EQ'ing of main speaker bass drivers?

[Malice]

Hiya all!!

Recently I invested in a S/H Denon power amp to biamp my front speakers. Really pleased with the result. On the whole.

To summarise the "issue" I am trying to solve, I had accidentally left the PAMP turned off when listening to some multi-channel music with low bass content and my AV set to EXT-IN with Pure Direct, i.e. no bass management at play. To my surprise I found that the bass sounded tighter than with the PAMP in play. This is perhaps not too surprising given that without bass management my main speakers are producing 90db @ 26Hz on a 75db sweep in REW.

Anyway, as I have to take my mains pre-out to power the PAMP for the bass drivers in a biamp setup, could I introduce another BFD and use both channels to provide the same sort of EQ to my main bass drivers as I do to my sub?

Now I know there has been some concern or reservation about EQ mains frequencies, but let me explain a little about my speakers.

The B&W 604s3 have a tweeter, midrange and two bass driver units. In biwire or biamp setup, the 2 x bass drivers only are driven off the LF terminals. The tweeter and midrange are driven off the HF terminals.

The signal to the bass drivers effectively go through a crossover or high pass filter (or is that low pass, can't remember!) where the bass drivers have a 450Hz "crossover" with an 18db roll off. Now in addition to perhaps a BFD to tame the troublesome room-mode frequencies, I could also introduce a shelf filter which would mimic the roll off of the speaker at 450Hz @ 18db. In this way would I have a psuedo active crossover prior to amplification of the bass drivers? If so then that would also tend to improve the load on the power amp for bass duties only.

What do you think?


Bob

PS Sonnie, it was Floyd's DTS version of Wish You Were Here!!

[Wayne A. Pflughaupt]

Anyway, as I have to take my mains pre-out to power the PAMP for the bass drivers in a biamp setup, could I introduce another BFD and use both channels to provide the same sort of EQ to my main bass drivers as I do to my sub?

The BFD is generally thought not to be a good equalizer for the mains – the typical complaint is that it sounds “gritty.” This is probably due to its cheap AD/DA converters. However, in the application you’re describing, using it for lower mid-range and below, it might work okay. Still, I think I’d be inclined to use a better quality equalizer. I wouldn’t be too thrilled about having another analog to digital conversion either.

I could also introduce a shelf filter which would mimic the roll off of the speaker at 450Hz @ 18db. In this way would I have a psuedo active crossover prior to amplification of the bass drivers? If so then that would also tend to improve the load on the power amp for bass duties only.

Probably not a good idea to use the shelving. Let the speaker’s crossover to their job.

Regards,
Wayne

[Malice]

Thanks for the input Wayne

Wayne A. Pflughaupt wrote:

Still, I think I’d be inclined to use a better quality equalizer. I wouldn’t be too thrilled about having another analog to digital conversion either.

As we're talking only about 450Hz and below, the "A2D" will be no different to the extra A2D on the sub side. What EQ would you suggest?

Probably not a good idea to use the shelving. Let the speaker’s crossover to their job.

Regards,
Wayne

I think the penny has dropped! If I introduce a lesser rolloff say -16db from the 450Hz point, it will be added to by the speaker crossover where they overlap! Not a good idea. Can you suggest I way how I could prevent the higher frequencies even getting to the amp? Would say 2 octaves above the 450Hz would be a reasonable area to introduce a sharp shelf filter, round about 1.8kHz? Dunno really.

[terry j]

Hi bob

450 hz is rather high perhaps for the bfd, and according to all reports may not be clean enough up there (never experienced on myself).

Not really sure what PAMP is...Power AMP??

Personally, I would be very comfortable in using the DEQ in this situation, it is considerably more expensive than the BFD but to my ears does sound pretty clean and carries a heck of a lot more power.

I was going to do some test's on it earlier, indeed Wayne suggested what type of test's I could run on it for everyone, don't recall where to find his suggestions now!!

Wiyhout fully understanding your setup yet, I would put it between the pre and the bass amp and imply integrate it by using REW sweeps.

As Wayne mentioned though, perhaps the only sticking point could be that all the processing is done in the digital domain, so would have extra ad/da conversions in the bass only, which may even introduce some sort of processing delay between the bass and mid/highs, which nay not be ideal.

The only alternative to that might be to run the entire signal thru the unit (digital in), avoiding a un-needed extra conversion and controlling the bass response that way.

I perhaps wouldn't put this unit on a $6000 pair of speakers, but feel reasonably confident that the gains on anything else would outweigh the negatives.

If I can answer any questions I would be glad to,assuming of course that you may want to investigate further.

[Malice]

Thanks Terry.

Yeah, PAMP is Power Amplifier. 'Fraid old habits die hard...... playing online Quake 2 capture the flag has some "power ups" like speed, shields, health and the last one was a power amplifier, or PAMP in short for the players to communicate who had what in the team!

Bob

[Wayne A. Pflughaupt]

Malice wrote:

As we're talking only about 450Hz and below, the "A2D" will be no different to the extra A2D on the sub side.

Hopefully, but since 450 Hz is way higher than a sub operates, I’d for sure do some A/B comparisons before I’d pronounce it untainted.

What EQ would you suggest?

A Rane PE-17 is probably all you need for this application.

Can you suggest I way how I could prevent the higher frequencies even getting to the amp? Would say 2 octaves above the 450Hz would be a reasonable area to introduce a sharp shelf filter, round about 1.8kHz? Dunno really.

I don’t know why you would want to do that. The speakers’ crossover is going to take care of all that. Besides, the BFD doesn’t shelve, and I doubt you’re going to find an analog EQ that will shelve all the way up to 450 Hz, much less an octave or two above. If you really want to do this, get an electronic crossover.

Backing the boat up a bit:

If so then [shelving response] would also tend to improve the load on the power amp for bass duties only.

Hardly an issue, unless it’s a really low-powered amp, or you listen to music at the same levels you do movies.

Regards,
Wayne

[Wayne A. Pflughaupt]

terry j wrote:

I was going to do some test's on it earlier, indeed Wayne suggested what type of test's I could run on it for everyone, don't recall where to find his suggestions now!!

A broadband pink noise source will usually do it, as long as the EQ has full bypass capabilities. With the EQ set to flat, if you hear any tonal or timbre changes when you switch it in, it’s not passing a clean (read neutral) signal.

Regards,
Wayne