Advice on rear ported speakers "rasping"

Hi,

I am new to this forum and this is my first post. I am wondering if anyone can help me. I have some rear ported Epos M12.2 speakers and prior to that had some Epos ES11s which were also rear ported. I notice an audible "rasping" when I listed to the bass pulses coming out of the rear ports - a kind of "fluttering" sound. Seems to make no difference where the speakers are placed - how near the wall. Has anyone come across this phenomenon themselves - is is normal? Any advice/info much appreciated. Thanks, Phil.

Hi Phil,

Welcome to the forum :)

I'm sorry but I haven't come across your problem before, so perhaps someone else will be able to help you better.

The only questions I would ask are is the "rasping" occurring when playing CD or vinyl, or both? How old are your speakers, and have you checked the drive unit surrounds for signs of wear and/or the bolts securing the drive units to make sure they're as tight as possible?

Marco.

Marco,

Thanks for your reply. The speakers were new this year and have been treated pretty well, although I do play my music at decent volumes! I play both vinyl and CD, but at the moment owing to space limitations I am just using CD. My previous speakers were Epos ES11s, considered somewhat a bookshelf classic, and these seemed to display a similar phenomenon to the new Epos's - the LF pulses coming out of the rear port sound somewhat "phutty" or "rasping" or even like there is a "flutter". I am not sure if this is normal or a fault or even an artifact of my particular system/set up. I would be interested for any other views from Forum members. Thanks! Phil.

Phil.

It might be an idea to ask this question on other forums as well. Ideally you need to find someone with Epos speakers.
Try this one. http://wduk.worldomain.net/

The "phutty sound" you mention could be due to air exiting from relatively small ports, often desribed as a chuffing sound. But i would expect Epos to do better than that.
Of course you may have a very different problem, and it's difficult to describe sounds for other people.
Like Marco said, make sure everything is tight and that there's nothing loose inside.....crossover, terminals, wire etc.

If you had the same with your last speakers, and you have the same amplifier, maybe something has aged(capacitors?) or otherwise become faulty inside.

Thanks alb, There is an Epos forum on the Creek site and I am waiting to gain access. That would appear the best place. I have also e-mailed Epos; Mike Creek often gets back in touch personally.

A mystery this one. I must get round to listing my modest system details, but basically the LF units are driven by original Audiolab 8000M monoblocks which have recently been given an upgrade/service by a fine chap who specialises in servicing Audiolab/Tag gear - Kevin Green (the Audiocellar). P.S I am also currently using a passive pre-amp from a fine founder member of the Forum I believe, Filterlab.

I recently sold a pair of cheap Wharfedale Diamond bookshelf speakers on ebay. They were rear ported and when I tested them they did exactly the same thing - "rasping" from the rear port. There is one particular track which I use to highlight this if anyone can get hold of it to try - Track 5 (Moldavian Triptych) off Donal Lunny's "Coolfin" CD (EAN 7 24349 35422 7). This starts with a long extended LF note and sets my Epos's "rasping" like mad - anyone fancy giving it a go?

Thanks all

Phil

Phil Hi, have you tried putting some foam ( or old socks) loosely in the ports? Keith.

Ports used to augment the bass performance of smaller speakers DO "chuff and whooffff" and even those with drinking straws in can do so too (some Mission 737R's I once owned did this spectacularly). In the case of early Spendor BC1's the port was little more than a hole in the baffle and the sound from this hole was known as a "honk" all at one frequency and gave a lumpy bass with huge distortion, only minimised with certain amps with huge amounts of damping.

The ES11 wasn't too bad as I remember (did they originally have optional grey sponge bungs supplied?). The ES14 was the one. The magority of them had the tongue/phase plug at cone centre and these should be used close to a wall with the sponge bungs IN SITU (or at least placed in sideways). Of course everyone took the sponge out (even when they were stuck in place) and the bloomin' things sounded off like a fog-horn at 80Hz like noones business. Trouble is, people liked it...................

Thanks all...."chuffing" - that's it, thats what they do. To be honest, can't really hear it generally in overall listening, but you can when you listen to the back port. But certain LF notes, like the one on the aforementioned CD, do sound foghornish - a "vibrating, chuffing, fluttering" forghorn. Anyway, your replies have reassured me that it is probably not a fault with the speakers per se - I will wait to see what reply I get from Epos - Mike Creek often replies personally which I find very impressive. Thanks again, Phil.

Glad we could be of some help. Try a bit of fiddling about as per my email, you may just hit upon something good. :) If you do then tell Mike Creek!

Changed my mind, I am sure there is something wrong. Just played some bass heavy Bob Marley and the rasping/chuffing was clearly audible above the music, honking away! I am sure this has got worse and the speakers were new this year! I will be interested to see what Epos/Creek say, but I fear the speakers may be going back!

Anybody else out there had similar problems?

Thanks again,

Phil

Do you have access to another amplifier?
At least you could eliminate a possible cause, while you are waiting for Epos to respond.

Thanks Alb, I do have a Tag p60 amp recently purchased off ebay - I will try just using this and see what happens. Phil.

I have tried blocking the rear ports with tissue and it reduces the problem, but of course one loses bass! A question for DSJR - with the ES14s having sponge bungs etc, why was this? Surely, one does not design a speaker with a hole and then block it up? I'm on a steep learning curve. Thanks, Phil.

It's not uncommon for ported 'speakers to be provided with some form of bungs. This is to allow for tuning the bass to the room. In some cases, especially with smaller rooms, the bass can be excessive. Blocking the ports can reduce this. Alternatively, altering the distance from rear walls can affect the bass characteristic as well.:)

A slightly amusing story about ported speakers.
Years ago, I had a pair of B&W DM110's in a 2nd system. I often had the opportunity to play music very, very loudly without upsetting anyone. I was trying to explain the theory behind putting ports in speaker cabinets to a friend, and to illustrate a particular point, I held a small strip of paper up near to the port - while he turned the volume up.....way, way up. Of course the paper flapped about in the flow of air. Now, I wondered to myself, how far across the room can we get the port to blow the paper? So I let go. This is where I lost sight of the piece of paper as it got sucked into the hole. So my friend learnt that reflex ports suck as well as blow!

About a year later I was listening to something at a reasonable volume and happened to be looking directly at the port in question when something flopped out & landed on the floor. It was of course, the piece of paper, but the thing that I found quite interesting (and please bear in mind here before you pronounce me insane, that I work in the forestry industry and have an interest in the structure and properties of wood products) was that it had broken down into a matted blob of broken fibres. I find it intriguing that it was subjected to quite such a battering inside the cabinet.

Charming story there Wazoo, and a true indication of how much spare time you've had over the years. :lol:

It is amazing though just how much energy is transmitted through a port and indeed inside a speaker cabinet.

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Originally Posted by The Grand Wazoo

So my friend learnt that reflex ports suck as well as blow!

About a year later I was listening to something at a reasonable volume and happened to be looking directly at the port in question when something flopped out & landed on the floor.

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I forgot to mention that I didn't actually sit there waiting patiently for a year for the paper to reappear - I did, in fact, manage to drag myself away and conduct something of a fulfilling and interesting life in the interim period.

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Originally Posted by Phil Bishop

Thanks Alb, I do have a Tag p60 amp recently purchased off ebay - I will try just using this and see what happens. Phil.

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hi phil,
this might be a daft question, but, are you sure both speakers are in phase!
in other words, positive terminal to positive on both speakers etc, because if they arent, and one bass unit is out of phase not only will you get an unusual sound, but the bass response will be lacking, and the cones on the speakers will move further than their normal travel and make the kind of sound you describe!
just a thought.
regards,anthony,TD...:)
PS, when checking this dont take for granted that just because the plug thats in the positive socket is red that is on the positive side of the cable!
trace it all the way back to the amp and make sure its going to the positive terminal!

Wow, What a lot of interesting debate and reminiscences this subject has generated! As for the phase issue Antony, reds certainly go to red, black to black, etc. However, someone once told me to muck around with this and experiment with different permutations. Also, I remember once having a hi fi test disc which was suposed to check phase (years ago) and my speakers then certainly did not do what they wer supposed to. I seem to have a lot of bass....perhaps too much "boomy" bass, but it seems to vary a lot. What do you suggest I should do to experiment? Just swap the terminals round on one speaker? Many thanks - all so helpful - Phil.

Quote:

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Originally Posted by Phil Bishop

Wow, What a lot of interesting debate and reminiscences this subject has generated! As for the phase issue Antony, reds certainly go to red, black to black, etc. However, someone once told me to muck around with this and experiment with different permutations. Also, I remember once having a hi fi test disc which was suposed to check phase (years ago) and my speakers then certainly did not do what they wer supposed to. I seem to have a lot of bass....perhaps too much "boomy" bass, but it seems to vary a lot. What do you suggest I should do to experiment? Just swap the terminals round on one speaker? Many thanks - all so helpful - Phil.

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hi phil,
all speaker drive units have to be in phase with each other, ie, both bass units must be either positive or negative phased, sometimes the tweeter is deliberately put out of phase with the main driver on both speakers. what you can try is this, if the speakers your using are bi -wire-able, and thats how you are using them, then you can try putting the tweeters [high frequency units] out of phase with the bass drivers and see if that helps.
if your not sure how to do that, all it means is instead of the positive wire going to the positive of the tweeter, put the negative wire to the positive on both the speakers but leave the wires as they are on the bass drivers, see how that sounds, any thing your not sure about just ask...
anthony.;)

Thanks Antony, I had not thought of this. By the way, I am biwiring and also bi-amping. Is there another permutation, that is reversing the +ve/-ve on just one speaker (both sets of terminals) to see if that makes any difference?

Epos have got back to me and have not added much, apart from to check that tweeter wires inside cabinet are not touching port. They have recommended removing tweeter to check. Is this safe, i.e., I assume there is no seal I will be breaking? I guess if they are asking me to do it, it must be OK. Thanks again, Phil.

Quote:

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Originally Posted by Phil Bishop

Thanks Antony, I had not thought of this. By the way, I am biwiring and also bi-amping. Is there another permutation, that is reversing the +ve/-ve on just one speaker (both sets of terminals) to see if that makes any difference?

Epos have got back to me and have not added much, apart from to check that tweeter wires inside cabinet are not touching port. They have recommended removing tweeter to check. Is this safe, i.e., I assume there is no seal I will be breaking? I guess if they are asking me to do it, it must be OK. Thanks again, Phil.

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hi phil,
should be fine to remove the tweeter as these are not sealed cabinets.[ported]
just make sure when replacing the tweeter to do up the screws evenly, and not too tight.
if you cannot find anything obvious, then it could be that the voil coil is damaged due to excessive heat from either large amounts of clipping [amplifiers running out of steam] or prolonged high volume use causing speech coils to distort and rub...:(

Thanks Antony, I have generally been using two recently serviced 125W Audiolab 8000Ms so I would have thought clipping was unlikely, although I grant I don't fully understand this phenomenon. I do play music at relatively high volumes, but for relatively short periods (no more than an hour at a time) and not at "party" levels and not loud enough for the neighbours to complain! To see whether they are damaged, I guess all I can do is return them to Epos - they are under guarantee. Phil.

To check the voice coil; push the bass driver gently and with even pressure back and forth. If there's a rough grind to the feel then chances are it's damaged, if it's super smooth then it's fine.

Rob, Seems super smooth to me. I can't imagine I have damaged the speakers. When I get a chance I will remove tweeters and check for wires near port (as recommended by Epos) and also muck around with the phasing a bit. Thanks for advice, Phil.

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Originally Posted by Filterlab

To check the voice coil; push the bass driver gently and with even pressure back and forth. If there's a rough grind to the feel then chances are it's damaged, if it's super smooth then it's fine.

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i agree with rob,
this is the only way of checking realy without test equipment!
let us know the outcome, also, if this test dosent show anything obvious, [be gentle, and use even presure at oposite sides of the cone] this test will not rule out the posibility of the speech coil windings having come loose on their former due to excesive heat but this would be an extreeme fault!:( my advice would be to try a diffrent amp and see if the problem is still present at similar volume on the tracks you know.
regards,anthony,TD...

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Originally Posted by Phil Bishop

Rob, Seems super smooth to me. I can't imagine I have damaged the speakers. When I get a chance I will remove tweeters and check for wires near port (as recommended by Epos) and also muck around with the phasing a bit. Thanks for advice, Phil.

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No problem. I'm glad your voice coils are fine, it's a rare problem these days but when it does happen it can be expensive to sort.

Good luck with the phase checking!

From The Grave

Any more thoughts on chuffin', socks & voice coils?

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Originally Posted by DSJR

Ports used to augment the bass performance of smaller speakers DO "chuff and whooffff" and even those with drinking straws in can do so too (some Mission 737R's I once owned did this spectacularly). In the case of early Spendor BC1's the port was little more than a hole in the baffle and the sound from this hole was known as a "honk" all at one frequency and gave a lumpy bass with huge distortion, only minimised with certain amps with huge amounts of damping.

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Quite a few speaker used the drinking straw method, i think the Mission ports was more proffesionally manufactured than others.

There was a piece in Hi-Fi World back in the 90s (may have been in the DIY supplement) in which NK experiments with ports. IIRC he tapes a plastic funnel (the kitchen type) onto the end of a port to improve it's behaviour, which he confirms with measurement. Not sure what issue or what 'speakers he was using.

Can't help Phil's issue, but this has made me want to dig out all those spare socks from the drawer and stuff them in my ports for a bit of fun... I think this forum may finally have got to me!

Glad you posted Alex, i was going to earlier but forgot about it :doh:

Sounds to me like there is a lot of port turbulence, now this can be caused by a combination of things but the most usual is simply that the port has been made too small. Either that or there has been no thought to rounding over the edges to decrease turbulence..

One of the biggest problems is that most manufacturers simply don't pay enough attention to decent port design. If you look at the outside of an enclosure you'll find that 99.9% of the time the port is flush with the front or rear baffle, however if you take a look inside most of the time all you'll see is the port tube ending in free space :mental: It might not at first appear to be a problem...

What happens with this mismatch is that air finds it far easier to flow into the enclosure than out of it & what tends to happen is the enclosure gets pressurised somewhat under sustained bass notes. The result is the bass driver is gradually pushed out from it's naturally centred position & all sorts of distortions rear there ugly head in both the bass & any other frequency the driver is dealing with.

The simple answer is to give the interior end of the port a small baffle so air can escape just as easily as enter.

Another good thing to do is rout the edges of the port inside & out so that there are no sudden edges to create turbulence.

So to sum it up, use as big a port as possible, place a small baffle on the inside end of the port & rout the edges of the port with something like a 12 - 18mm round over router bit :)

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Originally Posted by Alex_UK

Can't help Phil's issue, but this has made me want to dig out all those spare socks from the drawer and stuff them in my ports for a bit of fun... I think this forum may finally have got to me!

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Well, this was interesting. Although all it did was prove the ports on my speakers are there for a very good reason! I discovered that the front ports are linked to the bass enclosure, the rears to the mid (and treble?) - and that blocking either or both does what you would expect, really. I can't detect any "chuffing" but then who knows, as I have happily lived with these speakers for nearly 7 years. The ports seem to be well designed following the principals Mark mentions - a 2" tube, and the "exit" is a rolled funnel-type arrangement.

Anyway, that's my curiosity sated, I shall keep my socks on and stop sticking things in my ports from now on! :)

Rasping from rear port = your playing music too loud for the speakers!

The woofers are shifting too much air for the design of the ports to cope with and you just end up with thoroughly confused air. You could argue it's bad design or you could could argue the manufacturer never intended for you to try and get 125db out of them??

I would say your only options are either turn the volume down or buy bigger speakers!!

Butuz

+1 on the too loud. i've never ever had a port problem becuase i use speakers at realistic levels.