B&C speaker builds some common questions

Masis Ingilizian

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I am new to this forum but I do get around. I am really keen to build the B&C speaker suggestion on their website, great drivers but not much information about the design concept. I found some info on this forum with Bennet providing some great info and mentioning he was ready to help, hopefully he chimes in. So I thought ill post my questions here and perhaps I can get a response.

To be honest, I will be using them for home hifi and looking for narrow dispersion speakers. I am also keen on dynamics and a massive punch and slam for the 12 inches and the compression driver. There are no polar plots with the speaker suggestions which is disappointing and we don't even get the crossover point.

My biggest worry is the transient response, the drivers for the F122A and the F122AN are made for a ported design but I hate the transients on a ported design. Can someone tell me how these two will fair compared to a closed box at around .5 QTC...? Ultimately, can I tweak it in any way to improve the transients response down low or is it already designed with a SBB4 alignment in mind...?

I am also guessing the cabinet is designed for PA use so a tweak in the cabinet design won't effect the overall sound of the speaker if the volume is kept and the same baffle dimensions?

Any other info about a smooth response or B&C drivers that have a non fatiguing response for home listening or any options recommended for DIY designs will be greatly appreciated.
 
Oct 25, 2018
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Bideford, Devon. UK
Hi there, and welcome,

The only part of your post I can comment upon through experience is the bass end. I too build my speakers for optimum transient response and dynamic headroom, and similarly dislike the sloppy and muddled sound of ported enclosures. I was lucky enough to find six B&C 18PZB100 drivers for a bargain price, and being on a very tight budget was not overly worried about their suitability for sealed enclosures. The sealed enclosures I built were heavily damped with a design Qtc of 0.5, and ignoring the ridiculously low efficiency and massive EQ required, I could not be more pleased with them - far and away the best sounding subs I've built by a long margin, and I've built a few different types! (I did build a prototype ported enclosure to a B&C design using the same driver to compare with the sealed, and listened to it for 10 minutes before removing the driver and recycling the enclosure, it was that bad...).
A very good test is twin pedal bass drum, such as used by Metallica et al, where each impact can be heard as a distinctly separate event instead of the blurred phhhhhtttttttt you hear from ported and horn enclosures. Research the transient decay times of different enclosure types and the reason becomes obvious - typically 5-10ms of ringing compared with over 100ms for a large ported or horn enclosure on step response measurement. Yes, deep and extremely clean bass is possible, but even with three 2kW amps each driving a pair of sealed 18s it's still not very loud in PA terms, however quality and transient response were my goal and I am happy to have achieved this. I don't think it's confirmation bias on my part as others have commented very positively too. Bear in mind, however, that they are crossed over at 120Hz so you must find some way to satisfy yourself that the 12s you choose will be suitable up to a higher frequency. An active crossover and EQ are, of course, obligatory.
I see no reason why a pair of 12" sealed drivers should not be sufficient for home use unless you have a penchant for Genesis or the church organ, when you will run out of steam on Moog Taurus/pedalboard pipe low-end! If you could stretch to trying BMS drivers they specify and measure really well, but I have never been able to afford them myself.

My mantra for bass reproduction is: "Move a lot of air - GENTLY" and no decent-sounding system I have ever heard has broken this rule; small drivers flapping around to Xmax and beyond do not clean bass make...

All the best and keep us posted with your project.
Stay safe, Carl
 

Bennett Prescott

Just This Guy, You Know?
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Jan 10, 2011
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Hey Masis,

Fun that you're thinking of building our suggested designs! FYI we have some new ones coming, but they will also be ported so perhaps not any more interesting or relevant to you.

It's hard to give advice on punch and smooth response without a bit of context. I think ported designs get a bad rap for being ringy or "slow", when this is more often a consequence of cabinet design than some inherent flaw in ported designs. A sealed design can be made very resonant as well, just make the box large - as many designers do in order to get flat sensitivity response in the low frequencies. Basically the big box spreads the low frequency energy way out in time, and when the frequency response is taken all that energy is integrated into one graph and makes the graph look flat. In reality it's not so flat, but it does go on a long time...

We don't design transducers to have flat response and I don't suggest designing cabinets to have a flat response, unprocessed. That is full of tradeoffs that mostly reduce sound quality and durability. If you use a driver with a strong motor, in a small box, with higher port tuning, you will have all the impact and tight sound you want - because the system is not very resonant (e.g. it is low-Q). Maybe my presentation on transducer design goals below could be helpful. Also linked from my personal website: 7.1MB PDF
 

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Masis Ingilizian

New member
Jun 1, 2020
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The sealed enclosures I built were heavily damped with a design Qtc of 0.5, and ignoring the ridiculously low efficiency and massive EQ required, I could not be more pleased with them - far and away the best sounding subs I've built by a long margin, and I've built a few different types! (I did build a prototype ported enclosure to a B&C design using the same driver to compare with the sealed, and listened to it for 10 minutes before removing the driver and recycling the enclosure, it was that bad...).
Yes, but the B&C suggested design only plays to 100hz approximately so the roll off will be different hence the transients should be significantly better as the lower frequencies are not being played. I totally agree with you in general my subs are closed and their great and I will be crossing them over with the B&C designs. But I am just not a 100% convinced on the intransigents with the B&C design.

I see no reason why a pair of 12" sealed drivers should not be sufficient for home use unless you have a penchant for Genesis or the church organ, when you will run out of steam on Moog Taurus/pedalboard pipe low-end! If you could stretch to trying BMS drivers they specify and measure really well, but I have never been able to afford them myself.
I am not looking for an extremely low end as my subs will take over. The drivers seem very good so they should be good for home use.
 

Masis Ingilizian

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Jun 1, 2020
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Hey Bennet,

Really appreciate you getting to this. Its a pity there isn't much info on these designs. My local music shop is a dealer for B&C and I would like to build these designs to show off B&C in general in the country I live in.

Fun that you're thinking of building our suggested designs! FYI we have some new ones coming, but they will also be ported so perhaps not any more interesting or relevant to you.
If you think the new designs are an improvement then please let me know about them? When they are coming out and where to find the designs? I am not totally against ported just that I am suspicious of them as they are built for the trade offs that I am quite fond of. I am well aware that ported designs can be great, just need reassurance that these particular designs have an alignment that is transient and are void of slow bosomy bass and if not can I tweak them?

It's hard to give advice on punch and smooth response without a bit of context. I think ported designs get a bad rap for being ringy or "slow", when this is more often a consequence of cabinet design than some inherent flaw in ported designs.
When you say cabinet design you mean the overall design such as volume or the actual shape?


A sealed design can be made very resonant as well, just make the box large - as many designers do in order to get flat sensitivity response in the low frequencies. Basically the big box spreads the low frequency energy way out in time, and when the frequency response is taken all that energy is integrated into one graph and makes the graph look flat. In reality it's not so flat, but it does go on a long time...
I'm really not after a flat response, I have dual subs that can take anything from about 160hz and down, plus I have DSP(audiolense) so I can tweak the frequency curve. I am aware I can make the box bigger which is what I usually do but in this case both the drivers of the F122A and the F122AN are specifically for ported designs so I am guessing its best to stick to the specific design given...?

We don't design transducers to have flat response and I don't suggest designing cabinets to have a flat response, unprocessed. That is full of tradeoffs that mostly reduce sound quality and durability. If you use a driver with a strong motor, in a small box, with higher port tuning, you will have all the impact and tight sound you want - because the system is not very resonant (e.g. it is low-Q). Maybe my presentation on transducer design goals below could be helpful. Also linked from my personal website: 7.1MB PDF
https://bennettprescott.com/downloads/TechTalk_Design_202002.pdf

Thank you I will take a look at the PDF and understand the concepts better. In saying that, now that you understand my design priorities would you recommend the F122A or teh F122AN? Or do you have a better design in mind...? Or is it possible to tweak them.

Overall your opinion would be greatly appreciated and if you can point me in the right direction I would be very happy to utilise B&C drivers with a potential of using them for a high end surround system infuture.

PS. Any polar plots with the suggested designs?
 

Stef Smits

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Apr 4, 2017
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I have build the F122AN (with some adjustments here and there) and it does have good impact.
Main problem I found out is the port placement, you will have more problems regarding wall reflections of the back.
Putting some acoustic foam behind the 12" will help but space is limited. For the rest, I used the DE800 (instead of 820TN) and did not use the light bulbs for HF driver protection.
 
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Bennett Prescott

Just This Guy, You Know?
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If you think the new designs are an improvement then please let me know about them?
We'll have them on the website as soon as they're ready, they're completely new designs and a little more comprehensive including active DSP settings. The current designs are perfectly good but require some interpretation, and don't highlight our latest components.

I am well aware that ported designs can be great, just need reassurance that these particular designs have an alignment that is transient and are void of slow bosomy bass and if not can I tweak them? ... When you say cabinet design you mean the overall design such as volume or the actual shape?
Honestly I don't know, I've never heard the designs on the website... and won't hear the new ones before they're released either! Both were designed by an outside consultant, we are not cabinet designers for sure. If you're going to tweak them it seems less important to use our designs in the first place, I think.

...now that you understand my design priorities would you recommend the F122A or the F122AN? Or do you have a better design in mind...? Or is it possible to tweak them.
They're the same cabinet with different components. I would use the best components you can afford, especially in a sealed design where you don't have to worry about port velocity. Personally I would use the 12NDL88 and DE880TN or DE980TN, whichever you can lay your hands on!

P.S. Any polar plots with the suggested designs?
Unfortunately not with the current ones. I'll ask if we can include them with the new ones but it's pretty much up to the horn above crossover, and the face size of the cabinet below...
 
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Masis Ingilizian

New member
Jun 1, 2020
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Australia
I have build the F122AN (with some adjustments here and there) and it does have good impact.
Main problem I found out is the port placement, you will have more problems regarding wall reflections of the back.
Putting some acoustic foam behind the 12" will help but space is limited. For the rest, I used the DE800 (instead of 820TN) and did not use the light bulbs for HF driver protection.
Please tell me more...? Have you listened to much horn type large woofer style speakers? How does it compare? Any fatigue while listening...?

I am presuming you used active crossovers hence why you chose different drivers or did you tweak the passive crossover?
 

Stef Smits

Freshman
Apr 4, 2017
57
12
8
The F122AN was my first top I have build, so I was in deep waters.
I build the same crossover but without the HF-protection bulbs.

I have gotten those DE800's because I could get them at a really good price at the time. Furthermore, I would say the 800 and 820 are comparable to each other. Eventually I just build the passive XO and tested, results where good enough so I build the second one. I have some REW traces somewhere but it would take some searching.

Regarding sound:
-I have some experience with other cabinets, but not that much that I can give a 'true' comparison.
-When flat (with DSP) I always like some less 3/4k, however, that's my preference with almost all cabs.
-One other plus is the good speech intelligibility.

PS: these are probably for sale in the coming time due to new projects. But, not because they are not good enough ;)