Irritating sound from HDS 8' woofers - diyAudio
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Old 19th April 2006, 01:05 AM   #1
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Default Irritating sound from HDS 8' woofers

I have got the mid and high frequencies sound as good as a dream but have not been able to get the woofers sound optimal in my WWMTMWW speakers. They are the Peerless 8' HDS 850490 woofers actively crossed at 200Hz. There are 4 separate ported enclosures for them. Each enclosure houses 2 woofers connected in parallel. I have tried a number of topologies - 2nd LR, 4th LR, 3rd Butterworth and Bessel.

The final topology chosen (active 3rd Bessel) sounds pretty fine as far as flat frequency response and transients are concerned. Overall, the speakers now sound probably better than most commercial speakers under 5-10k mark.

However, I found there are some distortions coming from the woofer boxes making the sound very irritating to listen to if I just run the woofers alone. If I also run the mid and high the irritating sound is masked but I could still feel they are there. They are some very unpleasant higher frequency (definitely higher than 200Hz) sounds that do not seem to relate to the music at all. In theory the 3rd order network will bring down the FR to 36dB at around 400Hz which would have no effect on the sound. I remember once I unplugged the speakers for the mid and high leaving only the woofers running, my wife said the sound drove her crazy and she left the scene quickly.

What is the cause of problem? I could come up with the following but I am not totally convinced it is any of them (perhaps with the exception of 2):

1. cutting out the higher frequencies do sound like that.

2. The resonances of the 25mm thick MDF panels. Note that damping and light stuffing is used. Bracing is not used.

3. Incorrect box volume, port size, port volume or leakage.

4. Port noise (The irritating sound is there even if I don't play very low frequency stuff).

5. Back EMF causes the high-feedback power amp to distort (it is a very good amp!).

6. These Peerless 8' HDS are no good (I can confirm the 5' HDS are very good).

Please help me to get the woofers sound right.

Best regards,
Bill
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Old 19th April 2006, 05:08 AM   #2
infinia is offline infinia  United States
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Hi
Maybe you can run some tests to try to locate source of noises.
Use a stethoscope or better yet a microphone to locate noises. Record noises at single freq.'s when you find them for further analyses. Use your trouble shooting skills best you can.

1) Run each woofer enclosure without xover one at a time.
2) Sweep freq response slowly and look for anomolies.
3) Plug tuning ports run sweep again.
4) Repeat for each enclosure.

One possible source for air noises besides tuning ducts are around dustcap or VC cooling vents. Also firstly check drivers for loose or rubbing parts , gaskets, etc.
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Old 19th April 2006, 06:41 AM   #3
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Thanks Infinia. Unfortunately, I don't have a scope or microphone and can't do any measurement. So far I relied on SW simulation and judgement by ears.

I tried stuffing the port and the noise was still there.

I tend to think the noise is either due to the box resonance or some kind of intermodulation distortions that I can't trace the source.
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Old 19th April 2006, 08:56 AM   #4
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You really need to measure to sort out this problem. SW can do all that, but you'll need a mic. However, for the frequencies you're interested in, an ordinary computer headset mic will suffice to get a rough idea what's going on.
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Old 19th April 2006, 11:37 AM   #5
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If you already have Speaker Workshop, you can create a swept tone signal and play it back through your speakers. You should be able to listen for resonances that way without any measuring equipment. If you hear something unpleasant, then you can take further steps to localize the problem.

Click the image to open in full size.
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Old 19th April 2006, 01:22 PM   #6
rabbitz is offline rabbitz  Australia
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I agree that the 5" HDS 850488 is brilliant but never had any success with the 8" HDS 850490 due to different reasons.... not getting a good bass performance from them.

IMO if you are using 2 850290's in the one enclosure you are going to need bracing with at least 1 behind the baffle between the 2 woofers and then run along the sides to the back. Others will help to break up the panel sizes to raise the resonance frequencies to they can be absorbed by the damping material.

Check your mounting as well like how tight the screws are and the gasket material as I remember a woofer making an odd noise with the baffle flexing and the gasket sort of rubbing on a smooth painted surface and was solved with some bracing and machining the baffle under the driver back to raw MDF with the woofer mounted with no gasket.

Try running them without the xo as a test to see if it's enclosure induced.

I hope you solve it soon as those sorts of things are a pain.
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Old 19th April 2006, 01:23 PM   #7
mazurek is offline mazurek  United States
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One of my peerless woofers had this sort of problem, and I think it was due to overheated voice coil to due low freq equalization. When I did a test sweep, it sounded like it was ripping. The next day the problem worked itself out, I did a couple more frequency sweeps and played with the driver and then it was gone.
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Old 19th April 2006, 01:55 PM   #8
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Sounds very similar to a problem I had when using a PC for crossover duties. What exactly are you using for source and active crossover?

In the end I gave up and bought a DEQX. Its been fine ever since but I concluded that the distortion was being introduced in the crossover and was due to incompatiblity issues with the PC and RME Fireface soundcard.

A description of the issues I had at that time can be found here:

http://www.diyaudio.com/forums/showt...897#post834897
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Old 20th April 2006, 07:27 PM   #9
Bose(o) is offline Bose(o)  Canada
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Yes, I find that Peerless over rates the power handling of their drivers. It seems they really can't take near maximum mechanical excursion for very long. Otherwise the coil/speaker takes on damage and is never the same. Over excursion once and speaker is damaged.

I haven't tried the HDS though, CD series definitely can't be pushed. Seas and Illusion Audio can. So can Audax.
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Old 21st April 2006, 02:23 AM   #10
stu.dio is offline stu.dio  Greece
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Just a thought - try stiffening up the internal end of the reflex port - and/or use thicker dampening - I had a similar problem (with a completely different set up) and fixed it by making a square with a hole from mdf glued to the internal end of the port- simple but very effective plus I used almost 10mm thick bitumen sheets for the dampening of the faces. - not a very technical approach but it may help.
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