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Bob Brines 2nd April 2012 03:04 AM

My New Dipoles
 
1 Attachment(s)
Fired up my latest project Ė Alpair 7.3ís on small OBís over Goldwood GW-1858ís in H-frames. My initial impression is that I am underwhelmed. Tomorrow, I will try my T7-A7 TLís as tops.

Design decisions will dictate the results. For the same reasons that I donít do big double BVRís and back-horns, I wonít do big OBís. I have no place to put speakers much bigger than the 43Ēx12Ē MLTLís. If I built one commercially, I would have no reasonable way to ship it. Anyway, a large OB is out of the question. The OBís in the picture are 20Ē tall, 10Ē wide at the base and 5Ē wide at the top. These are strictly test mules cut out of scrap plywood. If I decide to go with them, I will do them out of walnut lumber double thick at the edges. The H-baffles are already done in walnut veneer.

The cross-over is done in Foobar2000 on a laptop. There is a basic XO plug-in that works pretty well. It is a 3-way XO at any frequency and any order. Cross-over points do not have to be symmetric. 31- band graphic EQ is also available within the player. (I have a miniDSP on the way, but as well a Foobar2000 is working, I may have wasted $150.) The output goes via USB to an M-Audio Ultra Track which splits to output into four channels and converts to analog. The treble goes to a Topping TP-60 and on to the Alpair 7.3ís. The bass goes to a Dayton DTA-100 and on to the GW-1858ís.

Because of their size, the OBís have an acoustic roll-off at ~300Hz. I high-passed them at 100Hz 4th order just to reduce excursion. I could probably cut them higher and will play with that if I go with the OBís. The H-baffles are low passed at 125Hz 3rd order. The cross-over appears to be working. The SPL is pretty flat across as measured with an SPL meter. (Since my laptop, my only computer, is running the DSP, I canít use it to run my measurement suite!
)
Basically, the system sounds pretty good. On the pop stuff I test with (Alison Krauss, Diana Krall, Fleetwood Mac, Pink Floyd and a bunch of other stuff), I have no problems. The bass is just a bit tubby (Iíd say slow it I didnít know that bass isnít slow, the midís are). With classical music, there is a big problem. The low celloís are hollow and muddy. Bass is fine, treble is great. Upper bass is screwed up. Since this range is handled by the H-frames, the problem probably resides there. I will have to investigate. I may not be able to run the H-frames that high. If so, the OBís are out and the TLís are in. I can run TLís at least as deep as 80Hz and still reduce the excursion to reasonable limits. At 80dB@8í with pretty strong kick drum, neither driver moves visibly. Since both amps are sitting at 10 oíclock, ear bleed SPL is assured.
More tests tomorrow.

Bob

Godzilla 2nd April 2012 04:00 AM

>>> The H-baffles are already done in walnut veneer.

They look great.

I have Alpha 15s in H frames and think they begin contaminating the overall sound if crossed over too high (as in over 90hz). These things are meant to play bass ONLY. If the 15 inch drivers become audibly intrusive than the 18 inch Goldwoods probably even more so. I'd keep them below 70hz (estimated of course... i've never heard the Goldwoods).

When i built the H frames i knew i would not be happy with a small OB on top like yours because they would not go low enough to allow a low enough crossover. Mated to BIBs i was able to blend the H frames well between 50 and 70hz with excellent results. When i made my OB I found the Eminence Beta 12lta went to around 150hz on a 20 x 20 inch baffle and was able to fiddle with the variable crossover on the sub amp to get a good blend. I listened to them for hours today and they just make me happy with their great, full, relaxed sound. I love them.

As neat as the Alpair's are... not sure i would enjoy them in the configuration you are listening to right now. I had the TB 1808s on OB and they just barely blended with the H frames for good results to my ears. I will be doing something else with those drivers in the future.

One of the great advantages of H frames (if you like their sound and they fit your room) is they serve as speaker stands too. I hope you try other bookshelf type designs to sit atop your lovely H frames... personally, i think many boxed speakers tailored to the H frames dimensions would work excellently!

Don't give up on them and please let us know your progress.

Thanks!
Zilla

Bob Brines 2nd April 2012 04:10 AM

I am thinking that the problem is cavity resonance. The range I am hearing the problem in is somewhere 60-100Hz. The Goldwoods in a different cabinet should be good to 200Hz or so.

Given the same rough volume, if I can't make the H-frames work with the small TL's, the Dayton RSS315HF will give both deeper bass and go up to 500Hz. I do have high hopes for the H-frames and the TL's. though.

Bob

DYNABLASTERTUNERS 2nd April 2012 07:11 AM

I think the bass is too big and Alpair too small, and also where is the body in music if you cross the tiny Alpair so low... I don't know much, either in theory nor in praxis, but I know that driver size, crossover, etc. must be in harmony :)

zmyrna 2nd April 2012 11:05 AM

Well, if the bass is fine and treble is great, then you should focus on in between.
I think it is impossible to have good mids with such a small driver on open baffle.
For full cello and probably piano and voices, you will need a 8" or 12" with a qts around 0.7.
And also, you are trying to blend a driver with a 3gr membrane with one that is over 100gr.
Since you already have the 3 way capability, I would add a light papercone 12" in the middle on OB with shallow wings around it.

Rudolf 2nd April 2012 02:06 PM

Quote:

Originally Posted by Bob Brines (Post 2969358)
Fired up my latest project Ė Alpair 7.3ís on small OBís over Goldwood GW-1858ís in H-frames. My initial impression is that I am underwhelmed.

Did you design them with the MJK worksheet? Including the room situation? I'm not sure those H frames are far enough from the front wall. As mentioned by others, the size difference between the drivers is an issue too. Makes it difficult to find a good Xover frequency.

bigaudioscotto 2nd April 2012 06:30 PM

Bob

I would try a solid baffle for both units,The H frames are great
but I could never get them to blend with other drivers,
something strange in the 200Hz to 300Hz range for sure.
I used a pair of CSS el70 with Eminence Alpha 15a for a while on
single flat baffle 20 wide 40 high with the EL70 off set to one side
and it actually sounded very good.
I will tell you that size matters greatly when it come to OB
driver and baffle I tend to like 8 inch on up to 15 inch full range
units better than the smaller drivers personally.


Quote:

Originally Posted by Bob Brines (Post 2969395)
I am thinking that the problem is cavity resonance. The range I am hearing the problem in is somewhere 60-100Hz. The Goldwoods in a different cabinet should be good to 200Hz or so.

Given the same rough volume, if I can't make the H-frames work with the small TL's, the Dayton RSS315HF will give both deeper bass and go up to 500Hz. I do have high hopes for the H-frames and the TL's. though.

Bob


zmyrna 2nd April 2012 06:55 PM

I think those H frames are nicely built. It would be a shame to break them up.
They should be fine if crossed low enough.
Plus putting the 18" driver on the same baffle with the FR will make the FR sound worse because of the vibration.

Bob Brines 2nd April 2012 06:58 PM

Quote:

Originally Posted by bigaudioscotto (Post 2970144)
Bob

I would try a solid baffle for both units....

As I said in my OP. large single panel OB's are not allowed.

I am in the midst of testing the small TL's with the H-frames. I have confirmed that my problem is a cavity resonance around 100Hz. Using a 4th order Chebyshev low-pass on the H-frames and 4th order Butterworth at 100 on the TL's.The cross-over is smack-dab in the middle of a room mode. Bass into the hole, treble out. Seamless. I still need to play a while. More later.

Bob

soundaatma 2nd April 2012 09:05 PM

Using a small TL on an H-frame bass unit is only as good as a good musical subwoofer mated with a bookshelf speaker :( with none of the boxless spacious sound of a full spectrum OB speaker.

I would hate to see you throwing out the baby with the bath, if you dismiss the wide ranger on OB atop the h-frame, so early:eek: !! Martin has pioneered this concept with excellent results from so many including myself. The lifelike transient response of the mid-bass and bass frequencies ( ie upwards from 40Hz) produced by an H-frame rivals even dedicated high output midbass modules like the Hsu MBM unit. I am yet to hear the very expensive Rythmiks.

Going by Martin's sheets you simply need some deep "wings", maybe 8-10", on your narrow OB on top, to make it fly !! Or even better and with the same dimensions, do a 2 way OB on top with an 8-10" midrange and tweeter...like the Basszilla.:D

I had started with 15" GW in H-frame and then switched to the ubiquitous Eminence 15 alpha, giving a harder punch. :D


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