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-   -   Help with MA CHP-70 gen 2 (http://www.diyaudio.com/forums/full-range/228661-help-ma-chp-70-gen-2-a.html)

satx 26th January 2013 01:07 AM

Help with MA CHP-70 gen 2
 
Hi,
I'm having a bit of trouble with a small full range that I've built. It's a CHP-70 Gen 2 in a 8L BR tuned to 60. I've tried anywhere from 52 to 60hz and like the bass from 60. Tuning confirmed with impedance measurement. The issue I'm having is with the way they sound. Everything has kind of a cupped hand effect, if that makes sense, and they sound kind of thin with not much texture or richness. I have tried adding a bsc of anywhere from 2 to 5db and they do gain some bass and become more laid back but the traits mentioned above never disappear. Run without any filter seems to sound best, but they still don't sound good.

I'm running it off a Lepai 2020A+ and when I connect other speakers they sound fine.

They only have about 20 hours on them, but it doesn't seem like they should sound like this only from lack of run-in. Maybe this is the problem though.

Also, I know the Chp-70 have a reduced output after 7K and maybe this is just the natural quality of the speaker and I choose wrong.

Any input at all would be appreciated.

Thanks,
Evan

zman01 26th January 2013 06:25 AM

Evan,

No experience with the CHP-70 gen 2, but a few things come to mind:

1. Your drivers need more hours of break-in
2. Your cabinet is not optimized - what are the dimensions?
3. Did you do a 45 degree chamfer on the inner side of the driver mounting hole (recommended for MA drivers)

satx 26th January 2013 07:18 AM

Hey zman, thanks for responding.

1. I think they probably do need more break-in
2. I think it is fairly optimal, dim are 7.25x12.75x9.5" WxHxD. 3/4 mdf for now(test cabnet)
3. I did chamfer the back of driver hole.

I have gotten them to sound a bit better by removing the acoustic stuffing and just leaving the walls lined. Also, I didn't recess the driver since this is a test cab; not sure if this could cause any of the effects I'm experiencing.

Evan

Scottmoose 26th January 2013 09:18 AM

It may well do; diffraction can have odd effects like this. The drivers do need a couple of hundred hours on them before they start to give of their best (and don't try thrashing them with heavy rock etc.: the MA units prefer a more gradual process, like car engines). Equally, the shelved down top end on the 2nd gen. CHP does make a fairly idiosyncratic balance, & it could be you just don't care for it. On the up-side, you can add a tweeter easily enough if that does prove to be the case.

satx 26th January 2013 04:52 PM

Quote:

Originally Posted by Scottmoose (Post 3342800)
It may well do; diffraction can have odd effects like this. The drivers do need a couple of hundred hours on them before they start to give of their best (and don't try thrashing them with heavy rock etc.: the MA units prefer a more gradual process, like car engines). Equally, the shelved down top end on the 2nd gen. CHP does make a fairly idiosyncratic balance, & it could be you just don't care for it. On the up-side, you can add a tweeter easily enough if that does prove to be the case.

Thanks, they actually are starting to sound better, so I may have jumped the gun a bit without giving them a proper run in. The thing that seemed to help the most was removing the stuffing. I tried anything from a handful to pretty heavily stuffed. Do the MA's not respond well to stuffing? I usually still lightly stuff a BR. Walls are lined with what I had laying around (1.5" acoustic foam and fiberglass insulation).
Also, switching to 2.5 and 3 ways I certainly become aware of the lack of tweeter, but that doesn't seem to be what's bothering me. It's more of an echo and muddy sound, lack of clarity. Maybe that's the "classic sound" mentioned? I don't have really any experience with older speakers.

Evan

Scottmoose 26th January 2013 06:09 PM

They're fine with stuffing, although it's best to avoid placing any too close to the driver, since you can mass-load & thereby slightly deform the cone under dynamic loads.

Acoustic foam is horrible stuff (no pun intended) IMO, although fiberglass works well.

Possibly. The 'classic' sound mentioned presumably refers to the fact that many (not all) older wideband units didn't have much on the top end, i.e. above about 10KHz. However, the gen.2 CHP still does have output to about 15KHz; it's just been rather abruptly shelved down at about -6dB relative to the nominal. So you still have harmonics etc. present in that region, but at a lower level. YMMV. Some people love them, others don't care for it. They seem to go down well in Japan, presumably as a tonic against the Fostex / Diatone etc. sound which tends to have considerable HF energy. Me, I think they make a useful midbass, although there's a dedicated version for that purpose.

planet10 26th January 2013 07:13 PM

Quote:

Originally Posted by satx (Post 3343286)
Do the MA's not respond well to stuffing?

BR boxes should be lined, not stuffed.

dave

satx 27th January 2013 06:01 AM

Quote:

Originally Posted by planet10 (Post 3343456)
BR boxes should be lined, not stuffed.

dave

Yes, I know that's the general consensus on BR boxes, though read many designers recommend stuffing lightly and away from port. In this case not stuffing seems to be the way to go.

So anyways, I'm starting to like them more and I'm going to let them run in some more. Do you guys have anymore advice to get the best sound from these in an 8L BR. I'm just starting to build the real boxes for them, so still time to make adjustments.

On the foam, I've used it before with decent results, but I didn't do an a/b with anything else in the same speaker. I would of liked to use felt or cotton insulation, but I couldn't really find any around. This time I'm going to probably try the fiberglass.

Evan

satx 28th January 2013 03:21 PM

update
 
Okay, so I have built permanent enclosures for these and let them run in some more. I also have worked in a some bsc; they sound good and lively without it, but I prefer a more laid back speaker. I used 1mh and 4.2 ohm in a 7" baffle for 4db.
I must say that my earlier misgivings have disappeared. They sound excellent. Good tonal balance, voices, piano, violin, electric and acoustic guitar all sound really nice. They have quite a bit of bass for a speaker this size. I originally thought I like port tuning of 60hz to give it a little boost, but I think 57-58 sounds best, still playing with this though. Also they are a little rolled off up top, but the information is still there, just reduced. I don't really miss it unless switching to something with a tweeter.

Thanks for the help guys

Evan

Bare 28th January 2013 06:18 PM

Erm.. imo It's a Toy speaker..
Charitably these do give a vignette of 'good'.
But Only a small preview. Much more is lacking than is actually delivered.
One could build the truly odd combination of a refrigerator sized box to house a 4" driver, hoping to extract hidden goodness.. or not. Try it?
But what's the sense in that?
Want better sounds? Go much bigger and pay Lots more. Or buy time proven used ?
Caveat Emptor does apply.. as always.


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