Odd low frequency bumps

[Chris v]

Hi, I am new to REW so come here to develop my skills

Its working fine, but with the UMIK at my listening chair and with 3 way open baffles I very regularly get humps at about 28 and 60 Hz. In OBs with passive 15" bass drivers I'm not sure these are 'real'.

Any ideas

 

[Wayne A. Pflughaupt]

Please post some graphs so we can see what you see.

Regards,
Wayne

 

[Chris v]

Trying to teach myself to do that

 

[Chris v]

Sorry. This is the best I can do at present. Its a photo of my computer screen ;(

This is my 3 way open baffle. The UMIK is at my seating position (ears). The mid is running full range (no filters). The tweeter has single cap (about 5KHz) and the bass has currently a low pass filter (at about 400Hz).

 

[Wayne A. Pflughaupt]

There's a camera icon at the top corner of the REW graph that will let you save it as a .jpg. But, the screenshot certainly helps!

Well, there is nothing unusual about your graph, really. They all have deviations from flat.

Regards,
Wayne A. Pflughaupt

 

[Chris v]

Thanks
The mid ranger is an SEAS W8 exotic alnico driver which I run full range. Its published frequency pictures are dead flat, so I was quite surprised to see peaks and troughs throughout. Is this typically what you get when you measure open baffles?

 

[John Mulcahy]

It is what you get when you measure in rooms rather than anechoic chambers.

 

[Chris v]

Excellent. Thanks for being so helpful. So are all those features a result of room reflections, room nodes etc?

 

[Wayne A. Pflughaupt]

That is correct!

Regards,
Wayne

 

[Chris v]

So without going as far as to create an anechoic chamber do people ever use REW to help tune a room. If so, are the any good reference documents I should read?

 

[Wayne A. Pflughaupt]

Tuning a room is probably the primary use for REW. Check Youtube, there is no shortage of videos.

Regards,
Wayne

 

[Chris v]

OK thanks. I have no desire to use room EQ which is where most of the info is. I was thinking about selection, type and positioning of acoustic panels, but I will look again at You tube.

 

[skid00]

Chris,

I have 35 year old Carver Amazing ribbon & woofer panels. They have quite 'interesting' interactions with the room. I have used the REW EQ screen to provide 20 Hz to 17,000 Hz equalization, with my UMIK-1 microphone at 4 feet from the panels. (I believe, and the measurements seem to agree, that at 4 feet I'm as close to an 'anechoic' measurement as I can get). They sound *much* better with that EQ, including the mid and high frequency range. I also have effective/loud bass at 18 Hz, where without EQ the peak was at 36 Hz. It is an incredible difference.

Since it is absurdly easy to try many EQ curves out, and using your ears to decide how much EQ to use, why not do so?

 

[Chris v]

Chris,

I have 35 year old Carver Amazing ribbon & woofer panels. They have quite 'interesting' interactions with the room. I have used the REW EQ screen to provide 20 Hz to 17,000 Hz equalization, with my UMIK-1 microphone at 4 feet from the panels. (I believe, and the measurements seem to agree, that at 4 feet I'm as close to an 'anechoic' measurement as I can get). They sound *much* better with that EQ, including the mid and high frequency range. I also have effective/loud bass at 18 Hz, where without EQ the peak was at 36 Hz. It is an incredible difference.

Since it is absurdly easy to try many EQ curves out, and using your ears to decide how much EQ to use, why not do so?

Interesting Do you use separate amps and additional electronics?

 

[skid00]

Interesting Do you use separate amps and additional electronics?

I happen to have two Adcom 555 amps, but you can run separate EQ to each channel through Equalizer APO for Windows. I use a Microsoft Surface Go (at my chair) to run eqAPO and foobar2000, into a Chord Mojo DAC/Amp, thru a 15 foot RCA cable to an Adcom preamp.

 

[Chris v]

Hi again

I have been down this route a couple of times over the last 20 years, first with TACT gear and more recently with miniDSP. On neither occasion was I very happy with the results. The output of the bass driver on OBs is partly cancelled by the rear waves travelling around the baffle. To try and put this right requires massive amounts of processing and big amps, neither of which adds to SQ.

We all have our own way of getting the best SQ and everything is a compromise. My way is to use high quality drivers in a 3 way baffle and single low powered triode amps. The sound is excellent, but I want to use REW to see what more may be achieved by mechanical mods to the baffles, changes to crossovers and room mods.

I'm sure you have had great success in your EQ, but I'm afraid its not for me.

 

[skid00]

"I'm sure you have had great success in your EQ, but I'm afraid its not for me. "

So you are saying that you will NOT use REW to make your frequency response 'flatter'?

There is absolutely nothing you can do to any room, to flatten to within a dB or 3. The drivers aren't flat, and the xover and baffle reflections will also change response.

I believe that there are NO downsides to sensible EQ.

I will wait for pictures of your room treatment...

 

[Chris v]

"I'm sure you have had great success in your EQ, but I'm afraid its not for me. "

So you are saying that you will NOT use REW to make your frequency response 'flatter'?

There is absolutely nothing you can do to any room, to flatten to within a dB or 3. The drivers aren't flat, and the xover and baffle reflections will also change response.

I believe that there are NO downsides to sensible EQ.

I will wait for pictures of your room treatment...

I refuse to have an argument about this, and I'm confident most of these don't apply to you, but my main reasons are.

1. It requires lots of additional (digital) processing which is against my philosophy of minimising component count in my entire system. For instance my 3 way OBs have a total component count of 3. - two high quality capacitors, 1 high quality inductor and no resistors. I ascribe to the notion that every component degrades SQ

2. There is additional cost with amps and processors which I think is better spent upgrading main components

3. Most applied examples of EQ use far too much correction, particularly boost, which is bad.

4. Many people target a flat frequency curve as the holy grail. It unfortunately is not the arbiter of sound quality.

5. Many people choose to ignore room issues and use EQ as a hammer to smash the egg.

So yes, I will use REW plots to judge what if any improvements I am making elsewhere. It has also proved invaluable in measuring the effects of changes in drivers and crossover components.

 

[skid00]

Chris, you can ignore this.

I want to address some of the things Chris said, for the lurkers out there. As in 99.9444444% of all forum posts, everywhere, these are my beliefs and opinions, but I believe they are backed by current audio knowledge as published by Toole, Harman Corp, et al. If you want easily attainable background info, I suggest reading the many forums hosted at Audio Science Review (a forum based on repeatable, verifiable *measurements* of audio equipment, without regard to the myriad of observation biases humans are so prone to). I am not a member of ASR.

"I ascribe to the notion that every component degrades SQ "

Audio electronics (and cables!) are so good that this just is not defensible. The 'shoutometer' gives an easily understandable example of how distortion in an audio chain, of a few dB, is inaudible.

"Most applied examples of EQ use far too much correction, particularly boost, which is bad. "

I'm not sure where you are seeing these examples. Certainly, boosting bass can lead to amplifier clipping and drivers bottoming out. As in all things, people need to use 'common sense'. REW already includes boost/cut limits. There has been a nonsense meme out for at least 50 years, that *any/all* EQ is bad. 1.) That is just pure nonsense. 2.) You have NEVER heard reproduced audio that has not gone through some type of EQ. (Chris-I'm NOT saying that this is what you said!)

"Many people target a flat frequency curve as the holy grail. It unfortunately is not the arbiter of sound quality. "

Actually, according to Harman Corp, who have spent (in my humble guesstimate) hundreds of thousands of dollars blind-testing a large variety of trained and untrained listeners, in custom-built rooms, with many different speakers, a 'flat' response, that *generally* drops around 10 dB in loudness from sub-bass to high treble, IS the most important arbiter of quality. Common sense would also say that gross speaker problems would be assumed non-existent, for obvious reasons. (This FR has been found to *sound* flattest in testing over the decades, due to room effects.

"Many people choose to ignore room issues and use EQ as a hammer to smash the egg. "

Or it could just be so much easier (and more acceptable) to get great results, without plastering the walls with eggshell-cut foam?

 

[Chris v]

Chris, you can ignore this.

I want to address some of the things Chris said, for the lurkers out there. As in 99.9444444% of all forum posts, everywhere, these are my beliefs and opinions, but I believe they are backed by current audio knowledge as published by Toole, Harman Corp, et al. If you want easily attainable background info, I suggest reading the many forums hosted at Audio Science Review (a forum based on repeatable, verifiable *measurements* of audio equipment, without regard to the myriad of observation biases humans are so prone to). I am not a member of ASR.

"I ascribe to the notion that every component degrades SQ "

Audio electronics (and cables!) are so good that this just is not defensible. The 'shoutometer' gives an easily understandable example of how distortion in an audio chain, of a few dB, is inaudible.

"Most applied examples of EQ use far too much correction, particularly boost, which is bad. "

I'm not sure where you are seeing these examples. Certainly, boosting bass can lead to amplifier clipping and drivers bottoming out. As in all things, people need to use 'common sense'. REW already includes boost/cut limits. There has been a nonsense meme out for at least 50 years, that *any/all* EQ is bad. 1.) That is just pure nonsense. 2.) You have NEVER heard reproduced audio that has not gone through some type of EQ. (Chris-I'm NOT saying that this is what you said!)

"Many people target a flat frequency curve as the holy grail. It unfortunately is not the arbiter of sound quality. "

Actually, according to Harman Corp, who have spent (in my humble guesstimate) hundreds of thousands of dollars blind-testing a large variety of trained and untrained listeners, in custom-built rooms, with many different speakers, a 'flat' response, that *generally* drops around 10 dB in loudness from sub-bass to high treble, IS the most important arbiter of quality. Common sense would also say that gross speaker problems would be assumed non-existent, for obvious reasons. (This FR has been found to *sound* flattest in testing over the decades, due to room effects.

"Many people choose to ignore room issues and use EQ as a hammer to smash the egg. "

Or it could just be so much easier (and more acceptable) to get great results, without plastering the walls with eggshell-cut foam?

Hi again
Using passive inductors etc to set the low pass filter on the Emminence Alpha bass driver is looking an expensive and laborious process. I want to cross over at about 100hz and experiment with steeper slopes. I will start a new thread.