Dr V's Twin Acoupower 18" Build

[Kevin Haskins]

Bah.... X-max has had several definitions and companies DO jockey with the number to sell product, no doubt.

We report X-max @ 30% down on the BL curve. One the Tempest-X the 10% down is around 24mm and its essentially within 1% at 20-21mm. Its certainly not a hard and fast number but its easy enough to quantify those characteristics in terms of the BL curve and report them. It tells you nothing about the suspension linearity so its good for consumers to understand that X-max is JUST the linear range of motor BL. It says nothing about Le or Cms nonlinearity nor does it tell you anything about power compression, an area the Acupower probably excels at.

[vinculum]

vinculum wrote:

Hey, If i didn't like it I could always plug the ports with a couple basketballs?

Dr V

I just realized that this would not work. Regulation basketballs are only 9" in diameter!

I was struggling with the fact that a 10" port takes a LOT of length to change the tune. It appears that by changing box volume is much easier to lower the tune. This might set my mind at ease with tuning, as my length dimension is somewhat flexible.

Possible scenario's (as of today!)

1. Build big honkin' boxes (25 cubic feet external) with the beautiful flared 10" ports I have and I should be near 16Hz tune with massive SPL. I'm sure I won't be disappointed. Big boxes SOAF approved. They will just dominate the look of the front of my room.

2. Build large (7-10 cubic feet) sealed boxes, as my listening preferences are mostly music anyhow. HOWEVER, leave enough room for an option to cut holes in each side for the addition of passive radiators down the road IN CASE the low end isn't sufficient. By then we should have some decent variable mass PRs back on the market.

My thoughts lean towards #1, as I already have the ports. #2 is very tempting as well - SQ should be guaranteed, manageable boxes and upgradable.

I'm probably driving everyone nuts. You're probably thinking "start making some sawdust already!"

Dr V

[SteveCallas]

Dr V wrote:

#2 is very tempting as well - SQ should be guaranteed

LLT, or in this case EBS, guarantees much more bass accuracy than sealed.

[noah katz]

Catching up here...

“you would get considerable output with a sealed design, LT would have lower distortion, higher output and some wicked looking ports!”

Except below Fb, ported will have much lower excursion for the same output and thus less distortion.

“If I remember right stuffing only increases the 'enclosure size' in a sealed design?? When porting you just need enough on the inside walls for dampening.”

Stuffing increases the effective volume of ported the same as sealed; the port makes the box open only well below Fb.

V, if you’re willing to trade some output for smoother response, see here

http://www.harman.com/wp/pdf/multsubs.pdf

“A low enough tuning frequency is a good thing, but at some point you are starting to get more negative than positive effects.”

Illka, I agree that less of the audio range is benefited, but what what negative effects?

“High sensitivity. 90+dB with a a low moving mass. 305 grams. most other non-prosound drivers are lead sled 400+ grams with 88-89dB sensitivity. Remember, just 3dB more sensitivity means you only need half the power to produce the same SPLs!”

Within a wide range of parameters the reference efficiency becomes almost meaningless at low freq, where Hoffman's Iron Law rules.

In this case the poarticulars are, as you noted, the low mass raises Fs and reduces low freq efficiency

“Sd = 0.108 m^2
Cms = 106.6 um/N
Vas = 174 liters
Re = 6.2 ohms
Mms = 305 g See Below
Fo = 28.2 Hz
BL = 23.3 t*m See Below
Qe = 0.62
Qm = 8.90
Qt = 0.58
SPL = 90.5 see below”

That’s a disappointingly high Q, and not very suitable for ported or PR.

I don’t know why more of the graphs don’t show the expected low freq peaking like V’s in post #49.

“Hmm, I think those CSS passives could work just fine.”

Ilkka, what value did you use for the PR Qp? In my modeling, low end output is quite sensitive to it.

“Passive Radiators: Keep in mind these drivers are so powerful that they overdrive radiators quickly in any kind of standard configuration.”

That makes no sense to me; the power comes from the amp.

[ISLAND1000]

SteveCallas wrote:

LLT, or in this case EBS, guarantees much more bass accuracy than sealed.

At this point the "bass accuracy" of this particular driver is what we're all interested to find out. Which alignment, which box size, how much power at what frequency is what I'm interested in.

I'm not ready to concede your blanket statement above just yet.

[Mike P.]

I was reading up on the box recommendation from the Acoupower site, regarding passive radiators. They state:

""we recommend (2) long throw 24" radiators per 18" driver""

Do these exist? I've never come across anything that big.

[avaserfi]

Mike P. wrote:

I was reading up on the box recommendation from the Acoupower site, regarding passive radiators. They state:

""we recommend (2) long throw 24" radiators per 18" driver""

Do these exist? I've never come across anything that big.

I think the closest you will come to something like that are Audiopulse's offerings. They are simply designed superbly, but you sure to pay for their new name. Also, last time I contacted them the VMPs were not in production due to some supply issues, but that was a couple months ago.

[vinculum]

Never heard of 24" passive radiators either. Hopefully the author of that statement will have some suggestions.

Those TC/AP passives sure are nice. I'm almost afraid to know what they would sell new ones for if they were available. The OLD price was $250 ea. Any major price hike and it would be financially prudent to just buy 2 more drivers and gain +6dB across the board.

Lets not get too excited over the sealed vs. reflex. debate. We're all aware of the measurement differences of the alignments. Which works best for this driver will be most beneficial.

The EBP is 45.5 Most modeling programs will recommend a sealed alignment for this number. I've also read 45-55 can go either way. What are the ramifications of going against this general rule?

Dr V

[noah katz]

"it would be financially prudent to just buy 2 more drivers and gain +6dB across the board."

Per what I said earlier, you won't get that +6dB in the low bass unless you double box volume.

Though even if you did have 24" PR's, they would take a huge amount of mass unless the enclosure is also large.

Kevin, I wonder if you could come up with a super excursion PR by using existing spiders and surrounds used in series to double excursion.

The lower radial position stability would be unacceptable if there were a voice coil, but there wouldn't be.

[Ricci]

DrV.
Would you be willing to try both a sealed system and an EBS(or whatever you decide)? Since you are one of the few that actually has these it would be interesting to hear your impressions of the drivers in both alignments.

[vinculum]

noah katz wrote:

Per what I said earlier, you won't get that +6dB in the low bass unless you double box volume.

Yes, I just assumed everyone knew I meant to build 2 more boxes for additional drivers.

Ricci wrote:

DrV.
Would you be willing to try both a sealed system and an EBS(or whatever you decide)? Since you are one of the few that actually has these it would be interesting to hear your impressions of the drivers in both alignments.

I thought about throwing together a small sealed box out of some scrap I have in the shop. Its not entirely out of the question. I'm still amplifier shopping at the moment! Dreaming of an I-tech, but Xti isn't out of the equation. Twin bridged Xti's would get any alignment moving in the right direction for the right price.

I remember Steve once said that nobody who has built an LLT has ever gone back to sealed!

Dr V

[Ricci]

Yes that's what I meant, nothing fancy or "finished", just something rough to schlep one in and try it out so you can see how they sound sealed.

[SteveCallas]

ISLAND wrote:

I'm not ready to concede your blanket statement above just yet.

Umm, doesn't really matter if you do or not, it's already been proven and documented through Ilkka's testing.

viniculum wrote:

I remember Steve once said that nobody who has built an LLT has ever gone back to sealed!

Correct. If you have the space to play around with, I don't see any compelling or logical reason to turn down the multiple performance benefits of going LLT (or in this case EBS) when using a suitable driver. It's only when you are tight on space that you need to start compromising.

[Ilkka]

noah katz wrote:

“A low enough tuning frequency is a good thing, but at some point you are starting to get more negative than positive effects.”

Illka, I agree that less of the audio range is benefited, but what what negative effects?

By negative effect I mean much larger enclosure. It isn't simply practical to build a <10 Hz tuned subwoofer.

That’s a disappointingly high Q, and not very suitable for ported or PR.

I don’t know why more of the graphs don’t show the expected low freq peaking like V’s in post #49.

It's not just the Qts that defines whether the driver is suite for ported or PR. Just model it and you'll see that it behaves well in ported or PR.

“Hmm, I think those CSS passives could work just fine.”

Ilkka, what value did you use for the PR Qp? In my modeling, low end output is quite sensitive to it.

I used the announced Qmp of 67.62. I agree that low end output is quite sensitive to it.

“Passive Radiators: Keep in mind these drivers are so powerful that they overdrive radiators quickly in any kind of standard configuration.”

That makes no sense to me; the power comes from the amp.

I think Carlos means that the driver has so much excursion ("power") that they overdrive radiators quickly.

[noah katz]

> I used the announced Qmp of 67.62.

That's excellent; I guess that's all loaded up with mass, which increases Q

> I think Carlos means that the driver has so much excursion ("power") that they overdrive radiators quickly.

OK, but no more quickly than another driver with the same excursion capability

[TheEAR]

Dr V ,

I will be joining the Acoupower club soon. 18's , these drivers model quite well !

They have displacement,thermal and built quality on their side !

Thank you for the inspiration,the pictures of your Acoupower beasts made me make the plunge.

The GENESIS DEVICE or well done EBS ...EBS 90% decided.

[vinculum]

Ear,

Welcome aboard the "A-team"!
Good to see another jumping in to give this driver a chance. No doubt there will be more as people looking for high quality drivers discover that Acoupower is shipping and other others are not!

I look foward to seeing your project, and encourage you to post your build thread here on HTS so the builds are in one place. With some luck, Ilkka will aquire one of these drivers for tests also. Pledge a few bucks his way so we can get data!

I've been a little stagnant on my project, as others must come first. I really must get some more pictures up atleast because I think many will think the lead wires and spider are interesting!

Dr V

[Ricci]

Yes more pictures please!

DrV.,
Do the Acoupower ports come already assembled? I was wondering how hard it would to change the length on them.

[vinculum]

No, the spun aluminum flares are seperate and fit into the small, stepped end of the flare. They are 3/16" thick and fit really well. Not hard to cut them shorter, or buy longer ones. For really low tuning a 10" port need to be really long. So much that pipe resonance and box size becomes an issue. This is the trade off for a 10" port. Around 18Hz tuning seems to be the lowest practical point for 10". Any lower will require a PR system or room sized box!

Dr V