How does a Trace Bright Box Work Impedence wise?

[Delberthot]

I'm about to take delivery of some nice old Trace items but there's one thing I've never been able to work out or find an answer to-

If I am running an amp that is designed to go down to 4 ohms with either 2 8 ohm speakers or 1 4ohm one, how is it possible then to be able to add a Trace Bright Box or 4052h without melting the amp?

I know that you can but I don't understand the technicallities of it. It took me long enough to get to grips with ohms so can't work out why I am able to add another speaker box without doing harm to my amp.

[martinbass7750]

[quote name='Delberthot' post='807958' date='Apr 16 2010, 06:55 AM']I'm about to take delivery of some nice old Trace items but there's one thing I've never been able to work out or find an answer to-

If I am running an amp that is designed to go down to 4 ohms with either 2 8 ohm speakers or 1 4ohm one, how is it possible then to be able to add a Trace Bright Box or 4052h without melting the amp?

I know that you can but I don't understand the technicallities of it. It took me long enough to get to grips with ohms so can't work out why I am able to add another speaker box without doing harm to my amp.[/quote]


I haven't been able to find a spec for the bright box, but I suspect it has a built in AC coupled high pass filter which presents a high impedance at all frequencies except those that the bright box shoves out (i.e. high frequencies), and infinity at DC.

It's impendace for most of the frequency range is then much higher than the speaker cab so can be ignored.

That's my guess anyway!

[Phil Starr]

Not sure of the details of the bright box but any cab with a crossover built in should have the effect of not increasing the impedance. Basically it splits the signal so some only goes to the bottom cab and some goes to the bright box.

I think in fact the Bright Box has a high pass filter, which is half a crossover. This usually consists of a capacitor in series with the speakers. This has an impedance the same as the speaker at the crossover frequency and it rises as you get to lower frequencies so that at really low frequencies the impedance is very high and the speaker passes no current.

At higher frequencies most speakers including your 1x15 will have a rising impedance curve. An 8 ohm speaker is only roughly 8 ohms and only at the bottom of its frequency range. at the crossover frequency it may well already be 16 ohms so bringing in an extra speaker at this point will leave the overall impedance back to 8ohms.

As I say this is all theory, I couldn't find anything about the technical details of the bright box only that they are very desireable items. You've done well to get hold of one.

[crez5150]

I had a bright box which was an 8ohm impedance. I just linked it like an extension cab. Obviously had a filter inside though.

[27 frets]

From my understanding of impedences of different speakers etc across the frequency range, Phil Starr (above) gives a pretty accurate description, i.e that the impedence only drops to the 8 ohms at high frequencies due towhatever circuitry there is in the bright box, and the characteristics of the high frequency drivers themselves, whereas the impedence of the main speaker rises at high frequencies.

Same applies if you add a piezo-electric tweeter to a speaker system, though with that an attenuating resistor would usually be added too.

[Bloodaxe]

[quote name='Delberthot' post='807958' date='Apr 16 2010, 06:55 AM']If I am running an amp that is designed to go down to 4 ohms with either 2 8 ohm speakers or 1 4ohm one, how is it possible then to be able to add a Trace Bright Box or 4052h without melting the amp?[/quote]
Google turfed up a fair bit of Trace Elliot bumf...

Exhibit A: A not-very-good-resolution jpeg scan of the [url="http://www.quicksound.co.uk/articles/trace_elliot/images/16.jpg"]back page[/url] of an [url="http://www.quicksound.co.uk/articles/trace_elliot/index.shtml"]'80s TE Brochure[/url]. It's just legible & gives the following about the 4052H:

Power: 200W NOMINAL
Impedance: 8 Ohms NOMINAL

Exhibit B however, a [url="http://www.britishaudioservice.com/inst/V-Type.pdf"]V-Type Manual[/url], has the following on Page 6:

(my italics)

[quote][b]LOUDSPEAKER CABINETS[/b]

The high end frequency response of any system can be further improved by
the addition of either a high frequency horn unit or a 4052H "Bright Box"
These should be connected to the jack sockets on the cabinets or the jacks on
the combo or amp lead. [i][b]The impedance of these high frequency units can be
ignored as they have internal crossovers.[/b][/i][/quote]

Exhibit C: Page 23 of the [url="http://mail.foretold.nl/foretold/equipment/GP12SMX.pdf"]SMX Range Manual[/url]

[quote][b]Adding a high frequency horn unit or 4052H “Bright Box”[/b]
If you wish to improve the high end frequency response of your system, simply add one of either of these models and
connect one of the jack sockets on your full range cabinet. [i][b]You can ignore the impedance of the HF horn or the 4052H[/b][/i],
which means you can use them in addition to two cabinets already connected to the output stage of any TRACE ELLIOT
bass amplifier.
You can also add one of these units to a combo amplifier by connecting it to the combo extension speaker output
(N.B. except the 715, BLX80 and BLX150 models which have no extension speaker facility).[/quote]

So there you have it... it's 8 Ohms but Trace Elliot say you can disregard it.

Pete.

[Delberthot]

Fantastic - thanks for that.

So if it all goes up in a ploom of smoke then I can blame Trace Elliot cos they said it was alright?