bumpy]

Your assumption is off.  The 98dB you refer to is average sensitivity across the woofer's usable response, and that driver is designed to play higher than most. Adding a 6mH coil and 48uF cap (Butterworth alignment) will likely result in output closer to 88dB @ 300Hz and significantly less below that. I personally think your starting point of 300Hz/2nd order electrical is too high for what you are looking to accomplish. 

An all passive design like this would likely benefit from a steeper/lower xo, which would further necessitate the FC8's attenuation. There are ways to accomplish this without seriously degrading the FC8's SQ.

Thanks M. I'm always happy to hear constructive comments. I am far from an expert and keen to learn

I will take some frequency sweep measurements to determine where the FC8 runs out of output - would you like to hesitate a guess at what frequency this may be

Equally can you direct me to 'off the shelf' or components to build the quality attenuator for the FC8

[matevana]

From the photos I'm guessing your baffles are about 20" wide? (51 cm).  As a starting point I might try 150Hz 2nd order or 300Hz 4th order.

Regarding driver matching, I use an inexpensive 8 ohm potentiometer (rotary speaker level control) for testing purposes. Once I get the full range driver dialed-in exactly, I use a multimeter to measure the resistance for each of the two potentiometer legs. I then order fixed value audio grade resistors with the same values as tested, and build a simple l-pad circuit.  Be sure to do this last, after your woofer's crossover value has been determined and the other crossover components have been selected.

I like repeating this process several times over a few days and recording the measured resistance values. I then usually average my results for each resistor. 

For full range drivers of the highest caliber, I would recommend Duelund silver/graphite cast resistors.  They are absolutely transparent and will not detract at all. If these are a bit pricey, Mundorf M-Resist Supreme resistors make for a more affordable alternative and are about 80% as good. I wouldn't recommend anything less if you plan to run your FC8s wide-open.  Just remember that future changes to crossover components will likely require new resistor values. 

[Bumpy]

Thanks so much M. Spot on advice.

Those Duelund look good, but as you advise I must make sure I have the right values before splashing out.

You've got me thinking, so I am also going back to the alternative and revisiting going active on the Altec and looking again at the low pass. I have a choice of two amps that may suit namely a 35 watt A/B and a 1000W Class D.  This should have the additional benefit of relieving my 1.8W 45 triode amps of the grunt work.

[matevana]

Great.  Just a word of caution about the Altecs being driven by a 1000 watt class-D amp. Popular Altec woofers like the 416 and 515 used in VOTT applications were essentially woofers designed for horn enclosures (often in multiples). Due to the enclosure, they were very efficient in their day and driven by low powered amplifiers, even in movie theatre settings.

Because they are not high excursion modern-day woofers, they may lack the geometry necessary for open baffles... depending on your listening level. At the same time they are also very stiff. Because of this, you may notice very little cone movement when they play... but are still subject to damage with excessive power.

Their strength is in their ability to play higher than most traditional 15" woofers. They were often crossed at 800Hz, which would not coincide with your stated goals.     
 

[Bumpy]

Great.  Just a word of caution about the Altecs being driven by a 1000 watt class-D amp. Popular Altec woofers like the 416 and 515 used in VOTT applications were essentially woofers designed for horn enclosures (often in multiples). Due to the enclosure, they were very efficient in their day and driven by low powered amplifiers, even in movie theatre settings.

Because they are not high excursion modern-day woofers, they may lack the geometry necessary for open baffles... depending on your listening level. At the same time they are also very stiff. Because of this, you may notice very little cone movement when they play... but are still subject to damage with excessive power.

Their strength is in their ability to play higher than most traditional 15" woofers. They were often crossed at 800Hz, which would not coincide with your stated goals.   

Thanks M. I've picked up on this from previous postings on here, but you have summarised it perfectly. You are right that there is almost imperceptible cone movement and it was a bit tongue in cheek talking about the 1000W amp. If damaged they would be almost irreplaceable (8ohm version).  I listen at modest levels up to about 70dB

I did buy a pair of Eminence Alpha 15a drivers for experimentation but they were poor SQ compared to the Altecs and went back in the box. Maybe this was because of the higher frequencies they were being asked to cover with my previous Saba Greencones midrangers.

Interestingly if I'm now targeting low pass around 200 Hz they may come back into play. Any comments on this or other 15" suggestions for this sub 200 Hz duty.

I know cost isn't everything, but it seems a bit incongruous pairing the 'cheap' Alphas with the Cube Audio FC8s

Thanks again, your help is proving invaluable.

[matevana]

Have you ever heard your Altecs in a proper cabinet?  They can sound VERY good. Although I like open baffle bass, I find it sometimes easier to integrate woofers in sealed or ported boxes with open baffle full range drivers. They also load the room differently and can be more satisfying depending on your design goals. You also get the added advantage of higher efficiency, which could make the difference between a single amp design vs active woofers. 

With the combination of drivers and amps that you own, I would be tempted to try the FC8s full range, open baffle, with the Altecs in their own proper cabinets. They are just not the best design choice for OB, generally speaking.     

[alaska_grown]

Curious about how these speakers made out for you. Still using as OB? Any changes to your set-up?

[Bumpy]

Curious about how these speakers made out for you. Still using as OB? Any changes to your set-up?

Still by far and away the best 8 inch drivers I have experienced. The added benefit is that the high frequencies are fully taken care of so no need for tweeters and high frequency crossovers. I run the FC8 full range - no crossovers, notch filters etc to degrade the sound. It reaches happily to about 200Hz in my baffles and the whizzer cones are 'invisible' unlike Lowthers (even rolled cones)

Aside from sounding real, the sound stage is very big, sometimes instrumentalists are standing beside me - its a bit unnerving at times.

Also I have recently added a First Watt B1 no gain pre amp into the mix to replace a top quality ladder passive volume control. I like it a lot. I have also upgraded the digital cable to great affect.

I continue to play with the 15" driver.

Some time ago I was told that my vintage Altec 416Bs would never give very strong bass in OBs (physics) so I took them out and experimented with Eminence Alphas including passive and active low pass filters and separate dedicated amps. I was never happy with the sound.
Recently between experiments I had taken out all crossovers, running both the Eminence and FC8s full range together, and was amazed at how sweet the system was - that's serendipity. Perhaps it was the First Watt, perhaps it was the digital cable, but I just sat and enjoyed it for over a week.
I am taking stock at present. As a scientist I broke the golden rule of making more than one change at a time, but was anxious to try out my latest purchases.  Its all good fun

Update
The Altecs are back out the cupboard, their sound quality even in open baffles leaves the Alphas for dead. Even against the stronger bass of the Alphas, quality will always win with me. My excursion into pushing a single 15" driver into the very low frequencies in OBs is over. I will find another way to achieve that.

[bladesmith]

Why not drive the woofers with a separate amp and a low pass filter...?

Or do you feel like you need a higher quality woofer to match the more expensive full range speakers you have now..?

[Bumpy]

Why not drive the woofers with a separate amp and a low pass filter...?

Or do you feel like you need a higher quality woofer to match the more expensive full range speakers you have now..?

Tried that. Of course it sounded good, but my system has sounded better.. Its not the amp, as my 15" driver, when played full range on its own full ,runs wonderfully on even a Rotel amp, so I guess its the low pass components and these varied from very high quality passive to miniDSP active. And yes I believe the low pass filter on 15" driver was 'disturbing' the 8".

One way I do the ground work on my OBs is to play each driver on its own, where possible without crossovers,. If they don't sound great on their own then those issues will persist and only be partly masked by bringing in the other driver(s). Of course another thing to consider is matching sensitivities or, at the least, you will need to add volume pots which again degrade sound. You can learn so much about your drivers by playing them individually.

[Bumpy]

Your assumption is off.  The 98dB you refer to is average sensitivity across the woofer's usable response, and that driver is designed to play higher than most. Adding a 6mH coil and 48uF cap (Butterworth alignment) will likely result in output closer to 88dB @ 300Hz and significantly less below that. I personally think your starting point of 300Hz/2nd order electrical is too high for what you are looking to accomplish. 

An all passive design like this would likely benefit from a steeper/lower xo, which would further necessitate the FC8's attenuation. There are ways to accomplish this without seriously degrading the FC8's SQ.

I am guessing that putting the Altecs in a box would once again restore the output sensitivity should it fall below what is required to match the FC8s (removal of rear cancellation waves). As you can see I am desperately trying to avoid adding any attenuation to the FC8s - its a personal preference  thing

If this is so can anyone refer me to any sites that have box volumes for the vintage Altec 416Bs. I am OK with woodwork.

[Bumpy]

The only box with Altec 418b's I could find is internal volume of 4.4 litres closed back for use with guitar.

My existing baffles and side cheeks allow a box 15" wide, 28" tall and 12" deep - internal volume 5 litres. The depth could be a variable feast up to 17" deep giving 7 litres internal volume.

The plan is to have it totally open to the rear. It will operate from say 500Hz down.

Any observations