Crossover Design Changes Based on Horn Dispersion

[toddalin]

Server was down all day yesterday.

When I had the woofers done, I had three done at the same time (all 2205s to 2235s). To my ear, and crude equipment, all three exhibit the same tendancies.

I would love to get to the bottom of this as it's been bumming me out since I replaced the 130As back in Dec 2005.

If it is a recharge ($35/each) that would certainly beat $190/each for recones. (Still, as I just had them done... it's ) And yes, as I recall, the cones did look to be JBL (with #s).

[4313B]

AFAIC ,,, a thread becomes a blog once it has become nothing more than a "one-way" dictation of personal information or experience .

Perfect. And we've had a few of them.

I've personally deleted posts when I perceived that I was talking to myself.

However, we also have a few bloggers who are constantly encouraged by at least one other member to continue to do so.

- I see no need for an apology.

Agreed!

Refreshing! Thanks Grumpy!

[grumpy]

Well, thanks.

Hope to make it back over to Todd's sometime soon... now that there are some specific
things identified that really -need- measuring and I know what to bring. -grumpy

[toddalin]

Well, thanks.

Hope to make it back over to Todd's sometime soon... now that there are some specific
things identified that really -need- measuring and I know what to bring. -grumpy

Thanks. I bought the woofers on ebay as baskets and they went straight in to OCS for recharge/recone to replace the 130As. As I noted, these woofers have been a thorn in my side (ear) since I put them in.

Zilch can attest to how frustrated I was at the time. I went to the point of building the new "keeper" crossovers, thinking that the old N1200s may have been the trouble (i.e., horn not reaching low enough to meet the new woofer). And while the crossovers are sweet (and were costly to build), evidently, that wasn't the cause and they weren't the cure.

[glen]

Thanks for coming by. Was a ball! We'll all have to do it again sometime. Maybe when you have time to sit through a move and listen to some SACD.

Glen, it was great! Still don't know how I let you talk me "down" on the 421A. Come on by sometime and lunch/dinner is on me.

Todd and Linda were great hosts, opening up their fun and beautiful home to show off the great sound system, GIANT train layout and cool cars.

Grumpy had a really nice and compact setup for measuring the speaker performance and his proficiency with it was quite impressive as he could focus in on nuances of the speaker response.

You know you're having fun when your butt is shaking to the Star Wars pod race!

[grumpy]

Follow up: Tested 2205/2235 using WT2...

BL was down ~17-18 vs a new 2235H (and an older/used one) that
came in around 23. Qes (and hence Qts) was also much higher than spec,
presumably due to the weak magnet... someone tell me if they know this
is cause and effect is true or false.

All other parameters, whether using Delta-Mass or In-Box
measurement techniques, indicated that the cone/suspension was correct
for a 2235H. Time to talk to OCS about the recharge?

Replacing Alnico-framed 2235 with a new one did alter the response some
but after many measurements and mic placement changes, we decided to
move the speakers relative to the walls. Sidewall reflections appear to
be the main suckout culprit in the 500-900Hz octave.

Scooting the systems closer (inches) to the rear walls helped smooth the
response a bit elsewhere.

http://www.acoustimac.com/products.asp , some light cloth, and a bit
of molding

Good news: when the speakers are wired with one cabinet out of phase,
it's now -really- obvious (a brief mix-up which was sorted out quickly).

Doing a L-R comparison FR plot also brought out that there was a polarity
issue with the 075 in one channel (Todd, I looked at the impulse plots
later, and this was indeed an issue, which we corrected near end of day).

+/- 3dB from ~40-14KHz (albeit 1/3 octave) is still nothing to sneeze at
and some by-ear tweaking of levels for the listening position made the
system pretty smooth to listen to (the point, after all). L-R matching (FR
tracking is within 1/2dB almost throughout the useful bandwidth... in
no small part due to Todd's carefully measured speaker placement and
fairly symmetrical room.

Looking at a few more options w/Todd.

-grumpy

[Mr. Widget]

I know that the W-series were intended as automotive "subwoofers", but here is the measured response of the W10GTI in a 1.4 cu ft cabinet with just a 2" hole in the cabinet front to serve as a port. This is not bad for a very simple project! The keeper crossovers actually seem to flatten out the downslope trend making the curve even flatter.

That is a rather odd looking plot... could you tell us more about it? i.e. is it a nearfield measurement?, a groundplane measurement?, one taken at a meter or more? ...also, is it of just the woofer, or woofer and network?


Widget

PS: I reposted the plot so that it could be viewed without the need to download it.

[toddalin]

That is a rather odd looking plot... could you tell us more about it? i.e. is it a nearfield measurement?, a groundplane measurement?, one taken at a meter or more? ...also, is it of just the woofer, or woofer and network?


Widget

PS: I reposted the plot so that it could be viewed without the need to download it.

This one is the very nearfield (almost touching the woofer cone where the dustcap is glued to the cone) with just the woofer in the 1.4 cu ft box with a 2" diameter hole (where tweeter was) with no crossover at all.

[grumpy]

That is a rather odd looking plot... could you tell us more about it? i.e. is it a nearfield measurement?, a groundplane measurement?, one taken at a meter or more? ...also, is it of just the woofer, or woofer and network?

"2) Blue - WT10GTi in CV cab, no crossover (5mm, between dustcap and cone)"

a very nearfield measurement. I agree it's an interesting response, but I wouldn't fuss
over it too much.

BTW, the 3110 referred to earlier may very well be ... impaired. I haven't had time to
run tests with it solo, so I'd toss out any "data" related to that. Just because we could
shift levels around to make it look flatter, doesn't make it a good test.

I would expect that Todd's surround speaker update idea could benefit from a
bit more thought before putting a lot of money into specific passive crossover parts,
but the general idea of using something like the WT sub when there are space
limitations doesn't bother me if it's used within it's limits.

-grumpy

[Earl K]

Follow up: Tested 2205/2235 using WT2...

BL was down ~17-18 vs a new 2235H (and an older/used one) that
came in around 23. Qes (and hence Qts) was also much higher than spec,
presumably due to the weak magnet... someone tell me if they know this
is cause and effect is true or false.

- Since BL is the "product" ; of the length of wire ( in the gap ) times the gauss strength ( as measured in the gap ) , it stands to reason that reducing either of these factors ( or both ) , will result in a lower value ( BL ) .
- Right now it's only a working assumption that the gauss strength in the gap is down in value. ( gap strength needs to be measured with the cone removed )
- A similarly smaller ( than stock ) BL product could be achieved by a reconer using a voice coil that has less turns than the stock JBL . A dead giveaway of a coil with fewer turns is an "Le" that is lower than JBL spec .
- Anyways, a higher Qts woofer will have more bass / though at a price of reduced motional control over the cone ( ie; resulting in, less defined musical "notes" ) .

All other parameters, whether using Delta-Mass or In-Box
measurement techniques, indicated that the cone/suspension was correct
for a 2235H. Time to talk to OCS about the recharge?

- If you're confident those TS parameters ( that you've recently measured ) are accurate / it's time to let OCS know that their rebuilds don't measure up ( literally ) . I'd ask them if they have a recommendation to rectify the situation .

Replacing Alnico-framed 2235 with a new one did alter the response some
but after many measurements and mic placement changes, we decided to
move the speakers relative to the walls. Sidewall reflections appear to
be the main suckout culprit in the 500-900Hz octave.

- That's interesting, I thought Todds walls were too far away to be the "obvious" culprit . But measurements rarely lie. Nice sleuthing, Grumpy .

<>

[grumpy]

If you're confident those TS parameters ( that you've recently measured ) are accurate...

Never confident with new toys... that's why I brought an old and new 2235H with me
to Todd's. Consistent, relative measurements I have more faith in. Both ferrite 2235's
were in the right ballpark... The Alnico version was consistenly not. Le's were all spot
on. Concur on the query to OCS.

note: WT2 users, make sure you re-measure Fs, Q for each driver before performing
Vas test (accidentally skipped this once & had to think and scratch for a minute)...
Vas test (includes BL calc) uses currently loaded Fs, Q info as part of basis.

I thought Todds walls were too far away to be the "obvious" culprit

Me too. We tried that late, for grins. Lo & behold, a FR dip moved about the same
delta-F as you would expect for the two-way air-travel distance change. I'd really like
to nail this as truth or bogus (spend time looking for this specifically... e.g.,
turn speaker to directly reflect off side wall to see major interference frequencies,
etc...) Next time ... at least the pay is good (mmm... hamburgers)

[grumpy]

OK, Todd sent the WT2 .woo files and I've had a refreshed look.

Todd's Alnico 2235 in L200 cab, network and other drivers connected.

When 20ohm resistor was added, it appears that it was in series with
more than just the 2235 (plot is uniformly 20 ohms more, across the
entire frequency range). Red is ohms. I'm going to call this test invalid
for now. -grumpy

Sorry about the resolution and inconsistent window scaling.

[toddalin]

OK, Todd sent the WT2 .woo files and I've had a refreshed look.

Todd's Alnico 2235 in L200 cab, network and other drivers connected.

When 20ohm resistor was added, it appears that it was in series with
more than just the 2235 (plot is uniformly 20 ohms more, across the
entire frequency range). Red is ohms. I'm going to call this test invalid
for now. -grumpy

Sorry about the resolution and inconsistent window scaling.

Resistor was simply hung between the crossover and the woofer.

The phasing goes weird in the problem area. The dip seems to corrospond with the hump created by the Zobel network. The resistor actually reduces the phasing effects to some extent. Maybe this is what I hear? How could this area be flattened?

[grumpy]

Thinking we should run separate LF/MF measurements and look at the
overlap in the crossover area, and run a higher resolution impedance plot
(keep in mind this is electrical phase of the network and drivers, not
audio phase).

Again, overall this isn't "bad", it's learning what might be done better
and more suited to the owner. See first attached plot.

Then "no more Mr. 1/3 octave nice guy" ... see second plot along
with my theory... should be able to "mask" the sidewall reflection
at the higher frequencies by artificially making the omni mic less omni...
if the nulls are reduced, ... well, there you go. -grumpy

[Mr. Widget]

This one is the very nearfield (almost touching the woofer cone where the dustcap is glued to the cone) with just the woofer in the 1.4 cu ft box with a 2" diameter hole (where tweeter was) with no crossover at all.

Based on the apparent notch around 47Hz, I thought that the measurement might be a nearfield measurement... nearfield measurements of woofers do tend to jack up the bottom a bit, but not this much. A lot of what we are seeing is the actual performance of this woofer in this enclosure. I'd guess that grump's measurements are reasonably accurate and useful.

Your two inch port is tuning the cabinet to ~47Hz... not ideal for a subwoofer. I haven't studied those woofers, but I am sure you would be happier with a lower tuning frequency or perhaps a sealed box. Either modification will likely extend the bass and make it a bit truer sounding.

As for the extended midrange performance, I wouldn't count on a heavy coned sub to provide "quality" reproduction above a few hundred hertz... sure it will make noise at 700Hz and above, but it will also very likely sound pretty colored and wooly.

Another interesting thing about ported boxes that your mentioning tweeter holes has reminded me. I discovered that simply having four unfilled 1/4" holes for tweeter mounting can measurably change the tuning frequency.


Widget