Bought some speakers, they're big and heavy but they don't have any indication of what ohm they are, i connected my turntable and all i can get is a high pitch noise from the speakers and no audio from the turntable (audio-technica 120L). I've tried phono and regular inputs (and making sure to switch on my turntable since it has a switch and pre-amp).

You can only connect an amp which has an output of 8 ohms to speakers that are 8 ohms are greater. You must NOT connect to speakers less than 8 ohms.
If the amp is 4 ohms you can connect speakers of 4 ohms or greater.
If the amp says 4 to 16 ohms then you can't go lower than 4 ohms.
As long as you stick to that rule the choice of speakers is up to you.

If the set has a connection for external speakers they have be the same impedance (ohms) and the set will likely have to be switched from internal to external.

I don't think it has anything to do with the impedance. The amp and speakers are well in the allowed limits. The only time this is a problem is if you connect an amp with a greater impedance then the speakers.
This sounds like something to do with the HK 990. It could have a fault on it. You could try listening with headphones if the HK 990 has a socket for them. If they have low sound, there's an electrical fault in the power amp of the HK 990.

ohms is a big factor. also it will probably take more power to drive the W-6 so it won't sound as good. I suggest you don't do it. especially if you can't match up the ohms. You will fry the amp, or it will sound like ****.

I’m happy to help further over the phone at https://www.6ya.com/expert/chris_7f7f91eb941fb23f

Check first to make sure impedance marked on speakers is same as original---two sets of positive and negative terminals suggests original ones were dual element speakers----

If for example original were marked 8 ohm and you put 16 or 32 ohm speakers in----volume will be greatly diminished and even distorted.

This is only a suggestion as I do not know what original speakers were or what new ones are----but the key is originals had two sets each of connections.

JST USE BIG PIN TO THREE PINS AS IN THE PIC

Hi, Most car amps run on 4 ohm or 8 ohm. Don't use larger ohm rated speakers on your system you can damage your amp. Also check that speakers are connected properly + to + and - to - (polarity is wrong) check wires for shorts or grounding too. Good luck

Hello
Check the impedence of the connected speakers. if any impedence mismatch is there, the amp will sense it and will cuto the output OFF. Use only specified speakers only. The impedence of speakres are expressed in "Ohms". Select all speakers of same impedence. If 6 Ohms is the output impedence of the amp, use only that Ohms speaker. Never use a speaker less that this Ohms. You can use a higher impedence speaker, say 8 Ohs or 16Ohms. But never use lower impedence speakers, of connect two speakers in parellel connection, which will relult in overloading. I think that I've made a satisfactory solution to you. Please don't hesitate to rate this solution. Good luck
Wish you a Merry X'mas and Happy 2012.
Gopakumarg43

Sorry, but you have a problem. The amp is rated to 4 ohms per side. Your speakers would have to be 16 ohm type to allow 3 per side in parallel. The Bose ratings are usually consumer type ratings and they would have to be set to 200 watts each (twice the rating that the amp can produce per side) to be safe connected to that amp. Your speakers are likely 8 ohm so you could parallel ONLY two per side OR if they are 4 ohm, then you would have to series them. You could series two or three per side safely for the amp. You don't tell us what model Bose speakers you have. Anyway, one has to first meet the specs of the amp and the speakers to avoid damage. It is likely the amp is too BIG for the speakers. For the setup of the mixer portion of this problem I want you to view videos on YouTube. Search for "mixer setup". Don't worry that they are different mixers than yours... there is enough commonality and the functions are nearly the same for MOST analog mixers. Recommendation: forget about two of the speakers... keep them as spares and run low volume to avoid blowing the speakers. I can't imagine any competent audio equipment supplier configuring your system this way.

G'day John,

I feel you have not connected speakers of the proper impedance. If you connect speakers of lower impedanc than it should have, you will overload the ouput amp and this could blow your speakers. So I suggest you go up one level of impedance. If you have fitted 4 ohm speakers and they blew, try fitting a pair of 8 ohm speakers. Or if they were 8 ohm, fit 16 ohm Doing this will reduce the output volume from the speakers, it it will also improve the sound. The speakers will have heavier windings too.