New speakers - masses of boomy bass

[Mikeandvan]

The performance of the mid bass and bass drivers will depend on the pressure or lack of it inside the cab. Added to that some drivers will only work optimally in a vented enclosure. If you block the port you change the loading on the driver and this will change how it performs across the entire frequency band, almost certainly for the worse and certainly in a way not intended by the designer.

My guess, and it is only a guess, is that the low damping factor of the Naim amp, plus the room, placement of the speakers and possibly the characteristics of the speaker cable are combining to produce the problem. The problem is not inherent to the speakers, since they were not designed to give 'masses of boomy bass', so modifying the speakers is not likely to be a satisfactory solution.

Hi Macca, what do you mean by the 'low damping factor' of the Naim amp? (the pre or power?). Thanks.
Mike.

[Macca]

Hi Macca, what do you mean by the 'low damping factor' of the Naim amp? (the pre or power?). Thanks.
Mike.

Here's an explanation: http://www.hi-fiworld.co.uk/amplifie...ng-factor.html

In short, an amplifier with low damping factor (like your Naim power amp) might give soft or boomy (or both) bass when driving a lightly damped loudspeaker (like your Ruarks). I think you might have some room/placement issues too, and it all adds up. You get over the tipping point and you get the boominess. If you can borrow a different power amp off someone local, you can see if that is the problem.

[Starterman]

Although I partially agree, port tuning is not an exact science. The drive unit parameters vary too much with sample to sample variation and with temperature and voice coil position etc.
Blocking the port is a quick and easy experiment to check if the port output (which is inherently stores energy) is causing the OP's problems. Of course it will affect the loading of the bass/mid driver but this will not dramatically change the mids and has no effect on the tweeter o/p.

All ported speakers produce low fequencies with compromised transient response. If the port tuning frequency coincides with a room mode then boomy bass is the result - scientific fact!
Naim amps have ~.25 Ohms output impedance. The effect this has on lf response is audible but not that significant.

Actually doing something trumps forum opinions most of the time IMO.

[Mikeandvan]

Although I partially agree, port tuning is not an exact science. The drive unit parameters vary too much with sample to sample variation and with temperature and voice coil position etc.
Blocking the port is a quick and easy experiment to check if the port output (which is inherently stores energy) is causing the OP's problems. Of course it will affect the loading of the bass/mid driver but this will not dramatically change the mids and has no effect on the tweeter o/p.

All ported speakers produce low fequencies with compromised transient response. If the port tuning frequency coincides with a room mode then boomy bass is the result - scientific fact!
Naim amps have ~.25 Ohms output impedance. The effect this has on lf response is audible but not that significant.

Actually doing something trumps forum opinions most of the time IMO.

OK, delayed response, I blocked the ports on my old Epos es11 and the results were good, boominess reduced with no other musical losses.

[walpurgis]

Blocking reflex ports or partially blocking them with porous foam bungs raises the system bass resonance, so bottom end roll-off point is higher. This may not be audibly detrimental though.

[Mr.Ian]

I have a concrete floor so not exactly the same, the biggest improvement I got was by getting some rubber gromments, sort with a solid bottom and lip all the way round and then putting a small coin inside ro rest the speaker spikes on. cheap and easy to try.

I have to be honest that whilst it helped it didnt fully cure the problem so I ended up adding an external crossover a couple of subs and put a DSpeaker equaliser on them

[cooky]

All ported speakers produce low fequencies with compromised transient response. If the port tuning frequency coincides with a room mode then boomy bass is the result - scientific fact!

It's all relative and frequency dependent. A room mode is just that, if you exite it you will get a boom regardless of how the speaker is loaded.
The issue is many ported standmounts are tuned to give the illusion of (low) bass, this looks like a hump around 60hz and in uk homes at least is often a room mode problem area. Larger ported boxes wont have this fake bass hump in low end response and so wont energise a room any worse than a sealed enclosure.

[Pharos]

Are you sure about your post 75 Geoff? Although a long time ago I did a lot of playing with this.

If you use the example of a DC movement of the cone, a lower Xsectional area of the port produces a larger 'squirt' time constant from the port, and this corresponds with a lower resonant frequency.

I do appreciate that the resonance depends directly on the mass of air in the port though. Crammed large black drinking straws perhaps?

Also re damping factor, many do not understand that there is a limit to how good this can be, and assume that the 'numbers game' played by manufacturers represents the reality.

It doesn't because the DC resistance of the voicecoil limits it, and 20 or 30 is good enough because of this.

The touted idea that an amp with an O.P Z of 0.001 ohms feeding a speaker of 10 ohms has a damping factor of 10/0.001 = 10,000 is pure fantasy because it ignores the voicecoil resistance.

[cooky]

If you completely block the ports the system resonance goes up-and the roll off becomes shallower-it becomes a sealed enclosure. Porous bungs damp the port output, changing Q whilst the nature and length of the foam bung will affect the tuning to greater or lesser degree.The openness of the foam will dictate wether it will only marginally alter the csa of the port.

[Mikeandvan]

Well I put socks in the ports, it does indeed help. Trouble is my dog keeps pulling them out.

Here is a pic of my lounge (and kitchen). I rent so I can't spend money changing the basics, but I should be here another few years I guess. Any ideas on room lay out? I can;t really set it up any other way, due to juliet balcony. Please advise on any obvious faults with my set up if any. Thanks.
IMG_20171113_130810860 by Mike Van, on Flickr

IMG_20171113_130826218 by Mike Van, on Flickr

IMG_20171113_131048034 by Mike Van, on Flickr