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Re: David - Just For Fun
Posted: Sun Feb 13, 2011 3:26 pm
by ewetho
Bill Fitzmaurice wrote:I've never experienced any of your dispersion issues with mine, though of course I have different drivers. Still, things shouldn't be all that different. But an MTM is intended for listening on the vertical axis, so that may be all you're experiencing.
I can't try mine with your crossover as it's in my workshop, current temperature 15 degrees, but once the weather warms I'll fool with it.
As to your crossover, a couple of things jump out. First is the 1st order high pass on the tweeter, which doesn't offer much protection. Its corner is up around 5kHz, though, so that helps. But I'd make it 2nd order at least. Second is the lack of a low pass on the mids, which will cause bandwidth overlap with the tweeter. I'd be rolling them off at 5kHz. That's a bit higher than usual with fives, but the GRs have good off-axis that high, so it's not problematic. Also be sure to try swapping the tweeter polarity, in an MTM it's critical, especially with respect to vertical dispersion.
With the new crossover dispersion issues are almost non-existent. Less than a melded array without the diffuser.
As for tweet protection Steve is going to add a poly-switch and resistor in parallel for tweet protection.
Sound is overall very smooth right now not overly hot in the mids clear and distinct. Sound is VERY close to our big SLA in the shop. Think we are very VERY close.
chaywood wrote:
Good thing you watched all the episodes of McGyver and know how to build crossovers using the parts off a junk microwave oven !
Looking good so far... and it must sound perfect to make it through quality control !
Hope to see some cherry wood soon !!!!
CH
The old Sharp was only sitting on top of the stove taking up space anyway. JK...
Prepping for veneer as I write.
Also starting a second 612 SLA based on the Pyles and Goldwoods.......
Re: David - Just For Fun
Posted: Sun Feb 13, 2011 8:58 pm
by Steve Regier
All sanded and veneer is on.
Cherry veneer with Red Walnut Stain in gloss finish
Re: David - Just For Fun
Posted: Sun Feb 13, 2011 10:17 pm
by ewetho
Had to leave before the staining unfortunately (sort of, went to dinner with the WIFE!!! YUMM!) so I had to see the color by picture...
Steve good pic and choice for color!
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 11:57 am
by chaywood
Hey Steve,
What frequency is the High Pass on the Mid-Woofers ? Looks like you have them in series ?
Charlie
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 11:58 am
by ewetho
Sub to MTM crossover is ~140 Hz
Tweet has a 1st order High Pass
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 12:05 pm
by Steve Regier
chaywood wrote:Hey Steve,
What frequency is the High Pass on the Mid-Woofers ? Looks like you have then in series ?
Charlie
Misprint. They are in parallel.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 12:25 pm
by Steve Regier
Thanks for the catch. I was too busy stripping the old microwave for spare parts and was distracted when documenting.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 1:08 pm
by Steve Regier
...now that I am on to making diagram corrections; Here is the crossover with tweeter protection. It uses a 0.9A Erse Poly Swtich which goes to high resistance when tripped. Current then flows though the 20Ohm resistor allowing the tweet to still play but at a 10Db reduction. This should happen at about 70watts.
I just noticed that the T6 tweeters are not on the GR-Research product page at this time. I hope this is temporary and they have not been discontinued. I'm glad I got my matched pair already...but I was planning on building a couple more Davids.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 2:43 pm
by Bill Fitzmaurice
baronvonsteve wrote:.
I just noticed that the T6 tweeters are not on the GR-Research product page at this time.
The T3 seems to have been upgraded, it's a couple of dB less sensitive than the T6 but still suitable.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 6:06 pm
by Steve Regier
Bill Fitzmaurice wrote:baronvonsteve wrote:.
I just noticed that the T6 tweeters are not on the GR-Research product page at this time.
The T3 seems to have been upgraded, it's a couple of dB less sensitive than the T6 but still suitable.
Thank goodness...
OK, just got out of the shop and here are some more build pics. I will be finisheing the sides and back a bit later tonight I hope.
I also measured the response of the cab. I measure 110Db at 6.5V without any boundary loading. The cab is just sitting in the middle of a bare shop floor.
Can't wait to get it corner loaded and connected to my Kenwood M2 linear power amp
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 6:13 pm
by LelandCrooks
Niiiice.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 6:38 pm
by chrapladm
Has anyone ever just made a SLA top a tuba?
I will probably be making myself some Davids but was hoping to have everything I could out of the SLA but with the extension of the tuba cab.
I think it would be cool to have a SLA baffle on the front of a tall tube design or something keeping it under 48" tall and maybe 16" deep.
Anyways sorry for babbling.
Awesome build and finish.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 7:02 pm
by Bill Fitzmaurice
baronvonsteve wrote:...now that I am on to making diagram corrections; Here is the crossover with tweeter protection. It uses a 0.9A Erse Poly Swtich which goes to high resistance when tripped. Current then flows though the 20Ohm resistor allowing the tweet to still play but at a 10Db reduction.
When that happens the lowered impedance also causes the high-pass frequency to drop to the vicinity of 1.2kHz. That greatly increases the potential for over-excursion damage, while the overall power density is reduced more on the order of 4dB. Increasing the HP filter slope is the better option.
Has anyone ever just made a SLA top a tuba?
Put an SLA atop an AT and you have it.
Re: David - Just For Fun
Posted: Mon Feb 14, 2011 9:49 pm
by Steve Regier
An excellent point, Bill. I will eliminate R1, the 20 Ohm resistor, so the tweet circuit will just open when overpowered.
Thanks.
Re: David - Just For Fun
Posted: Tue Feb 15, 2011 3:34 pm
by Steve Regier
Build Update!
Build Update!
Build Update!
David is completed and ready for the living room test.
I added floor spikes, buffed the urathane, installed grille fasteners, masked and duratexed the back bottom and sides, installed the access panel and VIOLA! I tried using T-nuts and cap screws for the access cover and the results were excellent. I will be doing covers that way from now on.
...move into the living room for a glamour shot or two and when I return from this thing we call "making a living" I'll fire it up in a room and report.