Fixing the bass hump in my speakers.....

I have owned a pair of Infinity Kappa 5 speakers for about 10 years but have always had a problem with a ridiculous hump in their frequency response between 50Hz and 65Hz. This isn't a problem with all music as not all recordings have much below 65Hz - but for some things (eg Steve's Pet Sounds ) they go beserk! As a result of this they are relegated to a second system in my house but they can actually sound pretty good when the bass isn't too deep - the "emit" tweeters (see here) are great if you ask me .

What I want to know is how best to solve the problem. I have tried stuffing the cabinets with damping material (previously they had very limited amounts) which helped a bit but didn't really solve the problem.

I figure the best thing is to treat the signal going into the speaker using some kind of notch filter. I'm thinking along the lines of a filter with a profile centred at 58Hz with a width of 15Hz with adjustable attenuation. Once I have found the right attenuation by trial and error I can then hard wire the circuit for that value. Can anyone help me with a good circuit design? Is this the best approach to solving the problem?

Where does the hump come from? I have heard that some speakers are designed this way to give the impression of more bass - if only these speakers didn't have this hump they would be great! If the hump is intentional is it likely to be incorporated in the design of the crossovers somehow or is it down to cone/cabinet design?

For info and pics on these speakers click here. You'll also find a link to the crossover circuit diagram if that helps....


Thanks!

 

Have you experimented with placement? Maybe pull them out from the back wall a little bit?

 

Yep, for the last ten years - they have the same bass resonance wherever you put them.....even in the middle of the room!

The problem is definitely with the speaker design - I've moved house 3 times (at first I put it down to the room dimensions and eigentones!) and have had them running with countless different amps and sources.....always the same bass resonance from about 50Hz to about 65Hz (I've checked with a signal generator).

 

I have the same problem w/ the KEF Q11s I bought a few months ago. They're floorstanders, so I thought maybe too much bass was resonating through the hardwood floors. I raised them on the included spikes, sitting on top of some cheap insulating discs, but that doesn't help much, so I don't think the floor is the main culprit.

I mentioned this to Ray of the Speaker Factory in Maryland when picking up my rebuilt EPI 100Vs. He said many manufacturers build the hump into their speaker design, we guess to appeal to dudes who want to hear the thumpin' bass, mannn. He said he can work with them to fix it. I was in a hurry and didn't have time to ask what he could do or how much it would cost. I might think about it again after I complete my current upgrade plans in a year or so (HT receiver; universal player; separates for my EPIs).

Doug

 

At first I thought there were a couple of fish (bass) doing naughty things in your speaker.

An idea: I wonder if something like a "Variovent" would help? IIRC, it was Dynaudio who made the Variovent, which is like a port for your speaker, but damped. In other words, not an open port like you'd find in a vented speaker. Scan Speak makes something similar:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=296-546

What I believe it does is relieve pressure inside the cabinet at the resonant frequency, and also levels out the electrical impedance (due to it controlling the woofer's motion). I don't know if it would help, but might be worth considering. If it didn't work, you could always plug the hole back up. (These are usually mounted on the rear.) It does have the effect of making the cabinet appear slightly larger at some frequencies, so even if it lowers that response hump in frequency, it may not be as pronounced or intrude on the music as much. Short of that, you'd probably have to redesign the cabinet and build something yourself. A larger cabinet would probably get rid of the hump, but would also drop the level of extreme low frequencies along with it.

 

- I was struggling with the thread title and it was the best I could come up with!

As for your suggestion - I am reluctant to actually physically alter the cabinet design in case I want to re-sell them in the future.

My thinking is now along the lines of a high-pass filter which kicks in below 65Hz - this would be much simpler than a notch filter. I could add the circuit onto the crossover's woofer output - if you like it would turn it into a three way crossover but without a subwoofer to take the signal below 65Hz. Does this sound plausible to you electronics wizards out there? Maybe I should get a subwoofer to make use of the signal below 65Hz....

 

That might not be a bad idea. If your response hump is near 65Hz, you might start rolling it off
a bit higher than that, then cross it over to a subwoofer. The lowest fundamental note on a bass guitar (with the lowest string tuned to "E") is around 40Hz, so I would be hesitant to forgo the bass completely. I have a couple of discs with bass notes below 32Hz (a low "C"), so deep response is very important to my listening experience. A notch filter would be more difficult to design, but IMHO would be better than rolling off all the bass frequencies.

 

According to the specs the speaker hasn't got much going on below 49Hz so a subwoofer may be a good idea.

However, my main goal is to flatten out the hump rather than filter everything below 65Hz completely - presumably it is fairly simple to design a filter with adjustable attenuation and once I have found the right ammount by trial and error I can hard wire the filter accordingly.

Anyone got any circuit ideas?

 

I do know with a simple capacitor, you can place it in series with the woofer and get a 6dB/octave drop in response. (So if your crossover started at 70Hz, response would be -6dB at 35Hz.) So keeping it simple, the falloff is gradual. If you put a resistor in series with it, you'd be bypassing part of what the cap is doing. (I'm sure there is a formula for this--Parts Express and other companies sell crossover design software, and I think Madisound or another speaker supplier even offers crossover design for a small fee.) Thing is, for bass you'd need quite a large resistor to take the full power coming into the speaker, with a wattage rating that won't overheat and cause other problems.

Hopefully now someone will chime in with something more useful.