Lower Bass Robbed

[halba]

After months of antisipation and excitment I collected my PMC FB1+ speakers, connected them up and... well I was disapointed.

The top and middle showed significant improvement, the upper bass was well controlled but the lower bass is missing... I say missing but what I mean is that is has lost its 'thump' (the bass drum sounds weak).

Has anyone any suggestions.

 

[chebby]

halba:The top and middle showed significant improvement, the upper bass was well controlled but the lower bass is missing... I say missing but what I mean is that is has lost its 'thump' (the bass drum sounds weak).

Improvement over what? What is the comparison?

"Lost its 'thump'" Since when? Since you heard them at a demo maybe?

If they are straight out of the box then give them at least 50 hours of playing before they 'relax' and their sound starts to reach full potential.

These are a 'transmission line' design so positioning is going to be critical. (More critical maybe than standard boxes especially with bass.) This type of speaker design will react with you room more than than most others. Experiment with positioning especially with regard to corners and walls.

Does your system differ from that used when you first heard them? Are yours the ones with the optional Bryston PowerPacT modules? (In which case there is a whole other bunch of stuff that needs to 'run in' also.)

[Edit.] This link.. http://www.positive-feedback.com/Issue25/pmc_fb1.htm suggests 200 hours 'run-in' so be patient! Also gives tips on positioning.]

I will quote here for your convenience....

" Things You Need to Know About the PMC FB1+ Loudspeakers

1.) These loudspeakers are very sensitive to toe-in and room positioning, vis a vis side-wall reflections. Make sure the relevant distances are identical from your listening position, for the best imaging and staging. It is not a case of a small 'window', but rather a place and angle where these things will interact with your ears and your room in a way that really is jaw-dropping. I know, because I thought I had them set, and recently moved them slightly because I wanted to tighten the floor spikes, and voila-even tighter deeper soundstage and low-end extension kicked in.

2.) The FB1+'s require a long break-in period-I'm talking in the 200 hour ballpark rather than the customary 100. Be patient. Until they "come around for you", as Brian Smith at Audio Classics Ltd. put it, these speakers will appear to be guilty initially of a bunch of speaker no-no's. Early on they will sound harsh, etched, with a bleached mid-range, etc.... Then they turn the corner and its magic time. Why is this? My hunch is that this has something to do with the transmission line's grip on the woofer, such that it takes longer to loosen up. But whatever the technical reason, there truly is a real break-in period with these loudspeakers that you will need to take into account. But when these things open up and simmer down, look out; you will be simply amazed at the incredible combination of dynamic fireworks and precision imaging, along with real actual tactile beauty in the harmonics.

3.) Toe-in. In regards to #1 above, though your room and listening position may yield a different result, I agree with the other writers who felt that what ended up working best with these speakers is a slight to moderate amount of toe-in, one that aims the speakers at an imaginary point quite some distance behind the listener. Too much, and all sins listed in #2 are going to seem to be happening, too little, and you are going to lose the fantastic holographic imaging these speakers are capable of and bred to produce, just like the recently banned fox-hounds of that fair isle. One pejorative you can just throw on the dustbin right now-the phrase 'polite British studio monitor'. If it ever applied, it certainly does not with the PMC FB1+. "

 

[Tear Drop]

"These are a 'transmission line' design so positioning is going to be critical. (More critical maybe than standard boxes especially with bass.) This type of speaker design will react with you room more than than most others. Experiment with positioning especially with regard to corners and walls."

Lol, you really have no experience with proper TLs have you? Do you even understand the concept of their design?

 

[chebby]

Yes but a long time ago! (TLS50s)

I probably got wires crossed with folded horn enclosures which very much interract with a room.

Did a quick bit of revision...

A TL enclosure eliminates the tendency of sound energy from the rear of a bass driver diaghragm bouncing off the inside rear cabinet wall and transmitting back through the cone material itself. It does this by channelling the sound waves through a folded pathway that is heavily damped with anechoic wadding and designed in such a way that the phase of the lowest frequencies are shifted 90 degrees by the time they emerge from the vents. The other benefit is that the frequency response of the design can extend down to frequencies half an octave below the resonant frequency of the bass driver itself.

 

[drummerman]

Yes they will fill out a little bit though not a lot. I find PMC's smaller 'transmission line' bass a bit odd ie. overdamped, soft and sometimes wonder why they go down that route for small floorstanders/standmounts. Lovely speakers nevertheless but I certainly would consider adding a sub.

 

[Anonymous]

Hi all, being a FB1+ owner I am pretty amazed that it is viewed that the lower bass has gone. Not saying Halba is wrong, because we hear what we hear and nothing will change that.

They are spec'd to go down to 28hz, and having received advice on another thread and researching on the web, this covers most instruments bar the organ. One link I read on mixing advice even suggested that some recordings filter out sounds below 40hz because this noise is viewed as accidental, as it can't have come from an instrument and may be footsteps or unintentional. I'm not sure how this works with electronic music though.

The biggest factor I have found is size and dynamics of the room. That said, mine are in a reasonable size room, and really fill it.

I have ordered a BK Monolith because I wanted too see what sub 28hz sounds like. I spoke to BK and asked if I could hear much below 28 hz. They guy said no...but you will physically feel it. This made me laugh........and my house is detached from neighbours.

The delivery is in 3 weeks and I can let you know how a FB1+ and sub sound like. I am really worried that my room causes lumpiness and I need an equaliser between amp and sub. I am also a bit worried that I might drown out the mid, but this is probably better expressed as getting the gain level, phase and crossover right.

If all doesn't go well is anyone here interested in buying a 46kg coffee table?

 

[Tear Drop]

Yes chebby, in a nutshell the bass of a TL is tuned inside the cabinet, not using the room (like bass reflex for eg.). If a TL bass response is affected in any significant way by positioning then it is 'faulty' and not a true TL - one of the reasons I suspect why there are so few of them around, they are very hard to do properly. Apologies if I came across as combative - I must try and change my writing style!

 

[Tear Drop]

Back on topic - which speakers did you have before halba? Bass reflex or similar? TLs produce bass in a different way and what you are likely hearing is more accurate, not less bass. TLs are the only speaker design which give truly accurate bass response, IMO, but going to them after living with other types of speaker can seem a little odd at first.

 

[Anonymous]

I've heard the PMC EB1i's and the bass they produce is amazing...deep, fast and accurate.

 

[halba]

Tear Drop & all,

I have placed the speakers further back about one foot infront of the wall, slight toe in and the differance is amazing - my bass is back. Thanks for your help in your earlier posts.

My previous speakers were Monitor Audio BR5's which now a realise were 'boomy' and that was what I think I was missing... which I do not now need.

I suppose you get use to hearing your familiar tunes to you current kit.

Also, has anyone any experiance with Cyrus 8 series kit and FB1's ?