Preamp difference : if it's not the frequency, not the slew rate, and not the harmonics, what is it ?

[Mihobro]

You would think so, but it was a happy result. The summing amps on the older boards reached overload a lot sooner than the newer ones. So I observed that the newer board would have greater headroom and lower noise floor.
I mentioned digital circuits because in the digital domain there is near perfect matching of two channels, whereas analog consoles would often have some variation between channels. Some consoles had "special" channels, that just seemed to sound better than the adjoining identical channel.

 

[Mihobro]

Oh, one more thing. In my experience, going back to my high school days, My friends (the sound geniuses of their days) used to tell me that feedback and would be the result of acoustical parameters, most significantly, the amount of parallel surfaces in a room that would create standing waves. like a pipe organ's pipe. While some venues may have some treatments or other designs that limit this. And sometimes they can be diminished by speaker and mic placement. It is my experience that most small or medium venue's first feedback frequency will be the room's standing wave or one of it's harmonics. A standing wave can amplify a frequency tone easily by 6 to 12 dB or more. Further, there can be multiple parallel walls, floor and ceiling, that create multiple standing waves. The good news is that they are very narrow and can be notched out, manually like in the old days, (thank you George M for the EQ to do that) or nowadays, automatically. (thanks to all the engineers who have contributed to this process.). Notching out standing waves also has the additional benefit of limiting din and increase clarity and intelligibility. By reducing what some engineers call the masking effect where one loud resonant frequency masks everything else.

 

[Cqwet Dbdfte]

Actually Bose lost, but Consumer reports felt the sting from Bose's lawyers.

Peavey has sold more than a few guitar amps, and all kinds of audio equipment.

I shared a common lab space with the guitar amp engineers, they knew how to make them loud.

JR

Eventually Bose lost, after 14 years of legal battles, but originally had legal success. Anyway who would have any regard for an audio review in a magazine normally evaluating different brands of mayonnaise ?
My friends Peavey amplifier experience was with some speaker I didn't investigate, it was not a Peavey integrated speaker amp. His speaker could have been very inefficient.

 

[JohnRoberts]

Oh, one more thing. In my experience, going back to my high school days, My friends (the sound geniuses of their days) used to tell me that feedback and would be the result of acoustical parameters, most significantly, the amount of parallel surfaces in a room that would create standing waves. like a pipe organ's pipe.

Standing waves are not a proximate cause of feedback while in extreme cases room modes can be excited enough to feed back. Reflections off flat surfaces near microphones and/or speakers can create issues from the alternate path (wavelength).

While some venues may have some treatments or other designs that limit this. And sometimes they can be diminished by speaker and mic placement. It is my experience that most small or medium venue's first feedback frequency will be the room's standing wave or one of it's harmonics.

Um no again. The first (dominant) feedback mode is the frequency with the strongest amplitude response in the speaker/microphone/electronics path. In my experience ringing out many rooms, the feedback modes rarely if ever fall on neat harmonic intervals.

A standing wave can amplify a frequency tone easily by 6 to 12 dB or more.

Sound energy can accumulate or build up inside standing room modes. A sound system loudspeaker feeding into a room mode can cause obvious problems. This is mostly an issue regarding sub placement.

Further, there can be multiple parallel walls, floor and ceiling, that create multiple standing waves. The good news is that they are very narrow and can be notched out, manually like in the old days, (thank you George M for the EQ to do that) or nowadays, automatically. (thanks to all the engineers who have contributed to this process.). Notching out standing waves also has the additional benefit of limiting din and increase clarity and intelligibility. By reducing what some engineers call the masking effect where one loud resonant frequency masks everything else.

You are welcome. My FLS invention helped many sound system operators manage feedback problems with their monitors. FWIW I also sold a Parametric EQ kit through my kit company (Phoenix Systems) back in 1979. For hifi not for feedback suppression. At Peavey I designed one dedicated monitor mixer with adjustable notch filters in each monitor send.
==
Masking is not specifically related to resonances, but loud sounds that make it harder to perceive quieter sounds at nearby frequencies.
===
I spent at least a half dozen years making acoustic feedback on purpose during trade show demos, to show off my FLS EQ reducing feedback in the 1990s. There were no standing waves inside our show booth. But I made lots of feedback simply by pointing a hand held mic at a speaker and turning up the gain. By dipping the dominant feedback frequencies I could get the overall gain several dB louder but at some point there would be multiple frequencies trying to break into oscillation at the same time.

JR

 

[RoadrunnerOZ]

I know a little about feedback. One of my patents was for the LEDs over the GEQ sliders in Peavey FLS equalizers.

Great idea that one. Don’t other manufacturers use that as well - I seem to recall seeing it on other gear??

 

[RoadrunnerOZ]

I’ve found that most of the problem with HF feedback is the facial reflections and rear wall reflections from the foldback monitor into the mic. Notching the relative frequencies out using a GEQ for the stage monitors and judicious placement and angling of wedges will usually cure that. I used to do sound regularly for a band that always had a heavy velvet curtain with a light truss on stands for a backdrop - great for those small venues with hard walls behind the stage - one place we did regular gigs at had glass floor to ceiling behind a tiny stage looking out onto a bowling green and that was a nightmare until the curtains were purchased.
The LF slow buildup in rooms due to subs feeding back through mics can be controlled using the HP filters on desk mic channel strips and/or notching out the dominant frequencies from the FOH and also keeping the subs off to the side of stage front moving them around and even angling the face to minimise the feedback during soundcheck. I’ve done weddings where they want the sound (especially the subs) to really pump for the post ceremony dancing and we would spend quite a bit of time making sure we had no creeping buildup.
Reverbs can also contribute to feedback problems.

 

[JohnRoberts]

Great idea that one. Don’t other manufacturers use that as well - I seem to recall seeing it on other gear??

Uli copied it, he actually patented his similar version.

He had/has better lawyers than Peavey. Peavey sued him for patent infringement. Uli won by not losing that lawsuit (don't get me started. ) .

JR

 

[RoadrunnerOZ]

Seem to recall a similar instance involving Mackie

 

[JohnRoberts]

Seem to recall a similar instance involving Mackie

more than just Mackie, but lets not get lost down that rabbit hole.

JR

 

[ruffrecords]

It's the music.

Cheers

Ian

 

[Mihobro]

Every setup is unique. In a simple setup with house speakers and a mic. standing waves in hall become the main impediment to clear sound and mic gain. House systems have to deal with that. When you are using only close monitors, they do not react with the room as much. so off axis response of mics and speakers are a bigger factor. while it is nice to have the gain. monitors should never overpower the house in the house. I prefer a setup where the front of house takes the lead and the spot monitors fill in what is missing. As a musician it always gave me a better perspective on what is happening in the audience to hear that indirect resonance of the house. Blend was always better. But as you get to larger and larger venues it gets washed out so spot monitors start becoming mixes of their own and distance creates the possibility of better isolation between speakers. And of course, with in the ear monitoring we take almost all bleed and feedback out of consideration from the monitor system, leaving us with, yes, the house PA and how is reacts with the room acoustics.

 

[Mihobro]

Yes, a narrow standing wave in a small to medium, size room will mask adjacent frequencies, it can resonate up to 12dB louder.
I setup my DBX GoRack in one of the tape loops in my ONKYO reciever with a mic in the input to get it to start ringing. After getting the Automatic Feedback to notch out two or three frequencies I listened to a variety of music, Eagles, Bob Seager mostly rock from my Shure V15 type IV needle. After balancing the levels between the Go Rack in and bypassed the comparison of the two was quite revealing. The bass was so much better,I could hear all the way down to the very bottom of the low end and with clarity through to the mids. there was a lot better definition of all the different parts. Compared with the filters bypassed, the resonances created a din and things sounded fuzzy or muddled together. It improved the sound so much I may have to get another AF device to leave at home for my stereo. Don't like all the ADDA stuff but if could find one that did 192@24 FS that may work.

 

[RoadrunnerOZ]

Stage monitors have to be a mix on their own to allow each performer to monitor what part of the band including themselves to key off - foldbacks don’t overpower the house sound - but the opposite can apply to the detriment of the performer if the foldbacks aren’t focused, mixed and EQ’d properly. Stage sound from drums, keyboard, guitar and bass amps all are a part of the FOH sound - as FOH engineer you adjust accordingly - foldback wedges are a part of that but usually to a way lesser degree than forward facing guitar amps etc as they face backwards, or sideways for the drummers side-fill. There’s no control over the direct sound of a drum kit unless it’s sound-screened (I did a gig with Roger Hodgson and the drums were enclosed in 1” thick acoustic clear panels which due to clever stage lighting you couldn’t see from the audience perspective). There is so much imbalance in the stage sound to the performers ear that in-ear monitors are a great solution - they reduce the clutter of fighting foldbacks.

 

[abbey road d enfer]

Oh, one more thing. In my experience, going back to my high school days, My friends (the sound geniuses of their days) used to tell me that feedback and would be the result of acoustical parameters, most significantly, the amount of parallel surfaces in a room that would create standing waves.

If that was the case most feedback woud be at low frequencies, not at the typical high midrange frequency we're used to.
The actual feedback frequency is the result of global frequency response of the system and acoustic pathes between speakers and mics.

 

[RoadrunnerOZ]

I prefer a setup where the front of house takes the lead and the spot monitors fill in what is missing. As a musician it always gave me a better perspective on what is happening in the audience to hear that indirect resonance of the house. Blend was always better

The delay in signal returning to the ears from wall reflections from the FOH monitors in a large room plays havoc with timing for the performers on stage - 20 to 30mSec and up will really throw off time perspective. If the FOH slapback is well below stage monitors it won’t be a problem but if the stage monitor level is low enough it will be one. It’s not like having a bit of reverb in the cans when recording - the late signal if it dominates can destroy a performance.

 

[abbey road d enfer]

Yes, a narrow standing wave in a small to medium, size room will mask adjacent frequencies, it can resonate up to 12dB louder.
I setup my DBX GoRack in one of the tape loops in my ONKYO reciever with a mic in the input to get it to start ringing. After getting the Automatic Feedback to notch out two or three frequencies I listened to a variety of music,

When you do that, you are triggering two things: the system's resonances (including room response) and the delays between speakers and mic.
Regarding the first element, if your system's response has a boost of X dB, when you close-loop it, the boost increases till it rings.
By principle ringing means the boost is becoming infinite. The notch will take out the necessary amount to stop ringing. Since the closed loop boost is much higher than the open-loop, the end result will be too much attenuation.
Regarding the second element, you're introducing a new parameter, the acoustic delays between speakers and mic, that do not exist when the system is in normal (open-loop) operation.
So, yes, the FB killer will determine correctly some of the troublesome frequencies, but it will generally apply too much notch, and the frequencies that are due to the multiple acoustic pathes are simply invalid artefacts.
I've been the distributor for Sabine (the originator of FB exterminator); what started out as an interesting concept turned out to be rejected by professional users.
I believe that JR's concept of offering a visual clue to the ringing frequencies is a much better approach.

 

[abbey road d enfer]

I prefer a setup where the front of house takes the lead and the spot monitors fill in what is missing. As a musician it always gave me a better perspective on what is happening in the audience

I concur with your preference of hearing what is acually delivered to the audience, but what's coming from the back of a speaker, via a long acoustic path is not my idea of precision.
I like having side-fill monitors that have the same mix as the FOH.

 

[JohnRoberts]

I concur with your preference of hearing what is acually delivered to the audience, but what's coming from the back of a speaker, via a long acoustic path is not my idea of precision.
I like having side-fill monitors that have the same mix as the FOH.

Not to feed this veer but last century I visited a sound company in SoCal who was making esoteric loudspeaker cabinets out of high tech carbon fiber. Besides being extremely light weight these very rigid carbon fiber boxes had significantly lower sound leakage from the backs of those cabinets. This is too expensive for wider commercial use but cabinet rigidity matters.

JR

 

[kags]

Not to feed this veer but last century I visited a sound company in SoCal who was making esoteric loudspeaker cabinets out of high tech carbon fiber. Besides being extremely light weight these very rigid carbon fiber boxes had significantly lower sound leakage from the backs of those cabinets. This is too expensive for wider commercial use but cabinet rigidity matters.

JR

My studio monitors, made by Wayne Jones Audio, now come with carbon fiber boxes and the new model does sound different than my model without the carbon fiber. Not a huge difference, but noticeable.

 

[abbey road d enfer]

The issue of back spillage is now commonly dealt with cardioid design.
The active solution, which uses additional drivers and amps, is quite expensive.
The passive solution, based on a principle similar to that used in cardioid mics (acoustic delay in the backpath) is more suitable for cost effective products.
It is applied only to the LF section, since the mid and HF are usually horn-based, with a natural directivity.