Setting up bryston crossover FAO James Tanner

guest2521 · « **on:** 25 Feb 2006, 09:24 pm »

Hi!

I have an active PMC MB2 with Bryston custom crossovers - there seem to be three screws on each mono unit on the front panel - what does each of them do and which direction do I have to turn them for which effect?

Regards,

Nick.

James Tanner · « **Reply #1 on:** 26 Feb 2006, 01:11 pm »

Hi biovizier,

The PMC Active systems use a 10B crossover but it is a lot different than our standard 10B units. Each Crossover is setup specifically for each speaker and tested accordingly.

There are no adjustments on the PMC Electronic Crossover because all the crossover slopes on each driver, the independent speaker 'gain' settings as well as peak level adjustments on the drivers and bass management are all matched internally to the speaker.

There is no specific setting on the standard 10B-LR I can recommend because it would depend on what the internal settings are set at. The screws adjust gain on the drivers only.

Also are you sure there are 3 screws ? There should only be 2 screws on the Bryston 10B-LR and NO screws on the PMC version.

james

guest2521 · « **Reply #2 on:** 26 Feb 2006, 03:01 pm »

Yes 3 screws per xover and you can hear they affect the level - I presume because the sst bryston pro variants dont have the level pot of the st pro.

James Tanner · « **Reply #3 on:** 26 Feb 2006, 03:42 pm »

Can you post a picture - I have never seen this before - where did you get the unit?

james

James Tanner · « **Reply #4 on:** 26 Feb 2006, 04:10 pm »

Quote from: biovizier

Yes 3 screws per xover and you can hear they affect the level - I presume because the sst bryston pro variants dont have the level pot of the st pro.

The ST and SST Pro units do have Gain Controls but the gain adjustments are not used on the PMC Active Systems

james

Jon L · « **Reply #5 on:** 26 Feb 2006, 05:00 pm »

James, I just wanted to hijack the thread to thank Bryston for making the superb 10B crossover, which overall is the best I've used, and I have used many, including units costing way more.

I thought my 10B was finally dying after almost? 20 years, but a quick spray of "switch cleaner" brought it back to new life. I still wish the gain controls adjusted the woofer, not tweet/mid, but I'm sure Bryston has its reasons.

James Tanner · « **Reply #6 on:** 26 Feb 2006, 05:09 pm »

Well thank you Jon - the 10B is really unique among electronic crossovers. The 10B is a fully discrete Class A circuit topology with no IC's. You can certainly hear the difference.

james

guest2521 · « **Reply #7 on:** 26 Feb 2006, 06:51 pm »

Yes it sounds great... James shall I post the pic here or should I email to you?

James Tanner · « **Reply #8 on:** 26 Feb 2006, 06:53 pm »

Post it here.

james

guest2521 · « **Reply #9 on:** 26 Feb 2006, 10:08 pm »

James Tanner · « **Reply #10 on:** 27 Feb 2006, 01:21 pm »

Ok I see now what's up. I did not realize you had removed the front panels.

They are PMC versions of the crossovers. The far left screw is the Bass contour, the 2nd screw is the mid range gain and the right screw is the tweeter gain.

I must caution you though that any changes to these setings will alter the "accuracy" of the speaker relative to factory setup.

james

guest2521 · « **Reply #11 on:** 27 Feb 2006, 01:43 pm »

I assume the gain screws turned clockwise decrease the gain? What exactly does the bass slope screw do when turned each way?

Thanks!

Nick.

James Tanner · « **Reply #12 on:** 27 Feb 2006, 01:46 pm »

Hi Nick,

Not sure on the bass slope as that is installed by PMC depending on the system- single MB2 vs Stacked MB2 etc.

Clockwise increases gain by 1 dB per click on mid and tweeter.

james

Synergy · « **Reply #13 on:** 28 Feb 2006, 10:19 am »

Hi Nick,

I dug out the manuals for the system in question......the manual I have for the crossover is for a normal 10B so is of no use to you really. Give Andy a call at PMC....he can tell you the specs of the adjustments etc!

Regards

Mike

guest2521 · « **Reply #14 on:** 28 Feb 2006, 10:18 pm »

James,

Thanks! The active system I bought from the studio was mb2 stacked. However I am not going to use the xbd and will sell it as it is just too big. Does this mean i will need to change the treble and mid levels and also the slope? Any idea roughly how much?

Regards,

Nick.

James Tanner · « **Reply #15 on:** 28 Feb 2006, 11:35 pm »

Yes - the extra bass cabinet adds 3 dB to the low end.

james

guest2521 · « **Reply #16 on:** 1 Mar 2006, 07:42 am »

So I will need to descrease the mid and treble 3 clicks? What about the slope? Thanks!

Given that one amp is driving both xbds does it actually double the output in practice?

James Tanner · « **Reply #17 on:** 1 Mar 2006, 11:35 am »

Yes decrease the mids and tweeters 3 dB.
The slopes stay the same.

james

guest2521 · « **Reply #18 on:** 2 Mar 2006, 11:07 pm »

Thanks - and what does the slope do? Just so I can complete my understanding.

James Tanner · « **Reply #19 on:** 2 Mar 2006, 11:23 pm »

The slope is the rolloff on each driver after the crossover point - highpass and lowpass - so the woofer rolls off (low pass) at 380 Hz and the Mid rolls off (high-pass) at 380Hz as well.

That way the drivers maintain a flat frequency response and off axis even polar response through the crossover region. Slopes vary - depending on the speaker and drivers from 6db - 12db - 18db -24dB per octave generally.

james

Setting up bryston crossover FAO James Tanner

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