Bass leaves after amp warms up?

Thanks Atmasphere
You're really smart,I will follow your suggestions & report back

In addition to the experiments that Ralph (Atmasphere) suggested, if readily practicable it may be worthwhile to try running the amp with its top cover removed, which would lower its internal temperatures.

You would suggest I get 8ohm speakers?

If you are happy with the sound of the speakers during the first hour, and if the conclusion is reached that either the speakers or the amplifier has to be changed, it would probably make the most sense to either change the amplifier, or to purchase a separate power amplifier and drive it from the M6i's pre-outs.

Regards,
-- Al

Although you don't listen loud, it could still be the acoustic reflex changing how your ears perceive sound--the net effect when our ears involuntarily "tighten up" is a loss of sensitivity to low frequencies and a perceived emphasis of treble frequencies. Your _body_ cuts out the bass. Check out the links below.

If your system tips at all toward being "bright" or "forward" triggering this reflex could be possible even at low volumes. Though my system is on the warm side, the acoustic reflex kicks in sometimes when I listen as low as 60 dB if a CD is poorly mastered or if I'm just plain tired or stressed. (Atmasphere's discussion of odd-ordered harmonics and intermodulation distortion in another thread might be relevant here, too: I have an ss amp.) My car has 70 dB interior noise on the highway--again, not that loud--and my acoustic reflex kicks in there, too. It's one piece of the listening-fatigue puzzle.

https://en.wikipedia.org/wiki/Acoustic_reflex

http://www.innerfidelity.com/content/loud-music-sucks

In short, there's always a chance it isn't purely the equipment, but your ears. On the other hand, changing equipment (say to a less "forward" amp or speaker) can change how your ears respond to the sound. Grado headphones (forward) wear me out in minutes at 60 dB, but I can enjoy my Sennheisers (warmer) at 70 dB for much longer periods.

Atmasphere's idea to walk away for 1/2 an hour with the system on is a good one but also might reset your ears as much as anything.

I go back to my original assertion. As Almarg says the results suggest that these amps could not hack it with these speakers (not a good match into a 4 ohm load). I would look at trying an amp with the PSB'a that doubles its power into 4 ohms. (high current)

Ooops. TO3 mosfets.

Can you suggest integrated amps that double it's power into 4 ohms
Not Bryston or Musical Fidelity..I'm not familar with other integrateds

Atmasphere
After enjoying the system sounding great for 2 hrs the bass dried up.
I waited 1 hr.tried again but no improvement.
Turned off amp for 1hr.returned & the presentation was still awful.
I also observed when I change source on the amp it seems to create a break in the circut & the bass leaves soon after.
I've sometime observed after turning a record around/changing channels on a cable box or changing imput buttons on the amp may upset the delicate balance.

Disregard previous post:
Makes no sense!@
But there is no pattern when system sounds optimal:
Could be am or pm

If changing source impfoves thingx temporarily, its possible the source
selector switch on the amp has a problem. Could be dirty or defective.

Ops comment tnat hs is not listening at hign volume would seem to work
against the amp not being abl to drive the speakers well theory, as well as
swirching sources making a temporary difference. Having tne same
problem with two different amps could point to both being underpowered
and heating up over time and negatively affecting sound.

200 watts,underpowered?

Is this plausible?
1. You bought your PSBs used,
2. Whomever you purchased from blew out the woofers and had them reconed.
3. The new surround is nice and springy when you first start listening but "poops out" when it gets warm,
4. Most amps put out more power after they warm up which contributes to the problem.
Problem solved!

Fishing716, So you have tried different speakers, different amps, different sources and different cables and are still having the same problem. The only thing left is the pre amp. Install a different pre amp in the system and see what happens. Other than than I would try a new house as maybe yours is haunted.

All my equipment is brand new from autuorized dealer

I too experienced bass playing disappearing act with my Audio research VT120 mono amps. It happened that when the amp is cold, the bass is not as extended but concentrated more in the mid bass so it sounded more punchy, when it is warmed up and gets lower, the mid bass hum is smoothed out and sounded like it has lose its dynamics, instead, it is more smoothed out and gets lower. My dealer told me I will hear this if the amp does not have enough current to drive the speaker. I later got a more efficient speaker and all the dynamics are back!

I'm jumping in here since I own PSB Synchrony's and I think Almarg and Mapman are correct in that your 4 ohm speaker requires an amp with higher current. At times, your speaker may even drop below 4 ohms.

mapman..."One red flag I see that might help account for what the OP hears is that his PSB speakers show 4 ohm nominal impedance and the MF amp specs indicate power into 8 ohms only."

Fishing716, if your amp is rated 200 watts/8 amps, you really would need about 350-400 wpc into 4 ohms. My amp is 300wpc and doubles to 600 watts/4 ohms; there is a ton of bass pumping out of my speakers continuously and at various volume. Try and look at amps that rate the current output, not just wpc. This spec is usually not listed, maybe ask the dealer or call the manufacturer.

Acoustic reflex seems like a natural defense system against what I have read where 80-85 db is the general limit for safe listening without causing damage to hearing.

It is very possible that when sound seems to change systematically over time, at least part of it is due to our hearing senses adapting or changing as needed.

We tend to think of many things like this as a constant, but no doubt people react differently to things at different times. WHy would hearing be any different?

Thanks to the PSB owner for chiming in. I do not doubt both amps used are underpowered to drive the nominal 4 ohm load. Whether that accounts for all that is being heard is a different story.

One might think any 200 w/ch amp is up to the task of driving most any speaker optimally (not just well). One would be wrong. I've had 360 w/ch and 180 w/ch amps that cannot.

The current delivery and ability to double down at 4 ohms matters. If the OPs MF amp could do that, it would likely warrant being in the published specs. That and being a conventional Class A/B type integrated, which most always has physical constraints that limit what can be done with power supply in close proximity to pre-amp circuitry, I am very confident that it does not.

I disagree with hearing perception changes
Simply put the bass when working has punch,heft,depth & moves air while creating excitment & emotion.
After about an hour the bass notes are still there but the kick of the bass drum no longer has the correct punch,the bass does not move air,the bass notes are no longer rounded but flat,etc.

The bass is similar to a Tuba where the notes are full sounding & you can "sing" along with the bass line if desired.This is the foundation of the music that is receding into the background.
I personality think there is something wrong with my electric.I'm having an Electrician come to tighten all the connections as I think something is causing a misfire.

FWIW, I'd just like to emphasize that the impedance curve I linked to earlier shows that the speaker's impedance is in the vicinity of 2.7 ohms at several frequencies in the deep bass and the mid-range, and is less than 4 ohms throughout most of those regions.

Also, I would not attach much significance to amplifier current capability specs, as they usually do not indicate how long the specified current can be sustained for, and my impression is that in many cases that amount of time may be measured in milliseconds.

Regards,
-- Al

Almark what is the conclusion to be drawn from your post?
My MF amp should be adequate @ 200wpc or no

My MF amp should be adequate @ 200wpc or no

My strong suspicion, consistent with points that were made earlier by Foster_9, Mapman, and others, is "no." As I previously indicated, the three amplifiers you have tried either do not have a 4 ohm rating, or have a 4 ohm rating that is not particularly good relative to their 8 ohm rating. That would certainly cast doubt on their ability to handle 2.7 to 4 ohm impedances, which occur in parts of the frequency range that typically require lots of energy.

Regards,
-- Al

Fishing716, it could definitely be the amp or electricity as others have said, but with all respect the loss of bass weight and "flatness" you describe does correspond very well to the changes in hearing that come with the acoustic reflex. I'm not saying this is absolutely the issue--just that it's worth considering, especially as you've had the same experience with multiple different speakers and amps.

Note that in Tyll's InnerFidelity article he hypothesizes that the acoustic reflex is one reason systems tend to sound edgy and bright at audio shows--a pretty reasonable notion when you consider that it creates a subjective 20 dB bass roll-off (check out the graph). He notes that his reflex kicks in at 55-60 dB with pink noise. This is probably a bit different for all of us, but for me it's about the same. It's one reason I'm also (like you) a low-volume listener most of the time--though for me that often goes up to 75 dB or so.

As an experiment, you could try starting with the volume turned all the way down and turn it up till you just begin to feel the bass weight (this could be at an even lower volume than you usually listen at), then listen for a while and see if the same thing still happens or if it happens as quickly. I mean no offense, it's just that we usually (myself included) look first at the gear itself for problems--a lot like when someone keeps buying new speakers w/o paying attention to placement with the speakers they have (not your situation, just an analogy).

I just got off the phone with Musical Fidelity..
I was assured the M6i is more than capable of handling PSB Synchrony one speakers.

I'm not sure that an issue with eletrical power supply would be consistent with the pattern OP describes for sound deteriorating over time.

The amp would appear to NOT be up to the task of driver the PSBs OPTIMALLY given its bench measurements Al identified. That is a clear issue that would account for deficiencies in bass and dynamics.

Find an amp to try that doubles down mostly from 8 to 4 ohms. You might not even need more than 100-200 w/ch to do a good job assuming you do not listen at high volumes. If you do, then throw the kitchen sink at those puppies. Modern Class D amps make it more practical than ever to do this when needed.

Check power rating into 4 ohms to see if double or close to double from 8 ohm. That is a good indicator. Published bench measurements in reviews to confirm is best to be sure.

I could recommend some to try as could others I am sure if a price point were known?

"I just got off the phone with Musical Fidelity..
I was assured the M6i is more than capable of handling PSB Synchrony one speakers."

This is a subjective statement. Most listeners out there might be more than satisfied. There is no reason for MF to say otherwise. But there are doubts based on published specs and bench measurements that should matter to a very discriminating listener, which OP appears to be. So there is a CLEAR red flag worth consideration.

I've heard the PSBs sound very good off 100w/ch Rowland Class D switching amp. That would be a good place to start as a reference. I truly believe a good modern Class D amp with good power supply that can mostly double down to 4 ohms can solve OPs problem in a relatively inexpensive and very compact package.

Rowland 100 w amp for reference.

I would ask suggestions for more efficient integrated amp to drive PSB speakers..

There are many well received integrateds out there these days that use CLass D amplifiers, even inexpensive Japanese ones from companies like Onkyo. Quality of power supply, which matters might vary widely with an integrated more so than separates. If the specs indicate mostly doubling down to 4 ohm, it is probably worth consideration. There are still limitations with amp and pre-amp in close proximity in same box with Class D, but technical aspects relating to noise and shielding are different. I have not used Class D integrateds so cannot vouch, but many have received good reviews and acceptance. To be safe, I'd say separates are better (and with Class D amps smaller as well). But why not try a well reviewed integrated for reasonable cost first and see? If it does not work out then move on eot separates. I think there is a decent chance the right integrated could work for OP.

Fishing, is it related to the time of day? Early mornings and late nights it sounds good? Middle of the day, it sounds bad? I've noticed my system sounds better late at night, around 9pm and later.

Also, are you able to demo another amp from a local hifi shop?

If none of that works, maybe you should sell me the psb's at a highly discounted rate, since they're obviously defective ;-)

The voltage is normal
By the end of the day there is nothing left in the bass dept.
I turn off the amp for the evening and return in AM
Plenty of deep bass & sounds excellent
I listened to Abbey Road this morning but by the end of the first side
McCartney's bass lost his groove.
I didn't bother listen to the second side.
Sometimes I switch speaker cables from L/R to R/L
And lower bass returns for an hour or less.
It's quite a dilemma

OK. Based on the testimony so far we can safely assume that hearing has nothing at all to do with it.

I am also doubting that the interface between the amp and speaker is an issue. If it was, the bass would be a problem as soon as you turned the amp on. So that is not it.

The only clue we have is that doing something with the speaker cables sometimes has an effect. Letting the system cool off does not.

If none of *that* has any effect then I become more suspicious that its not the amp/speaker setup at all. But- the fact that moving the speaker cables has an effect is an important clue. Let's start with the recommendations above and see what happens.

At this point I would be looking at the cables. How long are they? How tight are the connections at either end? After listening until the bass dries up, is there any heat on either end of the cable? It might be as simple as a loose connection.

FWIW, speaker cables become very critical when used with lower impedance loads! If your connectors are only finger-tight you are missing a bet. You should get the connections as tight as you can without damaging them. I usually use a small wrench to tighten things down. That can have a big effect on bass, especially with lower impedances.

Its also true that you really should not run speaker cables longer than about 5 feet if you have low impedances in the speaker.

04-11-13: Fishing716
After enjoying the system sounding great for 2 hrs the bass dried up. I waited 1 hr.tried again but no improvement. Turned off amp for 1hr.returned & the presentation was still awful. I also observed when I change source on the amp it seems to create a break in the circut & the bass leaves soon after. I've sometime observed after turning a record around/changing channels on a cable box or changing imput buttons on the amp may upset the delicate balance.

04-11-13: Fishing716
Disregard previous post: Makes no sense!@ But there is no pattern when system sounds optimal: Could be am or pm

04-12-13: Fishing716
Sometimes I switch speaker cables from L/R to R/L
And lower bass returns for an hour or less.

04-12-13: Atmasphere
The only clue we have is that doing something with the speaker cables sometimes has an effect. Letting the system cool off does not.

Not sure that we can say that conclusively at this point, Ralph, although the checks you suggested of the connections are certainly in order. I believe it was only one experiment that indicated that letting the system cool off did not result in recovery, and the report about swapping the speaker cables included the word "sometimes." I would be hesitant to conclude at this point that those results would be consistently repeatable over many trials.

Presumably the amp was turned off when the speaker cables were switched, and perhaps the recovery was actually the result of it being allowed to cool off. Or perhaps it resulted from something else that occurred during that time.

Also, I would repeat my suggesting of trying, as an experiment, running the amp with its top cover removed, if that is practicable.

Concerning candidates for possible replacement of the integrated amplifier, while I'm not particularly familiar with the integrateds that are out there these days, my feeling is that finding one that can deliver 100 or 200 watts or more, provide good sound quality, be able to handle 2.7 to 4 ohm impedances gracefully, and cost in the vicinity of the $3K or so price of the M6i, is likely to be a tall order.

Personally, I would go with a separate power amplifier, driven from the pre-out terminals of the M6i.

Regards,
-- Al

No All the connections are always tight
I have spades and the speaker cables are (2nd) pair of AudioQuest comet biwire 6 ft.
No heat on either end of the cables

Amp could be defective.

Not likely though that two amps would have the same inherent defect though.

Switching source has an effect I recall. COuld be defective source control switch. COuld be defective volume control if volume is adjusted at all in test cases.

Fishing,

Any difference at all in when the problem occurs between old amp and new? If so, equating the two to produce exactly the same problem may be confusing the issue.

My guess at this point is it is some combination of these that is causing the problem.

1) defect in the amp that affects performance over time
2) amp is having problem with speaker load
3) patterns of human hearing as identified above.

Trying a different amp that is up to the task on paper or better as measured on the bench would address both 1 and 2.

Not much one can do about 3 except be aware when doing listening tests.

You might also try a different pair of easy to drive speakers as a test and see what happens there.

The problems are exactly the same with all 3 amps
(2)bryston & Musical Fidelity
Deep bass for about 1 hr
Longest it lasted was 3 days then sound changes with loss of defination.

I seem to notice it's easier to retrieve deep bass with just one speaker connected rather than both.
(Either side)
Sill fades away after apx. 1 hr

Do you have any other speakers around? What happens with them? Results would help determine if speaker/amp match or defect in amp is an issue.

I only have these speakers

The bass is firm & lasts longer with just one speaker connected.Eventually leaves but right now it is working for about 30 minutes
Listening to Chicago V on Rega P5 TT w/dynavector.
I would keep this sound w/one speaker & loss of half information.
But soon it will leave.
I am monitering the situation

Please let me know if anyone notices contradictions in my observations.
As I've tried everything
Could it be reasonable that loss of deep bass is normal?
Perhaps I need to augment my system with a subwoofer.
I feel bass is adequate when I have it

FIsh,

It is what it is but for future reference, its not a bad idea to always keep a spare component around to switch in as needed to help diagnose a problem or even to pinch hit when a starter piece goes down.

For testing purposes, an inexpensive receiver or integrated with preamp outputs and amp inputs can be used to replace another integrated, power amp, or pre-amp when needed. Cheap spare CD players are readily available these days, just check out the local Goodwill store. Cheap spare speakers can be had easily off Ebay, as can most home audio components.

This way you can do "regression tests" to help isolate a problem to a specific component when needed.

Subwoofer would be a band aid.

BEtter to get to the root of the problem and fix it. The PSBs should leave nothing to want if set up well.

IF either speaker alone sounds better, that would seem to indicate the problem is not in either speaker, like detached/loose voice coil or something like that.

Have amps always had this issue? DId any work good initially at least for some time before the pattern started? ANy nasty sound accidents prior, like loud feedback due to improper connection, or anything else similarly abnormal?

Since having the PSB all 3 amps have given the same results with exact same symptoms.
Irony is I like the PSB Synchrony sound
I borrowed Thiels for a very brief period and found them to be bright.Bass not being consistant was inconclusive.

Currently just listened 2 complete LP's without losing the bass using just the right speaker connected.
I don't know why that is
I'm currently monitering this effect & duration

Timeing & pace seem much better when lower bass is cooperating.

Currently just listened 2 complete LP's without losing the bass using just the right speaker connected. I don't know why that is.

Connecting just one speaker will certainly make life easier for the amplifier, and reduce the internal temperatures that it will reach, compared to playing music into two speakers at a similar volume setting.

Regards
-- Al