where to get graphed freq response for PMC speakers

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ec

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where to get graphed freq response for PMC speakers
« on: 29 Aug 2003, 01:22 am »
Where can I find graphed freq responses for PMC speakers namely the TB2?  The PMC website just says 40Hz to 40 Khz.  What I want to know is @ how much -db it is at 40Hz 45 Hz 50 Hz 55 Hz etc.  I simply just don't trust my Radio Shack SPL meter with a few sweep test CD.

Why would I want this?  I like to cross over my speakers to the sub at the lowest possible reasonable freq.  I just received the SP 1.7 firmware upgrade which will allow x-over freqs down to 25 Hz.  The current firmware on my SP 1.7 has a floor of 60 Hz.  The 60 Hz x over point sounds more cohesive to me than the "recommended" 80 Hz.

nicolasb

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where to get graphed freq response for PMC speakers
« Reply #1 on: 29 Aug 2003, 09:57 am »
As noted elsewhere on this forum, remember that for home cinema or any source which has a dedicated LFE (subwoofer) channel, you will lose everything in the LFE channel above the cross-over frequency if any of speakers are set to "Small". There isn't usually much above 80Hz, but there certainly can be between 60 and 80Hz.

Obviously this isn't an issue for (say) music CDs.

ec

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where to get graphed freq response for PMC speakers
« Reply #2 on: 29 Aug 2003, 01:49 pm »
Nicolasb

Thanks to this forum, I found the 060 code for the subwoofer on in 2 ch bypass mode.  When in this mode I tuned the the sub's freq xover by ear and the sub's gain by ear.  I want to match or approximate these settings using similar settings for 5.1 listening.  I also want to fine tune the 2 ch bypass mode sub on and the freq resp graphs should help me approximate.  Again to my ears I find the lower x-over in 5.1 material a bit more pleasing.

My understanding is that anything above the xover freq will be directed to the surround speaker and not lost if the speakers are set to small.  Naturally the surrounds have to have the ability to handle these frequencies.

nicolasb

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where to get graphed freq response for PMC speakers
« Reply #3 on: 29 Aug 2003, 04:12 pm »
You don't lose anything from the main 5 channels, you lose stuff from the LFE channel.

Subwoofer output using bass management on 5.1 or 6.1 sources works like this:

1) Mix together the LFE (subwoofer) channel and all the "Small" channels.
2) Apply a low-pass filter, i.e. throw away anything in the mixture that is above the cross-over frequency.
3) Send what's left to the subwoofer.

Then for each "Small" speaker separately:

1) Apply a high-pass filter to the original signal (i.e. throw away anything below the cross-over frequency).
2) Send what's left to the speaker.

So if you have a 5.1 recording:

- Anything in the main 5 channels intended for "Large" speakers just goes straight to the speaker.
- Anything in the main 5 channels intended for "Small" speakers that is above the cross-over frequency goes to the speaker.
- Anything in the main 5 channels intended for "Small" speakers that is below the cross-over frequency goes to the subwoofer.
- Anything in the LFE (the .1 of the 5.1) channel that is below the cross-over frequency goes the subwoofer.
- Anything in the LFE channel above the cross-over frequency is simply thrown away.

In theory the LFE channel (the .1 of the 5.1) can contain material at anything from zero to 120Hz. In practice it very rarely contains anything above 80Hz, so throwing away everything above 80Hz is not a problem. But if you set the cross-over below 80Hz then the 5 main channels still work fine, but you start to lose what's in the LFE channel.

I don't think you're going to be able to do what you want to do. I don't know how the cross-over on your subwoofer works: if it has stereo line-level inputs and high-pass line-level outputs then perhaps you could unplug the subwoofer from the SP1.7's sub output, set the subwoofer setting to "None", the front speakers to "Large", and the other speakers to "Small", then connect the subwoofer to the processor's L&R front speaker outputs and the front-channels of the power amplifier to the subwoofer outputs. This makes the SP1.7 send all of what would otherwise be the subwoofer output (both LFE and redirected bass) to the front speakers; the subwoofer then intercepts it and handles everything below your sub cross-over frequency and passes everything above it to the front speakers.

But this isn't ideal, for several reasons.

ec

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where to get graphed freq response for PMC speakers
« Reply #4 on: 29 Aug 2003, 05:32 pm »
The sub being used in a Mirage BPS400 which has no high level (ie speaker inputs) and three line level inputs via RCA.

Input #1 is for use for an external xover and gain stage. The internal x-over and gain adjustment is bypassed.

Input #2 is a stereo connection but if using only the left input, you can adjust the gain and the x-over (50 - 100 @ 24 db octive)  freq via two knobs.  This is how I have my unit hooked up

Input #3 same as # 2 but if you use both the left and right connections, the internal x-over is bypassed but the gain is available.  This scenario is designed for stereo integrated amps with pre outs according to the manual.


The way my current setup is that I have the SP1.7's unbalanced sub out to input # 2 and all the surround speakers set to small.  You are probably thinking why not use input # 1?  Using the speaker gain, actually attenuation settings on the SP 1.7 still makes the sub over powering even when the attenuation is at the max level on SP 1.7 when using input # 1 on the sub.  The only way around this to use Input # 2 on the sub and use the gain on the sub to dial it down.

Here is where it gets tricky in my scenario ....... because I recently discovered the 060 bypass code on the SP 1.7 I now can get some decent bottom end in two ch.  But using 2 ch bypass mode with the sub on option does not use any type of bass management from my understanding.  In this 2 ch with sub on mode, my understanding is that a full range signal is sent to the sub.  So I have to use the x-over on the Mirage sub to "roll in" where the PMC TB2's naturally roll off at.  I think the sub is set for 60 Hz x over or shall I say nothing above 60 Hz is outputted from the sub.  I am assuming this is where the PMC TB2's start rolling off on the bottom end at least by ear.

Since I am beginning to listen to SACD and DVD-A I use the SP 1.7's 5.1 bypass and again I believe this bypasses the bass management features of the SP 1.7 and uses those of the SACD/DVD-A player (in my case they are quite poor).

Your accurate descriptions of how bass management works apply most to movies for my scenario when using the SP 1.7.  Right now, the surrounds and sub seem to sound correctly blended and cohesive when watching movies and playing multi channel music via DTS and DD using the SP 1.7's DSP's vs the 5.1 bypass.  

The reason why I wanted the freq resp charts of the speakers is to see if I can effectively lower the x-over freq.  I ran into one small hurdle with the new firmware that won't let me change the x-over freq below 60 Hz but Bryston is correcting this for me.  I like to experiment and tweak as you can probably tell.

James Tanner

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where to get graphed freq response for PMC speakers
« Reply #5 on: 31 Aug 2003, 02:20 pm »
Hi Eric,

The quoted frequency response with PMC is the -3dB point. One thing to remember though is that transmission line speakers roll-off at 6dB per octave rather than the 24dB per octave of ported systems - so you have much more usable bass response with a transmission line speaker.

james

ec

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where to get graphed freq response for PMC speakers
« Reply #6 on: 31 Aug 2003, 03:49 pm »
James thanks for the info.  I will start experimenting again next week.  Have a good long weekend off.

nicolasb

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where to get graphed freq response for PMC speakers
« Reply #7 on: 5 Sep 2003, 11:04 am »
Eric,

I have to say, I'm not sure you're going the right way with this. Cross-over circuitry is designed to separate a signal into two components - high frequency and low frequency - in such a way that the two outputs added together recreate the original signal. You're effectively using two different cross-over circuits (one in your subwoofer and the other in your main speakers) to generate the two different frequency components. It is unlikely that the bass filtered out by your main speakers will match the bass selected by your subwoofer cross-over. I think you'd be better off using the same cross-over circuit for both parts of the signal.

What's more, your main speakers are likely to sound better if you don't ask them to produce sound right at the lower limit of their range, and your power amp will be less stressed if it doesn't have to deal with high-amplitude deep bass signals.

For stereo sources you could just use the SP1.7's DACs rather than using bypass mode. But for DVD-A or SACD this is obviously more of a problem.

There are basically three possible solutions:

1) Get a decent DVD-Audio player which does a better job of bass management :). Perhaps an Arcam DV27A?

2) Sell your SP1.7 and buy a Lexicon MC-12. (Possibly a little pricey! ;))

3) Set all speakers to Large and use some sort of external bass management device. There are lots of two-channel possibilities, not as many 5.1 possibilities, but there are some. But you could try, for example, the rather histrionically named "Outlaw ICBM" - click here for more info.

ec

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where to get graphed freq response for PMC speakers
« Reply #8 on: 7 Sep 2003, 08:14 pm »
Nicolasb,

It is all about comprimises,  for me this is the best comprimise.  I used to own an Acurus ACT-3 and they suggest a similar method of tuning the sub xover in their user manual.  I have the components pretty integrated / seemless with a 50 Hz x over with the speakers set to large on the Bryston for movies.  My main focus for listening is:

1. 2 ch audio from Vinyl and redbook CDs
2. multi channel music
3. movies

For stereo sources (vinyl) I prefer to keep the signal purely in the analog domain.  

As for your suggestions:

1. Most Universal players have crappy bass management and my player is no exception especially since it is the cheapest one on the market (Pioneer 563).  I use a Denon 1600 for Video. I am keeping the Pioneer and Denon until something I like comes out.  I did see ads for the BelCanto universal player and it has Faroudja processing inside and may look into that unit.

2. I know someone who has an MC12 but I love the 2 ch analog bypass on the Bryston.  This is the primary reason I bought the SP 1.7.  The second reason is that it is simple to use and the third reason is it has no video switching (I run all my video through a scaler).  The Bryston is the perfect fit for me.  I combined my 2 ch setup with my HT setup so I got rid of decent tube preamp and wanted to something with decent 2 ch abilities.  And of course the Bryston repuatation and warranty doesn't hurt either.

3.  I am also aware of the ICBM but you can't set delays on this unit.  If it had two inputs - I'd go for it because I would use the Denon 1600 for DVD-A and get a decent SACD player.  The Bryston like most pre/pros only had one 5.1 bypass.  Yes Lexicon does have two.

With the new firmware upgrade that allows a x-over point below 60 and the sub on during 2 ch bypass mode - I am quite happy with my setup now.

ec

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where to get graphed freq response for PMC speakers
« Reply #9 on: 23 Apr 2004, 04:59 am »
After reading the post on the IB1s and CB6 and no sub.  I thought I would update this thread.  Here is where I am currently:

Got a decent universal transport (Denon 5900) which does have decent Bass management.  The input I'm using for this is "CD" but have the SP 1.7 set to 5.1 bypass whenever CD is chosen.  The Denon even has BM for 2 ch redbook CDs from my understanding.

Got another sub.  My old Mirage Sub is connected to the Front Right and Left RCA outputs from the SP 1.7.  The Front Right and Left XLRs are connected to a 3B SST.  So when listening to 2 ch stereo in bypass mode everything works well and seems blended in.  I turned off the option 060 so that no sub output is present when in 2 ch bypass mode.  The new sub is passive and its outboard amp is connected to the SP 1.7 via the XLR connection.  The amp is triggered to turn on when my scaler turns on.  The assumption is that when I'm watching movies (eg scaler on) then I would want this second sub to kick in.  I do have to turn on my scaler when I listen to DVD-A or SACD though.  

I do know someone who has an RTA and he has offered to bring it over to my place a few times.  I will take him up offer sooner or later.