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Any reason NOT to do a THT? - Page 2

post #31 of 211
Sell the SVS and build two THT's.
post #32 of 211
Quote:
Originally Posted by MKtheater View Post

Sell the SVS and build two THT's.

now we're talking. two co-located THT's will give you more bass than you know what to do with
post #33 of 211
Well, I had the pb2/plus and F-20s which are similar to the THT from what I have read and trust me, the THT will be better! Much bigger but you get much more spl in the same band and they rolloff more like a sealed sub than ported which is always nice in a sealed room. So below the THT's knee they will act like sealed 15's although not high excursion 15's so their THD will rise but much slower than the ported SVS.
post #34 of 211
Thread Starter 
MKtheater!!

I was JUST about to post this as a suggestion to myself! Great minds think alike smile.gif

I think I could definitely get enough for it to fund another monster.

What would be the most cost effective way to amp two of them? Also, for EQ purposes, I can let audyssey EQ just one, but how would I EQ the other? With a BFD? If so, I am confused about how that signal chain would work...
post #35 of 211
I would wire them up as one load to one channel of a bridged EP-4000 and audyssey can EQ the sub system as one! You just won't use all the power on tap.
post #36 of 211
Quote:
Originally Posted by MKtheater View Post

I would wire them up as one load to one channel of a bridged EP-4000 and audyssey can EQ the sub system as one! You just won't use all the power on tap.

why bridge it? you could run both off one channel is parallel and STILL have more power than a THT can handle
post #37 of 211
Well, you could run them separate and use a y-splitter from the sub out but I like using no splitters now that I got a taste for it. One amp channel from the EP-4000 can provide 850 watts into 2 ohms so he could still run one channel off the EP with the other for his next two THT's! wink.gif
post #38 of 211
Quote:
Originally Posted by MKtheater View Post

Sell the SVS and build two THT's.

This is much better.
post #39 of 211
Quote:
Originally Posted by MKtheater View Post

Well, you could run them separate and use a y-splitter from the sub out but I like using no splitters now that I got a taste for it. One amp channel from the EP-4000 can provide 850 watts into 2 ohms so he could still run one channel off the EP with the other for his next two THT's! wink.gif

Doesn't the EP have a dual mono out? Wouldn't need a splitter if you get A -> A+B
post #40 of 211
I never used it that way, just ran it stereo or bridged. Even in stereo and running one channel would have enough power.
post #41 of 211
1kW+ through a THT would be crazy. In an corner placement it would cause breathing issues.
post #42 of 211
Quote:
Originally Posted by diaz View Post

1kW+ through a THT would be crazy. In an corner placement it would cause breathing issues.

1000 watts+ through a THT would BLOW that driver so fast it's not even funny. 300 watts is about the max I'd put through one of those
post #43 of 211
Thread Starter 
Good idea...I think I'll go with the Bash 300w and see how one THT sounds...If I want more I'll sell the SVS and build another smile.gif Now to find the amp where it's not sold out...Thanks again guys!
post #44 of 211
I was talking about running 2 THT's off of one ep-4000- channel in stereo.
post #45 of 211
Thread Starter 
OK, quick piece of advice, make this VERY primitive model of my room in sketchup and wanted to get some opinions. I am wondering if I should set things up the way they are in this diagram or if they should be exactly reversed, with the screen and speakers and THT on the other side by the other door. I would RATHER have everything on the side that it's on in the diagram, but I am wondering whether having the THT behind the mains would be ok. The mains would be just on either side of the screen and the THT would sit kind of in the corner behind the left main. Thoughts? Thanks!

post #46 of 211
I would try what you have there with another THT on the other side of the screen, both with mouths 18" from the corners as suggested by BFM - then see what you get for LP's responses.
post #47 of 211
Quote:
Originally Posted by jkkwaz View Post

OK, quick piece of advice, make this VERY primitive model of my room in sketchup and wanted to get some opinions. I am wondering if I should set things up the way they are in this diagram or if they should be exactly reversed, with the screen and speakers and THT on the other side by the other door. I would RATHER have everything on the side that it's on in the diagram, but I am wondering whether having the THT behind the mains would be ok. The mains would be just on either side of the screen and the THT would sit kind of in the corner behind the left main. Thoughts? Thanks!


Where they look best in a sketchup and where they sound best may not end up being the same. Building two THT's allows you to tame room nodes but you need to allow for flexible placement.
post #48 of 211
Quote:
Originally Posted by koturban View Post

Where they look best in a sketchup and where they sound best may not end up being the same. Building two THT's allows you to tame room nodes but you need to allow for flexible placement.

He needs a starting point though, might as well start with a best location, then move if needed..
post #49 of 211
I say center the screen to the back wall. Your THT's and speakers go behind the screen and this way your surrounds can all be the same distance and location around you.
post #50 of 211
Thread Starter 
Thanks, guys. MKtheater, when you say center on the back wall, do you mean the opposite wall as it is currently in the picture?
post #51 of 211
Keep the screen where it is but slide it up a little so it is centered to the 16 foot wall. I will assume you will sit at that 16 foot wall and all the surrounds will be in perfect locations.
post #52 of 211
Thread Starter 
Got it. Great idea. Thanks again, guys.
post #53 of 211
Thread Starter 
Finally got my driver yesterday from PE so will start building tonight. Quick question though so I can get something ordered in case I need it... Will I need a HPF with this sub? I know need is a strong word but is that what I should be using to make sure I don't bottom out below 20hz? Or should I just be aware of the voltage running to the driver and I'll be fine as long as I am not driving it to insane volume levels. I have seen a lot of people mention them (I have been reading all of the build threads) and wanted to know if it is a given that I should have one of these...
post #54 of 211
Quote:
Originally Posted by jkkwaz View Post

Finally got my driver yesterday from PE so will start building tonight. Quick question though so I can get something ordered in case I need it... Will I need a HPF with this sub? I know need is a strong word but is that what I should be using to make sure I don't bottom out below 20hz? Or should I just be aware of the voltage running to the driver and I'll be fine as long as I am not driving it to insane volume levels. I have seen a lot of people mention them (I have been reading all of the build threads) and wanted to know if it is a given that I should have one of these...

BFM has previously mentioned an HPF was not required with the THT as long as it is built properly with proper driver. Calculate the natural HPF of your current equipment and it should be a non issue.. you have to think that most of your listening will never go near the 300 watts anyways. Maybe when you do stress testing... but during a movie, it would have to be ridiculously loud to start producing xmax issues.

I'm sure Bill will chime in.
post #55 of 211
Thread Starter 
Thanks Diaz, that's what I thought. I'll concentrate on getting everything EQed and measured and then decide if I'll be playing loud enough to need something like that.
post #56 of 211
Quote:
Originally Posted by diaz View Post

BFM has previously mentioned an HPF was not required with the THT as long as it is built properly with proper driver.

Are you sure he said that? That's a ridiculous statement.

Front loaded horns definitely need a hpf, and they need a hpf at a higher frequency than you might expect by looking at the frequency response graph. Ported boxes and tapped horns need a hpf right around or a bit below the frequency where response starts to drop like a rock but front loaded horns need a hpf a bit higher than f0.

I don't have tht plans and I've never studied any BFM designs but I chose a flh from my records that is at least similar to show this effect. This is a corner loaded flh of roughly the same size and tuning.



With this example, you can see that if the media contains a strong 18 hz note and it's reproduced at high power, the driver is going to be destroyed. The tht doesn't play as low as this example (looks like around 25 hz or so), so it's very unlikely the rolloff or hpf on any of your current electronics are going to save the driver. I'm guessing the tht would need a 30 or 35 hz hpf to keep excursion below tuning to the level of peak excursion above tuning. This is especially important for people that like to eq the response flat below the horn's tuning. (I strongly recommend not doing that.)

If you are only using the horn for music I wouldn't worry about a hpf but if it's for home theatre I personally wouldn't operate without one.
Edited by diy speaker guy - 8/22/13 at 2:27pm
post #57 of 211
Quote:
Originally Posted by diy speaker guy View Post

Are you sure he said that? That's a ridiculous statement.

I might be wrong.. however modeling the DVC in WINISD shows a different story.. I never liked the way hornresp shows xmax.

Either way it is not a ridiculous statement.. maybe needs some backing up / explanation though
post #58 of 211
The THT looks like a sealed sub below Fc. No HPF required.
post #59 of 211
Thread Starter 
Yes, while doing some further reading I did see a few times where Bill noted that there is no need for a HPF. Here is a copied quote:

If it's got a switch try turning it off. THT has maximum excursion at 22Hz, below that excursion drops, so there's no need to use a HP filter for driver protection.
post #60 of 211
Quote:
I might be wrong.. however modeling the DVC in WINISD shows a different story.. I never liked the way hornresp shows xmax.

Either way it is not a ridiculous statement.. maybe needs some backing up / explanation though

Hornresp (and WinISD) show excursion, not xmax.

WinISD can't model a horn so I don't know what you are talking about. Hornresp shows excursion accurately. Like I said in the previous post, front loaded horns need a hpf at a higher frequency than ported boxes (and tapped horns and transmission lines, etc) of the same f0. Regardless of whether you like the way Hornresp shows excursion you can use Hornresp to compare a ported box to a front loaded horn with the same f0 and you will SEE that flh's need a higher hpf setting. You can't do that with WinISD because WinISD can't simulate horns.

I suspect you may be talking about Hornresp's Maximum SPL tool when you say you dislike the way Hornresp shows xmax. I don't like this tool either. But it is a valid way of showing power AND xmax limited SPL at the same time. But you don't have to use that tool at all to get the same info, most people just set the desired power and check the regular SPL and excursion graphs (as I just showed in my previous post) which are very similar to WinISD's graphs.
Quote:
Maybe when you do stress testing... but during a movie, it would have to be ridiculously loud to start producing xmax issues.

From that statement in your last post I think I know what the basis of the "no hpf required" comment is but I still strongly disagree. Sure, by the time you reach excursion limits in the lower bass, the upper bass is going to be very very loud. But that does not account for room size and leakage (larger and non-airtight rooms with less rigid walls will require exponentially more excursion to pressurize the room). Placement in the room (corner loading) can also help to reduce excursion demands but many people may not place the sub in the corner. Furthermore, some people may place the sub outside (an outdoor theatre) and place the subs a great distance from the listening position. Some people (especially the ones with outdoor theaters) may wish to eq the response to flat, some people will eq flat well below the sub's natural tuning.

In any of these cases the "no hpf required" may not be applicable and may cause considerable damage.

In any case it wouldn't surprise me if he did make this claim, he's been known to make some ridiculous claims. This is why he doesn't mind discussing other designs publicly but he prefers to talk about his own designs on his own forum. For example he claimed the tht was flat to 1 hz in room:
Quote:
Not impressed yet? Add in the cabin gain of an average room (12dB per octave below 30 Hz) and you end up with flat response to 1Hz with 110dB sensitivity. Not even the most expensive theatrical subs made can make that claim.

From here: http://web.archive.org/web/20080220032527/http://www.billfitzmaurice.com/THT.html
The wayback machine never forgets.
Quote:
The THT looks like a sealed sub below Fc. No HPF required.

All front loaded horns have a massive peak right below tuning. Play with Hornresp a bit and you will see it. This kind of misconception is what happens when you believe marketing hype instead of spending a couple of minutes with a simulator.
Edited by diy speaker guy - 8/22/13 at 3:49pm
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