Are my def tech speakers really bad?

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   Running Denon AVR X4500 H. 9.2 system with DefTech mythos ST towers for front left and right and CS9080 center.

My receiver went into protect mode, so I sent to a certified denon 
repair shop. They told me left front channel in the amplifier circuit 
was blown. They told me to check that speaker before I reconnect the 
system. Disassembled the speaker and tested resistance at the woofer… 
3.8 ohms. This is a 8 ohm speaker so that concerned me. Checked the 
CS9080 and the right speaker and they both also read 3.8 ohms. All of 
the other speakers in the system are reading at roughly 7 ohms. I 
contacted deftech-support and they said they must all be blown and 
offered to sell me $600 worth of replacement parts. This seems really 
odd to me that three speakers that were working perfectly fine before I 
sent my AVR off all blew at the exact same time and it was only the 
powered DefTech speakers.

I’m thinking that maybe because these are powered speakers perhaps they 
read differently than a non-powered speaker and there’s actually nothing
 wrong with them. I’m just afraid to connect and test and damage my AVR 
again. Anyone have any experience or information on this?

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Johnpu Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 07 April 2023 Location: Oak Ridge Status: Offline Points: 2	Post Options Post Reply Quote Johnpu Report Post Thanks(0) Quote Reply Topic: Are my def tech speakers really bad? Posted: 07 April 2023 at 4:26am
	Running Denon AVR X4500 H. 9.2 system with DefTech mythos ST towers for front left and right and CS9080 center. My receiver went into protect mode, so I sent to a certified denon repair shop. They told me left front channel in the amplifier circuit was blown. They told me to check that speaker before I reconnect the system. Disassembled the speaker and tested resistance at the woofer… 3.8 ohms. This is a 8 ohm speaker so that concerned me. Checked the CS9080 and the right speaker and they both also read 3.8 ohms. All of the other speakers in the system are reading at roughly 7 ohms. I contacted deftech-support and they said they must all be blown and offered to sell me $600 worth of replacement parts. This seems really odd to me that three speakers that were working perfectly fine before I sent my AVR off all blew at the exact same time and it was only the powered DefTech speakers. I’m thinking that maybe because these are powered speakers perhaps they read differently than a non-powered speaker and there’s actually nothing wrong with them. I’m just afraid to connect and test and damage my AVR again. Anyone have any experience or information on this?

csg Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 17 September 2007 Location: bedford Status: Offline Points: 6086	Post Options Post Reply Quote csg Report Post Thanks(0) Quote Reply Posted: 07 April 2023 at 7:19am
	Firstly, measuring driver impedance with a normal meter will only get you a DC reading which will usually read approximately 30% lower than the nominal impedance. 3.8ohms DC equates to around 5.5-6 ohms which, whilst unusual, is used by manufacturers to match to amplifiers in self powered designs. Secondly if the driver moves smoothly when you push the cone (gently and evenly) while reading a reasonable DCR the chances of it being burned out is remote. I guess the manufacturer is trying to sell you expensive parts. Am i right in thinking that you have your self powered speakers connected to the speaker output of your Denon unit ? If so, does your powered speaker have a dedicated high level input or just a line level one? Either type is unlikely to damage the amplifier but obviously you can not connect the speaker output of the denon to a line level input. Connecting your self powered speakers from a line level output on your Denon couldn’t hurt the denon’s output stage
	“The fact is this is about identifying what we do best and finding more ways of doing less of it better”

Lucasdude Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 March 2013 Location: London Status: Offline Points: 636	Post Options Post Reply Quote Lucasdude Report Post Thanks(0) Quote Reply Posted: 07 April 2023 at 7:40am
	Im not sure you will find much help for HT on this forum, but ill try. A passive 8ohm speaker shouldn't measure 3.8 ohms, but bear in mind that this is a dc resistance you're measuring and not an ac impedance so don't expect an 8ohm speaker to have a dcr of that value. Those Mythos speakers are a mixture of active and passive. The top section with tweeter and 2 midrange drivers is purely passive, and the bottom driver flanked by 2 abrs is effectively an active subwoofer. This subwoofer can either be driven from the speaker terminals or from its own line input. That may be why your DC measurement is lower than expected. There are various ways to connect that system. Setting the front left and right speaker size to "Large" in the Denon setup menu and driving them with just the speaker cables is the most obvious, but if you're not using a separate active subwoofer then setting the front speakers to "Small" and connecting the 2 subwoofer line outputs from the Denon to the line inputs might be a better idea. That Denon AVR also has preamp outputs for all channels, so setting the speakers to "Large" and using both speaker and line level may take the stress off the amp. Those multi channel Denon AVRs don't like driving difficult loads on all channels. There may be a way to select 4 or 8 ohm speakers in the menu, but I can't remember so do check the manual as it might be a hidden menu item.

Lucasdude Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 March 2013 Location: London Status: Offline Points: 636	Post Options Post Reply Quote Lucasdude Report Post Thanks(0) Quote Reply Posted: 07 April 2023 at 9:40am
	https://manuals.denon.com/AVRX4500H/NA/EN/DRDZSYrhoargxb.php If you haven't done it already, I would suggest you follow the above steps and try 4 ohms for your speakers. Edited by Lucasdude - 07 April 2023 at 9:45am