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Unexpected improvement from crossover adjustment!


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Hello everyone, 

 

Thought I would share something that others might get some benefit from. 

 

Lockdown has given me lots of time to play with settings etc.. at least I've had one upside! 

 

Whilst I dont go over board, I do like my bass and have been playing with lots of different things to bring it out. 

 

I have REL T9i and a set of PMC Twenty5.23's which go down to 28hz and I've always wanted to take advantage of that and set my crossover to about 60-80hz. Today I put it up to 100hz and the bass seems so much better and rounder. I have no idea of the science behind this but my system has had a sudden increase in sound quality and bass definition. Very happy! 

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Since you are now giving your subwoofer most of the bass duties then it is taking the pressure so to speak off your main speakers.  Hence the main speakers are doing their job and the specialist subwoofer is doing its thing.  That may explain the improvement you have obtained.

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Or you had a bass null/peak somewhere near 80hz due to all of your speakers putting out SPL at that frequency. Now the null/peak is gone with just the sub outputting 80hz (ish)

Edited by niterida
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Hi John

If we look at some low distortion designs of bass system like acoustic suspension, and observe a 3 way crossover with two such 8 inch drivers,

the crossover frequency chosen is usually 450- 500 hz.      http://0339436.netsolhost.com/WordPress/gs401-speaker/

 

This is in consideration of a midrange driver needing similarly approx 500 hz where it begins, however what happens where we use a 2 way crossover, is that the crossover frequency then goes up to match to the tweeter, typically at 2000 Hz  - the bass driver still has useful output - particularly with smaller drivers to 8 inch at these higher frequencies.  Whilst a vintage design, there is much to learn from what Acoustic Research did  http://www.classicspeakerpages.net/library/acoustic_research/

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As you have a REL sub, @Jhsg, I assume you are using the REL "high level" connection (ie. driving it from your spkr terminals)?

 

So you are running your PMCs full range (not rolling them off to match the sub's LP filter)?

 

If I am correct in my assumption then by increasing the REL's roll-off point to 100Hz means you now have a much wider range of frequencies which both the sub and your PMCs are contributing to.  Hence the bass will seem more apparent.

 

However, if you are doing what @MrC thinks you're doing (ie. rolling off your PMCs to match the REL's XO point) ... then, yes, by upping the XO frequency to 100Hz you're "taking the pressure " off your PMCs (and the amp driving them) and, hence, your SQ will have improved as a result.

 

Andy

 

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Your speakers probably were creating a null in a room mode of around 45hz and again at around 90 Hz plus or minus 20 percent , upping the frequency on the sub has filled it in. Another trick worthwhile is put a bit of masking tape on the floor at the front of both speakers and place a bit of paper with cm marked off in cm increments till 150mm, gradually increase one side a cm at a time and listen . Often more times than not having one speaker 5 cm foreward or thereabouts cures the room mode. 

Edited by DEANO23
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25 minutes ago, DEANO23 said:

Your speakers probably were creating a null in a room mode of around 45hz and again at around 90 Hz plus or minus 20 percent , upping the frequency on the sub has filled it in. Another trick worthwhile is put a bit of masking tape on the floor at the front of both speakers and place a bit of paper with cm marked off in cm increments till 150mm, gradually increase one side a cm at a time and listen . Often more times than not having one speaker 5 cm foreward or thereabouts cures the room mode. 

Good advice! I will give that a go. 

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27 minutes ago, andyr said:

As you have a REL sub, @Jhsg, I assume you are using the REL "high level" connection (ie. driving it from your spkr terminals)?

 

So you are running your PMCs full range (not rolling them off to match the sub's LP filter)?

 

If I am correct in my assumption then by increasing the REL's roll-off point to 100Hz means you now have a much wider range of frequencies which both the sub and your PMCs are contributing to.  Hence the bass will seem more apparent.

 

However, if you are doing what @MrC thinks you're doing (ie. rolling off your PMCs to match the REL's XO point) ... then, yes, by upping the XO frequency to 100Hz you're "taking the pressure " off your PMCs (and the amp driving them) and, hence, your SQ will have improved as a result.

 

Andy

 

Hello @andyr - I am not using the high level connector on the REL.. Will need to give that a go sometime to see if it makes a difference. 

 

Thanks. 

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3 minutes ago, Jhsg said:

Hello @andyr - I am not using the high level connector on the REL.. Will need to give that a go sometime to see if it makes a difference. 

 

Thanks. 

But you haven't answered the important question. Are you still running your PMC's full range and just getting more from the sub? Or are you using some form of high pass filter to your PMC's giving the amp and speakers an easier time of things?

Edited by blybo
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34 minutes ago, andyr said:

As you have a REL sub, @Jhsg, I assume you are using the REL "high level" connection (ie. driving it from your spkr terminals)?

 

So you are running your PMCs full range (not rolling them off to match the sub's LP filter)?

 

If I am correct in my assumption then by increasing the REL's roll-off point to 100Hz means you now have a much wider range of frequencies which both the sub and your PMCs are contributing to.  Hence the bass will seem more apparent.

 

However, if you are doing what @MrC thinks you're doing (ie. rolling off your PMCs to match the REL's XO point) ... then, yes, by upping the XO frequency to 100Hz you're "taking the pressure " off your PMCs (and the amp driving them) and, hence, your SQ will have improved as a result.

 

Andy

 

I'm glad someone asked rather than making assumptions and potentially giving wrong advise.

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14 minutes ago, blybo said:

I'm glad someone asked rather than making assumptions and potentially giving wrong advise.

 

Thank you, Neil.  :thumb:

 

20 minutes ago, Jhsg said:

Hello @andyr - I am not using the high level connector on the REL.. Will need to give that a go sometime to see if it makes a difference. 

 

Thanks. 

 

The important answer we need to know though, John, is ... do you have a HP filter in front of the amp feeding your PMCs?

 

That is how subs should be implemented, IMO.  :)

 

Andy

 

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3 hours ago, blybo said:

But you haven't answered the important question. Are you still running your PMC's full range and just getting more from the sub? Or are you using some form of high pass filter to your PMC's giving the amp and speakers an easier time of things?

 

2 hours ago, andyr said:

 

Thank you, Neil.  :thumb:

 

 

The important answer we need to know though, John, is ... do you have a HP filter in front of the amp feeding your PMCs?

 

That is how subs should be implemented, IMO.  :)

 

Andy

 

Hi @andyr & @blybo

 

you might have to excuse my lack of tech knowledge... 

 

I am running the PMC's from a marantz 6014 and a ROTEL power amp and set the PMC front speakers up as 'small' in the marantz speaker settings. 

 

Therefore, based on my knowledge of things, they are-not being ran full range. 

 

Keen to understand if I am doing things right or missing something that might give me a SQ boost. 

 

Thanks! 

Edited by Jhsg
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If you set them to small ordinarily it would send signals below say 80hz or 100hz to the sub and signals above 80hz or 100hz to your speakers so yes your amp ( guessing a surround amp) is acting an low/ high pass filter . Thats what they're called . 

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24 minutes ago, Jhsg said:

 

Hi @andyr & @blybo

 

you might have to excuse my lack of tech knowledge... 

 

I am running the PMC's from a marantz 6014 and a ROTEL power amp and set the PMC front speakers up as 'small' in the marantz speaker settings. 

 

Therefore, based on my knowledge of things, they are-not being run full range. 

 

Sorry, John - you would need to read the User Manual for the Marantz and tell me what it says, regarding 'small'.  :(

 

I'm afraid I'm strictly a stereo guy and have never owned a home theatre receiver.  But Neil should have some good input.

 

What you should be aiming at, IMO, when you run a sub (or two) with main spkrs is:

  • you choose an XO frequency
  • the low pass (LP) section of the XO rolls off the sub at this frequency, at the selected slope
  • and the HP section of the XO rolls off the main spkrs at this frequency - and with the same slope.

 

This way, you get a symmetric handover from the subs to the mains ... with the minimum amount of overlap where the sub is outputting the same frequencies as the mains.  The steeper the slope ... the less the overlap - but a steep slope with a low hand-over frequency can produce unwanted side-effects.  Hence I don't use any steeper than 24dB.

 

24 minutes ago, Jhsg said:

Keen to understand if I am doing things right or missing something that might give me a SQ boost. 

 

Thanks! 

 

One thing I'm wondering is ... the Marantz 6014 seems to be a 9.2 HT Receiver, able to deliver 110w to each of the 9 channels.  So why use a "ROTEL power amp "?

 

Andy

 

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Just looking online at the 6014 instructions, it appears when you set front speakers to small, you can choose the crossover frequency with default at 80hz

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1 hour ago, andyr said:

 

Sorry, John - you would need to read the User Manual for the Marantz and tell me what it says, regarding 'small'.  :(

 

I'm afraid I'm strictly a stereo guy and have never owned a home theatre receiver.  But Neil should have some good input.

 

What you should be aiming at, IMO, when you run a sub (or two) with main spkrs is:

  • you choose an XO frequency
  • the low pass (LP) section of the XO rolls off the sub at this frequency, at the selected slope
  • and the HP section of the XO rolls off the main spkrs at this frequency - and with the same slope.

 

This way, you get a symmetric handover from the subs to the mains ... with the minimum amount of overlap where the sub is outputting the same frequencies as the mains.  The steeper the slope ... the less the overlap - but a steep slope with a low hand-over frequency can produce unwanted side-effects.  Hence I don't use any steeper than 24dB.

 

 

One thing I'm wondering is ... the Marantz 6014 seems to be a 9.2 HT Receiver, able to deliver 110w to each of the 9 channels.  So why use a "ROTEL power amp "?

 

Andy

 

thanks for the above.. appreciate it. 

 

I use the power amp for cleaner power and to allow more power to other speakers as when running 5.1 (or more) the channels aren’t necessarily getting 110w per channel.. compounding this is the PMC's are very hungry speakers. Bottom line, it made a small yet noticeable SQ improvement and was worth doing. 

 

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I agree surround amps when alleviated of the bass below 80hz and the two front channels function a lot better .

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