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-   -   Replaced speakers and results not as expected. (http://www.diyaudio.com/forums/multi-way/225285-replaced-speakers-results-not-expected.html)

greyhnd 8th December 2012 10:08 PM

Replaced speakers and results not as expected.
 
Hello folks and good day.

This is my first post here, so I hope I can explain my situation so it makes sense.

I picked up a pair of Kenwood KS-401HT front speakers at a local thrift shop on the cheap. I was originally going to only use the boxes, but they sounded ok for my needs except they are lacking in the bass department. I've been unable to find much in the way of specs other than the frequency response is rated at 100Hz to 20Khz. The speakers are 3 ways with two 4" "woofers" and a 1" tweeter. They have a cheesy little crossover, but I haven't yet took it out to look at it.

I purchased two house brand 4" woofers from MCM electronics, The frequency response is 50HZ to 17Khz. I have the other specs if needed. I replaced one of each of the stock speakers with the new ones and now they sound worse than before. The overall sound is "sloppy" and the tweeters seem more overpowering.

I'm not all that smart, but I'm assuming I have a crossover problem to deal with. And I suppose along with that the new speakers are not a good match with the remaining originals. I'm not certain where I need to start to correct the problem. Unhook the factory speakers in each and just use the new? Make some kind of adjustment to the crossovers? I realize I'm not getting full benefit of the lower freq resp with the current crossovers.

I'm using a Lepai TA2020 t-amp to power them and my source is my pc soundcard. I also have an older DAC that I'm not using, but should I be?

Any suggestions or guidance is appreciated.
Thanks in advance.

wintermute 8th December 2012 10:40 PM

Hi greyhnd and welcome to the forum :)

There are a few things that could be contributing to your less than favourable results.

1. The new speakers may not be as efficient as the ones that they replaced, resulting in an imbalance between the bass and the treble.

2. The new speakers may not work well in the original cabinet (especially if it is a vented cabinet). Best thing to do would be to work out what the volume of the box is and if it is vented the dimentions of the vent, and model the new speakers in something like winisd or unibox. suboptimal box for the speakers may lead to similar results as point 1.

3. the new drivers have a different impedance to the old ones which when combined with the original crossover have shifted the crossover point. This may be resulting in either a hole in the reponse or a boost in levels at a particular range of frequencies.

One way to try and get some balance back would be to put an lpad on the tweeter.

You said this is a three way, but I'm wondering if it is actually a 2.5 way? Are there any speakers other than the 2 X 4" and the tweeter?

Tony.

greyhnd 8th December 2012 11:22 PM

Hello Tony and thanks for the welcome.
Let me see if I can answer your questions so they make sense.

1. The new speakers are rated at 86db sensitivity. I've been unable to find that info for the original speakers for comparison.

2. The enclosures are a sealed design. I have the specs for the new woofers provided by MCM and I think they are complete enough to use with the programs you mentioned.

3. Both the original and new drivers are rated at 8ohms. The new have RE: 6.8ohms and again, I'm unable to find that info about the originals.

An lpad may be a viable solution for taming the tweeters if needed.

And finally, there are only 2 4" woofers and the single 1" tweeter in each enclosure. without looking I can't tell you how the woofers are wired to the crossovers, if needed I'll get that info for you.

One thing I will mention and it may or may not be important. The enclosures were originally a part of a Kenwood 5.1 HT system, being the front speakers in that system. Not sure if that makes a difference but it might be worth mentioning.

This link is for the new woofers at MCM.
MCM Audio Select 4'' Shielded Aluminum Cone Woofer | 55-1853 (551853) | MCM Audio Select
Perhaps the info there will help.

planet10 8th December 2012 11:39 PM

Pictures inside & out would be useful. Dimensions as well (inside more useful then outside).

The speakers are likely MTM, so in fact a 2-way.

You took a crap-shoot with the MCM drivers without doing the simulations needed to see if they work sealed & in the volume of enclosure you have. Just replacing 1 likely tells you nothing, as 2 different drivers in the sam evolume will have them fighting each other. House brand 4" often means cheap & nasty.


We'll be able to tell you more once we see pictures.

greyhnd 9th December 2012 01:43 AM

Okay, I'll yank the drivers out of one of the enclosures and see if I can get some clear pics. Just bought a new digital camera so I'll find out how good it is.

The 2 different drivers fighting each other makes sense to me now that its been mentioned. I also didn't think about vented or ported enclosures and the MCM description didn't give an indication of preference.

wintermute 9th December 2012 07:52 AM

oh I didn't pick up on that! I thought you replaced both the 4" dirvers. Definitely two different drivers sharing the same volume would likely be problematic.

I threw the T/S params (taking a guess for sd at 50 square centimeters) into unibox. The MCM drivers look to be more suited to vented than sealed.

Certainly to get any decent bass out of them seems to require a vented alignment. Also power handling will tend to be better (down to Fb) with vented.

As sealed is pretty forgiving you could get away with between 3L and 18L for two of the MCM's in the same enclosure. I'd suggest taking both of the MCM's and putting them into just one of the enclosures and see how that sounds. Note that power handling with the big box will be very low.

Tony.

BlueWizard 9th December 2012 10:02 AM

Make Absolutely Positively beyond any Shadow of a Doubt sure that the new driver is wired properly. That in every case, the Red(+) of the amp, Red(+) of the speaker terminal, and the (+) of the drivers are connected.

If one driver is wired backwards, then it is going to be out of phase, and huge blocks of frequencies are going to be canceled out.

You should be able to determine which wires are tied to the common ground, and that in turn tells you which wire are the hot or (+) wires.

Also, describe the surrounds of the original speakers. Surrounds being that ring of rubber that attaches the Driver Frame to the Driver Cone. If it has several accordion like pleats in it, then it is probably an acoustic suspension driver. If it has a single large half-circle of foam or rubber, then it is likely a standard driver.

Acoustic Suspension drivers depend on the cabinet being sealed. They have very loose suspensions, and depend on the tension of the air in the cabinet to keep them under control.

Also, just out of curiosity, how much did the replacement speaker cost?

Remember, you get what you pay for.

Steve/bluewizard

Hsmeets 9th December 2012 11:18 AM

there is no point in just replacing one driver with another.

Drivers have certain electro-mechanical characteristics expressed in the so called Thiele-Small parameters. Especially for woofers these TS parameters are key to calculate the cabinet size (wether that is a closed, vented or other type of cabinet).

A driver has a certain impedance (a complex product of resistance and phase) and an inductance (part of the TS parameters) and when designing the cross-over filter the TS parameters of the driver must taken into account as the driver itself is also part of the crossover network and (again, repeat myself) as such any calculated textbook x-over will not work as the working is influenced by the driver is part of the network

As said, just replacing drivers is a crap shot, to have these new drivers work properly you most likely would end up with building new cabinets and x-overs.

greyhnd 9th December 2012 06:47 PM

Tony - I truly wasn't expecting miracles from the speaker swap, just wanted to add a little low end to the sound. Did you get the parameters from the MCM website? That was all I had to work with. Nothing in the speaker description suggests vented or sealed, so I took a stab at it. I don't think power handling will be an issue since I'm using one of Lepai T-amps to run them. I'll try what you suggested and put both of the MCM speakers in the same box and see how it sounds. Thanks for that suggestion.

Steve - As you suggested, I checked all my connections again and they are all correct. The speakers have different sized spade terminals, so they'll only wire one way. I make a habit of wrapping a piece of electrical tape around the + leads so I don't get them mixed up.

As far as the surrounds are concerned, the factory speakers have a "mottled" appearance to the surrounds. Not pleated or ribbed, but not smooth either. The MCM speakers have a normal rubber surround that is smooth.

The speakers were on sale for something like $11 US each. Retail is about $30 if I remember correctly. The build quality is actually pretty good and I've paid more for drivers that were put together like crap.

This was just a speaker pair I picked up at the thrift store for the cabinets originally. When I connected them they sound fine and are in good working condition. That's why I decided to swap in some speakers to see if I could give them a bit more low end. I'm not expecting miracles by any means, thank goodness.

I'll try to post some pics a bit later in the day.

Dissi 9th December 2012 09:03 PM

The MCM 55-1853 has been measured by Zaph and seems to be decent:

Zaph|Audio

As the impedance of the speaker is 8 ohm, the two original midwoofers are either 4 ohm and in series or 16 ohm and in parallel. The replacement driver is 8 ohm, no wonder the crossover doesn't work anymore.


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