Any reason NOT to do a THT? - Page 4 - AVS Forum
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Old 08-25-2013, 08:20 PM
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Having run two THT's, I can tell you running them without a HPF is a bad idea if you push them. I've seen the dust cover literally blown off the dayton woofer. Also, the claim they have any decent response at 10hz is just as laughable as the previous claims that they went down to 1 or 2hz or whatever was previously posted. This was my in room response from 2 36" tht's. The got loud, but they don't have anything below 20hz.

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Old 08-25-2013, 08:59 PM
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Notnyt, was that eqed response? id say it looks pretty sick regardless of no "10hz". whzt driver?
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Old 08-25-2013, 10:46 PM - Thread Starter
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Impressive, Notnyt. So I have started the THT build and it is going great! I have one question, though, and before I ask I want you to know that I have taken the time to search before asking smile.gif I found a thread that asked about the driver spacer and why it was in some of the builds but not others, and also asked whether is was completely necessary. The question never got answered, and then I saw another thread that said that the spacer adds extra strength to the driver baffle and also give the screws more "meat" to grab on to, and may eliminate having to use t-nuts or hurricane bolts, which is fine by me because I was not looking forward to dealing with those. If I use the spacer included in the plans can I just use a hex head or alan head screw with lock washer?
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Old 08-25-2013, 11:13 PM
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Wow, look what I missed... Lots of good discussion in this thread, and quite a bit of real information, experience, and advice being shared here.

Not a hater here, and not trying to hate. I'm not gonna bother responding to Bill's jab about "not having a forum" other than to point out that I'm not a vendor. This is a hobby for me, not a business. I design and build cool subs of all types for grins. I give the designs, plans, and as much support as I can away, and I share the data I collect, warts and all, that way we can all learn. Enough said there.

Flat to 1Hz has been thoroughly debunked, and Bill's website was changed years ago. Among others, I own Bill's THT plans (and I have all the Speaker Builder / Audio Xpress articles too), I was an active member of Bill's forum, the best thing I learned there was about this piece of software called HornResp. To be entirely fair, Bill's instructions are well written, and they made it relatively easy for to construct my first folded horns. I'd consider them my "gateway drug".

+1 to NotNyt. Simply put, running any sub outside of its intended passband without some sort of protection (limiter, highpass, whatever) in place is a BAD idea. Clanking the moving parts into the stationary ones, or letting all the magic smoke out of the voicecoil means the party's over till the credit card comes out to play and the big brown van stops at your door. Been there and done that. That extra 3 dB on paper isn't worth needing a new driver after I've had a few beers and I twist the knob off. Know the limits of your junk, and respect them. This gets to be an expensive hobby otherwise.

Like DSG says, IM distortion matters, a lot, and it can't really be modeled or predicted, it has to be measured. We don't listen to pure sine wave tones. Acoustic loading (impedance and reactance) matters a lot too, and little changes have big differences. Again - the model is only so useful, since the math starts its way out the window as soon as you fold up the horn. Any distortion that happens to be "on the horn" when the fundamentals are not also causes problems. In the case of the F-20, that would be anything below ~20 Hz, with the 2HD at ~40 Hz and the 3HD at ~60 Hz. I'd expect that the THT would be similar.

Hornresp is eerily accurate, but it is based on small signal parameters. Small signal parameters go right out the window when you apply a large signal. Things do change, and not always for the better. Knowing when to be concerned is important.

Anyhow - carry on. I'll sit back and watch.
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Old 08-26-2013, 09:31 AM
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@ the O.P.
I also have the 2007 design article for the THT. I would advise you read it as it answers many of the questions posed on this thread.
There was NO mention of limiters in the article.
There were numerous graphs; all show a linear drop from 25Hz to 20Hz ( approx -6db ), no data points below 20Hz.
Thus NOT flat to 10hz or 1Hz etc.
From the article " The Tempest Xmax is a very impressive 16mm, but a value of 8mm is sufficient for most home theater applications"

Having a long history of correspondence with both Mike and DIYSG: I can attest that they have always been open to learning.
And they have generously shared without expectation of financial compensation.
Statements that suggest otherwise are baseless attempts to attack character.

IMO: The title "Any reason NOT" is potentially confrontational. Positive anecdotes are apparently acceptable. If someone offers a reason NOT then they appear to be a target.
Like Mike I tried several BF designs and they did NOT meet my needs, that should be accepted and appreciated especially in the context of the thread title.
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Old 08-26-2013, 10:34 AM - Thread Starter
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WVSyd,

I certainly did not intend for the title of my post to be confrontational. I was simply asking whether I was missing something when looking at choices for a DIY sub. Basically saying, is there any reason that I am not considering why this sub would not meet my needs? It seems like a great bang for the buck... I don't need or expect a flat response to 10hz and I have room for a big cab so why not? Again, certainly not trying to be confrontational to someone who decides that a THT is not for them.

I didn't think that asking a few simple questions would start such an uproar. This is supposed to be fun right?!?!

So anyway, back on topic, I did a lot more reading last night and I think I got an answer on the baffle/spacer question. I'm not sure which tht "article" you are referring to but I would be happy to read it if you could supply a link. If anyone else has any tips regarding that part of the build, that would be great, there are certainly a lot of people here that have been doing this longer than I have. If not, that's cool, too... I'll figure it out smile.gif
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Old 08-26-2013, 10:38 AM
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Building any proven horn is worth the experience - especially for a first timer. Once you corner load that sucker, you will not regret it. When I say corner load, I mean the mouth of the horn is pointed at the corner.
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Old 08-26-2013, 10:41 AM - Thread Starter
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I just read your post again, and I think your are referring to the design plans? Are you trying to prove that it calls for a certain driver that is insufficient or something? All I said was that the current plans that I have do not call for that driver, and they don't. So sorry if that was misinterpreted... So I guess a driver with an xmax of 8mm would have a greater need for a HPF?

What I have found out is that there is not a clear cut answer for this question because many people have differing opinions, and that is great! I'll just have to try it for myself and see what works best. Thanks in advance for your input on that.
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Old 08-26-2013, 10:42 AM - Thread Starter
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Thanks, Diaz, the build is coming along great. I'm excited to hear it. I'll try to post some pics and my impressions when I fire it up.

By the way, Notnyt, just checked out the pics of your setup. Looks amazing. I have always been super impressed whenever I have heard those same jbls. They had them in a demo room in a shop here and I was always blown away. I gotta hear that system!
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Old 08-26-2013, 01:08 PM
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Jkkwzak:
No offense to you was intended.
I became aware of this thread via an e-mail notification.
I don't spend much time on forums because they can be very uncivil.

DIY often reflects the needs of a one person implemented with their personal philosophy.
Such as what speaker performance criteria are important, and others aspects such as aesthetics and cost.
Not all needs are the same and approaches vary accordingly.

The THT article is from Ed Dell's AudioXpress Feb 2007 ( I don't know if it available on-line )
I've been reading Ed Dell's publications since the first issue in 1970.
His magazines were geared towards a DIY audience and as such they contained a lot of different projects reflecting personal implementation philosophy.
Some very sophisticated, some very simple, but none declared the ultimate design for everyone.
Some aspects of needs can be quantified, some cannot.

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Old 08-26-2013, 02:29 PM - Thread Starter
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Well said. I have honestly been very passionate about t for his hobby for a long time but often ignored and put of tweaking and EQing because I have never had what I considered to be a worthwhile room and setup for my gear. Now when my first DIY horn is complete I am super excited to finally be able to jump in and tweak like crazy. I am a big believer in playing with placement, room treatments, etc to get the most out of less than perfect equipment to get the most value for the money and time invested. This is the fun stuff smile.gif
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Old 08-26-2013, 03:57 PM
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Some advise I'd give is to be aware of "Builder's Bias".
This is what I call the tendency of a builder to not evaluate a build objectively against established designs of high reputation.
Compare and contrast
A builder tends to believe his build is better than it is - until they hear something better.
There is a lot of psychoacoustics and bias in audio perception, and so valid extensive measurements are absolutely necessary.
And there is a lot more to speaker performance than sensitivity and SPL
As detailed in these articles which I consider essential reading:

http://www.stereophile.com/features/103/
http://audioamateur.com/files/2008/09/dappolito2959.pdf
http://audioamateur.com/files/2008/10/dappolito2960.pdf

Regards
Syd
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Old 08-26-2013, 05:57 PM
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Quote:
Originally Posted by jkkwaz View Post

a great bang for the buck... I don't need or expect a flat response to 10hz and I have room for a big cab

If you have the room and a small budget, THT, F-20 and diaz's new design (very similar to both, but pending measurements) would all be great choices.

JSS
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Old 08-26-2013, 07:25 PM - Thread Starter
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Awesome, thanks for the links, WVSyd, I'll take a look, and I definitely agree with the builders bias. I'm going to build it, measure it, and see if it meets my needs. If yes, than great. If I decide an upgrade is in order down the road, then I will have the experience from building this one to help me out smile.gif I'm definitely going to need more advice once I get the room response measured...
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Old 08-26-2013, 10:53 PM
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Of course there's builders bias, if there wasn't, no one would ever build anything because they would never pick a design!

Blasting brown notes for 10 years and counting!

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Old 08-26-2013, 10:57 PM
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I'd say go for it. it's a CHEAP build considering, and if you don't like it you can always sell it or just dump the cab and create another type of sub out of the driver.
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Old 08-27-2013, 06:40 AM
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Quote:
Originally Posted by WVSyd View Post

Some advise I'd give is to be aware of "Builder's Bias".
This is what I call the tendency of a builder to not evaluate a build objectively against established designs of high reputation.
Compare and contrast
A builder tends to believe his build is better than it is - until they hear something better.
There is a lot of psychoacoustics and bias in audio perception, and so valid extensive measurements are absolutely necessary.
And there is a lot more to speaker performance than sensitivity and SPL
As detailed in these articles which I consider essential reading:

http://www.stereophile.com/features/103/
http://audioamateur.com/files/2008/09/dappolito2959.pdf
http://audioamateur.com/files/2008/10/dappolito2960.pdf

Regards
Syd

This is a great post with even greater links.

JSS
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Old 08-27-2013, 10:02 PM
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I've got nothing better to do right now so I have time to present some more info to explore this issue in a bit more detail. Hopefully this will greatly clarify my position. The last paragraph is a simplified summary for the tldr folks.

So how to decide if a flh needs a hpf or not?

The first thing that needs to be addressed is that front loaded horns are different than resonant enclosures that do not use a sealed rear chamber in some important ways. This is extremely important, especially when comparing performance aspects of different alignments, but this issue is never mentioned and different alignments are almost never compared fairly. Here's a picture of three different alignments all using the same driver. Each alignment has the same 300 watts input. The top two pics are frequency response and excursion of a front loaded horn, the middle two pics are a ported box and the bottom two pics are a sealed box.



I didn't include examples of transmission lines, tapped horns and other examples of chamberless resonant alignments, but those alignments are fairly accuately represented by the ported box shown above as far as the points I am going to discuss.

Tuning (as defined by the lowest frequency sharp notch in excursion) happens to be ABOVE the low frequency knee in front loaded horns but BELOW the knee in resonant enclosures which do not employ a sealed rear chamber. This is the trade off that the chamber provides - for the same LF knee in both alignments the flh excursion control is traded for a higher actual tuning. This is a very important consideration because the ported box (or tapped horn or tl) can use a hpf to knock down and control the excursion peak below tuning without affecting the frequency response curve shape or magnitude of SPL at the low knee significantly. Front loaded horns will see a reduction in SPL at the low knee of about 3 db if they use a hpf to reduce the excursion peak below tuning to the level of the next highest excursion peak, as shown in post 61 - http://www.avsforum.com/t/1484963/any-reason-not-to-do-a-tht/60#post_23659531
This means that you CANNOT accurately compare front loaded horns without a hpf to resonant alignments that do not have sealed rear chambers unless you consider the front loaded horn's highest magnitude excursion peak as it's xmax limited spl. Otherwise the front loaded horn will appear to have a huge advantage that doesn't actually exist.

To explain this further in case it's not clear, when we present our excursion limited max spl graphs the common convention is to show the SECOND highest magnitude excursion peak as the xmax limited max spl. It's generally accepted that the highest magnitude peak (the one below tuning) will be controlled with a hpf. This means that if you show a flh in this manner without intending to use a hpf in real life the highest excursion peak will NOT be filtered and will push the driver considerably past xmax at the simulated power level - usually by a factor of 2x or more. If you don't intend to use a hpf with a front loaded horn, you must limit the highest magnitude excursion peak (not the second highest) to the value of the driver's xmax in simulations and that makes front loaded horns look a lot less appealing when compared fairly to resonant enclosures that do not use a sealed rear chamber. Since ALL chamberless resonant devices should use a hpf to protect the driver below tuning it's fair to show them with the second highest magnitude excursion peak as the xmax limited max spl but it's NOT fair to show front loaded horns in the same way if they won't be using a hpf.

When compared fairly, front loaded horns almost never outperform tapped horns (especially in terms of LF output vs size in acoustically small single subs or stacks) except in very specific situations. But of course it depends on the exact goals for the system, the design and the driver used, and whether or not the flh uses a hpf. This is a whole topic in itself but the point here is that they are almost never compared fairly. This difference between chambered and chamberless alignments has enormous implications when deciding whether to choose a flh vs any other alignment in the first place, and in fairly evaluating their respective performance envelopes. This info is also extremely important in determining WHERE to put the hpf if one is used with a flh.

On to the next point of interest. In the above graphs it's easy to see that the alignments with sealed rear chambers do in fact control excursion to a large degree. But with front loaded horns there's always going to be a big excursion peak right below tuning. Excursion does level out to a lower level at frequencies below the peak but the peak itself cannot be ignored because the driver will be destroyed if it is driven to xlim forcefully at the frequency of the peak. Even if not driven to xlim the driver will flop around like a fish out of water at that frequency and cause IM distortion. This will simply not happen with ported boxes or tapped horns since the required hpf for these latter alignments will limit the excursion peak below tuning to the same level (or at least close to the same level) as the much smaller next highest excursion peak.

Next, in order to decide if a hpf is required or not for any particular flh it's important to evaluate how bad this flh excursion peak below tuning really is. Below is a quick example to show that it can be somewhere between negligible and catastrophic at high power. This shows two very different horns using the same driver. In the first example the excursion peak below tuning is only 1.5x higher than the next highest excursion peak but in the second example it's 3x higher.



And herein lies the problem with buying an IP protected design with no objective excursion data and that has not been honestly and clearly assessed and described (wrt to performance, limitations and potentially necessary protection filters) in detail by the designer. There's no way to know how bad the peak will be unless you simulate it. Most of the time with competently designed and realistically sized bass horns the highest magnitude excursion peak is going to be around 2x (or a bit more) than the next highest peak (and my tht guess simulation is right in that range) but you really should have hard data in order to make an informed decision.

These first two points combined with my guessed tht simulation in post 61 (assuming it's close to accurate, and I'm pretty sure it is) indicate that a tht with 300 watts and no hpf has an excursion peak that is signifcantly past xmax when used with a 16 mm xmax driver. That excursion peak will be below xlim (assuming the classic Tempest is used with 300 watts) but definitely past xmax. Power should be reduced to limit the excursion peak below tuning to 16 mm to evaluate it fairly or compare it to other alignments like ported boxes or tapped horns OR a hpf needs to be added to keep that excursion peak down. In that light the tht without a hpf is not nearly as impressive as it might seem when compared to a similarly tuned tapped horn that does use a hpf.

The next thing to look for when deciding if a hpf is appropriate for a flh is a bunch of different end user system goals and unique room considerations that I'll lump together here - the expected frequency range of media content, the acoustic environment and the desired max SPL level. It's trivially easy to use Audacity (or similar software) to find out the frequency range of media. If the media does not go as low as the frequency of the excursion peak below tuning you do not need a hpf at all. Next, the acoustic environment must be measured to find specifics about room gain, but in general a small sealed concrete bunker will have more acoustic gain (up to 12 db/oct) than an open concept house with thin single sheet drywall and vinyl siding exterior walls (which may actually have closer to 0 db than 12 db of room gain at 20 hz and below). Corner loading the sub will produce more spl vs excursion at all applicable frequencies than placing the sub against a single wall or in the middle of the room or outside with no boundary loading. And desired spl is self explanatory but goes hand in hand with the acoustic environment. So to put this in perspective, a guy with a corner loaded sub in a small sealed concrete bunker that doesn't need more than 90 db peaks isn't going to need a hpf (but there will still be the consequence of higher than necessary IM distortion even at low levels). On the other hand, a guy with a single sub for an outdoor theater with the subwoofer placed 20 meters away from an audience that expects reference level spl is probably going to benefit from a hpf, especially if he's got more than 300 watts on tap. Add to this the fact that the tht webpage advocates eq'ing below tuning and Bill says a hpf is not necessary and you have potential for disaster.

Next let's look at the driver itself. Drivers with medium xmax and medium power handling (like the classic Tempest) are hard to assess for the necessity of a hpf when used in a flh without specific objective data on the driver AND horn combination and other factors as outlined above. Drivers with low xmax like the Dayton Classic which used to be recommended simply don't have enough xmax to provide much SPL without a hpf, making the size of a horn a wasteful proposition. Drivers with even more xmax than the classic Tempest can be useful to provide more LF SPL output potential but at the same time higher xmax drivers (especially those that also have higher power handling) usually have problems with high inductance which can severely limit the useful HF corner in a way that simulations cannot accurately predict. In any case it's incredibly useful to be able to simulate the horn with the driver to be used (with measured t/s parameters, not manufacturer published specs) and also to know how the driver reacts wrt power compression and inductance related HF rolloff.

So in summary the choice to use a hpf or not with a flh is not a simple single sentence answer even when talking specifically about a single particular design. There are advantages and disadvantages. A hpf (if used with a flh) will take away significant spl at the LF knee, unlike a ported box or tapped horn since the actual tuning frequency does not correlate with the LF knee in these different alignments in the same way. This means that front loaded horns are almost never compared fairly to other alignments that do not use a sealed rear chamber because of the way xmax limited max spl is usually shown (especially here in the forums it's almost universally shown as the second highest magnitude excursion peak being the max spl limit which gives the flh a fictional advantage unless it's used with a hpf) and this is very important because it has implications for frequency response curve shape, xmax limited power handling, IM distortion, etc. For a flh, it's important to know the magnitude of the excursion peak below tuning in order to decide if a hpf is required. Additionally, the frequency range of the media, the acoustic environment and the desired spl level is very important in deciding if a hpf is required for a flh, but ideally no design (other than simple sealed boxes) should be boosted below tuning. If a hpf is used with a flh there will be less chance of hitting xlim, less excursion in general, less IM distortion, and overall higher excursion limited spl if the driver can thermally handle it. But probably most important in this discussion is the fact that if my sim is anywhere near accurate the tht with a 16 mm xmax driver and 300 watts applied with no hpf is considerably past xmax at 22 hz by a factor of about 3 db. In fact it can only handle 170 watts within xmax. The situation is exponentially worse with an 8 mm xmax driver as per the plans circa 2007. I didn't bother inputting the Dayton Classic specs into my tht guess simulation but using the Tempest specs and adjusting excursion to 8 mm xmax in my sim, it took only 45 watts for the excursion peak below tuning to reach and exceed 8 mm as shown in the pic below (12.55 volts into 3.5 ohms is 45 watts). In fact there's a good chance that drivers with 8 mm xmax may even be destroyed with 300 watts in the tht if used without a hpf regardless of the wiggle room that may be provided by decreasing Bl and increasing compliance considerations that are seen when pushing the driver to the ragged edge of mechanical destruction. And while I realize the current plans may say the Dayton Classic is not acceptable it was a recommended driver for this same design just a few years ago. I would love to be able to present a 100 percent accurate simulation of the tht but I can't and regardless, I am confident that my simple guess simulation is way closer than it needs to be to demonstrate the broad strokes of the issue. To wrap this up, while using a hpf or not will always come down to an end user personal choice, that choice should be informed by objective info, and once that info is processed it will be found that the correct answer is almost never to just run a flh without protection unless the system is WAY more capable than it needs to be. So is it me that doesn't understand this issue or is there something else going on here?

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Old 08-27-2013, 11:06 PM
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long write up and some good points.

most tht folks are using plate amps with high pass filters around 20hz though, no?, so down 3db or so at that point in power. that is probably why folks aren't running into problems.

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Old 08-27-2013, 11:16 PM - Thread Starter
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Hey guys... Sorry, but I'm test fitting the driver right now with the spacer, and I'm wondering how much I am supposed to compress the gasket when I tighten it. Want to make sure it is at the right level when I test whether it hits the spacer.
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Old 08-27-2013, 11:20 PM
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make sure to caulk the gasket if it has gaps. and compress it pretty damn well, let it sit for a day or so, then retighten a bit.

forgive me if I missed it but what driver are you using ?
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Old 08-27-2013, 11:21 PM
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Quote:
Originally Posted by WVSyd View Post

Some advise I'd give is to be aware of "Builder's Bias".
This is what I call the tendency of a builder to not evaluate a build objectively against established designs of high reputation.
Compare and contrast
A builder tends to believe his build is better than it is - until they hear something better.
There is a lot of psychoacoustics and bias in audio perception, and so valid extensive measurements are absolutely necessary.
And there is a lot more to speaker performance than sensitivity and SPL
As detailed in these articles which I consider essential reading:

http://www.stereophile.com/features/103/
http://audioamateur.com/files/2008/09/dappolito2959.pdf
http://audioamateur.com/files/2008/10/dappolito2960.pdf

Regards
Syd

+1

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Old 08-27-2013, 11:24 PM - Thread Starter
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It's the Dayton Dvc 385-88... I compressed it about half way... Maybe a little more. I'll make sure I caulk the gaps as well. I'm using the spacer and screws... We'll see how that works. Seems to clear the spacer just fine...
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Old 08-27-2013, 11:58 PM
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Quote:
Originally Posted by LTD02 View Post

long write up and some good points.

most tht folks are using plate amps with high pass filters around 20hz though, no?, so down 3db or so at that point in power. that is probably why folks aren't running into problems.

Well thanks for reading it, I know it was long but believe it or not that was the version that was edited down, the original was easily twice that long but I didn't think anyone would actually read it.

I have no idea what amps people use with their tht or what hpf (if any) may be typically included in or applied to those amps. But based on your comment, here's a pic showing my tht guess sim with 300 watts. Top image is excursion with no hpf applied, bottom image is a 4th order hpf at 20 hz. The hpf makes a small difference (about 4 mm excursion difference) but really not much. The hpf would have to be a bit higher in frequency to have a significant effect. (All sims here shown in .5 pi space. Not sure when I changed that but I didn't notice it until after I hosted the pics and I'm not going to change it now.)



At high power levels even this little bit would help, but it's still past xmax (16 mm for the classic Tempest) and as mentioned earlier, this excursion reduction afforded by the hpf comes at the price of slightly reduced output at the LF corner and as such it changes the frequency response curve a bit. Since it's a fairly ineffective hpf it only pulls the LF response down about 1/2 db. Top image is frequency response with no filter, bottom is with the 4th order 20 hz hpf.

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Old 08-28-2013, 02:14 AM
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Quote:
Originally Posted by diy speaker guy View Post

Top image is excursion with no hpf applied, bottom image is a 4th order hpf at 20 hz. The hpf makes a small difference (about 4 mm excursion difference) but really not much. The hpf would have to be a bit higher in frequency to have a significant effect.

What hpf freq would match the previous excursion peak of 10mm? 25Hz?

.
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Old 08-28-2013, 03:42 AM
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diy sound guy. most people use the dayton 240 watt amp or bash 300 watt amp from PE to run a THT and usually don't drop more than 150 watts into it MAX
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Old 08-28-2013, 07:31 AM
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Diy: Two things that may make your sim more relevent to the OP. OP is using the Dayton 385-88 which has a 15mm xmax but no more than 20mm xlim. This driver bottoms hard just past xmax. Second, I don't believe plate amps have 4th order x-overs. The ones I have seen are 2nd order so down 3db in the 20-25hz range.
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Old 08-28-2013, 09:13 AM
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Thanks for the positive feedback on those links. It's nice to see an exchange without condescension and snappy repartee. Snark passed off as humour is tiresome.

Anthony:
You are correct in that "details" are omitted on a forum that is profit oriented. Probably because the assumption that such detail would allow reverse-engineered and insight to "secrets" etc.

Could you also generate a sim for the example driver in a Free Air or Infinite Baffle?
There is a point I would like to make in context to the "historical" approach to Excursion.

Thanks
Syd

"Beware of Salesmen: They are the modern Svengali, immune to Science and Reality"
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Old 08-28-2013, 09:38 AM
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999 liters (more or less 'free air'), 100 watts, 0.5 space.



Listen. It's All Good.
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Old 08-28-2013, 12:15 PM
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Quote:
Originally Posted by martinq View Post

What hpf freq would match the previous excursion peak of 10mm? 25Hz?

That info is in post 61 but I'm going to do it again with the Dayton dvc. It took a 27 hz 4th order hpf, here's post 61 if you want to see it with pictures - http://www.avsforum.com/t/1484963/any-reason-not-to-do-a-tht/60#post_23659531
Quote:
Originally Posted by wormraper View Post

diy sound guy. most people use the dayton 240 watt amp or bash 300 watt amp from PE to run a THT and usually don't drop more than 150 watts into it MAX

Thanks.
Quote:
Originally Posted by nograveconcern View Post

Diy: Two things that may make your sim more relevent to the OP. OP is using the Dayton 385-88 which has a 15mm xmax but no more than 20mm xlim. This driver bottoms hard just past xmax. Second, I don't believe plate amps have 4th order x-overs. The ones I have seen are 2nd order so down 3db in the 20-25hz range.

Good points, I'll do a couple quick sims with the Dayton dvc - but remember this is just a quick and simple guess at what's in the tht, not a 100 percent accurate simulation. I'd recommend the OP sim this for himself using the data from the plans and measured driver specs (not manufacturer published specs).

More pretty pics.

Top row - FR and excursion of the Dayton dvc in my tht guess sim, shown at xmax with 225 watts, no hpf, 2 pi space
Middle row - same driver and horn but shown with a 27 hz 4th order hpf, now it can take 900 watts within xmax and it's 6db louder
Bottom row - same driver and horn but shown with a 32 hz 2nd order hpf, also with 900 watts.

The driver might not be able to actually handle 900 watts thermally, although data-bass.com shows us that a lot of drivers can handle a lot more than their rated power handling. But even if it could handle 900 watts it would lose some of the spl to power compression so this is optimistic but it shows that a hpf changes thing a LOT. Power compression would also change the shape of the frequency response curve. Also it's easy to see how much the hpf changes the response curve shape at the LF knee. The second order hpf isn't as steep and affects a much wider frequency range than the 4th order hpf. In order to knock down the excursion peak below tuning it also has a significant effect on the first peak above tuning, knocking that one down a bit as well. With a 2nd order filter and 900 watts it's a couple mm shy of xmax but I'm not really comfortable showing this sim with more than 900 watts. 2nd order filters are not as precise in targeting the problem, this is why I don't really like 2nd order high pass filters and prefer to use and simulate with 4th order.


Quote:
Originally Posted by WVSyd View Post

Could you also generate a sim for the example driver in a Free Air or Infinite Baffle?
There is a point I would like to make in context to the "historical" approach to Excursion.

Looks like LTD02 has you covered. Let me know if you need anything else.
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