***Official*** Rotel RSP 1066 Fact and LOGICAL discussion thread (1 Viewer)

[Steven Phipps]

HOLY SH

T JOHN! I AGREE! Just being facetious John. But yes, it seems like a great idea, in a manner of speaking, for some, it is having your cake and eating it too. As I said, I still have to check out analog before I can comment realisticly though. Maybe tonight, who knows.
BruceD, I have sent an e-mail to Mike at Rotel with your question attached. I will wait for his reply and post it here when I receive it.

 

[Steven Phipps]

Here is the reply I got from Mike:

Got your voicemail, in regards to the subwoofer output, what your friend had proposed as to how the analog passthru works in stereo is exactly correct in that the signal is split at the input, and a full-range signal is sent straight to the analog outputs only passing through volume control for the front L/R speakers, and a second signal is sent to the ADC for conversion to digital. Then it is passed through the subwoofer crossover, then sent to

the DAC to be converted back to analog and then passed to the subwoofer output for use in 2 channel mode. If you do not wish to use the sub in 2 channel you are correct, you would need to either turn the sub off via the On Screen Display, on the sub itself, or just lower the output to minimum.

And per our conversation earlier, turning the sub off in the OSD will not prevent the split at the input, it just will not pass anything to the sub output but the signal is still split and sent to the DAC regardless.

Best Regards,

Mike Sheehan

Customer Support Specialist

This Mike guy is pretty quick to reply, kinda reminds me of the SVS guys. Anyhow BruceD, I hope that helps...

BTW Just FYI, he is answering whatever questions by schematics, or by contacting the proper sources such as designers. So far, if he has not been able to answer my questions, he says he will find out for me and usually does pretty quickly.

 

[BruceD]

Steven,

Thanks for the quick answer.

So for those with monitor or mini-monitor speakers as L&R mains and could use some bass assist on 2-channel analog sources, this is definately a viable option.

 

[Will]

I think it can be viable, but only if (mini-) monitor can handle low frequency of full range music without distortion, and if sending the same low frequency to both the subwoofer and the (mini-) monitor won't be a problem.

 

[Steven Phipps]

oops:b

 

[John Morris]

I think it can be viable, but only if (mini-) monitor can handle low frequency of full range music without distortion, and if sending the same low frequency to both the subwoofer and the (mini-) monitor won't be a problem.

Will: Good point. I would have that same concern, but then again, the user also has the choice to not use the analog bypass and instead use the Stereo mode, under which the digital crossover is used and the mini-monitors don't get a full range signal and the sub is active. So I still think that having choice of using either the analog bypass OR analog bypass + subwoofer OR stereo mode + subwoofer means that the pre-pro is suited for almost any speaker types you wanna throw at it. Does that make sense to you?

 

[BruceD]

Will,

Yes I agree, and what I forgot to say, is that it wouldn't be applicable to main speakers that are towers or monitors with good bass response. As that would tend to cause the same bass problems as multiple subwoofers -- cancellations and reinforcements of bass frequencies.

 

[Craig_Kg]

Well in that case, you'd

a) turn the subwoofer level to off,

b) turn the subwoofer crossover down to the -3dB point of the speakers or

c) set the bass redirection frequency to around the -3dB point of the speakers, wouldn't you?

 

[brian a]

Do most speakers not have high pass filters of some sort in them to keep them from playing too low a signal?

Could this new processor decision get any more tough to make?

 

[Will]

Do most speakers not have high pass filters of some sort in them to keep them from playing too low a signal?

Some do, some don't. High and low pass filters in the speaker can add distortion. That's one reason why, generally speaking, you would want the filtering to be in the digital domain (in the pre/pro) and not in the speaker. Of course if a speaker can't produce low or high frequencies, there probably does need to be a filter in the speaker as well. Subwoofers generally have filters for example, but there, since the subwoofer is powered externally, the filter can be an active analog filter rather than a passive analog filter. If a filter is going to be analog, an active analog filter generally has less phase distortion problems. Unpowered speakers if filtered, generally have passive analog filters.

Will

 

[BruceD]

brian,

I'm not aware of any direct radiating main speakers (except powered towers like Def Tech) with a high-pass filter that filters out bass, because most main speakers are designed with what is called a natural roll-off of the low frequencies from the woofer due to the sealed or ported construction of the speaker.

Most sealed speakers have a -12dB low frequency rolloff below the low frequency -3dB spec.

Ported speakers typically have a higher (steeper slope) -18dB or -24dB or higher rolloff for this same low frequency rolloff below the low frequency -3dB spec.

This effectively means they automatically reduce the bass output all by themselves without the addition of a filter.

 

[BruceD]

Craig,

Well in that case, you'd

a) turn the subwoofer level to off,

b) turn the subwoofer crossover down to the -3dB point of the speakers or

c) set the bass redirection frequency to around the -3dB point of the speakers, wouldn't you?

To expand on these a lttle more:

a) yes that would work

Having mains and sub both producing the same bass output signals at the same time is not recommended because it causes in-room frequency response anomolies.

The following comments assume a digital input to the prepro and normal bass redirection.

b) this will cause some unpredictable interference because of the double xover effect (receiver xover + sub xover). Typically you always want the sub xover turned off or set to it's highest setting.

c) You can try this, but you will find this creates a frequency response with a bass hole (loss of some bass). In most cases you should try to select a xover that is higher than the main speakers low frequency -3dB spec.

Example:

With main speakers that have a -3dB of 45Hz, the best integration with a sub will likely be obtained with a receiver bass re-direct xover somewhere between 60Hz-90Hz.

 

[Will]

Yes, and also asking a speaker to play louder bass than the speaker can handle at any frequency, even the -3dB point of the speaker, may cause the speaker to audibly distort. If really excessive, it may be bad for the woofer as well.

For example, playing 35 Hz loudly on a speaker with a -3dB point of 35 Hz may result in audible distortions. If the 35 Hz is played loudly enough, it could damage the woofer.

 

[brian a]

I guess I don't understand why speakers wouldn't protect themselves against that sort of thing with a high pass filter. Why have speakers try to reproduce a frequency that they are clearly not able to handle?

 

[Will]

Some speakers protect themselves more than others. The price of protection is distortion artifacts. Sometimes the more protection, the more distortion artifacts.

 

[Craig_Kg]

The following comments assume a digital input to the prepro and normal bass redirection.
b) this will cause some unpredictable interference because of the double xover effect (receiver xover + sub xover). Typically you always want the sub xover turned off or set to it's highest setting.
c) You can try this, but you will find this creates a frequency response with a bass hole (loss of some bass). In most cases you should try to select a xover that is higher than the main speakers low frequency -3dB spec.

I was referring to the digital direction of bass occuring in parallel to the analog bypass (which is what the original) discussion was about.
For b), I would be assuming the receiver bass direction frequency was set somewhat higher than the speakers -3dB rollof point (as is normally the case in HT setups). I was assuming that one might set the crossover frequency for the sub so it merged smoothly with the main speaker rolloff for analog use (with the understanding that you would max out or bypass the crossover for digital use to get full LFE effect).
For c), I would have assumed that the 12dB/octave filtering used by the bass direction would crossover the bass smoothly to the subwoofer (which in this case would have its crossover bypassed or maxed). Since no bass is being removed from the main speakers, the receiver would merge the bass to the sub without creating a hole.
This was mainly to demonmstrate the options that this cute feature would give us. If the 1066 had a triple crossover for bass management, then it would be the absolute honey.
As for the speaker protection issue, the analog bypass would just function like a traditional preamp so the normal amp power/speaker capability matching would be the consideration.

 

[BruceD]

Craig,
I guess what I was really trying to say is that you don't want main speakers and a sub trying to produce the same frequencies in the analog pass-thru mode (i.e. the reason for Rotel stating you can lower the volume/turn the sub off). You will never get a smooth transition.
A smooth handoff of bass to the sub is the essential purpose of a prepro's crossover, which you are not really using in the above analog+ digital bass example.
But I should also say it's up to your own ears to decide what you like.

For b), . . . . .I was assuming that one might set the crossover frequency for the sub so it merged smoothly with the main speaker rolloff for analog use

In your b) example above, the sub will likely see a -24dB slope from the sub's internal xover for the low-pass signals and your main speakers will be doing their natural rolloff at the -3dB level (maybe a -12dB or -18dB slope). These slopes will not match regardless of the frequency chosen for sub's internal xover. This just means no smooth transition is likely.
In your c) example, the sub will see a -24dB slope from the prepro for the low-pass signals and your main speakers will be doing their natural rolloff at the -3dB level (maybe a -12dB or -18dB slope). These slopes will not match regardless of the frequency chosen for the bass re-direct. This just means no smooth transition is likely.
Maybe a xover in the analog domain (I use a separate electronic xover myself) is a good idea.

 

[Craig_Kg]

But where do you get the 24dB sub and receiver rolloffs from? Is that the standard for all receivers and subs? I know THX specifies a 24dB rolloff from 80Hz upwards for subs but don't M&K have a variable frequency 12dB/octave rolloff on their subs? I think you are generalising a bit, BruceD.

 

[BruceD]

Craig,

Yes, many receivers and prepros implement a digital THX xover for the sub, which has an 80Hz -24dB slope low-pass filter (i.e reduces the output of the sub by 24dB/octave above 80Hz).

Generalizing? I'm not sure what you mean.

I know THX specifies a 24dB rolloff from 80Hz upwards for subs but don't M&K have a variable frequency 12dB/octave rolloff on their subs? I think you are generalising a bit, BruceD.

M&K sub Low-Pass Frequency xover specs:

M&K MX-105 . . . . 36dB/Octave 50Hz-125Hz

M&K MX-125 . . . . 36dB/Octave 50Hz-125Hz

M&K MX-150THX. . . 36dB/Octave 50Hz-125Hz

M&K MX-200 . . . . 36dB/Octave 50Hz-125Hz

M&K MX-350 . . . . 36dB/Octave 50Hz-125Hz

M&K MX-5000THX . . 36dB/Octave 50Hz-125Hz

M&K MX-700 . . . . 36dB/Octave 50Hz-125Hz

A 12dB/octave slope for a sub xover is not very desirable, as it will be tough to blend smoothly because it will bleed energy pretty far above the low-pass crossover frequency. It will also tend to produce an SPL bump at the xover frequerncy because it doesn't ideally counteract the rolloff of the main speakers (unless they are sealed).

 

[Craig_Kg]

Where did you get those M&K figures from?

This is from the MX350/5000THX manual:

The control is a means of fine-tuning the transition between your Subwoofer and Satellite speakers, and it provides a rolloff of 12dB/octave up to 125Hz, where the filter shifts to 36dB/octave.

Actually above 125Hz, the filter shifts to 24dB/octave but the cabinet and driver add another 12dB/octave rolloff.

Anyway, I'm not trying to argue subwoofer cutoffs. I just wanted to point out that the 1066 gives some more tuning options even when using analog pass through and that the bass needn't be compounding (your original assertion).