HELP -- SUB sounds good OUT of the box but not.........

broguearcher

when I put it back into the box!!!! If you've read any of my previous posts, then you remember me asking for help with my 10" MOMO SVC Sub due to it sounding "bad"..... broken/blown sound when played, almost like the speaker is torn....

Well, I had numerous people here tell me that the problem was probably due to the cheap amp I was using..... fair enough.... went and bought a Kenwood KAC-7201. I know it's not top notch, but better than what I had.

Prior to buying the new amp though I went and purchased a brand new in the box 10" MOMO DVC sub because at that point I believed the problem to be with the sub itself. I experienced the same trouble with the new DVC sub as the sound was virtually identical...... So, I eliminated the sub as an issue.

Next, I purchased new RCA cables and installed them. New amplifier arrived today. Installed it tonight, get it all rigged up and then tested both the SVC and DVC speakers.....SAME old response!!! The speakers perform very well when sitting outside the box (being driven only moderately). The speaker excursion on both is perfect and there is no noticeable distortion of any kind. Put the speaker down into the enclosure and bang, all of sudden, sounds like garbage!!!..... as if the speaker is about to break apart!! I even tried out the speaker-level inputs so I could be sure that the CD Player itself wasn't sending a bad signal out to the amp. Same response as with RCA cables.

A little background on the enclosure itself: I built it myself from 3/4" MDF. It's almost exactly .6 cu ft interior. The front panel where the sub is mounted is actually double thickness as I adhered two boards together for more stability. I completely sealed all of the seams internally. The cutout hole for the sub is a little rough (not round really) as I did not have a pattern for the original SVC I used and had to cut around the edges of the hole to create a good fit. I filled the box about half full with fiberglass insulation. I took ALL of the insulation out tonight and dropped the sub back in to quickly test......sounded even WORSE!!! The speaker wires run directly through the side of the box (instead of using terminals) and this hole is sealed thoroughly from the inside. The outside of the box is covered with carpeting left over from an installation of carpet in our home.

Back when I actually had the SVC secured down into the box with screws, it did sound "good".... sort of.... but only from the cab of the car. When I would get in front of the sub and listen it was clear that some problem was existing.

So, experts, please help me. What would cause BOTH of these subs to sound perfect when played in the free air but when faced with the slightest amount of air resistance (even as they are just being set down into the hole cutout!!) they sound like they are blown and play all sorts of distortion?

Thanks..... I'm out of patience and done with spending money at the moment to fix this mess.

kenstewart

If your box is sealed completely, I wonder if you have any problems with any air gap on your double thick front panel. It's gotta be something with your box if it sounds decent outside, then like crap when you put it in the box. New box is cheap to build, maybe try it with just single front panel since you're using 3/4" mdf, is plenty strong.

broguearcher

sounds like crap is right.....they both do when set into the box. Like I said in the first post, as the speakers are just being introduced down into the hole (not even touching the wood yet!!) they start to sound distorted. Any other help on this one?

Thanks,

Sam

kenstewart wrote:

If your box is sealed completely, I wonder if you have any problems with any air gap on your double thick front panel. It's gotta be something with your box if it sounds decent outside, then like crap when you put it in the box. New box is cheap to build, maybe try it with just single front panel since you're using 3/4" mdf, is plenty strong.

MacLeod

How do you have it wired to the amp? Correct me if Im wrong but isnt the 7201 a 2 channel amp? If so, and you bridged it to a DVC sub youre running it at 2 ohms mono which it isnt rated to handle so its not only sending a distorted and clipped signal but its also sending way more power than the sub is rated to handle. If you have it wired in stereo, one channel to one voice coil then youd be fine.

A quick way to tell is to go to the show where you bought your sub and ask if you can borrow one of their premade boxes for some trouble shooting. Stick your sub in there running off your amp and setup and if it still distorts then you know the problem lies in your system as with too much power or whatever. If it works fine then you know you need to build a new box.

1996blackmax

Mac is right, your running that amp at too low of an impedance.

The advice of using another box is good.

One thing stuck out to me... Are you doing you listening test without the sub actually being screwed down onto the box? You mentioned that you only had the other sub screwed down. If so, do your listening with the sub screwed down. Air leaks will make a sub sound like crap when it's playing at louder volume levels.

broguearcher

couple of things........ I'm not running the DVC at 2 ohms. I actually wired each coil separately to test it. With the SVC sub (also tested it yesterday) the sound is the same so it doesn't seem to matter anyway..... like I was saying though..... the sound is precisely the same as when the sub WAS screwed down into the box ..... no difference really that I can tell. I guess a new box is in order..... holy crap...... that will mean that I'm on my 2nd generation of every component other than the stereo itself!!! geeezzzzz

Sam

1996blackmax wrote:

Mac is right, your running that amp at too low of an impedance.

The advice of using another box is good.

One thing stuck out to me... Are you doing you listening test without the sub actually being screwed down onto the box? You mentioned that you only had the other sub screwed down. If so, do your listening with the sub screwed down. Air leaks will make a sub sound like crap when it's playing at louder volume levels.

MacLeod

broguearcher wrote:

couple of things........ I'm not running the DVC at 2 ohms. I actually wired each coil separately to test it.

Ya lost me on this one bro. Are you saying you only hooked up to one voice coil?

The ONLY way you can run the DVC subs with 2 channel amp safely is by hooking up the left channel of the amp to one VC and the right channel of the amp to the other VC at the same time. You cant run a DVC sub by hooking up to only one voice coil.

Either way, something is very much wrong. And my guess is either youre overpowering the sub, overdriving the amp or the box is the culprit which I kinda doubt. Im still leaning to improper amp setup. That is a 460 watt amp and only a 300 watt sub so this is further evidence of an overpowered sub.

**EDIT**
I went back and re-read some of your old posts. Youre describing a buzzing sound. That points me back to the box. Are you sure the buzzing sound isnt coming from the box itself?

broguearcher

I had the new amp running one channel into each of the voice coils..... two channel amp, two voice coils........ it's hardly the point though!!!! the sub sounds exactly the same as the SVC model that I still have and that I tested out as well. You guys are also missing something else!!! the previous amp I had was by no means overpowering the sub!! it was only running 150 RMS and the sound was the same. Also, I was barely even pushing my new Kenwood amp last night when I tried it out. There was no way that I was overpowering anything!!!! I think I'm just cursed with this gear of late. Also, I do know for a fact that the amp is wired correctly.... don't know of any particular issues that might be related to the wiring but it seems I have done everything correctly.... the amp is being powered up just fine from what I can tell.... clear signal from the RCAs apparently..... it's just a mystery.

broguearcher

it is quite possible that the box itself is the issue..... when I built it I though that I had securely put it together but maybe not so much....... I think it's just time for me to locate a new enclosure and be done with the nonsense.

Sam

MacLeod wrote:

Ya lost me on this one bro. Are you saying you only hooked up to one voice coil?

The ONLY way you can run the DVC subs with 2 channel amp safely is by hooking up the left channel of the amp to one VC and the right channel of the amp to the other VC at the same time. You cant run a DVC sub by hooking up to only one voice coil.

Either way, something is very much wrong. And my guess is either youre overpowering the sub, overdriving the amp or the box is the culprit which I kinda doubt. Im still leaning to improper amp setup. That is a 460 watt amp and only a 300 watt sub so this is further evidence of an overpowered sub.

**EDIT**
I went back and re-read some of your old posts. Youre describing a buzzing sound. That points me back to the box. Are you sure the buzzing sound isnt coming from the box itself?

MacLeod

You say your sub is playing very distorted and sounding like its blown, the amp is going to be the first place anybody would look cause a box will not cause this unless its extremely small or large but an overpowering or overdriven amp will cause this every time.

Second, a tiny 150 watt amp could easily be the culprit. An amp that small wont give you the power you need to you may have turned up the gain way to far to compensate and then cranked on the volume and BAMMO! Instant clipping which is a heavily distorted signal.

Now that Ive re-read your old posts and saw where its not a distorted or blown sound coming from the sub but rather a buzzing, I now think the box is the culprit.

Do like I said, run down to the shop where you bought your subs and ask to use one of their premade boxes. Since youve bought 2 subs there already Im sure they wouldnt mind helping you out a bit. This way you can stick your sub in their box......that kinda sounds dirty.........with your existing setup and see if it fixes it or not.

broguearcher

both amps produced the same result with both speakers so it really must be the box.... I don't fully understand how or why but it must be. I ordered a new box just this evening (much nicer than what I have anyway) so we'll see what happens when that one arrives at the end of this week. Thanks for the help!!

MacLeod wrote:

You say your sub is playing very distorted and sounding like its blown, the amp is going to be the first place anybody would look cause
a box will not cause this unless its extremely small or large but an


overpowering or overdriven amp will cause this every time.

Second, a tiny 150 watt amp could easily be the culprit. An amp that small wont give you the power you need to you may have turned up the gain way to far to compensate and then cranked on the volume and BAMMO! Instant clipping which is a heavily distorted signal.

Now that Ive re-read your old posts and saw where its not a distorted or blown sound coming from the sub but rather a buzzing, I now think the box is the culprit.

Do like I said, run down to the shop where you bought your subs and ask to use one of their premade boxes. Since youve bought 2 subs there already Im sure they wouldnt mind helping you out a bit. This way you can stick your sub in their box......that kinda sounds dirty.........with your existing setup and see if it fixes it or not.